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.     

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.     

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.     

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.     

High-frequency oscillatory ventilation in adult acute respiratory distress syndrome

Objective This study examined whether ARDS patients in whom predefined ventilator settings fail to maintain oxygenation and CO₂ removal can be safely transitioned to high-frequency oscillatory ventilation (HFOV), and whether HFOV use is efficacious.Design and setting Prospective observational study in the 14-bed intensive care unit of a university hospital.Patients and participants 42 patients with ARDS (APACHE II score 28 (IQR 24–37) and ventilation time prior HFOV 3.0 days (0.7–9.1).Measurements and results Gas exchange parameters and ventilator data were recorded before and during HFOV treatment (–12 h, –6 h, baseline, 10 min, 1 h, 6 h, 12 h, 24 h). Primary endpoints included: (a) P_aO₂/FIO₂ ratio 24 h after start of HFOV treatment or the last point of measurement if HFOV ended within the first 24 h; (b) HFOV-related complications. Post hoc analysis assessed the relationship between outcome and the response to HFOV, and between outcome and time of mechanical ventilation prior to HFOV. At baseline the median P_aO₂/FIO₂ ratio was 95 (IQR 62–129); after 24 h of HFOV the P_aO₂/FIO₂ ratio had increased significantly to 165 (88–225); only one patient developed a unilateral pneumothorax. Of the 42 patients 18 (43%) had died by day 30. Subset analyses showed a significantly higher 30-day mortality rate in patients with at least 3 days of mechanical ventilation prior to HFOV (64%) and in patients without oxygenation improvement after 24 h on HFOV (71%).Conclusions HFOV is an effective and safe method to ventilate ARDS patients. Failure to improve oxygenation within 24 h of HFOV is associated with high mortality.An editorial regarding this article can be found in the same issue     

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.     

Lung collapse during low tidal volume ventilation in acute respiratory distress syndrome

BACKGROUND: Current ventilator management for acute respiratory distress syndrome (ARDS) incorporates low tidal volume (V(T)) ventilation in order to limit ventilator-induced lung injury. Low V(T) ventilation in supine patients, without the use of intermittent hyperinflations, may cause small airway closure, progressive atelectasis, and secretion retention. Use of high positive end-expiratory pressure (PEEP) levels with low V(T) ventilation may not counter this effect, because regional differences in intra-abdominal hydrostatic pressure may diminish the volume-stabilizing effects of PEEP. CASE SUMMARY: A 35-year-old man with abdominal compartment syndrome (intra-abdominal pressure > 48 cm H2O developed ARDS and was treated with V(T) of 4.5 mL/kg and PEEP of 20 cm H2O. Despite aggressive fluid therapy, appropriate airway humidification and tracheal suctioning, the patient developed complete bronchial obstruction, involving the entire right lung and left upper lobe. After bronchoscopy the patient was placed on a higher V(T) (7.0 mL/kg). Intermittent PEEP was instituted at 30 cm H2O for 2 breaths every 3 minutes. This intermittently raised the end-inspiratory plateau pressure from 38 cm H2O to 50 cm H2O. With the same airway humidity and tracheal suctioning practices bronchial obstruction did not reoccur. CONCLUSION: Low V(T) ventilation in ARDS may increase the risk of small airway closure and retained secretions. This adverse effect highlights the importance of pulmonary hygiene measures in ARDS during lung-protective ventilation.     

Nitric oxide delivery during high-frequency oscillatory ventilation

BACKGROUND: Inhaled nitric oxide (NO) is used increasingly in the care of infants with hypoxemic respiratory failure and is frequently combined with high-frequency oscillation (HFO). The aim of this study was to evaluate delivery of NO during HFO using titration into the ventilator circuit or using the INOvent Delivery System. METHODS. NO was delivered into the HFO circuit at three sites (pre-humidifier, post-humidifier, and after the bellows) by continuous titration using a rotameter. The target NO concentration ([NO]) was initially adjusted using a rapid-response chemiluminescence NO analyzer without oscillation at 5, 10, and 20 parts per million (ppm). During the study, gas was sampled 5 cm from the bellows (proximal), 35 cm from the bellows (middle), and at the distal end of the circuit (distal). The ventilator was set at frequencies of 5, 10, and 15 Hz, mean airway pressures of 15, 20, and 25 cm H(2)O, and amplitudes of 20, 30, and 40 cm H(2)O. Soft and hard circuits were evaluated. The fraction of inspired oxygen was 0. 90, the inspiratory time fraction was 33%, and the bias flow was 20 L/min throughout the study. An INOvent Delivery System was also evaluated with the same HFO settings. RESULTS. The fluctuation of [NO] was minimal with continuous titration pre-humidifier at all HFO settings. [NO] fluctuated with titration post-humidifier and after the bellows, especially at the proximal sampling site. At the lung model, however, fluctuation of [NO] was always < 1.5 ppm and usually < 1 ppm. Delivered [NO] was lower than target [NO] with injection after the bellows (> 5%). The soft circuit showed better mixing of NO than the hard circuit. The INOvent Delivery System delivered a stable and accurate [NO] at all settings. [NO(2)] was < 1 ppm at all settings. CONCLUSIONS. Mixing of NO during HFO was acceptable at all the injection sites evaluated, although injection pre-humidifier was preferable because of small fluctuations of [NO]. The INOvent Delivery System was simple to use and delivered an accurate and precise [NO] during HFO.     

Efficacy and adverse events of high-frequency oscillatory ventilation in adult patients with acute respiratory distress syndrome: a meta-analysis

Introduction

Theoretically, high-frequency oscillatory ventilation (HFOV) achieves all goals of a lung-protective ventilatory mode and seems ideal for the treatment of adult patients with acute respiratory distress syndrome (ARDS). However, its effects on mortality and adverse clinical outcomes remain uncertain given the paucity of high-quality studies in this area. This meta-analysis was performed to evaluate the efficacy and adverse events of HFOV in adults with ARDS.

Methods

We searched PubMed, EMBASE and Cochrane Central Register of Controlled Trials through February 2014 to retrieve randomized controlled trials of HFOV in adult ARDS patients. Two independent reviewers extracted data on study methods, clinical and physiological outcomes and adverse events. The primary outcome was 30-day or hospital mortality. Risk of bias was evaluated with the Cochrane Collaboration’s tool. Mortality, oxygenation and adverse effects of HFOV were compared to those of conventional mechanical ventilation. A random-effects model was applied for meta-analysis.

Results

A total of five trials randomly assigning 1,580 patients met inclusion criteria. Pooled data showed that HFOV significantly improved oxygenation on day one of therapy (four studies; 24% higher; 95% confidence interval (CI) 11 to 40%; P <0.01). However, HFOV did not reduce mortality risk (five studies; risk ratio (RR) 1.04; 95% CI 0.83 to 1.31; P = 0.71) and two early terminated studies suggested a harmful effect of HFOV in ARDS (two studies; RR 1.33; 95% CI 1.09 to 1.62; P <0.01). Safety profiles showed that HFOV was associated with a trend toward increased risk of barotrauma (five studies; RR 1.19; 95% CI 0.83 to 1.72; P = 0.34) and unfavorable hemodynamics (five studies; RR 1.16; 95% CI 0.97 to 1.39; P = 0.12).

Conclusions

HFOV improved oxygenation in adult patients with ARDS; however, it did not confer a survival benefit and might cause harm in the era of lung-protective ventilation strategy. The evidence suggests that HFOV should not be a routine practice in ARDS and further studies specifically selecting patients for this ventilator mode should be pursued.     

Prospective trial of high-frequency oscillation in adults with acute respiratory distress syndrome.

OBJECTIVE: To evaluate the safety and efficacy of high-frequency oscillatory ventilation (HFOV) in adult patients with the acute respiratory distress syndrome (ARDS) and oxygenation failure. DESIGN: Prospective, clinical study. SETTING: Intensive care and burn units of two university teaching hospitals. PATIENTS: Twenty-four adults (10 females, 14 males, aged 48.5 +/- 15.2 yrs, Acute Physiology and Chronic Health Evaluation II score 21.5 +/- 6.9) with ARDS (lung injury score 3.4 +/- 0.6, Pao2/Fio2 98.8 +/- 39.0 mm Hg, and oxygenation index 32.5 +/- 19.6) who met one of the following criteria: Pao2 < or =65 mm Hg with Fio2 > or =0.6, or plateau pressure > or =35 cm H2O. INTERVENTIONS: HFOV was initiated in patients with ARDS after varying periods of conventional ventilation (CV). Mean airway pressure (Paw) was initially set 5 cm H2O greater than Paw during CV, and was subsequently titrated to maintain oxygen saturation between 88% and 93% and Fio2 < or =0.60. MEASUREMENTS AND MAIN RESULTS: Fio2, Paw, pressure amplitude of oscillation, frequency, blood pressure, heart rate, and arterial blood gases were monitored during the transition from CV to HFOV, and every 8 hrs thereafter for 72 hrs. In 16 patients who had pulmonary artery catheters in place, cardiac hemodynamics were recorded at the same time intervals. Throughout the HFOV trial, Paw was significantly higher than that applied during CV. Within 8 hrs of HFOV application, and for the duration of the trial, Fio2 and Paco2 were lower, and Pao2/Fio2 was higher than baseline values during CV. Significant changes in hemodynamic variables following HFOV initiation included an increase in pulmonary artery occlusion pressure (at 8 and 40 hrs) and central venous pressure (at 16 and 40 hrs), and a reduction in cardiac output throughout the course of the study. There were no significant changes in systemic or pulmonary pressure associated with initiation and maintenance of HFOV. Complications occurring during HFOV included pneumothorax in two patients and desiccation of secretions in one patient. Survival at 30 days was 33%, with survivors having been mechanically ventilated for fewer days before institution of HFOV compared with nonsurvivors (1.6 +/- 1.2 vs. 7.8 +/- 5.8 days; p =.001). CONCLUSIONS: These findings suggest that HFOV has beneficial effects on oxygenation and ventilation, and may be a safe and effective rescue therapy for patients with severe oxygenation failure. In addition, early institution of HFOV may be advantageous.     

高频振荡通气在成人急性呼吸窘迫综合征中的应用进展

随着对急性呼吸窘迫综合征机械通气过程中呼吸机相关性肺损伤的理解加深,高频振荡通气被认为是一种理想的通气支持策略。高频振荡通气仍有多点不足,在成人急性呼吸窘迫综合征的临床应用中仍存在较大争议,尤其是最近两项大型多中心随机对照研究的结果令人失望。关于高频振荡通气机制、技术、通气策略,监测体系需要进一步探索。     

Survival of a 300-g infant ventilated by high-frequency oscillatory ventilation for respiratory distress syndrome

We report a case of an infant delivered before the completion of 26 wks' gestation, weighing 300 g at birth, and treated with high-frequency oscillatory ventilation for respiratory distress syndrome. Her neurologic examination at 18 months of age is compatible with mild delay in gross and fine motor skills.