Tracheal gas insufflation: a useful adjunct to ventilation?

Intrabronchial Catheter Resuscitation for Respiratory and Cardiorespiratory Arrest

INTRODUCTION

We sought to determine whether intrabronchial oxygenation would provide adequate gas exchange during both anesthesia induced apneic and cardiopulmonary arrest and cardiac massage (CPR).

METHODS

Ten pigs underwent general anesthesia with mechanical ventilation. Blood gases were measured in each animal at 4 min intervals for up to 28 min. An intrabronchial catheter (4 L/min O2) was inserted through an endotracheal tube after respirator cessation. Group A animals (6) were resuscitated with the catheter but without CPR. Group B animals (4) were rendered apneic and cardioplegic and resuscitated by CPR for 28 min using the intrabronchial device.

RESULTS

All group A animals were resuscitated and survived after 24 min of apnea. Mean pO2 decreased from 378 mmHg (95% confidence interval [CI], 288-468) to 292 mmHg (95% CI, 246-339), P = 0.009; pCO2 increased from 52 mmHg (95% CI, 43-61) to 137 mmHg (95% CI, 116-158), P < 0.0001; and pH decreased from 7.32 (7.29-7.36) to 6.98 (6.92-7.03), P < 0.0001. In a control animal bronchial catheter oxygen flow ceased at baseline and pO2 decreased from 268 to 30 mmHg by 20 min. In group B animals mean pO2 decreased from 426 mmHg (95% CI, 273-579) to 130 mmHg (95% CI, 92-168) after 28 min, P < 0.0001; pCO2 increased from 49 mmHg (95% CI, 41-58) to 73 mmHg (95% CI, 61-86), P = 0.03; and pH decreased from 7.34 (7.33-7.35) to 7.07 (6.98-7.16), P < 0.0001. In the control receiving intratracheal oxygen pO2 decreased from 324 to 88 mmHg after 16 minu of CPR.

CONCLUSIONS

Intrabronchial oxygenation provides sustained hyperoxemia during complete apnea and cardiac arrest with CPR.

Re-inspiration of CO(2) from ventilator circuit: effects of circuit flushing and aspiration of dead space up to high respiratory rate

Introduction

Dead space negatively influences carbon dioxide (CO₂) elimination, particularly at high respiratory rates (RR) used at low tidal volume ventilation in acute respiratory distress syndrome (ARDS). Aspiration of dead space (ASPIDS), a known method for dead space reduction, comprises two mechanisms activated during late expiration: aspiration of gas from the tip of the tracheal tube and gas injection through the inspiratory line - circuit flushing. The objective was to study the efficiency of circuit flushing alone and of ASPIDS at wide combinations of RR and tidal volume (V_T) in anaesthetized pigs. The hypothesis was tested that circuit flushing and ASPIDS are particularly efficient at high RR.

Methods

In Part 1 of the study, RR and V_T were, with a computer-controlled ventilator, modified for one breath at a time without changing minute ventilation. Proximal dead space in a y-piece and ventilator tubing (VD_{aw, prox}) was measured. In part two, changes in CO₂ partial pressure (PaCO₂) during prolonged periods of circuit flushing and ASPIDS were studied at RR 20, 40 and 60 minutes^-1.

Results

In Part 1, VD_{aw, prox} was 7.6 ± 0.5% of V_T at RR 10 minutes^-1 and 16 ± 2.5% at RR 60 minutes^-1. In Part 2, circuit flushing reduced PaCO₂ by 20% at RR 40 minutes^-1 and by 26% at RR 60 minutes^-1. ASPIDS reduced PaCO₂ by 33% at RR 40 minutes^-1 and by 41% at RR 60 minutes^-1.

Conclusions

At high RR, re-breathing of CO₂ from the y-piece and tubing becomes important. Circuit flushing and ASPIDS, which significantly reduce tubing dead space and PaCO₂, merit further clinical studies.

Tracheal gas insufflation

Tracheal gas insufflation is a technique in which gas is injected intratracheally during positive pressure ventilation. The fresh gas rinses expired gas from the tracheal tube and anatomical dead space, aiding carbon dioxide elimination. This reduces ventilatory volume and pressure, helping to reduce ventilator-induced lung damage. Complications of tracheal gas insufflation include interference with ventilator function, tracheal damage and barotrauma. Expiratory washout is a variation of tracheal gas insufflation. We designed and constructed an original expiratory washout system and evaluated its safety and performance in lung and animal models. We found that expiratory limb and tracheal tube occlusion tests caused the device to disable itself at acceptable intratracheal pressures. We also demonstrated up to 31% reduction in tidal volume compared with conventional ventilation, supporting the possibility of using this device clinically to lessen volutrauma. We concluded that aspects of this design might alleviate many of the safety concerns of using tracheal gas insufflation.

[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.

Partial liquid ventilation decreases serum tumor necrosis factor-alpha concentrations in a rat acid aspiration lung injury model

OBJECTIVE

To examine the hypothesis that partial liquid ventilation (PLV) with perfluorocarbon would decrease serum tumor necrosis factor-alpha concentrations in a rat acid aspiration lung injury model.

DESIGN

Prospective, controlled animal study.

SETTINGS

Research laboratory in a university setting.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Treatment with intratracheal perflubron or control mechanical ventilation beginning 30 mins after acid aspiration.

MEASUREMENTS AND MAIN RESULTS

PLV with perfluorocarbon compared with control ventilation resulted in significantly greater mean arterial blood pressures at 3 and 4 hrs and greater arterial Po2 at all times. Serum tumor necrosis factor-alpha at 2, 3, and 4 hrs was significantly less than that observed in the control group (4-hr values: 80+/-64 pg/mL vs. 658+/-688 pg/mL; p<.05), although no significant difference in tracheal fluid tumor necrosis factor-alpha concentrations (1425+/-1347 pg/mL vs. 2219+/-1933 pg/mL) was found.

CONCLUSION

We conclude that the effects of PLV with perfluorocarbon can extend beyond improvements in pulmonary physiology and that PLV may be beneficial in reducing systemic sequelae of acute lung injury and inflammation.

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.

Aspiration of airway dead space. A new method to enhance CO2 elimination

Alveolar ventilation and CO2 elimination during mechanical ventilation can be enhanced by reducing dead-space ventilation. Aspiration of gas from the dead space (ASPIDS) is a new principle, according to which gas rich in CO2 during late expiration is aspirated through a channel ending at the distal end of the tracheal tube. Simultaneously, fresh gas injected into the inspiratory line fills the airway down to the same site. We hypothesized that ASPIDS would allow a reduction of tidal volume (VT) and airway pressure (Paw). To test our hypothesis we studied six anaesthetized and mechanically ventilated pigs (24 +/- 4 kg). The intention was to decrease VT while keeping PaCO2 constant by using ASPIDS. VT was reduced by decreasing the minute ventilation (V E) in two steps, of 1.8 L/min (VE - 1.8) and 2.2 L/min (VE - 2.2), respectively, and by increasing respiratory rate (RR) from 20 to 46 breaths/min. At ASPIDS, peak Paw was reduced by 35% at VE - 1.8 and at VE - 2.2 (p < 0.001), and by 20% at an RR of 46 (p < 0.01). PaCO2 was maintained or reduced at ASPIDS. No intrinsic positive end-expiratory pressure developed. Arterial blood pressure and heart rate were unaffected. The results show that ASPIDS allows a reduction in VT and Paw while PaCO2 is kept constant. ASPIDS does not lead to problems associated with jet streams of gas or with gas humidification, and can be developed as a safe technique.

Intratracheal pulmonary ventilation and continuous positive airway pressure in a sheep model of severe acute respiratory failure

STUDY OBJECTIVES

Previously we have shown that optimal pulmonary gas exchange can be sustained at normal airway pressures in a model of severe acute respiratory failure (ARF), using intratracheal pulmonary ventilation (ITPV), with weaning to room air. In an identical model of ARF, we have now explored whether ITPV, combined with continuous positive airway pressure (CPAP), can sustain adequate ventilation, with weaning to room air.

DESIGN

Randomized study in sheep.

SETTING

Animal research laboratory at the National Institutes of Health.

INTERVENTIONS

ARF was induced in 12 sheep, using mechanical ventilation at peak inspiratory pressure of 50 cm H2O, but excluding 5 to 8% of lungs. Sheep were then randomized into two groups: the CPAP-ITPV group (n=6), in which ITPV was combined with a novel CPAP system; and a control group (n=6) in which the same CPAP circuit was used, but without ITPV.

MEASUREMENTS AND RESULTS

All sheep in the CPAP-ITPV group were weaned to room air in 38.7+/-14 h. PaO2/fraction of inspired oxygen (FIO2) progressively increased from 108.8+/-43 to 355.7+/-93.1; PaCO2 remained within normal range; respiratory rate (RR) ranged from 18 to 120 breaths/min, and tidal volume (VT) was as low as 1.1 mL/kg. All sheep in the control group (CPAP alone) developed severe respiratory acidosis and hypoxemia after 4.8+/-4 h. PaO2/FIO2 decreased from 126.6+/-58.2 to 107.2+/-52.5 mm Hg, with a final PaCO2 of 166.8+/-73.3 mm Hg.

CONCLUSIONS

All sheep treated with CPAP-ITPV maintained good gas exchange without hypercapnia at high RR and at low VT, with weaning to room air. All control animals treated with CPAP alone developed severe hypercapnia, respiratory acidosis, and severe hypoxemia, and were killed.

Tracheal gas insufflation reduces requirements for mechanical ventilation in a rabbit model of respiratory distress syndrome

Tracheal gas insufflation is known to lower PaCO2 in larger animal models of respiratory distress syndrome, but its ability to reduce the ventilator pressures and tidal volume needed to achieve an acceptable PaCO2 has not been examined in small animals using modes of ventilation employed in neonatal intensive care. In this study, the effect of insufflating humidified gas into the lower trachea was examined in a saline lung lavage model of respiratory distress syndrome in rabbits, while the peak airway pressure during conventional pressure-limited ventilation was adjusted to keep the PaCO2 approximately constant. Tracheal gas insufflation significantly reduced the peak airway pressure required and reduced the delivered tidal volume but did not affect the AaDO2. The effects were more marked at a ventilator rate of 30 breaths per minute than at 60 bpm and more during continuous insufflation than when gas was insufflated only during expiration. These results suggest that tracheal gas insufflation may reduce the risk of ventilation-induced lung disease in the newborn.

Tracheal gas insufflation combined with high-frequency oscillatory ventilation

OBJECTIVES

To determine the efficacy of tracheal insufflation delivered by two different catheter designs on CO2 elimination when used in conjunction with high-frequency oscillatory ventilation.

DESIGN

A nonrandomized before and after trial. Each animal served as his own control.

SUBJECTS

Ten mongrel dogs weighing 20.9 +/- 1.9 kg. Four animals were assigned to a normal lung group and six animals underwent lung injury by large volume saline lavage.

INTERVENTION

Permissive hypercapnia was allowed to occur by selecting oscillator settings that would lead to alveolar hypoventilation. Proximal mean airway pressure was kept constant. Tracheal gas was insufflated at 1 cm above the carina for 30 min periods at gas flows of 5 to 15 L/min.

MEASUREMENTS AND MAIN RESULTS

Carinal pressure, hemodynamic parameters (cardiac output, mean arterial pressure, pulmonary artery occlusion pressure), and gas exchange parameters (PaCO2, PaO2, PaO2/FIO2, shunt fraction, D O2) were measured. For the normal dogs, at catheter flow of 15 L/min; the forward thrust catheter increased carinal pressure and Pao2/FIO2 BY 30% (p<.003) and 105% (p<.005), respectively. The forward thrust catheter reduced Paco2 by 40% (p<.04). The reverse thrust catheter increased PaO2/FIO2 by 102% (p<.001) and decreased pressure and PaCO2 by 44% (p<.001) and 34% (p<.003), respectively. For the injured dogs, at catheter flow rate of 15 L/min, the forward thrust catheter increased carinal pressure, PaO2, and PaO2/FIO2 by 6% (p<.001), 23% (p<.001), and 24% (p<.02), respectively. The forward thrust catheter reduced PaCO2 by 29% (p<.002). The reverse thrust catheter increased PaO2 and PaO2/FIO2 both by 11% (p<.02) and reduced carinal pressure and PaCO2 by 23% (p<.001) and 18% (p<.002), respectively.

CONCLUSIONS

Tracheal gas insufflation is capable of improving oxygenation and ventilation in acute lung injury when combined with high-frequency oscillatory ventilation. The addition of this second gas flow at the level of the carina raises or lowers distal airway pressure, the magnitude of which is dependent on the direction and rate of gas flow. The beneficial effects of tracheal gas insufflation may be tempered by the long-term effects of altering distal airway pressure; lowering distal airway pressure may lead to atelectasis, whereas raising distal airway pressure may lead to an auto-positive end-expiratory pressure (auto-PEEP) effect.