CHAPTER 54

#### KEY POINTS

• Acute-on-chronic respiratory failure (ACRF) occurs when often minor, although commonly multiple, insults cause acute deterioration in a patient with chronic respiratory insufficiency.

• ACRF is usually seen in patients known to have severe chronic obstructive pulmonary disease (COPD), but occasionally it manifests as cryptic respiratory failure or postoperative ventilator dependence in a patient with no known lung disease.

• The wide variety of causes of ACRF may be compartmentalized into causes of incremental load, diminished neuromuscular competence, or depressed drive, superimposed on a limited ventilatory reserve.

• Intrinsic positive end-expiratory pressure (PEEPi) is a central contributor to the excess work of breathing in patients with ACRF.

• The most important therapeutic interventions are administration of oxygen, bronchodilators, corticosteroids, and noninvasive positive-pressure ventilation (NIV).

• NIV can be used in most patients to avoid intubation and has been shown to improve survival.

• The decision to intubate a patient with ACRF benefits from clinical judgment and a bedside presence. Hypotension and severe alkalemia commonly complicate the immediate periintubation course, but they are usually avoidable. However, delaying intubation when NIV is ineffective may worsen outcomes.

• Ventilator settings should mimic the patient’s breathing pattern, with a modest respiratory rate (eg, 20/min) and small tidal volume (eg, 450 mL); some positive end-expiratory pressure (eg, 5 cm H2O) should be added.

• Prevention of complications such as gastrointestinal hemorrhage, venous thrombosis, and nosocomial infection is a crucial component of the care plan.

• The key to liberating the patient from the ventilator is to increase neuromuscular competence while reducing respiratory system load.

• In selected patients, extubation to NIV despite failed spontaneous breathing trials reduces ventilator and ICU days and further improves survival.

In the past three decades, mortality from chronic obstructive pulmonary disease (COPD) has risen dramatically,1 making chronic lower respiratory disorders the third leading cause of death in the USA in 2009.2 COPD was fifth internationally in 2002 and projected to be the fourth leading cause of mortality by 2030.3 Compared with people with normal lung function, subjects with severe COPD (FEV1 <50% predicted) followed for 22 years as part of the National Health and Nutrition Examination Survey (NHANES I) had a 2.7-fold increased risk of death (95% confidence interval [CI] 2.1-3.5) in an adjusted analysis.4 This trend is apparent in men and women, more prominent in black Americans, and clearly related to cigarette smoking. More women than men have died of COPD in the USA since 2000.4,5 Internationally COPD bears a significant morbidity and mortality burden accounting for 27,700 disability adjusted life years (DALYs).6 Admissions to ICUs for exacerbations of COPD account for a substantial portion of bed-days,7 since these patients often require prolonged ventilatory support. Between 1998 and 2008 in the USA, there were an average of 765,067 (95% CI 764,360-765,773) hospitalizations for acute exacerbation of COPD of which 8.1% required a period of respiratory support8; 13.2% of patients with respiratory failure requiring mechanical ventilation in a recent survey USA survey of 180,326 hospitalizations had significant comorbid pulmonary disease.9 In surgical ICUs, COPD is an important problem as well, since it is one of the more common ...

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