The Effects of High Frequency Oscillatory Ventilation (HFOV) with Volume Guarantee (VG) on Left Ventricular Function, Systemic and Regional Oxygenation, and Ventilation When Compared to HFOV and Conventional Mechanical Ventilation (CMV) in A Newborn Piglet Model of Respiratory Distress Syndrome (RDS)

BACKGROUND: RDS due to surfactant deficiency is commonly seen in preterm infants. These infants often require ventilatory support such as CMV and HFOV. HFOV with VG (HFOV+VG) is an alternative mode that delivers a set tidal volume. There is limited data on either HFOV mode regarding the effects on left ventricular (LV) function, systemic and regional oxygenation, and ventilation.

OBJECTIVES: We primarily compared the effects of CMV with VG, HFOV, and HFOV+VG on cardiac index (CI). Secondary parameters included heart rate (HR), mean arterial pressure (MAP), LV ejection fraction (EF), stroke volume (SV), dP/dt max, LV end-systolic volume and pressure (ESV, ESP), end-diastolic volume and pressure (EDV, EDP), and measures of oxygenation and ventilation. Oxygenation parameters included cerebral and renal near-infrared spectroscopy (NIRS), partial pressure of arterial oxygen (PaO2), and carotid artery flow index (CAFI). Ventilation parameters included partial pressure of arterial carbon dioxide (PaCO2) and minute ventilation (MV).

DESIGN/METHODS: Piglets (1.4-2.4 kg; 1-3 days old) were acutely anesthetized and instrumented with the placement of a right femoral arterial catheter for blood gas analysis, NIRS probes (Invos®), Transonic® flow probe on right common carotid artery, and Millar® catheter in the LV. Warm saline lung lavage was performed to achieve an AaDO2 of 300-450 mmHg to simulate moderate to severe RDS. Piglets were then block-randomized to CMV, HFOV or HFOV+VG for 4 hours using a Fabian HFO ventilator (Acutronic Medical Systems AG, Switzerland)(n=8 per group). Sham-operated piglets without RDS were monitored for the same duration under CMV (n=6). Two-way repeated measures ANOVA was used to analyze the data between modes or time points.

RESULTS: Piglets developed moderately severe RDS with comparable AaDO2 and Paw along with stable hemodynamic parameters. Both HFOV and HFOV+VG groups had similar PaCO2 whereas the CMV group had elevated PaCO2 when compared to that of the Sham (p<0.01). Switching to HFOV resulted in a higher MV than its baseline. HFOV+VG but not HFOV or CMV groups had lower regional oxygenation and CAFI than its respective normoxic baseline (all p<0.01). HFOV and HFOV+VG had higher CI, EF, and SV than CMV at 4 hours of recovery (p<0.05) with similar HR, MAP, dP/dt max, ESV, ESP, EDV and EDP.

CONCLUSION: In our piglet model of RDS, HFOV shows benefits to LV function and ventilation when compared to CMV. HFOV+VG does not show benefits compared to HFOV.

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