The Science Journal of the American Association for Respiratory Care

2012 OPEN FORUM Abstracts

EFFECT OF CIRCUIT VARIATIONS ON TIDAL VOLUME DELIVERY AND GAS EXCHANGE DURING HIGH FREQUENCY OSCILLATORY VENTILATION.

Christine N. Kearney1, Christoph Hornik2,3, Natalie Spencer1, Walter L. Williford1, Michael A. Gentile2, Ira M. Cheifetz1,2; 1Respiratory Care Services, Duke University Hospital, Durham, NC; 2Pediatric Critical Care Medicine, Duke University Hospital, Durham, NC; 3Duke Clinical Research Institute, Durham, NC

Objective. Substantial variation exists in clinical practice for the setup of high frequency oscillatory ventilator (HFOV) circuits based on clinician preference, departmental policies, and individual patient requirements. Clinicians may place a variety of adapters in an HFOV circuit to assist with suctioning and/or positioning. Others avoid placing adapters in-line due to the belief that tidal volume (Vt) delivery and/or gas exchange may be negatively impacted. We hypothesize that inserting any adapter in-line adversely affects delivered Vt and gas exchange by combined pressure amplitude attenuation and deadspace effects. Methods. To assess the effect of in-line adapters with a HFOV circuit, three juvenile swine (9.7 ± 0.81 kg) were studied on a 3100A Oscillator. A pneumotachometer using a pulmonary mechanics monitor was placed between the ventilator circuit and endotracheal tube. Data were collected with six circuit setups at frequencies of 4-10 Hz in increments of 2 Hz. Amplitude and mPaw were maintained at 45 and 20 cm H2O, respectively. Circuit variations studied: no adapter, elbow adapter, Y-adapter, and flexible adapter as well as two combinations of adapters (Y- and elbow adapters each placed in line with the flexible adapter). Continuous Vt data were collected over a 4 min period for each combination of frequency and adapter. Arterial blood gases were obtained at the end of each 4 min period to assess effect on gas exchange. Main Results. The highest Vt (mean, sd) was measured with the elbow adapter at 4 Hz (3.96, 0.317), and the lowest Vt was measured with the combination of Omniflex+Y-adapters at 10 Hz (1.22, 0.194). When controlling for adapter deadspace, only the Y adapter remained associated with a statistically significant increase in PaCO2 (6.70, p=0.027), irrelevant of a decrease in Vt. Conclusion. The addition of any adapter to a HFOV circuit can affect delivered Vt. Gas exchange can also be detrimentally affected, from either pressure attenuation or the addition of deadspace. These findings provide the clinician with additional information regarding the potential impact on Vt and gas exchange when considering HFOV circuit setup. Sponsored Research - None