title: Capillary and arterial blood gases in hemorrhagic shock: a comparative study.
abstract: OBJECTIVE
  To determine whether capillary blood gas samples accurately reflect the information obtained from arterial blood gas samples in a porcine hemorrhagic shock model.
  
  
  METHODS
  Randomized prospective study.
  
  
  METHODS
  Animal research laboratory at a children's hospital.
  
  
  METHODS
  Fifteen adult Yorkshire pigs.
  
  
  METHODS
  Tracheally intubated, ventilated, and anesthetized pigs were randomly assigned to either a control group (n = 10) or a hemorrhagic shock group (n = 5). After instrumentation, the hemorrhagic shock group underwent a 40-mL/kg hemorrhage over 2 hrs, while the control group did not. Animals were then monitored over a 3-hr period.
  
  
  RESULTS
  Simultaneous arterial blood gas and capillary blood gas samples were obtained from each animal by using standardized technique. Capillary blood gas pH accurately predicted arterial blood gas pH in both control and hemorrhagic shock groups (r = .94, p < .01, and r = .78, p < .01, respectively). Bland-Altman analysis revealed a mean difference between arterial blood gas pH and capillary blood gas pH of 0.016 (95% limit of agreement, +/-0.037) in the control group vs. a mean difference between arterial blood gas pH and capillary blood gas pH of 0.075 (95% limit of agreement, +/-0.142) in the hemorrhagic shock group. Capillary blood gas Pco2 accurately predicted arterial blood gas Pco2 in the control group but not in the hemorrhagic shock group (r = .80, p < .01, and r = .13, p = .41, respectively). By Bland-Altman analysis, the mean difference between arterial blood gas Pco2 and capillary blood gas Pco2 was 3.9, with a 95% limit of agreement of +/-3.61 in the control group. In the hemorrhagic shock group, the mean difference between arterial blood gas Pco2 and capillary blood gas Pco2 was 11.7 with a 95% limit of agreement of +/-38.8. Hemorrhagic shock group capillary blood gas samples significantly overestimated Pco2 (Delta = 11.7, p < .01) and underestimated pH (Delta = 0.075, p < .01) compared with arterial blood gas samples.
  
  
  CONCLUSIONS
  Capillary blood gas samples are poor predictors of Pco2 and pH in porcine hemorrhagic shock. These findings should be taken into account when capillary blood gas samples are used in the monitoring and management of subjects diagnosed with shock.
authors.affiliation: Division of Critical Care Medicine, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA.
authors.forename: Ikuya
authors.initials: I
authors.lastname: Ueta
authors.forename: Brian R
authors.initials: BR
authors.lastname: Jacobs