Automatic adjustment of noninvasive pressure support with a bilevel home ventilator in patients with acute respiratory failure: a feasibility study.

OBJECTIVE: To test the feasibility of applying noninvasive ventilation (NIV) using a prototype algorithm implemented in a bilevel ventilation device designed to adjust pressure support (PS) to maintain a clinician-set alveolar ventilation in patients with acute respiratory failure after initial stabilization. DESIGN AND SETTING: Prospective crossover interventional study in an intensive care unit, university hospital. PATIENTS: 19 patients receiving NIV for acute hypercapnic respiratory failure (13 men, 6 women; mean age 70+/-11 years). METHODS: The same bilevel ventilator was used with manually adjusted PS and with the automated algorithm (autoPS), set to maintain the same alveolar ventilation as in PS. Sequence (measurements at end of each period): (a) prior to initiating NIV (baseline 1); (b) 45 min with manually set PS; (c) 60 min without NIV; (d) 45 min with autoPS; (e) 60 min without NIV; (f) 45 min with manually set PS. RESULTS: The magnitude of decrease in PaCO(2) and increase in pH with autoPS was comparable to that of conventional PS, with the same alveolar ventilation and level of PS. No technical problem occurred in autoPS mode, and no NIV trial had to be discontinued because of patient discomfort. CONCLUSIONS: These results suggest that the alveolar ventilation based automatic control of PS during NIV with a bilevel device is feasible and leads to beneficial effects in patients with acute respiratory failure comparable to those of manually set PS. Further studies should now explore the potential of this system over longer periods in patients with acute and chronic respiratory failure.

Automatic adjustment of pressure support by a computer-driven knowledge-based system during noninvasive ventilation: a feasibility study.

OBJECTIVE: To evaluate the feasibility of using a knowledge-based system designed to automatically titrate pressure support (PS) to maintain the patient in a "respiratory comfort zone" during noninvasive ventilation (NIV) in patients with acute respiratory failure. DESIGN AND SETTING: Prospective crossover interventional study in an intensive care unit of a university hospital. PATIENTS: Twenty patients. INTERVENTIONS: After initial NIV setting and startup in conventional PS by the chest physiotherapist NIV was continued for 45 min with the automated PS activated. MEASUREMENTS AND RESULTS: During automated PS minute-volume was maintained constant while respiratory rate decreased significantly from its pre-NIV value (20+/-3 vs. 25+/-3 bpm). There was a trend towards a progressive lowering of dyspnea. In hypercapnic patients PaCO(2) decreased significantly from 61+/-9 to 51+/-2 mmHg, and pH increased significantly from 7.31+/-0.05 to 7.35+/-0.03. Automated PS was well tolerated. Two system malfunctions occurred prompting physiotherapist intervention. CONCLUSIONS: The results of this feasibility study suggest that the system can be used during NIV in patients with acute respiratory failure. Further studies should now determine whether it can improve patient-ventilator interaction and reduce caregiver workload.

Performance characteristics of 10 home mechanical ventilators in pressure-support mode: a comparative bench study.

OBJECTIVE: Inspiratory pressure (Pi) support delivered by a bilevel device has become the technique of choice for noninvasive home ventilation. Considerable progress has been made in the performance and functionality of these devices. The present bench study was designed to compare the various characteristics of 10 recently developed bilevel Pi devices under different conditions of respiratory mechanics. DESIGN: Bench model study. SETTING: Research laboratory, university hospital. MEASUREMENTS: Ventilators were connected to a lung model, the mechanics of which were set to normal, restrictive, and obstructive, that was driven by an ICU ventilator to mimic patient effort. Pressure support levels of 10 and 15 cm H(2)O, and maximum were tested, with "patient" inspiratory efforts of 5, 10, 15, 20, and 25 cm H(2)O. Tests were conducted in the absence and presence of leaks in the system. Trigger delay, trigger-associated inspiratory workload, pressurization capabilities, and cycling were analyzed. RESULTS: All devices had very short trigger delays and triggering workload. Pressurization capability varied widely among the machines, with some bilevel devices lagging behind when faced with a high inspiratory demand. Cycling was usually not synchronous with patient inspiratory time when the default settings were used, but was considerably improved by modifying cycling settings, when that option was available. CONCLUSIONS: A better knowledge of the technical performance of bilevel devices (ie, pressurization capabilities and cycling profile) may prove to be useful in choosing the machine that is best suited for a patient's respiratory mechanics and inspiratory demand. Clinical algorithms to help set cycling criteria for improving patient-ventilator synchrony and patient comfort should now be developed.

Helium-oxygen decreases inspiratory effort and work of breathing during pressure support in intubated patients with chronic obstructive pulmonary disease.

OBJECTIVE: To evaluate the impact of helium-oxygen (He/O2) on inspiratory effort and work of breathing (WOB) in intubated COPD patients ventilated with pressure support. DESIGN AND SETTING: Prospective crossover interventional study in the medical ICU of a university hospital. PATIENTS AND PARTICIPANTS: Ten patients. INTERVENTIONS: Sequential inhalation (30 min each) of three gas mixtures: (a) air/O2, (b) He/O2 (c) air/O2, at constant FIO2 and level of pressure support. MEASUREMENTS AND RESULTS: Inspiratory effort and WOB were determined by esophageal and gastric pressure. Throughout the study pressure support and FIO2 were 14+/-3 cmH2O and 0.33+/-0.07 respectively. Compared to Air/O2, He/O2 reduced the number of ineffective breaths (4+/-5 vs. 9+/-5 breaths/min), intrinsic PEEP (3.1+/-2 vs. 4.8+/-2 cmH2O), the magnitude of negative esophageal pressure swings (6.7+/-2 vs. 9.1+/-4.9 cmH2O), pressure-time product (42+/-37 vs. 67+/-65 cmH2O s(-1) min(-1)), and total WOB (11+/-3 vs. 18+/-10 J/min). Elastic (6+/-1 vs. 10+/-6 J/min) and resistive (5+/-1 vs. 9+/-4 J/min) components of the WOB were decreased by He/O2. CONCLUSIONS: In intubated COPD patients ventilated with pressure support He/O2 reduces intrinsic PEEP, the number of ineffective breaths, and the magnitude of inspiratory effort and WOB. He/O2 could prove useful in patients with high levels of PEEPi and WOB ventilated in pressure support, for example, during weaning.

Non-invasive ventilation in the recovery room for postoperative respiratory failure: a feasibility study.

BACKGROUND: Non-invasive ventilation (NIV) has become a standard of care in acute respiratory failure. However, little data is available on its usefulness in recovery ward patients after general surgery. The present study aimed to document the feasibility of implementing NIV in this setting, and its impact on lung function. METHODS: During a 12-month period, all adult patients who underwent elective general surgical procedures under general anaesthesia during weekdays, were transferred to the recovery ward after extubation, and those who required NIV were included in this prospective observational study. NIV was applied with a bilevel device (VPAP II ST, ResMed, North Ryde, Australia). RESULTS: 4622 patients were admitted to the recovery ward, 83 of whom needed NIV. NIV increased pH (7.38 +/- .06 vs 7.30 +/- .05), reduced PaCO2 (7.38 +/- .06 vs 7.30 +/- .05) in hypercapnic patients (44 +/- 9 vs 55 +/- 10 mm Hg), and increased PaO2 in non-hypercapnic patients (80 +/- 10 vs 70 +/- 11 mm Hg). No complications attributable to NIV occurred. Most patients improved after 1-2 NIV trials, and all were transferred to the ward the same day. CONCLUSIONS: In recovery ward patients after general surgery, NIV is seldom required. When applied, NIV seems to exert favourable effects on lung function. NIV can be safely implemented with a bilevel device in a recovery ward not accustomed to the use of ICU ventilators. The cost-effectiveness of its systematic use in this setting should be assessed.

Performance characteristics of five new anesthesia ventilators and four intensive care ventilators in pressure-support mode: a comparative bench study.

BACKGROUND: During the past few years, many manufacturers have introduced new modes of ventilation in anesthesia ventilators, especially partial-pressure modalities. The current bench test study was designed to compare triggering and pressurization of five new anesthesia ventilators with four intensive care unit ventilators. METHODS: Ventilators were connected to a two-compartment lung model. One compartment was driven by an intensive care unit ventilator to mimic "patient" inspiratory effort, whereas the other was connected to the tested ventilator. The settings of ventilators were positive end-expiratory pressures of 0 and 5 cm H2O, and pressure-support ventilation levels of 10, 15, and 20 cm H2O with normal and high "patient" inspiratory effort. For the anesthesia ventilators, all the measurements were obtained for a low (1 l/min) and a high (10 l/min) fresh gas flow. Triggering delay, triggering workload, and pressurization at 300 and 500 ms were analyzed. RESULTS: For the five tested anesthesia ventilators, the pressure-support ventilation modality functioned correctly. For inspiratory triggering, the three most recent anesthesia machines (Fabius, Drägerwerk AG, Lübeck, Germany; Primus, Drägerwerk AG; and Avance, GE-Datex-Ohemda, Munchen, Germany) had a triggering delay of less than 100 ms, which is considered clinically satisfactory and is comparable to intensive care unit machines. The use of positive end-expiratory pressure modified the quality of delivered pressure support for two anesthesia ventilators (Kion, Siemens AG, Munich, Germany; and Felix, Taema, Antony, France). Three of the five anesthesia ventilators exhibited pressure-support ventilation performance characteristics comparable to those of the intensive care unit machines. Increasing fresh gas flow (1 to 10 l/min) in the internal circuit did not influence the pressure-support ventilation performance of the anesthesia ventilators. CONCLUSION: Regarding trigger sensitivity and the system's ability to meet inspiratory flow during pressure-supported breaths, the most recent anesthesia ventilators have comparable performances of recent-generation intensive care unit ventilators.

Impact of expiratory trigger setting on delayed cycling and inspiratory muscle workload.

RATIONALE: During pressure-support ventilation, the ventilator cycles into expiration when inspiratory flow decreases to a given percentage of peak inspiratory flow ("expiratory trigger"). In obstructive disease, the slower rise and decrease of inspiratory flow entails delayed cycling, an increase in intrinsic positive end-expiratory pressure, and nontriggering breaths. OBJECTIVES: We hypothesized that setting expiratory trigger at a higher than usual percentage of peak inspiratory flow would attenuate the adverse effects of delayed cycling. METHODS: Ten intubated patients with obstructive disease undergoing pressure support were studied at expiratory trigger settings of 10, 25, 50, and 70% of peak inspiratory flow. MEASUREMENTS: Continuous recording of diaphragmatic EMG activity with surface electrodes, and esophageal and gastric pressures with a dual-balloon nasogastric tube. MAIN RESULTS: Compared with expiratory trigger 10, expiratory trigger 70 reduced the magnitude of delayed cycling (0.25 +/- 0.18 vs. 1.26 +/- 0.72 s, p < 0.05), intrinsic positive end-expiratory pressure (4.8 +/- 1.9 vs. 6.5 +/- 2.2 cm H(2)O, p < 0.05), nontriggering breaths (2 +/- 3 vs. 9 +/- 5 breaths/min, p < 0.05), and triggering pressure-time product (0.9 +/- 0.8 vs. 2.1 +/- 0.7 cm H2O . s, p < 0.05). CONCLUSIONS: Setting expiratory trigger at a higher percentage of peak inspiratory flow in patients with obstructive disease during pressure support improves patient-ventilator synchrony and reduces inspiratory muscle effort. Further studies should explore whether these effects can influence patient outcome.