From MCQs Flashcards
What are the three main problems that can arise when giving three drugs through one TIVA line?
Common Dead Space: an alteration in the administration rate of one drug will affect the others
Reflux: obstruction can cause drugs to go up gravity-fed lines (they need anti-reflux valves)
Siphoning: if a syringe driver is placed above the patient and the syringe plunger is not held firmly in place, the difference in hydrostatic pressure can make the drug flow freely. They have anti-siphon valves.
Which airway devices are commonly used in ENT surgery?
Armoured ETT (kink resistant)
Ring-Adair-Elwyn tube (north- or south-facing)
Laser tubes (for laser surgery)
Flexible LMAs
Which factors affect whether a drug would cross the placenta or not?
Lipid solubility: More lipid soluble, more transfer
Ionisation: More ionised, less transfer
Protein binding: More protein binding, less transfer
pH: Determines degree of ionisation, which in turn affects transfer
Molecular weight: Large, bulky molecules, pass less readily.
How does cardiac output change in pregnancy?
Increases
Due to a 30% increase in stroke volume
Also 25% increase in heart rate
List the structures in the bronchial tree from largest to smallest.
Trachea
Main bronchus
Lobar bronchus
Segmental bronchus
Terminal bronchiole
Respiratory bronchiole
Alveolus
What is the peak absorbance of infrared radiation for anaesthetic gases, nitrous oxide and carbon dioxide?
Anaesthetic Gases: 8-9 µm
Nitrous Oxide: 4.6 µm
Carbon Dioxide: 4.3 µm
What is the interaction between omeprazole and clopidogrel?
Omeprazole inhibits CYP2C19 which is responsible for converting clopidogrel into its active form
What is the maximum dose of levobupivacaine that can be used?
2 mg/kg
What are the parasympathetic ganglia in the head and neck?
Ciliary
Pterygopalatine
Submandibular
Otic
What measure is most important in reducing the risk of delivering a hypoxic mixture via a cylinder of entonox?
A dip tube to the bottom of the entonox cylinder will mean the lowest % of oxygen delivered will be 20%.
List the appropriate sizes of blood pressure cuff for different groups of people.
3cm – infant.
6cm – child.
9cm – small adult.
12cm – adult.
15cm – large adult.
What is the partial pressure of oxygen and oxygen saturation of blood in the umbilical vein?
Umbilical vein goes from the mother to the baby
pO2 4.7
SpO2 80-90%
What type of reaction occurs between neostigmine and the active site of acetylcholinesterase?
Carbamylation
Hydrolysing this bond takes longer than hydrolysing the bond between acetylcholine and acetylcholinesterase
What is the mechanism of action of dipyridamole?
Phosphodiesterase inhibitor
Inhibits the breakdown of cAMP
In the platelet, cAMP reduces aggregation
Which receptors are found in the chemoreceptor trigger zone?
Histmine (H1)
Muscarinic
Dopaminergic (D2)
Serotonergic (5-HT3)
Opioid
Adrenoceptors (alpha 1 and alpha 2)
In a galvanic fuel cell, which type of reaction takes place at each electrode?
Lead Anode: electrons are lost in an oxidation reaction
Gold Cathode: electrons are gains in a reduction reaction
Outline the NAPSE coding of cardiac pacemakers.
Position I: chamber(s) paced – V (ventricle), A (atrium), D (ventricle and atrium), O (none).
Position II: chamber(s) sensed – V (ventricle), A (atrium), D (ventricle and atrium), O (none).
Position III: mode of response – T (triggered), I (inhibited), D (triggered or inhibited), O (none).
Position IV: programmable functions – R (rate modulated), O (none).
Position V: multi-site pacing – O (none), A (atria), V (ventricles), D (dual).
Describe the mechanism of action of opioids on opioid receptors.
Via GPCRs (Gi)
Ligand binding leads to closure of VGCCs on the presynaptic membrane and CAMP levels fall
Potassium efflux leads to hyperpolarisation
Leads to decreased neurotransmitter released and pain transmission
Outline the mechanisms of heat loss from the body in theatre and their relative contributions.
Radiation (40%)
Convection (30%)
Evaporation (15%)
Conduction (5%)
Respiratory losses (10%)
What are the 8 methods of classifying a ventilator?
Method of cycling: volume, time, pressure.
Inspiratory phase gas control: volume, pressure.
Source of power: electric, pneumatic.
Suitability of use: operating theatre, ICU.
Paediatric use: yes, no.
Method of operation: pressure generator, flow generator.
Sophistication: SIMV, PS, CPAP etc.
Function: minute volume divider, bag squeezer, intermittent blower.
How does a Haemocue work?
STEP 1: sodium deoxycholate haemolyses erythrocytes releasing haemoglobin
STEP 2: sodium nitrite converts haemoglobin to methaemoglobin. Methaemoglobin reacts with sodium azide to give azidemethaemoglobin.
STEP 3: absorbance is measured at two wavelengths: 570nm and 880nm to compensate for turbidity in the sample.
STEP 4: after each reading the photometer zeros self and checks the intensity of the light source and photocell.
A Hemocue has an accuracy of +/- 0.5g/dL of lab measured values and the result takes 45-60 seconds.
What are the components of the Apfel score?
1) Female sex.
2) Non-smoker.
3) History of PONV or motion sickness.
4) Planned use of post-operative opioids.
What is the Bainbridge reflex?
Increase in heart rate in response to atrial stretch
Aims to clear the central circulation of this extra volume and returning atrial and ventricular pressures back to normal
What is the hydrogen ion concentration at physiological pH?
40 nmol/L
What does sodium nitroprusside look like?
Red/brown powder which is reconstituted in 5% dextrose used for infusions
What are some manifestations of cyanide toxicity?
Tachycardia
Arrhythmia
Hyperventilation
Sweating
Metabolic acidosis
Rising venous oxygen saturations
What is the major determinant of the diameter of a fibreoptic endoscope?
Size of the main working channel
What is a Wheatstone bridge?
Pair of voltage dividers
Designed to measure an unknown resistance by balancing two limbs of a bridge circuit so that the voltage between them is 0
Has 2 fixed resistors (R1 and R2), a variable resistor (R3) and the resistance to be measured (Rx)
To produce a voltage of 0, R3:R1 and Rx:R2 must be the same. R3 is altered until the voltmeter reads 0.
Why does glycopyrrolate not cause much sedation?
It is a synthetic quaternary amine that does not readily cross the BBB
Define a Farad with regards to capacitors.
A capacitor with capacitance of 1 Farad will store 1 Coulomb of charge when 1 Volt (not Amp) is applied across it.
What is the main reason why high flows are used at the start of anaesthesia?
Denitrogenate the breathing system and the patient’s FRC as well as increasing the rate of uptake of volatile anaesthetics
What effect do benzodiazepines have on GABA receptors?
Increase the FREQUENCY of activation of the receptors resulting in increased chloride influx
Why is a Newton valve useful when using a Penlon Nuffield 200 Ventilator to ventilate a child?
Newton valve affords the user greater control over tidal volume, and thus reduces the risk of volutrauma in paediatric patients.
What are the three main types of antifungal agent?
Azoles inhibit formation of ergosterol from lanosterol via inhibition of lanosterol 14 α-demethylase e.g. fluconazole, voriconazole, itraconazole.
Polyenes bind to ergosterol and create pores in the fungal cell membrane resulting in a disrupted electrochemical gradient and cell death. They are nephrotoxic e.g. amphotericin B, nystatin.
Echinocandins inhibit β1-3 glucan synthase. They are used to treat invasive candidiasis e.g. caspofungin, anidulafungin, micafungin.
What are the pin index configurations for: oxygen, air, carbon dioxide, nitrous oxide and entonox?
Oxygen: 2,5
Medical Air: 1,5
Carbon Dioxide: 1,6
Nitrous Oxide: 3,5
Entonox: 7
What are the differences between pencil point and cutting needles?
A pencil-point needle (e.g., Whitacre or Sprotte) has a rounded, non-cutting tip with a side hole for drug delivery. It spreads dural fibers rather than cutting them, reducing the risk of post-dural puncture headache (PDPH).
A cutting needle (e.g., Quincke) has a sharp, beveled tip that slices through tissues, making dural puncture easier but increasing the risk of PDPH due to greater dural trauma.
What humidity can be achieved with a HMEF?
HMEFs can achieve a relative humidity of 60-70%. At 37ºc the maximum absolute humidity of air is 44 g/m³.
60-70% of 44 g/m³ is 26.4 – 30.8 g/m³
Which types of gases can be detected by infrared gas absorption spectroscopy?
When a gas contains two or more dissimilar atoms
The bond between the atoms can absorb energy at specific wavelengths leading to absorption spectra that can be used to identify and quantify the gas
E.g. N2O can be detected but not O2
What is the mechanism of action of remifentanil?
Ester hydrolysis by non-specific plasma and tissue esterases
What is the Seebeck effect?
When two conductors made from dissimilar materials are joined together, a potential difference is produced at the point of contact, the magnitude of which depends on the temperature
How does a thermocouple work?
At the junction of two dissimilar metals, a voltage will be produced in direct proportion to the temperature difference between two such junctions. Typically copper and constantan are the metals used. The response is nearly linear and passes through the origin as a temperature difference of 0 produces 0 output voltage.
Uses the Seebeck effect
What is the difference between relative and absolute humidity?
Relative humidity refers to the amount of water vapour in a gas sample relative to the mass if the gas sample was fully saturated. It is measured in %.
Absolute humidity refers to the total mass of water within a given volume of gas, and is measured in g/m3.
Which device is used to measure absolute humidity?
Mass spectrometer
How does aspirin interact with warfarin?
Aspirin and warfarin are highly protein bound
Aspirin can displace warfarin from protein resulting in a greater free fraction of aspirin
What are the triggers for renin release?
Decreased sodium delivery to the macula densa
Decreased renal perfusion pressure
Sympathetic stimulation acting via beta-1 adrenoreceptors.
What is the pKa, potency and lipid solubility of alfentanil?
pKa: 6.5
Potency (relative to morphine): 10
Lipid Solubility (relative to morphine): 90
What is the pKa, potency and lipid solubility of fentanyl?
pKa: 8.4
Potency (relative to morphine): 100
Lipid Solubility (relative to morphine): 600
Why does alfentanil work faster than fentanyl?
Opioids are bases and ionise below their pKa. At physiological pH (7.35 – 7.45) fentanyl is much more ionised than alfentanil. This means that the relatively unionised alfentanil is able to exert its action more quickly, despite being less lipid soluble.
Which classes of antimicrobials inhibit bacterial cell wall synthesis?
Penicillins (e.g. tazocin), cephalosporins, carbapenems (e.g. imipenem), monobactams (e.g. aztreonam) and glycopeptides (e.g. vancomycin) inhibit cell wall synthesis.
What type of blade should be used to intubate a 1 year old?
Infants have a floppy V shaped epiglottis so a straight blade is advanced over the posterior aspect to lift the epiglottis.
Wisconsin is an example of a straight blade (similar to Miller)
What is the order of components in a scavenging system?
Collecting system
Transfer system
Receiving system
Disposal system.
Which indicators are used in dilutional techniques to estimate different fluid volumes?
Deuterium oxide – Total body water
Inulin – Extracellular fluid
Plasma – Radiolabelled albumin, Evan’s blue
Red cell volume – Radiolabelled red cells
What should blood pressure in the community be controlled to prior to having an operation?
< 160/100 mm Hg
List some key differences between the respiratory system of a child vs an adult.
Narrowest point of airway
Child: cricoid cartilage
Adult: laryngeal inlet
Minute ventilation
Child: higher (100-150 ml/kg/min vs 60)L
Basal oxygen consumption
Child: higher (6 vs 3.5 ml/kg/min)
Epiglottis
Child: larger
List factors that reduce transfer factor on lung function testing.
Emphysema, primary pulmonary hypertension, pulmonary embolism and pulmonary fibrosis
Why does diclofenac increase INR when coadministered with warfarin more than aspirin?
Diclofenac is 99.5% protein bound whereas aspirin is 85% protein bound
What dose of propofol is used for induction in adults and children?
Adults: 1-3 mg/kg
Children: 2-6 mg/kg
What is the onset and offset time of a bolus of propofol?
Onset: 30 seconds
Offset: 3-7 mins
What is the induction dose of thiopentone?
5-7 mL/kg
What is the onset and offset of a bolus of thiopentone?
Onset: 30 seconds
Offset: 5-10 mins
What is the induction dose of ketamine?
IV: 0.5-2 mg/kg
IM: 2-10 mg/kg
What is the onset and offset time of a bolus dose of ketamine used for induction?
Onset: 1-2 mins
Offset: 5-10 mins
What dose of fentanyl is used for co-induction of anaesthesia?
1-2 mcg/kg
What is the rapid sequence dose of rocuronium used?
1 mg/kg
What are the main indications for using neuromuscular blockade?
Tracheal intubation
Aid mechanical ventilation
Surgical access
How protein bound is propofol?
98%
Which antibiotics exacerbate weakness in myasthenia gravis?
Aminoglycosides
Fluoroquinolones
Macrolides
Outline the Mallampati scoring system.
Class I – soft palate, uvula, fauces and pillars visible.
Class II – soft palate and fauces visible, tip of uvula obscured.
Class III – soft palate and base of uvula only visible.
Class IV – hard palate only.
Why is sevoflurane better than isoflurane for gas induction?
Isoflurane has a longer onset time than sevoflurane (blood:gas coefficient 1.4 vs 0.7), and so this is less suitable
Why is there a lower threshold for RSI in trauma cases?
Trauma is associated with delayed gastric emptyin
What does the recurrent laryngeal nerve supply?
Supplies all of the intrinsic muscles of the larynx except cricothyroid which is supplied by the external branch of the superior laryngeal nerve
What are the effects of ANP?
Reduced sodium reabsorption in the collecting duct
Reduced renin secretion (and, hence, reduced aldosterone activity)
Reduced pulmonary capillary wedge pressure
Vasodilation of the afferent arteriole (increase glomerular filtration)
What is a Cardiff aldasorber?
Method of passive scavenging which can be connected directly to scavenging tubing
Absorbs volatile gases onto the charcoal
Must be replaced every 12 hours and only indication of exhaustion is increased weight of the canister
Heating the aldasorber will release volatile anaesthetics so the adsorber can be reused
What is the difference between absolute and relative humidity?
The absolute humidity is the mass of water vapour in a given volume of gas at a given temperature and pressure and is often expressed in g/m³.
The relative humidity is the ratio of the actual mass of water vapour compared to the maximum amount of water vapour the gas could contain at the same temperature and pressure.
What is the dew point?
The temperature to which a given volume of gas must be cooled for water vapour to condense.
This occurs when the relative humidity is 100%. If air has a lower humidity therefore a greater temperature drop is required to reach the dew point.
What is the maximum possible absolute humidity at body temperature?
44 g/m³
What does COSSH specify as the maximum exposure to anaesthetic agents over an 8 hour period
Nitrous Oxide: 100 ppm
Enflurane and Isoflurane: 50 ppm
Halothane: 10 ppm
No recommendation made for sevoflurane (but advised < 20 ppm)
What factors affect the angle of refraction when light passes into a different medium?
Angle of incident ray
Refractive index of air
Refractive index of material
Speed of light in material
What is the difference between pleated hydrophobic filters and electrostatic filters?
Pleated hydrophobic filters are made of sheets of resin bonded glass fibres, these have a very small pore size and rely on naturally occurring electrostatic interactions. Electrostatic filters are made from polypropylene fibres which an electrostatic charge may be applied to.
Electrostatic filters create less resistance to flow
Pleated filters have higher filtration efficiency
What is the pKa, lipid solubility, potency, volume of distribution and protein binding of Alfentanil?
pKa 6.5
Relative Lipid Solubility: 90 x Morphine
Potency: 10 x Morphine
Volume of Distribution: 0.6 L/kg
Protein Binding: 90%
In short, why does the context sensitive half life of fentanyl increase with a prolonged infusion?
This is because clearance due to distribution is high compared to clearance due to elimination. In other words, fentanyl is being stored in tissues instead of being cleared from the plasma. Fentanyl CSHT reaches a peak of approximately 5 hours after a duration of infusion of 12 hours.
How often should a galvanic fuel cell be calibrated?
Calibrate daily using a two point method with 21% (room air) and 100% oxygen.
Describe the phases of the vomiting reflex.
In the pre-ejection phase there is a prodromal nausea, increased salivation, gastric relaxation and retrograde peristalsis of the stomach. Protective airway changes occur: a deep inspiratory breath elevates the hyoid and larynx, relaxes the upper gastro-oesophageal sphincter, elevates the soft palate and importantly closes the glottis.
In the ejection phase abdominal and diaphragmatic contraction occurs alongside retrograde oesophageal contraction leading to the forceful ejection of gastric contents.
Describe the blood flow to the liver.
The liver receives around 25% of the cardiac output at rest.
The majority (~70%) of this flow is provided by the hepatic portal vein (made up of splenic vein and superior mesenteric vein)
NOTE: hepatic artery provides the majority of the oxygen to the liver
How is atracurium metabolised?
Ester hydrolysis: 60%
Hofmann degradation: 40%
NOTE: atracurium is a benzylisoquinolinium muscle relaxant
What is the blood: gas partition coefficient of enflurane?
1.8
What is the MAC of enflurane?
1.68%
What is the blood: gas partition coefficient of desflurane?
0.45
What is the molecular weight of halothane?
197
How much is halothane metabolised?
20%
How can linezolid precipitate serotonin syndrome?
It is a weak, non-selective monoamine oxidase A and B inhibitor. It may react with SSRIs and precipitate serotonin syndrome.
What is a major clinical difference between R and S-ketamine?
R-ketamine is less potent and has more hallucinogenic effects than S-ketamine
How is S-warfarin different from R-warfarin?
S-warfarin is more protein bound than R-warfarin
What are the main differences between cisatracurium and atracurium?
Cisatracurium is more potent and leads to less histamine release than ‘atracurium’, which is actually a mixture of 10 isomers
What is a main difference between L-bupivacaine and D-bupivacaine?
L-bupivacaine is less cardiotoxic than D-bupivacaine
How is a transversus abdominis plane block performed and which nerves does it target?
Infiltrate LA into plane between internal oblique and transversus abdominis
Nerves: iliohypogastric, ilioinguinal and subcostal
What effect does neostigmine have on the duration of action of mivacurium and suxamethonium?
Neostigmine also inhibits pseudocholinesterase leading to increased duration of action of suxamethonium and mivacurium
What is the mechanism of halothane hepatitis?
The generation of the metabolic trifluoroacetyl chloride, which forms covalent bonds with hepatic proteins, inducing antibody formation and subsequently necrosis.
