title: Platelet function and adrenoceptors during and after induced hypotension using nitroprusside.
abstract: BACKGROUND
  Hypotension induced by sodium nitroprusside can minimize intraoperative blood loss. The release of endogenous catecholamines can influence adrenoceptors of platelets and thus might change the ability of platelets to aggregate.
  
  
  METHODS
  Forty patients undergoing nasal septum, tympanoplastic, or sphenoid sinus surgery were randomly divided into two groups, those having controlled hypotension (A) and those serving as controls (B). Blood samples were drawn before the operation, after induction of anesthesia, 1 h after the start of the operation, and on the day after surgery.
  
  
  RESULTS
  Epinephrine-induced platelet aggregation only increased in the controls on the day after surgery (A: from 49 +/- 25% to 47 +/- 29%; B: from 53 +/- 24% to 72 +/- 14%; mean +/- SD; P < 0.01). Spontaneous platelet aggregation increased in the controls from a median of 1.2 omega/h to 2.4 during the operation and 2.9 on the day after surgery but not after hypotension. On the day after surgery, alpha 2 receptors reached their maximum (A: 238 +/- 164; B: 234 +/- 80 per platelet). During the operation, the norepinephrine concentrations were significantly greater in group A (median, 419 pg/ml) than in group B (median, 217 pg/ml; P < 0.05). Blood loss was greater in the controls (A: 180 +/- 75; B: 379 +/- 120 ml; P < 0.05).
  
  
  CONCLUSIONS
  Controlled hypotension using sodium nitroprusside reduces epinephrine-induced and spontaneous platelet aggregation. Even on the day after hypotension, the usual postoperative reactive increase in platelet aggregation did not occur. These results may be explained by the direct effect of nitroprusside on platelets, the augmented stress response, lower shear stress on platelets due to the lower blood pressure, or the decreased blood loss compared with the controls.
authors.affiliation: Department of Anaesthesiology and Intensive Care Medicine, Justus-Liebig-University, Giessen, Germany.
authors.forename: G V
authors.initials: GV
authors.lastname: Dietrich
authors.forename: M
authors.initials: M
authors.lastname: Heesen
authors.forename: J
authors.initials: J
authors.lastname: Boldt
authors.forename: G
authors.initials: G
authors.lastname: Hempelmann
mesh_terms: D000328:Adult; D000959:Antihypertensive Agents / Q000627:therapeutic use*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D007023:Hypotension, Controlled; D008297:Male; D009599:Nitroprusside / Q000627:therapeutic use*; D009638:Norepinephrine / Q000097:blood; D010974:Platelet Aggregation / Q000187:drug effects*; D011184:Postoperative Period; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects*
chemical_list: D000959:Antihypertensive Agents; D011942:Receptors, Adrenergic, alpha; D009599:Nitroprusside; D009638:Norepinephrine