Is high frequency oscillation the best lung protective ventilatory approach for ARDS?
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High-Frequency Ventilation↗
Biomedical subjects
Robert M Kacmarek
Publications and source records attributed to Robert M Kacmarek.
In vitro evaluation of aerosol bronchodilator delivery during mechanical ventilation: pressure-control vs. volume control ventilation.
OBJECTIVE: To determine the effect of inspiratory time and inspiratory flow pattern on albuterol delivery by aerosol during mechanical ventilation. DESIGN: A ventilator was connected to a lung model and set to deliver a tidal volume of 0.6 l, PEEP 5 cmH(2)O, and respiratory rate of 15/min. We evaluated inspiratory times of 1 and 2 s, lung mechanics of 0.05 l/cmH(2)O compliance and 50 cmH(2)O/l/s resistance, or 0.02 l/cmH(2)O compliance and 5 cmH(2)O/l/s resistance, and three inspiratory flow patterns (constant flow volume-controlled ventilation, descending ramp flow volume-controlled ventilation, and pressure-controlled ventilation). Albuterol was delivered into the ventilator circuit by a nebulizer containing 5 mg (4 ml) albuterol or a pMDI and spacer (four actuations; 360 micro g). A filter between the Y-piece and the lung model collected the aerosol, which was analyzed for albuterol by spectrophotometry. RESULTS: For the nebulizer there were significant differences in albuterol delivered for inspiratory time, flow pattern, and lung mechanics. For the pMDI there were no significant differences for the amount of albuterol delivered for inspiratory time, flow pattern, or lung mechanics. CONCLUSIONS: Albuterol delivery by nebulizer is affected by inspiratory time and inspiratory flow pattern. When a pMDI is used, the amount of albuterol delivered is not affected by inspiratory flow pattern or inspiratory time.
Aerosols↗
Determinants of tidal volume during high-frequency oscillation.
OBJECTIVE: High-frequency oscillation has been proposed for use in adult acute respiratory distress syndrome. However, limited data are available on the effect of pressure amplitude and rate (Hz) on tidal volumes delivered during high-frequency oscillation in adults. DESIGN: Prospective, animal model, lung injury study. SETTING: Large-animal laboratory of a university-affiliated medical center. SUBJECTS: Nine sheep (29.2 +/- 2.4 kg). INTERVENTIONS: Severe lung injury was induced by repeated saline lung lavage. After stabilization, high-frequency oscillation was initiated at a mean airway pressure equal to the point of maximum curvature on the deflation limb of the pressure-volume curve (26 +/- 1.9 cm H2O). Tidal volume at all combinations of rates of 4, 6, 8, and 10 Hz, pressure amplitudes of 30, 40, 50, and 60 cm H2O, and inspiratory/expiratory ratios of 1:1 and 1:2 (using the Sensormedics 3100B oscillator) were measured. Flow was measured by a pneumotachometer, amplified and digitized at 1000 Hz. Three breaths were analyzed at each setting. MEASUREMENTS AND MAIN RESULTS: At both inspiratory/expiratory ratios, tidal volume was directly proportional to pressure amplitude and inversely proportional to frequency. During an inspiratory/expiratory ratio of 1:1, at 60 cm H2O pressure amplitude and 4 Hz, a tidal volume of 129.1 +/- 34.8 mL (4.4 +/- 1.2 mL/kg) was delivered. CONCLUSIONS: At low rates and high-pressure amplitudes in this model, tidal volumes approaching conventional mechanical ventilation can be delivered during high-frequency oscillation.
Analysis of Variance↗
Position of exhalation port and mask design affect CO2 rebreathing during noninvasive positive pressure ventilation.
OBJECTIVE: Noninvasive positive pressure ventilation may be considered a first line intervention to treat patients with hypercapnic respiratory failure. However, CO2 rebreathing from the ventilator circuit or mask may impair CO2 elimination and load the ventilatory muscles. This study was conducted to evaluate the effect of exhalation port location and mask design on CO2 rebreathing during noninvasive positive pressure ventilation. DESIGN: Lung model evaluation. SETTING: Experimental laboratory of a large university-affiliated hospital. SUBJECTS: A dual-chamber test lung was used to simulate the ventilatory mechanics of a patient with obstructive lung disease. INTERVENTION: Hypercapnic respiratory failure (end-tidal CO2 of 75 mm Hg) and obstructive lung disease were simulated in a double-chamber lung model. A facial mask (inner volume of 165 mL) with exhalation port within the mask (Facial-MEP) or the same mask with exhalation port in the ventilator circuit (Facial-WS) and a total face mask with exhalation port within the mask (inner volume 875 mL, Total Face) were tested during continuous positive airway pressure and pressure support ventilation provided by a single-limb circuit ventilator at the same frequency and tidal volume. MEASUREMENTS AND MAIN RESULTS: A capnometer and a flow transducer were placed in the lung model upper airway to measure the volume of CO2 rebreathed and tidal volume (Vt). The inspiratory load was estimated from the pressure variation in the lung model driving chamber (PDR). Volume of CO2 rebreathed was smaller during Facial-MEP compared with the other masks in all tested conditions (p <.001). The Vt and PDR necessary to decrease end-tidal CO2 20% (from 75 to 60 mm Hg) was different among the tested masks (Facial-MEP, Vt 701 +/- 9 mL, PDR 8.1 +/- 0.1 cm H2O/sec; Facial-WS, Vt 745 +/- 9 mL, PDR 10.2 +/- 0.1 cm H2O/sec; Total Face, Vt 790 +/- 12 mL, PDR 11.4 +/- 0.2 cm H2O/sec, p <.001). CONCLUSION: Facial-MEP with its exhalation port within the mask and the smallest mask volume demonstrated less rebreathed CO2 and a lower PDR than either the Facial-WS or Total Face masks. Additional studies are necessary to confirm if mask design can clinically affect patient's inspiratory effort during noninvasive positive pressure ventilation.
Carbon Dioxide↗
Pro/con clinical debate: is high-frequency oscillatory ventilation useful in the management of adult patients with respiratory failure?
In neonatal and pediatric intensive care units, high-frequency oscillatory ventilation (HFOV) has become an increasingly common therapy. This may not have been the case if researchers had not persisted in investigating the therapy after early disappointing clinical trials. Devices capable of providing this therapy to adults have become commercially available relatively recently. However, there are many questions that need to be answered regarding HFOV in adults: Is HFOV in adults superior to conventional mechanical ventilation? Who is the ideal candidate for HFOV? When should it be applied? What is the best technique with which to apply it? When should a patient on HFOV be converted back to conventional ventilation? What is the safety and efficacy of the device? As outlined in the following debate, there are several compelling arguments for and against the use of HFOV at this point in adults.
Clinical Trials as Topic↗
Liquid ventilation.
In laboratory models, PLV is clearly more effective than conventional ventilation alone; however, this advantage has not been observed in any human study. The reasons for this are unclear, but the approach to ventilation during PLV may have been inappropriate. HFO may require further study or perhaps PLV should be combined with nitric oxide or some other vasoactive agent. Additionally, perfluorocarbons may need to be aerosolized instead of instilled. Kandler et al. recently demonstrated better gas exchange that was sustained for a longer period in lavage-injured piglets when a perfluorocarbon was aerosolized. This preliminary result demonstrates that there are other options for the delivery of perfluorocarbons in the management of critically ill patients. Based on the failure of the two trials in adult ARDS patients, however, a long time may pass before another human PLV trial is undertaken.
Animals↗
Continuous positive airway pressure in new-generation mechanical ventilators: a lung model study.
BACKGROUND: A number of new microprocessor-controlled mechanical ventilators have become available over the last few years. However, the ability of these ventilators to provide continuous positive airway pressure without imposing or performing work has never been evaluated. METHODS: In a spontaneously breathing lung model, the authors evaluated the Bear 1000, Drager Evita 4, Hamilton Galileo, Nellcor-Puritan-Bennett 740 and 840, Siemens Servo 300A, and Bird Products Tbird AVS at 10 cm H(2)O continuous positive airway pressure. Lung model compliance was 50 ml/cm H(2)O with a resistance of 8.2 cm H(2)O x l(-1) x s(-1), and inspiratory time was set at 1.0 s with peak inspiratory flows of 40, 60, and 80 l/min. In ventilators with both pressure and flow triggering, the response of each was evaluated. RESULTS: With all ventilators, peak inspiratory flow, lung model tidal volume, and range of pressure change (below baseline to above baseline) increased as peak flow increased. Inspiratory trigger delay time, inspiratory cycle delay time, expiratory pressure time product, and total area of pressure change were not affected by peak flow, whereas pressure change to trigger inspiration, inspiratory pressure time product, and trigger pressure time product were affected by peak flow on some ventilators. There were significant differences among ventilators on all variables evaluated, but there was little difference between pressure and flow triggering in most variables on individual ventilators except for pressure to trigger. Pressure to trigger was 3.74 +/- 1.89 cm H(2)O (mean +/- SD) in flow triggering and 4.48 +/- 1.67 cm H(2)O in pressure triggering (P < 0.01) across all ventilators. CONCLUSIONS: Most ventilators evaluated only imposed a small effort to trigger, but most also provided low-level pressure support and imposed an expiratory workload. Pressure triggering during continuous positive airway pressure does require a slightly greater pressure than flow triggering.
Humans↗
Set positive end-expiratory pressure during protective ventilation affects lung injury.
BACKGROUND: The most appropriate method of determining positive end-expiratory pressure (PEEP) level during a lung protective ventilatory strategy has not been established. METHODS: In a lavage-injured sheep acute respiratory distress syndrome model, the authors compared the effects of three approaches to determining PEEP level after a recruitment maneuver: (1) 2 cm H(2)O above the lower inflection point on the inflation pressure-volume curve, (2) at the point of maximum curvature on the deflation pressure-volume curve, and (3) at the PEEP level that maintained target arterial oxygen partial pressure at a fraction of inspired oxygen of 0.5. RESULTS: Positive end-expiratory pressure set 2 cm H(2)O above the lower inflection point resulted in the least injury over the course of the study. PEEP based on adequate arterial oxygen partial pressure/fraction of inspired oxygen ratios had to be increased over time and resulted in higher mRNA levels for interleukin-8 and interleukin-1beta and greater tissue inflammation when compared with the other approaches. PEEP at the point of maximum curvature could not maintain eucapneia even at an increased ventilatory rate. CONCLUSION: Although generating higher plateau pressures, PEEP levels based on pressure-volume curve analysis were more effective in maintaining gas exchange and minimizing injury than PEEP based on adequate oxygenation. PEEP at 2 cm H(2)O above the lower inflection point was most effective.
Air Pressure↗
In vitro evaluation of aerosol bronchodilator delivery during noninvasive positive pressure ventilation: effect of ventilator settings and nebulizer position.
OBJECTIVE: Respiratory failure due to exacerbation of obstructive lung disease has been successfully treated with noninvasive positive pressure ventilation (NPPV). However, there have been no reports of factors affecting aerosol delivery during NPPV. Our objective was to determine the effect of ventilator settings and nebulizer position on albuterol delivery during NPPV. DESIGN: Bench model study. SETTING: University laboratory. SUBJECTS: None. INTERVENTIONS: A Respironics BiPAP S/T-D30 with a standard circuit was attached to a lung model simulating spontaneous breathing. Inspiratory/expiratory pressures of 10/5, 15/5, 20/5, 15/10, 20/10, and 25/10 cm H2O were tested at respiratory rates of 10 and 20/min. A nebulizer was filled with 5 mg of albuterol in 4 mL of solution, driven with 8 L/min oxygen, and placed at either a proximal (ventilator outlet) or distal (between leak port and lung model connection) position. Albuterol delivery was estimated by measuring the amount of the albuterol collected on a filter placed at the inlet of the lung model. MEASUREMENT AND MAIN RESULTS: Albuterol delivery varied from 5.2 +/- 0.4% to 24.5 +/- 1.3% of the nominal dose and was significantly affected by the position of the nebulizer, respiratory rate, and BiPAP settings (p <.001 in each case). The greatest albuterol delivery was observed with the nebulizer operating at the distal position and a respiratory rate of 20/min. At this respiratory rate and nebulizer placement, albuterol delivery increased with increasing inspiratory pressure levels and decreased as expiratory pressure levels were increased. Nebulizer flow did not affect function of the ventilator. CONCLUSIONS: At optimum nebulizer position (between the leak port and patient connection) and ventilator settings (high inspiratory pressure and low expiratory pressure), as much as 25% of the nominal albuterol dose may be delivered during NPPV.
Aerosols↗
Ventilatory adjuncts.
A number of adjuncts to mechanical ventilation have been the focus of recent research. Automatic tube compensation (the regulation of airway pressure by estimation of tracheal pressure) appears to be an ideal approach to unloading the resistive effort imposed by the endotracheal tube. Randomized controlled trials have recently been performed with high frequency oscillation (HFO), partial liquid ventilation (PLV), and prone positioning. Unfortunately, all of those trials were negative; however, it appears the only technique that will be abandoned for the near future is PLV. The HFO trial trended toward benefit with HFO, and one must question the protocol used in the prone positioning trial. With both HFO and prone positioning we will have to wait for additional randomized clinical trials before the status of those techniques can be determined. No randomized trials of tracheal gas insufflation have been performed. Of major concern with tracheal gas insufflation is the lack of a commercial product.
High-Frequency Ventilation↗