The use of muscle relaxants in burnt children

Anaesthetic-associated mortality and anaesthetic contributory death: the South African medicolegal approach

The medicolegal approach to cases of anaesthetic-associated mortality and anaesthetic contributory death (ACD) occurring in Johannesburg, South Africa is presented. The approach adopted has been found to be reasonably workable in practice and places heavy emphasis on the surgical and anaesthetic-related reasons for perioperative deaths and, in particular, on their multifactorial aetiology. It is recognised that in view of the multifactorial nature of the anaesthetic environment certain errors in clinical anaesthetic management are neither precisely quantifiable nor assessable. It is further emphasized that perioperative quality control programs as well as Inquest Court proceedings should comprise input by a team of specialists and which include clinical anaesthesiologists, surgeons and forensic pathologists.

[Curare and burns]

Burns of more than 15% of the body surface area result in major physiological changes with an alteration of cardiovascular, pulmonary, hepatic and renal functions, as well as modifications in the pharmacokinetics and the pharmacodynamics of many drugs. Among these, a major change in the activity of muscle relaxants occurs which can be specific to this pathology. Succinylcholine is contra-indicated during recovery from a burn trauma because of a possible hyperkaliemic response, directly related to the dose, the post-burn delay and the area of burned body surface. The kaliemic response and the related cardiac complications remain unpredictable. The height of twich depression with small doses of succinylcholine such as 0.1 to 0.2 mg.kg-1, demonstrates the hypersensitivity to this agent and does cause neither metabolic disturbances nor cardiac arrest. Nevertheless, the administration of succinylcholine is contra-indicated for from the 5th day on at least two years after the burn injury. Conversely, the action of non-depolarizing muscle relaxants is characterized by a resistance, which is correlated to both the post-traumatic delay and the extent of the burned area. It starts on about the seventh day, reaches peak intensity between day 15 and day 40 and can persist up two years after the thermal injury. In the course of a burn, the so-called "immature" acetylcholine receptors, characterized by the substitution of the sub-unit epsilon by a protein gamma, increase at the level of the end plate areas and the extra-synaptic muscle membrane. These receptors explain both the hyperkaliemic response and the hypersensitivity to succinlycholine.(ABSTRACT TRUNCATED AT 250 WORDS)

[Cardiac arrest during anesthesia and recovery period]

Cardiac arrests (CA) occurring during anaesthesia and recovery can be classified into three groups: CA not related to anaesthesia (NACA), CA related to anaesthesia (ACA), whether partially (PACA) or totally (TACA). In the French survey, NACAs were three times more frequent than ACAs. Nearly 25% of ACAs occurred at induction and consisted mainly in TACAs. Another quarter of ACAs occurred during maintenance and consisted mainly in PACAs. About 50% of ACAs occurred after the end of anaesthesia and had the highest mortality rate. Cardiac arrest corresponds to the status of a heart unable to generate the minimum aortic blood flow required for functioning of vital organs. For the brain, a zero-blood flow of more than 4 seconds results in coma. Consequently CA exists when the time interval between two subsequent efficient systoles is greater than 4 seconds. Anaesthetic agents can result in CA by 1) overdose (absolute, relative), 2) anaphylactoid/anaphylactic reactions, 3) specific effects (acetylcholine-like effect, hyperkalaemia and malignant hyperthermia for succinylcholine; vagal effect of vecuronium and atracurium; cardiotoxicity of bupivacaine) and 4) drug interaction. In hypoxic CA, severe neurologic impairment often still exists at the time of onset of CA. The anaesthesia machine and controlled ventilation can induce CA by hypoxic ventilation, overdose of anaesthetic vapour, excessive CO2 reinhalation, hypoventilation, disconnection, excessive pressure in airways. Cardiac hypothermia can be a cause of CA as well as a cause of unsuccessful CPR. Massive infusion of unwarmed fluids and IPPV with unheated gases generate a temperature gradient within the heart which may result in severe arrhythmias and CA.(ABSTRACT TRUNCATED AT 250 WORDS)

Serious morbidity attributable to anaesthesia. Considerations for prevention

The types and frequency of complications attributable solely to anaesthesia, and which caused serious morbidity and substantial negative outcome, were examined in a prospective study of 7306 anaesthetics. The analysis demonstrated that severe complications and mortality attributable to anaesthesia occurred in 0.59% (1:170) and 0.04% (1:2500) of patients respectively. The data suggest that "high-risk' patients are more likely to be affected by errors and a substantial negative outcome than more healthy patients. We judged one-third of the anaesthesia-related morbidity to be preventable. Anaesthetists are faced with an increasing number of patients who are at high risk, and who undergo increasingly extensive surgical interventions. Concomitant with the increasing complexity of care and increasing demands on the anaesthetists may be an expected increase in the incidence of errors. Recognition of the importance of human factors in morbidity and mortality attributable to anaesthesia is a necessary first step.

Clinical pharmacology of muscle relaxants in patients with burns

Pathophysiologic changes accompanying burn trauma can alter the pharmacokinetics and pharmacodynamic responses to neuromuscular relaxants. Pathophysiologic changes that can potentially affect kinetics in the hypermetabolic phase of burn injury include increased hepatic blood flow, increased glomerular filtration, and increased protein binding. Except for D-tubocurarine, the pharmacokinetics of neuromuscular relaxants relative to burn trauma have not been studied. The unbound volume of distribution, clearance, and half-life of D-tubocurarine were not significantly different from controls, but the plasma binding and renal elimination at 24 hours was increased in burn patients. The aberrant pharmacodynamic responses to neuromuscular relaxants in burn patients include the potential for lethal hyperkalemia with the administration of depolarizing relaxant, succinylcholine, and a 2.5- to 5.0-fold increase in the dose or plasma concentration requirement for nondepolarizing relaxant, including D-tubocurarine, metocurine, pancuronium, and atracurium. The altered pharmacodynamic responses are probably related to an increase in nicotinic acetylcholine receptor number. An alternative to succinylcholine to produce rapid-onset neuromuscular paralysis include the administration of 3XED95 doses of pancuronium and metocurine in combination (but recovery from paralysis is prolonged). Vecuronium and atracurium have good cardiovascular stability and faster recovery times even in high dosages in healthy patients, but the pharmacokinetics and pharmacodynamics of these drugs in patients with burns have not been fully characterized.

Plasma cholinesterase variants and the anaesthetist

Biochemical properties of plasma cholinesterase of significance to the anaesthetist are reviewed. The role of the genetic variants of the enzyme in suxamethonium sensitivity and hyperthermia are discussed with emphasis on the pregnant patient. Altered gene frequencies of the enzyme variants in some mental disorders is commented upon.

Rapid intubation with fazadinium. A comparison of fazadinium with suxamethonium and alcuronium

The speed of onset and intubation conditions have been compared for suxamethonium 1 mg/kg, alcuronium 0-32 mg/kg and fazadinium 1 mg/kg and 1-25 mg/kg. Fazadinium 1 mg/kg was not significantly different in times to intubation from suxamethonium although the latter gave a highly significant greater number of patients with excellent conditions. The higher dose of 1-25 mg/kg fazadinium did not give significantly better intubating conditions than the lower dose. Although the times to intubation for the two dose levels of fazadinium did not differ statistically, the higher dose was significantly slower in onset than suxamethonium. Alcuronium was slower than either suxamethonium or fazadinium 1 mg/kg in producing satisfactory conditions. The nondepolarizing drug, fazadinium, may be a useful neuromuscular blocking agent in emergency cases where rapid intubation is required and when it is wished to avoid possible or probable adverse effects from the depolarising drug suxamethonium.

Serum cholinesterase activity in burned patients. I: biochemical findings

The purpose of the study was to determine the magnitude and the aetiology of alterations in serum cholinesterase activity (pseudocholinesterase) in burned patients. Sixty burned patients with an estimated area of burn between 3 and 72% of body surface were investigated. Serum cholinesterase activity, serum albumin concentration and serum bilirubin were measured at various time intervals. The magnitude as well as the rate of fall of serum cholinesterase activity was found to be closely correlated with the severity of burn injury. Minimum levels were often reached 5 to 6 days after the burn injury, at which time the activity might have been depressed by more than 80 per cent. In the most severely burned patients, the activity sometimes remained low for months despite wound healing. Apart from the severity of the burn injury in the individual patient, several important factors determined the level of serum cholinesterase activity at a given time. These included the presence or absence of local or systemic infections, the event of recent surgery such as slough removal or skin grafting, and blood transfusions. The decrease in serum albumin concentration following the burn injury occurred earlier than the decrease in serum cholinesterase activity. Minimum levels were often reached during the first 24 h, after which time the concentration rose to reach fairly constant but decreased levels after 4 to 5 days. Apart from this initial phase, the changes in serum albumin concentration were roughly proportional to the changes in serum cholinesterase activity. The possible reasons for these findings are discussed.