The etiology of acute respiratory failure (ARF) among different patient populations is highly variable.1 In general, pulmonary infections are the leading cause of ARF followed by heart failure, exacerbation of chronic obstructive pulmonary disease (COPD), and sepsis.2 Early and appropriate diagnostic strategies are vital for the initial choice of therapy and subsequent treatment decisions. With advances in medicine, aggressive treatments have been introduced to achieve the highest possible cure which in turn, has resulted in the concomitant rise in the incidence of life-threatening toxic and infectious complications, particularly involving the lungs.
There are many practical questions surrounding the diagnostic work-up of critically ill patients with ARF. What is the utility of noninvasive testing? Is empiric treatment enough? What are the risks and benefits of invasive diagnostic procedures? Does invasive testing result in improved outcomes? To answer these questions, a review of the literature has produced mixed results. The apparent dilemma between the need to identify the cause of ARF and complications associated with invasive procedures may have created this uncertainty. To this end, there is some data in hematology and oncology patients which can only be extrapolated to other groups of immunocompromised hosts for whom further testing guided by clinical and epidemiologic data may reveal unsuspected diagnoses. In this chapter, we discuss the utility of noninvasive and invasive testing for diagnosing ARF and provide a diagnostic algorithm based on the best available data (Figure 66–1).
Diagnostic algorithm for diagnosing acute respiratory failure.
(ARF = acute respiratory failure; FOB = fiberoptic bronchoscopy; BAL = bronchoalveolar lavage; PCP = Pneumocystis jiroveci; MTB = Mycobacterium tuberculosis; TBB = transbronchial biopsy; PBS = protected brush specimen; OLB = open lung biopsy; DPLD = diffuse parenchymal lung disease)
This approach consists of obtaining chest imaging studies, cardiac biomarkers (eg, B-type natriuretic peptide) and echocardiography to exclude cardiogenic pulmonary edema, and serologic and microbiologic studies of sputum, nasopharyngeal (NP) aspirates, blood, and urine to diagnose infection. In addition, newer molecular techniques are being implemented along with conventional methods in order to identify specific pathogens not only faster but more accurately without exposing patients to additional risks.
The most commonly performed noninvasive tests for diagnosing ARF are shown in Table 66–1.
Table 66–1Noninvasive tests for diagnosing acute respiratory failure. |Favorite Table|Download (.pdf) Table 66–1Noninvasive tests for diagnosing acute respiratory failure.
|Investigation ||Diagnosis/Specific Pathogen |
|Imaging (chest radiograph, high-resolution CT, chest ultrasound) ||Pattern of different radiologic findings may help in narrowing differential diagnosis |
|Transthoracic echocardiogram ||Congestive heart failure, cardiac tamponade, pulmonary embolism |
|Expectorated sputum ||Bacteria (S pneumoniae, Staphylococcus aureus, Hemophilus influenza, Enterobacteriaceae, Pseudomonas), Candida, other fungi (Histoplasma, Coccidioides) and M tuberculosis...|