CO crosses the pulmonary capillary membrane easily and rapidly binds the iron-group of hemoglobin (Hgb) with an affinity that is 250 greater than that of oxygen, forming carboxyhemoglobin (COHgb). Due to the binding of CO, the other three sites of the heme molecule increase their affinity to oxygen molecules, causing a leftward shift of the oxyhemoglobin dissociation curve and further inhibiting the off-loading of oxygen to the deprived peripheral tissue.¹⁷ CO can have direct toxicity on muscle tissue, as well as impair oxygen delivery, oxygen utilization, and cellular respiration.^1,26,28 In terms of CO kinetics, upon removal from the source of exposure, CO will eventually dissociate from Hgb, with the following half-lives: (1) Breathing room air: 300-360 minutes; (2) Breathing high-flow oxygen: 60-90 minutes; (3) Hyperbaric oxygen at three atmospheres: 30 minutes.¹⁹