Sympathetic blockade by thoracic epidural anaesthesia suppresses renin release in response to hypotension, but activates the vasopressin system.
To determine whether or not the blockade of sympathetic efferents by epidural anaesthesia blunts the normal increase in plasma renin activity in response to hypotension, we assessed the effect of hypotensive thoracic epidural anaesthesia with widespread sympathetic blockade on plasma renin activity. Plasma renin activity and vasopressin concentration, arterial pressure, and serum osmolality were measured in 17 patients before and after random epidural injection of either 6.7 ml of 0.75% bupivacaine (n = 7) or the same volume of saline (n = 10). As an indicator for efferent sympathetic drive, skin temperatures were measured on the hand and foot. A decrease in mean arterial pressure by more than 25% of baseline values was prospectively defined as hypotension requiring intervention. Thoracic epidural anaesthesia induced a decrease in mean arterial pressure of 24 mmHg (range 16-47) from 101 mmHg to 77 mmHg (P less than 0.001 vs. saline). Despite hypotension, plasma renin activity remained unchanged [medians 2.9 ng ml-1 h-1 (0-9.1) vs. 3.4 ng ml-1 h-1 (0-13.8)]. In contrast, vasopressin concentrations increased from a median of 3.8 pg ml-1 (0.5-8.2) to 6.0 pg ml-1 (4.2-33.6; P = 0.025). Both hand and foot skin temperatures increased significantly indicating widespread extent of sympathetic blockade. Serum osmolality did not change. With epidural saline, variables remained unchanged. Thus, during hypotension induced by widespread attenuation of efferent sympathetic drive through thoracic epidural anaesthesia, renin activity did not change, whilst vasopressin concentrations increased significantly.(ABSTRACT TRUNCATED AT 250 WORDS)
Hopf
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Abteilung für Klinische Anaesthesiologie, Zentrum für Anaesthesiologie, Heinrich-Heine-Universität Düsseldorf, Germany.
Arand
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Peters
J
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D000767:Anesthesia, Epidural; D001340:Autonomic Nerve Block; D002045:Bupivacaine; D005260:Female; D006801:Humans; D007022:Hypotension / Q000097:blood / Q000209:etiology*; D008297:Male; D012083:Renin / Q000097:blood*; D014667:Vasopressins / Q000097:blood*
D014667:Vasopressins; D012083:Renin; D002045:Bupivacaine