Phrenic nerve conduction studies in acute organophosphate poisoning.

Phrenic nerve conduction studies were performed within 48 h of admission and subsequently in 29 patients (14 of whom required mechanical ventilation) with acute organophosphate (OP) poisoning. The mean (±SD) amplitude of the diaphragmatic compound muscle action potential (CMAP) in patients requiring mechanical ventilation (119.09 ± 173.85 μV) was significantly lower than in those not requiring mechanical ventilation (461.63 ± 138.69 μV) (P < 0.0001). Diaphragmatic CMAP amplitudes in ventilated patients increased with time during the course of hospitalization and were normal in 5 (36%) patients and only mildly reduced in another 6 (43%) patients prior to discontinuation of mechanical ventilation, which was undertaken 4–18 days (mean 7 ± 3 days) after poisoning. Eleven patients (79%) were successfully weaned from mechanical ventilation at the first attempt. In the 3 (21%) remaining patients, mechanical ventilation had to be reestablished because of weaning failure. The mean (±SD) diaphragmatic CMAP amplitude, prior to discontinuation of ventilatory assistance, was 242.6 ± 94.1 μV in these 3 patients. After ventilatory discontinuation, it fell to 95.5 ± 105.8 μV. Thus, reduced diaphragmatic CMAP amplitudes correlate with the need for mechanical ventilation in acute OP poisoning. © 2000 John Wiley & Sons, Inc. Muscle Nerve 23: 627–632, 2000.