Respiratory failure requiring mechanical ventilation (MV) makes up a significant
... COPD, chronic obstructive pulmonary disease; ECMO, extracorporeal ...
M e c h a n i c a l Ven t i l a t i o n Mollie M. James,
DO, MPH*,
Greg J. Beilman,
MD
KEYWORDS Mechanical ventilation Respiratory failure ARDS Algorithm KEY POINTS The goal of therapy in patients with acute respiratory distress syndrome should be to optimize oxygenation while minimizing the risk of ventilator-induced lung injury and providing adequate ventilation. Appropriate use of ventilation modes and strategies, positive-end expiratory pressure levels, and recruitment maneuvers can improve oxygen delivery. Salvage therapies, such as prone positioning, inhaled epoprostenol and nitric oxide, and high-frequency oscillatory ventilation, have a well-established role in supportive management and are associated with improved oxygenation but not survival.
INTRODUCTION
Respiratory failure can be broadly defined as the inability of the lungs to provide adequate oxygenation or ventilation to support the organism’s systemic metabolic functions. Symptoms of respiratory failure are distressing for patients and can lead to rapid clinical decompensation without appropriate and timely intervention. The authors’ goal is to familiarize the reader about the most current supportive therapies available for respiratory failure and provide an algorithm (Fig. 1) for implementing these interventions in clinical practice. BACKGROUND
Respiratory failure requiring mechanical ventilation (MV) makes up a significant portion of health care costs. Nearly 30% of intensive care unit (ICU) admissions in the United States are for MV. The rate of MV is 2.8 per 1000, accounting for 700 000 episodes annually. Treatment costs for this diagnosis in 2005 was $34 257 per patient, with an average stay of 14 days. This expense accounts for $27 billion annually. Respiratory failure actually accounts for 12% of all hospital costs and 7%
Division of Critical Care and Acute Care Surgery, Department of Surgery, University of Minnesota, 420 Delaware St SE, MMC 11, Minneapolis, MN 55455, USA * Corresponding author. E-mail address:
[email protected] Surg Clin N Am 92 (2012) 1463–1474 http://dx.doi.org/10.1016/j.suc.2012.08.003 surgical.theclinics.com 0039-6109/12/$ – see front matter Ó 2012 Elsevier Inc. All rights reserved.
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Fig. 1. The algorithm for ventilator management of ARDS. CHF, congestive heart failure; COPD, chronic obstructive pulmonary disease; ECMO, extracorporeal membrane oxygenation; FIO2, fraction of inspired oxygen; HFOV, high-frequency oscillatory ventilation; I:E, inspiratory/expiratory ratio; IRV/APRV, inverse ratio ventilation/airway pressure release ventilation; LTVV, low tidal volume ventilation; NIPPV, noninvasive positive-pressure ventilation; NO, nitric oxide; PCV, pressure control ventilation; PEEP, positive end-expiratory pressure; P/F, PaO2:FiO2; Pplat, airway plateau pressures; RR, respiratory rate; SaO2, saturation of arterial oxygen; VCV, volume control ventilation; Vte, minute ventilation.
Mechanical Ventilation
of all hospital days. More than 50% of these expenditures involve patients older than 65 years.1 The incidence of acute lung injury (ALI) is nearly 80 per 100 000 person-years, with a mortality rate up to 40% for hospitalized patients.2 Fifty-nine percent of patients with ALI present to community-based hospitals. Despite an increasing fund of knowledge regarding support for patients with acute respiratory distress syndrome (ARDS), survival remains minimally impacted. The first report of ARDS included a mortality risk of 58%, a number that declined through 1993.3 Since 1994, the mortality remains stable at approximately 30%.4 Heterogeneity in disease process results in varied mortality in subgroup populations (ie, younger patients do better than older patients); nonpulmonary sources leading to ARDS have better outcomes when compared with pulmonary-based ARDS, and trauma patients do better than most other groups.2 ALI and ARDS are both on the spectrum of the most severe form of respiratory failure. ALI is defined as a PaO2/fraction of inspired oxygen (FIO2) ratio of 300-200, whereas the more severe form, or ARDS, is defined as a PaO2:FIO2 ratio less than 200. To meet the complete definition, patients must be hypoxemic with new pulmonary infiltrates on chest radiograph, have a normal pulmonary capillary wedge pressure (to exclude left heart failure as a cause), and a predisposing condition associated with ARDS. The list of predisposing conditions is extensive but includes bacteremia, sepsis, pancreatitis, pneumonia, and trauma. The pathophysiologic hallmark of ARDS is extensive inflammation and loss of capillary permeability in the lung tissue initiated by either a direct pulmonary insult (aspiration, exposure, infection) or an indirect process (pancreatitis, bacteremia, septic shock). This results in difficulty transporting oxygen from the alveoli into the bloodstream. The lungs lose compliance, becoming stiff and inelastic, which further limits gas exchange. MV to improve oxygenation and provide support can lead to ventilator-induced lung injury (VILI).5 Injury to the lung parenchyma is in part caused by repeated opening and closing of alveoli causing injury of the tissue, with the volume and pressure used to ventilate the stiff lung resulting in an increased inflammatory cascade.6 Long-term effects of this process can lead to pulmonary fibrosis. Acute Support of Pulmonary Function Noninvasive positive-pressure ventilation
Noninvasive positive-pressure ventilation (NIPPV) is used as a first-line therapy with increasing frequency for patients with respiratory failure. This therapy provides bilevel positive-pressure ventilation through a facemask. Because it is less invasive than endotracheal intubation, it is usually better tolerated and may require less sedation. NIPPV may be associated with lower rates of ventilator-associated pneumonia (VAP) because of the lack of a foreign body in the upper airway. NIPPV can improve oxygenation by increasing mean airway pressure with the resulting recruitment of alveoli, thus reducing the work of breathing. Ventilation is improved because of a higher effective tidal volume, which improves minute ventilation while lowering the work of breathing.7 Indications include hypoxemic respiratory failure caused by congestive heart failure and hypercapnic failure caused by exacerbations of chronic obstructive pulmonary disease (COPD).7 Attempts to expand the indication to other disease processes, such as ARDS, pneumonia, and postoperative respiratory failure, produce varied results. Criteria for NIPPV include awake, alert patients who can tolerate the therapy. One must set defined treatment goals and proceed to intubation if those goals are not met within the predetermined timeframe. NIPPV is avoided in patients with any of the
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following contraindications: mental status change caused by traumatic brain injury, stroke, or seizure; active hemorrhage; hemodynamic instability; cardiac issues, such as arrhythmia or active ischemia; gastrointestinal (GI) issues that could lead to aspiration, such as nausea and vomiting, ileus, and recent GI surgery; facial trauma; secretions; and more than 2 organs with acute failure.7 NIPPV in ARDS NIPPV in ARDS has demonstrated some clinical success. Antonelli
and colleagues8 evaluated 147 patients admitted to the ICU with new-onset hypoxemic respiratory failure that were not endotracheally intubated. NIPPV advantages included avoiding intubation in 54%, lowering VAP rates (2% vs 20%, P
