Respiratory failure in acute organophosphorus pesticide self-poisoning

Abstract

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. Delayed failure appears to be due to respiratory muscle weakness, but its pathophysiology is unclear.

Aim: To describe the clinical patterns of OP-induced respiratory failure, and to determine whether the two syndromes are clinically distinct.

Design: Prospective 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 h of admission while unconscious with cholinergic features. Twenty-nine (32%) were well on admission but then required intubation after 24 h 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 consciousness 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 distinct clinical syndromes.

Figure 1

Time to A) first intubation and B) final extubation according to OP ingested. There were marked differences in time to intubation and to extubation between pesticides. The dotted lines in A indicate the 24 to 96 hr period during which late respiratory failure is classically said to occur. Some patients developed sudden respiratory failure both before and after this time period, up to 115 hours post- intubation. A large proportion of patients with chlorpyrifos, dimethoate, and quinalphos poisoning were intubated around admission (see figure 2).

Figure 1

Time to A) first intubation and B) final extubation according to OP ingested. There were marked differences in time to intubation and to extubation between pesticides. The dotted lines in A indicate the 24 to 96 hr period during which late respiratory failure is classically said to occur. Some patients developed sudden respiratory failure both before and after this time period, up to 115 hours post- intubation. A large proportion of patients with chlorpyrifos, dimethoate, and quinalphos poisoning were intubated around admission (see figure 2).

Figure 2

Timing of respiratory failure and outcome Pie charts showing the timing of respiratory failure according to outcome for A) all intubated patients, and patients poisoned by B) chlorpyrifos, C) dimethoate and D) fenthion. There were too few quinalphos poisoned patients to be represented in this way. Green colouring is for intubations within 2 hrs of admission, blue for intubations after 24 hrs, and yellow for intubations at intermediate times. Dark colouring indicates patients who died after intubation.

Figure 2

Timing of respiratory failure and outcome Pie charts showing the timing of respiratory failure according to outcome for A) all intubated patients, and patients poisoned by B) chlorpyrifos, C) dimethoate and D) fenthion. There were too few quinalphos poisoned patients to be represented in this way. Green colouring is for intubations within 2 hrs of admission, blue for intubations after 24 hrs, and yellow for intubations at intermediate times. Dark colouring indicates patients who died after intubation.

Figure 3

Comparison of time to first intubation with need for ventilation Patients intubated within 24hrs of admission had a shorter time to A) first extubation and B) final extubation compared to patients intubated after 24hrs. The bars show the median time.