e-LFH - Core Training - Clinical Flashcards

Question

What is the sensory supply to the larynx above the vocal cords? Which branches are there and what do they do? How can laryngoscopy induce vagal reflexes?

Answer 1

The sensory supply to the larynx is from the: **Superior laryngeal nerve** - above the vocal cords * The external laryngeal branch provides the motor supply to the cricothyroid muscle. * The internal laryngeal branch passes beneath the mucosa of the piriform fossa, and provides the sensory supply to the interior of the larynx as far as the vocal cords. Laryngoscopy may induce vagal reflexes via stimulation of the internal laryngeal nerve, which provides the sensory supply to the vallecula.

Answer 2

**Recurrent laryngeal nerve** - below the vocal cords This provides the **sensory supply to the larynx below the vocal cords** and the **motor supply to all the intrinsic muscles of the larynx**, apart from the cricothyroid muscle.

Answer 3

The right recurrent laryngeal nerve passes under the subclavian artery to ascend to the larynx in the groove between the oesophagus and the trachea. The left recurrent laryngeal nerve passes under the aortic arch to ascend in the groove between the oesophagus and the trachea.

Answer 4

Superior laryngeal nerve damage Damage to the superior laryngeal nerve results in: * A hoarse voice due to loss of function of the tensor of the cord (cricothyroid). The hoarseness is temporary as the muscle on the other side compensates * An increased risk of aspiration resulting from loss of sensation above the cords

Answer 5

Unilateral recurrent laryngeal nerve damage produces the following problems: * **Vocal cord palsy,** with complete inability to abduct and a resulting cord position towards the midline. This produces a hoarse voice that is corrected to an extent as the other cord moves across to compensate. It also means the glottis is unable to close tightly so that the patient cannot generate a positive intrathoracic pressure to cough effectively, which can lead to respiratory problems postoperatively. * The **risk of aspiration** is increased because of the infraglottic loss of sensation. Bilateral vocal cord palsy resulting from damage to both recurrent laryngeal nerves produces **severe respiratory distress, presenting as stridor** as the flaccid vocal cords flap together. Urgent intubation is required acutely, with a tracheostomy likely to follow.

Answer 6

The cricothyroid membrane lies between the thyroid cartilage above and the cricoid cartilage below. The vocal cords are in close proximity and may be damaged during cricothyroid puncture.

Answer 7

The trachea extends from its attachment to the cricoid cartilage (**C6**) to the tracheal bifurcation at the carina (**T5-6**). ## Footnote In adults it is **15 cm in length**; **5 cm above the suprasternal** **notch**, 8 cm if the neck is fully extended. The diameter of the trachea is approximately the same as the patient's index finger.

Answer 8

Patency is maintained by C-shaped cartilages anteriorly. The trachea is completed posteriorly by the trachealis muscle.

Answer 9

The trachea lies in the midline, anterior to the oesophagus, with the thyroid isthmus overlying the **2nd to 4th tracheal rings.**

Answer 10

The right upper lobe bronchus arises 2.5 cm from the carina.

Answer 11

The right lung is divided into three lobes and the left lung into two lobes, plus the lingula: the remnant of the left middle lobe.

Answer 12

The pleural cavity be inadvertently opened to cause a pneumothorax during: * Insertion of a central line, i.e. subclavian or internal jugular * Supraclavicular brachial plexus block * Intercostal nerve block * Surgery on the kidney or adrenal gland

Answer 13

Ten segments **Right lung** * Upper lobe - Apical, posterior, anterior * Middle lobe - Lateral, medial * Lower lobe - apical, medial basal, anterior basal, lateral basal, posterior basal **Left lung** * Upper lobe - Apical, posterior, anterior * Middle lobe - Superior lingular, inferior lingular * Lower lobe - apical, medial basal, anterior basal, lateral basal, posterior basal

Answer 14

The apical segment of the right lower lobe. Aspiration is more likely to occur into the right side than the left. The apical bronchus of the right lower lobe is the first segmental bronchus to arise posteriorly and is most commonly affected in the supine patient.

Answer 15

The bronchiolar wall contains smooth muscle but no cartilage. It is lined by ciliated cuboidal epithelium.

Answer 16

The alveoli are lined by a single fine layer of non-ciliated cuboidal epithelium

Answer 17

The mediastinum is the space between the two pleural cavities. It is divided into four compartments by relationship to the pericardium: * Anterior * Middle (containing the pericardium) * Posterior * Superior

Answer 18

A mass in the anterior mediastinum is a major risk factor for anaesthesia. Loss of muscle tone after induction may allow the mass to fall back to compress the heart, great vessels and major airways.

Answer 19

The nerve supply to the diaphragm is from the phrenic nerves which originate from the spinal cord at cervical level C3, C4 and C5.

Answer 20

The diaphragm contributes 60-75% of the tidal volume.

Answer 21

Phrenic nerve palsy causes upward paradoxical movement of the diaphragm on that side during inspiration. Diagnosis is made by screening the diaphragm by fluoroscopy.

Answer 22

**External** * The external intercostal muscles slope downward and forward. * They contract on inspiration to pull the ribs upward and outward, increasing the anteroposterior and lateral diameter of the thorax. **Internal** * The internal intercostal muscles slope downward and backward. * They are only used in active expiration and pull the ribs downward and inward to decrease the volume of the thoracic cavity. They stiffen the intercostal spaces to prevent them from bulging during straining. **Innermost** * The innermost intercostals consist of a thin layer of muscle linking the ribs together to stabilize the chest wall.

Answer 23

**Scalene** * These muscles elevate the first two ribs. **Sternomastoids** * The sternomastoid muscles elevate the sternum. **Alae nasi** * The indicative flaring of the nostrils is commonly seen in children with mild respiratory distress. **Small muscles of the head and neck** * 'Head bobbing' is a sign of severe respiratory distress in children.

Answer 24

In an adult male, the depth of the tracheal tube is usually around 23 cm at the lips. In an adult female, the depth is 21 cm at the lips.

Answer 25

At least six ribs should be visible anteriorly and 10 ribs posteriorly.

Answer 26

The pericardium has three layers: fibrous, parietal and visceral. The attachments of the fibrous pericardial sac are to the great vessels superiorly, to the posterior aspect of the sternum and the central tendon of the diaphragm.

Answer 27

In an adult, the cardiothoracic ratio should be less than 50% on a posterior-anterior (P-A) film. A misleadingly high cardiothoracic ratio can result from: * Taking an A-P film rather than a P-A * The heart being pushed more horizontally by upward abdominal pressure, such as obesity or pregnancy

Answer 28

The A-V node is supplied by the right coronary artery in 80% of people.

Answer 29

The sympathetic supply originates from the lateral horns of the spinal cord (T1-4).

Answer 30

Dose - 1-2mg Onset - 1-3 mins (IV), 2hr (PO) Respiratory depression Metabolised by the liver - half life 14 hours

Answer 31

* Commonly used as a 'night time' hypnotic at a dose of 10-20 mg * A similar dose may also be used to produce anxiolysis preoperatively. Higher doses are usually required during the day to produce sleep. The effects of larger doses may continue to be seen in the postoperative period * Usually administered 1-2 h prior to surgery * Has no significant effect on the cardiovascular system and only depresses the respiratory system at higher doses * Is metabolized in the liver and mainly excreted in the urine

Answer 32

Giving an anaesthetic involves three stages: * Induction - putting the patient to sleep * Maintenance - keeping the patient asleep * Reversal - waking the patient up

Answer 33

IM opioids - morphine, papaveretum, pethidine These are occasionally used today, but have, in the main, been replaced by oral anxiolytics.

Answer 34

A Rapid Sequence Induction (RSI) is the technique of choice for these patients. The goals of premedication in reflux disease are an increased gastric pH and a reduced gastric volume.

Answer 35

PPI: Omeprazole, 20 mg orally H2 antagonist: Ranitidine, 150 mg orally Metoclopramide 10-20mg

Answer 36

Ibuprofen - Up to 1200mg daily in divided doses - PO Diclofenac - Up to 150mg daily in divided doses - PO, PR, IV Ketorolac - Up to 40mg daily - IV (usually 10-30mg)

Answer 37

Gastric irritation Exacerbation of asthma Renal injury Platelet dysfunction

Answer 38

There is a potential conflict between the use of LMWH for thromboembolic prophylaxis and neuraxial blockade, i.e. spinal or epidural anaesthesia or analgesia, since such procedures are contraindicated within 10 h of a dose of LMWH. This is to prevent the rare complication of epidural haematoma.

Answer 39

_Minor risk_ * Minor surgery \<30min, no risk factor other than age * Major gen surg (\>30 min), age \<40, no other risk factors _Medium risk_ * Major general, urological, gynaecological, cardiothoracic, vascular or neurological surgery; age \>40 or with one or more risk factors * Major medical illness: heart or lung disease, cancer, inflammatory bowel disease * Minor surgery, trauma or illness in patients with previous DVT or PE, thrombophilia _High risk_ * Fracture or major orthopaedic surgery of pelvis, hip or leg * Major pelvic or abdominal surgery for cancer * Major surgery, trauma or illness in patients with previous DVT or PE, thrombophilia * Lower limb paralysis * Critical leg ischaemia or major leg amputation

Answer 40

* ACEi/ARBs - should be omitted on day of surgery * Warfarin - stop 5-7 days before surgery * Clopidogrel - ideally 7 days prior to neuraxial blockade * Oral contraceptive - ideally 6 weeks prior

Answer 41

**_VRIII_** A variable rate intravenous infusion of insulin plus concomitant intravenous dextrose and potassium containing fluid * A syringe containing 50 units of human actrapid in 50 ml of 0.9% saline. * Intravenous dextrose-containing fluids must also have potassium added to run at 100 ml/h. While a patient is managed with intravenous insulin, they should have their blood sugar monitored hourly. **_Alberti regimen_** The Alberti regimen is based upon the addition of actrapid insulin to intravenous dextrose-containing fluids. The amount of insulin added can be varied. The standard intravenous fluid used is 10% dextrose with ten units of actrapid and 1 g of potassium in 500 ml.

Answer 42

Short-acting hypoglycaemic agents * Gliclazide * Repaglinide Long-acting hypoglycaemic agents * Glibenclamide * Metformin * Glipizide * Rosiglitazone

Answer 43

* On the day of surgery, the patient should be starved to the local protocol and their morning dose of hypoglycaemic agent withheld. * Ideally, long-acting agents should be converted to short-acting agents a week or so before surgery. * The risk to the patient is hypoglycaemia, particularly after an overnight fast. * For minor surgery, no further action is required as long as the blood sugar is well controlled. * Where it is poorly controlled, and for major surgery, an insulin sliding scale is required with regular blood sugar measurements.

Answer 44

IV induction agents are identified by yellow labels.

Answer 45

They must all be very lipid-soluble to cross the blood-brain barrier.

Answer 46

* Propofol is an emulsion containing 1% propofol in a lipid medium. * Thiopental is a weak acid and can be dissolved in water as long as it is mainly in the ionized form, i.e. when the pH is very high. Therefore, it is stored as its sodium salt, as a powder mixed with sodium carbonate, so that when 20 ml of water is added it produces a 2.5% solution of thiopental with a pH of 10.5. * Etomidate is soluble, but is stabilized by 35% propylene glycol to give a 0.2% solution.

Answer 47

Multiply by 10

Answer 48

The effect of the IV agent lasts only a few minutes. To maintain anaesthesia it is important to introduce a volatile agent as soon as possible. Although the anaesthetic effects of induction agents and volatile agents are synergistic, i**t takes longer for the alveolar concentration of the volatile agent to reach a maximum than it does for the effect of the induction agent to wear off.**

Answer 49

* For propofol: 1-2.5 mg/kg * For thiopental: 3-7 mg/kg * For etomidate: 0.25-0.3 mg/kg

Answer 50

* Onset time - 30 seconds * Offset time - 3-7 minutes * Metabolism? - Two pathways: conjugated in the liver to the glucuronide and hydroxylated to the quinol, which is subsequently glucuronidated. * CVS side effects (2) - Direct myocardial depression and reduction in SVR causing hypotension * RS side effect - Dose-dependent respiratory depression. * Other effects (3) * Pain on injection, which can be reduced by the use of lidocaine. * Nausea and vomiting is much less likely after propofol than other agents. * Hypersensitivity reactions: Approximately 1 in 100 000. * Relative contraindication to use - Not licensed for children under three.

Answer 51

It is a phenol derivative and extremely lipid-soluble, more so than thiopental. It has a pKa of 11, so exists almost entirely in the unionized, i.e. more lipid-soluble, form. About 98% is bound to plasma proteins.

Answer 52

* Onset time: 30 seconds * Offset time: 5-10 minutes * Metabolism: In the liver to the active oxybarbiturate derivative pentobarbital and two other inactive metabolites. * CVS: Direct myocardial depression with hypotension and reduction in cardiac output. Use with caution in the hypovolaemic patient. * RS: Dose-dependent reduction in minute ventilation, commonly with a short period of apnoea. * Problems with use * Extremely painful and limb-threatening if given intra-arterially. Urgent treatment includes: Saline dilution, papaverine 40 mg to dilate the artery and sympathetic blockade to improve blood flow. * Hypersensitivity reactions: Approximately 1 in 15 000. * Absolute contraindication to use - Porphyria.

Answer 53

It is a **thiobarbiturate**, highly lipid-soluble and a weak acid with a **pKa of 7.6**. Approximately 60% of free thiopental is in the unionized form, which is more lipid-soluble. About **75-80% is bound to plasma proteins**. 3-7 mg/kg.

Answer 54

* Onset time - 30 seconds * Offset time - 3-7 minutes * Metabolism - Etomidate is an ester and undergoes ester hydrolysis in both plasma and the liver. * CVS side effect - Very little effect on heart rate (HR), CO and systemic vascular resistance (SVR). * RS side effect - Minimal and transient dose-dependent respiratory depression. * Other effects * Pain on injection, which is reduced by the use of the preparation in lipid, i.e. Etomidate-Lipuro®. * Nausea and vomiting is common compared with propofol. * Adrenocortical suppression, especially if used by infusion. * Hypersensitivity reactions: Approximately 1 in 75 000. * Relative contraindication to use * Sedation in intensive care. Avoid in porphyria.

Answer 55

It is a carboxylated imidazole derivative, both lipid-soluble and water-soluble, i.e. much more water-soluble than propofol. About 70% is bound to plasma proteins. 0.25-0.3 mg/kg.

Answer 56

Pharmacokinetics is often described as 'what the body does to the drug' to distinguish it from pharmacodynamics, which describes the effects a drug has on the body, i.e. 'what the drug does to the body'.

Answer 57

* The drug is moving out of the bloodstream and is being distributed to other tissues (main process) * The drug is being metabolized and/or excreted from the body The blood flow. Tissues that have a high blood flow, i.e. vessel-rich tissues, take up the drug more quickly.

Answer 58

Propofol and thiopental are metabolized by the liver. Propofol is much more rapidly broken down than thiopental and has no active metabolites, whereas thiopental is metabolized more slowly, but has an active metabolite-pentobarbital.

Answer 59

Are any agents absolutely contraindicated? * Previous hypersensitivity reaction to the active agent * Thiopental and etomidate in porphyria Are there any patient-related factors that may influence choice? * Resuscitation state of patient: propofol and thiopental produce more CVS depression than etomidate, so hypovolaemia is a relative contraindication * Rapid sequence induction needed: thiopental has a slightly faster onset than propofol * Epilepsy: thiopental is antiepileptic * Age of patient: presence of ischaemic heart disease Are there any drug-related factors that may influence choice? * Previous reaction to a drug presented in propylene glycol: this should exclude use of etomidate * Egg allergy: some consider this a relative contraindication to propofol, although there is no supporting evidence

Answer 60

Any agent that can exist as a liquid at room temperature is correctly called a vapour. Any agent that cannot be liquefied at room temperature, whatever the pressure, is correctly called a gas. Volatile anaesthetic agents are all liquids at room temperature, so strictly speaking are vapours and not gases.

Answer 61

The MAC is that concentration required to prevent 50% of patients moving when subjected to a standard midline incision

Answer 62

Isoflurane -1.2 Sevoflurane - 2.0 Nitrous oxide - 103.0

Answer 63

1. Stimulants 2. Chronic alcohol dependence 3. Exogenous catecholamine use 4. Hyperthyroidism 5. Hyperthermia 6. Young age 7. Anxiety and stress

Answer 64

1. Nitrous oxide 2. Alpha2 adrenergic agents 3. Benzodiazepines 4. Intravenous anaesthetics used by infusion 5. Opioid analgesics 6. Acute alcohol intoxication 7. Reduced GCS 8. Hypothermia 9. Hypothyroidism 10. Increasing age

Answer 65

There are two important partition coefficients that describe solubility of volatile agents in body tissues. One is the blood:gas (B:G) partition coefficient and the other the oil:gas (O:G) partition coefficient. Volatiles must reach the CNS to have their effect and this requires them to cross the blood-brain barrier. Only lipid-soluble drugs can gain access to the brain. Potency follows the order of O:G solubility

Answer 66

Isoflurane - 98 Sevoflurane - 80 N2O - 1.4

Answer 67

The speed of onset of anaesthesia when using a volatile agent for induction of anaesthesia depends on **how rapidly the alveolar concentration reaches the inspired concentration** of the agent. The curves for each agent all reach the same end-point, but at different rates, dependent on their **blood:gas solubility coefficient**. The more insoluble the agent is in blood, the faster its FA/FI ratio approaches 1.

Answer 68

Overpressure involves s**etting the initial concentration on the vaporizer above that actually needed for maintenance and then, over 5 min or so, reducing it towards a maintenance value** of approximately 1 MAC. This is easy to achieve in practice with sevoflurane, but **harder with isoflurane** as it is an airway irritant, and may precipitate coughing in unparalyzed patients. Initial steady increases over a minute or so will minimize this.

Answer 69

Volatile agents with a low blood-gas partition coefficient have a **rapid speed** of onset of anaesthesia.

Answer 70

If minute ventilation is increased, more volatile agent reaches the alveoli, so speed of onset of anaesthesia is quicker. If a cardiac output increases, then blood passes more quickly through the lungs and less anaesthetic is taken up in the same time. As a result speed of onset of anaesthesia is slower. The converse is true if the cardiac output falls.

Answer 71

Isoflurane - 1.4 Sevoflurane - 0.6 Nitrous oxide - 0.47

Answer 72

The concentration-effect refers to the principle that the concentration of inspired anesthetic gas influences both (1) the alveolar concentration that may be attained and (2) the rate at which that concentration may be attained. The rate of rise of alveolar end tidal concentration is thus dependent upon and accelerated by a high initial inspired concentration of anesthetic gas. The concentration effect is only clinically relevant with nitrous oxide, although it may occur with other gases.

Answer 73

The second gas effect When a high inspired concentration of N2O is used for induction along with a volatile, not only does the alveolar concentration of N2O rise more rapidly than predicted, but so does that of the volatile. As a result induction is more rapid than might be expected.

Answer 74

Diffusion hypoxia At the end of an anaesthetic N2O will diffuse back into the alveoli more rapidly than N2 can diffuse into blood. If air is given without oxygen supplementation this will have the effect of diluting the amount of oxygen, and so reducing its concentration in the alveoli. This carries a risk of hypoxia, so all patients should be given supplementary oxygen at the end of an anaesthetic when N2O has been used.

Answer 75

All volatile agents cause a dose-dependent reduction in tidal volume accompanied by an increase in respiratory rate. However, with high concentrations, alveolar ventilation will become inadequate.

Answer 76

Sevoflurane. Isoflurane is an irritant vapour and may cause coughing.

Answer 77

Sevoflurane is more potent than isoflurane in reducing minute ventilation and may cause apnoea. For a gaseous induction using sevoflurane overpressure with 8% is commonly used. Once the patient is almost asleep it is important to reduce the vaporizer setting to maintain adequate alveolar ventilation. If this reduction is not made and 8% sevoflurane is continued then alveolar ventilation is reduced and eventually apnoea will follow.

Answer 78

All volatile agents, including isoflurane and sevoflurane, cause a **dose-dependent reduction in systemic vascular resistance** (SVR). Both agents **slightly reduce cardiac contractility.** * Isoflurane causes a greater reduction in SVR than sevoflurane. This drop in SVR is accompanied by reflex tachycardia. Isoflurane has also been associated with coronary steal. * Sevoflurane causes a less pronounced fall in SVR; blood pressure and heart rate are better preserved. * Nitrous oxide reduces cardiac contractility very slightly, but this is usually offset by an increase in sympathetic activity so that there is little overall effect.

Answer 79

Isoflurane causes vasodilatation of normal coronary arteries. Blood may be diverted away from stenotic vessels by vasodilatation of normal vessels. As a result, cardiac muscle supplied by the stenosed coronary vessel may become ischaemic.

Answer 80

Isoflurane (Fig 1) and sevoflurane (Fig 2) are both **halogenated ethers** and are **metabolized in the liver by CYP2E1**, one of the cytochrome P450 family of enzymes. Sevoflurane is metabolized to a greater extent than isoflurane. Metabolism produces significant amounts of fluoride ions, which are known to cause renal impairment. Despite this, sevoflurane does not appear to impair renal function, even after prolonged exposure.

Answer 81

Increasingly, breathing systems with carbon dioxide absorbers are being used. These interact with sevoflurane to **produce a range of potentially toxic compounds**, which have, rather unimaginatively, been called compound A, compound B, etc, through to compound E. **Only compound A has the potential to induce significant clinical effects**. However, even after prolonged exposure, and despite potentially toxic levels being reached, there have been no reports of actual renal toxicity.

Answer 82

Megaloblastic anaemia Although nitrous oxide is not metabolized to any significant extent, it does interfere with DNA synthesis in the bone marrow. Prolonged exposure may start to produce megaloblastic changes.

Answer 83

The term '**opiate**' is usually reserved for **naturally-occurring** opioid drugs such as morphine. '**Opioid'** is a more **generic term that includes the synthetic drugs** such as fentanyl.

Answer 84

An initial bolus dose of 1-3 µg/kg is usually given at induction, often before the intravenous induction agent, as it takes about 5 min to have an effect. One of fentanyl's effects is to reduce the response to laryngoscopy. Repeated doses of fentanyl may be given intraoperatively, usually 50-100 µg, depending on the duration of surgery and analgesic plans. The duration of analgesic effects of fentanyl depend on the dose given and the level of surgical stimulation, but for the doses described above analgesia lasts about 15-30 min

Answer 85

It comes in 2 ml and 10 ml ampoules, each containing a clear solution of **50 μg/ml**

Answer 86

Fentanyl is 580 x more lipid soluble. When given as a single intravenous bolus dose, fentanyl is a **short-acting drug**. Its plasma concentration falls rapidly due to distribution to vessel-rich tissues. If multiple repeated doses or an infusion are used, then there is some accumulation in fat and the recovery time increases. Metabolism, to inactive products, occurs in the liver.

Answer 87

* Bradycardia * Hypotension * Respiratory depression * Nausea and vomiting postoperatively * Urinary retention * Constipation and itching Occasionally **chest wall rigidity** is seen when fentanyl is used in a large dose as part of induction of anaesthesia.

Answer 88

The intraoperative dose of morphine, after initial use of fentanyl, is usually a **2-5 mg bolu**s, depending on how stimulating the surgery is and the duration of the procedure. Requires redosing every 30-40 mins. An intravenous bolus dose of morphine of **0.1-0.15 mg/kg** can be given about 45 min before the end of surgery. The longer onset time to peak effects means that the timing of intraoperative morphine requires care.

Answer 89

1 ml ampoules containing a clear solution of 10 mg/ml. For intravenous use, this is normally diluted with saline to give a solution of 1 mg/ml.

Answer 90

Around 100x less potent. Metabolism occurs in the liver; an active metabolite is morphine-6-glucuronide, which is more potent than morphine. The presence of an active metabolite is only important in patients with renal failure who receive repeated doses of morphine.

Answer 91

NMBs are used to facilitate: * Tracheal intubation * Surgery where muscle relaxation is essential * Mechanical ventilation

Answer 92

Depolarizing

Answer 93

Depolarising * Speed of onset - Fast * Activation before block - Yes, see twitching * Speed of offset - Fast * May require reversal - No Non-depolarising * Speed of onset - Slower * Activation before block - No * Speed of offset - Slower * May require reversal - Yes

Answer 94

Indicated in situations where the patient is at **risk of aspiration** of gastric contents. Preoxygenation is followed by an induction agent and then immediately by the depolarizing neuromuscular blocker succinylcholine, **without checking for mask ventilation**. There are two reasons for this: This technique aims to **minimize the time between induction and intubation** **Succinylcholine wears off after a few minutes**, allowing spontaneous respiration to restart. The alveolar reservoir of oxygen achieved by preoxygenation should limit any hypoxia until spontaneous respiration restarts

Answer 95

To exclude **succinylcholine apnoea**. Occasionally, patients have genetically abnormal plasma cholinesterase (the enzyme that metabolizes succinylcholine) so that its effects are significantly prolonged. In this situation paralysis could be still be present at the end of surgery. If a non-depolarizing relaxant had been given without using the nerve stimulator to confirm recovery from succinylcholine, it would be unclear which muscle relaxant was responsible for the continued paralysis.

Answer 96

The national colour-coding for labels on syringes containing non-depolarizing NMBs is **red.** Succinylcholine (Fig 3) has a **black and red** label to show that it is a depolarizing rather than a non-depolarizing NMB.

Answer 97

Intubating doses are based on body weight while maintenance doses are titrated according to response determined by the peripheral nerve stimulator.

Answer 98

* Standard concentration - 2mg/ml * Intubating dose - 0.1mg/kg * Maintenance dose - 1-2mg

Answer 99

Standard concentration - 10mg/ml Intubating dose - 0.5mg/kg Maintenance dose - 10-20mg

Answer 100

Presentation - 2 ml glass vial, 100 mg total. Intubating Dose - 1-2 mg/kg Succinylcholine should not be used to maintain neuromuscular blockade.

Answer 101

Succinylcholine is structurally related to acetylcholine and produces muscle relaxation by x As a result, muscle fasciculation is seen in many patients soon after succinylcholine administration. Succinylcholine has a short duration of action as it is metabolized in the plasma by **pseudocholinesterase**. Patient-related contraindications, history of: * Malignant hyperpyrexia * Anaphylaxis to succinylcholine * Succinylcholine apnoea

Answer 102

Patient-related contraindications, history of: * Malignant hyperpyrexia * Anaphylaxis to succinylcholine * Succinylcholine apnoea Clinical contraindications: * The presence of widespread denervation injury, especially after burns and spinal cord injury * The presence of an open, penetrating eye injury

Answer 103

When it is used in presence of denervation injuries, altered expression of acetylcholine receptors (throughout the muscle membrane rather than the junctional area only) leads to a greater efflux of intramuscular potassium upon depolarisation.

Answer 104

* Hyperkalemia * Bradycardia (due to structural similarity to acetylcholine, most often seen after a second dose) * Sux pains - uncoordinated muscle fasciculations leading to jaw and neck pain that persist for a day or two (most likely in women) * Transient raised pressure in the eye, stomach and cranium

Answer 105

The non-depolarizing NMBs are all competitive antagonists of acetylcholine at the neuromuscular junction. They are classified according to their structure. There are two groups: * Aminosteroids, e.g. Vecuronium * Benzylisoquinoliniums, e.g. Atracurium

Answer 106

It is metabolized in the liver and excreted in the bile and urine. Its effects may be prolonged with hepatic and renal dysfunction. Patients with induced liver enzymes, e.g. due to carbamazepine therapy, have a higher dose requirement.

Answer 107

**Hofmann degradation** is unique to atracurium and involves spontaneous breakdown to laudanosine and acrylate. **Ester hydrolysis** is caused by non-specific esterases, which are distinct from plasma cholinesterase In the body this breakdown is independent of enzyme systems, so atracurium can be eliminated by an organ-independent mechanism, which is an advantage in **patients with renal or hepatic failure**

Answer 108

Atracurium commonly causes local histamine release, with redness or a wheal-and-flare reaction. Occasionally there is systemic histamine release, which may precipitate small airway obstruction and wheeze, **especially in asthmatics** and when a large dose is given quickly. It may also cause vasodilation and hypotension

Answer 109

The effects of both agents may be potentiated by: * acidosis * high-dose gentamicin * magnesium therapy

Answer 110

Although acetylcholine only needs to occupy a small proportion of receptors to trigger muscle contraction, non-depolarizing muscle blockers need to occupy the majority (**about 90%**) of the receptors to produce blockade.

Answer 111

Question: Neostigmine acts at all sites where AChE is present and this includes the heart. What effect might this have? Answer: **Bradycardia.** Question: How might this be overcome? Answer: **Give an anticholinergi**c, such as glycopyrrolate or atropine, with neostigmine.

Answer 112

The recommended dose of neostigmine is 0.05 mg/kg. It is presented in a 1 ml ampoule of 2.5 mg alone or premixed with glycopyrrolate 0.5 mg.

Answer 113

The Train of Four (TOF) describes four supramaximal stimuli, each with a duration of 0.1 msec, delivered at 2 Hz Typically a current \>60 mA is sufficient.

Answer 114

The TOF count - this relates to the number of twitches seen The TOF ratio - this is the ratio of the fourth twitch height to the first twitch height, T4:T1.

Answer 115

4 - 0-85% 3 - 90% 2 - 92% 1 - 95% A TOF count of four covers a huge range of receptor occupancy, which in a clinical context makes it unhelpful when assessing reversal of neuromuscular blockade.

Answer 116

During partial non-depolarizing block the TOF ratio is \<0.7, i.e. T4 is much smaller than T1. As the non-depolarizing block wears off or is reversed, the TOF ratio approaches one.

Answer 117

* The Train of Four (TOF) * The Double Burst * Tetany

Answer 118

Tetany describes a constant stimulus to the nerve at 50 Hz. At 60 mA it is very painful for an awake patient. Tetanic fade refers to the **diminishing muscle twitch response** from an evoked potential stimulation of muscle under the effect of a non-depolarizing neuromuscular blocking agent.

Answer 119

Following a tetanic stimulus the response to a single twitch is greater than normal, a phenomenon known as 'post-tetanic facilitation'. The TOF is stronger and the TOF count may increase when a tetanic stimulus is applied during partial blockade.

Answer 120

The more lipid soluble the agent, the more potent it is

Answer 121

Bupivacaine: it is approximately four times more potent than lidocaine.

Answer 122

The unionized form of the local anaesthetic must cross the axonal lipid membrane to reach the inside. Once inside, it is the ionized form of the drug that is effective in blocking the channel.

Answer 123

There are three factors: * Whether the drug is a weak acid or a weak base * The pKa of the drug, i.e. the pH at which the ionized and unionized forms are present in equal amounts * The pH of the environment

Answer 124

Local anaesthetics are **weak bases**; weak bases are ionized below their pKa. Both lidocaine and bupivacaine have a pKa above plasma pH. **At pH 7.4 both these drugs are mainly ionized**, but for **lidocaine approximately 25**% is unionized, whereas for **bupivacaine just 15%** is unionized. **Lidocaine has a faster onset** of block than bupivacaine.

Answer 125

Once placed around the nerve, the duration of a block is determined by two main factors: * Protein binding * Rate of removal from the site and subsequent metabolism

Answer 126

The addition of 1 in 200 000 adrenaline can be used to **prolong the duration of a block**. It can be useful when added to lidocaine. However, because the duration of action of bupivacaine is determined mainly by tissue binding, the addition of adrenaline is not clinically useful. By restricting lidocaine absorption into the blood stream, the addition of adrenaline **allows a higher dose of lidocaine to be used**: 7 mg/kg rather than 3 mg/kg.

Answer 127

Lidocaine alone - 3 mg/kg With adrenaline - 7 mg/kg

Answer 128

The local anaesthetic agents fall into two chemical groups, depending on the chemical linkage present: * Amide local anaesthetics * Ester local anaesthetics Ester linkages are more readily broken down, because esterases are present in a variety of tissues as well as in the bloodstream. Amide bonds are broken by amidases, which are found in the liver. Therefore, **ester local anaesthetics have a shorter duration of action than amide local anaesthetics** and are **less commonly used for local blocks**. In addition, amides are more highly protein-bound, which also increases their relative duration of action.

Answer 129

All local anaesthetics have a lipid-soluble ring linked to an amine-containing group. The two groups of local anaesthetic differ in the type of linkage.

Answer 130

Marcain®. Colourless solution 0.25% and 0.5%. Marcain®. Heavy: 0.5% bupivacaine with glucose 80 mg/ml, 4 ml ampoule, for subarachnoid block.

Answer 131

2 mg/kg Myocardial depression CNS convulsions then coma Levobupivacaine less toxic.

Answer 132

Tetracaine (amethocaine) Cocaine

Answer 133

Ametop: Tetracaine (amethocaine) 4% as a gel EMLA: Lidocaine 2.5% and prilocaine 2.5% in a cream Ametop takes 30 minutes to work effectively It is faster-acting than EMLA Does not last as long. It does not cause vasoconstriction like EMLA Can cause hypersensitivy

Answer 134

Presentation - 30mg in 10ml normal saline (3mg/ml) Dose - 3-6mg titrated to effect. Less effective beyond total dose 30mg. Mode of action - indirect action, causing release of noradrenaline at the sympathetic nerve terminals. Acts on alpha and beta adrenoreceptors causing increase CO + SVR. What effect is seen with repeated doses - Tachyphylaxis due to depletion of noradrenaline stores

Answer 135

Presentation - 10mg in 100ml normal saline (100µg/ml) Dose - 50-100µg, titrated to effect Mode of action - Acts only on alpha adrenoceptors. Causes vasoconstriction and in increased SVR. Adverse effect - Reflex bradycardia which can cause a fall in cardiac output if a large dose is given

Answer 136

Presentation - 10mg in 20ml normal saline (0.5mg/ml) Dose - 0.5mg dose titrated to effect Mode of action - It acts mainly via alpha-adrenoceptors causing an increase in BP via an increase in systemic vascular resistance. It has only minimal effects on beta-adrenoceptors and hence cardiac contractility Adverse effect - Reflex bradycardia

Answer 137

Intraoperative bradycardia, i.e. rate \<50 bpm, is usually due to either **vagal stimulation** or the combination of a well **beta-blocked patient and a general anaesthetic**.

Answer 138

Vagal stimulation may be due to stretching or pulling of any part of the airway or gut that is innervated by the vagus nerve. Stimulation of the **inferior surface of the epiglottis**, **pneumoperitoneum** (especially higher pressures) and **manipulation of the bowel** may all cause bradycardia. Traction on structures innervated by the sacral parasympathetic outflow, particularly those of the **genito-urinary system**, may also cause bradycardia.

Answer 139

Atropine can cross the blood-brain barrier but glycopyrrolate cannot because, unlike atropine, it carries a permanent charge on its nitrogen atom, which makes it much less lipid soluble.

Answer 140

Presentation - Usually 600µg/ml but for cardiac arrests prepacked 3mg in 10ml (300µg/ml) Dose - 500g up to max 1.2mg Mechanism - Blocks acetylcholine (cholinergic muscarinic antagonist)

Answer 141

Presentation - Usually presented at a concentration of 200 μg/ml. Dose - Titrated to effect with doses of 100-200 μg, up to 600 μg. Mechanism - Blocks acetylcholine (cholinergic muscarinic antagonist)

Answer 142

Three non-pharmalogical interventions are: * Adequate expiratory time when ventilated, to avoid air trapping * Consider pressure-controlled ventilation * Optimizing patient position, i.e. minimize pneumoperitoneum Immediate pharmacological interventions * Oxygen * Inhaled anaesthetics * Salbutamol * Aminophylline * Adrenaline

Answer 143

Presentation - 1 ml ampoules containing 500 μg/ml; there is also a 5 ml ampoule containing 5 mg salbutamol. The recommended dilution is 50 μg/ml. The recommended dose is **250 μg** by slow IV injection. In theatre this should be given **over at least 20 minutes**, taking care to avoid tachycardia. The intensive care unit (ICU) recommended rate of infusion is 5 μg/min. For inhalers, the patient is required to produce a high inspiratory flow rate in order to get the drug into the lungs. It is not possible to achieve this in an anaesthetized patient. Nebulizers can be successfully attached to ICU ventilators, but for the most part this is not possible in theatres.

Answer 144

Presentation - It is presented as 250mg in a 10 ml ampoule, so further dilution is not required Dose - 250 mg titrated to effect over 20 minutes. Mechanism - It acts as a non-specific phosphodiesterase inhibitor to increase cAMP within cells, leading to smooth muscle relaxation. Caution - Should not be used in patients who are normally controlled on a preparation containing theophylline, because the plasma concentrations may easily enter the toxic range and result in seizure activity and arrhythmias.

Answer 145

Low dose adrenaline, starting with 50 μg-0.5 ml of 1 in 10 000 adrenaline (100 μg/ml), titrated to effect. At low dose, adrenaline is mainly active at beta-adrenoceptors

Answer 146

Anaphylaxis due to anaesthetic drugs has an incidence of about 1 in 10-20 000. This translates into about 55 suspected anaphylactic reactions per year in the UK. Data from France suggests that **neuromuscular blocking drugs** are the most commonly-involved group.

Answer 147

Autosomal dominant condition. It may be triggered by volatile anaesthetic agents and succinylcholine, but not necessarily at the first exposure. The common clinical features are **increasing end tidal CO2, tachycardia and increased oxygen consumption. Hyperthermia** is not an early sign. Treatment involves: * Removing the suspected triggering agent * Ventilating with a high minute volume in a high FIO2 * Administering dantrolene at 2 mg/kg up to 10 mg/kg * Active cooling

Answer 148

Presentation - Dantrolene is presented in a glass vial containing only 20 mg Dose - 2mg/kg - For an average man of 80 kg, 2 mg/kg requires 160 mg (= 8 vials) Mechanism - uncouples the action potential from the contractile process within skeletal muscle by **binding to the ryanodine receptor** (i.e. stops the release of calcium from the sarcoplasmic reticulum).

Answer 149

A gas is a compressible fluid phase in which no liquid can be formed at that temperature.

Answer 150

The threshold above which a substance exists as a gas is its critical temperature

Answer 151

A vapour is a gaseous phase which is in a state of equilibrium with the same substance in liquid form. A vapour can only exist below its critical temperature

Answer 152

P is inversely proportional to V P ∝ 1/V The relationship of P and V for a gas in two different settings is therefore: P1V1 = P2V2

Answer 153

A 5 L cylinder containing oxygen at a pressure of 100 atmospheres provides a supply of 500 L at 1 atmosphere.

Answer 154

Volume is proportional to absolute temperature (in a closed system with a fixed mass of gas)

Answer 155

If a fixed mass of gas is kept at a constant volume in a closed system, its pressure is directly proportional to the absolute temperature P∝T

Answer 156

The laws of Boyle, Charles and Gay-Lussac are assimilated to produce the Combined Gas Law, which relates pressure, volume and temperature. PV/T=k

Answer 157

Because nitrous oxide has a critical temperature of 36.5°C, the cylinder contains liquid and vapour, so the gas laws do not apply. A cylinder of nitrous oxide has to be weighed to measure its contents.

Answer 158

The total pressure is the sum of the pressures of the individual gases, as if they were alone in the same volume (Dalton's Law). The pressure exerted by each gas is termed its partial pressure, and it is assumed that the temperature is constant and that they do not react with each other.

Answer 159

As a liquid continues to evaporate into a space above it, the pressure of its vapour increases. A point of equilibrium is reached at which the rate of evaporation equals that of condensation, when the space becomes saturated.

Answer 160

Liquid molecules require energy to become vapour. This is the **latent heat of vaporization**. If this energy cannot be obtained from external sources then it is drawn from the liquid causing it to cool. This occurs in a vaporizer or when a nitrous oxide cylinder is used.

Answer 161

The temperature at which the saturated vapour pressure equals the atmospheric presure is the boiling point.

Answer 162

The amount of a given gas dissolved in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.

Answer 163

As the temperature increases, the molecules in the solution have more energy to get out of the liquid and so solubility falls. Conversely, a fall in temperature increases the solubility of a gas in a liquid.

Answer 164

* Overall strength of current * Type and frequency of current * Local current density

Answer 165

In the UK, the mains supply is alternating current (AC), with a frequency of 50 Hz.

Answer 166

Voltage = Current × Resistance (V = IR).

Answer 167

For alternating current, the term impedance (Z) is used instead of resistance, and can be similarly used in Ohm's Law to calculate current. Impedance varies with frequency.

Answer 168

Electrical current is measured in amperes (A). Current (I) in a circuit depends on the electrical barrier presented to the voltage (V) applied.

Answer 169

* Up to 5mA - Tingling but generally harmless * 10-20 mA - Pain, sustained muscular contraction. * 50 mA - Risk of arrhythmias, e.g. ventricular ectopics * 100-300 mA - Risk of ventricular fibrillation.

Answer 170

A typical impedance value for dry skin is 10 kΩ. I=V/Z = 240/10000 =24 x 10^-3 A = 24mA Skin impedance falls, and therefore the risk becomes greater, with: * A high surface area of contact * Wet skin

Answer 171

A current passing through the body does so via all the tissues between the entry and exit points. As the **cross-sectional area becomes larger**, e.g. going from the arm to the thorax, the **current density is much reduced**. However, if there is a marked narrowing in the circuit at any point, the current density increases markedly in this area. Unipolar diathermy is used to cut tissues or cauterize vessels during surgery. A **high-frequency current is passed through a fine blade or forceps**, returning via a large, low impedance pad. The **current density is very high at the tip** producing an intense heating effect.

Answer 172

If an aberrant current were to occur in a faulty device connected to an intra-cardiac catheter, e.g. CVP line, external pacemaker, there is a risk that the entire current could enter the myocardium through a small area, thus generating a high current density Under these circumstances, a current as low as 0.1 mA may be sufficient to trigger VF. This effect, called microshock, may be evident even at low voltages.

Answer 173

Class I * Used in most low risk equipment * Any exposed metal parts, e.g. the case, must be connected to earth * Functions in combination with a cut-out device Class II * This equipment is often called double-insulated, all exposed parts having two layers of insulation * An earth connection is not required Class III * These devices are powered internally, usually by a battery, and run at a voltage of less than 40 V DC * If an AC supply is used then an isolating transformer is incorporated * Though there is still a risk of electric shock, the major hazard arising from mains voltage has been removed

Answer 174

For most standard major electrical items a fuse is incorporated into the live supply and the earth wire is connected to the equipment casing. In the event of a fault that makes the casing live, **the earth provides a low impedance return pathway to the sub-station**. The **sudden surge in current** melts the fuse, thereby disconnecting the live supply. The fuse must be appropriately rated so that it does not blow with normal use.

Answer 175

The Current-Operated Earth Leakage Circuit Breaker (COELCB) is a widely used device which **monitors the current flowing in the live and neutral conductor**s. ## Footnote A **difference in the flowing current indicates that current may be flowing to earth by another mean**s. If such a difference is detected, the circuit breaker rapidly operates a relay on the live conductor, switching off power. A current difference as low as 30 mA may trip the device and it can switch off in 30 ms. If it switches off, then the supply should not be re-established until the cause is rectified.

Answer 176

1 atmosphere equates to (approximately): * 1 bar * 15 pounds per square inch (psi) * 100 kPa * 1033.23 cmH2O

Answer 177

The SI unit of pressure is the pascal (Pa) and is equivalent to a force of 1 newton applied over an area of 1 m2.

Answer 178

In most hospitals oxygen is stored as a liquid in a large vacuum flask, i.e. a **Vacuum Insulated Evaporator** or VIE. The oxygen is liquefied by cooling it to **-150 degrees C** and is kept at a pressure of **1000 kPa** (10 atmospheres). The oxygen is allowed to warm up to room temperature so that it turns back into a gas and the pressure is regulated to a pressure of **440 kPa.**

Answer 179

Entonox is a 50:50 mixture of nitrous oxide and oxygen Entonox ® is stored in white or blue cylinders with blue and white shoulders. It is supplied in cylinders at a pressure of 137 bar and must be stored above its pseudocritical temperature of -6 degrees C. Below this temperature the nitrous oxide liquefies in a process called lamination.

Answer 180

White - Oxygen Blue - Nitrous oxide Black - Air Yellow - Suction Clear - Anaesthetic gas scavenging

Answer 181

**Desflurane** is the odd one out in terms of vaporization: because of its **low boiling point** it is delivered from a heated vaporizer which has to be plugged into a mains electricity supply to operate. It is also filled from a sealed bottle system and has a built in low level alarm.

Answer 182

The connectors used in adult breathing systems, up to the final connections to the endotracheal tube or laryngeal mask airway, are made up of a **22 mm** conical male and female connector. Another set of connectors used in the breathing system itself are the smaller **15 mm** male and female connectors. They are used on both endotracheal tubes and laryngeal mask airways The third commonly used connector in adult breathing systems is a **30 mm**-sized conical connector. It is used with Anaesthetic Gas Scavenging Systems (AGSS).

Answer 183

An adjustable pressure limiting (APL) valve The APL is a specialized valve that has three important functions: * As a one-way exhaust valve * As a mechanism to enable adjustable positive pressure ventilation using a reservoir bag * As a safety blow-off valve in the breathing system

Answer 184

An organ requiring a certain perfusion pressure (e.g. the kidney) A disease state in which an obstruction in the circulation requires a high pressure to overcome it (e.g. carotid stenosis)

Answer 185

Pressure = Flow x Resistance BP = CO x SVR

Answer 186

The most efficient type of flow is laminar, in which fluid layers move smoothly over each other. Under laminar conditions flow can be calculated from Poiseuille’s formula. Q = ΔPπr⁴/ 8ηL

Answer 187

The change in shape during the descending part of the wave is the dicrotic notch. It is generally thought to represent the elastic recoil of the aortic wall immediately after aortic valve closure.

Answer 188

The biggest fall in pressure in the circulation occurs in the arterioles, particularly those supplying the major organs. They are often called resistance vessels. Their small radius produces a high resistance. Resistance is inversely proportional to the fourth power of the radius.

Answer 189

The pressure in the veins is low, but they hold a large proportion of the circulating blood volume: the capacitance vessels. In hypovolaemia, when the body’s responses lead to vasoconstriction, particularly in the skin/gut with most of the blood kept in the central circulation to perfuse the vital organs.

Answer 190

Less time spent in diastole and therefore less time for perfusion.

Answer 191

* Autonomic nervous system (seconds to minutes) * Humoral system (minutes to hours) They are activated by stretch produced by a rise in blood pressure. Because they respond to stretch, activation of the baroreceptors results in an inhibitory effect on the cardiovascular system, causing a fall in heart rate and vasodilatation. Vasoconstriction and tachycardia result from a decrease in activity in the baroreceptors when the blood pressure falls.

Answer 192

Hypotension, leading to a reduction in flow through the renal tubule, is sensed by the juxtaglomerular apparatus. This releases renin that activates the cascade which ultimately produces angiotensin II, a powerful vasoconstrictor. Renin also stimulates aldosterone release from the adrenal cortex, leading to Na+ and H2O retention.

Answer 193

* Blood loss (ml) * Class 1 \<750ml, Class 2 750-1500, Class 3 1500-2000m Class 4 \>2000 * Blood loss (%) * Class 1 \<15%, Class 2 15-30, Class 3 30-40, Class 4 \>40 * HR * Class 1 \<100, Class 2 100-120, Class 3 120-140, Class 4 \>140 * CRT * Normal, \>2m \>5, Not detectable * BP * Normal, normal, reduced, v low

Answer 194

Simultaneous contraction of all fibres is achieved by the **specialized conduction system**, the **syncitial nature of cardiac muscle** and by **prolonging the action potentia**l via slow Ca2+ inflow through L-type channels, thus ensuring total ventricular depolarization.

Answer 195

100-120/min. The heart rate is normally slower because of dominant vagal parasympathetic activity.

Answer 196

80-90 m2, approximately half the size of a singles tennis court.

Answer 197

500ml 150ml

Answer 198

VT Tidal volume (500 mL) IRV Inspiratory reserve volume (3000 mL) ERV Expiratory reserve volume (1500 mL) RV Residual volume (1000 mL) TLC Total lung capacity (6000 mL) VC Vital capacity (5000 mL) FRC Functional residual capacity (2500 mL)

Answer 199

Its position is determined by the inward forces (**lung elasticity**) balanced against the outward forces (**respiratory muscle tone)**.

Answer 200

During apnoea it **provides the reservoir in the lungs from which oxygen can be taken to maintain arterial oxygenation** – the greater the oxygen reservoir, the longer the time before hypoxaemia develops FRC has a major influence on the distribution of ventilation within the lung by **determining where the starting position of each area of the lung is on the compliance curve**

Answer 201

From the trachea to the alveoli, branching of the airway occurs approximately **23 times**. Flow of gas resulting from respiratory effort only occurs down to **division 16**. Below this, gases **move passively by diffusion** along partial pressure gradients, between the alveoli and higher airways. Respiratory bronchioles.

Answer 202

When breathing spontaneously, inspiratory flow occurs by creating a small negative pressure in the alveoli (~ 2-3 cm H2O below atmospheric). A higher pressure is normally needed (~ 10-15 cm H2O) to deliver the same tidal volume during IPPV.

Answer 203

``` Rising CO2 (central chemoreceptors) - most important (Arterial PCO2 is closely maintained between 5.1–5.5 kPa) ``` Falling O2 (peripheral chemoreceptors) Voluntary control (cortex) Muscle activity (stretch receptors)

Answer 204

As the arterial PaCO2 rises, the Vmin increases in an attempt to bring it back to the normal range. The lower end of the curve flattens out because automatic firing from the respiratory centre maintains a minimum Vmin. Drugs that depress the CNS make the chemoreceptors less sensitive to PaCO2, moving the curve to the right and making it less steep

Answer 205

An increase in resistance is seen in obstructive airways disease. A decrease (worsening) in compliance occurs with restrictive lung disease.

Answer 206

Ventilation In a normal patient breathing spontaneously, the resting position of the lung is such that the apices are already reasonably expanded, whilst the bases are more squashed (though not collapsed). The resulting positions on the compliance diagram mean that the **bases and mid-zones are on the steep part of the curve and receive more ventilation**. Perfusion The effect of gravity **reduces the perfusion pressure by 1 cm H2O for every cm in height above the level of the heart**, with a similar increase below. This means that perfusion at the apices reduces to virtually zero, and increases progressively down to the bases.

Answer 207

No ventilation (V/Q = 0)

Answer 208

No perfusion (V/Q = ∞) Perfusion may cease because of occlusion by embolus (thrombus or air) or because of a fall in cardiac output leading to an inadequate pressure to perfuse the upper part of the lung.

Answer 209

The end-tidal CO2 will fall because the gas not involved in respiratory exchange will dilute the CO2 concentration coming from areas of lung that have been.

Answer 210

General anaesthesia almost inevitably produces some degree of V/Q mismatching because of the **associated fall in FRC**, which moves the lung down the compliance curve. The **bases** are now on the lower (unfavourable) part of the curve and r**eceive less ventilation**, whilst the apices become more compliant and receive more. The **distribution of perfusion** - influenced largely by gravity - is u**nchanged**, with the mid-zones and bases receiving most of the blood flow, resulting in V/Q mismatch.

Answer 211

The body uses approximately **250 mL O2/min** at rest. Oxygen consumption at rest can be calculated by measuring the difference between inspired (Fi = 21%) and expired (FE = 16%) oxygen concentration and then multiplying that by the alveolar minute volume (VA = 5 L/min): O2 consumption = VA x (Fi – FE) = 5000 x (0.21 – 0.16) = 250 mL/min

Answer 212

0.23 mL/L/kPa

Answer 213

The main regulator of Hb production is erythropoietin (EPO), which is secreted by kidney in response to tissue O2 level.

Answer 214

Four - one to each haem group ## Footnote Initial binding of O2 is difficult, but as the first O2 molecule binds it changes the shape of the Hb molecule slightly, making other binding sites more accessible. Subsequent binding of the second and third O2 molecules is therefore easier (**cooperativity**), but once these sites are occupied, full saturation with the fourth molecule becomes more difficult as only one free binding site remains.

Answer 215

At rest, approximately 25% of the available O2 is extracted by the tissues, resulting in a venous saturation of 75% and a PO2 of around 5.3 kPa. The P50 is the PO2 at which the Hb-O2 saturation is 50%, normally around 3.5 kPa. It is a reference point that describes the position of the curve and changes as the curve moves under different conditions.

Answer 216

Partial pressure (PaO2) Saturation (SpO2) Content (CaO2)

Answer 217

Oxygen cascade The normal PaO2 (13 kPa) is reached after a three stage fall from the atmospheric level (21 kPa), known as the oxygen cascade: * In the upper airway, humidification adds water vapour * In the alveoli, O2 is taken up in exchange for CO2 * In the circulation, from the small physiological shunt caused by the bronchial circulation and thebesian veins

Answer 218

CaO2= Hb-bound + dissolved = ([Hb] x 1.34 x satn) + (0.23 x PO2) = (150 x 1.34 x 0.98) + (0.23 x 13) = 197 + 3 = 200 mL/L

Answer 219

The **rate of O2 consumption (VO2)** is higher during **muscular activity** (including shivering), in **pregnancy**, in **childhood** and in states that increase metabolic rate (e.g. **pyrexia, thyrotoxicosis)**. The maximum extent to which an individual can increase his/her O2 consumption during exercise (VO2 max) is increasingly being used as a measure of cardiopulmonary fitness.

Answer 220

It is detected clinically when ≥ 5 g/dL deoxy-Hb can be seen in the skin or mucous membranes. Cyanosis is seen in capillary blood, whilst a pulse oximeter reading is based on the arterial value, which will be substantially higher because: * PO2 is slightly higher in the artery than the capillary * The saturation curve in the capillary has a small right shift (Bohr effect)

Answer 221

Because almost all O2 is carried bound to Hb, anaemia reduces O2 content approximately in proportion to the fall in Hb. The saturation will be unaffected as all the Hb present is saturated and the PO2 is unchanged as it measures the level in plasma.

Answer 222

Cholinergic receptors are subdivided into nicotinic and muscarinic receptors. They can be artificially stimulated respectively by the alkaloids: * Nicotine, found in the tobacco plant * Muscarine, from the poisonous amanita mushroom Nicotinic receptors are transmembrane channels that open to allow Na+ ions to flow through in response to activation by ACh. This is an example of a **ligand-gated ion channel**. Nicotinic receptors exist throughout the body in: * All autonomic ganglia * The adrenal medulla * The neuromuscular junction Muscarinic receptors are predominantly found at parasympathetic postganglionic junctions and work instead by **G-protein linkage**.

Answer 223

Neurones have a constant resting membrane potential (RMP), set at about -70 mV. The inside is negative relative to the exterior.

Answer 224

* PPI - 90 mins prior * H2 antagonist - 90 mins prior * Antacids - Immediately before * Prokinetics- 90 mins prior

Answer 225

Hypercoagulability Vessel wall injury Venous stasis

Answer 226

The efferent pathways for both the SNS and PNS consist of two sets of neurones, 'preganglionic' and 'postganglionic', that synapse in an intermediary ganglion. The cell bodies of the preganglionic neurones are in the brain or spinal cord. Each preganglionic cell anastomoses with 8-9 postganglionic cells to produce the diffuse responses characteristic of the ANS Preganglionic axons are myelinated slow conducting B fibres. The axons of the postganglionic neurones are mainly unmyelinated C fibres.

Answer 227

The sympathetic efferents have a t**horacolumbar outflow from spinal roots T1-L2**. Preganglionic cell bodies are found in the **l****ateral horns of the spinal cord**, and their axons can terminate in one of three ways: 1. Most synapse in the **paravertebral sympathetic chain** 2. Some pass through the sympathetic chain via the splanchnic nerves to synapse in a **peripheral autonomic ganglion** in the abdomen or pelvis (e.g. coeliac, mesenteric) 3. **Direct synapse with chromaffin cells** in medulla of adrenal gland

Answer 228

The parasympathetic efferents have a **cranio-sacral outflow** from **cranial nerves III, VII, IX and X and spinal roots S2-4**. The preganglionic cell bodies are in the **cranial nerve nuclei** or the **lateral horns of the sacral spinal cor**d. Parasympathetic **ganglia from the vagus and sacral efferents** are **usually diffusely located in the walls of the viscera they supply** (heart, lungs, gut). Cranial nerves III, VII and IX that supply the head and neck synapse in **four discrete intermediary ganglia: the ciliary, sphenopalatine, submaxillary or otic ganglion.**

Answer 229

There is no direct sympathetic outflow to the head and neck or pelvic region, rather neurones **travel up or down from the thoracolumbar sympathetic chain to** cervical or sacral ganglia ## Footnote The sympathetic outflow to the head and neck is via the **superior, middle and inferior cervical ganglia**. The inferior cervical ganglion is often fused with the first thoracic ganglion to form the **stellate ganglion** at the level of C6, just in front of the neck of the first rib.

Answer 230

Visceral autonomic afferents and pain fibres **travel with autonomic efferent nerves** (but synapse in the brain and spinal cord). Pain fibres from the **lungs, bronchi and pelvis** travel with parasympathetic nerves Pain fibres from the a**bdominal viscera and heart** travel with sympathetic nerves.

Answer 231

Thoracic sympathectomy is used for the treatment of severe Reynaud's phenomenon or hyperhidrosis (sweaty palms). Lumbar sympathectomy is used for circulatory insufficiency of the lower limb or phantom limb pain. Coeliac plexus block is used for the pain associated with upper GI malignancy or acute or chronic pancreatitis.

Answer 232

Acetylcholine + Noradrenaline Which neurotransmitter is used by: * all pre-ganglionic neurones - ACh * all post-ganglionic parasympathetic neurones - ACh * post-ganglionic sympathetic neurones that innervate sweat glands - ACh * All other post-ganglionic sympathetic neurones - NA

Answer 233

**Muscarinic** receptors, M1-M5, are: * Found in **smooth muscle, glands, the heart and the brain** * **G protein-linked**; their actions are mimicked by muscarine * **Blocked by atropine** **Nicotinic** receptors are: * Found in the **sympathetic ganglia** and the **motor end-plates of skeletal muscle** * **Ligand-gated ion channel receptor**s; their actions are mimicked by nicotine, but u**naffected by atropine**

Answer 234

An anticholinesterase (neostigmine) is given to **increase ACh levels.** at the motor end-plate of the neuromuscular junction blocker (**nicotinic**) this reverses the effect of the muscle relaxant. Unwanted muscarinic effects of the ACh are prevented by the use of an agent such as atropine or glycopyrrolate.

Answer 235

There are two main types of adrenergic receptors, **alpha (α) and beta (β)**, both **linked to G-proteins** and each with subtypes

Answer 236

α1, β1 and β2 receptors are all post-synaptic. α2 receptors may be presynaptic and post-synaptic. Noradrenaline has a greater affinity for α receptors, adrenaline for β receptors.

Answer 237

* Alpha 1 - Phospholipase C - Smooth muscle contraction, glycogenolysis * Alpha 2 - Adenyl cyclase - Inhibition of norad release, smooth muscle contraction * Beta - Adenyl cyclase - Contraction of cardiac muscle, smooth muscle relaxation, glycogenlysis

Answer 238

The sphincter of the iris: parasympathetic stimulation produces pupil constriction (miosis) The radial muscle of the iris: sympathetic stimulation produces pupil dilation (mydriasis) (α1)

Answer 239

Blood pressure falls due to associated sympathetic block that produces widespread vasodilation (T4-L2). Fluid loading and use of a directly acting vasoconstrictor such as phenylephrine. More profound hypotension due to greater sympathetic block and bradycardia from loss of sympathetic supply to the heart (T1-4).

Answer 240

The risk of dying in the month after an MI is about 50 times the risk of dying in the month before an MI. By 12 months the relative risk has fallen to between 3 and 1.5 times average. Between the first and twelfth month the relative mortality risk probably falls exponentially. Normally surgery should be delayed for **3-6 months following MI**. Six months after placement of stents the risk of dying is no longer elevated. But if clopidogrel is stopped (for surgery) in patients with drug-eluting stents their risk of dying will increase, **perhaps five times**. he management of patients with stents who are receiving anti-platelet medication should be jointly planned with the cardiologist.

Answer 241

In patients with atrial fibrillation (AF) a marked sudden increase in ventricular rate may **compromise adequate ventricular filling.** Patients in AF should ideally should have their rate controlled to \<100 bpm pre-operatively.

Answer 242

The risk of bleeding if aspirin is continued is exceeded by the risk of thromboses, except for surgeries in: * The brain * Spinal canal * Prostate Orthopaedic surgeons and general surgeons vary in their practices. If stopping aspirin, this should be done at least five days pre-operatively.

Answer 243

Failed intubation occurs about 1 in 2000 elective general anaesthetics and 1 in 300 emergency anaesthetics. Failed mask ventilation occurs in about 1 in 1500 anaesthetics.

Answer 244

Trauma, rheumatoid arthritis, Down’s syndrome

Answer 245

1. Small mouth 2. Receding chin 3. High arched palate 4. Large tongue 5. Bull neck 6. Morbid obesity 7. Large breasts

Answer 246

Obvious acquired problems include: 1. Burns 2. Tumours 3. Abscesses 4. Radiotherapy 5. Other scars

Answer 247

Fixed cervical spine, reduced temporo-mandibular movement and mouth opening.

Answer 248

The tests have low specificity and low positive predictive value. This means there are a large number of false positives, and a positive test is only infrequently followed by true difficulty.

Answer 249

2a - Partial view of the glottis 2b - Posterior vocal cords or arytenoids just visible

Answer 250

Easy - Views require no adjuncts Restricted - Views require a gum elastic bougie Difficult - Views require advanced techniques

Answer 251

If the gap is less than 3 cm, intubation difficulty is more likely. If the gap is less than 2.5 cm LMA insertion will also be difficult.

Answer 252

**History** * A history of snoring * A history of sleep apnoea **Examination** * Facial abnormalities preventing mask seal * Markedly receding jaw * Markedly prognathic jaw * Gross obesity * Facial hair * Poor dentition

Answer 253

ECG - \>60yrs and surgical severity at least 3 or Any cardiovascular disease or severe renal disease? FBC - Older than 60 years AND surgical severity at least grade 2. All adults if surgical severity at least grade 3. Severe renal disease. U+E - Older than 60 years AND surgical severity at least grade 3. All adults if surgical severity at least grade 4.Any renal disease. Severe cardiovascular disease.

Answer 254

Opioids - Act at opioid receptors in the CNS: both in the brain and the dorsal horn of the spinal cord Paracetamol - Central COX3 inhibition to reduce prostaglandin synthesis Clonidine - Alpha-agonst, mainly central via pre-synaptic alpha 2 but also some spinal action Ketamine - Acts central in brain and spinal cord.

Answer 255

* **Propofol** * 10 - 20 mg * ½ - 1 min * 1 - 2 mins * **Midazolam** * 1-2mg * 1-2 mins * 3-4 mins * **Ketamine** * 10-30 mg * 1/2 - 1 min * 1-2 mins * **Fentanyl** * 25-75mcg * 1-2 mins * 3-5 mins

Answer 256

Spinal/subarachnoid block Epidural/caudal block Combined spinal epidural

Answer 257

The following are listed as minimum standards of monitoring for sedation in AAGBI guidelines: * Anaesthetist present * Pulse oximeter * ECG * NIBP Although not essential, monitoring ETCO2 is very useful.

Answer 258

Monitoring of SpO2, ECG and BP is required. The AAGBI states that 'The same standards of monitoring apply when the anaesthetist is responsible for a local/regional anaesthetic or a sedative technique for an operative procedure'.

Answer 259

Patient fasting is mandatory for most regional techniques, because failure of the block or complications of the block might necessitate rapid conversion to a general anaesthetic (GA).

Answer 260

Three techniques are commonly used to confirm the correct placement of the needle in relation to the nerves: * Seeking of paraesthesia * Nerve stimulators * Ultrasound guidance

Answer 261

Intercostal and interpleural

Answer 262

Common complications of neuraxial blocks include * **post-dural puncture headache** * **hypotension** * **nausea** * **inadequate block** * **shivering** * **urinary retention**. Rare (all 1 in \>5000) complications are: * Cardiac arrest * Respiratory failure * Systemic LA toxicity * Meningitis * Spinal/epidural haematoma Additional rare (all 1 in \>5000) complications are: * Anaphylaxis * Spinal/epidural abscess * Paraplegia * Radiculopathy * Conus medullaris injury * Cauda equina syndrome * Anterior spinal artery syndrome

Answer 263

There are three absolute contraindications to neuraxial anaesthesia: * Patient refusal * Local, overlying, sepsis * Significant uncorrected hypovolaemia Relative contraindications include: * Coagulopathy/anticoagulant therapy * Aortic/mitral stenosis. There is a risk of profound hypotension from sympathetic blockade * Previous back surgery. There may be a technical difficulty * Systemic sepsis. There is a risk of 'seeding' an abscess * Pre-existing neurological disease. There may be medicolegal disputes about 'new' symptoms

Answer 264

Epidural \<100 Spinal \<50

Answer 265

Heating allows the gases to become more saturated with water vapour. Thus humidifiers have an essential role in maintaining a healthy respiratory tract.

Answer 266

Hepatitis C.

Answer 267

There are two main types of filter: * Electrostatic * Hydrophobic Hydrophobic filters are the most efficient and long-lasting type of filter. Associated problems are: * An increase in dead-space, especially in children * An increased resistance to flow, especially if wet * In severe cases the filter may block with secretions, blocking the anaesthetic circuit