title: Gastric intramucosal PCO2 and pH variability in ventilated critically ill patients.
abstract: OBJECTIVE
  Gastric intramucosal PCO2 (PiCO2) and pH (pHi) are currently used as indices of the adequacy of splanchnic perfusion and as end points to guide therapeutic intervention. However, little is known about their spontaneous variability over time. The present study was designed to define the magnitude of spontaneous variability of PiCO2 and pHi in sedated medical intensive care unit (ICU) patients using an automated recirculating air tonometer and to test whether high-level positive end-expiratory pressure (PEEP) or inverse inspiratory/expiratory (I:E) ratio ventilation resulted in a greater variability than low PEEP with conventional I:E ratio ventilation.
  
  
  METHODS
  Prospective study.
  
  
  METHODS
  Medical ICU in a tertiary medical center.
  
  
  METHODS
  Twenty-three acute respiratory failure patients.
  
  
  METHODS
  After being sedated, patients were randomized to undergo pressure control ventilation at the following three settings: A, high PEEP (15 cm H2O) with conventional I:E ratio (1:2), and B, low PEEP (5 cm H2O) with inverse I:E ratio (2:1) alternately, and then C, low PEEP (5 cm H2O) with conventional I:E ratio (1:2). Each ventilation setting period lasted 1 hr.
  
  
  RESULTS
  The PiCO2 and pHi were measured at baseline (time 0), and at 15, 30, 45, and 60 mins thereafter. The corresponding coefficients of variation (CVs) of PiCO2 for overall pooled group and settings A, B, and C were 4.0%, 4.4%, 3.4%, and 4.2%, respectively. The corresponding CVs of pHi for overall pooled group and settings A, B, and C were 0.36%, 0.37%, 0.33%, and 0.4%, respectively. Analysis of variance showed no significant difference in the CVs of PiCO2 or pHi between the three settings. The 95% confidence interval is approximately +/-8% variability for PiCO2 and +/-0.7% variability for pHi.
  
  
  CONCLUSIONS
  In critically ill medical ICU patients with stable hemodynamics, the spontaneous variability of PiCO2 or pHi are not substantial. High PEEP (15 cm H2O) and inverse ratio ventilation (2:1), which does not change the cardiac output or hemodynamics, does not contribute to increased spontaneous variability in PiCO2 or pHi.
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Chang Gung Memorial Hospital, Taoyuan, Taiwan.
authors.forename: C C
authors.initials: CC
authors.lastname: Huang
authors.forename: Y H
authors.initials: YH
authors.lastname: Tsai
authors.forename: M C
authors.initials: MC
authors.lastname: Lin
authors.forename: T C
authors.initials: TC
authors.lastname: Tsao
authors.forename: K H
authors.initials: KH
authors.lastname: Hsu
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D002245:Carbon Dioxide / Q000378:metabolism; D005260:Female; D005753:Gastric Mucosa / Q000098:blood supply* / Q000503:physiopathology*; D006439:Hemodynamics; D006801:Humans; D006863:Hydrogen-Ion Concentration; D016014:Linear Models; D008297:Male; D008365:Manometry; D008875:Middle Aged; D010313:Partial Pressure; D011175:Positive-Pressure Respiration; D012121:Respiration, Artificial / Q000379:methods*; D012128:Respiratory Distress Syndrome / Q000503:physiopathology / Q000628:therapy
chemical_list: D002245:Carbon Dioxide