The Science Journal of the American Association for Respiratory Care

2012 OPEN FORUM Abstracts


Tiffany M. Youngquist1, C. Peter Richardson1,3, Robert M. DiBlasi2,1; 1Center for Developmental Therapeutics, Seattle Children’s Research Institute, Seattle, WA; 2Respiratory Care, Seattle Children’s Hospital, Seattle, WA; 3Pulmonary, Department of Pediatrics, University of Washington School of Medicine, Seattle, WA

Background B-CPAP is a form of noninvasive respiratory support that is frequently used in spontaneously breathing infants with lung disease. Recently, we observed condensate in the patient circuit oscillating as the bias gas flowed through the circuit. We questioned whether this partial or intermittent obstruction of gas flow could impact pressures delivered to the patient. Methods An anatomically accurate nasal airway model of a preterm infant was attached to an IngMar ASL 5000 lung model configured with R:150 cmH2O/L/s, C:0.5 mL/cmH2O, and tidal volumes of 5 mL (Pes:-10). A Fisher & Paykel B-CPAP system set to 5 cm was attached to the nasal airway with bi-nasal short prongs. The bias flow was set to 8 L/min. Airway pressures at the circuit “wye” were monitored digitally at 1024 Hz and analyzed to obtain mean airway pressures (MAP) and to estimate the amplitude of oscillations in airway pressure caused by the water oscillating in the circuit plus the oscillations caused by bubbling at the water seal of the CPAP generator. Measurements were obtained using a dry patient circuit and then repeated following the addition of 20 mL of water in the expiratory limb of the patient circuit. The circuit was U shaped to simulate a low point for condensate accumulation. Results The Figure shows dramatic alterations in the airway pressure waveforms when water was added to the exhalation limb of the patient circuit. The MAP increased from 6.1 cmH2O while using the dry circuit to 15.7 cmH2O when water was added. The amplitude of oscillations in airway pressure increased from 3.5 cmH2O (dry) to 11.9 cmH2O (wet). Discussion/Conclusion The major finding of this study was that condensate in the exhalation limb of the patient circuit during B-CPAP can greatly increase the MAP delivered to the patient. In addition, the intermittent obstruction causes oscillations in Paw that are much greater than the oscillations created by gas bubbling through water. Based on these findings, it is recommended that pressure be monitored at the nasal airway interface during B-CPAP. In order to avoid potential complications associated with barotrauma during B-CPAP, we encourage frequent assessment of condensate in circuit and removal when necessary, verification of proper heated humidifier settings, and application of a high pressure “pop-off” valve to the system. Sponsored Research - None