Bubble CPAP: A Clash of Science, Culture, and Religion
Article Outline
Abbreviations: BCPAP, Bubble continuous positive airway pressure, CPAP, Continuous positive airway pressure, IFD-CPAP, Infant Flow Driver continuous positive airway pressure, NICU, Neonatal intensive care unit, RDS, Respiratory distress syndrome, VCPAP, Ventilator continuous positive airway pressure
Every neonatal intensive care unit (NICU) has care practices believed by its staff to represent the highest standard of care. The assimilation of a new technology or practice paradigm in a NICU often is problematic, requiring staff to abandon or modify existing beliefs and incorporate new ones. Acceptance of new technologies or care practices commonly occurs in 3 stages. In the first stage, initial skepticism is counterbalanced by a desire to use the new technology as well or better than other units that have reported their experience. In the second stage, as outcomes improve, the practice becomes integrated into the unit's culture as routine care. At this stage, staff usually remains willing to examine other alternatives, however. The third stage is the most perilous; staff becomes convinced that their practice is the best and refuses to accept or consider any contradictory data. At this point, the practice has achieved the status of a religious belief. All units, including my own with regard to bubble nasal continuous positive airway pressure (CPAP), have some practices that fall into the third stage. In that stage, it is most critical to examine the results of well-designed studies to explore whether clinical outcomes can be improved by changes in practice.
See related article, p 645
CPAP is one of the oldest established methods of respiratory support for critically ill infants. In the 1960s, ventilators delivering a fixed tidal volume without positive end-expiratory pressure were used to ventilate newborn infants. But weaning infants from mechanical ventilation was difficult, and survivors often developed chronic lung disease. In the early 1970s, Gregory et al1 demonstrated that providing CPAP using an anesthesia bag improved oxygenation in preterm infants with respiratory distress syndrome (RDS). But despite its simplicity and low cost, this mode of CPAP delivery was eventually replaced by more sophisticated (and expensive) mechanical ventilators that also can deliver CPAP when necessary.
The past 10 years have seen renewed interest in noninvasive forms of respiratory support, such as nasal CPAP. Nonetheless, controversy remains about the usefulness of CPAP as an initial management strategy in infants with RDS, and little data are available. In addition, only limited data exist regarding the practical aspects of CPAP delivery, including the best way to provide the positive airway pressure (i.e., bubble CPAP [BCPAP], Infant Flow Driver CPAP [IFD-CPAP], or ventilator CPAP [VCPAP]), optimal pressures, need for intermittent breaths, and patient interfaces.
The randomized clinical trial of Gupta et al2 reported in this issue of The Journal provides a scientific basis for exploring the optimum system for delivering CPAP after extubation in preterm infants. The use of CPAP after extubation is an evidence-based strategy with considerable scientific support.3 In the trial of Gupta et al, infants born at 24 to 29 weeks' gestation were randomized to receive BCPAP or IFD-CPAP after cessation of ventilation for RDS. An infant's readiness for extubation was determined with the minute ventilation test, which measures the effectiveness of spontaneous breathing and respiratory muscle endurance. Each infant received caffeine before being extubated. Among a subset of infants ventilated for less than 14 days, the extubation failure rate (defined by the degree of uncompensated respiratory acidosis or the need for cardiopulmonary resuscitation) was significantly lower in those receiving BCPAP. The median duration of CPAP did not differ significantly (when deaths were included in the analysis) between the 2 groups (3 days for BCPAP, 4 days for IFD-CPAP); neither did the incidence of chronic lung disease. The short duration of CPAP use after extubation in this study is surprising. In our unit, most infants remain on CPAP until 33 to 34 weeks' gestational age. During the weaning phase, the infants are monitored for apnea, bradycardia, and uncompensated respiratory acidosis; however, the decision to continue CPAP often is based on the presence of tachypnea or retractions.
The choice of hardware for administering CPAP often is based on the nursing staff's familiarity with and acceptance of the device. Various in vivo and in vitro studies suggest that the devices may have some important physiological- and biological-related differences, however. The variable-flow IFD-CPAP has been associated with reduced work of breathing and less thoracoabdominal asynchrony compared with BCPAP;4 these benefits have not been demonstrated to be clinically important, however. In a clinical study of infants with birth weight < 1500 g, Kahn et al5 found that the intraprong pressure with BCPAP was always higher (by 0.7 to 2.2 cm H2O) than the predicted positive airway pressure based on the set immersion depth, and that it increased with increasing flow rate. Gupta et al measured the pressure as close to the nares as possible with both kinds of CPAP devices to ensure equivalent pressures. Because this study did not use chinstraps or pacifiers, which allowed excess pressure to exit via the infant's mouth, it is unlikely that differences in delivered pressure account for the greater effectiveness of BCPAP.
Using a preterm lamb model, Pillow et al6 compared arterial blood gas determinations and pulmonary function assessments in lambs allocated to BCPAP or constant-pressure VCPAP. The animals receiving BCPAP had higher pH and partial pressure of O2, better oxygen extraction, and lower partial pressure of CO2. Those receiving VCPAP had significantly higher alveolar protein levels, suggesting increased lung injury with VCPAP. These findings were interpreted as indicating improved lung recruitment, stabilization, and patency of peripheral airways with BCPAP.
The benefits of BCPAP are likely to be greater during the acute phase of RDS, when lung compliance is lowest.7 In the study of Gupta et al, the infants were recovering from RDS. Although lung compliance was not measured at the time of extubation, it likely was improving when the infants were started on CPAP.
The 4 deaths occurring in Gupta et al's BCPAP group are disconcerting. Two of the infants died of sepsis, and the other 2 died from necrotizing enterocolitis. Graham et al8 identified nasal CPAP as a significant risk factor in gram-negative bacteremia (odds ratio = 5.9; 95% confidence interval = 1.5 to 22.6). Other investigators have reported similar observations.9 The hypothesis behind this is that nasal CPAP traumatizes the nasal mucosa, allowing the invasion of colonizing bacteria. CPAP also may increase intestinal distention, interfere with feeding, and promote bacterial translocation. Whether any differences exist in the incidence of nasal mucosal erosion or feeding intolerance between BCPAP and IFD-CPAP is unclear.
In summary, this randomized clinical trial suggests that BCPAP may be preferable to IFD-CPAP in infants with RDS after extubation. The findings may not apply to infants with more acute lung disease or those with bronchopulmonary dysplasia, however. The authors correctly note that this was a single-center study, and that success with CPAP is likely to be center-dependent.10 The authors further suggest that the different types of devices for delivering positive airway pressure have different physiological effects and may not be equally effective. Before these findings can be used to support the purchase of new equipment and retraining of personnel, a larger multicenter trial is needed to determine whether the data are generalizable.
References
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PII: S0022-3476(09)00020-1
doi:10.1016/j.jpeds.2009.01.020
© 2009 Mosby, Inc. All rights reserved.
Refers to article:
- A Randomized Controlled Trial of Post-extubation Bubble Continuous Positive Airway Pressure Versus Infant Flow Driver Continuous Positive Airway Pressure in Preterm Infants with Respiratory Distress Syndrome , 23 February 2009
