If a patient shows muscle stiffness, dark blood in the operative field, tachycardia, and increased body temperature, what should you suspect?

The symptoms described—muscle stiffness, dark blood in the operative field, tachycardia, and increased body temperature—are indicative of malignant hyperthermia. This is a rare, potentially fatal condition that can occur during or after the administration of certain types of anesthesia, particularly volatile anesthetics and succinylcholine.

Muscle stiffness (or rigidity) is a hallmark of malignant hyperthermia, caused by a hypermetabolic state in the muscles, leading to increased levels of calcium in the muscle cells. Dark blood is a sign that the blood is not fully oxygenated, which can happen in states of profound metabolic disturbance. Tachycardia and increased body temperature often accompany this condition, as the body’s metabolic processes are significantly ramped up due to the stress on the muscles.

In contrast, the other options do not adequately explain the combination of symptoms. Hypothermia would lead to decreased body temperature, and an allergic reaction generally manifests with different symptoms, such as rash or bronchospasm. A normal response to anesthesia would not typically present with such severe symptoms and would not include muscle stiffness or dark blood. Thus, given the collection of symptoms, malignant hyperthermia is the most appropriate suspicion in this case.