Anaesthetic management of emergency caesarean section in a patient with Noonan's syndrome--case report and literature review.

Patients with Noonan's syndrome present a multiplicity of challenges to the anaesthetist, particularly with regard to cardiovascular, spinal, and airway abnormalities. Anaesthetist may have to deal with an increasing number of these patients presenting to anaesthesia departments requesting analgesia and anaesthesia for surgery of labour. Early detection and planing between obstetricians, midwives and anaesthetists will help successful management of these patients. Alternative methods of management should be discussed fully with patients. Regional anaesthesia, although may be difficult in these patients, is a safe alternative compared to expensive general anaesthesia.

Pulse oximetry: an added criterion for discharge from the post-operative care unit.

Based on the observation that the degree of wakefullness measured by Post Anesthetic Recovery (PAR) score in some patients does not correlate with their oxygen saturation, the authors decided to carry on a study to validate that assumption. Three hundred patient ASA I & II were studied. Oxygen saturation and PAR score were recorded from the time of arrival till their discharge by the recovery room staff nurses. Thirty one patients out of one three hundred (10%) were found to be hypoxic (saturation < 95%) despite their high PAR score. The degree of wakefullness as measured by PAR scores cannot be used to establish an end point for oxygen supplementation. Oxygen supplementation and SpO2 monitoring are recommended in all patients recovering from anesthesia.

Adverse effects of neuromuscular blockers and their antagonists.

Among all the drugs used for general anesthesia, neuromuscular blockers appear to play a prominent role in the incidence of severe adverse reactions. It now seems likely that most serious adverse drug reactions occurring during anesthesia are immunological in type. The frequency of life-threatening anaphylactic or anaphylactoid reactions occurring during anesthesia has been estimated to be between 1 in 1000 and 1 in 25,000 anesthetic procedures, with the neuromuscular blockers being involved in 80% of cases. The mortality from such serious reactions is reported to be in the range of 3.4 to 6%. The highly immunogenic drug, suxamethonium chloride (succinylcholine), was found to be the most hazardous agent. Drug-specific immunoglobulin E antibodies to suxamethonium chloride and other neuromuscular blockers have been demonstrated. This sensitivity to neuromuscular blockers seems to be a long-lasting phenomenon. During anesthesia, the clinical features of an allergic reaction are often masked. Tachycardia and circulatory collapse may be the only signs of an allergic reaction, and they are easily misdiagnosed. Bronchospasm is reported to be present in about 40% of cases. Successful management of these patients includes stabilisation during the acute reaction and avoidance of future reactions. The latter is based on the identification of the causative drug and potentially cross-reacting compounds. The use of suxamethonium chloride is associated with many other adverse effects, such as fasciculations, myalgia, potassium release, changes in the heart rate, increases in intragastric and intraocular pressures, and malignant hyperthermia. Because of the dangers of hyperkalemic cardiac arrest suxamethonium chloride administration in children with unrecognised muscular dystrophy, there have now been moves to limit the use of this drug in children. Although neuromuscular blockers are designed to specifically block nicotinic cholinergic receptors at the neuromuscular junction, many bind to muscarinic cholinergic receptors on ganglia and smooth muscle, and alter parasympathetically mediated heart rate and airway calibre. Most benzylisoquinolinium muscle relaxants can induce histamine release, especially when they are administered rapidly, which can lead to disturbances of cardiovascular function. In addition, nondepolarising neuromuscular blockers have been implicated in causing generalised weakness following their long term administration to patients on an intensive care unit. The problem with these adverse drug reactions is their upredictable nature. Therefore, prompt recognition with appropriate therapy can help to improve the outcome.

Adverse effects and drug interactions associated with local and regional anaesthesia.

Systemic and localised adverse effects of local anaesthetic drugs usually occur because of excessive dosage, rapid absorption or inadvertent intravascular injection. Small children are more prone than adults to methaemoglobinaemia, and the combination of sulfonamides and prilocaine, even when correctly administered, should be avoided in this age group. The incidence of true allergy to local anaesthetics is rare. All local anaesthetics can cause CNS toxicity and cardiovascular toxicity if their plasma concentrations are increased by accidental intravenous injection or an absolute overdose. Excitation of the CNS may be manifested by numbness of the tongue and perioral area, and restlessness, which may progress to seizures, respiratory failure and coma. Bupivacaine is the local anaesthetic most frequently associated with seizures. Treatment of CNS toxicity includes maintaining adequate ventilation and oxygenation, and controlling seizures with the administration of thiopental sodium or benzodiazepines. Cardiovascular toxicity generally begins after signs of CNS toxicity have occurred. Bupivacaine and etidocaine appear to be more cardiotoxic than most other commonly used local anaesthetics. Sudden onset of profound bradycardia and asystole during neuraxial blockade is of great concern and the mechanism(s) remains largely unknown. Treatment of cardiovascular toxicity depends on the severity of effects. Cardiac arrest caused by local anaesthetics should be treated with cardiopulmonary resuscitation procedures, but bupivacaine-induced dysrhythmias may be refractory to treatment. Many recent reports of permanent neurological complications involved patients who had received continuous spinal anaesthesia through a microcatheter. Injection of local anaesthetic through microcatheters and possibly small-gauge spinal needles results in poor CSF mixing and accumulation of high concentrations of local anaesthetic in the areas of the lumbosacral nerve roots. In contrast to bupivacaine, the hyperbaric lidocaine (lignocaine) formulation carries a substantial risk of neurotoxicity when given intrathecally. Drugs altering plasma cholinesterase activity have the potential to decrease hydrolysis of ester-type local anaesthetics. Drugs inhibiting hepatic microsomal enzymes, such as cimetidine, may allow the accumulation of unexpectedly high (possibly toxic) blood concentrations of lidocaine. Reduction of hepatic blood flow by drugs or hypotension will decrease the hepatic clearance of amide local anaesthetics. Special caution must be exercised in patients taking digoxin, calcium antagonists and/or beta-blockers.

Adverse effects of neuromuscular blockers and their antagonists.

Among all the drugs used for general anaesthesia, neuromuscular blockers appear to play a prominent role in the incidence of severe adverse reactions. It now seems likely that most serious adverse drug reactions occurring during anaesthesia are immunological in type. The frequency of life-threatening anaphylactic or anaphylactoid reactions occurring during anaesthesia has been estimated to be between 1 in 1000 and 1 in 25,000 anaesthetic procedures, with the neuromuscular blockers being involved in 80% of cases. The mortality from such serious reactions is reported to be in the range of 3.4 to 6%. The highly immunogenic drug, suxamethonium chloride (succinylcholine), was found to be the most hazardous agent. Drug-specific immunoglobulin E antibodies to suxamethonium chloride and other neuromuscular blockers have been demonstrated. This sensitivity to neuromuscular blockers seems to be a long-lasting phenomenon. During anaesthesia, the clinical features of an allergic reaction are often masked. Tachycardia and circulatory collapse may be the only signs of an allergic reaction, and they are easily misdiagnosed. Bronchospasm is reported to be present in about 40% of cases. Successful management of these patients includes stabilisation during the acute reaction and avoidance of future reactions. The latter is based on the identification of the causative drug and potentially cross-reacting compounds. The use of suxamethonium chloride is associated with many other adverse effects, such as fasciculations, myalgia, potassium release, changes in the heart rate, increases in intragastric and intraocular pressures, and malignant hyperthermia. Because of the dangers of hyperkalaemic cardiac arrest after suxamethonium chloride administration in children with unrecognised muscular dystrophy, there have now been moves to limit the use of this drug in children. Although neuromuscular blockers are designed to specifically block nicotinic cholinergic receptors at the neuromuscular junction, many bind to muscarinic cholinergic receptors on ganglia and smooth muscle, and alter parasympathetically mediated heart rate and airway calibre. Most benzylisoquinolinium muscle relaxants can induce histamine release, especially when they are administered rapidly, which can lead to disturbances of cardiovascular function. In addition, nondepolarising neuromuscular blockers have been implicated in causing generalised weakness following their long term administration to patients on an intensive care unit. The problem with these adverse drug reactions is their unpredictable nature. Therefore, prompt recognition with appropriate therapy can help to improve the outcome.

Clinically significant drug interactions with general anesthetics--incidence, mechanims and management.

The frequency of adverse drug interactions increases disproportionately with the increase in the number of drugs given to patients. It was shown that 40% of patients given 16 drugs experienced an adverse drug interaction, compared with 5% of patients given fewer than 6 drugs. The magnitude of the drug interaction problem increases substantially in anesthetised patients because of: (i) the increased use of multiple drugs in the preoperative and intraoperative periods; and (ii) the growing population of geriatric patients who, in addition to having diminished drug metabolising capacity, are often prescribed multiplied medications for concomitant medical illness. Drug interactions with volatile and intravenous anesthetics can be divided into those that are pharmacokinetic and pharmacodynamic in nature. Pharmacokinetic interactions occur when the absorption, distribution, metabolism or excretion of a drug is altered by the coadministration of a second drug. Pharmacodynamic interactions involve a change in the pharmacological effect of a drug as a result of the action of second drug at receptor sites.