Controlled hypotension in children: a critical review of available agents

Due to the potential for the transmission of infectious diseases with the homologous transfusion of blood products, there has been an increased interest in measures to limit intraoperative blood loss and avoid the need for homologous transfusion during high-risk surgical procedures including spinal surgery. Controlled hypotension (also referred to as deliberate or induced hypotension), defined as a reduction of systolic blood pressure to 80 to 90 mm Hg, a reduction of mean arterial pressure (MAP) to 50 to 65 mm Hg or a 30% reduction of baseline MAP, is one technique that has been used to limit intraoperative blood loss. In the adult population, several agents have been used alone or in combination for controlled hypotension including the inhalational anesthetic agents, direct-acting vasodilators such as nitroglycerin (glyceryl trinitrate) and nitroprusside, beta-adrenoceptor antagonists, and calcium channel antagonists. Despite clinical studies that have clearly demonstrated a reduction in blood loss with controlled hypotension when compared with the normotensive state and despite potential theoretical issues with each agent, there are no definitive studies demonstrating the preferred pharmacologic agent. When considering the pediatric-aged patient, studies have reported the use of the inhalational agent sevoflurane, the alpha(2)-adrenoceptor agonist dexmedetomidine as well as various vasodilators including sodium nitroprusside, nitroglycerin, fenoldopam, and alprostadil for controlled hypotension. Sevoflurane offers the advantages of easy dosage titration, no need for an additional intravenous infusion as well as providing anesthesia in addition to controlled hypotension. Disadvantages include a slightly higher cost than some of the intravenous agents and the inability to monitor evoked potentials with high sevoflurane concentrations. Whereas sodium nitroprusside, nicardipine and fenoldopam all provide the desired level of hypotension in pediatric-aged patients, nitroglycerin was not effective in this age group of patients in one study. When comparing nicardipine and sodium nitroprusside, nicardipine offers the potential advantages of fewer episodes of excessive hypotension, less rebound tachycardia and, in one study, less blood loss. Although fenoldopam has been shown to be effective, cost issues may limit is widespread application for this technique. The pharmacologic profile of dexmedetomidine indicates that this drug has potential in controlled hypotension and clinical data are needed to define its role.