Case Reports

Plasma cholinesterase levels in acute organophosphorus poisoning: a plausible marker for weaning?

Jasveer Singh, MD1, Dheeraj Kapoor, MD, FCCP, FACEE1, Manpreet Singh, MD, FCCP, FACEE, FIMSA1, Lakesh K. Anand, MD, FCCP, FIMSA, MAMS2

1Associate Professor; 2Professor

Department of Anesthesia and Intensive Care, Govt. Medical College and Hospital, Chandigarh, India.

Correspondence: Dr. Dheeraj Kapoor, 1207, Sector 32 B, Chandigarh-160030 (India); Phone: 911724622549, 919646121549; E-mail: kapoor.dheeraj72@gmail.com

ABSTRACT

Organophosphorus (OP) poisoning is an occupational hazard in developing countries. In addition to cholinergic toxidrome, serial levels of plasma cholinesterase (PCh) are routinely done for making early diagnosis and thereafter predicting the outcome of patients. We observed weaning failure from mechanical ventilation, in a patient with acute OP poisoning on mechanical ventilation, even after attaining standard weaning criteria, probably due to persistently low PCh levels. Patient was successfully weaned only after attaining near-normal levels of PCh. Serial levels of PCh may be incorporated as one of the requisite of extubation criteria beside objective clinical parameters, to reduce morbidity and mortality in this subset of patients.

Key words: Organophosphorus, Poisoning; Cholinesterase; Weaning; Extubation; Ventilator

Citation: Singh J, Kapoor D, Singh M, Anand LK. Plasma cholinesterase levels in acute organophosphorus poisoning: a plausible marker for weaning? Anaesth Pain & Intensive Care 2016;20(4):477-479

 INTRODUCTION

Organophosphorus (OP) poisoning is a serious occupational hazard in developing countries. Presently, there is an alarming rise of suicidal intake of these compounds with incidence as high as 43.8% in Indian subcontinent.1 Intoxication by these compounds are usually by inhalational or transdermal route and rarely by parental route.2,3 In addition to cholinergic toxidrome, serial levels of plasma cholinesterase (PCh) are routinely done for making early diagnosis and thereafter predicting the outcome of patients.1,4,5 In our ICU, we observed weaning failure in a patient with acute OP poisoning on mechanical ventilation, even after attaining standard weaning criteria.6 We observed that PCh levels were markedly low initially and during weaning, in this patient. Patient was successfully weaned from ventilator only after attaining near-normal levels of PCh.

CASE REPORT

A forty years old male presented in emergency room (ER) with altered sensorium and severe respiratory distress. History revealed accidental consumption of some unknown liquid followed by severe headache and 3 episodes of involuntary body movements. He had no other comorbid illness. On examination, pulse rate was 60/minute, blood pressure of 96/68 mmHg, Glasgow Coma Scale (GCS) of 7/15 with quadriparesis and bilateral pinpoint pupils.

Patient trachea was intubated by cuffed endotracheal tube; gastric lavage was performed and thereafter immediately shifted to intensive care unit (ICU) for further management. Patient was kept on ventilator support and all routine investigations including chest x-ray (CXR) reveals normal findings. Arterial blood gas analysis (ABG) reveals respiratory acidosis (PH -7.12, PO2 – 55, PCO2 – 62, HCO3 -26). Sample for plasma cholinesterase level was also sent in view of suspected organophosphorus (OP) poisoning. His cardiac enzymes and ECG were found normal. Differential diagnosis of metabolic encephalopathy, drug overdose (most likely OP poisoning), and brain stem disease was made. Computed tomography (CT) scan of brain was normal. Lumbar puncture was done and cerebrospinal fluid (CSF) was sent for complete biochemical and cytological analysis and was in normal limits. We observed very low levels of PCh (141 units/L; reference range – 5320-12920 units/L). Screening for other common drug overdose (such as opioids, benzodiazepines) was found negative.

Considering the strong possibility of OP poisoning, immediate treatment was started with atropine (5 mg bolus dose of IV atropine followed by 0.02-0.08 mg/kg/min IV infusion, titrated according to clinical response with signs of atropinization) and pralidoxime (1 gm IV infusion q 8 hours for initial 3 days) as per our institution protocol. Patient responded to the treatment dramatically, with improvement in sensorium and muscle power. On day 4, patient regains consciousness with normal sensorium. Patient was continued on ventilator support with sedation protocol as per our ICU policy and subsequently weaned with success. After following the standard extubation criteria, patient was extubated on day 7 and kept on non-invasive ventilator (NIV) support. On day 8, patient de-saturated with alteration in sensorium. His trachea was immediately intubated with cuffed endotracheal tube and kept on mechanical ventilator support. On day 10, percutaneous tracheostomy was done in anticipation of requirement of prolong ventilatory support. Meanwhile, we measured serial levels of PCh, which were initially low and gradually increased in subsequent days (day 4, 8, 14, 18, 23 were 221, 584, 783, 2042, 4623 Units/L respectively). In next 48 hours patient was weaned from ventilator support and was decannulated successfully on day 26 in ICU. No further events were reported during his stay in ICU and thereafter in step down ward.

 DISCUSSION

Exposure to OP compounds is frequent amongst farmers and is a common mode of accidental or suicidal poisoning.7 Clinical presentation may vary depending on the amount of compound exposure and include headache, altered sensorium and seizures due to accumulation of acetylcholine (Ach) at muscarinic and nicotinic receptors. Weakness of ocular, limb and respiratory muscles occur after 24-96 hours due to prolong action of Ach at nicotinic receptors and manifests as intermediate syndrome. Carboxylic esterases enzymes (plasma cholinesterase) are inhibited and most of the clinical manifestations are attributed to this.8 History of ingestion or mucocutaneous exposure and typical clinical features (salivation, lacrimation, urination, diarrhea, GI upset, emesis, diaphoresis, meiosis, bradycardia, bronchospasm and bronchorrhea), helps in making the diagnosis of OP poisoning.

In the present case, typical signs and symptoms suggestive of OP poisoning were absent which poses diagnostic dilemma. Low levels of plasma cholinesterase confirm the diagnosis, which leads to early institution of treatment with atropine as physiological antidote.4,9  On day 7, patient trachea was extubated after meeting the extubation criteria, however was reintubated within 24 hours. This maybe explained due to persistent low levels of PCh, which become near normal in nearly 4 weeks with concurrent improvement in patient clinical status.

Levels of plasma cholinesterase directly correlate with cellular hypoxia as OP compounds mainly act on cellular mitochondria.10 In the present case, persistently low levels of PCh may have precipitated the fall in oxygen saturation and subsequent respiratory distress, resulting in extubation failure. Many theorize that PCh levels may be useful in diagnosis; however, it lacks sensitivity and specificity and have poor correlation with severity of OP poisoning and subsequent prediction of morbidity and mortality.4,9,11 In contrast, Goswamy et al. demonstrated that PCh levels have a strong predictive value in acute OP poisoning.12 Prasad et al also reported a relative relationship between plasma cholinesterase level and clinical manifestations and outcomes.1 In addition, Chen et al. reported higher mortality with low plasma cholinesterase activity and non-rising trend within the first 48 hours of the presentation.5 Extrapolating these observations we deduce that PCh levels may d V, Kaushal SS, Gupta D. Self s.ntry o manuscript preparationbe considered as a strong determinant for extubation of these subset of patients.

In conclusion, we feel that serial levels of PCh may be incorporated as one of the integral component of extubation criteria in patients of OP poisoning. This may further avert weaning failure and reduce morbidity and mortality. However, further studies are required to establish its role in ventilator management during weaning in the patients suffering from acute OP poisoning.

Conflict of Interest: None.

Authors’ contribution: All of the authors took part in conduct of the case report, concept, manuscript writing, literature search and references.

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