What are the major anesthetic concerns in patients with carcinoid syndrome?
Although carcinoid tumors are relatively rare, patients with this disease frequently have concurrent medical problems. Thirty percent have carcinoid heart disease. The cause is unclear. Right-sided fibrous plaque deposited on the tricuspid valve and right ventricular walls is the most common finding. Tricuspid regurgitation is the most com-mon valvulopathy associated with carcinoid tumors. If the pulmonary valve is involved, stenosis rather than regurgi-tation is more prevalent. Carcinoid plaques are rarely found on the left side of the heart, but do occur.
Anesthetic concerns include right-sided heart failure and pulmonary hypertension. It is important to avoid increases in pulmonary vascular resistance to prevent hypoxemia. High-dose nitrous oxide may predispose to pulmonary hypertension. Patients with significant tricuspid regurgita-tion should be kept well hydrated and tachycardia should be avoided. These patients are more susceptible to supraven-tricular dysrhythmias as well. Endocarditis prophylaxis should be undertaken with a penicillin or variant, and under some circumstances an aminoglycoside. Treatment of hypotension with catecholamines may produce worse physiologic problems. Catecholamines stimulate secretion of substances from carcinoid tumors. Among these sub-stances are mediators that produce hypotension and other components of the carcinoid syndrome. Consequently treat-ment of hypotension with catecholamines can produce a paradoxical exacerbation of hypotension.
Gastric carcinoid generally releases histamine, thus bronchospasm can occur, which does not respond well to β-agonists or aminophylline. It is prudent to avoid drugs which release histamine such as d-tubocurarine, atracurium, mivacurium, and morphine.
H1-blockers, H2-blockers, and steroids have been used prophylactically to avoid severe reactions, but are unreliable. Succinylcholine should also be used with caution, as abdominal wall fasciculations can increase intra-abdominal pressure, thus squeezing the tumor causing further hormone release. Pretreatment with a nondepolarizing neuromuscular blocker can decrease fasciculations. If hypotension occurs intraoperatively it is important to give volume and avoid the use of cate-cholamines or β-agonists. The use of angiotensin in a dose of 1.5 mg/kg may improve hypotension. Prehydration is of great benefit in these patients as a generalized fluid deficit occurs due to secondary hormone release from the tumor. Invasive monitoring to assess cardiovascular status is helpful in some patients with cardiac disease, due either to carcinoid or intrinsic myocardial disease itself. Acute intraoperative hypertension is often associated with bron-chospasm, which is probably due to serotonin release. If hypertension occurs acutely, the use of vasodilating agents, such as nitroglycerin or sodium nitroprusside, is recom-mended.