Physicians are notoriously unreliable at clinically detecting airflow obstruction [Am J Med 68: 11, 1980], thus we rely on objective measures. FEV1/FVC < 0.7 is indicative of obstructive disease but is difficult to obtain at the bedside.
Peak expiratory flow rate ranges from 500 to 700 L/min in men and 380 – 500 L/min in women and depends on both age and height. PEFR should always be tested before and after the application of bronchodilators, as COPDers often do not respond. If PEFR increases by 15% after 20 minutes, treatment should be continued. If < 10%, they are considered ineffective.
For ventilated patients, two metrics may be useful in assessing bronchodilator response: peak inspiratory pressure and auto-PEEP (both of which should decrease).
Delivery options include nebulizers, MDI (ALWAYS use a spacer device), and dry powder inhalers (not recommended in COPD as inspiratory flow rates > 60 L/min are required). Note that in patients who can use them, MDI with spacers are just as effective as nebulizers [Chest 103: 665, 1993; J Crit Illness 11: 457, 1996; Am J Respir Crit Care Med 156: 3, 1997]. Both can be used in ventilated patients although the dose has to be increased.
Acute Management of Asthma
Albuterol works in < 5 minutes and lasts 2-5 hours. Several randomized controlled studies suggest that levalbuterol is more effective than albuterol in terms of hospitalization [J Pediatr 143:731, 2003] and pulmonary function tests [J Allergy Clin Immunol 102: 943, 1998], however other RCTs have suggested that they are no different in treating pediatric asthma [J Emerg Med 29: 29, 2005] and adult COPD [Chest 124: 844, 2003]. To treat asthma, start with 3 x 20 min treatments (20 min nebs or 4-8 puffs). If this fails, progress to one hour nebs. There is no difference between continuous and repetitive therapy [Chest 122: 1982, 2002] but continuous is easier to administer. If these fail, proceed to SQ epinephrine, but beware of side effects (ex. hyperglycemia, hypokalemia).
Despite conflicting results in the literature [Chest 121: 1977, 2002], ipratropium bromide is recommended for acute asthma therapy but only in combination with albuterol.
The National Asthma Education Program recommends steroids in all acute asthma cases, even those that respond to B-agonists (to prevent relapse). Points to note: 1) there is no difference between IV or PO, and effects take 12 hours to begin [Chest 116: 285, 1999] 2) A 10 day course does not require tapering [J Emerg Med 16: 15, 1998] and 3) some studies show no benefit to steroids in acute asthma [AIM 112: 822, 1990; Thorax 47: 588, 1992; Chest 102: 510, 1992]
Risk of Steroids in Paralyzed Patients
BEWARE STEROIDS AND PARALYTICS in ventilated patients, as they can cause an unusual myopathy associated with rhabdomyolysis [Chest 102: 510, 1992]. Etiology is unknown and this disorder is thought to be reversible.
Emphysema/Chronic Bronchitis (aka “COPD”)
Diagnosed when FEV1/FVC < 70%. Also treated with albuterol and ipratropium although in this case they are equally effective and ipratropium can sometimes be used alone. A 2 week course of steroids is recommended for all patients suffering from an acute exacerbation of COPD – the largest trial showed significant improvements in FEV1 [NEJM 340: 1941, 1999]
Upper airway infection is the likely culprit in 80% of exacerbations, however there are concerns about antibiotic resistance in this patient population. Pooled data from 11 clinical trials suggests using antibiotics in patients with severe exacerbations who are at high risk for poor outcomes (one of three: FEV1 < 50% predicted, comorbid conditions, 3 or more exacerbations in 12 months) [Chest 119: 1190, 2001]
Although the mechanism of elevated pCO2 is unknown (it is not decreased ventilatory drive [Am Rev Respir Dis 122: 191, 1980]), remember not to raise SaO2 > 90% in these patients, as there is no evidence it is beneficial.