Continuous positive airway pressure (CPAP) is a well-established and effective respiratory support used in preterm infants with mild respiratory distress syndrome (RDS) and apnoea or after extubation.1 A wide range of devices are now available for delivering CPAP. Short binasal prongs (nasal CPAP (nCPAP)) are the most widespread, although well-known disadvantages are nasal trauma and unstable pressure delivered to the airways because of mouth opening.2 3 Insufficiently applied pressure and the baby’s open mouth result in lowering of the pharyngeal pressure and may lead to failure of nCPAP.4

Good tolerability has been demonstrated with hood CPAP in adults and, more recently, in newborns. The potential advantage of this system is the absence of air leakage caused by the baby’s open mouth, producing more stable pressure in the airways.5

The aim of the study was to compare set CPAP values and pharyngeal pressure readings in premature infants with mild RDS treated with either hood CPAP or the conventional nCPAP system.

MATERIALS AND METHODS

The study was performed in the neonatal intensive care unit at the Ospedale Maggiore Policlinico, Mangiagalli e Regina Elena, University of Milan. Inclusion criteria were: mild RDS requiring CPAP, birth weight <1500 g, postnatal age >24 h. Informed parental consent was obtained. Infants were randomised to either nCPAP (Infant Flow-EME, Brighton, UK) or hood CPAP (Starmed, Mirandola, Modena, Italy) based on group assignment contained in sequentially numbered envelopes.

Babies were studied at a constant CPAP level of 5 cm H₂O and treated for at least 2 h regardless of the device used. The hood CPAP system, as previously described,5 consists of a rigid pressure chamber (sealed hood) separated from the rest of the bed by a transparent cone-shaped polyurethane membrane. The soft membrane becomes a loose collar adhering to the shoulders with an atraumatic sealing effect, and a soft nappy system allows proper sealing. The inspiratory line is connected to the chamber, and, at this pressure level, inspiratory fraction of oxygen and temperature are detected by a sensor and continuously displayed. An adjustable positive end-expiratory pressure valve allows the desired pressure to be regulated in the system, and a pressure-release valve prevents excessive pressure in the hood (fig 1).

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Figure 1 Neonatal hood continuous positive airway pressure device.

Pharyngeal pressure was measured using a 6 French gauge polyurethane water-filled catheter, inserted through the mouth; a disposable pressure transducer (DTX Plus DT-NN; Becton-Dickinson, Franklin Lakes, New Jersey, USA), calibrated before each measurement, connected to the pressure port of a monitoring system (Spacelab Medical Inc, Issaquah, Washington, USA) was used. Pharyngeal pressure was measured after a 10 min period of clinical stabilisation. The pressure was measured twice with an interval of 5 min between measurements, during quiet sleep, with arterial oxygen saturation above 90%. The mean pressure value was taken.

Statistical analysis was carried out using the statistical package SigmaStat V2.0 (Statistical Software). The unpaired t test was used to compare differences between the two groups. Values were expressed as mean (SD) and were considered significant at p<0.05.

RESULTS

Ten premature infants treated with nCPAP (group 1; gestational age 28.3 (3.6) weeks, birth weight 874 (284.6) g) were compared with 10 babies treated with hood CPAP (group 2; gestational age 28.3 (3.6) weeks, birth weight 930 (328.8) g) (table 1). The two groups were homogeneous in terms of gestational age at birth and birth weight. In both groups, CPAP was used as primary respiratory support for RDS in five of the infants and as ventilatory treatment after extubation in the other five (table 1). The pharyngeal pressure was measured at a set pressure of 5 cm H₂O in both groups.

A significant difference between the set CPAP and pharyngeal pressure values was detected in group 1 (mean fall 2.8 (0.42) cm H₂O; p<0.001), whereas constant pressure values were observed in group 2 (mean fall 0.3 (0.48) cm H₂O; p = 0.2).

The mean pharyngeal pressure was significantly different in the two groups (2.2 (0.42) cm H₂O vs 4.7 (0.48) cm H₂O in group 1 and group 2, respectively; p<0.001).

Babies treated with hood CPAP had no skin lesions at the seal or other visible complications.

DISCUSSION

CPAP is widely used in the neonatal intensive care unit to treat premature babies, although the optimum CPAP device for infants remains uncertain, as small differences in CPAP transmitted to the lower airways may be clinically relevant.1 4

Short binasal prongs are thought to be the best way to deliver CPAP, as they allow delivery of pressure to both nostrils with low resistance, although the pressures transmitted to the airway during nCPAP may be significantly affected by mouth opening, particularly at low set pressures.2 Previously reported data are inconclusive with regard to the safety and effectiveness of active mouth closure during nCPAP.4

The hood CPAP system may represent a potential improvement, as it allows good transmission of the applied pressure without the possible dislodgement of nasal prongs thereby avoiding nasal trauma.5 These features suggest high tolerability of the hood CPAP system, which should guarantee prolonged and effective use of this device in premature babies. The risk of infection and obstructive apnoea, due to excessive production of nasal secretions, is also potentially reduced with the use of hood CPAP compared with nCPAP.3

Our preliminary results show more effective pressure transmission during hood CPAP compared with nCPAP, because of the absence of the effect of the baby’s open mouth.

Previous studies have indicated some risks associated with the use of hood CPAP, such as a rapid and dangerous increase in CO₂ rebreathing resulting from accidental discontinuation of gas flow.6 Our patients showed no complications in terms of O₂ and CO₂ levels and they had no skin lesions at the seal or other visible complications. On the other hand, interruption of CPAP during nursing care may be a potential problem with the use of this new device.

Zaramella et al7 assessed cerebral blood flow and relative changes in cerebral blood volume in infants treated with hood CPAP and nCPAP and found no differences in relative blood volume, although cerebral blood flow was lower during hood CPAP. No difference in occurrence of brain lesions was observed.

Further larger randomised trials are needed not only to demonstrate the clinical effectiveness and tolerability of this new device for longer periods of treatment, compared with other conventional techniques, but also to investigate potential limitations and unknown risks.