Targeted Minute Ventilation and Tidal Volume in an Animal Model of Acute Changes in Lung Mechanics and Episodes of Hypoxemia

Background: Acute episodes of hypoxemia in ventilated preterm infants are triggered by changes in ventilation, lung volume (LV) and respiratory system compliance (CRS) that are not prevented by conventional synchronized intermittent mandatory ventilation (SIMV). Objective: To assess in a rabbit model of episodic hypoxemia the individual and combined efficacy of targeted tidal volume (VT) and minute ventilation (V’E) by automatic adjustment of peak inspiratory pressure (PIP) and ventilator rate, respectively. Methods: Six young New Zealand white rabbits were ventilated with SIMV, targeted VT, targeted V’E, and combined targeted V’E + VT in random sequence. Hypoxemia episodes were induced by apnea alone or by apnea combined with a reduction in LV and CRS. Apnea was induced by a bolus of propofol. The reduction in LV and CRS was induced by chest compression with a cuff. PaO2 and PaCO2 were measured continuously by an indwelling arterial electrode. Results: During SIMV, apnea caused a decrease in ventilation and PaO2. This was attenuated during targeted V’E and targeted V’E + VT. Apnea plus a reduction in LV and CRS caused a greater decrease in ventilation and PaO2 during SIMV. These changes were attenuated during targeted VT and targeted V’E. The attenuation was more pronounced during targeted V’E + VT. Conclusion: In this animal model, targeted V’E was effective in reducing hypoxemia caused by apnea. When apnea was accompanied by a reduction in LV and CRS, the combined adjustment of PIP and ventilator rate was more effective than each individually. This combined strategy may be effective in ameliorating acute episodes of hypoxemia in preterm infants but this remains to be proven

Use of a Mechanical Ventilator with Respiratory Function Monitoring Provides More Consistent Ventilation during Simulated Neonatal Resuscitation

Introduction: Positive pressure ventilation (PPV) with T-Piece and self-inflating bag (SIB) during neonatal resuscitation after birth is associated with variability in ventilation. The use of a ventilator with respiratory function monitoring (RFM) for PPV, however, has not been evaluated. Objective: To determine if ventilator + RFM can reduce ventilation variability compared to T-Piece and SIB in a preterm manikin at different combinations of target tidal volume (V T ) and lung compliance (C L ). Methods: Twenty clinicians provided PPV via mask and endotracheal tube (ETT) using SIB, T-Piece, T-Piece + RFM and Ventilator + RFM to a manikin with adjustable lung C L . Three combinations of C L and target V T : Low C L -Low V T , Low C L -High V T and High C L -Low V T were used in a random order. Results: The use of ventilator + RFM for PPV via ETT during High C L -Low V T period reduced the proportion of breaths with expiratory V T above target when compared to the other 3 devices (56 ± 35%, 85 ± 20%, 90 ± 25%, 92 ± 12% for ventilator + RFM, T-Piece + RFM, T-Piece, SIB, respectively; p < 0.05). During PPV via both mask and ETT, ventilator + RFM maintained the set Ti and rate, whereas SIB and T-Piece use resulted in higher rates, and T-Piece in higher proportion of breaths with prolonged Ti. During PPV via mask, ventilator + RFM reduced gas leakage compared to other devices. Conclusion: In this simulation study, use of a mechanical ventilator with RFM led to an overall improvement in volume targeting at different settings of C L and reduced the gas leak during mask ventilation. The efficacy and safety of using this strategy to neonatal resuscitation in the delivery room needs to be evaluated

Cerebral oxygenation in preterm infants receiving transfusion

The influence of severity of anemia and cardiac output (CO) on cerebral oxygenation (CrSO ) and on the change in CrSO following packed red blood cell (PRBC) transfusion in preterm infants has not been evaluated. The objectives of the current study were to evaluate the effect of pre-transfusion hemoglobin (Hb) and CO-weighted oxygen delivery index (ODI) on CrSO and on the post-transfusion CrSO change. Preterm infants of <32 weeks gestational age (GA) receiving PRBC transfusion were enrolled. Infants received 15 ml/kg PRBC over 3 h. CrSO by near-infrared spectroscopy and CO by electrical velocimetry were recorded for 1 h pre-ransfusion and post transfusion. ODI was defined as pre-transfusion Hb × CO. Thirty infants of 26.6 ± 2.0 weeks GA were studied at 19 ± 12 days. Pre-transfusion Hb was 9.8 ± 0.6 g/dl. Pre-transfusion CrSO correlated with pre-transfusion ODI (R  = 0.1528, p = .044) but not with Hb level. The pre-transfusion to post-transfusion CrSO change correlated with pre-transfusion ODI (R  = 0.1764, p = .029) but not with Hb level. CrSO increased from 66 ± 6% to 72 ± 7% post transfusion (p < .001), while arterial oxygen saturation, heart rate, and CO did not change. In these infants, the pre-transfusion ODI was a better indicator of brain oxygenation and its improvement post transfusion than Hb alone. The role of CO and tissue oxygenation monitoring in assessing the need for transfusion should be evaluated