What life-threatening symptoms can occur with serum carboxyhemoglobin levels above 50%?

Serum carboxyhemoglobin levels above 50% indicate a severe level of carbon monoxide (CO) poisoning, which can lead to critical alterations in the body's oxygen transport and utilization. At this threshold, the symptoms become very serious and can lead to neurological impairment.

Coma and seizures are definitive symptoms that can arise from such high levels of carboxyhemoglobin because carbon monoxide profoundly affects the central nervous system by binding to hemoglobin, thereby reducing the amount of oxygen delivered to the brain and other vital organs. This can lead to a loss of consciousness (coma) or seizures due to cerebral hypoxia, where the brain is deprived of adequate oxygen.

While other options refer to symptoms that may occur at lower levels of carboxyhemoglobin or in other contexts of illness, they do not adequately represent the most severe outcomes seen with life-threatening levels of carbon monoxide exposure. This makes coma and seizures the appropriate symptoms to associate with carboxyhemoglobin levels exceeding 50%.