A 55-year-old man comes to the emergency department due to right lower quadrant pain and is diagnosed with acute appendicitis. The patient is admitted to the hospital after undergoing an emergency appendectomy. He has a history of Graves disease treated with methimazole but has not been taking his medications regularly. One day after the procedure, the patient becomes restless, tremulous, agitated, and short of breath. Temperature is 38.9 C (102 F), blood pressure is 210/110 mm Hg, and pulse is 140/min. Lung examination is notable for fine bibasilar crackles. ECG shows sinus tachycardia. Which of the following parameters are most likely to be seen on hemodynamic measurement?
This patient with untreated hyperthyroidism has new-onset fever, severe hypertension, and tachycardia following appendectomy. This presentation raises concern for thyroid storm (ie, severe overactivity of thyroid hormone). Nonadherence with antithyroid drugs (eg, methimazole) and acutely stressful events (eg, surgery, trauma, infection) are common precipitants of thyroid storm.
The hemodynamics of thyroid storm involve the following:
Reduced systemic vascular resistance (SVR): Thyroid hormone causes increased metabolic demand in the tissues and has a direct vasodilatory effect on the endothelium; these effects result in peripheral vasodilation and reduced SVR.
Increased cardiac output (ie, cardiac index): In response to the reduced SVR, a reflexive increase in myocardial contractility and heart rate occurs. In addition, thyroid hormone has a direct sympathetic-like effect on the myocardium, further increasing contractility and heart rate. Stroke volume is markedly increased, which increases pulse pressure and systolic blood pressure. The increases in stroke volume and heart rate increase cardiac output and cause hyperdynamic circulation (ie, high blood flow).
High venous oxygen content: The hyperdynamic circulation allows less time for the tissues to extract oxygen from the bloodstream, resulting in high venous oxygen content (ie, low arterial-venous oxygen difference).
Untreated hyperthyroidism can eventually lead to high-output heart failure; this develops quickly in thyroid storm. Because the increased cardiac output flows against low SVR, blood returns to the heart quickly and easily and venous return is markedly increased. Despite a sustained elevation in cardiac output, the left ventricle cannot keep up with the increased venous return and pressure backs up into the lungs, causing increased pulmonary capillary wedge pressure and pulmonary edema.
Educational objective:
The hemodynamics of thyroid storm involve decreased systemic vascular resistance and increased cardiac output, leading to hyperdynamic circulation and increased venous return to the heart. High-output heart failure quickly develops, leading to backup of pressure from the left ventricle with increased pulmonary capillary wedge pressure.