A Case of Dimethoate Poisoning Requiring Prolonged Skin Decontamination

Ponampalam R, MBBS, FRCS (Ed), FAMS, GDOM

Senior Consultant, Department of Emergency Medicine, Singapore General Hospital, Outram Road 169608, Singapore; Tel. (65) 63213558; Fax: (65) 63214873; E-mail: ponampalam@singhealth.com.sg

INTRODUCTION

Organophosphorus (OP) compounds are widely used as pesticides in countries where agriculture forms a predominant part of the economy. Poisoning from exposure to OP are uncommon in the Singapore context with its limited use posing exposure hazard in certain high-risk occupations. However, with the increasing availability of potent industrial and chemical warfare agents, the possibility of it landing in the wrong hands is high and the potential for mass casualty incidents from terrorism have heightened. The sarin incident in Tokyo subway in 1995,¹ had set the stage for a new reality in todays’ world. Disgruntled members of a cult had used nerve agents, usually meant as weapons in warfare, on unsuspecting civilians resulting in mass casualties. This incident had demonstrated a high incidence of secondary exposures amongst healthcare workers as a result of lack of casualty decontamination.^2,3 The significant morbidity and mortality from toxic exposures in chemical incidents are well appreciated and the acute and chronic consequences of secondary exposure to healthcare and emergency responder is notable.^4-9 Since the Tokyo incident, there have been many other occasions where nerve agents have been used by individuals and governments on civilians.^10,11 Appreciating this situation and the dire consequences of secondary exposure, there have been recommendations for countermeasures, such as mass casualty decontamination to be made readily available at healthcare facilities to deal with chemical contamination spread and to limit the damage from ongoing chemical exposures.^12-16 This case of dimethoate poisoning, a commonly used industrial OP, is notable for the prolonged period of skin decontamination to remove residual skin contamination and illustrates potential implications for patient and health care worker safety.

CASE REPORT

A young gardener consumed dimethoate at the workplace in a suicidal attempt. The victim developed vomiting, abdominal discomfort and urge to defecate and was noted to be increasingly drowsy by a colleague who called the emergency ambulance service.

Paramedics noted the patient to be drowsy and diaphoretic but otherwise haemodynamically stable with 100% oxygen saturation. While being evacuated a prehospital stand-by activation message was sent to the receiving emergency department (ED) to prepare for arrival of a critically ill patient. En-route the patient vomited multiple times and was drenched in vomitus.

On arrival in the resuscitation area of the ED, the patient was diaphoretic, with Glasgow Coma Scale GCS of 10 (E2V3M5) and pupils 2 mm reactive. The patient was afebrile with blood pressure of 116/72 mm of Hg and pulse rate of 106 per minute. The patient was tachypnoeic but maintaining airway with a respiratory rate of 20 per minute and oxygen saturation of 98% on room air. It was noted that vomiting had stopped, but patient’s clothes were drenched in vomitus emanating a pungent odour suggestive of chemical fumes off gassing. There was excessive salivation and crepitation in the lung bases. The clinical picture was consistent with OP poisoning with features of cholinergic toxidrome.

As the patient was clinically stable, and in view of the significant external contamination with potential risk of further cutaneous absorption and secondary exposure to health care workers (HCW) and facility, decision was made to perform external decontamination at the hospital decontamination station (HDS)17 located just outside the ED entrance.

The HDS shower was deployed and ED staff donned personal protective equipment (PPE) comprising impermeable decontamination suits with air purifying respirators prior to starting the decontamination process. The patient was disrobed, and the clothing bagged before proceeding with showering using water and liquid soap-soaked sponges. Following the hospital’s decontamination protocol,¹⁸ the patient was showered systematically from head to toe, covering the entire body surface area. The shower took 10-minutes and the patient was then brought to the drying area and dried before a systematic chemical agent screen was initiated from head to toe using the chemical agent monitor (CAM), ChemPro100i from Environics. After the initial shower, the first CAM scan sounded an alarm around the region of the patients left mastoid indicating the presence of an unidentified industrial chemical. The patient was moved back into the HDS to get a targeted shower for the specified area using soap and water for 5 more minutes. Following the second shower patient was again dried and scanned. The CAM alarm sounded the second time at a region below the left breast again indicating the presence of an unidentified industrial chemical. The patient was moved back into the HDS for a repeat targeted decontamination of the contaminated site for an additional 5 more minutes. Following this third and final shower, the CAM did not trigger again, and the patient was clothed with hospital gown before being brought back to the resuscitation area for further management. Notably it took a total of 20-minutes of showering with soap and water before the patient was declared clean, excluding preparation time for the deployment of the decontamination showers and crew. The entire process took a total of 56-minutes based on video footage from activation of the HDS until completion of the decontamination process.

Upon return to the resuscitation area patient was put on vitals monitoring and reassessed. A random blood glucose done was 13.8 mmol/L and electrocardiograph showed sinus tachycardia. Chest X-ray showed prominent pulmonary vasculature with mild congestion. Blood investigations including a full blood count, electrolytes, liver function, amylase were normal except for hypokalaemia of 2.9 mmol/L, glucose of 14.4 mmol/L and serum amylase of 203 U/L (38-149 U/L). The initial red blood cell cholinesterase was 4293 (7700-14600 U/L) and serum cholinesterase level was low 1502 (range 4700-12000 U/L) with further drop to below 1000 over the next 2 days in keeping with OP poisoning.

The patient was given a total of 2.4 mg atropine and was started on pralidoxime 1 g at the ED followed by continuous infusion of atropine and pralidoxime for the next 24-hours. The patient remained haemodynamically stable with improvement in respiration and clearing of crepitation’s in the lungs. While in the ED, patient’s consciousness level improved to GCS 13 (E3V4M6) becoming more responsive to questioning. The patient was admitted to the medical intensive care unit (ICU) for monitoring where clinical condition improved over the next 24-hours before being sent to the general ward. The patient was referred to psychiatrist for evaluation in the ward and had an uneventful recovery and was subsequently discharged well from hospital 5-days later.

DISCUSSION

Dimethoate is significantly absorbed via the dermal and respiratory route, when used as a pesticide by workers in the occupational setting. This exposure can be reduced with the use of appropriate dermal and respiratory protection.¹⁹ Hence it is critical that these patients have proper decontamination as part of medical therapy to reduce absorption and toxicity. The standard decontamination protocol in our setting involves disrobing followed by 10-minute shower using soap sponges and water. In our patient, due to the persistence of skin contamination repeated showering was done for a prolonged total time of 20-minuted econtamination. The actual reason for this is uncertain but is postulated to be related to its chemical stability in aqueous solution and presence of petroleum distillates which resulted in persistence of the chemicals on the skin.

There are a variety of decontaminant solutions and powders that may contribute to effective decontamination. In a study, involving decontamination with reactive skin decontaminant lotion (RSDL) at different times in hairless guinea pigs percutaneously challenged with venomous agent X (VX) a potent low volatile nerve agent, it was noted that the compound persisted on the skin for prolonged period providing a long window of opportunity for decontamination even after 90-minutes post exposure.²⁰ The study concluded that, decontamination of VX-exposed skin is one of the most important countermeasures to mitigate the effects of exposure and the delay in absorption presents a window of opportunity for decontamination and treatment. However, the use of such decontamination solutions in the clinical context requires further study.

Most international mass casualty decontamination guidelines do not include screening for residual contamination post-decontamination due in part to resource and time constraints.^21,22,23 As demonstrated in our case, it is incorrect to assume that patients are cleared of contamination after initial rapid decontamination. However, it is unclear as to the clinical significance of residual chemical contamination following a single shower and further research will need to be done to demonstrate its effectiveness. To make the decontamination process robust, it will be prudent to screen casualties for residual contamination following initial decontamination to ensure patient safety from further cutaneous exposure and the safety of staff who will be managing the patient subsequently. Hence, the need for further evaluation using CAM post decontamination to confirm before being cleared for entry into the receiving hospital should be considered crucial to prevent escalation.²⁴

Dimethoate belongs to the same class of toxic OP compounds used in chemical warfare as nerve agents. These nerve agent analogues are commonly used as pesticides and readily available are considered potential agents for chemical terrorism.²⁵

Organophosphorus poisoning is known to occur from intentional ingestion or accidental exposure in the occupational setting. It has been the choice agent in some recent assassination attempts including Kim Jong-Nam and the former Russian spy Sergei Skripal and his daughter, Yulia.^26,27 In the last two decades, terrorism with OP agents have become an increasing concern and the potential for mass casualty incidents involving such chemicals remain high.^28,29 Lessons from past incidents involving OP exposure have demonstrated the risk of secondary exposure of emergency first responders, HCW and the significant impact on the hospital facility from secondary contamination.^30,31,32

CONCLUSION

The chemical incidents in the past, had demonstrated the high incidence of secondary exposures amongst healthcare workers as a result of lack of casualty decontamination. This case report suggest that effective decontamination takes time to achieve its intended objective and need verification for quality control. Extrapolating this experience to hazmat mass casualty incidents, it is important to note that rapid decontamination of casualties in the field or hospital may have limitations. Measures to ensure effectiveness of decontamination are paramount to ensure staff and patient safety.³³

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