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Organophosphate poisoning: Diagnosis of intermediate syndrome

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Author(s): Poojara L | Vasudevan D | Arun Kumar A | Kamat V

Journal: Indian Journal of Critical Care Medicine
ISSN 0972-5229

Volume: 7;
Issue: 2;
Start page: 94;
Date: 2003;
Original page

Keywords: Organophosphate compound | Intermediate syndrome | Repetitive nerve stimulation.

ABSTRACT
Organophosphate compound (OPC) poisoning with suicidal intent is common in Indian ICUs. The effect of OPCs is to produce a persistent depolarization of the neuromuscular junction leading to muscle weakness. After initial recovery from cholinergic crisis, some patients have resurgence of respiratory muscle paralysis requiring continued ventilatory support. This is termed intermediate syndrome (IMS). This could be due to a change in the type of neuromuscular block to a non depolarisation block characterized by a fade on tetanic stimulation. However peripheral nerve stimulation using train-of-four ratio (TOF) and/tetanus have failed to consistently show such a change. We elected to study whether electro physiological monitoring using repetitive nerve stimulation might show a decremental response during IMS. Material & Methods: This was a prospective blinded study done from April 2002 to March 2003 in our ICU. 45 consecutive patients of OPC poisoning admitted during this period were included in this study. Repetitive nerve stimulation (RNS) using a train of ten at 3Hz 10Hz and 30Hz (slow , intermediate and fast speeds respectively) at the median nerve was done on all patients on day 1, 4, 7 and every 4th day thereafter until discharge. Patients were ventilated until ready to wean as per our usual protocol. The results of the RNS study were not revealed to the intensivist. Results: 9 out of 45 patients required ventilation for more than 6 days and showed overt signs of intermediate syndrome - proximal muscle weakness, twitching and respiratory weakness. Only 2 patients out of the 9 had a decremental response on RNS at 3Hz indicating a post-junctional dysfunction at the motor end-plate, Both patients had consumed a very large quantity of OPC and were deeply comatose for >4 days and required ventilation for >12 days. All other patients with IMS showed no changes on RNS. The exact type of poison consumed varied with each individual patient. Conclusion: RNS is a poorly sensitive marker in diagnosing intermediate syndrome after OPC poisoning. We need to develop more sensitive markers to diagnose IMS.

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