I. Components of acute on chronic respiratory failure (JAMA 1989; 261:3444-53)

A. Increased resistive loads (airway obstruction)

1. bronchospasm

2. heart failure with airway edema ("cardiac asthma")

3. obstructive sleep apnea

4. herpetic tracheobronchitis

B. Increased lung elastic loads (lung stiffness)

1. pulmonary edema

2. pneumonia

3. atelectasis

4. interstitial inflammation

C. Increased chest wall elastic loads (chest wall stiffness)

1. obesity

2. rib fracture

3. pneumothorax

4. ascites

5. abdominal distention

D. Minute ventilation loads

1. anemia

2. fever

3. sepsis

4. excess carbohydrate load

5. pulmonary embolus

6. hypovolemia

E. Depressed ventilatory drive

1. hypothyroidism

2. sedatives & narcotics

3. central sleep apnea

F. Impaired neuromuscular transmission

1. phrenic nerve injury

2. aminoglycosides

3. neuromuscular blockers

4. Guillain-Barré syndrome

5. myasthenia gravis

G. Muscle weakness

1. fatigue and lack of sleep

2. malnutrition

3. myopathy

4. electrolyte disorder

5. hypoxemia

II. Medical evaluation:

A. chest x-ray

B. arterial blood gas

C. cardiac rhythm/EKG

1. atrial fibrillation

2. multifocal atrial tachycardia

3. ischemia

D. electrolytes (including calcium, phosphorus, magnesium)

E. CBC

F. TSH

G. sputum culture (?)

H. cardiac echo (?)

I. V/Q scan or chest CT angiogram (?)

J. bronchoscopy (?)

K. sleep study (?)

III. Treatment (NEJM 2002; 346:988-94; Chest 2001; 119:1190-209; Am J Respir Crit Care Med 2001; 163:1256-76 [GOLD summary])

A. Oxygen

1. insure pO2 > 55 (SaO2 > 90%) even if pCO2 rises

a) following an oximeter is usually sufficient

b) oxygenation assessment should be made at least daily

2. too much oxygen may depress the ventilatory drive in some patients with COPD

3. if pCO2 rises unacceptably with correction of pO2 to 55-60 mm Hg, then there is evidence of respiratory failure not excess oxygenation

B. Pharmacology

1. bronchodilators

a) ipratropium bromide

b) beta agonists

(1) be cautious of hypokalemia in patients receiving high doses for a long time

c) aminophylline

(1) efficacy is questionable when added to other bronchodilators (Ann Intern Med 1987; 107:305-9)

(2) reserve for patients with the worst bronchospasm/respiratory failure (bottom line: almost never used anymore)

(3) dose:

(a) load with 5 mg/kg

(b) maintenance drip = 0.5 mg/kg/hr

(c) adjust drip according to levels

2. corticosteroids

a) methylprednisolone 0.5-2 mg/kg Q6 hours (eg, 125 mg IV Q 6 hours)

b) most value is in the first 3 days; thereafter, detrimental side effects (muscle weakness, increased catabolic state, etc.) may predominate

c) total duration uncertain but there does not appear to be any value in treatment for 8 weeks as opposed to 15 days (N Engl J Med 1999; 340:1941-7)

d) the bottom line with steroids is that the "perfect" recipe is still uncertain; this is my usual practice:

(1) Inpatients:

(a) 60 - 125 mg IV Q6 hours x 3-5 days (duration dependent on how quickly the patient is clinically responding) then:

(b) convert to 60 mg PO/day until dyspnea and hypoxemia improved and close to baseline then:

(c) tapering course used for outpatients (below)

(2) Outpatients:

(a) 60 mg/day x 5 days

(b) 40 mg/day x 5 days

(c) 20 mg/day x 5 days

3. antibiotics (JAMA 1995; 273:957-60)

a) antibiotics do improve short term outcome in patients with exacerbation of COPD

b) there is no clear proven "best" antibiotic in this setting

c) if oral therapy is given: consider drugs with good compliance (infrequent dosing) and low cost

(1) TMP-SMX

(2) doxycycline

(3) ampicillin

(4) azithromycin

C. Secretion reduction

1. DNase (Pulmozyme) is effective in cystic fibrosis but not exacerbations of COPD

2. percussion & postural drainage helpful in patients with excessive secretions

a) flutter valves

b) chest vests

3. acetylcysteine may loosen mucus plugs but is likely to irritate airways and induce bronchospasm; therefore it is not recommended

D. CPAP & BiPAP (Chest 1994; 105:1053-60; Lancet 2000; 355:1931-5)

1. start with CPAP of Å 5 cm

2. start with BiPAP Å 4 cm expiratory pressure & 8 cm inspiratory pressure

E. Nutrition

1. choosing caloric needs:

a) Harris Benidict equation:

(1) men: 66.5 + 13.7(weight) + 5(height) - 6.78(age)

(2) women: 655 + 9.56(weight) + 1.85(height) - 4.68(age)

(3) in general, for patients with impending respiratory failure, add about 20% to the above values to insure sufficient caloric needs

b) 25-30 Kcal/day

2. respiratory quotient (ratio of CO2 production to O2 consumption)

a) carbohydrates = 1.0

b) protein = 0.8

c) fat = 0.7

(1) therefore lipids are generally good for the patient with an exacerbation of COPD accompanied by carbon dioxide retention since relatively little CO2 is produced for a given amount of O2 consumed)

(2) there are a number of "designer" enteral feedings made to give a higher percentage of total calories from lipid rather than carbohydrate in order to minimize carbon dioxide production

(3) probably the most important aspect of feeding is to avoid overfeeding; in other words, total calories are more important than the carbohydrate:fat ratio

3. additional nutritional needs:

a) protein = 1.2 - 1.5 gm/kg

b) N-6 fatty acids = at least 7% (about 1 gm/kg)

c) multivitamin daily

d) 15-39% fat

e) 2-5 gm/kg glucose

4. monitoring nutrition:

a) glucose should be less than 225; if higher, add insulin

b) BUN should be less than 100

c) triglyceride level should be less than 500

d) potassium, calcium, phosphorus, magnesium

F. When do you intubate the patient?

1. this is a subjective judgment best made by an experienced physician at the bedside

2. arterial blood gases are not useful as a sole indicator and are best used as a confirmation of clinical assessment

3. signs of impending respiratory failure:

a) respiratory rate > 35-40 or rising respiratory rate

b) use of all accessory muscles

c) thoracoabdominal paradox (inward movement of abdomen during inspiration)

d) patient's subjective sense of exhaustion

e) mental status changes

Last updated: October 2, 2002

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