title: Spontaneous variability of cardiac output in ventilated critically ill patients.
abstract: OBJECTIVE
  To define the magnitude of spontaneous cardiac output variability over time in sedated medical intensive care unit patients attached to a continuous cardiac output monitor, and to determine whether high level positive end-expiratory pressure or inverse inspiratory-to-expiratory (I:E) ratio ventilation resulted in greater variability over time than low positive end-expiratory pressure with conventional I:E ratio ventilation.
  
  
  METHODS
  Prospective study.
  
  
  METHODS
  Medical intensive care unit in a tertiary medical center.
  
  
  METHODS
  A total of 22 hemodynamically stable acute respiratory failure patients with a pulmonary artery catheter inserted for hemodynamic monitoring
  
  
  METHODS
  After being sedated, patients were randomized ultimately to receive pressure control ventilation first at setting A (high positive end-expiratory pressure [15 cm H2O] with conventional I:E ratio [1:2]) and then at setting B (low positive end-expiratory pressure [5 cm H2O] with inverse I:E ratio [2:1]), or vice versa, and then at setting C (low positive end-expiratory pressure [5 cm H2O] with conventional I:E ratio [1:2]). Each ventilation setting period lasted 1 hr.
  
  
  RESULTS
  Cardiac output (CO) was measured continuously. The continuous CO value displayed was updated every 30-60 secs. The updated value reflected an average of the previous 3-6 mins. The coefficient of variation (CV) of CO for each setting in each patient was calculated to represent the spontaneous variability. The mean CO+/-SD and CV of each setting was 5.7+/-1.8 L/min and 4.4% for setting A, 5.6+/-1.5 L/min and 4.6% for setting B, and 5.9+/-1.7 L/min and 4.8% for setting C. Analysis of variance revealed no significant differences between the CVs of the three settings. The 95% confidence interval for the COs for each setting was approximately the mean CO+/-0.1 x mean CO measured.
  
  
  CONCLUSIONS
  In critically ill sedated medical intensive care unit patients with stable hemodynamics, the spontaneous variability of cardiac output over time was not significant. High positive end-expiratory pressure (15 cm H2O) and inverse ratio ventilation (2:1) did not contribute to increased spontaneous variability of cardiac output.
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Chang Gung Memorial Hospital, Taipei, Taiwan.
authors.forename: C C
authors.initials: CC
authors.lastname: Huang
authors.forename: Y H
authors.initials: YH
authors.lastname: Tsai
authors.forename: N H
authors.initials: NH
authors.lastname: Chen
authors.forename: M C
authors.initials: MC
authors.lastname: Lin
authors.forename: T C
authors.initials: TC
authors.lastname: Tsao
authors.forename: C H
authors.initials: CH
authors.lastname: Lee
authors.forename: K H
authors.initials: KH
authors.lastname: Hsu
mesh_terms: D018806:APACHE; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D002302:Cardiac Output / Q000502:physiology*; D016001:Confidence Intervals; D016292:Procedural Sedation / Q000379:methods; D016638:Critical Illness; D005260:Female; D006334:Heart Function Tests / Q000295:instrumentation / Q000379:methods / Q000706:statistics & numerical data; D006801:Humans; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic / Q000295:instrumentation / Q000379:methods / Q000706:statistics & numerical data; D011446:Prospective Studies; D012121:Respiration, Artificial / Q000379:methods / Q000706:statistics & numerical data; D013997:Time Factors