Tidal volume delivery during high-frequency oscillatory ventilation in adults with acute respiratory distress syndrome

OBJECTIVE: a) Characterize how ventilator and patient variables affect tidal volume during high-frequency oscillatory ventilation; and b) measure tidal volumes in adults with acute respiratory distress syndrome during high-frequency oscillatory ventilation. DESIGN: Observational study. SETTING: Research laboratory and medical intensive care unit. PATIENTS: Test lung and patients with acute respiratory distress syndrome. INTERVENTIONS: Using a previously validated hot wire anemometer placed in series with a Sensormedics 3100B high-frequency ventilator, an endotracheal tube, and a test lung, tidal volume was measured at different combinations of frequency (4, 6, 8, 10, and 12 Hz), pressure amplitude (50, 60, 70, 80, and 90 cm H2O), mean airway pressure (20, 30, and 40 cm H2O), test lung compliance (10, 30, and 50 mL/cm H2O), endotracheal tube internal diameter (6, 7, and 8 mm), bias flow (20, 30, and 40 L/min), and inspiratory/expiratory ratio (1:2 and 1:1). In patients, tidal volume was measured at baseline ventilator settings and at baseline frequency +/-2 Hz and baseline pressure amplitude +/-10 cm H2O. MEASUREMENTS AND MAIN RESULTS: Measured tidal volumes were 23-225 mL during high-frequency oscillatory ventilation of the test lung. A 2-Hz increase in frequency and a 10-cm H2O increase in pressure amplitude caused a 21.3% +/- 4.1% decrease and 21.4% +/- 3.4% increase in tidal volume, respectively. Decreasing endotracheal tube internal diameter from 8 mm to 7 mm and from 7 mm to 6 mm caused a 15.3% +/- 1.7% and 18.9% +/- 2.1% reduction in tidal volume, respectively. Increasing bias flow from 20 L/min to 30 L/min increased tidal volume by 11.2% +/- 3.9%. Further increases in bias flow, changes in compliance, and changes in mean airway pressure had little effect. Tidal volumes measured in acute respiratory distress syndrome patients were 44-210 mL. A 2-Hz increase in frequency was associated with a 23.1% +/- 6.3% decrease in tidal volume. In contrast to the test lung data, a 10-cm H2O increase in pressure amplitude resulted in only a 5.6% +/- 4.5% increase in tidal volume. CONCLUSIONS: Tidal volumes are not uniformly small during high-frequency oscillatory ventilation. The primary determinant of tidal volume in adults with acute respiratory distress syndrome during high-frequency oscillatory ventilation with the Sensormedics 3100B is frequency. Test lung findings suggest that endotracheal tube internal diameter is also an important determinant of tidal volume.     

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

OBJECTIVE: In acute respiratory distress syndrome (ARDS), high-frequency oscillation (HFO) improves oxygenation relative to conventional mechanical ventilation (CMV). Alveolar ventilation is improved by adding tracheal gas insufflation (TGI) to CMV. We hypothesized that combined HFO and TGI (HFO-TGI) might result in improved gas exchange relative to both standard HFO and CMV according to the ARDS Network protocol. DESIGN: Prospective, randomized, crossover study. SETTING: A 30-bed university intensive care unit. PATIENTS: A total of 14 patients with early (<72 hrs in duration), severe (PaO2/FiO2 of <150 mm Hg and prerecruitment oxygenation index of 22.8 +/- 1.9 [mean +/- SEM]), primary ARDS. INTERVENTIONS: Patients were ventilated with HFO without (60 mins) and combined with TGI (6.1 +/- 0.1 L/min, 60 mins) in random order. HFO sessions were repeated in inverse order within 24 hrs. HFO sessions were preceded and followed by ARDS Network CMV. Four recruitment maneuvers were performed during the study period. During HFO sessions, mean airway pressure was set at 1 cm H2O above the point of maximal curvature of the respiratory system expiratory pressure-volume curve. MEASUREMENTS AND MAIN RESULTS: Gas exchange and hemodynamics were determined before, during, and after HFO sessions. HFO-TGI improved PaO2/FiO2 relative to HFO and CMV (174.5 +/- 10.4 vs. 136.0 +/- 10.0 and 105.0 +/- 3.7 mm Hg, respectively, p < .05 for both) and oxygenation index relative to HFO (17.1 +/- 1.3 vs. 22.3 +/- 1.7, respectively p < .05). PaO2/FiO2 returned to baseline within 3 hrs after HFO. During HFO-TGI, shunt fraction and mixed venous oxygen saturation improved relative to CMV (0.36 +/- 0.01 vs. 0.45 +/- 0.01 and 77.8% +/- 1.2% vs. 71.8% +/- 1.3%, respectively, p < .05 for both). PaCO2 and hemodynamics were unaffected by HFO sessions. Respiratory mechanics remained unchanged throughout the study period. CONCLUSIONS: In early onset, primary, severe ARDS, short-term HFO-TGI improves oxygenation relative to standard HFO and ARDS Network CMV.     

High-frequency oscillatory ventilation in adults with acute respiratory distress syndrome

The last decade has seen increased appreciation of ventilator-induced lung injury. The understanding that the process of mechanical ventilation can itself damage lungs has spurned the search for ventilation strategies that are more lung protective. High-frequency oscillatory ventilation is a mode of high-frequency ventilation that may accomplish all of the current goals of lung protection. Historically, much of the data evaluating high-frequency oscillatory ventilation came from neonatal and pediatric populations. In the past year, a number of provocative and exciting studies have been published that contribute significantly to our understanding of high-frequency oscillatory ventilation, its role in preventing and reducing ventilator-induced lung injury, and its use in the support of adult patients with lung injury. In this article, we discuss the current understanding of high-frequency oscillatory ventilation and highlight the most recent literature addressing its application in adult patients with acute respiratory distress syndrome.     

Physiological predictors of survival during high-frequency oscillatory ventilation in adults with acute respiratory distress syndrome

Introduction

Data that provide clinical criteria for the identification of patients likely to respond to high-frequency oscillatory ventilation (HFOV) are scarce. Our aim was to describe physiological predictors of survival during HFOV in adults with severe acute respiratory distress syndrome (ARDS) admitted to a respiratory failure center in the United Kingdom.

Methods

Electronic records of 102 adults treated with HFOV were reviewed retrospectively. We used logistic regression and receiving-operator characteristics curve to test associations with oxygenation and mortality.

Results

Patients had severe ARDS with a mean (SD) Murray''s score of 2.98 (0.7). Partial pressure of oxygen in arterial blood to fraction of inspired oxygen (PaO₂/FiO₂) ratio and oxygenation index improved only in survivors. The earliest time point at which the two groups differed was at three hours after commencing HFOV. An improvement of >38% in PaO₂/FiO₂ occurring at any time within the first 72 hours, was the best predictor of survival at 30 days (area under the curve (AUC) of 0.83, sensitivity 93%, specificity 78% and a positive likelihood ratio (LR) of 4.3). These patients also had a 3.5 fold greater reduction in partial pressure of carbon dioxide in arterial blood (PaCO₂). Multivariate analysis showed that HFOV was more effective in younger patients, when instituted early, and in patients with milder respiratory acidosis.

Conclusions

HFOV is effective in improving oxygenation in adults with ARDS, particularly when instituted early. Changes in PaO₂/FiO₂ during the first three hours of HFOV can identify those patients more likely to survive.     

Comparison of high-frequency jet ventilation to conventional ventilation in adults with respiratory distress syndrome

Sixteen patients with acute respiratory failure (ARF) were studied. In group I (12 patients, 15 explorations) patients were treated with continuous positive pressure ventilation (CPPV) during conventional ventilation (CV), pulmonary lesions (PL) were severe (Q_sp/Q_t=0.24–0.16 with PEEP=14±7 cm H₂O) and high-frequency jet ventilation (HFJV) was performed without spontaneous ventilation (SV). In group II (5 patients, 12 explorations) patients were treated with intermittent mandatory ventilation (IMV) during CV, PL were moderate (Q_sp/Q_t=0.13–0.05 with PEEP=8±3 cm H₂O) and HFJV was performed with SV. In both groups, frequency was 120 c/mn and I:E ratio=1:2. The cannula size, the driving pressure and the PEEP (water column) were progressively adapted to obtained the same blood gases as those observed during CV, FIO₂ being the same. Results on HFJV were compared to CV. In both groups there were no differences between PaCO₂, PaO₂, FIO₂, Q_sp/Q_t during CV and HFJV. In group I peak airway pressure (PAWP), mean artery pressure (MAP), heart rate (HR), transmural mean pulmonary and wedge pressure (MPAP_tm, PWP_tm) were not different. Mean airway pressure (MAWP), PEEP and pleural pressure (PP) were higher, cardiac index (CI) was lower. In group II, PP, CI, MAP, HR, MPAP_tm, MPWP_tm were not different. PAWP was lower, MAWP and PEEP were higher. We conclude that during HFJV it is possible to obtain the same blood gas as during CV, but HFJV without CV may not be indicated in patients with severe PL, because circulatory impairment is higher.     

Surfactant therapy in adults with acute lung injury/acute respiratory distress syndrome

PURPOSE OF REVIEW: Several phase II and phase III studies have been performed to investigate safety, efficacy and the improvement of survival due to exogenous surfactant instillation in patients with acute lung injury or acute respiratory distress syndrome. In this review we will discuss the most recent of these studies, paying particular attention to differences in the composition of the exogenous surfactant used, the diverse modes of delivery and dose of therapy and the influence of mechanical ventilation. RECENT FINDINGS: Several phase II studies performed on patients with acute lung injury or acute respiratory distress syndrome and a phase III study performed on a pediatric population have shown beneficial effects of surfactant on oxygenation and survival. No effect of exogenous surfactant has been shown on survival in phase III studies in adult patients. SUMMARY: The changes in the surfactant system of patients with acute lung injury and acute respiratory distress syndrome form the rationale for the instillation of exogenous surfactant. There is enough evidence to use surfactant instillation for pediatric patients with acute lung injury. Due to the results of the randomized controlled trials performed so far, however, exogenous surfactant is not recommended for routine use in patients with acute lung injury or acute respiratory distress syndrome. In the future, other surfactants with different compositions may show beneficial effects.     

Acute oxygenation response to inhaled nitric oxide when combined with high-frequency oscillatory ventilation in adults with acute respiratory distress syndrome

OBJECTIVE: To prospectively evaluate the oxygenation effect of inhaled nitric oxide (INO) delivered during high-frequency oscillatory ventilation in adult patients with the acute respiratory distress syndrome and oxygenation failure. DESIGN Prospective, clinical study. SETTING: Intensive care unit of a university teaching hospital. PATIENTS: A total of 23 adults (14 women, 9 men, 44.9 +/- 17.5 yrs, Acute Physiology and Chronic Health Evaluation II score of 28.6 +/- 7.1) with acute respiratory distress syndrome (lung injury score, 3.5 +/- 0.4) with Fio2 of > or = 0.6 and mean airway pressure of >or=28 cm H2O. INTERVENTIONS: INO was initiated at a dose of 5 ppm, and subsequently titrated according to a protocol, to determine the dose (5, 10, or 20 ppm) resulting in the greatest increase in Pao2/Fio2. Blood gas measurements were obtained 10-15 mins after initiation or any increase in INO dosage to assess the effect on Pao2/Fio2. MEASUREMENTS AND MAIN RESULTS: Arterial blood gases and ventilator settings were recorded at four time points: during conventional ventilation just before initiating high-frequency oscillatory ventilation, during high-frequency oscillatory ventilation just before initiating INO, after 30 mins on the optimal dose of INO, and 8-12 hrs after starting INO. Oxygenation index ([Fio2 x mean airway pressure x 100]/Pao2) and Pao2/Fio2 ratios were calculated at the same time intervals. At 30 mins after INO initiation, 83% of patients had a significant increase in blood oxygen tension, defined as > or = 20% increase in Pao2/Fio2. The mean change in Pao2/Fio2 at 30 mins was 38%. In these 19 patients, Pao2/Fio2 was highest at 20 ppm in four patients, at 10 ppm in eight patients, and at 5 ppm in seven patients. Compared with baseline measurements, Pao2/Fio2 improved significantly at both 30 mins (112 +/- 59 vs. 75 +/- 32, p=.01) and 8-12 hrs after INO initiation (146 +/- 52 vs. 75 +/- 32, p<.0001). In addition, oxygenation index was reduced at 8-12 hrs compared with baseline measurements (26 +/- 13 vs. 40 +/- 17, p=.08). CONCLUSIONS: INO delivered at doses of 5 to 20 ppm during high-frequency oscillatory ventilation increases Pao2/Fio2 and may be a safe and effective rescue therapy for patients with severe oxygenation failure.     

Comparison of prone positioning and high-frequency oscillatory ventilation in patients with acute respiratory distress syndrome

OBJECTIVE: Both prone position and high-frequency oscillatory ventilation (HFOV) have the potential to facilitate lung recruitment, and their combined use could thus be synergetic on gas exchange. Keeping the lung open could also potentially be lung protective. The aim of this study was to compare physiologic and proinflammatory effects of HFOV, prone positioning, or their combination in severe acute respiratory distress syndrome (ARDS). DESIGN:: Prospective, comparative randomized study. SETTING: A medical intensive care unit. PATIENTS: Thirty-nine ARDS patients with a Pao2/Fio2 ratio <150 mm Hg at positive end-expiratory pressure > or =5 cm H2O. INTERVENTIONS: After 12 hrs on conventional lung-protective mechanical ventilation (tidal volume 6 mL/kg of ideal body weight, plateau pressure not exceeding the upper inflection point, and a maximum of 35 cm H2O; supine-CV), 39 patients were randomized to receive one of the following 12-hr periods: conventional lung-protective mechanical ventilation in prone position (prone-CV), HFOV in supine position (supine-HFOV), or HFOV in prone position (prone-HFOV). MEASUREMENTS AND MAIN RESULTS: Prone-CV (from 138 +/- 58 mm Hg to 217 +/- 110 mm Hg, p < .0001) and prone-HFOV (from 126 +/- 40 mm Hg to 227 +/- 64 mm Hg, p < 0.0001) improved the Pao2/Fio2 ratio whereas supine-HFOV did not alter the Pao2/Fio2 ratio (from 134 +/- 57 mm Hg to 138 +/- 48 mm Hg). The oxygenation index ({mean airway pressure x Fio2 x 100}/Pao2) decreased in the prone-CV and prone-HFOV groups and was lower than in the supine-HFOV group. Interleukin-8 increased significantly in the bronchoalveolar lavage fluid (BALF) in supine-HFOV and prone-HFOV groups compared with prone-CV and supine-CV. Neutrophil counts were higher in the supine-HFOV group than in the prone-CV group. CONCLUSIONS: Although HFOV in the supine position does not improve oxygenation or lung inflammation, the prone position increases oxygenation and reduces lung inflammation in ARDS patients. Prone-HFOV produced similar improvement in oxygenation like prone-CV but was associated with higher BALF indexes of inflammation. In contrast, supine-HFOV did not improve gas exchange and was associated with enhanced lung inflammation.     

Bench-to-bedside review: High-frequency oscillatory ventilation in adults with acute respiratory distress syndrome

Mechanical ventilation is the cornerstone of therapy for patients with acute respiratory distress syndrome (ARDS). Paradoxically, mechanical ventilation can exacerbate lung damage – a phenomenon known as ventilator-induced lung injury. While new ventilation strategies have reduced the mortality rate in patients with ARDS, this mortality rate still remains high. High-frequency oscillatory ventilation (HFOV) is an unconventional form of ventilation that may improve oxygenation in patients with ARDS, while limiting further lung injury associated with high ventilatory pressures and volumes delivered during conventional ventilation. HFOV has been used for almost two decades in the neonatal population, but there is more limited experience with HFOV in the adult population. In adults, the majority of the published literature is in the form of small observational studies in which HFOV was used as 'rescue' therapy for patients with very severe ARDS who were failing conventional ventilation. Two prospective randomized controlled trials, however, while showing no mortality benefit, have suggested that HFOV, compared with conventional ventilation, is a safe and effective ventilation strategy for adults with ARDS. Several studies suggest that HFOV may improve outcomes if used early in the course of ARDS, or if used in certain populations. This review will summarize the evidence supporting the use of HFOV in adults with ARDS.     

Combined high-frequency ventilation in children with severe adult respiratory distress syndrome

Six children conventionally ventilated for acute pulmonary parenchymal failure developed severe hypoxemia (mean PaO₂ 48±7 mmHg at an FiO₂ of 0.95±0.08) persisting for more than 6 h despite a progressive increase in positive end expiratory pressure (PEEP) to 14.7±1.5 cmH₂O. Combined high-frequency jet ventilation (HFJV, mean rate 225 b/min superimposed on small tidal volume conventional ventilation) resulted in a sustained increase in PaO₂ to 93±21 mmHg,p<0.05 while peak inspiratory pressure decreased from 47±8 to 35±6 cmH₂O and positive end expiratory pressure could be reduced to 5.8±4.5 cmH₂O,p<0.05 and FiO₂ to 0.88±0.10. This improvement occurred without new barotrauma nor deleterious effects on hemodynamic function or diuresis. After a mean of 62 h of combined HFJV, persistant improvement in gas exchange allowed us to resume conventional mechanical ventilation at lower airway pressures in 4 children who continued to improve and survived. The 2 other children maintained satisfactory gas exchange on combined HFJV, but ultimately died from multiple organ failure. We conclude that combined HFJV might prove helpful to relieve profound hypoxemia and possibly decrease the risk of barotrauma in children with catastrophic pulmonary failure.This study was presented in part at the Annual Meeting of the Swiss Society of Intensive Care Medicine, Basel, Switzerland, October 1989.     

Prospective, randomized, controlled clinical trial comparing traditional versus reduced tidal volume ventilation in acute respiratory distress syndrome patients.

OBJECTIVE: To assess the safety and potential efficacy of a mechanical ventilation strategy designed to reduce stretch-induced lung injury in acute respiratory distress syndrome. DESIGN: Prospective, randomized, controlled clinical trial. SETTING: Eight intensive care units in four teaching hospitals. PATIENTS: Fifty-two patients with acute respiratory distress syndrome. INTERVENTIONS: Traditional tidal volume patients: tidal volume 10-12 mL/kg ideal body weight, reduced if inspiratory plateau pressure was > 55 cm H2O (7.3 kPa). Small tidal volume patients: tidal volume 5-8 mL/kg ideal body weight, to keep plateau pressure < 30 cm H2O (4.0 kPa). MEASUREMENTS AND MAIN RESULTS: Mean tidal volumes during the first 5 days in traditional and small tidal volume patients were 10.2 and 7.3 mL/kg, respectively (p < .001), with mean plateau pressure = 30.6 and 24.9 cm H2O (3.3 kPa), respectively (p < .001). There were no significant differences in requirements for positive end-expiratory pressure or FIO2, fluid intakes/outputs, requirements for vasopressors, sedatives, or neuromuscular blocking agents, percentage of patients that achieved unassisted breathing, ventilator days, or mortality. CONCLUSIONS: The reduced tidal volume strategy used in this study was safe. Failure to observe beneficial effects of small tidal volume ventilation treatment in important clinical outcome variables may have occurred because a) the sample size was too small to discern small treatment effects; b) the differences in tidal volumes and plateau pressures were modest; or c) reduced tidal volume ventilation is not beneficial.     

俯卧位对急性肺损伤患者作用效果临床随机对照试验的Meta分析

目的 采用Meta分析方法综合评价俯卧位与仰卧位对急性肺损伤或急性呼吸窘迫综合征患者(ALI或ARDS)的作用效果.方法 制定原始文献的纳入标准、排除标准及检索策略,检索多个中英文文摘型数据库及全文数据库,获得俯卧位辅助治疗AU或ARDS的临床随机对照试验(RCT),进行文献质量评价后,采用RevMan 4.2软件进行数据分析.结果 共纳入4篇RCT研究,Meta分析结果显示,俯卧位较仰卧位具有较好的改善氧舍指数(PaO2与FiO2)的作用,但在提高PaO2、降低二氧化碳分压(Pa-CO2)和病死率方面无统计学意义;除俯卧位压疮的发生率较高以外,两种体位在其他并发症方面无统计学意义.结论 俯卧位具有改善AU或ARDS患者PaO2与FiO2的作用,但对其他呼吸参数的改善情况,并发症情况及降低病死率方面的效果还需要大样本多中心RCT研究进一步验证.     

Pediatric acute respiratory distress syndrome

The data available to guide clinical management of acute lung injury and acute respiratory distress syndrome are much more limited for infants and children than for adult patients. This paper reviews the available medical data and the pertinent physiology on the management of pediatric patients with acute lung injury. With the collaboration of multicenter investigation networks, definitive pediatric data may be on the horizon to better guide our clinical practice.     

The acute respiratory distress syndrome

The acute respiratory distress syndrome (ARDS) is an important cause of acute respiratory failure that is often associated with multiple organ failure. Several clinical disorders can precipitate ARDS, including pneumonia, sepsis, aspiration of gastric contents, and major trauma. Physiologically, ARDS is characterized by increased permeability pulmonary edema, severe arterial hypoxemia, and impaired carbon dioxide excretion. Based on both experimental and clinical studies, progress has been made in understanding the mechanisms responsible for the pathogenesis and the resolution of lung injury, including the contribution of environmental and genetic factors. Improved survival has been achieved with the use of lung-protective ventilation. Future progress will depend on developing novel therapeutics that can facilitate and enhance lung repair.