Carbon Dioxide Clearance Using a Critical Care Ventilator With a Dual Limb Circuit to Provide Noninvasive Ventilation

Abstract

Background:

Noninvasive ventilation (NIV) provides ventilatory support for spontaneously breathing patients without requiring an artificial airway. Questions remain regarding carbon dioxide (CO₂) clearance while using a conventional ventilator and dual limb circuit with various patient interfaces. The purpose of this study is to determine the PEEP level required to effectively washout CO₂ for full-face and oronasal masks, and assess their comfort.

Methods:

This randomized crossover trial was conducted at an academic medical center in the Midwest. After obtaining informed consent, 8 healthy volunteers were placed on a 980 Puritan Bennett (Medtronic, Minneapolis, MN) ventilator operating in the NIV mode. All subjects performed 20 minutes of breathing on 4 levels of PEEP (0, 2, 4, and 5 cm H₂O) and pressure support of 5 cm H₂O. NIV settings were applied to 4 masks (2 oronasal and 2 full-face masks) that were randomly selected with a 5-minute wash out period between each mask. Fraction of inspired carbon dioxide (FICO₂) was sampled/monitored with a nasal cannula using a CapnostreamTM 20p monitor (Medtronic, Minneapolis, MN) and reported as percentages. Additionally, subjective mask comfort was assessed via visual analog scale (VAS). A Kruskal-Wallis test was used to reveal significance difference across PEEP levels. Pairwise comparisons of the groups were made using Mann-Whitney tests with a Bonferroni correction.

Results:

FICO₂ was significantly lower at PEEP of 5 (0.0%, IQR: 0, 0.92) compared to PEEP of 0 (1.83%, IQR 0.66, 4.0, P < .001) or PEEP of 2 (1.0%, IQR 0.33, 2.66, P = .002). FICO2 was significantly lower at PEEP of 4 (0.5%, IQR: 0, 1.92) compared to PEEP of 0 (P = .001). Comparison of masks’ level of comfort showed no significance differences.

Conclusions:

A PEEP level of at least 5 cm H₂O was required to minimize the likelihood of CO₂ rebreathing while using a critical care ventilator with a double limb circuit and full-face or oronasal masks. Although masks comfort level was not significantly different, it should be assessed in a larger sample size.

Median Fraction of Inspired CO2 at Various PEEP Levels During NIV Using a Critical Care Ventilator with Full-Face and Oronasal Masks