The Science Journal of the American Association for Respiratory Care

2012 OPEN FORUM Abstracts


Tony Diez1, Lee Williford1, Christoph Hornik2, Angela Gutierrez1, David Turner2, Ira Cheifetz1,2; 1Respiratory Care Services, Duke University Medical Center, Durham, NC; 2Pediatric Critical Care Medicine, Duke Children’s Hospital, Durham, NC

Background: Circuit compliance algorithms in newer generation ventilators compensate for the volume of gas ‘lost’ due to the distensibility of the ventilator circuit. However, these algorithms are generally only active in volume targeted modes. We hypothesized that in pressure targeted modes, tidal volume (Vt) measurements at the endotracheal tube (ETT) would be significantly lower than at the expiratory valve of the ventilator, especially for neonatal circuits. Methods: Every 6 hours, tidal volumes were measured at the expiratory valve of the ventilator (AVEA; CareFusion) and at the ETT with a standalone monitor and pneumotachometer (NICO or NM3; Philips-Respironics) for a heterogeneous group of pediatric patients. Ventilator settings were at the discretion of the clinical care team as part of routine care. We report median and interquartile ranges and performed pairwise comparisons of the distribution of Vt measured by the different modalities using the non-parametric Wilcoxon signed-rank test. Analyses were conducted using Stata 12, and p < 0.05 was considered statistically significant. Results: A heterogeneous population of 63 patients were enrolled in the Pediatric ICU and Pediatric Cardiac ICU. When performing pairwise comparisons for each circuit type, ventilator and ETT measured Vt (see Table) are significantly different for the neonatal circuit (p < 0.001), but no difference was found for the adult (p=0.07) and pediatric (p=0.5) circuits. The overall correlation between pairs of tidal volumes (ventilator vs. ETT) was high (R2=0.92). Conclusion: In ventilator modes in which circuit compliance is not active, clinicians should be aware that the tidal volume displayed at the ventilator does not accurately reflect the volume seen at the endotracheal tube for neonatal circuits. This difference occurs as the percent of volume ‘lost’ due to the distensibility of the circuit can represent a relatively large percent of the tidal volume delivered. This discrepancy was not noted for pediatric or adult circuits. Further investigation is needed to determine the effect of time as the compliance of the ventilator circuit may change. Clinicians should consider monitoring tidal volume at the endotracheal tube for neonates ventilated in modes without circuit compliance algorithms (e.g., pressure limited modes). Sponsored Research - None Tidal volumes as measured at the ventilator and ETT. Data displayed as median (25th, 75th %ile).