>Background: Acute organophosphorus (OP) pesticide poisoning is a major clinical problem in the developing world. Textbooks ascribe most deaths to respiratory failure occurring in one of two distinct clinical syndromes - acute cholinergic respiratory failure or the intermediate syndrome. The delayed failure appears to be due to respiratory muscle weakness, but its pathophysiology is not yet clear.>Aim: To describe the clinical patterns of OP-induced respiratory failure and to determine whether the two syndromes are clinically distinct.>Design: Prospective cohort study of 376 patients with confirmed OP poisoning.>Methods: Patients were observed throughout their admission to three Sri Lankan hospitals. Exposure was confirmed by butyrylcholinesterase and blood OP assays.>Results: Ninety of 376 patients (24%) required intubation, 52 (58%) within 2 hrs of admission while unconscious with cholinergic features. Twenty-nine (32%) were well on admission but then required intubation after 24 hrs while conscious and without cholinergic features. These two syndromes were not clinically distinct and had much overlap. In particular, some patients who required intubation on arrival subsequently recovered conscious but could not be extubated, requiring ventilation for up to 6 days.>Discussion: Respiratory failure did not occur as two discrete clinical syndromes within distinct time frames. Instead, the pattern of failure was variable and overlapped in some patients. There seemed to be two underlying mechanisms - an early acute mixed central and peripheral respiratory failure, and a late peripheral respiratory failure - rather than two defined clinical syndromes.
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