Tracheal gas insufflation

Intratracheal injection of nitric oxide, generated from air by pulsed electrical discharge, for the treatment of pulmonary hypertension in awake ambulatory lambs

OBJECTIVES

To test the feasibility, safety, and efficacy of intratracheal delivery of nitric oxide (NO) generated from air by pulsed electrical discharge via a Scoop catheter.

STUDY DESIGN

We studied healthy 3- to 4-month-old lambs weighing 34 ± 4 kg (mean ± SD, n = 6). A transtracheal Scoop catheter was inserted through a cuffed tracheostomy tube. U46619 was infused to increase mean pulmonary arterial pressure (mPAP) from 16 ± 1 to 32 ± 3 mmHg (mean ± SD). Electrically generated NO was delivered via the Scoop catheter to awake lambs. A sampling line, to monitor NO and nitrogen dioxide (NO₂) levels, was placed in the distal trachea of the lambs. The effect of varying doses of electrically generated NO, produced continuously, on pulmonary hypertension was assessed.

RESULTS

In awake lambs with acute pulmonary hypertension, NO was continuously delivered via the Scoop catheter at 400 ml/min. NO induced pulmonary vasodilation. NO₂ levels, measured in the trachea, were below 0.5 ppm at intratracheal NO doses of 10-80 ppm. No changes were detected in the levels of methemoglobin in blood samples before and after 5 min of NO breathing.

CONCLUSIONS

Continuously delivering electrically generated NO through a Scoop catheter produces vasodilation of the pulmonary vasculature of awake lambs with pulmonary hypertension. Transtracheal NO delivery may provide a long-term treatment for patients with chronic pulmonary hypertension as an outpatient without requiring a mask or tracheal intubation.

A high-flow nasal cannula system with relatively low flow effectively washes out CO2 from the anatomical dead space in a sophisticated respiratory model made by a 3D printer

Background

Although clinical studies of the high-flow nasal cannula (HFNC) and its effect on positive end-expiratory pressure (PEEP) have been done, the washout effect has not been well evaluated. Therefore, we made an experimental respiratory model to evaluate the respiratory physiological effect of HFNC.

Methods

An airway model was made by a 3D printer using the craniocervical 3D-CT data of a healthy 32-year-old male. CO₂ was infused into four respiratory lung models (normal-lung, open- and closed-mouth models; restrictive- and obstructive-lung, open-mouth models) to maintain the partial pressure of end-tidal CO₂ (P_ETCO₂) at 40 mmHg. HFNC flow was changed from 10 to 60 L/min. Capnograms were recorded at the upper pharynx, oral cavity, subglottic, and inlet sites of each lung model.

Results

With the normal-lung, open-mouth model, 10 L/min of HFNC flow decreased the subglottic P_ETCO₂ to 30 mmHg. Increasing the HFNC flow did not further decrease the subglottic P_ETCO₂. With the normal-lung, closed-mouth model, HFNC flow of 40 L/min was required to decrease the P_ETCO₂ at all sites. Subglottic P_ETCO₂ reached 30 mmHg with an HFNC flow of 60 L/min. In the obstructive-lung, open-mouth model, P_ETCO₂ at all sites had the same trend as in the normal-lung, open-mouth model. In the restrictive-lung, open-mouth model, 20 L/min of HFNC flow decreased the subglottic P_ETCO₂ to 25 mmHg, and it did not decrease further. As HFNC flow was increased, PEEP up to 7 cmH₂O was gradually generated in the open-mouth models and up to 17 cmH₂O in the normal-lung, closed-mouth model.

Conclusions

The washout effect of the HFNC was effective with relatively low flow in the open-mouth models. The closed-mouth model needed more flow to generate a washout effect. Therefore, HFNC flow should be considered based on the need for the washout effect or PEEP.

High-frequency oscillation and tracheal gas insufflation in patients with severe acute respiratory distress syndrome and traumatic brain injury: an interventional physiological study

Introduction

In acute respiratory distress syndrome (ARDS), combined high-frequency oscillation (HFO) and tracheal gas insufflation (TGI) improves gas exchange compared with conventional mechanical ventilation (CMV). We evaluated the effect of HFO-TGI on PaO₂/fractional inspired O₂ (FiO₂) and PaCO₂, systemic hemodynamics, intracranial pressure (ICP), and cerebral perfusion pressure (CPP) in patients with traumatic brain injury (TBI) and concurrent severe ARDS.

Methods

We studied 13 TBI/ARDS patients requiring anesthesia, hyperosmolar therapy, and ventilation with moderate-to-high CMV-tidal volumes for ICP control. Patients had PaO₂/FiO₂ <100 mm Hg at end-expiratory pressure ≥10 cm H₂O. Patients received consecutive, daily, 12-hour rescue sessions of HFO-TGI interspersed with 12-hour periods of CMV. HFO-TGI was discontinued when the post-HFO-TGI PaO₂/FiO₂ exceeded 100 mm Hg for >12 hours. Arterial/central-venous blood gases, hemodynamics, and ICP were recorded before, during (every 4 hours), and after HFO-TGI, and were analyzed by using repeated measures analysis of variance. Respiratory mechanics were assessed before and after HFO-TGI.

Results

Each patient received three to four HFO-TGI sessions (total sessions, n = 43). Pre-HFO-TGI PaO₂/FiO₂ (mean ± standard deviation (SD): 83.2 ± 15.5 mm Hg) increased on average by approximately 130% to163% during HFO-TGI (P < 0.01) and remained improved by approximately 73% after HFO-TGI (P < 0.01). Pre-HFO-TGI CMV plateau pressure (30.4 ± 4.5 cm H₂O) and respiratory compliance (37.8 ± 9.2 ml/cm H₂O), respectively, improved on average by approximately 7.5% and 20% after HFO-TGI (P < 0.01 for both). During HFO-TGI, systemic hemodynamics remained unchanged. Transient improvements were observed after 4 hours of HFO-TGI versus pre-HFO-TGI CMV in PaCO₂ (37.7 ± 9.9 versus 41.2 ± 10.8 mm Hg; P < 0.01), ICP (17.2 ± 5.4 versus 19.7 ± 5.9 mm Hg; P < 0.05), and CPP (77.2 ± 14.6 versus 71.9 ± 14.8 mm Hg; P < 0.05).

Conclusions

In TBI/ARDS patients, HFO-TGI may improve oxygenation and respiratory mechanics, without adversely affecting PaCO₂, hemodynamics, or ICP. These findings support the use of HFO-TGI as a rescue ventilatory strategy in patients with severe TBI and imminent oxygenation failure due to severe ARDS.

The role of high-frequency oscillatory ventilation in the treatment of acute respiratory failure in adults

PURPOSE OF REVIEW

High-frequency oscillatory ventilation (HFOV) is increasingly used in adults with the acute respiratory distress syndrome (ARDS), who remain hypoxemic during conventional mechanical ventilation. In this review, we will summarize the trials evaluating HFOV in adults with ARDS and discuss issues relevant to the clinician regarding the use of HFOV.

RECENT FINDINGS

Several observational and randomized trials support the safety of HFOV and improvements in oxygenation in adult patients with severe ARDS, who remain hypoxemic during conventional mechanical ventilation.

SUMMARY

HFOV theoretically meets the goals of lung-protective ventilation. On the basis of the current evidence, HFOV is associated with improvements in oxygenation in severe, adult ARDS. However, whether HFOV influences mortality, length of ICU stay, ventilator-free days, quality-of-life factors and is cost-effective remains to be determined. Large, prospective, randomized controlled trials such as the ongoing OSCAR and OSCILLATE trials will help further define the role of HFOV in adult ARDS.

Comparison of high-frequency oscillation and tracheal gas insufflation versus standard high-frequency oscillation at two levels of tracheal pressure

PURPOSE

In acute respiratory distress syndrome (ARDS), combined high-frequency oscillation (HFO) and tracheal gas insufflation (TGI) may improve oxygenation through a TGI-induced increase in mean tracheal pressure (P(tr)). We compared standard HFO and HFO-TGI matched for P(tr), in order to determine whether TGI affects gas exchange independently from P (tr).

METHODS

We conducted a prospective, randomized, crossover, physiological study in a 37-bed intensive care unit. Twenty-two patients with early acute lung injury (ALI) or ARDS were enrolled. On day 1, patients were ventilated with HFO, without (60 min) and combined with TGI (60 min) in random order. HFO/HFO-TGI sessions were repeated in inverse order within 7 h. HFO/HFO-TGI mean airway pressure (P(aw)) was titrated to a P(tr) that was either equal to (low P(aw)) or 3 cmH(2)O higher than (high P(aw)) the P(tr) of the preceding conventional mechanical ventilation. On day 2, the protocol was repeated at the alternative P(tr) level relative to day 1.

RESULTS

Gas exchange and hemodynamics were determined before, during, and after HFO/HFO-TGI sessions. HFO-TGI-high P(aw) versus HFO-high P(aw) resulted in significantly higher PaO(2)/inspired O(2) fraction (FiO(2)) [mean +/- standard error of the mean (SEM): 281.6 +/- 15.1 versus 199.0 +/- 15.0 mmHg; mean increase: 42%; P < 0.001]. HFO-TGI-low P(aw), versus HFO-low P(aw), resulted in significantly higher PaO(2)/FiO(2) (222.8 +/- 14.6 versus 141.3 +/- 8.7 mmHg; mean increase: 58%; P < 0.001). PaCO(2) was significantly lower during HFO-TGI-high P(aw) versus HFO-high P(aw) (45.3 +/- 1.6 versus 53.7 +/- 1.9 mmHg; mean decrease: 16%; P = 0.037).

CONCLUSIONS

At the same P(tr) level, HFO-TGI results in superior gas exchange compared with HFO.

Novel use of a portable ventilation device with low-flow tracheal insufflation of oxygen in a Swine model

INTRODUCTION

Mechanical ventilation of intubated patients is standard to meet oxygenation and ventilation goals. This can require significant energy and oxygen resources. In military operations and mass casualty disasters, oxygen conserving strategies may be important. Low flow tracheal insufflation of oxygen (TRIO) is a technique that provides adequate oxygenation while conserving oxygen during apnea. This technique, however, is limited by increases in carbon dioxide (CO2) when used for extended periods. The addition of passive pressure release ventilation could potentially improve CO2 elimination and the acceptance of this technique. The purpose of this study was to determine whether TRIO combined with the novel configuration of a portable ventilator used to provide passive pressure release ventilation improves CO2 levels during apneic oxygenation.

METHODS

Animals (n = 7) were anesthetized, paralyzed, and intubated. Oxygen (O2) was insufflated through the capillary lumen of the Boussignac endotracheal tube at 2 L/min. The low flow O2 was the only source of power and gas for ventilation. A modified Oxylator EMX transport ventilator connected to the endotracheal tube was configured to release when pressure in the subjects lungs reached 30 cm H2O. No electrical or pneumatic sources were required. Hemodynamic measurements and arterial blood gases were taken at various intervals for 2 hours.

RESULTS

All pigs remained adequately oxygenated with Pao2 >390 mm Hg in all subjects at every blood gas measurement and survived the 2-hour experiment. Baseline Paco2 (43 +/- 4 mm Hg) increased and pH (7.48 +/- 0.03) decreased to 72 +/- 5 mm Hg and 7.29 +/- 0.02 at 1 hour and 83 +/- 8, 7.24 +/- 0.03 at 2 hours. This is significantly less than would be expected during apnea over this time period. Hemodynamic measurements remained stable.

CONCLUSION

The combination of low flow TRIO with a modified Oxylator in this novel configuration provides acceptable Pao2, Paco2, and hemodynamic parameters for 2 hours in apneic swine. This could be a valuable technique in situations where oxygen and power are limited.

Acute effects of combined high-frequency oscillation and tracheal gas insufflation in severe acute respiratory distress syndrome

OBJECTIVE

In acute respiratory distress syndrome (ARDS), high-frequency oscillation (HFO) improves oxygenation relative to conventional mechanical ventilation (CMV). Alveolar ventilation is improved by adding tracheal gas insufflation (TGI) to CMV. We hypothesized that combined HFO and TGI (HFO-TGI) might result in improved gas exchange relative to both standard HFO and CMV according to the ARDS Network protocol.

DESIGN

Prospective, randomized, crossover study.

SETTING

A 30-bed university intensive care unit.

PATIENTS

A total of 14 patients with early (<72 hrs in duration), severe (PaO2/FiO2 of <150 mm Hg and prerecruitment oxygenation index of 22.8 +/- 1.9 [mean +/- SEM]), primary ARDS.

INTERVENTIONS

Patients were ventilated with HFO without (60 mins) and combined with TGI (6.1 +/- 0.1 L/min, 60 mins) in random order. HFO sessions were repeated in inverse order within 24 hrs. HFO sessions were preceded and followed by ARDS Network CMV. Four recruitment maneuvers were performed during the study period. During HFO sessions, mean airway pressure was set at 1 cm H2O above the point of maximal curvature of the respiratory system expiratory pressure-volume curve.

MEASUREMENTS AND MAIN RESULTS

Gas exchange and hemodynamics were determined before, during, and after HFO sessions. HFO-TGI improved PaO2/FiO2 relative to HFO and CMV (174.5 +/- 10.4 vs. 136.0 +/- 10.0 and 105.0 +/- 3.7 mm Hg, respectively, p < .05 for both) and oxygenation index relative to HFO (17.1 +/- 1.3 vs. 22.3 +/- 1.7, respectively p < .05). PaO2/FiO2 returned to baseline within 3 hrs after HFO. During HFO-TGI, shunt fraction and mixed venous oxygen saturation improved relative to CMV (0.36 +/- 0.01 vs. 0.45 +/- 0.01 and 77.8% +/- 1.2% vs. 71.8% +/- 1.3%, respectively, p < .05 for both). PaCO2 and hemodynamics were unaffected by HFO sessions. Respiratory mechanics remained unchanged throughout the study period.

CONCLUSIONS

In early onset, primary, severe ARDS, short-term HFO-TGI improves oxygenation relative to standard HFO and ARDS Network CMV.

Intratracheal pulmonary ventilation versus conventional mechanical ventilation: continuous carinal pressure monitoring at low and high flows and frequencies

We continuously measured proximal and carinal pressures at low and high flow rates and frequencies during conventional mechanical ventilation (CMV) and intratracheal pulmonary ventilation (ITPV), using an artificial lung. The proximal peak inspiratory pressure (PIP), carinal PIP, proximal positive end expiratory pressure (PEEP), and carinal PEEP, or negative end expiratory pressure (NEEP), were measured during simulated CMV and ITPV. Two levels of frequency (30 and 90 per min) and two gas flow rates (3 and 6 L/min) were examined, in both dry and humid states (four combinations of gas flow and frequency at each state). The gas flow and inspiratory time were held constant throughout the CMV and ITPV trials. Humidification of the ventilatory circuit during ITPV prevented the accurate measurement of carinal pressures. This problem was solved by introducing a continuous "bias flow" of 11 ml/min into the pressure monitoring line. A combination of low gas flow and low frequency with CMV showed no significant differences between the proximal and carinal PIP, as well as the proximal and carinal PEEP. The same combination with ITPV, however, resulted in a significantly lower carinal PIP and PEEP, compared to proximal PIP and PEEP. Carinal PIP and PEEP during ITPV were also significantly lower than those observed during CMV with a low flow and low frequency rates. During both CMV and ITPV, using a combination of a high flow rate with a high breathing frequency, carinal PIPs were significantly lower than proximal PIPs. ITPV, however, generated much larger differences between proximal and carinal PIPs than the CMV. A significant NEEP was generated at the carinal level during ITPV with high flow rates, both with high and low frequencies. The NEEP did not occur with a low gas flow, in combination with either a low frequency or a high frequency. The "bias flow" had no significant effect on carinal pressures. In conclusion, ITPV, compared with CMV, generates a significantly lower carinal PIP, but it may also generate carinal NEEP. For safety reasons, therefore, it is essential to monitor carinal pressures continuously in patients treated with ITPV.

Intratracheal pulmonary ventilation in a rabbit lung injury model: continuous airway pressure monitoring and gas exchange efficacy

OBJECTIVES

To compare carinal pressures vs. proximal airway pressures, and gas exchange efficacy with a constant minute volume, in lung-injured rabbits during conventional mechanical ventilation (CMV) and intratracheal pulmonary ventilation (ITPV); and to evaluate performance of a prototype ITPV gas delivery and continuous airway pressure monitoring system.

DESIGN

Prospective controlled study.

SETTING

Animal research laboratory at a teaching hospital.

SUBJECTS

Sixteen adult female rabbits.

INTERVENTIONS

Anesthetized rabbits were tracheostomized with a multilumen endotracheal tube. Anesthesia and muscle relaxation were maintained continuously throughout the study. Proximal airway pressures and carinal pressures were recorded continuously. The injection port of the multilumen endotracheal tube was used for the carinal pressure monitoring. To prevent obstruction of the port, it was flushed with oxygen at a rate of 11 mL/min. CMV was initiated with a pressure-limited, time-cycled ventilator set at an FiO2 of 1.0 and at a flow of 1.0 L/kg/min. The pressure limit of the ventilator was effectively disabled. A normal baseline for arterial blood gases was achieved by adjusting the inspiratory/expiratory time ratios. ITPV was established using a flow of 1.0 L/kg/min through a reverse thrust catheter, at the same baseline and inspiratory/expiratory ratio. Carinal positive end-expiratory pressure was maintained at a constant value of 2 cm H2O by adjusting the expiratory resistance of the ventilator circuit Lung injury was achieved over a 30-min period by three normal saline lavages of 5 mL/kg each. After lung injury, all animals were consecutively ventilated for 1 hr with CMV, for 1 hr with ITPV, and again for 1 hr with CMV. Six rabbits were ventilated at 30 breaths/min (group 1), and ten rabbits were ventilated at 80 breaths/min (group 2). Four rabbits in group 2 were subjected, 1 hr after return to CMV from ITPV, to another session of ITPV, with positive end-expiratory pressure gradually being increased to 4, 6, and 8 cm H2O for 15 mins each.

RESULTS

No significant differences were observed in carinal peak inspiratory pressure between CMV and ITPV modes, at both low and high frequencies of breathing, indicating that the inspired tidal volume remained constant during both modes of ventilation. Significant gradients were noted between proximal airway and carinal peak inspiratory pressure during ITPV but not during CMV. Initiation of ITPV, at a flow of 1.0 L/kg/min, required an increase in the ventilator expiratory resistance to maintain a constant level of positive end-expiratory pressure (2 cm H2O) as measured at the carina. During ITPV, the PaCO2 was significantly reduced by 20% at 30 breaths/min (p < .05) and by 22% at 90 breaths/min (p < .01), compared with CMV. Arterial oxygenation was significantly enhanced with a positive end-expiratory pressure of 6 and 8 cm H2O (p < .05 and .001, respectively), compared with a positive end-expiratory pressure of 2 cm H2O during ITPV. All components of the new prototype gas delivery and airway pressure monitoring system functioned without failure, at least for 3 hrs of the CMV, ITPV, and CMV trials.

CONCLUSIONS

ITPV in saline-lavaged, lung-injured rabbits at breathing frequencies of 30 and 80 breaths/min, compared with CMV at the same minute ventilation, can improve CO2 exchange. During ITPV, significant pressure gradients can develop between carinal and proximal airway pressures. Continuous carinal pressure monitoring is therefore necessary for the safe clinical application of ITPV. Reliable carinal pressure monitoring can be achieved by adding a small bias flow through the carinal pressure monitoring port. Although ITPV can remove CO2 from injured lungs efficiently, simultaneous addition of positive end-expiratory pressure can further improve arterial oxygenation.