Bronchoscopy in specific conditions

Pneumonia

The microbiological yield from bronchoscopy is low (13-48%) in ventilated patients with community acquired pneumonia (CAP), possibly because of the frequency of antibiotic administration before admission to the ICU.28-30 By contrast, patients who have been mechanically ventilated for several days generally have extensive colonisation even of the lower respiratory tract. In these patients with suspected VAP, negative microbiological culture predicts the absence of pneumonia but false positives arise frequently. Invasive investigation has not been shown in patients with either CAP or VAP to alter treatment and outcome significantly11 29 31-33 and may be reserved for patients failing first line treatment or those from whom specimens are not readily obtainable by blind tracheobron-chial aspiration (see chapters 3 and 4). Patients with common causes of immunosuppression, such as the acquired immune deficiency syndrome (AIDS) and malignancy, have a poor prognosis when admitted to the ICU with ARF (see chapter 20). For example, bone marrow transplant recipients requiring mechanical ventilation have an in-hospital mortality in excess of 95%.34 Although these data have deterred referral of such patients to the ICU, temporary endotracheal intubation may be required for sedation and FOB to be performed safely.

The sensitivity of BAL in the detection of AIDS related pneumocystis pneumonia (PCP) is high (86-97%).35-37 Fewer organisms may be recovered by BAL from patients using nebulised pentamidine prophylaxis38 39 or with non-AIDS related PCP, but the yield may be increased by taking samples from two lobes and targeting the area of greatest radiological abnormality.40 Cytomegalovirus (CMV) pneumonia is a common cause of death after transplantation, particularly in recipients of allogeneic bone marrow and lung grafts.41 The definitive diagnosis of CMV pneumonitis is made by the finding of typical cytomegalic cells with inclusions on BAL or TBB,42 the latter being more sensitive. Detection of early antigen fluorescent foci (DEAFF)43 performed on virus cultured from BAL fluid allows a presumptive diagnosis to be made.

Invasive pulmonary aspergillosis occurs predominantly in neutropenic patients44 in whom early diagnosis and treatment are essential.45 The incidence of aspergillosis may be rising in this patient group, probably secondary to more aggressive chemotherapy regimens and more widespread use of prophylactic broad spectrum antibiotics and anticandidal agents. The sensitivity of BAL is high in the presence of diffuse radiological changes.46 A positive culture has a specificity of 90% but results may take up to 3 weeks.47 The sensitivity of culture alone (23-40%) is greatly increased by the addition of microscopic examination for hyphae (58-64%).48 49 Galactomannan antigen testing of blood provides an early warning of infection50 and may prove useful in BAL fluid.

Respiratory failure due to non-infectious lung disease

Patients presenting with ARF and pulmonary infiltrates are generally assumed to have pneumonia and further investigation is prompted by treatment failure. Analysis of BAL fluid may distinguish the differential diagnoses and/or pulmonary risk factors for ARDS, many of which have specific treatments (table 1.1). The BAL white cell differential provides information that may be diagnostically helpful (table 1.2).51 A moderate eosinophilia (>15%) implicates a relatively small number of conditions including Churg-Strauss syndrome, AIDS related infection, eosinophilic pneumonia, drug induced lung disease, or helminthic infection.52 53

Apart from helping to uncover a cause or differential diagnosis for ARDS, the BAL fluid cell profile may give prognostic information. In patients with ARDS secondary to sepsis a BAL

fluid neutrophilia had adverse prognostic significance while a higher macrophage count was associated with a better outcome.54 The fibroproliferative phase of ARDS may be amenable to treatment with steroids55 and it is recommended that either BAL or PSB is performed before starting treatment to exclude infection.

For patients with suspected or confirmed ARDS a sensitive and specific marker of disease would have several benefits. Firstly, it might improve the ability to predict which patients with risk factors develop ARDS56 so that potentially protective measures could be assessed and developed. Secondly, it may help to quantify the severity of disease and to predict complications such as fibrosis and superadded infection. Most studies have involved assays on plasma samples or BAL fluid.56 Analysis may provide information about soluble inflammatory mediators and by-products of inflammation (such as shed adhesion molecules, elastase, peroxynitrite) in the distal airways and air spaces. Analysis of samples from patients at risk has revealed increased alveolar levels of the potent neutrophil chemokine interleukin 8 (IL-8) in those patients who progress to ARDS.57 The development of established fibrosis conveys a poor prognosis in ARDS.58 Type III procollagen peptide is present from the day of tracheal intubation in the pulmonary oedema fluid of patients with incipient lung injury, and the concentration correlates with mortality.59 Less invasive methods of sampling distal lung lining fluid using exhaled breath60 61 or exhaled breath condensates62 63 are being examined in critically ill patients. The assay of potential biomarkers is currently used exclusively as a research tool.

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