Internal Medicine

0521779407-C02 CUNY1086/Karliner 0 521 77940 7 June 4, 2007 20:53

354 Chronic Respiratory Failure

■Hypoventilation: Neurologic injury with impaired consciousness,

quadriplegia with C3 or above lesion, chronic progressive myopa-

thy or neuropathy

■Hypersecretion: Impaired secretion clearance, cystic fibrosis

■Pulmonary: Pneumonia, end-stage restrictive lung disease, COPD,

ARDS

■Obesity: Pickwickian Syndrome

Signs and Symptoms

■Tachypnea, shallow tidal volumes

■Poor cough, impaired secretion clearance

■Recurrent episodes of acute respiratory failure, or

■Failure to wean from mechanical ventilation

tests

■Diagnosis of chronic respiratory failure is based on history

Basic Studies

■ABG: hypercarbia, hypoxia, respiratory acidosis

■CXR: assess reversible causes (pneumonia, CHF, exacerbation of

COPD, CF)

Advanced Studies

■RR/TV index (Tobin) >105 – predicts unsuccessful extubation

■Dead space ventilation (%)=(PaCO 2 – PetCO 2 )/PaCO 2 × 100

➣>70% suggests persistent ventilator dependence.

differential diagnosis

■Cardiac: Unilateral or bilateral pulmonary edema

■Pulmonary: pneumonia, pleural effusion, COPD, interstitial lung

disease, carcinoma, diaphragm dysfunction, splinting and hypoven-

tilation after thoracic or upper abdominal surgery

■Neuromuscular disorders

management

What to Do First

■Treat reversible causes of respiratory failure

■Optimize nutrition: enteral route preferred to augment anabolism

■Consider anabolic steroids oxandralone, nandralone

■Initiate physical therapy

General Measures

■Monitoring in an ICU and serial ABGs with arterial catheter is usually

appropriate