title: The hemodynamic effects of prolonged respiratory alkalosis in anesthetized newborn piglets.
abstract: OBJECTIVE
  To test the hypothesis that prolonged alkalosis decreases cardiac output and, furthermore, exacerbates hypoxic pulmonary vasoconstriction, as respiratory alkalosis is frequently induced as a therapy for persistent pulmonary hypertension of the newborn despite a lack of controlled evidence of improved outcomes. Potential adverse effects of prolonged alkalosis have been demonstrated.
  
  
  METHODS
  Two groups (control, n = 6, and hypocapnic alkalosis, n = 6) of 1-3 day old fentanyl-anesthetized, vecuronium-paralyzed piglets were instrumented to measure cardiac index (CI) and mean systemic (MAP) and pulmonary (PAP) arterial pressures. Baseline values were recorded. Alveolar hypoxia was then induced to achieve an arterial oxygen saturation of between 50 and 60% for 15 min. Respiratory alkalosis was then induced, by increasing ventilation to achieve a pH between 7.55-7.60, and was continued for 240 min. Inspired carbon dioxide was used with hyperventilation in the control group to maintain pressure of arterial carbon dioxide (PaCO2) at 35-45 mmHg and pH of 7.35-7.45. Hypoxia was induced again at 15 and 240 min. Pulmonary and systemic vascular resistances (PVR and SVR) were calculated.
  
  
  RESULTS
  Prolonged alkalosis led to a significant and progressive fall in mean MAP from 61 (SD 7) mmHg at the start of the study falling to 50 (SD 6.9, p = 0.043), with no effect on CI. Calculated SVR decreased (0.45 SD 0.03 vs 0.36 SD 0.05). There were no statistically significant changes in any of the variables in the control group. Neither acute nor prolonged respiratory alkalosis had a significant effect on hypoxic pulmonary vasoconstriction.
  
  
  CONCLUSIONS
  Prolonged hyperventilation leads to systemic hypotension, however it does not exacerbate hypoxic pulmonary vasoconstriction.
authors.affiliation: University of California, San Diego Medical Center, Department of Pediatrics 92103, USA.
authors.forename: K
authors.initials: K
authors.lastname: Jundi
authors.forename: K J
authors.initials: KJ
authors.lastname: Barrington
authors.forename: C
authors.initials: C
authors.lastname: Henderson
authors.forename: R G
authors.initials: RG
authors.lastname: Allen
authors.forename: N N
authors.initials: NN
authors.lastname: Finer
mesh_terms: D000472:Alkalosis, Respiratory / Q000503:physiopathology*; D000704:Analysis of Variance; D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D001794:Blood Pressure; D002302:Cardiac Output; D006439:Hemodynamics; D006863:Hydrogen-Ion Concentration; D006985:Hyperventilation; D007022:Hypotension / Q000503:physiopathology; D000860:Hypoxia / Q000503:physiopathology*; D013552:Swine; D014655:Vascular Resistance; D014661:Vasoconstriction