Wednesday, June 11, 2014
By Brendan Mcgrath MD; Jacob Drake, Medical Student
The paper explains the flexible bronchoscopic techniques for bronchoalveolar lavage and bronchial wash on the Intensive Care Unit.
Bronchoalveolar lavage (BAL) and bronchial wash (BW) are both common flexible bronchoscopic (FB) techniques performed routinely on the Intensive Care Unit (ICU). BAL is a diagnostic procedure used to obtain samples of airway secretions for microbiological, cytological or immunological analysis, by means of injecting relatively large volumes of saline into the distal airways of interest. The saline is retrieved by suctioning, along with any secretions liberated by the saline wash. It is a procedure which can isolate a particular section of the bronchial tree by occlusion and obtain samples distal to this occlusion. This allows specific lobes or segments to be targeted according to clinical need. BW involves injecting smaller aliquots of saline into the lumen of the bronchus, but does not typically involve endobronchial occlusion. In the context of the ICU, bronchial washing is commonly performed to facilitate removal of mucus plugs, debris or to clear retained secretions. This technique can be used to treat lobar collapse. BAL and BW are generally safe and well-tolerated but introduction of an FB into the breathing circuit, airway adjunct or trachea-bronchial tree can risk potential complications, as can instilling potentially irritant saline (see complications). Following published peri-procedure safety-precautions may reduce these risks.1
Common indications for FB broadly fall into three categories, with varying levels of supporting evidence. Firstly, saline washes and suctioning delivered via FB are commonly used to treat lobar collapse/atelectasis. British Thoracic Society (BTS) guidelines indicate that FB should only be used as a treatment for lobar atelectasis in intubated and mechanically ventilated patients where conventional physiotherapy and suctioning have failed to resolve this. The best quality evidence indicated that there was no benefit of FB treatment compared to suction and physiotherapy, which is non-invasive and has a far lower complication rate. Guidance also states that prophylactic bronchoscopy and lavage should not be used to prevent post-lobectomy atelectasis in ventilated patients.
The diagnosis and treatment of persistent, non-resolving endotracheal haemorrhage may be another indication for FB in intubated patients. Damage to the tracheal endothelium during routine suctioning can result in abrasions and bleeding through the endotracheal tube. Evidence shows that high resolution CT is superior to FB as first-line for identifying the site of origin for the haemorrhage, although bronchoscopic techniques allow for concomitant diagnosis and management of haemorrhage using saline/adrenaline injections. Evidence of its efficacy in managing endotracheal bleeding is not abundant or conclusive. Guidance states that when CT imaging or angiography has been performed and does not identify the site of the bleed, bronchoscopy may be considered.
Finally the most established indication for FB on the ICU utilises BAL or brushing for the diagnosis of suspected ventilator-associated pneumonia. BAL may also be useful in the diagnosis of parenchymal lung-disease. BAL is recommended only as a second-line when non-invasive techniques (such as blind catheter-aspiration) have failed to identify a responsible organism or are unavailable. Once an organism has been identified, culture and sensitivity can effectively direct antibiotic therapy. Transbronchial biopsy and needle aspiration (TBNA) has also been used for histological diagnosis on the ICU, however due to significant complication rates and a low diagnostic-yield (<50%) it is recommended that TBNA may only be useful in a selective group of mechanically ventilated patients.
BAL site selection is guided with most-recent available radiology.
After site-selection and set-up of equipment:
Therapeutic BW is usually guided by the endobronchial appearances at bronchoscopy. A blocked segment will usually be cleared by repeated targeted flushing and suction, typically with 20ml aliquots of saline. Samples can be captured for microbiological analysis as with BAL.
In the mechanically ventilated patient, care must be taken when advancing and withdrawing the FB not to displace the airway device. It is usual for an assistant to support the endotracheal or tracheostomy tube and for sterile lubrication to be used. Routine monitoring including waveform capnography will aid early detection of potential problems. Repeated accessing of the ventilator circuit will cause pressure loss and de-recruitment of the lung and ventilation may prove ineffective with the bronchoscope in the airways. Instilling saline and repeated suctioning may also cause a degree of atelectasis. It is usual to adjust the ventilator to deliver larger tidal volumes with 100% inspired oxygen concentration during the procedure. Following the procedure, ventilator recruitment manoeuvres may limit the amount of atelectasis.
General complications of any FB procedure include potential cardiovascular and respiratory instability, infection (introducing new infection or cross contamination from other lung areas), as well as potential local trauma and haemorrhage caused by the bronchoscope itself or any interventions performed. Pneumothorax is a significant but uncommon complication which occurs in approximately 1 in 1000 bronchoscopies, but is significantly more likely following a biopsy. There is no evidence to support routine chest X-ray after bronchoscopy, if no clinical indication is evident. Post-bronchoscopy fever (PBF) is a complication featuring pyrexia
> 38°C, neutrophilic leucocytosis, elevated C-reactive protein, and elevations in proinflammatory cytokines, all with no evidence of bacteraemia. It is most commonly reported approximately 8 hours after BAL. Although smaller studies report high PBF rates following BAL (13%), one large prospective study (>20,000 patients) did not report PDF. There is no evidence that antibiotic prophylaxis can prevent PBF. True bacteraemia also occurs in 6-8% of patients.
Hypoxaemia and arterial desaturation are commonly observed during any bronchoscopy. Although respiratory depression caused by sedation used prior to FB may account for some proportion of the hypoxaemic effect seen, oxygen saturation does decrease on passage of the bronchoscope through the vocal cords. This may also be exacerbated by suctioning. Commonly, desaturations are transient, and are only considered significant if prolonged (>1 min.) Risk factors for hypoxaemia include: low baseline FEV1 or PEFR, pre-existing need for oxygen supplementation, low baseline SaO2, sedation and co-morbidity. Intubated patients have an increased vulnerability to desaturation during FB due to the relatively small internal diameter of an endotracheal or tracheostomy tube in comparison to the natural airway anatomy, as well as frequently reduced baseline lung function. A 5.7mm external diameter bronchoscope will only occlude 10-15% of the cross-sectional lumen of a patient’s trachea, whereas a 9mm external diameter endotracheal tube will be 40% occluded by the same endoscope. For this reason adequate pre-oxygenation with 100% oxygen is mandatory, as well as the usage of 100% oxygen during FB and the immediate recovery period. Desaturations are more common in BAL and may be positively associated with volume of saline injected.
Cardiovascular complications can include tachycardia or bradycardia, other cardiac arrhythmias, and elevations in blood pressure. The increase in cardiac workload may be associated with silent myocardial ischaemia during FB. While in routine diagnostic bronchoscopy, arrhythmias are rare, ICU patients frequently present with electrolyte imbalances and cardiac arrhythmias. Bronchoscopy performed within 30 days of a myocardial is associated with increased mortality. Endotracheal bleeding is also a complication of FB, although it is uncommon (0.19% moderate, 0.26% severe, for all bronchoscopies). Bleeding is more common when biopsies are obtained.
Many patients undergoing FB on the ICU will have significant co-morbidities; frequently they are intubated and ventilated mechanically. This necessitates an additional set of considerations to prevent or reduce complications in this vulnerable patient group, which should always be considered high-risk. Bronchoscopy with BAL is associated with changes in multiple physiologic values for intubated and mechanically ventilated patients, such as lung compliance, pulmonary artery pressure and PaCO2, although often not clinically significant. Hypercapnia during the procedure may increase intra-cranial pressure (ICP). Reductions in PaO2:FiO2 ratio do not appear to be dependent upon the BAL volume used. Additionally, post-bronchoscopy pneumothoraces are known to occur in mechanically-ventilated patients even without biopsy. Adjusting alarm limits for affected physiological values will facilitate close monitoring and early detection of patient deterioration.
In order to achieve a more satisfactory risk-profile for ICU patients, adjustments to ventilation setting can be made, such as increasing the pressure limit to overcome the increased airway resistance conferred by the presence of a bronchoscope. In non-mechanically-ventilated patients with hypoxia, CPAP with oxygen has been shown to reduce the incidence of desaturations and the need for mechanical ventilation post-procedure. In patients with closed head injury, hyper-ventilation with the ventilator may mitigate the common rise in ICP caused by bronchoscopy in these patients.
BTS Guideline for diagnostic flexible bronchoscopy in adults. British Thoracic Society BTS Flexible Bronchoscopy Guideline Group. Thorax, August 2013, Vol 68, Supplement 1.
An Official American Thoracic Society Clinical Practice Guideline: The Clinical Utility of Bronchoalveolar Lavage. Myer K et al. Am J Respir Crit Care Med Vol 185, Iss. 9, pp 1004–1014, May 1, 2012
Cellular Analysis in Interstitial Lung Disease
Merck manual diagnostic bronchoscopy.
Bronchoscopy in the ICU: An overview of broncho-alveolar lavage and bronchial washing