Acute cyanide poisoning

Can the cyanide metabolite, 2-aminothiazoline-4-carboxylic acid, be used for forensic verification of cyanide poisoning?

PURPOSE

Forensic verification of cyanide (CN) poisoning by direct CN analysis in postmortem blood is challenging due to instability of CN in biological samples. CN metabolites, thiocyanate (SCN-) and 2-aminothiazoline-4-carboxylic acid (ATCA), have been proposed as more stable biomarkers, yet it is unclear if either is appropriate for this purpose. In this study, we evaluated the behavior of CN biomarkers in postmortem swine and postmortem blood to determine which serves as the best biomarker of CN exposure.

METHODS

CN, SCN-, and ATCA were measured in postmortem swine (N = 8) stored at 4 °C and postmortem blood stored at 25 °C (room temperature, RT) and 37 °C (typical human body temperature, HBT).

RESULTS

Following CN poisoning, the concentration of each CN biomarker increased well above the baseline. In postmortem swine, CN concentrations declined rapidly (t1/2 = 34.3 h) versus SCN- (t1/2 = 359 h, 15 days) and ATCA (t1/2 = 544 h, 23 days). CN instability in postmortem blood increased at RT (t1/2 = 10.7 h) and HBT (t1/2 = 6.6 h). SCN- and ATCA were more stable than CN at all storage conditions. In postmortem swine, the t1/2s of SCN- and ATCA were 15 and 23 days, respectively. While both the t1/2s of SCN- and ATCA were relatively lengthy, endogenous levels of SCN- were much more variable than ATCA.

CONCLUSION

While there are still questions to be answered, ATCA was the most adept forensic marker of CN poisoning (i.e., ATCA produced the longest half-life, the largest increase above baseline levels, and most stable background concentrations).

Diagnosis of lethal cyanide poisoning. Analysis by Anion-Exchange Chromatography with Pulsed Amperometric Detection

Cyanide is a poison widely used in cases of suicide or homicide. Although various methods to identify and quantify this substance are reported in the literature, they are mainly validated on biological fluids (e.g., blood and urine). In the present study, the Anion‐Exchange Liquid Chromatography with Pulsed Amperometric Detection (IC‐PAD) method was validated on blood and, for the first time, on gastric content, and organs (brain, lung, and liver). For each matrix, linearity, accuracy, precision, limit of detection (LOD), lower limit of quantification (LLOQ), matrix interferences, and carryover were assessed. The samples were extracted by steam distillation in acid environment for the following analysis by IC‐PAD. Furthermore, cyanide values found in two real poisoning cases are reported. For each investigated matrix, the analytical method satisfied all acceptance criteria for validation: it showed a good precision and accuracy, selectivity, and sensitivity with no carryover and matrix interference. The extraction by steam distillation in acid environment REDUCED the interference of the matrices and ALLOWED to perform the analysis with good precision and accuracy. In case #1, analysis showed a blood cyanide concentration of 0.99 μg/ml. In case #2, cyanide concentrations were 1.3 μg/g in brain, 0.8 μg/g in lung, 1.6 μg/g in liver, and 1.2 μg/g in gastric content. The cyanide concentrations found in the two reported cases have been suitable to cause death by poisoning.

Plasmapheresis for the management of acute cyanide poisoning: A case report and review of literature

In case of mild to moderate cyanide poisoning, especially when standard antidote kits are not readily available, plasmapheresis can be utilized as an alternative option alongside supportive measures.

Neuroterrorism Preparedness for the Neurohospitalist

In this review article, we highlight several potential biologic and chemical agents of "neuroterrorism" of which neurohospitalists should be aware: anthrax, botulism toxin, brucella, plague, smallpox, organophosphates and nerve agents, cyanide, and carfentanil. Such agents may have direct neurologic effects, resulting in encephalopathy, paralysis, and/or respiratory failure. Neurohospitalists should be on the lookout for abnormal neurologic syndrome clustering, especially among patients presenting to the emergency department. If use of such a "neuroterrorism" agent is suspected, the neurohospitalist should immediately consult with emergency department personnel, infection control, infectious disease physicians, and/or Poison Control to make sure the scene is safe and to stabilize and isolate patients if necessary. The neurohospitalist should also immediately contact their local and/or state health department (or alternatively the US Centers for Disease Control and Prevention Emergency Operations Center) to report their suspicions and to obtain guidance and assistance.

Case Files of the University of Massachusetts Toxicology Fellowship: Does This Smoke Inhalation Victim Require Treatment with Cyanide Antidote?

Cyanide toxicity is common after significant smoke inhalation. Two cases are presented that provide framework for the discussion of epidemiology, pathogenesis, presenting signs and symptoms, and treatment options of inhalational cyanide poisoning. An evidence-based algorithm is proposed that utilizes point-of-care testing to help physicians identify patients who benefit most from antidotal therapy.

Linezolid-induced lactic acidosis: the thin line between bacterial and mitochondrial ribosomes

INTRODUCTION

Linezolid inhibits bacterial growth by targeting bacterial ribosomes and by interfering with bacterial protein synthesis. Lactic acidosis is a rare, but potentially lethal, side effect of linezolid. Areas covered: The pathogenesis of linezolid-induced lactic acidosis is reviewed with special emphasis on aspects relevant to the recognition, prevention and treatment of the syndrome. Expert opinion: Linezolid-induced lactic acidosis reflects the untoward interaction between the drug and mitochondrial ribosomes. The inhibition of mitochondrial protein synthesis diminishes the respiratory chain enzyme content and thus limits aerobic energy production. As a result, anaerobic glycolysis and lactate generation accelerate independently from tissue hypoxia. In the absence of any confirmatory test, linezolid-induced lactic acidosis should be suspected only after exclusion of other, more common, causes of lactic acidosis such as hypoxemia, anemia or low cardiac output. Normal-to-high whole-body oxygen delivery, high venous oxygen saturation and lack of response to interventions that effectively increase tissue oxygen provision all suggest a primary defect in oxygen use at the mitochondrial level. During prolonged therapy with linezolid, blood drug and lactate levels should be regularly monitored. The current standard-of-care treatment of linezolid-induced lactic acidosis consists of drug withdrawal to reverse mitochondrial intoxication and intercurrent life support.

Time- and temperature-dependent changes in cytochrome c oxidase activity and cyanide concentration in excised mice organs and mice cadavers

Postmortem stability of cyanide biomarkers is often disputed. We assessed the time and temperature-dependent changes in cytochrome c oxidase (CCO) activity and cyanide concentration in various organs of mice succumbing to cyanide. Immediately after death, excised mice organs and mice cadavers were stored at room temperature (35°C ± 5°C) or in frozen storage (-20°C ± 2°C). At various times after death, CCO activity and cyanide concentrations were measured in excised mice organs or organs removed from mice cadavers. The study revealed that (i) measuring both the biomarkers in mice cadavers was more reliable compared to excised mice organs, (ii) measuring temporal CCO activity and cyanide concentration in vital organs from mice cadavers (room temperature) was reliable up to 24 h, and (iii) CCO activity in the brain and lungs and cyanide concentration in organs from mice cadavers (frozen) were measurable beyond 21 days. This study will be helpful in postmortem determination of cyanide poisoning.

Metformin overdose, but not lactic acidosis per se, inhibits oxygen consumption in pigs

INTRODUCTION

Hepatic mitochondrial dysfunction may play a critical role in the pathogenesis of metformin-induced lactic acidosis. However, patients with severe metformin intoxication may have a 30 to 60% decrease in their global oxygen consumption, as for generalized inhibition of mitochondrial respiration. We developed a pig model of severe metformin intoxication to validate this clinical finding and assess mitochondrial function in liver and other tissues.

METHODS

Twenty healthy pigs were sedated and mechanically ventilated. Ten were infused with a large dose of metformin (4 to 8 g) and five were not (sham controls). Five others were infused with lactic acid to clarify whether lactic acidosis per se diminishes global oxygen use. Arterial pH, lactatemia, global oxygen consumption (VO2) (metabolic module) and delivery (DO2) (cardiac output by thermodilution) were monitored for nine hours. Oxygen extraction was computed as VO2/DO2. Activities of the main components of the mitochondrial respiratory chain (complex I, II and III, and IV) were measured with spectrophotometry (and expressed relative to citrate synthase activity) in heart, kidney, liver, skeletal muscle and platelets taken at the end of the study.

RESULTS

Pigs infused with metformin (6 ± 2 g; final serum drug level 77 ± 45 mg/L) progressively developed lactic acidosis (final arterial pH 6.93 ± 0.24 and lactate 18 ± 7 mmol/L, P < 0.001 for both). Their VO2 declined over time (from 115 ± 34 to 71 ± 30 ml/min, P < 0.001) despite grossly preserved DO2 (from 269 ± 68 to 239 ± 51 ml/min, P = 0.58). Oxygen extraction accordingly fell from 43 ± 10 to 30 ± 10% (P = 0.008). None of these changes occurred in either sham controls or pigs infused with lactic acid (final arterial pH 6.86 ± 0.16 and lactate 22 ± 3 mmol/L). Metformin intoxication was associated with inhibition of complex I in the liver (P < 0.001), heart (P < 0.001), kidney (P = 0.003), skeletal muscle (P = 0.012) and platelets (P = 0.053). The activity of complex II and III diminished in the liver (P < 0.001), heart (P < 0.001) and kidney (P < 0.005) while that of complex IV declined in the heart (P < 0.001).

CONCLUSIONS

Metformin intoxication induces lactic acidosis, inhibits global oxygen consumption and causes mitochondrial dysfunction in liver and other tissues. Lactic acidosis per se does not decrease whole-body respiration.

A case of cyanide poisoning and the use of arterial blood gas analysis to direct therapy

Cyanide poisoning is a difficult diagnosis for health care professionals. Existing reports clearly demonstrate that the initial diagnosis is often missed in surreptitious cases. The signs and symptoms can mimic numerous other disease processes. We report a case in which a suicidal patient ingested cyanide and was found unresponsive by 2 laboratory coworkers. The coworkers employed cardiopulmonary resuscitation with mouth-to-mouth resuscitation. The suicidal patient died shortly after arrival to the hospital, while the 2 coworkers who performed mouth-to-mouth resuscitation presented with signs and symptoms that mimicked early cyanide toxicity but were instead due to acute stress response. An arterial blood gas analysis may help aid in the diagnosis of cyanide toxicity. Electrocardiographic findings in a patient with cyanide poisoning range significantly, depending on the stage of the poisoning.

Where does the lactate come from? A rare cause of reversible inhibition of mitochondrial respiration

Biguanide poisoning is associated with lactic acidosis. The exact mechanism of biguanide-induced lactic acidosis is not well understood. In the previous issue of Critical Care, Protti and colleagues demonstrated that biguanide-induced lactic acidosis may be due in part to a reversible inhibition of mitochondrial respiration. Thus, in the absence of an antidote, increased drug elimination through dialysis is logical.

Oxygen consumption is depressed in patients with lactic acidosis due to biguanide intoxication

INTRODUCTION

Lactic acidosis can develop during biguanide (metformin and phenformin) intoxication, possibly as a consequence of mitochondrial dysfunction. To verify this hypothesis, we investigated whether body oxygen consumption (VO2), that primarily depends on mitochondrial respiration, is depressed in patients with biguanide intoxication.

METHODS

Multicentre retrospective analysis of data collected from 24 patients with lactic acidosis (pH 6.93 +/- 0.20; lactate 18 +/- 6 mM at hospital admission) due to metformin (n = 23) or phenformin (n = 1) intoxication. In 11 patients, VO2 was computed as the product of simultaneously recorded arterio-venous difference in O2 content [C(a-v)O2] and cardiac index (CI). In 13 additional cases, C(a-v)O2, but not CI, was available.

RESULTS

On day 1, VO2 was markedly depressed (67 +/- 28 ml/min/m2) despite a normal CI (3.4 +/- 1.2 L/min/m2). C(a-v)O2 was abnormally low in both patients either with (2.0 +/- 1.0 ml O2/100 ml) or without (2.5 +/- 1.1 ml O2/100 ml) CI (and VO2) monitoring. Clearance of the accumulated drug was associated with the resolution of lactic acidosis and a parallel increase in VO2 (P < 0.001) and C(a-v)O2 (P < 0.05). Plasma lactate and VO2 were inversely correlated (R2 0.43; P < 0.001, n = 32).

CONCLUSIONS

VO2 is abnormally low in patients with lactic acidosis due to biguanide intoxication. This finding is in line with the hypothesis of inhibited mitochondrial respiration and consequent hyperlactatemia.

Chemical Terrorism Attacks: Update on Antidotes

There is well-founded concern that a chemical or radioactive agent will at some point be used as a weapon of terror. There are several antidotes that, if used correctly in a timely fashion, can help lessen the harm caused by these agents. This article is meant to introduce the clinician to several such agents, along with the antidotes useful in the management of exposure to these. It covers the indications, administration, and precautions for using these antidotes.