A client with untreated hyperthyroidism develops a thyroid storm. Which complication should the nurse monitor for most closely?

Thyroid storm is a life-threatening manifestation of severe thyrotoxicosis, characterized by an acute, catastrophic surge in circulating thyroid hormones. This hypermetabolic crisis dramatically upregulates systemic metabolic demands, forcing a massive increase in cardiac output and profound tachycardia. The resulting workload exhausts myocardial reserves, precipitating high-output cardiac pump failure and pulmonary congestion. A. Hypoglycemia: The severe thyrotoxic state accelerates metabolic pathways, causing glycogenolysis and lipolysis that typically drive blood glucose levels upward. While cellular metabolic demands are high, acute central hypoglycemia is not a characteristic life-threatening complication of this crisis. Glycemic fluctuations remain secondary to cardiovascular strain. B. Hypothermia: Thyroid hormone excess dramatically uncouples oxidative phosphorylation, leading to uncontrolled thermogenesis and severe, life-threatening hyperthermia >40 degrees Celsius. Hypothermia is pathophysiologically impossible in this state, as the body lacks the ability to cool down. Extreme pyrexia is the expected finding. C. Renal failure: Acute kidney injury can occasionally occur late in shock states due to prolonged systemic hypoperfusion or rhabdomyolysis from extreme hyperthermia. It does not represent the primary, immediate life-threatening driver of mortality in thyrotoxic crisis. Cardiovascular collapse occurs far sooner than renal shutdown. D. Heart failure: Extreme tachycardia and catecholamine hypersensitivity profoundly shorten ventricular filling times, reducing stroke volume while coronary demand skyrockets. This combination induces severe cardiomyopathy and high-output cardiac collapse, making it the primary source of mortality. Cardiorespiratory monitoring is the highest priority.