Anaesthesia

Question 1

General Anaesthesia can be induced with

Answer 1

either a volatile gas or by IV administration.

Question 2

Drugs used for IV anaesthesia: Common side effects

Answer 2

include pain at injection site and extraneous muscle movements (movement during surgery). Pain on injection can be overcome by injecting into larger veins or by giving an opioid analgesic just before induction. Extraneous muscle movement can be minimised also by an opioid analgesic or a short acting benzodiazepine.

Question 3

Drugs used for IV anaesthesia examples

Answer 3

• Propofol
• Thiopental sodium
• Etomidate
• Ketamine

Question 4

Propofol

Answer 4

is the most commonly used IV anaesthetic in adults and children, but it is not commonly used in neonates. Propofol is associated with rapid recovery and less hangover effect than other IV anaesthetics.
Common side effects: Arrhythmias, hypotension, headache

Question 5

Thiopental sodium

Answer 5

is a barbiturate that is used for induction of anaesthesia but has no analgesic properties. Thiopental once administered redistributes into other tissues, therefore awakening from a moderate dose is rapid. However, metabolism is slow and sedative effects can persist for 24 hours.

Question 6

Etomidate

Answer 6

is an IV agent associated with rapid recovery without a hangover effect. Etomidate causes less hypotension effect than Propofol and Thiopental during induction. It is mainly used in paediatrics, usually when repeated administrations are required. It produces a high incidence of extraneous muscle movements, which can be minimised by an opioid analgesic or short-acting benzodiazepine given just before induction.
Common side effects: hypotension, movement disorders, respiratory disorders, nausea and vomiting.

Question 7

Ketamine

Answer 7

is rarely used; it causes less hypotension than thiopental sodium and propofol during induction. It is mainly used for paediatrics, particularly when repeated administration is required. The main disadvantages of Ketamine are the high incidence of hallucinations, nightmares and other psychotic effects; these effects can be reduced by Benzodiazepines e.g. Diazepam and Midazolam.

Question 8

Volatile liquid anaesthetics

Answer 8

Volatile liquids can be used for inducing and maintaining anaesthesia and also following induction with an IV anaesthetic.

• isoflurane, desflurane, sevoflurane, nitrous oxide

Question 9

Isoflurane

Answer 9

can cause an increase in heart rate, particularly in younger patients. Muscle relaxation effects also occur. Isoflurane is the preferred inhalation anaesthetic for the use in obstetrics (pregnancy and child-birth)

Question 10

Desflurane

Answer 10

is less potent than Isoflurane, with a rapid recovery time from anaesthesia. The drug is not recommended for induction of anaesthesia, as it can irritate the upper respiratory tract system.

Question 11

Sevoflurane

Answer 11

is more potent than desflurane. It has non-irritant effects and therefore can be used for inhalation induction of anaesthesia. It has little effects on the heart rhythm compared to other volatile liquid anaesthetics.

Question 12

Nitrous oxide

Answer 12

can be used for the maintenance of anaesthesia and in sub-anaesthetic concentrations. Nitrous oxide is not very potent and therefore is used in combination with other anaesthesia drugs.

Question 13

Malignant hyperthermia

Answer 13

Malignant hyperthermia is a rare but potentially lethal complication of anaesthesia. Symptoms include rapid increase in temperature, increased muscle rigidity, tachycardia and acidosis. Most common triggers are volatile anaesthetics.
- Dantrolene sodium is used to treat malignant hyperthermia

Question 14

SEDATION, ANAETHETICS and RESUSCITATION IN DENTAL PRACTICE:

Answer 14

• Diazepam and Temazepam are effective anxiolytics for dental treatment in adults.
• Sedating patients during procedures is used to reduce fear and anxiety, to control pain, and to minimise excessive movement. The patient should be monitored from when the sedative is given and until awakening of the patient.

Question 15

LONG-TERM MEDICATION to CONTINUE DURING SURGERY:

Answer 15

• Corticosteroids: Patients on long term steroids (>10mg prednisolone within 3 months of surgery) may suffer adrenal atrophy. Therefore, if stopped before surgery they can suffer hypotension. Hence should be continued. This includes high-dose inhaled corticosteroids.
o Minor Surgery: Oral steroid in the morning of surgery or IV hydrocortisone.
o Moderate-Major Surgery: Oral steroid in the morning, IV hydrocortisone at induction, then IV hydrocortisone TDS for 24h for moderate and 48-72h for major.
• Type 1 diabetics should start adjustable, continuous IV infusion of insulin.
o Inject patient’s normal insulin night before surgery
o Early in the day operation start IV infusion of glucose in KCl and also give IV soluble insulin in NaCl in a syringe pump (if pump not available add in glucose solution)
o Once patients start to eat/drink give S.C insulin before breakfast and stop insulin 30 min later. If patient not on insulin previously give initial dose of 30-40 U daily of soluble insulin in 4 divided units (before meals) and intermediate acting insulin at bedtime.
• Antiepileptic’s
• Antiparkinsonian drugs
• Antipsychotics
• Anxiolytics
• Bronchodilators
• Cardiovascular drugs
• Glaucoma drugs
• Immunosupressants
• Drugs of dependence
• Thyroid or antithyroid drugs
• Anticoagulation or antiplatelet drugs should be assessed + switched to unfractionated heparin or LMWH

Question 16

LONG-TERM MEDICATION to STOP DURING SURGERY:

Answer 16

• Potassium-sparing diuretics may need to be withheld on the morning of the surgery because hyperkalaemia may develop if renal perfusion is impaired or if there is tissue damage.
• ACE inhibitors and ARB’s can be associated with severe hypotension after induction of anaesthesia, thus these drugs may need to be discontinued 24 hours before surgery.
  Herbal medicines may be associated with adverse effects when given with anaesthetic drugs and consideration should be given to stopping them before surgery.
• MAO-I Can interact with drugs during surgery eg: pethidine.
• TCA Don’t have to be stopped but they can increase risk of arrhythmias and hypotension.
• Lithium Stop 24 hours before major surgery. Not needed in minor surgery.
• COC Stopped 4 weeks before major surgery and all surgery to legs and long immobilisation of lower limbs. Restarted at the first mensuration cycle occurring 2 weeks’ full mobilisation. Progesterone can be offered as an alternative. If oestrogen containing contraceptive cannot be stopped thromboprophylaxis with LWM heparin or unfractionated heparin and compression hosiery is advised.

Question 17

PERI-OPERATIVE ANALGESIA:

Answer 17

• Drugs that affect Gastric pH: H2 receptor antagonists can be used 1-2 hours before surgery to increase pH + reduce volume of gastric fluid because regurgitation and aspiration can occur in general anaesthesia.
• Antimuscarinics: Glycopyrronium bromide reduces salivary secretions and used with neostigmine for reversal on non-depolarising neuromuscular blocking drugs.
• Sedative Drugs: Benzodiazepines (Diazepam, Temazepam, Lorazepam, Midazolam) can be used the night before and on the day to reduce anxiety about surgery. Flumazenil in a benzodiazepine antagonist and reverses its effects. It has a short half-life therefore requires repeat dosing.
• Reversal of Respiratory Depression: Is a major concern with opioid analgesics therefore Naloxone can be given (short half-life; need repeat dosing). However, will also reduce the analgesic effects of the opioid.
• Analgesia: moderate pain- NSAID (ibuprofen, diclofenac, acemetacin, paracetamol). Opioids rarely used.
• Non-opioid analgesics:
  NSAID’s are useful alternatives or adjuncts to opioids for the relief of postoperative pain as they don’t depress respiration, do not impair GI motility and also don’t lead to dependence. However, NSAID’s may be not effective for severe pain. Diclofenac and paracetamol can be given via mouth and injection.
• Opioid analgesics:
  Given in small doses before or with induction reduce dose requirements of some drugs during anaesthesia
  Alfentanil, Fentanyl + Remifentanil are useful as they act within 1-2 mins and have short duration of action. Repeated intra-operative doses of opioids should be given with care as respiratory depression can persist postoperatively. Alfentanil, Fentanyl and Remifentanil can cause muscle rigidity, mainly of the chest wall or jaw; and this can be managed by neuromuscular blocking agents.
  Remifentanil is rapidly metabolised causing it to have a short duration of action; which allows prolonged administration at high doses imposing little risk of postoperative respiratory depression. Do not give as IV injective intraoperatively, but a continuous infusion is suited. Before stopping remifentanil, a supplementary analgesic should be given

Question 18

• Intravenous –

Answer 18

Propofol, thiopental

Question 19

• Inhalational –

Answer 19

nitrous oxide, desflurane

Question 20

• Analgesics –

Answer 20

alfentanil, fentanyl, remfentanyl

Question 21

• Neuromuscular blockers –

Answer 21

suxamethonium

Question 22

• Reversal of neuromuscular blockade –

Answer 22

neostigmine

Question 23

• Antimuscarinics –

Answer 23

atropine, glycopironium

Question 24

Local anaesthetics act by

Answer 24

causing a reversible block to conduction along nerve fibres. Local anaesthetics cause dilation of blood vessels and the addition of a vasoconstrictor e.g. adrenaline preparations; diminishes local blood flow, slowing the rate of absorption and thereby the anaesthetic effects.

Question 25

Adrenaline/ephedrine must be used

Answer 25

in a low concentration when administered with a local anaesthetic. It is not advisable to give adrenaline/epinephrine with a local anaesthetic injection because the risk of ischaemic necrosis.

Question 26

In patients with severe hypertension or unstable cardiac rhythm

Answer 26

the use of adrenaline/ epinephrine with a local anaesthetic may be hazardous. For these patients an anaesthetic without adrenaline/ epinephrine should be used.

Question 27

Bupivacaine

Answer 27

has a longer duration of action than other local anaesthetics, but has a slow onset of action, taking up to 30 minutes for full effect. Bupivacaine is particularly useful for continuous epidural analgesia in labour. It can also be used in postoperative pain relief. Bupivacaine is principal drug for spinal analgesia.

Question 28

Levobupivacaine

Answer 28

has similar anaesthetic and analgesic properties with Bupivacaine, however is it thought to have fewer side effects.

Question 29

Lidocaine

Answer 29

is effectively absorbed from the mucous membranes and has a duration of action of 90 minutes.

Question 30

Prilocaine

Answer 30

is a local anaesthetic with low toxicity with similar properties to Lidocaine. A solution form may be used for spinal anaesthetic.

Question 31

Ropivacaine

Answer 31

is a similar local anaesthetic to bupivacaine however it is less cardiotoxic and is also less potent.

Question 32

Tetracaine

Answer 32

is rapidly absorbed from mucous membranes BUT should never be applied to inflamed, traumatised or high vascular surfaces. It should never be used to provide anaesthesia for bronchoscopy or cystoscopy as lidocaine is a safer alternative.

Question 33

Dental anaesthesia

Answer 33

Lidocaine hydrochloride is widely used in dental procedures and is mostly used in combination with adrenaline/ephedrine. In patients with severe hypertension or unstable cardiac rhythm, meprivacaine without adrenaline may be used.