New therapies for adults with acute lung injury. High-frequency oscillatory ventilation

High-Frequency Oscillatory Ventilation in Adults With ARDS: Past, Present, and Future

High-frequency oscillatory ventilation (HFOV) is a unique mode of mechanical ventilation that uses nonconventional gas exchange mechanisms to deliver ventilation at very low tidal volumes and high frequencies. The properties of HFOV make it a potentially ideal mode to prevent ventilator-induced lung injury in patients with ARDS. Despite a compelling physiological basis and promising experimental data, large randomized controlled trials have not detected an improvement in survival with the use of HFOV, and its use as an early lung-protective strategy in patients with ARDS may be harmful. Nevertheless, HFOV still has an important potential role in the management of refractory hypoxemia. Careful attention should be paid to right ventricular function and lung stress when applying HFOV. This review discusses the physiological principles, clinical evidence, practical applications, and future prospects for the use of HFOV in patients with ARDS.

Lessons learned from airway pressure release ventilation

BACKGROUND

The aim of this article is to review a single institution's experience with airway pressure release ventilation (APRV) with respect to safety, complications, and efficacy at correcting hypercarbia and hypoxemia.

METHODS

Patients transitioned from either volume- or pressure-targeted ventilation to APRV in a university hospital surgical intensive care unit were retrospectively reviewed. Patients whose ventilator strategy started with APRV were excluded. Abstracted data included age, sex, diagnosis, ventilation parameters, indication for altering the ventilator strategy, laboratory values, and ventilator-associated complications. Data before and after transitioning to APRV were compared using a two-tailed unpaired t test or χ2 test as appropriate; significance assumed for p ≤ 0.05.

RESULTS

Patient mix (n = 38) was 43% trauma, 32% sepsis, 8% cardiac surgery, 12% vascular surgery, and 5% other. Transitioning to APRV was undertaken most often for hypoxemia (88%) and less frequently for hypercarbia (12%). The mean time to correct hypoxemia (SA(O2) >92%) was 7 minutes ± 4 minutes, while the mean time to correct P(CO2) (P(CO2) ≤40 mm Hg) was 42 minutes ± 7 minutes. The mean time to maximal CO2 clearance was 66 minutes ± 12 minutes. The mean minute ventilation decreased on APRV by 3.3 L/min ± 0.9 L/min but achieved superior CO2 clearance and oxygenation. The mean time to FIO2 ≤0.6 was 5.2 hours ± 0.9 hours. Four of the 38 patients developed a pneumothorax. Ninety-seven percent of patients on APRV who were transported out of the intensive care unit using bag-valve ventilation (with appropriate positive end-expiratory pressure valve settings) with P(high) ≥20 cm H2O developed hypoxemia within 5 minutes. Hundred percent of patients with a P(high) ≤20 cm H2O were safely hand ventilated during transport without developing hypoxemia.

CONCLUSIONS

APRV is a safe mode of ventilation for hypoxemic or hypercarbic respiratory failure. Improvements in PO2 and PCO2 are achieved at lower minute ventilations than with volume- or pressure-targeted modes.

LEVEL OF EVIDENCE

III.

High-frequency oscillatory ventilation in ALI/ARDS

In the last 2 decades, our goals for mechanical ventilatory support in patients with acute respiratory distress syndrome (ARDS) or acute lung injury (ALI) have changed dramatically. Several randomized controlled trials have built on a substantial body of preclinical work to demonstrate that the way in which we employ mechanical ventilation has an impact on important patient outcomes. Avoiding ventilator-induced lung injury (VILI) is now a major focus when clinicians are considering which ventilatory strategy to employ in patients with ALI/ARDS. Physicians are searching for methods that may further limit VILI, while still achieving adequate gas exchange.

Anesthesia for patients requiring advanced ventilatory support

The critically ill patient who requires anesthesia is frequently a concern for the anesthesiologist. In addition to having potential hemodynamic lability and coagulopathy, the critically ill patient frequently experiences profound respiratory failure. The approach to the patient requiring advanced ventilatory support requires an understanding of respiratory failure, the pathophysiology causing respiratory failure and hypoxia, the physiology of mechanical ventilation and the advanced modes of ventilation available in the intensive care unit (ICU). This article discusses the basic definitions of hypoxia and common pathologic states, reviews the physiology of mechanical ventilation and advanced forms of ventilation available in the ICU, and concludes with recommendations for the management of patients with severe respiratory failure when they are taken to the operating room.

Clinical application of ventilator modes: Ventilatory strategies for lung protection

INTRODUCTION

Identification of the mortality reducing effect of lung protective ventilation using low tidal volumes and pressure limitation is one of the biggest advances in the application of mechanical ventilation. Yet studies continue to demonstrate low adoption of this style of ventilation. Critical care nurses in Australia and New Zealand have a high level of responsibility and autonomy for mechanical ventilation and weaning practices and therefore require in-depth knowledge of ventilator technology, its clinical application and the current evidence for effective ventilation strategies.

AIM

To present an overview of current knowledge and research relating to lung protective ventilation.

METHOD

A multidatabase literature search using the terms protective ventilation, open lung, high frequency oscillatory ventilation, airway pressure release ventilation, and weaning.

RESULTS

Based on clinical trials and physiological evidence lung protective strategies using low tidal volumes and moderate levels of PEEP have been recommended as strategies to prevent tidal alveolar collapse and overdistension in patients with ALI/ARDS. Evidence now suggests these strategies may also be beneficial in patients with normal lungs. Lung protective ventilation may be applied with either volume or pressure-controlled ventilation. Pressure-controlled ventilation allows regulation over injurious peak inspiratory pressures; however no study has identified the superiority of pressure-controlled ventilation over low tidal volume strategies using volume-control. Other lung protective ventilation strategies include moderate to high positive-end expiratory pressure, recruitment manoeuvres, high frequency oscillatory ventilation, and airway pressure release ventilation though definitive trials identifying consistently improved patient outcomes are still needed. No ventilation strategy can be more lung protective than the timely discontinuation of mechanical ventilation. Despite the above recommendations, evidence suggests the decision to commence weaning and attempt extubation continue to be delayed. Critical care nurses play a vital role in the recognition of patients capable of spontaneous breathing and ready for extubation. Organisational interventions such as weaning protocols as well as computerised weaning systems may have less effect when nurses are able to manage weaning processes effectively.

CONCLUSIONS

Lung protective ventilatory strategies are not consistently applied and weaning and extubation continue to be delayed. Critical care nurses need to establish a strong knowledge base to promote effective and appropriate management of patients requiring mechanical ventilation.

What's new in critical care of the burn-injured patient?

The number of cases of mortality after burn injury continues to decline, in part because of advances in respiratory, fluid, and sepsis management. However, care needs to be exercised in the application of these new techniques and technologies, many of which have never been assessed or have been incompletely studied in patients who have burn injury. Use of any of these advances in critical care needs to be individualized for any given patient and altered based on the patient's response to therapy. Future advances in the critical care of burns will require multicenter prospective trials at dedicated burn centers to define the optimal therapy for the patient who has burn injury.

High-frequency oscillatory ventilation in adults: clinical considerations and management priorities

Recently, there has been renewed interest in high-frequency oscillatory ventilation (HFOV) as a lung-protective strategy in adults. It limits overdistension and prevents cyclic collapse by maintaining end-expiratory lung volume. Studies have shown that HFOV is safely tolerated in the adult population and may offer more benefit if applied early in the course of disease. These findings have implications for clinicians as the use of HFOV may increase in the coming decade. Gas transport mechanisms, ventilator settings, patient monitoring, and clinical considerations for HFOV are substantially different from conventional mechanical ventilation. This article reviews management strategies and monitoring priorities currently recommended for management of adults receiving HFOV.

Mechanical ventilation in ARDS: a state-of-the-art review

Mechanical ventilation is an essential component of the care of patients with ARDS, and a large number of randomized controlled clinical trials have now been conducted evaluating the efficacy and safety of various methods of mechanical ventilation for the treatment of ARDS. Low tidal volume ventilation (</= 6 mL/kg predicted body weight) should be utilized in all patients with ARDS as it is the only method of mechanical ventilation that, to date, has been shown to improve survival. High positive end-expiratory pressure, alveolar recruitment maneuvers, and prone positioning may each be useful as rescue therapy in a patient with severe hypoxemia, but these methods of ventilation do not improve survival for the wide population of patients with ARDS. Although not specific to the treatment of ARDS, protocol-driven weaning that utilizes a daily spontaneous breathing trial and ventilation in the semirecumbent position have proven benefits and should be used in the management of ARDS patients.

Alternative protocol to initiate high-frequency oscillatory ventilation: an experimental study

INTRODUCTION

The objective was to study the effects of a novel lung volume optimization procedure (LVOP) using high-frequency oscillatory ventilation (HFOV) upon gas exchange, the transpulmonary pressure (TPP), and hemodynamics in a porcine model of surfactant depletion.

METHODS

With institutional review board approval, the hemodynamics, blood gas analysis, TPP, and pulmonary shunt fraction were obtained in six anesthetized pigs before and after saline lung lavage. Measurements were acquired during pressure-controlled ventilation (PCV) prior to and after lung damage, and during a LVOP with HFOV. The LVOP comprised a recruitment maneuver with a continuous distending pressure (CDP) of 45 mbar for 2.5 minutes, and a stepwise decrease of the CDP (5 mbar every 5 minute) from 45 to 20 mbar. The TPP level was identified during the decrease in CDP, which assured a change of the PaO2/FIO2 ratio < 25% compared with maximum lung recruitment at CDP of 45 mbar (CDP45). Data are presented as the median (25th-75th percentile); differences between measurements are determined by Friedman repeated-measures analysis on ranks and multiple comparisons (Tukey's test). The level of significance was set at P < 0.05.

RESULTS

The PaO2/FiO2 ratio increased from 99.1 (56.2-128) Torr at PCV post-lavage to 621 (619.4-660.3) Torr at CDP45 (CDP45) (P < 0.031). The pulmonary shunt fraction decreased from 51.8% (49-55%) at PCV post-lavage to 1.03% (0.4-3%) at CDP45 (P < 0.05). The cardiac output and stroke volume decreased at CDP45 (P < 0.05) compared with PCV, whereas the heart rate, mean arterial pressure, and intrathoracic blood volume remained unchanged. A TPP of 25.5 (17-32) mbar was required to preserve a difference in PaO2/FIO2 ratio < 25% related to CDP45; this TPP was achieved at a CDP of 35 (25-40) mbar.

CONCLUSION

This HFOV protocol is easy to perform, and allows a fast determination of an adequate TPP level that preserves oxygenation. Systemic hemodynamics, as a measure of safety, showed no relevant deterioration throughout the procedure.

Nursing and infection-control issues during high-frequency oscillatory ventilation

OBJECTIVES

To review the specific nursing and infection-control issues that arise during the care of patients receiving high-frequency oscillatory ventilation (HFOV).

DATA SOURCE

Published articles, governmental guidelines, and hospital procedures and practices.

DATA SUMMARY

Nurses, respiratory therapists, and other clinicians caring for patients receiving HFOV need to be aware of specific differences in patient assessment, including close observation for symmetric chest-wall vibrations. In addition, management of sedation with or without neuromuscular blockade and effective communication with the patients are essential nursing skills needed with the use of HFOV. From an infection-control standpoint, HFOV is considered a high-risk respiratory procedure because of the inability to effectively filter all respiratory secretions. Appropriate infection-control precautions, including patient location and use of personal protective equipment, need to be considered when implementing HFOV in the intensive care unit.

CONCLUSIONS

Important infection-control and nursing issues exist that are specific to the use of HFOV. These issues should be addressed with appropriate staff education before the implementation of HFOV in an intensive care unit.

Combining high-frequency oscillatory ventilation and recruitment maneuvers in adults with early acute respiratory distress syndrome: The Treatment with Oscillation and an Open Lung Strategy (TOOLS) Trial pilot study*

OBJECTIVE

To determine the safety, feasibility, and lung-recruitment efficacy of an explicit ventilation protocol combining high-frequency oscillatory ventilation and recruitment maneuvers.

DESIGN

Prospective, multiple-center, single-intervention pilot study.

SETTING

Four university-affiliated intensive care units.

PATIENTS

Twenty-five patients with early acute respiratory distress syndrome and severe oxygenation failure.

INTERVENTIONS

Patients were transitioned from standardized conventional ventilation to high-frequency oscillatory ventilation beginning with an initial cycle of up to three sustained inflation recruitment maneuvers (40 cm H2O x 40 secs), followed by a decremental titration of Fio2 and then mean airway pressure. Recruitment maneuvers were repeated for hypoxemia and routinely at least twice daily if the Fio2 was >0.4. A specific protocol was used for weaning high-frequency oscillatory ventilation, for transitioning to conventional ventilation, and for judging intolerance of conventional ventilation whereby patients should be put back on high-frequency oscillatory ventilation.

MEASUREMENTS AND MAIN RESULTS

Patients (median [interquartile range] Acute Physiology and Chronic Health Evaluation II, 24 [19-32]; age, 50 [41-64]) were enrolled after 13 (range, 6-51) hrs of conventional ventilation. Following the initial cycle of recruitment, the mean (+/-sd) Pao2/Fio2 increased significantly compared with standardized conventional ventilation (200 +/- 117 vs. 92 +/- 36 mm Hg, p < .001). After a mean of 12 hrs of high-frequency oscillatory ventilation, the mean Fio2 was significantly reduced compared with prestudy levels (0.5 +/- 0.2 vs. 0.9 +/- 0.1, p < .001). A median of seven (four to 11) recruitment maneuvers was performed per patient over the study period, with only eight of 244 (3.3%) being aborted. Six of 19 patients transitioned to conventional ventilation (32%) were deemed intolerant and were switched back to high-frequency oscillatory ventilation. Protocol adherence was excellent with documented rates >90%.

CONCLUSIONS

The combination of high-frequency oscillatory ventilation and recruitment maneuvers resulted in rapid and sustained improvement in oxygenation, likely through lung recruitment. This explicit high-frequency oscillatory ventilation protocol appears well tolerated, feasible, and physiologically sound.

High frequency oscillatory ventilation in burn patients with the acute respiratory distress syndrome

BACKGROUND

High frequency oscillatory ventilation (HFOV) improves gas exchange while providing lung protective effects during the ventilation of patients with the acute respiratory distress syndrome (ARDS). The purpose of this study was to review our experience with HFOV in adult burn patients with oxygenation failure secondary to ARDS.

METHODS

Retrospective cohort review of all burn patients treated with HFOV at a regional adult burn center.

RESULTS

All values are reported as the mean +/- standard deviation (S.D.). HFOV was used on 28 occasions in 25 patients (age 44 +/- 16 years, %TBSA burns 40 +/- 15, and a 28% incidence of inhalation injury) who had severe oxygenation failure from ARDS (PaO2/FiO2 ratio 98 +/- 26, and oxygenation index (OI) (FiO2 x 100 x mean airway pressure/PaO2) 27 +/- 10) following 4.8 +/- 4.4 days of conventional mechanical ventilation (CMV). After switching from CMV to HFOV, there were significant improvements in the PaO(2)/FiO2 ratio within 1h and in the oxygenation index within 24 h. The duration of HFOV was 6.1 +/- 5.8 days. HFOV was continued during 26 surgeries for 14 patients where a mean of 18 +/- 9% TBSA burns were excised and closed. The only complications related to HFOV were three episodes of severe hypercapnia. In-hospital mortality was 32%.

CONCLUSIONS

HFOV was safe, and was highly effective in correcting oxygenation failure associated with ARDS in burn patients, and can be successfully used as an intra-operative ventilation modality for burn patients.

Ventilación mecánica en el síndrome de dificultad respiratoria aguda/lesión pulmonar aguda

Acute respiratory distress syndrome (ARDS), which was first described by Ashbaugh in 1967, consists of acute hypoxemic respiratory failure (PaO2/FiO2< or =200) associated with bilateral infiltrates on the chest radiograph caused by noncardiac diffuse pulmonary edema. Although ARDS is of multiple etiology, pulmonary or extrapulmonary injury can produce systemic inflammatory response that perpetuates lung disturbances once the initial cause has been eliminated. Most patients with ARDS require mechanical ventilation. Currently, the old standard is conventional ventilation optimized to protect against ventilator-associated lung injury. Other mechanical ventilation strategies such as high-frequency oscillatory ventilation, which is also based on alveolar recruitment and adequate lung volume, can be useful alternatives. In this review, the level of evidence for other therapies, such as prone positioning, nitric oxide and prostacyclin inhalation, exogenous surfactant, and extracorporeal vital support techniques are also analyzed.