title: pH effects on cardiac function and systemic vascular resistance in preterm infants.
abstract: OBJECTIVE
  To investigate the effect of pH on cardiac function and systemic vascular resistance (SVR) in preterm infants.
  
  
  METHODS
  In this prospective observational study, we evaluated hemodynamically stable, ≤ 30 weeks' gestation preterm infants during the first 2 postnatal weeks. Cardiac function was assessed by echocardiography at the time of arterial blood draw for clinically indicated blood gas analysis. Data were separately analyzed for the transitional (days 1-3) and post-transitional (days 4-14) periods.
  
  
  RESULTS
  We evaluated 147 pairs of arterial blood gases and echocardiograms in 29 preterm neonates (gestational age = 26.2 ± 1.5 weeks). Arterial pH ranged from 7.02-7.46. There was no linear relationship between pH and shortening fraction or stress-velocity index in transitional or post-transitional periods. We found a weak negative linear relationship between pH and left ventricular output and a positive linear relationship between pH and SVR only during the post-transitional period. These relationships were maintained after adjustment for the degree of base deficit. Arterial CO2 had effects similar to pH on myocardial function.
  
  
  CONCLUSIONS
  Unlike adults, myocardial contractility remains relatively unaffected by acidosis even at pH values close to 7.00 in hemodynamically stable preterm neonates during the first 2 postnatal weeks. However, as in adults, worsening acidosis in preterm neonates after the immediate transitional period is associated with a decrease in SVR along with an increase in left ventricular output. Thus, although myocardial contractility remains unaffected in preterm neonates during the first 2 postnatal weeks, the vascular response to acidosis undergoes a relatively rapid postnatal maturational process.
authors.affiliation: Division of Neonatology and the Center for Fetal and Neonatal Medicine, Department of Pediatrics, Children's Hospital Los Angeles and the LAC+USC Medical Center, Keck School of Medicine, University of Southern California, Los Angeles, CA 90027, USA. snoori@chla.usc.edu
authors.forename: Shahab
authors.initials: S
authors.lastname: Noori
authors.forename: Tai-Wei
authors.initials: TW
authors.lastname: Wu
authors.forename: Istvan
authors.initials: I
authors.lastname: Seri
mesh_terms: D001784:Blood Gas Analysis; D001794:Blood Pressure; D002302:Cardiac Output; D004452:Echocardiography; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007231:Infant, Newborn; D007234:Infant, Premature / Q000502:physiology*; D007235:Infant, Premature, Diseases / Q000503:physiopathology*; D011446:Prospective Studies; D014655:Vascular Resistance / Q000502:physiology*