Anaesthetic awareness

BOX 9.7 Anaesthetic awareness reducing the fear of future operations... 

ADRENERGIC NEURONE BLOCKERS-GUANETHIDINE LOCAL ANAESTHETICS l clinical efficacy of guanethidine when used in the treatment of complex regional pain syndrome-type 1 The local anaesthetic i the reuptake of guanethidine Be aware. Consider use of a local anaesthetic that minimally inhibits reuptake, e.g. lidocaine when possible... 

ASPIRIN ANAESTHETICS - GENERAL 1 requirements of thiopentone when aspirin (1 g) used as premedication Uncertain at present Be aware of possible 1 dose requirements for thiopentone... 

BETA-BLOCKERS LIDOCAINE 1. Risk of bradycardia (occasionally severe), 1 BP and heart failure with intravenous lidocaine 2. Risk of lidocaine toxicity due to t plasma concentrations of lidocaine, particularly with propranolol and nadolol 3. t plasma concentrations of propranolol and possibly some other beta-blockers 1. Additive negative inotropic and chronotropic effects 2. Uncertain, but possibly a combination of beta-blocker-induced reduction in hepatic blood flow (due to 1 cardiac output) and inhibition of metabolism of lidocaine 3. Attributed to inhibition of metabolism by lidocaine 1. Monitor PR, BP and ECG closely watch for development of heart failure when intravenous lidocaine is administered to patients on beta-blockers 2. Watch for lidocaine toxicity 3. Be aware. Regional anaesthetics should be used cautiously in patients with bradycardia. Beta-blockers could cause dangerous hypertension due to stimulation of alpha-receptors if epinephrine is used with focal anaesthetic... 

ANAESTHETICS, LOCAL -ROPIVACAINE CNS STIMULANTS -MODAFINIL May cause 1 plasma concentrations of these substrates if CYP1A2 is the predominant metabolic pathway and alternative metabolic pathways are either genetically deficient or affected Modafinil is moderate inducer of CYP1A2 in a concentration-dependent manner Be aware... 

SULPHONAMIDES ANAESTHETICS - GENERAL t effect of thiopentone but duration of action shortened Uncertain possibly displacement from protein-binding sites Be aware that a smaller dose may be needed... 

CANNABIS ANAESTHETICS-LOCAL-LIDOCAINE Unpredictable changes in plasma concentrations. Risk of toxicity or therapeutic failure with intravenous lidocaine Induction or inhibition of CYP3A4-mediated metabolism by cannabis. It is not yet known whether the effects are dependent on the degree of cannabis consumption Be aware. Watch for signs of toxicity, especially when cannabis use abruptly changes... 

B. Several studies suggest that beta blockers, such as atenolol and esmolol, given before induction reduce the anaesthetic dose requirement and may potentiate hypnosis. However, there are concerns that reducing the dose of anaesthetic may increase the risk of intra-operative awareness and it has been suggested that the use of BIS to predict the depth of anaesthesia in the presence ofbeta blockers may not be valid.There is a possibility that acute as well as chronic administration ofbeta blockers may prevent perioperative cardiac complications, but more study is needed on this. ... 

Information is fairly sparse, but these interactions appear normally to be of relatively minor importance. Be aware that changes in neuromuscular blockade (increases or decreases) can occur if beta blockers are used, but they seem to be unpredictable, and then often only modest in extent. The possible combined cardiac depressant effects of beta blockade and anaesthesia are well known (see Anaesthetics, general + Beta blockers, p.97). These effects may not be prevented when a neuromuscular blocker is used that has little or no effect on the vagus (such as atracurium or vecuronium). 

The interaction between metoclopramide and suxamethonium is an established but not extensively documented interaction of only moderate or minor clinical importance. However anaesthetists should be aware that some enhancement of blockade can occur. The interaction between metoelopra-mide and mivacurium has only more recently been demonstrated. Metoclopramide appears to allow a reduction in the infusion rate of mivaeurium and it causes a significant delay in recovery from neuromuscular block. Care is recommended during combined use. The authors of the suxamethonium reports also point out that plasma cholinesterase activity is reduced in pregnancy and so suxamethonium sensitivity is more likely in obstetric patients. Ester-type local anaesthetics also depend on plasma... 

A woman was admitted for an elbow replacement. During the operation she awoke, paralysed and able to hear the discussions amongst the surgical team. She was terrified, in great pain and absolutely helpless. The lack of anaesthetic was fortunately noticed, and she was next aware of waking in recovery screaming. 

One case of anaphylactic shock (27 ) and one of generalized exfoliative dermatitis (28 ) after the use of lidocaine as a local anaesthetic have been described. The intravenous administration of lidocaine in patients with myocardial infarction sometimes also leads to undesirable side effects, of which hypotension is the best known. The problem is mainly one for the cardiologist, but since inadvertent intravenous injection during local anaesthesia may occur, the anaesthetist must be aware of it. A case of sinusbradycar-dia after a bolus injection of 50 mg (29 -) and an atrioventricular block after 800 mg, given in the course of 12 hours (30 ) have been described. Two fatalities, one due to ventricular fibrillation after 50 mg and one to sinus arrest after 100 mg, have been re-... 

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