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From the *University College Hospital, London, and Centre for Anaesthesia, University College London; Centre for Behavioural and Social Sciences in Medicine, University College London; Department of Surgery, University College London; Centre for Behavioural and Social Sciences in Medicine, University College London, and Department of Psychology, Thames Valley University, London; ||Institute of Child Health, University College London; and ¶Centre for Behavioural and Social Sciences in Medicine, University College London, UK.
Address correspondence and reprint requests to Gareth L. Ackland, PhD, FRCA, Centre for Anaesthesia, University College London, University College London Hospital, 235 Euston Road, London NW1 2BU, UK. Address e-mail to g.ackland{at}ucl.ac.uk.
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).
CONCLUSION: Dehydration alone does not result in cognitive dysfunction.
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