Journal Review

by Suzanne Whitbourne, MD

Courtney SE, Pyron KH, Saslow JG, et al. Lung recruitment and breathing pattern variable versus continuous flow nasal continuous positive airway pressure in premature infants: An evaluation of three devices. Pediatrics 2001; 107: 304-308.

Introduction: Nasal continuous positive airway pressure (NCPAP) has been used to treat mild pulmonary disease including apnea in premature infants. This paper examined whether lung volume changes and breathing pattern parameters differ among 3 NCPAP delivery services.

Methods: Thirty-two premature infants receiving NCPAP for apnea or mild respiratory distress were enrolled. Birth weight was (mean ± SD) 1081 ± 316 g, gestational age 29 ± 2 weeks, age at study 13 ± 12 days. Three devices, applied in random order, were studied in each infant: continuous flow NCPAP via CPAP prongs, continuous flow NCPAP via modified nasal cannula, and variable flow NCPAP. With each device, CPAP was first increased over 10 to 15 minutes to 8 cm H₂O to allow comparable lung recruitment in all infants. After lung recruitment, changes in lung volume (ΔVL) were assessed at NCPAP of 8, 6, 4, and 0 cm H₂O using calibrated direct current-coupled respiratory inductance plethysmography.

Results: ΔVL was significantly greater overall with the variable flow device compared with both the nasal cannula and CPAP prongs; ΔVL was not different between the cannula and the prongs. However, respiratory rate, tidal volume, thoracoabdominal asynchrony, and fraction of inspired oxygen (Fio₂) were greater with the modified cannula than for either of the other 2 devices.

Discussion: The data suggests that, compared with 2 continuous flow devices, the variable flow NCPAP device leads to greater lung recruitment. Although a nasal cannula is able to recruit lung volume, it does so at the cost of increased respiratory effort and an increased Fio2 requirement and cannot be recommended. Variable flow NCPAP is unique because it allows a preferred CPAP level to be maintained during the entire respiratory cycle. This occurs as variable jet flows at high velocity at the airway entrains gas to assist inspiration on demand and allows expired gas to leave through an expiratory outlet. In contrast, the continuous flow NCPAP involves a varying airway pressure as the infant inhales and exhales at a set CPAP level.

Although this study supports the effectiveness of variable NCPAP in the recruitment of lung volume, limitations to the study exist:

• Variable nasal CPAP does not provide any improvement in respiratory rate, Fio₂ requirements, or thoracoabdominal dysynchrony when compared to NCPAP by prongs, despite changes in lung recruitment.
• Another concern focuses on the use of 3- to 5-minute intervals at each CPAP level to study lung de-recruitment. This interval does not allow for adequate time to evaluate loss of lung volume or de-recruitment.
• Further, this study enrolled patients with different diagnoses and post-natal and gestational ages. Also, no information was given regarding the use of pre- or postnatal steroids. The lack of homogeneity in the patient population may have accounted for the variation noted in lung compliance.
• Finally, the study was not blinded, leading to possible investigator bias. The clinical use of variable flow NCPAP devices should be further studied in the premature infant that fails continuous NCPAP and requires reintubation. It is also important to note that the prongs of the variable flow NCPAP are heavy, and its use may be associated with an increased risk of injury to the nose and nasal septum.