Overview
When Oxygen Is Present but Unusable
A patient with cyanide poisoning may have a reassuring pulse oximetry reading while the brain and heart are rapidly failing.
A patient with cyanide poisoning may have a reassuring pulse oximetry reading while the brain and heart are rapidly failing. The problem is not primarily that oxygen cannot enter the blood; cyanide prevents mitochondria from using oxygen to make ATP. That mismatch—adequate arterial oxygenation alongside severe lactic acidosis, altered mental status, or cardiovascular instability—is the pattern that should make a nurse act before a confirmatory cyanide result is available. The first response is simultaneous, not sequential: remove the patient from the source safely, support the airway and circulation, give 100% oxygen, and prepare the antidote. Hydroxocobalamin is the preferred first-line antidote in Canada. A normal SpO2 does not justify waiting.