Chest
Volume 137, Issue 5, May 2010, Pages 1203-1216
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POSTGRADUATE EDUCATION CORNER
CONTEMPORARY REVIEWS IN CRITICAL CARE MEDICINE
Severe Hypoxemic Respiratory Failure: Part 1—Ventilatory Strategies

https://doi.org/10.1378/chest.09-2415Get rights and content

Approximately 16% of deaths in patients with ARDS results from refractory hypoxemia, which is the inability to achieve adequate arterial oxygenation despite high levels of inspired oxygen or the development of barotrauma. A number of ventilator-focused rescue therapies that can be used when conventional mechanical ventilation does not achieve a specific target level of oxygenation are discussed. A literature search was conducted and narrative review written to summarize the use of high levels of positive end-expiratory pressure, recruitment maneuvers, airway pressure-release ventilation, and high-frequency ventilation. Each therapy reviewed has been reported to improve oxygenation in patients with ARDS. However, none of them have been shown to improve survival when studied in heterogeneous populations of patients with ARDS. Moreover, none of the therapies has been reported to be superior to another for the goal of improving oxygenation. The goal of improving oxygenation must always be balanced against the risk of further lung injury. The optimal time to initiate rescue therapies, if needed, is within 96 h of the onset of ARDS, a time when alveolar recruitment potential is the greatest. A variety of ventilatory approaches are available to improve oxygenation in the setting of refractory hypoxemia and ARDS. Which, if any, of these approaches should be used is often determined by the availability of equipment and clinician bias.

Section snippets

Positive End-Expiratory Pressure

Increasing the level of PEEP often is the first consideration when the clinician is faced with a patient with refractory hypoxemia. If PEEP results in alveolar recruitment, the shunt is reduced, and PaO2 increases. Three randomized controlled trials (RCTs) have evaluated modest vs high levels of PEEP in patients with ALI and ARDS (Table 1).27, 28, 39 Although none of these studies reported a survival advantage for use of higher PEEP, each reported a higher PaO2/FIO2 ratio in the higher PEEP

Lung Recruitment Maneuvers

A recruitment maneuver is a transient increase in transpulmonary pressure intended to promote reopening of collapsed alveoli 52, 53, 54 and has been shown to open collapsed alveoli, thereby improving gas exchange.17, 18, 55, 56, 57, 58 However, to our knowledge, there have been no RCTs demonstrating a mortality benefit from this improvement in gas exchange.

A variety of techniques have been described as recruitment maneuvers (Table 3).52, 54 One approach involves a sustained high-pressure

Pressure-Controlled Ventilation

In patients with severe ARDS, some clinicians choose PCV as an alternative to volume-controlled ventilation (VCV) based on several lines of reasoning. First, the peak inspiratory pressure is lower on PCV, but this is related to the flow pattern during pressure control and, for the same tidal volume delivery, there is no difference in plateau pressure for PCV and VCV. Second, patient-ventilator synchrony is believed to be better with PCV. However, Kallet et al66 reported that the work of

Pressure-Controlled Inverse-Ratio Ventilation

Following reports71, 72, 73, 74, 75 of improved oxygenation with pressure-controlled inverse-ratio ventilation (PCIRV) published 20 years ago, considerable enthusiasm for this method was generated. The approach to PCIRV is to use an inspiratory time greater than the expiratory time to increase mean airway pressure and, thus, improve arterial oxygenation. PCIRV most often is used with PCV, although VCV with inverse ratio also has been described.76 Following the initial enthusiasm for this

Airway Pressure Release Ventilation

APRV is a mode of ventilation designed to allow patients to breathe spontaneously while receiving high airway pressure with an intermittent pressure release (Fig 3). The high airway pressure maintains adequate alveolar recruitment. Oxygenation is determined by high airway pressure and FIO2. The timing and duration of the pressure release (low airway pressure) as well as the patient's spontaneous breathing determine alveolar ventilation (PaCO2). The ventilator-determined tidal volume depends on

High-Frequency Oscillatory Ventilation

High-frequency ventilation is any application of mechanical ventilation with a respiratory rate of > 100 breaths/min. This can be achieved with a small tidal volume and rapid respiratory rate with conventional mechanical ventilation, various forms of external chest wall oscillation, HFPV, high-frequency jet ventilation, or HFOV, which currently is the form of high-frequency ventilation most widely used in adult critical care.62, 93, 94, 95 It delivers a small tidal volume by oscillating a bias

High-Frequency Percussive Ventilation

HFPV was introduced in the early 1980s as the Volumetric Diffusive Respirator (Percussionaire Corporation; Sandpoint, ID). Compared with HFOV, only a few studies have investigated the use of HFPV in adult patients with ARDS.33, 108, 109, 110, 111, 112 HFPV is a flow-regulated, pressure-limited, and time-cycled ventilator that delivers a series of high-frequency (200–900 cycles/min) small volumes in a successive stepwise stacking pattern, resulting in the formation of low-frequency (upper limit,

Summary

Figure 5 summarizes a proposed algorithmic approach to ventilator management of refractory hypoxemia. We recommend that lung-protective ventilation (volume and pressure limitation with moderate levels of PEEP) be instituted in patients with ALI and ARDS requiring mechanical ventilation. Rescue therapies may be considered in patients who develop refractory hypoxemia, with the use of these therapies based on a variety of factors, such as the severity of hypoxemia, likelihood of alveolar

Acknowledgments

Financial/nonfinancial disclosures: The authors have reported to the CHEST the following conflicts of interest: Dr Hess has received royalties from Impact. He was a consultant for Respironics and Pari. He also discloses relationships with Cardinal (CaseFusion) and Ikaria. Dr George was a consultant to Eubien, Boehringer Ingelheim, from 2006 to 2007. She has received money from AstraZeneca, Pfizer, Penexel, and Talceda. Drs Esan, Raoof, and Sessler report that no potential conflicts of interest

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