title: Effect of stepwise reduction in minute ventilation on PaCO2 in ventilated newborns.
abstract: OBJECTIVE
  To study the effect of step reduction of expired minute ventilation (MV) on PaCO2 in ventilated newborns and to determine whether MV within a defined range can predict PaCO2.
  
  
  METHODS
  Prospective descriptive.
  
  
  METHODS
  Referral neonatal unit of a teaching hospital.
  
  
  METHODS
  Forty neonates stable on mechanical ventilation receiving minute ventilation in the range of 150-210 ml/kg/min. were studied. The spectrum of disorders for which the babies were ventilated included apnea of prematurity in 16, pneumonia in 14, meconium aspiration syndrome in 6 and hyaline membrane disease in 4. Median age at study was 6 days and median weight at study was 2.1 kgs. The MV was reduced from 210 to 150 mL/kg/min in three steps and concomitant PaCO2 was measured. Reductions were not done if PaCO2 was more than 50 mmHg. MVs were plotted against PaCO2 and a regression equation to predict PaCO2 from MV was calculated.
  
  
  RESULTS
  A stepwise increase was seen in CO2 with reduction of MV over the range studied. The median MV and median PaCO2 achieved in the three steps were 201 mL/kg/min and 36.7 mm of Hg, 180 mL/kg/min and 41.7 mm of Hg, 160 mL/kg/min, and 44.3 mm of Hg. The regression equation to predict PaCO2 was PaCO2 = 70 - 0.17 x MV in mL/kg/min, r = -0.45, r2 = 0.20, residual variance (s2) = 39.37; gave a predicted PaCO2 within 12.5 mmHg. for a given MV.
  
  
  CONCLUSIONS
  Reducing minute ventilation led to an increase in the levels of PaCO2. Minute volumes of 160 ml/kg/min correlated with PaCO2 value of 44.3 mm of Hg. MV as low as 160 mL/kg/min are well tolerated by newborns.
authors.affiliation: Referral Neonatal Unit, Department of Pediatrics, Maulana Azad Medical College and Associated Lok Nayak Hospital, New Delhi 110 02, India. drmathur@nda.vsnl.net.in
authors.forename: N B
authors.initials: NB
authors.lastname: Mathur
authors.forename: V
authors.initials: V
authors.lastname: Bhatia
mesh_terms: D001784:Blood Gas Analysis; D002245:Carbon Dioxide / Q000502:physiology*; D006801:Humans; D007231:Infant, Newborn; D010313:Partial Pressure; D012121:Respiration, Artificial / Q000379:methods*; D012140:Respiratory Tract Diseases / Q000503:physiopathology / Q000628:therapy; D013990:Tidal Volume
chemical_list: D002245:Carbon Dioxide