|
|
NewsletterVasopressin in the treatment of refractory hypotension Reviewer: KW Tim Park, MD
8-Arginine vasopressin (AVP) is an endogenous hormone produced in the posterior pituitary under conditions of water deprivation or extracellular volume depletion. Also known as the antidiuretic hormone (ADH), AVP acts on the V2 receptors of the renal collecting duct to increase water permeability and enhance water resorption down the osmotic gradient. This action is inhibited by prostaglandins and enhanced by chlorpropamide, acetaminophen, and indomethacin. AVP is also a potent vasoconstrictor acting on the V1 receptors in vascular smooth muscles. Because of these dual actions, the traditional indications for vasopressin derivatives have been for treatment of diabetes insipidus and control of esophageal variceal bleeding, the latter in doses of 4-16 U/hr or higher The sympathetic nervous system appears to be more important in maintaining blood pressure under normal conditions. However, when sympathetic outflow is reduced or conditions of acidosis and hypoxia impair the responses to sympathomimetics, exogenous vasopressin retains its potent vasoconstrictor action. Exogenous vasopressin administration has been shown to effectively increase blood pressure in septic shock where endogenous vasopressin concentrations were inappropriately low (1). In a recent report, De Kock et al. (2) compared ornipressin to norepinephrine and dopamine in treatment of hypotension during combined general/epidural anesthesia. Ornipressin is a V1-receptor specific AVP derivative with little antidiuretic action. The authors used clonidine and sufentanil as well as bupivacaine for epidural anesthesia, in order to not only block sympathetic outflow, but also inhibit endogenous vasopressin release. Under these conditions, ornipressin 2 U/hr was about as effective as norepinephrine 0.04 µg/kg/min and more effective than dopamine 6 µg/kg/min. At equipressor doses, dopamine increased heart rate significantly whereas ornipressin and norepinephrine did not. No ST changes were noted with any of the three agents. Ornipressin produced splanchnic vasoconstriction and gut intracellular hypercarbia, while dopamine preserved splanchnic flow. Usually the stress of cardiopulmonary bypass (CPB) is associated with an increase in endogenous release of vasopressin (3,4). This increase is more marked in patients undergoing valve replacement surgeries, especially of the mitral valve, than coronary artery bypass surgeries (3). However, in the study by Argenziano et al. (5), patients with post-CPB vasodilatory shock with excessive norepinephrine dependence tend to have inappropriately low serum AVP concentrations (12 ± 7 pg/ml). Predictors of such vasodilatory shock by multivariate analysis were preoperative left ventricular ejection fraction < 0.35 and use of angiotensin-converting enzyme inhibitors (Cf. ref. 6). In such patients, use of low-dose AVP produced rapid improvement in blood pressure and decreased norepinephrine requirement. A similar case report has been published by Overland and Teply (7). Argenziano et al. have also successfully used low dose infusions of vasopressin in left ventricular assist device recipients with vasodilatory shock after CPB, most of whom had inappropriately low plasma AVP levels (8). Doses used were 7-20 U/hr by Overland and Teply (7) and 6 U/hr by Argenziano et al. (5). Under steady state conditions, infusion of 6 U/hr of AVP gives a plasma concentration of at least 150 pg/ml, comparable to what is usually seen after CPB (5). REFERENCES:
© Society of Cardiovascular Anesthesiologists Questions or comments? Please send email to webmaster@scahq.org |