In CO poisoning, which symptoms would be observed when serum carboxyhemoglobin levels reach 30-40%?

When serum carboxyhemoglobin levels reach 30-40%, individuals typically experience significant neurological and cardiovascular effects due to carbon monoxide binding to hemoglobin, which impairs the delivery of oxygen to tissues. Symptoms like syncope (loss of consciousness) can occur because of reduced oxygen availability to the brain, leading to dizziness, lightheadedness, or even fainting. Along with this, an increased heart rate (tachycardia) is a compensatory response of the body as it attempts to deliver more oxygen to critical tissues.

While other options present symptoms associated with different levels of carbon monoxide exposure, they do not align with the specific impact observed at this higher concentration. The symptoms corresponding to lower levels of exposure, such as headaches and nausea, are associated with lower percentages of carboxyhemoglobin. Coma and seizures would indicate more severe exposure, beyond the 30-40% range. Therefore, the combination of syncope and increased heart rate serves as a clear indication of the physiological strain caused by the compromised oxygen transport at this specific saturation level.