Chest
POSTGRADUATE EDUCATION CORNERCONTEMPORARY REVIEWS IN CRITICAL CARE MEDICINESevere Hypoxemic Respiratory Failure: Part 1—Ventilatory Strategies
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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