Transtracheal delivery of gas decreases the oxygen cost of breathing

Intratracheal oxygen administration increases FIO2 and PaO2 compared with intranasal administration in healthy, standing horses

OBJECTIVE

To evaluate the efficacy of 2 different oxygen delivery strategies-intranasal and tracheal insufflation-on the inspired fraction of oxygen (FIO2) in standing horses and to determine the time needed for arterial oxygen partial pressure (PaO2) equilibration.

ANIMALS

6 healthy adult horses.

PROCEDURES

In this blinded, randomized crossover design study, horses were randomly assigned to receive oxygen via nasal cannula (group N) or transcutaneous tracheal catheter (group T). After placement of venous and arterial catheters, FIO2 was measured through a catheter placed into the distal portion of the trachea. After baseline measurements were obtained, horses received oxygen at up to 25 mL/kg/min for 1 hour via either intranasal or intratracheal catheter. The FIO2 and PaO2 were recorded at 5, 10, 15, 20, 25, 30, 45, and 60 minutes during and 5, 10, 15, 20, and 30 minutes after oxygen insufflation. Data were analyzed by use of a 2-way repeated measures ANOVA with Tukey-Kramer post hoc testing for pairwise comparisons (P < 0.05).

RESULTS

During oxygen administration, FIO2 and PaO2 increased significantly when compared with baseline, resulting in significantly higher values for group T (37.7 ± 2.4%; 214.6 ± 18 mm Hg) than for group N (34.3 ± 3.9%; 184.1 ± 11 mm Hg). The equilibration time was less than 10 minutes.

CLINICAL RELEVANCE

Intratracheal oxygen administration resulted in better oxygenation than nasal insufflation and should therefore be considered in standing horses that are experiencing severe respiratory compromise. The equilibration between FIO2 and PaO2 is rapid in adult horses.

Influence of apnoeic oxygenation in respiratory and circulatory system under general anaesthesia

Apnoeic oxygenation is an alternative technique of oxygenation which is recommended in the consecutive oxygen administration with varying flows (2-10 lt/min) through a catheter which is positioned over the keel of the trachea. Apnoeic oxygenation maintains for a significant period of time the oxygenation of blood in breathless conditions. This technique was first applied in 1947 by Draper, Whitehead, and Spencer and it was studied sporadically by other inventors too. However, the international literature shows few studies that have examined closely apnoeic oxygenation and its effects on Hemodynamic image and the respiratory system of the human body. Recently they have begun to arise some studies which deal with the application of this technique in several conditions such as difficult tracheal intubation, ventilation of guinea pigs in campaign conditions where the oxygen supply is limited and calculable, the application of this technique in combination with the use of extracorporeal removal of carbon dioxide (CO2). All the above indicate, the clinical use of this technique.

Transtracheal oxygen and positive airway pressure: A salvage technique in overlap syndrome

The coexistence of sleep apnea-hypopnea syndrome (SAHS) with chronic obstructive pulmonary disease (COPD) occurs commonly. This so called overlap syndrome leads to more profound hypoxemia, hypercapnic respiratory failure, and pulmonary hypertension than each of these conditions independently. Not infrequently, these patients show profound hypoxemia, despite optimal continuous positive airway pressure (CPAP) therapy for their SAHS. We report a case where CPAP therapy with additional in-line oxygen supplementation failed to accomplish adequate oxygenation. Adding transtracheal oxygen therapy (TTOT) to CPAP therapy provided better results. We review the literature on transtracheal oxygen therapy and how this technique may play a significant role in these complicated patients with overlap syndrome, obviating the need for more invasive procedures, such as tracheostomy.

Oxygen conserving devices and methodologies

Collective experience with pulmonary rehabilitation and disease management has shown that patients with lung diseases including COPD and restrictive lung diseases live a longer and more productive quality of life if they can remain active. Patients who require oxygen supplementation but can otherwise be active should have the most portable and non-encumbering systems possible. Oxygen conserving devices have made a high level of portability possible. Small gas, liquid and even some concentrators have replaced the 20 pound E cylinder with 4 and 5 pound systems. In a parallel physiological development, exercise plus oxygen increases the physiological benefits of exercise and thereby enhances the patient's ability to function in life. This paper examines available options and their mechanical and physiological foundations.

[Oxygen-conserving devices: a forgotten resource]

Oxygen-conserving devices include transtracheal catheters, reservoir cannulas, and demand oxygen delivery systems. They are designed to extend the amount of time portable oxygen cylinders will last and correct hypoxemia with a lower flow of oxygen. Transtracheal catheters increase the fraction of inspired oxygen by delivering oxygen directly to the trachea, bypassing the dead space of the oropharynx and improving the efficiency of the upper airway as a reservoir. Reservoir cannulas increase the fraction of inspired oxygen at the beginning of the inspiratory phase. Demand oxygen delivery systems have a valve that is activated during inspiration, meaning that oxygen is only delivered during this stage of the respiratory cycle. Each system has advantages and disadvantages arising from differing design features. Prescription should be based on individual tests in all cases to ensure optimal oxygen delivery during rest, exercise, and sleep.

The effect of tracheal gas insufflation on gas exchange efficiency

Transtracheal gas insufflation (TGI) improves gas exchange efficiency, but is associated with hyperinflation, and usually requires ventilator adjustment to compensate for the increased gas flow. Although bidirectional TGI (Bi-TGI) minimizes hyperinflation, it does not preclude the need to reduce tidal volumes to prevent hyperinflation. A flow-compensation system was developed by Respironics (Murrysville, PA) to match TGI flows; however, neither that nor the efficacy of Bi-TGI have been tested in vivo. We tested the hypotheses that flow compensation allows for a constant minute ventilation; Bi-TGI produces less hyperinflation than does unidirectional TGI (Uni-TGI), and endotracheal tube size influences the degree of hyperinflation during TGI. Seven anesthetized intact dogs were studied during positive-pressure ventilation using the Respironics flow compensation system. Measurements were made during steady-state conditions at constant and measured levels of CO(2) production. Gas exchange efficiency (assessed by expired gas analysis for dead space) and hyperinflation (measured as an increase in pleural pressure) were compared during Bi- and Uni-TGI and for endotracheal tube sizes varying from 7 to 10F. Bi- and Uni-TGI could be delivered at constant minute ventilation without adjusting ventilatory setting when the flow compensation circuit was present. Uni-TGI produced more hyperinflation than did Bi-TGI with all sizes of endotracheal tube, and hyperinflation was universally present as tube size decreased to 7.5F. We conclude that this new flow compensation system allows for the delivery of TGI without the need for adjustments to the ventilator settings, and that Bi-TGI produces less hyperinflation than does Uni-TGI, even with small diameter endotracheal tubes.

Transtracheal high-flow insufflation supports spontaneous respiration in chronic respiratory failure

STUDY OBJECTIVES

Transtracheal insufflation of oxygen-enriched air at a high flow rate has been proposed to support ventilation. The purpose of this study was to investigate the physiologic effects of high-flow insufflation unobtrusively with a respiratory inductive plethysmograph in patients with chronic respiratory failure. Using a respiratory inductive plethysmograph also permitted monitoring of end-expiratory lung volume, and respiratory variables could be quantified independently of the tracheal bias flow.

DESIGN

Prospective randomized comparison of low-flow vs high-flow transtracheal insufflation.

SETTING

Pulmonary division of a tertiary teaching hospital.

PATIENTS

Fourteen spontaneously breathing outpatients with chronic hypoxemic respiratory failure carrying a transtracheal catheter for long-term oxygen therapy.

INTERVENTIONS AND MEASUREMENTS

Oxygen-enriched air (fraction of inspired oxygen, 0.37) at 15 L/min and oxygen at 1.5 L/min were transtracheally administered for 1 h each. The breathing pattern and the end-expiratory lung volume were monitored by inductive plethysmography along with pulse oximetry and transcutaneous PCO2. Arterial blood gases were also analyzed at the end of the hour of both low-flow and high-flow insufflation.

RESULTS

High-flow insufflation decreased the mean (+/- SEM) minute ventilation (Ve) by 20% from 8.37 +/- 0.49 to 6.66 +/- 0.57 L/min, the mean respiratory rate from 19.2 +/- 0.9 to 15.7 +/- 1.0 breaths/min, while mean expiratory time increased from 2.0 +/- 0.1 to 2.8 +/- 0.2 s, and end-expiratory lung volume decreased by 0.55 +/- 0.15 L compared to low-flow oxygen insufflation (p < 0.05 for all comparisons). Mean arterial and transcutaneous PCO2 decreased from 45 +/- 1 to 43 +/- 1 mm Hg and from 54 +/- 2 to 53 +/- 2 mm Hg, respectively (p < 0.05 in both instances), while arterial PaO2 and oxygen saturation did not change.

CONCLUSIONS

High-flow transtracheal insufflation of oxygen-enriched air assists ventilation by reducing Ve without compromising gas exchange and by reducing end-expiratory lung volume, possibly through the reversal of dynamic hyperinflation.

Transtracheal oxygen catheters

Over the past 20 years a variety of transtracheal catheters have been developed for long-term oxygen therapy. A modified Seldinger technique has been the standard in the past, but a more recent procedure for surgical creation of the tracheocutaneous tract presents a number of potential advantages. TTO should be administered as a program of care, and recent advances with a streamlined and shortened program have simplified and improved the delivery of a technology that has a number of potential benefits and established safety. TTO may further increase the oxygen conservation efficiency of demand oxygen controller devices, and studies have shown TTO to be a potential alternative to nasal oxygen, continuous positive airway pressure, and tracheotomy for severe obstructive sleep apnea. Very high flows (> 10 L/minute) of a humidified air/oxygen blend, termed transtracheal augmented ventilation, extend the physiologic benefits of TTO and have promise in both the outpatient nocturnal ventilatory support of patients with severe respiratory disease and in liberation of patients from prolonged mechanical ventilation.

Effect of Tracheal Gas Insufflation During Weaning From Prolonged Mechanical Ventilation: A Preliminary Study

• Background Tracheal gas insufflation reduces inspired tidal volume and minute ventilation in spontaneously breathing patients and may facilitate weaning from mechanical ventilation.

• Objective To determine if tracheal gas insufflation can reduce ventilatory demand during weaning trials in patients who require prolonged mechanical ventilation.

• Methods A reduction in ventilatory demand was defined as a relative decrease in tidal volume, minute ventilation, and mean inspiratory flow during trials with tracheal gas insufflation compared with the values during trials without this therapy. A total of 14 subjects underwent T-piece trials with and without insufflation (flow rate 6 L/min) on 2 consecutive days; the order of insufflation was randomized. Tidal volume, minute ventilation, and mean inspiratory flow were measured at baseline (without insufflation) and 2 hours later.

• Results Differences in ventilatory demand were not significant when comparisons were made for condition (tracheal gas insufflation vs no flow) or time (baseline vs 2 hours) for the total group (P = .48). Subjects were classified post hoc as responders (n = 9) or nonresponders (n = 5). Comparisons between responders and nonresponders indicated a significant (P = .02) 3-way multivariate interaction for group (responder vs nonresponder), condition (tracheal gas insufflation vs no flow), and time (baseline vs 2 hours) for ventilatory demand variables.

• Conclusion Tracheal gas insufflation can reduce ventilatory demand during weaning trials in some patients who require mechanical ventilation.

Transtracheal oxygen catheters in a pediatric population

This is the first report to evaluate transtracheal oxygen catheter (TTOC) use in a pediatric patient series. Seven pediatric patients (4 boys and 3 girls) received TTOCs in 2 tertiary care medical centers. The medical indications included bronchopulmonary dysplasia in 4 patients and tracheomalacia in the other 3. The average age at the time of placement was 22 months (range, 2 weeks to 37 months). Catheter placement for 4 patients was through an open tracheotomy stoma. In 3, placement was through a percutaneous technique. The follow-up ranged from 2 weeks to 5 years. There were no long-term complications. Transient needs for supplemental oxygen were all met by the TTOC system. In 4 patients, the catheter has been removed because of resolution of the supplemental oxygen requirements. Minor complications included skin site infection and mucus plugging. In 1 patient, accidental dislodging of the catheter led to its replacement in the operating room. In 1 percutaneous placement, a pneumothorax occurred and resolved without any persistent morbidity. We conclude that transtracheal oxygen delivery can be a reasonable alternative to a nasal cannula or formal tracheotomy in selected pediatric patients in whom long-term oxygen delivery, but not an alternate airway, is required. In order to avoid complications, meticulous technique must be adhered to in using the percutaneous approach for placement.

[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.

Long-term clinical experience with transtracheal oxygen catheters

OBJECTIVE

To evaluate and discuss the use of transtracheal oxygen catheters for the treatment of chronic hypoxemia and to discuss the complications associated with the placement and care of these devices.

DESIGN

We conducted a retrospective study at a tertiary medical center and reviewed the pertinent literature.

MATERIAL AND METHODS

The medical records of 56 patients who received a transtracheal oxygen catheter between January 1987 and June 1992 at our institution were reviewed for demographic data, diagnosis leading to catheter placement, complications related to catheter use, reason for catheter removal, and duration of use. Follow-up results were established by documentation in the medical records or telephone interview.

RESULTS

During the study period, 39 men and 17 women received a transtracheal catheter. More than half the patients (52%) had chronic obstructive pulmonary disease. The duration of use of the catheter ranged from 2 days to more than 6 years, and the most frequent cause for removal of the catheter was death. Of the 56 patients, 42 died with the catheter in place, 24 within the first year after placement. Complications ranged from mucous plugging (38 % of patients) to pneumothorax (4%), and no patient died of a catheter-related complication. Overall, 55% of patients had their catheter for less than 1 year after placement.

CONCLUSION

In patients with transtracheal oxygen catheters, problems related to mucous plugging are common, but severe complications such as pneumothorax and pneumomediastinum are uncommon. Although selection factors that would identify ideal candidates for transtracheal oxygen therapy have not been established, such a catheter is best placed in highly motivated patients who can physically manage the daily care of this device.

Long-term oxygen therapy for COPD. Improving longevity and quality of life in hypoxemic patients

Long-term oxygen therapy can increase life expectancy in hypoxemic patients with COPD. Accurate identification of hypoxemia requires arterial blood gas measurements. Pulse oximetry can be used to measure trends in oxygenation, oxygen needs, and oxygen requirements during exercise and sleep. A detailed oxygen prescription indicates: (1) the oxygen dose (L/min), (2) the number of hours per day that oxygen therapy is required, (3) the dose required during exercise, (4) the oxygen supply system: concentrator, compressed gas cylinder, or liquid oxygen reservoir, and (5) the delivery device: nasal cannula, demand-flow device, reservoir cannula, or transtracheal oxygen catheter.

Home oxygen therapy

Home oxygen therapy has well-established benefits for patients with chronic obstructive pulmonary disease and resting hypoxemia. The indications for therapy have been clearly defined in the United States by the Health Care Financing Administration (HCFA), and these guidelines have been accepted by most third-party payers. Controversies regarding the use of oxygen during sleep and exercise when daytime hypoxemia is not present have important therapeutic and financial implications. HCFA has recently proposed a substantial reduction in reimbursement for home oxygen which could have a major adverse effect if done on a global, across-the-board, basis. Some of the new technological developments in oxygen delivery systems are presented in this article.

Tracheal gas insufflation improves ventilatory efficiency during metacholine-induced bronchospasm

INTRODUCTION

Barotrauma and cardiovascular insufficiency are frequently encountered problems in patients with acute bronchospastic disease who require mechanical ventilation. Permissive hypercapnia is a recognized strategy for minimizing these adverse effects; however, it has potential risks. Tracheal gas insufflation (TGI) has been shown to increase carbon dioxide elimination efficiency and thus could permit mechanical ventilation at lower peak airway pressures without inducing hypercapnia. However, caution exists as to the impact of TGI on lung volumes, given that expiratory flow limitation is a hallmark of bronchospastic disease.

PURPOSE

To examine these issues, we studied ventilatory and hemodynamic effects of continuous TGI as an adjunct to mechanical ventilation before and after methacholine-induced bronchospasm.

MATERIALS AND METHODS

Ten anesthetized, paralyzed dogs were ventilated on volume-controlled mechanical ventilation during administration of continuous TGI (0, 2, 6, and 10 L/min) while total inspired minute ventilation (ventilator-derived minute ventilation plus TGI) was kept constant. In an additional step, with TGI flow of 10 L/min, total inspired minute ventilation was decreased by 30%.

RESULTS

PaCO2 decreased (44 +/- 7 mm Hg at zero flow to 34 +/- 7 mm Hg at 6 L/min and 31 +/- 6 mm Hg at 10 L/min, respectively, P < .05), as did the dead space to tidal volume ratio at TGI of 6 and 10 L/min compared with zero flow. There were no significant changes in end-expiratory transpulmonary pressure, mean arterial pressure, or cardiac output. During the highest TGI flow (10 L/min), with a 30% reduction of total inspired minute ventilation, both PaCO2 and peak airway pressure remained less than during zero flow conditions.

CONCLUSION

We conclude that TGI increases carbon dioxide elimination efficiency during constant and decreased minute ventilation conditions without any evidence of hyperinflation or hemodynamic instability during methacholine-induced bronchospasm.

Treatment of respiratory failure using minitracheotomy and intratracheal oxygenation in selected patients with chronic lung disease

OBJECTIVE

To evaluate the efficacy of minitracheotomy (MT) insertion for intratracheal oxygen insufflation (ITO2) on arterial blood gases and survival in patients with respiratory failure from chronic lung disease.

DESIGN

Open, prospective clinical study.

SETTING

A 12-bed medical intensive care unit in a non-university hospital.

PATIENTS

20 patients (14 males and 6 females, mean age 74.8 +/- 2.6 years), admitted for respiratory failure and denied mechanical ventilation.

INTERVENTION

Percutaneous insertion of an MT for ITO2. Arterial blood gases were drawn just prior to, then 3, 24, 48 h and 1 week after MT insertion. Data are evaluated with a two-way analysis of variance for distribution-free data (Friedman's rank sums test).

MEASUREMENTS AND RESULTS

Three hours after starting ITO2, the partial pressure of oxygen in arterial blood (PaO2) and the arterial oxygen saturation (SaO2) both increased from 51.7 +/- 2.8 to 85.4 +/- 5.6 mmHg and from 79.7 +/- 3.1 to 93.7 +/- 0.9%, respectively (p < 0.001 for both), along with a slight worsening in the partial pressure of carbon dioxide in arterial blood (PaCO2), from 59.6 +/- 2.5 to 63.5 +/- 3.0 mmHg (p < 0.05). At 1 week, improvements in PaO2 and SaO2 were maintained in all patients, while PaCO2 decreased in 14 patients (mean decrease 8.3 mmHg) and increased in the remaining patients (mean 12.5 mmHg), when compared to pre-ITO2 values. Seven patients died during follow-up, leading to a success rate of 65%. Eight and 4 patients were discharged home and to a nursing home, respectively, 9 still receiving ITO2 via MT as chronic oxygen therapy.

CONCLUSION

Our results suggest that MT insertion for ITO2 may be a therapeutic option in selected patients with respiratory failure from CLD.

Transtracheal oxygen catheterization with pneumomediastinum and sudden death

A 69-year-old man with hypoxemic COPD underwent placement of a transtracheal oxygen (TTO) catheter. At 3 months, the catheter tract appeared mature with minimal erythema and no evidence of infection at the catheter site. The patient and his spouse were taught to remove and reinsert the catheter but were told to delay beginning the procedure due to erythema at the stoma site. Despite instructions not to remove the catheter for cleaning, the spouse removed the TTO catheter and attempted to reinsert it using the flexible metal cleaning rod. Subsequently, the patient suffered an acute episode of subcutaneous air and hemodynamic collapse resulting in death. Necropsy revealed a false catheter tract occluded by clotted blood and a defect in the platysma muscle where oxygen had dissected into the mediastinum. The patient died due to pneumomediastinum and cardiac tamponade.

Evolving concepts in the ventilatory management of acute respiratory distress syndrome

With few modifications, a high tidal volume, normoxic, normocapnic ventilation paradigm developed as the standard approach to supporting most critically ill patients. Large tidal volumes, high end-tidal (plateau) alveolar pressures, and low levels of positive end-expiratory pressure are still common in many ICUs during ventilation of acute respiratory distress syndrome (ARDS). A body of scientific literature now suggests that this traditional approach may retard healing of the injured lung. A relatively small but growing number of practitioners are shifting their first priority from optimizing oxygen exchange, oxygen delivery, or respiratory system compliance to ensuring adequate lung protection. This article reviews the basis for concern about traditional ventilatory support in ARDS and develops an approach based on current evidence and newer options for management.

Home oxygen therapy

Both the efficacy and the indications for LTOT have been well defined. Most of the studies performed have focused on patients with hypoxemia caused by COPD, and the benefits observed are assumed to apply to all patients with correctable hypoxemia. For Medicare patients, oxygen is reimbursed under a prospective payment system with all delivery systems considered to be cost and therapeutically equal. Because there are, in fact, substantial clinical differences in the medical indications for individual oxygen delivery systems, it is imperative that the prescribing physician be prepared to order the therapy that is most appropriate for each patient. Most home oxygen therapy is now being ordered by primary care physicians, often functioning as gatekeepers in managed care organizations. Education of primary care physicians in this area is often inadequate, and decisions for therapy should not be delegated to the equipment suppliers. If the study of home oxygen therapy conducted by the Office of the Inspector General were repeated today, less misuse of home oxygen would probably be found because of more clearly defined indications and requirements for therapy, but it is likely that the study would find that the level of knowledge of the prescribing physician has not maintained pace with the advances in technology. Continuing education for primary care physicians in this area of respiratory care is essential for appropriate medical management now and in the future.

Current thoughts regarding treatment of chronic obstructive pulmonary disease

The available evidence indicates that pulmonary rehabilitation benefits patients with symptomatic COPD. The effect of pulmonary rehabilitation programs on health care use is promising but requires further investigation. In contrast, aerobic lower extremity training is of benefit in several areas of importance to patients with COPD. These areas include exercise endurance, perception of dyspnea, quality of life, and self-efficacy. The exact role of upper extremity exercise training programs requires further studies but should be used in patients who develop symptoms with arm activities. Psychological support improves the awareness of the patient and increases his or her understanding of the disease, but when used alone it is of limited value. Pulmonary rehabilitation when coupled with smoking cessation, optimization of blood gases, and medications offers the best treatment option for patients with symptomatic airflow obstruction.

Is tracheal gas insufflation an alternative to extrapulmonary gas exchangers in severe ARDS?

Tracheal gas insufflation (TGI) of pure oxygen combined with mechanical ventilation decreases dead space and increases CO2 clearance. In the present study, TGI was used in six patients with ARDS who met extracorporeal membrane oxygenation criteria and who were severely hypoxemic and hypercapnic despite optimal pressure-controlled ventilation. This open clinical study aimed to investigate the effects of 4 L/min continuous flow of oxygen given via an intratracheal catheter. PaCO2 decreased from 108 +/- 32 to 84 +/- 26 mm Hg (p < 0.05), and no significant change in PaO2 (68 +/- 18 vs 96 +/- 43, p = 0.06). There was no change in airway pressures and hemodynamic variables. A slight increase in end-expiratory and end-inspiratory volumes with TGI possibly occurred, as seen on tracings from respiratory inductive plethysmography (Respitrace). We conclude that TGI improves tolerance of limited pressure ventilation by removing CO2, but it may induce changes in lung volumes that are not detected by ventilator measurements.

[Transtracheal catheter and liquid oxygen: 5 years of experience]

We studied clinical tolerance, complications, change in pulmonary function test results, arterial gasometrics, hemoglobin (Hb), 6 minute stress tests (6 wt) and subjective perception of dyspnea assessed on a visual analog scale (VAS) in a group of 18 patients (17 with obstructive disease and one with restrictive disease). These patients had previously been enrolled in a home oxygen therapy (HOT) program to deliver continuous oxygen therapy through nasal prongs, and had accepted portable oxygen therapy delivered by transtracheal catheter (TTC) from 1988 until 1993. Tolerance was good, there were no lethal complications of TTC, and excellent compliance with the prescribed HOT was achieved. Lung function test results worsened, while Hb and PaO2 improved and significant oxygen savings (50%) were achieved. The 6 wt test results had not worsened at the end of the first year but did so significantly at the end of the third year, in spite of a relative preservation of lung function. Dyspnea assessed on a VAS was not seen to worsen. We conclude that tolerance of the method was good and that no relevant complications occurred. HOT by TTC did not prevent worsening of bronchial obstruction. Oxygenation of patients was better, as shown by the decrease in Hb and the improvement in PaO2 at the end of the first year of monitoring. Changes in 6 wt showed that in order to achieve greater benefit from HOT by TTC, patients should follow a pulmonary rehabilitation program.

Tracheal gas insufflation augments CO2 clearance during mechanical ventilation

A technique that improves the efficiency of alveolar ventilation should decrease the pressure required and reduce the potential for lung injury during mechanical ventilation. Alveolar ventilation may be improved by replacing a portion of the anatomic dead space with fresh gas via an intratracheal catheter. We studied the effect of intratracheal gas insufflation as an adjunct to volume cycled ventilation in eight sedated, paralyzed patients with a variety of lung disorders. Continuous flows of 2, 4, and 6 L/min were delivered through a catheter positioned 1 or 10 cm above the carina. Carbon dioxide production, inspiratory minute ventilation, and peak and mean airway pressures did not change over the range of flows tested. PaCO2 and dead space volume/tidal volume decreased significantly as joint functions of catheter flow and position (p < 0.001). The highest catheter flow (6 L/min) and most distal catheter position (1 cm above the carina) were the most effective combination tested, averaging a 15% reduction in PaCO2 (range 9 to 23%). Certain characteristics of the expiratory capnogram were helpful in predicting the observed reduction in PaCO2. Tracheal gas insufflation may eventually prove a useful adjunct to a pressure-targeted strategy of ventilatory management (in either volume-cycled or pressure controlled modes), particularly when the total dead space is heavily influenced by its anatomic component.