Carbon dioxide rebreathing in non-invasive ventilation. Analysis of masks, expiratory ports and ventilatory modes.

ABSTRACT Carbon dioxide (CO2) rebreathing is a complication of non-invasive ventilation (NIV). Our objectives were to evaluate the ability of masks with exhaust vents (EV) to avoid rebreathing while using positive pressure (PP) NIV with different levels of expiratory pressure (EPAP). Concerning volume-cycled NIV, we aimed to determine whether cylindrical spacers located in the circuit generate rebreathing.
5 healthy volunteers were evaluated. Bi-level PP was used with 3 nasal and 2 facial masks with and without EV. Spacers of increasing volume attached to nasal hermetic masks were evaluated with volume NIV. Inspired CO2 fraction was analyzed.
Rebreathing was zero with all nasal masks and EPAP levels. Using facial masks 1 volunteer showed rebreathing. There was no rebreathing while using all the spacers.
In healthy volunteers, nasal and facial masks with EV prevent rebreathing. In addition, the use of spacers did not generate this undesirable phenomenon.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The purpose of this study was to evaluate whether carbon dioxide (CO2) rebreathing occurs in acute respiratory failure patients ventilated using the standard airway management system (BiPAP pressure support ventilator; Respironics; Murrysville, Pa) with positive inspiratory airway pressure and a minimal level of positive end-expiratory pressure (PEEP) and whether any CO2 rebreathing may be efficiently prevented by the addition of a nonrebreathing valve to the BiPAP system circuit. In the first part of the study, the standard device was tested on a lung model with a nonrebreathing valve (BiPAP-NRV) and with the usual Whisper Swivel connector (BiPAP-uc). With the BiPAP-uc device, the resident volume of expired air in the inspiratory circuit at the end of expiration (RVEA) was 55% of the tidal volume (VT) when the inspiratory pressure was 10 cm H2O and the frequency was at 15 cycles per minute. The BiPAP-NRV device efficiently prevented CO2 rebreathing but resulted in a slight decrease in VT, which was due to a significant increase in external PEEP (2.4 vs 1.3 cm H2O) caused by the additional expiratory valve resistance. For similar reasons, both the pressure swing necessary to trigger pressure support and the imposed expiratory work were increased in the lung model when the nonrebreathing valve was used. In the second part of the study, seven patients weaned from mechanical ventilation were investigated using a randomized crossover design to compare three situations: pressure support ventilation with a conventional intensive care ventilator (CIPS), BiPAP system use, and BiPAP-NRV. When we compared the BiPAP system use with the other two systems, we observed no significant effect on blood gases but found significant increases in VT, minute ventilation, and work of breathing. These findings are experimental and are clinical evidence that significant CO2 rebreathing occurs with the standard BiPAP system. This drawback can be overcome by using a non-rebreathing valve, but only at the expense of greater expiratory resistance.
    Chest 10/1995; 108(3):772-8. DOI:10.1378/chest.108.3.772 · 7.13 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: There were reports concerning the CO2 rebreathing during non-invasive positive pressure ventilation (NIPPV) with full face mask. It is our hypothesis that modification of the mask from one way connection to two ways connection by making a side hole in the mask makes it possible that CO2 inside the mask could be washed out by a constant flow through the mask. A randomized self-control study on CO2 rebreathing was conducted in 7 COPD patients to compare the modified set-up with the conventional one. A BiPAP-30 ventilator and a plateau exhaustion valve (Respironics USA) were employed in the study. In the modified two ways set-up, the exhaustion valve (with distal end blocked) was connected to the side hole of the mask, so that a constant base flow could pass through the mask to the exhaustion valve. The average base flow was 0.43 LPS. The parameters were set as following: S/T mode, f: 15 BPM, pressure support level: 8 cm H2O. Three different levels of PEEP (2, 3 and 5 cm H2O) were used to investigate the PEEP level on CO2 rebreathing. Flow and CO2% were constantly recorded with computer data acquisition and analysis system (Microcal Origin). In conventional set-up, there was obvious CO2 rebreathing (rebreathing volume: 83.1 +/- 32.9 ml). In modified connection, the rebreathing volume was only (0.1 +/- 0.4) ml (P < 0.001). There was obvious CO2 rebreathing during full face mask NIPPV in conventional set-up. A modified two ways connection could reduce CO2 rebreathing to be near zero, which might be important in the management of hypercapnic respiratory failure with NIPPV.
    Zhonghua jie he he hu xi za zhi = Zhonghua jiehe he huxi zazhi = Chinese journal of tuberculosis and respiratory diseases 12/2000; 23(12):734-6.
  • [Show abstract] [Hide abstract]
    ABSTRACT: To determine whether an exhalation valve designed to minimize rebreathing improves daytime or nocturnal gas exchange or improves symptoms compared with a traditional valve during nocturnal nasal ventilation delivered using a bilevel pressure ventilation device. Prospective direct comparison trial with each patient sequentially using both valves, during a 2-week run-in period with a traditional valve, a 2-week trial with the nonrebreathing valve, and a 2-week washout period with the traditional valve. Outpatient pulmonary function laboratory and home nocturnal monitoring. Seven patients who received long-term (> 1 year) nocturnal nasal bilevel pressure ventilation with an expiratory pressure of <or= 4 cm H(2)O. Symptoms, pulmonary function, and arterial blood gas levels were assessed at each of three daytime sessions after the sequential 2-week periods using the different valves. Nocturnal studies used a multichannel recorder that measured heart rate, chest wall impedance, nasal airflow, and oximetry. End-tidal PCO(2) (PetCO(2)) from the mask and transcutaneous PCO(2) (PtcCO(2)) were also monitored nocturnally. Seven patients with a variety of neuromuscular, chest wall, and obstructive defects were enrolled. No mean differences in daytime arterial blood gas levels, pulmonary functions, nocturnal vital signs or oximetry, or PtcCO(2) were apparent regardless of the exhalation valve used. The multichannel recording was indicative of an air leak at least one third of the time, and the PetCO(2) tracing detected a blunted signal or no signal from the mask during the majority of the recording time. The use of an exhalation valve designed to minimize rebreathing did not improve daytime or nocturnal gas exchange or symptoms in patients receiving long-term nasal bilevel pressure ventilation in comparison with a traditional exhalation valve, most likely because of air leakage and escape of CO(2) via other routes.
    Chest 07/2002; 122(1):84-91. DOI:10.1378/chest.122.1.84 · 7.13 Impact Factor


Available from