title: Dehydration induced by bowel preparation in older adults does not result in cognitive dysfunction.
abstract: BACKGROUND
  Postoperative cognitive dysfunction occurs in a proportion of patients after noncardiac surgery. Older patients are particularly vulnerable. We hypothesized that dehydration, a common perioperative problem in the elderly, may provoke cognitive dysfunction. We used a clinical scenario free of surgical/anesthetic intervention to determine whether dehydration caused by bowel preparation results in cognitive changes.
  
  
  METHODS
  Thirty-eight patients of an age associated with a significant incidence of postoperative cognitive dysfunction were recruited in a prospective observational study. A further control group of 14 patients undergoing sigmoidoscopy, who did not receive any bowel preparation, were matched for age, education, and gender.
  
  
  RESULTS
  Loss of total body weight (1.5 kg [95% CI: 0.9-2.2]; P < 0.001) occurred in patients undergoing bowel preparation (2.0 [95% CI: 1.3-2.6] percent total body weight), whereas sigmoidoscopy patients' weight did not change (0.17 kg [95% CI: -0.2-0.6 kg]; P = 0.26). Total body water, derived from foot bioimpedance, indicated dehydration in the bowel preparation group only (mean impedance change 36 [Omega] [95% CI; 25-46], P < 0.001) with a calculated decrease of 2.6% in total body water (95% CI: 1.1-4.8; P < 0.001). Hematocrit increased after bowel preparation only (prebowel prep 0.41 [0.40-0.43] versus postbowel prep 0.43 [0.42-0.45]; P = 0.003). Despite this degree of dehydration, all cognitive tests were within 1 SD of the population mean of normal values. Repeated measures analysis of variance did not reveal significant changes for within group comparisons over time for motor speed (P = 0.51), executive function (P = 0.57), Trail Making Tests and recall (P = 0.88), other than a 3 s slowing in learning ability (Rey Auditory Verbal Learning Test; P = 0.04). Hydration status did not affect learning (P = 0.42), recall (P = 0.30) motor speed (P = 0.36), or executive function tests (P = 0.26).
  
  
  CONCLUSIONS
  Dehydration alone does not result in cognitive dysfunction.
authors.affiliation: Centre for Anaesthesia, University College London, University College London Hospital, 235 Euston Road, London NW1 2BU, UK. g.ackland@ucl.ac.uk
authors.forename: Gareth L
authors.initials: GL
authors.lastname: Ackland
authors.forename: Jane
authors.initials: J
authors.lastname: Harrington
authors.forename: Paul
authors.initials: P
authors.lastname: Downie
authors.forename: James W
authors.initials: JW
authors.lastname: Holding
authors.forename: Deepak
authors.initials: D
authors.lastname: Singh-Ranger
authors.forename: Konstandina
authors.initials: K
authors.lastname: Griva
authors.forename: Michael G
authors.initials: MG
authors.lastname: Mythen
authors.forename: Stanton P
authors.initials: SP
authors.lastname: Newman
mesh_terms: D000368:Aged; D001823:Body Composition / Q000187:drug effects; D001834:Body Water / Q000187:drug effects / Q000378:metabolism; D016022:Case-Control Studies; D002400:Cathartics / Q000009:adverse effects*; D019343:Citric Acid / Q000009:adverse effects*; D003071:Cognition / Q000187:drug effects; D003072:Cognition Disorders / Q000209:etiology* / Q000378:metabolism / Q000503:physiopathology; D003113:Colonoscopy; D003681:Dehydration / Q000139:chemically induced / Q000150:complications* / Q000378:metabolism / Q000503:physiopathology / Q000523:psychology; D017097:Electric Impedance; D005260:Female; D006400:Hematocrit; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D008297:Male; D011939:Mental Recall / Q000187:drug effects; D008875:Middle Aged; D009048:Motor Skills / Q000187:drug effects; D009483:Neuropsychological Tests; D009942:Organometallic Compounds / Q000009:adverse effects*; D011300:Preoperative Care / Q000009:adverse effects*; D011446:Prospective Studies; D012812:Sigmoidoscopy; D011795:Surveys and Questionnaires; D015431:Weight Loss / Q000187:drug effects
chemical_list: D002400:Cathartics; D006454:Hemoglobins; D009942:Organometallic Compounds; D019343:Citric Acid; C110422:magnesium citrate