Organophosphorus poisoning and anaesthesia

Abstract

SummaryOrganophosphorus compounds, used as insecticides and agents of chemical warfare, are a major global cause of health problems. These irreversible inhibitors of cholinesterase produce three wellrecognised clinical entities: the initial cholinergic phase, which is a medical emergency often requiring management in an intensive care unit; the intermediate syndrome, during which prolonged ventilatory care is necessary; and delayed polyneuropathy. In addition, disturbances of body temperature and endocrine function, electrolyte imbalances, immunological dysfunction and disorders of reproduction have been reported in animals and man. Vocal cord paralysis, pancreatitis, cardiac arrhythmias and a wide range of neuropsychiatric disorders are known to follow acute and chronic exposure to organophosphorus compounds. As a result of the inhibition of plasma cholinesterase, there can be increased sensitivity to drugs hydrolysed by this enzyme, e.g. suxamethonium and mivacurium. The inhibition of acetylcholinesterase causes dysfunction at the neuromuscular junction which can produce altered responses to nondepolarising neuromuscular blockers. Anaesthetists may encounter patients exposed to organophosphorus compounds either following acute poisoning, trauma (warfare) or as patients with a wide range of nonspecific disorders presenting for surgery. The traditional use of oximes and atropine in treatment has failed to reduce the morbidity and mortality associated with poisoning. The roles of agents that have reduced the toxicity of organophosphorus compounds in animal experiments are discussed as potential therapeutic agents. There is an urgent need for accurate information on the problems associated with exposure to organophosphorus compounds. This would best be achieved by collaborative research between technologically advanced countries and developing countries, where organophosphorus compounds are a leading cause of ill health.

Late-onset intermediate syndrome due to organophosphate poisoning

“…It has been reported that IS can develop within first 96 hours of acute organophosphate poisoning (OP) (1,2). To the best of our knowledge, there is no reported case of IS developing over 96 hours after OP exposure.…”

“…The most important initial sign of IS is respiratory failure (1)(2)(3)(4)(5). The muscle weakness begins at first in the extremities, the neck, the eyes, and the respiratory system (6).…”

Delayed organophosphate - induced polyneuropathy

“…Organophosphate intoxication may occur during agricultural spraying, transport of organophosphate compounds, or domestic accidents, although suicide attempts are the most common way of intoxication (2,3). Organophosphate intoxication may occur via oral, respiratory, transdermal, or parenteral route (4).…”

“…Death typically occurs within the first 24 hours, usually due to respiratory failure (3). Some complications of organophosphate intoxication have been reported, including "delayed organophosphateinduced polyneuropathy" that has been only rarely reported (2).…”

Cholinesterase estimations revisited: the clinical relevance

“…The role of cholinesterase estimations in anaesthetic practice will continue to be valuable, for these enzymes are necessary for the hydrolysis not only of succinylcholine and mivacurium, but also for that of diamorphine, cocaine, esmolol, remifentanil, procaine and related local analgesics. Cholinesterase concentrations may also be depressed by a wide range of therapeutic agents that may be prescribed for subjects presenting for anaesthesia [37].…”