part0028

If a patient with severe ARDS has a contraindication to APRV, or doesn't do well on APRV, I think there is sufficient evidence to recommend prone positioning (usually in conjunction with neuromuscular blockade). The success of prone positioning depends greatly on a well-trained staff and meticulous avoidance of complications like pressure injuries and dislodgement of life support devices. Therefore, using a checklist each time the patient is turned is highly recommended. Regular training of the ICU staff is also necessary. The ventilator should be kept on ARDSNet-style settings to help protect the lungs from injury, and the same goals for gas exchange apply.

If neuromuscular blockade is used, cisatracurium is the preferred agent for the reasons described in the chapter in this book. Daily interruption of the paralytic drug is advisable to avoid accumulation and prolonged neuromuscular blockade.

Patients should be prone for 16 hours, followed by 8 hours in the supine position. For both proning and paralysis, the therapy should be continued until the patient begins to show signs of recovery. Most of the time, this will mean a PaO 2 /FiO 2 ratio > 150 while supine and off the paralytic agent.

While much of the treatment for ARDS focuses on respiratory support, it's important to recognize that volume overload, excessive pulmonary secretions, and cardiac dysfunction can also contribute to severe respiratory failure. In addition to providing optimal ventilator support, the following should be considered:

• Diuresis or ultrafiltration as tolerated, with a goal of reaching 105% of the patient's "dry weight." Volume overload is an especially common cause of persistent hypoxemia in ventilated patients.

• Therapeutic bronchoscopy to clear the tracheobronchial tree. This can also be diagnostic if the primary cause of respiratory failure is infection or alveolar hemorrhage.

VV ECMO is the ultimate rescue strategy for respiratory failure, and it works by essentially taking the lungs out of the equation so they can rest and recover. The indications for VV ECMO are outlined in the chapter in this book. VV ECMO carries very real risks—the cannulas are very large, and the anticoagulation necessary for the circuit often leads to significant bleeding and the need for multiple transfusions. It is also quite resource-intensive and can only be performed in ECMO centers. Nevertheless, VV ECMO is growing in popularity as a method of support for adults with severe respiratory failure. If a patient appears to be heading toward this and is not already at an ECMO center, early transfer should be arranged if possible.

Two rescue therapies for ARDS that are not supported by the medical literature, at least in adults, are inhaled nitric oxide (iNO) and high frequency oscillatory ventilation (HFOV). That doesn't mean that they are worthless, but based on the published data, they should not be included in a general treatment algorithm .

As discussed previously in the book, iNO can be helpful for the treatment of acute right ventricular failure. For patients with ARDS, however, no mortality benefit has been described and some trials have shown an increase in harm with iNO. For that reason, the use of iNO should be limited to those patients with demonstrable acute right ventricular failure and pulmonary arterial hypertension; or, ARDS with truly refractory hypoxemia (PaO 2 /FiO 2 < 55) when other rescue therapies have either failed or are not an option.

HFOV was, at one time, a commonly used rescue therapy. The OSCILLATE trial, published in 2013, was a multicenter trial examining the use of HFOV early in the treatment of moderate-to-severe ARDS. 37 The investigators found no evidence of benefit and a trend toward increased in-hospital mortality. This was validated by the OSCAR trial, another multicenter trial of HFOV in ARDS that found similar results. 38 For this reason, HFOV should be limited to those patients who have a specific need like a large bronchopleural fistula, or those with truly refractory hypoxemia (PaO 2 /FiO 2 < 55) when other rescue therapies have either failed or are not an option.