Welcome to FOAMcast, a podcast created by residents who love Free Open Access Medical education (FOAM). We are looking at cutting edge FOAM and distilling it down to the basics. We’re not doing this to replace reading and hard work but increase interest and direct listeners to linking sexy FOAM with core content. So listen, and go read it yourself.
What Did Weingart and Dr. Nelson say?
- Patient in extremis or arrest after a fire and burn size doesn’t correlate to severity of illness? Treat for cyanide toxicity.
- Treatment: hydroxocobalamin 5g IV in ~250mL normal saline in adults or 70 mg/kg in pediatric patients.
- Get labs, including lactate, carboxyhemoglobin level, and transaminases prior to giving hydroxocobalamin if possible because the drug turns everything red and interferes with these tests.
And the Basics of Chemical Asphyxiants?
If a patient presents after smoke exposure, consider cyanide and carbon monoxide toxicity (Case Quiz). These toxicities have many similarities such as: impaired oxygen delivery and utilization, metabolic acidosis with elevated lactate, and presence in patients with smoke inhalation.
Cyanide Toxicity – Tintinalli (7e) Ch 198; Rosen’s (8e) Ch 179
Mechanism – Binds to the iron of the cytochrome a3 of complex IV in the mitochondria, the last step of oxidative phosphorylation, effectively shutting down the mitochondria and ATP production leading to tissue hypoperfusion.
- Cyanide level is worthless in the acute setting. If suspicious, treat without waiting for labs.
- Labs often demonstrate a metabolic acidosis and, in a fire victim, a lactate >10 mmol/L is suspicious for cyanide toxicity.
- ABCs – 100% oxygen, crystalloids and vasopressors for hypotension
- Hydroxocobalamin 5 g IV for adults or 70 mg/kg IV for pediatrics
- Cyanide binds to hydroxocobalamin, forming cyanocobalamin (vitamin B12) which is renally excreted. It also turns everything red, which can interfere with labs and dialysis.
- Note: Tintinalli cautions that there’s no good evidence on hydroxocobalamin over the traditional sodium nitrite kits.
- There’s also the traditional cyanide antidotes which include: inhaled amyl nitrite, Sodium nitrite 3% – 300 mg IV (10 mL), and sodium thiosulfate.
- Sodium nitrite forms methemoglobin from hemoglobin, for which cyanide has enormous affinity. Cyanide leaves the cytochrome, setting the mitochondria free, forming cyanmethemoglobin. This is transformed to thiocyanate by an enzyme (rhodanese) and renally excreted.
- If using this approach in a patient with carbon monoxide poisoning, use only sodium thiosulfate given these patient already have impaired tissue oxygenation and methemoglobinemia only further exacerbates this.
Carbon Monoxide (CO) – Tintinalli (7e) Ch 217; Rosen’s (8e) Ch 159
Carbon monoxide poisoning is non-specific and may manifest as headache, flu like illness, or coma and death and occurs throughout the year, not just during heat/generator seasons.
- Most well recognized – CO has a far greater affinity for hemoglobin than oxygen, leading to impaired delivery of oxygen to tissues.
- Causes a left shift of the hemoglobin-oxygen dissociation curve (Right shift = Removal of oxygen from hemoglobin. Left shift = loaded hemoglobin).
- Inhibits the cytochrome system in aerobic metabolism, akin to cyanide toxicity, leading to a shift toward anaerobic metabolism.
- Clinical suspicion is key.
- Labs may show a metabolic acidosis with elevated lactate.
- Carboxyhemoglobin level is often available and for boards, remember that levels >15% in pregnant patients or >25% in other patients may be a trigger to think about hyperbaric oxygen therapy. These levels do not correlate with symptoms.
- ABCs, including high inspired oxygen which reduces the half-life of CO from ~4 hrs to 90 minutes.
- Hyperbaric oxygen (HBO) or “diving” patients in controversial but if a patient is near-dead, pregnant with significant toxicity (level >15), consider HBO, at least on the boards.
Questions generously donated by the Rosh Review
Question 1. [polldaddy poll=8074537]
Question 2. [polldaddy poll=8074535]
Gresham C, LoVecchio F. Chapter 198. Inhaled Toxins. Tintinalli’s Emergency Medicine: A Comprehensive Study Guide, 7e. New York, NY: McGraw-Hill; 2011. p 1317-1320.
Nelson RS, Hoffman RS. Chapter 159. Inhaled Toxins. Rosen’s Emergency Medicine, 8e. 2014. p 2036-2043.
Maloney G. Chapter 217. Carbon Monoxide. Tintinalli’s Emergency Medicine: A Comprehensive Study Guide, 7e. New York, NY: McGraw-Hill; 2011. p 1410-1413.
Answers. 1) A 2)A