title: Hypokalemia before induction of anesthesia and prevention by beta 2 adrenoceptor antagonism.
abstract: We have observed that serum potassium levels measured immediately before induction of anesthesia ("preinduction K+") are often lower than those measured 1-3 days preoperatively ("preoperative K+"). The purpose of this investigation was to determine, in two studies, the magnitude of this difference and to elucidate the mechanism by which this occurs. In the first study, preinduction K+ (3.6 +/- 0.4 mEq/L, mean +/- SD) was significantly lower than K+ levels measured during routine preoperative testing (4.4 +/- 0.4 mEq/L, n = 47, P less than 0.001). Twenty-three patients (49%) had preinduction K+ levels that were considered hypokalemic (less than or equal to 3.5 mEq/L), but 22 of these 23 patients had normal preoperative K+ levels. The second study tested the hypothesis that preinduction decreases in serum K+ are mediated by beta 2-adrenergic receptors. Preinduction K+ changes were determined in patients given a single preoperative dose of propranolol (beta 1/beta 2-antagonist), atenolol (beta 1-antagonist), or no beta-blocker (control). The difference between preoperative and preinduction serum K+ in patients receiving propranolol (0.1 +/- 0.4 mEq/L) was significantly attenuated (P less than 0.02) compared with the difference in control subjects (0.5 +/- 0.4 mEq/L), but was not significantly different from controls in patients pretreated with atenolol (0.3 +/- 0.4 mEq/L). These results demonstrate that serum K+ levels measured intraoperatively just before anesthetic induction are consistently and significantly less than those measured 1-3 days preoperatively. The ability of propranolol but not atenolol to block this change suggests that the acute decrease in K+ levels was due to beta 2-adrenergic receptor stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Anesthesiology, University of Washington Medical Center, Seattle.
authors.forename: E D
authors.initials: ED
authors.lastname: Kharasch
authors.forename: T A
authors.initials: TA
authors.lastname: Bowdle
mesh_terms: D000284:Administration, Oral; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000758:Anesthesia; D001262:Atenolol / Q000627:therapeutic use*; D006801:Humans; D007008:Hypokalemia / Q000209:etiology* / Q000517:prevention & control; D007432:Intraoperative Period; D008875:Middle Aged; D011188:Potassium / Q000097:blood; D011433:Propranolol / Q000627:therapeutic use*; D011943:Receptors, Adrenergic, beta / Q000502:physiology; D013514:Surgical Procedures, Operative; D013997:Time Factors
chemical_list: D011943:Receptors, Adrenergic, beta; D001262:Atenolol; D011433:Propranolol; D011188:Potassium