Secretion Removal in the ICU

In the ICU, the inability to manage secretions can lead to prolonged mechanical ventilation and hospitalization.

Airway secretions protect the airway epithelium from infection and mechanical damage. Mucus traps foreign particles, including infectious materials, and acts as a transport medium to clear the lungs of harmful objects. Impairments in mucociliary clearance lead to ventilation-perfusion mismatching, atelectasis, and pneumonia. In the intensive care unit (ICU), the inability to manage these secretions can lead to prolonged mechanical ventilation and hospitalization. Excessive secretions can create mucous plugging, necessitating increased ventilatory support.

The two main modalities of airway clearance are physical and pharmacological. Patients should be approached on a case-by-case basis to determine which interventions are necessary. Ventilator-management strategies may also aid airway clearance.

Physical Airway Clearance
Physical airway clearance can be further divided into therapies directed at the chest wall or the airway lumen. Many of these therapies have become the standard of care in the ICU and at home, despite the paucity of well-controlled studies.¹ Chest wall therapies include hand-percussion chest physiotherapy (CPT), postural drainage, and high-frequency chest-wall (HFCW) devices.

Hand percussive CPT for airway clearance has been well documented in cystic fibrosis (CF) care.^2,3 This technique may be performed with a cupped hand, plastic face mask, or specially made percussors and vibratory devices. Sessions are typically very time intensive and physically demanding. Patient comfort should always be kept in mind, along with oxygen saturation and heart rate. There has been some debate as to whether there is sufficient benefit to justify routine CPT in CF.⁴ Despite this controversy, data from CF studies have been extrapolated to other conditions with poor mucociliary clearance. For example, CPT in asthma exacerbations should be reserved for the removal of retained secretions due to the high risk of inducing bronchospasm. Similarly, CPT for atelectasis has not been studied intensively and should not be considered the standard of care.⁵

Postural drainage has been paired with CPT in the belief that certain head-down positions would aid mucus clearance. These positions may induce gastroesophageal reflux and, in turn, aggravate lung disease.⁶ A recent study⁷ showed that patients with CF who practiced postural drainage with CPT had worse chest-radiograph scores and pulmonary-function tests after 5 years than matched patients who performed CPT without head-down positioning. These patients, however, were healthy, nonhospitalized children with CF. In the intubated patient, Berney et al⁸ found that a head-down position during CPT improved sputum production, peak expiratory flow, and lung compliance, when compared with results for patients lying on their sides. This study is encouraging for patients in the ICU and should be repeated with a larger sample size.

A large amount of effort and money has been invested in HFCW devices. These work through a vest that rapidly inflates and deflates. HFCW devices are attractive, since the patient can operate them and achieve greater independence. Studies^2,9,10 in patients with CF have shown results similar to those for CPT. HFCW devices have yet to be studied in acute respiratory care.

Physical therapies directed at the airway include intra-percussive pulmonary ventilation (IPV), the use of cough-assisting devices, and flexible bronchoscopy. Due to the discomfort associated with chest-wall therapies, investigators have attempted to improve mucus clearance directly. IPV delivers pressures oscillating between 5 and 35 cm H2O through a mouthpiece to the airways in order to loosen mucus and improve clearance.10 IPV, like HFCW devices, has exhibited clinical results and patient preferences similar to those for CPT.²

Devices to assist coughing have been available for decades. They provide a large inspiration followed by a negative pressure to improve mucus clearance in patients with poor diaphragmatic function. The use of cough-assisting devices has been shown to improve cough and prevent pulmonary complications.^11,12 Patients with weak coughs and atelectasis warrant a trial of a cough-assisting device before more invasive procedures are attempted.

Flexible bronchoscopy is a well-tolerated, minimally invasive procedure that is most frequently used for diagnostic purposes.¹³ A recent study¹³ showed that, in pediatric ICU patients with lobar or segmental lung collapse, 75% had re-expansion visible in chest radiographs after flexible bronchoscopy.

Other therapies, such as positive expiratory pressure, active cycle of breathing, and autogenic breathing, are used more frequently to maintain lung function in the chronic setting than during acute exacerbations. Patients in the ICU are frequently unable to cooperate with these techniques.

Pharmacological Airway Clearance
Airway secretions are affected by many different medications. Some medications alter the volume of secretions, while others change their characteristics. Care should be taken to ensure that medications given for nonrespiratory purposes do not lead to further respiratory compromise.

b-Adrenergic agonists have been found to increase ciliary beat frequency.¹⁴ Long-acting b-agonists also have prolonged effects on ciliary activity.¹⁵ In vivo studies¹⁶ have shown increases in alveolar fluid clearance as high as 100% in animals with increased b-agonist receptors. These data support the use of b-agonists for airway clearance, even in the absence of bronchospasm.

Recombinant human deoxyribonuclease (DNase) has been used for years in the treatment of CF.^17,18 By decreasing the viscosity of mucus, DNase has been shown to improve lung function in patients with CF.¹⁹ DNase has also been shown to decrease the viscosity of mucus in patients with non-CF bronchitis.²⁰ Despite a lack of controlled trials, there are multiple reports of successful DNase use in the ICU.²¹ One such report²² found rapid improvement in a patient in status asthmaticus who had undergone flexible bronchoscopy that failed to remove plugs of mucus. DNase was given through the endotracheal tube, and the patient had rapid clinical improvement. Another group²³ reported success with DNase given through a flexible bronchoscope to treat CF patients with isolated mucous plugging who had not responded to prolonged courses of antibiotics and aggressive CPT.

Mucolytics and expectorants have exhibited mixed results in altering mucociliary clearance and have not been used extensively in the ICU.²⁴ One popular expectorant, guaifenesin, has been found to have no effect on nasal mucociliary clearance in healthy volunteers.²⁵ Other therapies, such as the administration of hypertonic saline, increase mucociliary clearance in CF, but need to be studied in the ICU.²⁶

Conclusion
In summary, patients in the ICU often need aggressive airway clearance. Many current therapies were established prior to research demonstrating their effectiveness. In the absence of research, clinical experience and ICU protocols are often called upon to decide which management strategies to use. Patients should be approached on a case-by-case basis prior to the institution of unnecessary and potentially disruptive therapy.

Jon Steinfeld, MD, is assistant professor of pediatrics, Drexel University School of Medicine, St. Christopher’s Hospital for Children, Philadelphia.

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