Effect of tracheal gas insufflation on demand valve triggering and total work during continuous positive airway pressure ventilation

Optimal phasic tracheal gas insufflation timing: An experimental and mathematical analysis

OBJECTIVE

To investigate the modulation of CO2 clearance by changes in the duration of tracheal gas flow application during tracheal gas insufflation (TGI).

DESIGN

Combination of bench studies using a commercial test lung and a commercially available intensive care ventilator and mathematical analysis using a clearance model derived from first principles.

SETTING

University pulmonary research laboratory.

PATIENTS

None.

INTERVENTIONS

Experiments using TGI were performed on a test lung at two combinations of tidal volume and frequency. TGI was limited to part of the expiratory phase (the terminal 10-100% of expiration), and two different TGI catheter flow rates were studied. Permutations over a range of compliances, dead-space volumes, catheter flows, and TGI durations were collected. A mathematical model incorporating key ventilatory and TGI-related variables was developed to provide a first-principles theoretical foundation for interpreting the experimental results.

MEASUREMENTS AND MAIN RESULTS

In the physical model, alveolar Pco2 attained a minimum value with TGI flow applied during the terminal 40-60% of the expiratory phase, a finding that was consistent over an almost eight-fold range of expiratory time constants. The mathematical model shows the same qualitative pattern as the experimental model, indicating that the observed behaviors are not an experimental artifact.

CONCLUSION

The optimal duration of expiratory TGI flow application is stable over a wide range of impedance characteristics. Such stability suggests that near maximal effect of expiratory TGI could be obtained by applying TGI flow solely within the final 50% of the expiratory phase. Such uniform restriction of the application profile might both simplify technique implementation and decrease adverse consequences.

Continuous tracheal gas insufflation in preterm infants with hyaline membrane disease. A prospective randomized trial

In mechanically ventilated neonates, the instrumental dead space is a major determinant of total minute ventilation. By flushing this dead space, continuous tracheal gas insufflation (CTGI) may allow reduction of the risk of overinflation. We conducted a randomized trial to evaluate the efficacy of CTGI in reducing airway pressure over the entire period of mechanical ventilation while maintaining oxygenation. A total of 34 preterm newborns, ventilated in conventional pressure-limited mode, were enrolled in two study arms, to receive or not receive CTGI. Transcutaneous Pa(CO(2)) (tcPa(CO(2))) was maintained at 40 to 46 mm Hg in both groups to ensure comparable alveolar ventilation. Respiratory data were collected several times during the first day and daily until Day 28. Both groups were similar at the time of inclusion. During the first 4 d of the study, the difference between peak pressure and positive end-expiratory pressure was significantly lower in the CTGI group by 18% to 35%, with the same tcPa(CO(2)) level and with no difference in the ratio of tcPa(O(2)) to fraction of inspired oxygen (245 +/- 29 versus 261 +/- 46 mm Hg [mean +/- SD] over the first 4 d). Extubation occurred sooner in the CTGI group (p < 0.05), and the duration of mechanical ventilation was shorter (median: 3.6 d; 25th to 75th quartiles: 1.5 to 12.0 d; versus median: 15.6 d; 25th to 75th quartiles: 7.9 to 22.2; p < 0.05) than in the non-CTGI group. CTGI allows the use of low-volume ventilation over a prolonged period and reduces the duration of mechanical ventilation.

Transtracheal oxygen delivery

Tracheal insufflation of oxygen has at least three major uses for chronic oxygen supplementation through a percutaneous catheter, it is an adjunctive measure to enhance gas exchange during mechanical ventilation, and it provides an emergency therapy for oxygen delivery with upper airway obstruction. In this article the mechanisms of gas exchange and techniques of oxygen delivery are described for each of these major uses.

[Tracheal gas insufflation associated with mechanical ventilation for CO2 removal]

OBJECTIVE

Tracheal gas insufflation (TGI) either continuously, or at inspiration, or at expiration, is a technique associated with mechanical ventilation aimed to enhance CO2 elimination in favouring washout of anatomical dead space. This article analyses the mechanism of action, the techniques and the effects of TGI in presence of hypercapnia, especially in the fame of ARDS in adults.

DATA SOURCES

In addition to some historical or major references, the articles on TGI published over the past five years have been searched in the Medline data base.

STUDY SELECTION

Articles with data on TGI associated with mechanical ventilation were selected.

DATA EXTRACTION

Data on mechanisms of action, technical and practical aspects of TGI were extracted.

DATA SYNTHESIS

CO2 elimination is increased when the TGI catheter tip is close to the carina, when the gas jet is directed towards the latter, by a continuous gas jet, by a high washing gas volume. The effect on oxygenation is minor. The work of breathing is decreased. An increased intracranial pressure is decreased. Circulatory effects are minor. The major risk is dynamic pulmonary over distension. Local complications include dessiccation and lesion of bronchial mucosa by the gas jet.

CONCLUSION

In mechanically ventilated patients, additional TGI is a valuable technique for decreasing anatomical dead space. TGI decreases hypercapnia during mechanical ventilation with limited tidal volumes in permissive hypercapnia. Further clinical studies with large series of patients are required to assess the benefits and the effect of TGI on outcome.

Efficacy of tracheal gas insufflation in spontaneously breathing sheep with lung injury

Tracheal gas insufflation (TGI) decreases dead space (V D) and can be combined with continuous positive airway pressure (CPAP) to decrease minute volume (VE) and effort of breathing. In 11 anesthetized sheep, we induced acute lung injury (ALI) through oleic acid (OA) infusion and studied the effects of TGI combined with CPAP (CPAP-TGI) at different TGI flows and with catheters of different designs. Sheep were randomized to two groups: Group A (n = 7) was placed on CPAP and CPAP-TGI at 10 and 15 L/min of insufflation flow delivered through a reverse thrust catheter (RTC). Group B (n = 4) was placed on CPAP and CPAP-TGI at a flow of 10 L/min delivered through a RTC, and through a straight flow catheter (SFC). Compared with CPAP alone, CPAP-TGI resulted in significantly lower VD, VE, pressure time product, and work of breathing. We found no additional benefit from TGI flow of 15 L/min, compared with 10 L/min, and no statistically significant difference between the SFC and the RTC. In conclusion, TGI can be combined with CPAP in this model of ALI to reduce ventilation and effort of breathing.