Randomised study comparing extent of hypocarbia in preterm infants during conventional and patient triggered ventilation

AIM—To determine whether patient triggered ventilation (PTV) leads to greater exposure to significant hypocarbia than conventional ventilation (CMV) in premature infants during the first 72 hours of life. METHODS—Infants of 32 weeks gestation or less were included. Randomisation yielded 74 infants on PTV and 68 infants on CMV. Arterial PaCO2 measurements were taken four hourly for the first 72 hours of life. RESULTS—The mean PaCO2 levels on days 1, 2, and 3 were not significantly different between the two groups. The proportion of infants with PaCO2 levels of 3.33 kPa or less did not differ between PTV and CMV infants. Mean percentages of infants with this level of hypocarbia at any time were 31.4%, 18.9%, 8.8% on days 1, 2, and 3 respectively. Cumulative hypocarbia, below a 3.33 kPa threshold, was 0.0084 kPa.h (PTV) versus 0.0263 kPa.h (CMV) per hour ventilated during the first 24 hours (p = 0.259). Risk factors associated with hypocarbia on day 1 were peak inspiratory pressure below 14 cm H2O (odds ratio 4.79) as well as FiO2 below 0.30 (odds ratio 3.42). CONCLUSION—Exposure to hypocarbia (PaCO2 3.33 kPa or below) was not significantly different between PTV and CMV infants during the first 72 hours of life. Hypocarbia was common in both groups on day 1 and to a lesser extent on day 2. Infants with the least requirements for ventilatory support were at highest risk of hypocarbia on day 1 of life. Preterm infants with mild hyaline membrane disease require a more aggressive approach to weaning on both modes of ventilation, followed by extubation to limit the risk of hypocarbia.