title: Elevated positive end-expiratory pressure decreases cardiac index in a rhesus monkey model.
abstract: BACKGROUND
  Clinicians are often concerned that higher positive end-expiratory pressure (PEEP) will decrease cardiac index (CI). PEEP affects CI through multiple inter-related mechanisms. The adult Rhesus monkey is an excellent model to study cardiopulmonary interaction due to similar pulmonary and chest wall compliances to human infants.
  
  
  OBJECTIVE
  Our goal was to examine the impact of increasing PEEP on CI in Rhesus monkeys as a model for critically ill children.
  
  
  METHODS
  Prospective, experimental animal study. Nine healthy anesthetized, intubated Rhesus monkeys were allowed to breathe spontaneously at a PEEP of 0, 5, 10, and 15 cm H2O while CI was measured with an ultrasonic Doppler (USCOM).
  
  
  RESULTS
  Cardiac index decreased between PEEP levels of 5 and 15 cm H2O. The mean decrease in CI for the entire cohort of monkeys was 18% (p < 0.01) with a range of -11 to 49%. Stroke volume and oxygen delivery also decreased between PEEP levels of 5 and 15 cm H2O (p < 0.01).
  
  
  CONCLUSIONS
  Between PEEP levels of 5 and 15 cm H2O, there was a decrease in CI, stroke volume, and oxygen delivery in intubated Rhesus monkeys. A plausible mechanism is that over-distention of normally compliant lungs at increased PEEP resulted in decreased preload to the right ventricle, outweighing the potentially beneficial decrease in left ventricular afterload or pulmonary vascular resistance. Further investigation is warranted, particularly in children with lung injury, who have historically benefited from increased PEEP levels without over-distention.
authors.affiliation: Children's Hospital Los Angeles, University of Southern California Keck School of Medicine , Los Angeles, CA , USA.
authors.forename: Patrick A
authors.initials: PA
authors.lastname: Ross
authors.affiliation: Children's Hospital Los Angeles, University of Southern California Keck School of Medicine , Los Angeles, CA , USA.
authors.forename: Robinder G
authors.initials: RG
authors.lastname: Khemani
authors.affiliation: Children's Hospital Los Angeles, University of Southern California Keck School of Medicine , Los Angeles, CA , USA.
authors.forename: Sarah S
authors.initials: SS
authors.lastname: Rubin
authors.affiliation: Children's Hospital Los Angeles, University of Southern California Keck School of Medicine , Los Angeles, CA , USA.
authors.forename: Anoopindar K
authors.initials: AK
authors.lastname: Bhalla
authors.affiliation: Children's Hospital Los Angeles, University of Southern California Keck School of Medicine , Los Angeles, CA , USA.
authors.forename: Christopher J L
authors.initials: CJ
authors.lastname: Newth
keywords: Macaca mulatta; cardiac index; oxygen transport; positive end-expiratory pressure