title: Hydration status after overnight fasting as measured by urine osmolality does not alter the magnitude of hypotension during general anesthesia in low risk patients.
abstract: BACKGROUND
  The increased distribution of crystalloid solution into the interstitial space may decrease the effectiveness of intravascular volume loading in patients. We investigated whether preoperative hydration status after overnight fasting affects interstitial fluid redistribution and thus the magnitude of hypotension during general anesthesia.
  
  
  METHODS
  Sixty ASA physical status I/II patients undergoing tympanoplasty fasted from midnight. Anesthesia was induced by fentanyl and propofol and maintained with sevoflurane and remifentanil. Coinciding with the induction of anesthesia, 15 mL/kg acetated Ringer solution was infused IV over 60 minutes followed by 1 mL/kg acetated Ringer solution over the next 30 minutes. Urine osmolalities after induction of anesthesia and during the study period (pre-U(osm), post-U(osm)) and percent decreases of whole-body bioelectrical resistance for extracellular fluid relative to baseline at the end of the study period (ΔR(e)) were measured. Patients with a pre-U(osm) < the 25th percentile or with a pre-U(osm) > the 75th percentile of pre-U(osm) were categorized in the hydrated or the dehydrated group, respectively. A range of variables, including mean arterial blood pressure during the 30- to 90-minute period relative to baseline, and ΔR(e), were compared between the groups.
  
  
  RESULTS
  The dehydrated group (pre-U(osm) >759.5 mOsm/kg, n = 15) had a lower age (44 vs 52 years, P = 0.049) and had a higher post-U(osm) (181 vs 55 mOsm/kg, P = 0.001) compared with the hydrated group (pre-U(osm) <378.5 mOsm/kg, n = 15). Mean arterial blood pressure during the 30- to 90-minute period relative to baseline (0.67 vs 0.67, P = 0.85) with 95% confidence interval for the difference of means (-0.070 to 0.084) and ΔR(e) (5.6% vs 6.0%, P = 0.58) with 95% confidence interval for the difference of means (-1.85% to 1.06%) were similar for the hydrated and dehydrated groups.
  
  
  CONCLUSIONS
  Preoperative dehydration after overnight fasting as measured by urine osmolality did not alter the magnitude of hypotension during general anesthesia. This finding suggests that intravascular volume loading with crystalloid solution to prevent hypotension during general anesthesia is an unfounded practice for low risk patients after overnight fasting.
authors.affiliation: Department of Anesthesiology, Hyogo College of Medicine, Nishinomiya, Hyogo 663-8501, Japan.
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Osugi
authors.forename: Tsuneo
authors.initials: T
authors.lastname: Tatara
authors.forename: Sachiko
authors.initials: S
authors.lastname: Yada
authors.forename: Chikara
authors.initials: C
authors.lastname: Tashiro
mesh_terms: D000328:Adult; D000768:Anesthesia, General / Q000009:adverse effects*; D001794:Blood Pressure; D003460:Crystallization; D017097:Electric Impedance; D005260:Female; D005283:Fentanyl / Q000008:administration & dosage; D006801:Humans; D007022:Hypotension / Q000175:diagnosis* / Q000517:prevention & control*; D008297:Male; D008738:Methyl Ethers / Q000008:administration & dosage; D008875:Middle Aged; D009994:Osmolar Concentration; D010880:Piperidines / Q000008:administration & dosage; D015742:Propofol / Q000008:administration & dosage; D000077208:Remifentanil; D012306:Risk; D000077149:Sevoflurane; D013997:Time Factors; D016896:Treatment Outcome; D014433:Tympanoplasty / Q000379:methods; D014556:Urine / Q000737:chemistry*
chemical_list: D008738:Methyl Ethers; D010880:Piperidines; D000077149:Sevoflurane; D000077208:Remifentanil; D005283:Fentanyl; D015742:Propofol