Transtracheal oxygen decreases inspired minute ventilation

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.

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.

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.

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.

Supportive therapy in COPD

Supportive therapy in COPD includes long-term oxygen therapy (LTOT) and patient support groups as two cornerstones in a comprehensive program of care known as pulmonary rehabilitation. The rich history of LTOT dating to the early 1960s and bolstered by excellent controlled clinical trials of the 1970s, along with additional advances, provided an effective therapy which improved both the quality and length of life in patients with COPD. Many patients with oxygen gain insight into coping with advanced COPD through patient support groups. The need for more cosmetically pleasing oxygen delivery systems to the nose, and future directions in providing oxygen in the home, remain challenges.

Disease management of COPD with pulmonary rehabilitation

Pulmonary rehabilitation is a set of tools and disciplines that attends to the multiple needs of the COPD patient. It extends beyond standard care by addressing the disabling features of chronic and progressive lung disease. It centers on self-management, exercise, functional training, psychosocial skills, and contributes to the optimization of medical management. Exercise enables other components by building strength, endurance, confidence, and reducing dyspnea. Patients who have undergone rehabilitation often enjoy a reduced need for health-care utilization. On the downside, rehabilitation is a one-time intervention, the benefits of which dissolve over time. The patient's physician is rarely a participant in the program; thus, the physician is at a disadvantage in being able to support a long-term response. Rehabilitation is available to a small percentage of a large patient population who could benefit. Optimal disease management would entail redesigning standard medical care to integrate rehabilitative elements into a system of patient self-management and regular exercise. It should emphasize physician involvement in self-management, which is essential in developing and maintaining an effective exacerbation protocol. Pulmonary rehabilitation should take its place in the mainstream of disease management through its integrative and reconciliative role in the multidisciplinary continuum of services, as defined by the National Institutes of Health, Pulmonary Rehabilitation Research, Workshop of 1994.

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.

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.

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.

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.

Respiratory effects of tracheal gas insufflation in spontaneously breathing COPD patients

OBJECTIVE

To evaluate the effect of tracheal gas insufflation (TGI) in spontaneously breathing, intubated patients with chronic obstructive pulmonary disease (COPD) undergoing weaning from the mechanical ventilation.

DESIGN

A prospective study in humans.

SETTING

Polyvalent intensive care unit (14-bed ICU) in a 700-bed general university hospital.

PATIENTS

Twelve patients with chronic obstructive pulmonary disease (COPD) who required intubation and mechanical ventilation were studied. All patients met standard criteria for weaning from mechanical ventilation. Seven patients (group 1) had been transorally intubated during episodes of acute respiratory failure. Five patients, all men (group 2), had previously undergone tracheostomy and had a transtracheal tube in place.

INTERVENTIONS

Intratracheal, humidified, O2-mixture insufflation (TGI) was given via a catheter placed in distal or proximal position. Gas delivered through the intratracheal catheter was blended to match the fractional of inspired gas through the endotracheal tube. Continuous flows of 3 and 6 l/min in randomized order were used in each catheter position. Prior to data collection at each stage, an equilibration period of at least 30 min was observed, and thereafter blood gases were analyzed every 5 min. A new steady state was assumed to have been established when values of both PaCO2 and V CO2 changed by less than 5% between adjacent measurements. The last values of blood gases were taken as representative. The new steady state was confirmed within 35-50 min. Baseline measurements with zero Vcath were made at the beginning and end of the experiment.

RESULTS

This study shows that VT, MV, PaCO2, and VD/VT are reduced in a flow-dependent manner when gas is delivered through an oral-tracheal tube (group 1). The distal catheter position was more effective than the proximal one. In contrast, when gas was delivered through tracheostomy (group 2), TGI was ineffective in the proximal position and less effective than in group 1 in distal position.

CONCLUSION

Under the experimental conditions, tracheal gas insufflation decreased dead space, increased alveolar ventilation and possibly reduced work of breathing. From the preliminary data reported here, we believe that TGI may help patients experiencing difficulty during weaning.

Percutaneous needle cricothyroidotomy with repetitive airway obstruction

To develop a technique for needle cricothyrotomy that mimics the normal respiratory cycle (using repetitive obstruction of the upper airway and relatively low flow oxygen through small catheters), a controlled trial in three anesthetized dogs was performed. Oxygen from a standard bottle and pressure reducer was delivered through the cricothyroid membrane at 0.36 L/kg/min, which is metabolically equivalent to 0.2 L/kg/min in an adult human. The upper airway was obstructed until the chest rose and then was unobstructed to allow exhalation. The animals were ventilated for 5 minutes to allow equilibration. Arterial PCO2 was measured after 2-minute periods of apnea and 3 minutes of ventilation, each repeated four times. The procedure was repeated in three other dogs at a flow of 0.18 L/kg/min to simulate a 50% air leak. Cricothyroid ventilation at 0.36 L/kg/min lowered the PCO2 from 65 mm Hg to 43 mm Hg, F = 258, P = .004. All PCO2 after 25 minutes were in the normal range. Ventilation at 0.18 L/kg/min stabilized the PCO2 at approximately 1.5 times normal (67 mm Hg versus 79 mm Hg for the preceding apnea, F = 77, P = .013). Flow rates achievable with 18- to 20-gauge catheters and standard oxygen sources are adequate for cricothyroid ventilation when the airway is repetitively obstructed to allow a normal respiratory cycle.

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 reduces the tidal volume while PaCO2 is maintained constant

OBJECTIVE

The aims of the present study were two-fold: first, to confirm the effect of tracheal gas insufflation (TGI) throughout the respiratory cycle on alveolar ventilation at various catheter flows and constant total inspired VT as an adjunct to conventional volume cycled mechanical ventilation in patients with acute lung injury; second, to test the efficacy of TGI in the reduction of toal VT, peak and mean airway pressure while maintaining PaCO2 in its baseline value. The hemodynamic effect and the consequences on oxygenation as result of the reduction of VT, were also estimated.

DESIGN

Prospective study of patients with acute lung injury requiring mechanical ventilation.

SETTING

12 bedded, adult polyvalent intensive care unit in a teaching hospital.

PATIENTS

7 paralyzed and sedated patients with acute respiratory failure were studied. All patients were clinically and hemodynamically stable without fluctuation of the body temperature. All patients were orally intubated with cuffed endotracheal tubes, and mechanically ventilated with a standard circuit of known compliance.

INTERVENTIONS

Continuous flows (4 and 6 l/min) were delivered through a catheter positioned 1 cm above carina while tidal volume or PaCO2 were maintained constant at their baseline value.

RESULTS

In this study a modest level of TGI significantly enhanced CO2 elimination in patients with acute respiratory failure. Improved ventilatory efficiency resulted from the functional reduction of dead space during TGI allowing the same PaCO2 to be maintained at the same frequency with lower tidal volume and lower airway pressure requirement. Tidal volume, peak and mean airway pressure decreased linearly with catheter flow, without significant changes in oxygenation, while PaCO2 remained stable.

CONCLUSION

The results of this study suggest that TGI may be an useful adjunct mode of mechanical ventilation that limits alveolar pressure and minute ventilation requirements.

Effect of low flow and high flow oxygen delivery on exercise tolerance and sensation of dyspnea. A study comparing the transtracheal catheter and nasal prongs

HYPOTHESIS

We hypothesized that high flow transtracheal oxygen (HFTTO) will improve exercise tolerance as compared with low flow transtracheal oxygen (LFTTO) and that transtracheal oxygen (TTO) will increase exercise tolerance with less dyspnea as compared with nasal prongs (NP) at equivalent oxygen saturation (SaO2).

PATIENT SELECTION

Ten subjects, six male and four female, who were already receiving TTO were recruited for the study.

STUDY DESIGN

Each subject underwent a total of four modified progressive treadmill tests in a single-blind randomized fashion on two separate days. Two tests were performed with the patients receiving LFTTO and HFTTO while the other two were performed with low- and high-flow oxygen by NP. The flows were adjusted to provide equivalent oxygen saturations at rest for respective groups.

RESULTS

The mean +/- SD exercise distance with HFTTO (1,134 +/- 631 ft) was 2.5 times greater than with LFTTO (446 +/- 328 ft; p < 0.006); and high-flow NP (HFNP [1207 +/- 763 ft]) was 2.38 times greater than with low-flow NP (LFNP[492 +/- 487 ft; p < 0.005]). There was no significant difference in exercise distance and dyspnea scores with HFTTO as compared with HFNP and LFTTO versus LFNP.

CONCLUSION

We conclude that the use of high-flow oxygen via both transtracheal catheter and NP significantly increased exercise tolerance in our COPD patients when compared to low-flow oxygen. Transtracheal oxygen did not increase maximum exercise tolerance with less dyspnea as compared with oxygen via NP at equivalent SaO2.

The effects of transtracheal gas delivery on central inspiratory neuromuscular drive

Previous studies have shown transtracheal delivery of low-flow oxygen (TTO) decreases inspired minute ventilation (Veinsp) and have postulated that this would result in a decrease in the work of breathing (WOB). We hypothesized that a fall in central inspiratory neuromuscular drive (CIND) with TTO would reflect a fall in WOB. We measured resting ventilatory parameters (RVP) and CIND by the mouth occlusion pressure technique (MOP) at different gas flow rates through the catheter in 21 subjects (13 men, 8 women; mean age, 60 +/- 10.6 years) with severe COPD with a mature intratracheal oxygen catheter (ITOC). We also constructed a lung/chest wall analog (LCA) to determine if flow through the catheter would alter pressure changes during inspiration. Inspiratory tidal volume (Vtinsp) and minute ventilation (Veinsp) decreased proportionally to the gas flow rate through the catheter. However, with increasing flow through the catheter, P0.1 increased in the LCA, presumably due to the Bernoulli effect. The lack of a similar change in the subject group suggests that CIND does, in fact, fall, and that possibly there is a decrease in WOB. This effect may be of benefit to patients with severe COPD.

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.

Transtracheal delivery of gas decreases the oxygen cost of breathing

Transtracheally administered gases decrease inspired minute ventilation in both dogs and humans. To test if this is associated with a decrease in the oxygen cost of breathing and to evaluate subsequent changes in the breathing pattern, we studied five patients with chronic respiratory diseases while they spontaneously breathed air and different flows of tracheally administered gases. In a blinded crossover design, the gas consisted of either oxygen or air at 2, 4, and 6 L/min. Oxygen cost of breathing was estimated by the calculation of pleural pressure-time index (PPTI). The pattern of breathing was evaluated utilizing the tension time index for the diaphragm (TTdi). There were significant decreases in PPTI when the patients received 2, 4, and 6 L/min of transtracheal oxygen or air. TTdi also decreased as gas flow increased. This drop was significant at 6 L/min flow for both gases. We conclude that transtracheally administered gas reduces the oxygen cost of breathing. It also changes the respiratory pattern of the diaphragm to a less demanding pattern. This may offer an alternative form of treatment to rest overworked respiratory muscles.

Gas exchange by intratracheal insufflation in a ventilatory failure dog model

Respiratory insufficiency patients who need only partial ventilatory support are, nevertheless, intubated and connected to a respirator. In search of a partial respiratory assistance method we evaluated the gas exchange, mechanisms, and hemodynamic effects of intratracheal insufflation (ITI) via a narrow (0.2-cm) catheter. The effects of flow rate (0.05-0.2 liter/min per kg), catheter tip position (carina, bronchus, and trachea), and superimposed chest vibration at 22 Hz were studied in seven anesthetized and partially paralyzed dogs. ITI in the carina induced CO2 removal (VCO2) of 48 +/- 16 ml/min in the periods between breaths, which was 39% of the control VCO2. CO2 removal rates between breaths with ITI in a bronchus and in the trachea were 63 and 28% of control, respectively (P < 0.05). ITI at 0.15-0.2 liter/min per kg augmented total VCO2 by > 50% over control (P < 0.05) and decreased PaCO2 by 10% (P < 0.05) despite a 28% fall in VE and 32% lower work of breathing (P < 0.05). Adding vibration to ITI at 0.15 liter/min per kg induced VCO2 of 162 +/- 34 ml/min, which was significantly greater than control, while PaCO2 fell from 69 +/- 24 to 47 +/- 6 mmHg (P < 0.05), despite complete cessation of spontaneous breathing. ITI with or without vibration did not cause any hemodynamic changes, except for a fall in the shunt fraction from 14.6 +/- 9.9% to 5.8 +/- 2.8% with vibration. Thus, ITI at low flow rates can support respiration with no hemodynamic side effects. Adding chest vibration further enhances gas exchange and can provide total ventilation.

Clinical experience and physiologic results with an implantable intratracheal oxygen catheter

Ten patients with chronic lung disease received an implanted ITOC. Seven patients continue to use their catheters after a mean period of 14.75 months. Four catheters were removed, 2 at 1 month, 1 after 10 months and 1 after 13 months. One patient requested a second catheter. Three patients experienced mucus plug formation; this was transient in two patients, but led to removal of the catheter in the third. To determine the degree of oxygen-saving afforded by the ITOC, SaO2 was measured at rest and during exercise for eight of the ten subjects using a double-blind technique. The calculated oxygen savings were around 40 percent both at rest and during exercise. The ITOCs were well received by the majority of our patients and were shown to produce a useful saving of oxygen which is of benefit to patients using portable systems and those who require high oxygen flow rates.

Nasal cannula and transtracheal oxygen delivery. A comparison of patient response after 6 months of each technique

The purpose of this study was to compare the efficacy of transtracheal (TT) oxygen delivery to that of nasal cannula delivery in subjects with chronic obstructive pulmonary disease (COPD). Twenty subjects (14 men, 6 women) were followed for 6 months during nasal cannula delivery. A TT catheter was then inserted, and measurements were repeated during TT use. With TT delivery, subjects required 45% less oxygen at rest and 39% less during exercise (p less than 0.0001). Oxygen use, measured by pounds of oxygen delivered to the home, also decreased, but the magnitude of change was less than anticipated (mean, 14%; range, +4% to -32%). Hospital days decreased from 12 +/- 10 during nasal cannula use to 4 +/- 6 during TT use (p less than 0.002). Exercise tolerance, as measured by a 12-min walk distance, was greater during TT use (p less than 0.0001). No change was seen in spirometry or acid-base balance. Also, no change was seen in Profile of Mood States, Sickness Impact Profile or Katz Adjustment Scale scores. Some problems were encountered relating to use of the catheter (displacement, mucus balls), but they were minor, and most were confined to the initial 2 months of TT use when the tract was immature. Our experience suggests that, in addition to decreasing oxygen flow rate, use of TT delivery may confer benefits that result in improved exercise tolerance and decreased hospitalization in patients with COPD.

Transtracheal oxygen delivery

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Airway insufflation. Increasing flow rates progressively reduce dead space in respiratory failure

We have previously shown that airway insufflation (AI) reduces dead space (VD) and minute ventilation (VL) in patients with respiratory failure, and when used chronically leads to lowered and more stable arterial PCO2. The present study was designed to measure the effect of increasing AI flow rate on VD and other aspects of gas exchange in respiratory failure in order to examine the hypothesis that AI exerts its main physiologic effect by progressive reductions of VD. Five patients with varying degrees of respiratory failure caused by either restrictive or obstructive lung disease were studied by means of the specialized techniques we developed to analyze gas exchange during AI. At 1 L/min (as in transtracheal oxygenation), at 5 L/min, and 8 L/min, AI produced progressive reductions in VD, tidal volume, and VL. Contrary to our previous study, some of these patients accompanied the decrease in VD with not only decreases in VL but with slight rises in alveolar ventilation (VA) and decrements in arterial PCO2. The greatest percentile decreases in VD and VL occurred in those with the smallest initial control values for each of these parameters. In summary, AI exerts its main effects on gas exchange through the reductions in VD that it produces, and the accompanying decreases in VL and/or slight increases in VA seem to stem from the latter.

Dyspnea: a sensory experience

Dyspnea--an unpleasant or uncomfortable awareness of breathing or need to breathe--is a common symptom of patients with cardiopulmonary disease. Although often thought of as a single symptom, dyspnea probably subsumes many sensations. Experimental conditions used to induce dyspnea are characterized by discrete groups or clusters of descriptive phrases. Similarly, as the language of dyspnea is refined further, different disease states may be distinguishable by the nuances of breathlessness described by patients. Evidence is gathering that the sensations of dyspnea are modified by information from a variety of receptors throughout the respiratory system. The sense of effort, although still important in the breathlessness associated with mechanical loads, is insufficient to explain the dyspnea arising from a number of experimental and clinical conditions. As our understanding of the interactions between effort and afferent information from the respiratory system grows, new therapeutic interventions to alleviate dyspnea are likely to follow.

Long term continuous domiciliary oxygen therapy by transtracheal catheter

Long term continuous oxygen therapy improves prognosis in patients with hypoxaemic chronic airflow limitation. Transtracheal delivery of oxygen permits adequate oxygenation of such patients at lower flow rates than are required for delivery by nasal cannulas, thus increasing the time for which portable oxygen cylinders can be used and improving the efficacy of domiciliary oxygen concentrators in patients with refractory hypoxaemia. In a study of the long term acceptability and risks of transtracheal oxygen in 37 patients, with a total follow up of 595 patient-months, most patients reported symptomatic benefit and four have used transtracheal oxygen successfully for more than four years. Problems have included surgical emphysema (4 patients), catheter fracture (9), local infection (34), and catheter dislodgement (21); but these have been relatively infrequent and in general have not caused important clinical problems. Transtracheal oxygen therapy was discontinued in 10 patients before death for various reasons, including infection (2 patients), catheter fracture (1), and surgical emphysema (1). Accumulation of mucus balls has not been a problem. It is concluded that transtracheal oxygen therapy is a safe and acceptable alternative to nasal cannulas in well motivated patients with hypoxaemia due to chronic airflow limitation who are keen to pursue an active life.

Home oxygen--a revolution in the care of advanced COPD

The state-of-the-art of oxygen delivery to the home has evolved remarkably in the past 25 years. Oxygen is established as not only safe but effective in selected patients with advanced COPD. Oxygen clearly has been shown to improve both the length and quality of life in many patients. Hospitalizations can be reduced by the use of home oxygen therapy. This appears to be most likely in ambulatory patients receiving long-term oxygen from portable liquid systems. It is likely that further advances will make home oxygen more suitable, acceptable, and perhaps less costly for a growing number of patients with progressive chronic respiratory diseases in whom significant hypoxemia and organ system damage are present.

Exercise tolerance during nasal cannula and transtracheal oxygen delivery

Previous studies have reported that exercise tolerance improves with transtracheal oxygen delivery. However, patients were not blinded to the delivery technique used, introducing a potential source of bias. The purpose of this study was to compare exercise tolerance during nasal cannula and transtracheal delivery using a randomized double-blinded technique. Subjects (n = 11) performed 12-min walks on the same day while receiving nasal cannula and transtracheal delivery. Nine of 11 subjects walked farther with transtracheal delivery, a significant increase (p less than 0.01). Mean increase in walk distance was 95 +/- 86 feet. In addition, a trend was seen toward greater improvement in walk distance with greater flows through the catheter (r = 0.58, p less than 0.06). Time into the walk when desaturation (SaO2 less than 90%) first occurred was not significantly different. We conclude that exercise tolerance improves when oxygen is delivered by transtracheal catheter. This improvement is unrelated to an increase in SaO2. We speculate that the increase in exercise tolerance may be related to other physiologic effects of flow through the catheter.

Airway insufflation: physiologic effects on acute and chronic gas exchange in humans

Reduction in dead space through conventional tracheostomy has been used to treat patients with chronic CO2 retention. The insufflation of air directly into the trachea by transtracheal catheter (airway insufflation, AI) provides reductions in dead space as great or greater than those of tracheostomy. The physiologic effects of AI on gas exchange have not been adequately studied because instillation of gases into the trachea contaminates minute ventilation (VL), dead space volume (VD), tidal volume (VT), and other indices of gas exchange, as measured by usual technics. We overcame this problem by devising special methods of measuring inspired and expired ventilation, alveolar and dead space ventilation, and VT and VD by using pneumotachographic timing of inspiration and expiration so that true inspired and expired ventilation were calculated. We studied 5 patients with chronic CO2 retention from either COPD, scoliosis, or muscular dystrophy (annual average PaCO2 = 45 to 75 mm Hg) during 75 min of AI with serial gas exchange and arterial blood gas measurements. AI at about 5 L/min of room air through the trachea in 5 patients reduced VL by 18% (from 7.91 to 6.48 L/min), VT by 25% (from 450 to 338 ml), and VD by 37% (from 223 to 141 ml), while not affecting PaCO2 (from 51.8 to 48.2 mm Hg) or PaO2 (from 65.1 to 63.4 mm Hg). In 2 patients, AI administered continuously for 4 to 12 months (as 30 to 50% O2) maintained PaCO2 as well as or better than breathing enriched O2 from a tracheal collar via an open tracheostomy.(ABSTRACT TRUNCATED AT 250 WORDS)