Acute formic acid poisoning in a rubber plantation worker.

Among the workers in a rubber plantation in South India, ingestion of formic acid either accidentally or with suicidal intention is a common problem. Formic acid is diluted and used for coagulation of rubber latex. Easy availability makes formic acid a common poison. The aim of this article is to study the case of formic acid poisoning, its complications and management. Patient was managed symptomatically. Antidote was not used and no nasogastric aspiration was done. Patient had dysphagia; nutrition was maintained with open gastrostomy done on day 5 and subsequent enteral feeding. Measures to prevent anticipated complications were undertaken. Stricture of the esophagus is a common complication leading to long-term morbidity. After initial management, all patients should be on follow-up for prevention and management of strictures. Workers should be educated on complications of formic acid poisoning and easy availability should be curtailed by enforcing remedial measures.

INTRODUCTION

Growing rubber is the major agricultural activity in Kerala. Rubber plantation workers collect the latex from the trees by tapping, and then coagulate it by mixing with formic acid, which is further processed before sales. As formic acid is easily available to the rubber growing population both suicidal and accidental ingestion is commonly seen.[1] Formic acid is also used in other industries such as paper, tanning electroplating, and manufacturing of disinfectants. This is a case study of one patient with accidental formic acid poisoning who was admitted in our hospital.

CASE REPORT

A 39-year-old female patient presented to our A and E department with alleged history of accidental consumption of concentrated formic acid (85%). She had consumed approximately 20 ml of formic acid. On admission, she was complaining of throat pain, difficulty in swallowing and epigastric discomfort. There was no history of breathlessness, chest pain, or hoarseness of voice. On examination, patient was anxious, and vitals stable. Patient had Glasgow coma score of 15/15; pupils were bilaterally equal and reacting. Other systemic examination was normal. Her arterial blood gas study was normal.

She was kept nil per orally, nasogastric tube was not inserted and stomach wash not given. Activated charcoal was not used. She was started on infusion of proton pump inhibitor and oral sucralfate 15 ml thrice daily. Intravenous (IV) fluids included 1000 ml of sodium chloride, 500 ml of 5% dextrose, and 500 ml of normal saline. Bladder catheterization was done and strict intake output chart was maintained. She was also prescribed amoxicillin and clavulanic acid injection 1.2 g IV twice daily empirically. Her pain was managed with injectable tramadol and oral lignocaine viscous solution.

After 4 h, her urine bag showed dark colored urine suggesting of hemoglobinuria and intravascular hemolysis [Figure 1]. Her biochemistry also revealed lysed samples. She was started on diuretics furosemide 40 mg IV twice daily along with fluids.

Figure 1

Dark red urine from a patient of formic acid poisoning

Subsequently, patient had two episodes of vomiting which were bloodstained and her throat pain worsened. By 1st day, patient had complications such as hematemesis, hematuria, and hemoglobinuria. However, her bleeding time, clotting time, and prothrombin time was normal suggesting that hemolysis is related to the degree of acidity. Her total white blood cell (WBC) counts were 18,900 on day one with predominant polymorph nuclear lymphocytosis.

On the 2nd day, patient did not have any hematemesis, her hematuria improved and her coagulation profile was normal. Bilirubin and liver enzymes were raised.

On the 3rd day, her liver enzymes and bilirubin levels started improving. Multiple whitish patches were noticed in her oral cavity, which was managed symptomatically with local hygiene.

On day 4, multiple ulcers were noted on the soft palate, buccal mucosa, base of tongue and right side of epiglottis [Figure 2]. Her WBC counts returned to 12,700 on day 4.

Figure 2

Mucosal ulcerations in the oral cavity

With informed consent patient was taken for open gastrostomy on day 5 and enteral feeding started [Figure 3].

Figure 3

Enteral feeding through gastrostomy tube

Patient was not started on any steroids. Patient was comfortable on day 4 and throat pain had reduced. She complained of mild dysphagia at the time of discharge. She was regularly followed-up for stricture formation and underwent regular esophagogastroduodenoscopy (OGD) at 4, 8, and 12 weeks. Patient was symptom free after 4 months.

DISCUSSION

The mortality rate after formic acid poisoning is 35% according to one study.[2] Bowel perforation, shock, and tracheoesophageal fistula are associated with 100% mortality.[2]

Fatal dose of formic acid is 15-200 ml.[3] It is colorless liquid with the pungent odor and the majority of victims are males, with most cases of suicidal intent and minority cases, which are accidental.

Respiratory distress, hematemesis, hematuria, and vomiting are the common presenting complaints.[4] Patients usually complain of abdominal pain and pass dark red urine.[4] Common complications are acute renal failure, metabolic acidosis, acute respiratory distress syndrome, oral cavity burns, esophageal strictures, gastrointestinal perforation, aspiration pneumonia, sepsis, shock and rarely tracheoesophageal fistula, pneumomediastinum, and chemical injury to the cornea.[45]

The patient should be immediately admitted, vomiting should not be induced and gastric lavage should not be attempted.[6] No role of activated charcoal exists in formic acid poisoning management.[6] Patient should be kept nil per orally and total parenteral nutrition considered.[6] If severe gastrointestinal hemorrhage is seen, no steroids should be given as it may precipitate impending perforation of the gut wall.[6] OGD should not be done in the acute phase.[6]

High doses of folinic acid (1 mg/kg IV bolus followed by 6 doses of 1 mg/kg IV doses at 4th hourly intervals) should be given in severe poisoning. Folinic acid acts by enhancing formate degradation in the liver.[7] Hemodialysis should be considered if electrolyte imbalance is uncorrectable.[7]

Daily urine output, serum creatinine, and serum potassium levels should be monitored to detect early onset of acute renal failure. Death is usually caused by massive acidosis, excessive hemolysis and bleeding.[8]

Treatment is essentially supportive. Patient has to be kept nil per orally and IV fluids should be administered to counter shock. Prophylactic antibiotics can be used. Pain relief should be done with viscous lignocaine and oral morphine along with light sedation if required. Diuretics promote renal function in acute renal failure, and should be judiciously used.[9]

Long-term complications include esophageal stricture, for which reparative surgery should be done if required.[9] Serial OGD should be performed during follow-up. Worker education on hazards of formic acid is important.

CONCLUSION

In a patient with formic acid poisoning, gastrointestinal perforation, hematemesis, respiratory distress, hematuria are associated with increased mortality. Increasing age, pH < 7.3, and hematemesis are risk factors for increased morbidity. Metabolic acidosis can be corrected with administration of IV bicarbonate during initial few hours to reduce the associated morbidity and mortality. Esophageal stricture is the long-term complication, which may require serial dilatation.

Workers of rubber plantation should be educated on safe handling of formic acid. Easy availability should be curtailed by enforcing remedial measures. Spreading the knowledge of side-effects of formic acid, both acute, and long-term is an important aspect of prevention.