Volume guaranteed? Accuracy of a volume-targeted ventilation mode in infants

Objectives Volume-targeted ventilation (VTV) is widely used and may reduce lung injury, but this assumes the clinically set tidal volume (V-Tset) is accurately delivered. This prospective observational study aimed to determine the relationship between V-Tset, expiratory V-T (V-Te) and endotracheal tube leak in a modern neonatal volume-targeted ventilator (VTV) and the resultant partial arterial pressure of carbon dioxide (PaCO2) relationship with and without VTV. Design Continuous inflations were recorded for 24 hours in 100 infants, mean (SD) 34 (4) weeks gestation and 2483 (985) g birth weight, receiving synchronised mechanical ventilation (SLE5000, SLE, UK) with or without VTV and either the manufacturer's V4 (n=50) or newer V5 (n=50) VTV algorithm. The V-Tset, V-Te and leak were determined for each inflation (maximum 90 000/infant). If PaCO2 was sampled (maximum of 2 per infant), this was compared with the average V-Te data from the preceding 15 min. Results A total of 7 497 137 inflations were analysed. With VTV enabled (77 infants), the V-Tset V-Te bias (95% CI) was 0.03 (-0.12 to 0.19) mL/kg, with a median of 80% of V-Te being +/- 1.0 mL/kg of V-Tset. Endotracheal tube leak up to 30% influenced V-Tset-V-Te bias with the V4 (r(2)=-0.64, p<0.0001; linear regression) but not V5 algorithm (r(2)=0.04, p=0.21). There was an inverse linear relationship between V Te and PaCO2 without VTV (r(2)=0.26, p=0.004), but not with VTV (r(2)=0.04, p=0.10), and less PaCO2 within 40-60 mm Hg, 53% versus 72%, relative risk (95% CI) 1.7 (1.0 to 2.9). Conclusion VTV was accurate and reliable even with moderate leak and PaCO2 more stable. VTV algorithm differences may exist in other devices.