Asphyxiation by Cake: An Unusual Case of Dyspnea

Upon learning this information, EMS was contacted and instructed to return to the hotel and rental vehicle. The hotel room was noted to have normal levels of O₂ and carbon monoxide (CO) on measurement. Investigation of the car revealed normal levels of CO but O₂ levels too low to read on the sensor. The emergency team concluded that the dry ice (the solid form of carbon dioxide [CO₂]) sublimed to CO₂ gas overnight. This displaced the O₂ in the vehicle, resulting in severe hypoxia and the symptoms of both the patient and hotel clerk.

The patient was initially placed on 15 L of O₂ via a nonrebreather mask, then switched to 2 L of O₂ via nasal cannula. He was observed for a total of four hours after arrival; as he remained symptom-free, he was discharged home. Postdischarge follow-up information was not obtainable.

DISCUSSION
Carbon dioxide is prevalent in everyday life, from an agent in fire extinguishers and carbonation in beverages to byproducts of cellular metabolism. Similar to CO, it is a colorless and odorless gas.

Carbon dioxide is commonly used in the food industry as dry ice to keep items cold. In its solid state, CO₂ can cause severe frostbite with direct contact, similar to a burn. However, when dry ice is warmed and sublimated to a gaseous state, large amounts of CO₂ are generated, and this heavy gas can accumulate and displace air (ie, atmospheric O₂), especially in confined spaces. In low concentrations, gaseous CO₂ appears to have minimal toxicologic effects, but at higher concentrations it can cause tachycardia, tachypnea, dyspnea, visual disturbances, arrhythmias, impaired levels of consciousness, and death.

Carbon dioxide primarily acts as a simple asphyxiant, but it also dissolves in serum as carbonic acid, resulting in a metabolic acidosis. Compensation for this acidosis is accomplished by an increased RR (ie, respiratory alkalosis), which further worsens the intake of CO₂.^1,2

The normal concentration of CO₂ in the atmosphere is approximately 0.04% (396 ppm). The Occupational Safety and Health Administration (OSHA) has set a maximum safe exposure level of CO₂ at 0.5% (5,000 ppm) over an eight-hour day.³ Concentrations as low as 1% (10,000 ppm) may cause drowsiness. Exposure to concentrations of 7% to 10% for several minutes to an hour results in headache, tachycardia, dyspnea, and hyperventilation. At levels of 10% to 15%, dizziness, severe muscle twitching, and loss of consciousness can occur after only a few minutes. Death occurs within minutes at concentrations greater than 30%.²

Carbon dioxide also acts as a potent cerebral vasodilator, which may explain symptoms such as headache and dizziness.² The severity of symptoms is dependent on the concentration of CO₂, the length of the exposure, and the underlying health of the patient. Elevated concentrations of CO₂ can occur in areas where there is limited or poor ventilation, such as in a mine (where it is known as blackdamp, stythe, or choke damp),⁴ submarine, grain silo, or a sealed building without mechanical ventilation.

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