Lack of evidence for a percent saturation gap in cyanide poisoning

High Anion Gap Metabolic Acidosis after a Suicide Attempt with Cyanide: The Rebirth of Cyanide Poisoning

A 33-year-old woman was admitted to our emergency department in a state of unconsciousness after attempting suicide with unknown substances. Severe metabolic acidosis (pH: 6.81), with a high anion gap (36.2) and high lactate level (20.2 mmol/L), was observed. After four hours of intensive medical treatment, the patient regained consciousness, with a return of the arterial pH to 7.42. Finally, cyanide intoxication was diagnosed based on the detection of a serum cyanide level of 3.5 mg/L. The presence of a high anion gap associated with severe lactic acidosis is a clue for making a rapid differential diagnosis of acute cyanide intoxication. Providing intensive and immediate supportive management is also crucial, even in cases without obtainable specific antidotes.

Toxicology in the ICU: Part 2: specific toxins

This is the second of a three-part series that reviews the generalized care of poisoned patients in the ICU. This article focuses on specific agents grouped into categories, including analgesics, anticoagulants, cardiovascular drugs, dissociative agents, carbon monoxide, cyanide, methemoglobinemia, cholinergic agents, psychoactive medications, sedative-hypnotics, amphetamine-like drugs, toxic alcohols, and withdrawal states. The first article discussed the general approach to the toxicology patient, including laboratory testing; the third article will cover natural toxins.

Mind the gap

The "oxygen saturation gap" is the difference between the calculated oxygen saturation from a standard blood gas machine and the reading from a pulse oximeter. If it is greater than 5%, the patient's hemoglobin may be abnormal, representing carbon monoxide poisoning, methemoglobinemia, or sulfhemoglobinemia. We report a case where awareness of the saturation gap led to the diagnosis of carbon monoxide poisoning.

Clarification of cyanide's effect on oxygen transport characteristics in a canine model

OBJECTIVE

To clarify the cardiovascular mechanisms of cyanide poisoning by evaluating oxygen transport characteristics using a canine model.

METHODS

A prospective controlled experiment was performed at a hospital-based animal laboratory. Five male beagle (17 (2) kg) dogs were anesthetised with alpha-chloralose, paralysed with pancuronium bromide and mechanically ventilated. Potassium cyanide was infused at 0.045 mg/kg/min for 110 min. Heart rate, blood pressure, cardiac output, oxygen delivery (DO2), oxygen consumption (VO2) and oxygen extraction ratio (OER) were measured every 10 min for 140 min. DO2 was measured by an indirect calorimeter.

RESULTS

Cyanide and lactate levels peaked at 1.52 (0.25) mg/l and 9.1 (1.5) mmol/l, respectively. Systolic blood pressure remained relatively constant whereas diastolic blood pressure decreased by 19%. Cardiac output, heart rate and DO2 increased to a maximum of 6%, 10% and 10%, respectively, at 40 min, after which they declined to a low of 32%, 28% and 30% below baseline, respectively. Stroke volume remained constant. Oxygen consumption initially increased by 5%, then decreased to 24% below baseline. The OER initially declined to 35% below baseline, then increased throughout the rest of the study.

CONCLUSION

Cyanide poisoning in the canine model showed two phases of injury. The first (compensated) phase had a mechanism consistent with a traditional global oxygen consumption defect. The second (decompensated) phase had a mechanism consistent with heart failure. This heart failure was due to bradycardia. These data suggest chronotropy as an avenue of further study in the temporary treatment of cyanide poisoning.

Acute cyanide poisoning

OBJECTIVE

Cyanide intoxication is an extremely rare event. We report a case of a teenager presenting with unresponsiveness, hemodynamic instability, and profound anion gap metabolic acidosis secondary to elevated lactate levels. It was later confirmed that he was a victim of cyanide poisoning.

DESIGN

Individual case report.

SETTING

Pediatric intensive care unit of a tertiary care hospital.

PATIENT

A 17-yr-old male presented with seizures, apnea, and cardiovascular collapse. His laboratory evaluation revealed extreme anion gap metabolic acidosis, elevated lactate levels, and absent arteriovenous saturation difference.

INTERVENTIONS

The patient required inotropic support and external cardiac pacing for hemodynamic instability. Serial measurements of electrolytes and arterial and central venous blood gases were performed. When cyanide poisoning was suspected he received antidote therapy, administered initially with interval dosing and then as a continuous infusion. The antidote infusions were stopped because of a high level of resultant methemoglobinemia and the belief that all ingested cyanide had been cleared, given the time from exposure. The patient never recovered neurologic function, was declared brain dead, and became a tissue and organ donor.

CONCLUSION

Cyanide poisoning is a rare and potentially fatal event. Prompt recognition of its possibility in a critically ill patient can lead to early intervention with antidote therapy and decrease the extent of morbidity and mortality.

National academy of clinical biochemistry laboratory medicine practice guidelines: recommendations for the use of laboratory tests to support poisoned patients who present to the emergency department

BACKGROUND

Exposure to drugs and toxins is a major cause for patients' visits to the emergency department (ED).

METHODS

Recommendations for the use of clinical laboratory tests were prepared by an expert panel of analytical toxicologists and ED physicians specializing in clinical toxicology. These recommendations were posted on the world wide web and presented in open forum at several clinical chemistry and clinical toxicology meetings.

RESULTS

A menu of important stat serum and urine toxicology tests was prepared for clinical laboratories who provide clinical toxicology services. For drugs-of-abuse intoxication, most ED physicians do not rely on results of urine drug testing for emergent management decisions. This is in part because immunoassays, although rapid, have limitations in sensitivity and specificity and chromatographic assays, which are more definitive, are more labor-intensive. Ethyl alcohol is widely tested in the ED, and breath testing is a convenient procedure. Determinations made within the ED, however, require oversight by the clinical laboratory. Testing for toxic alcohols is needed, but rapid commercial assays are not available. The laboratory must provide stat assays for acetaminophen, salicylates, co-oximetry, cholinesterase, iron, and some therapeutic drugs, such as lithium and digoxin. Exposure to other heavy metals requires laboratory support for specimen collection but not for emergent testing.

CONCLUSIONS

Improvements are needed for immunoassays, particularly for amphetamines, benzodiazepines, opioids, and tricyclic antidepressants. Assays for new drugs of abuse must also be developed to meet changing abuse patterns. As no clinical laboratory can provide services to meet all needs, the National Academy of Clinical Biochemistry Committee recommends establishment of regional centers for specialized toxicology testing.