Chapter 35

### Introduction

Objectives

1. List drugs commonly administered by inhalation to mechanically ventilated patients.

2. Describe the use of inhaled nitric oxide (iNO), heliox, and volatile anesthetics during mechanical ventilation.

3. Compare the use of nebulizers and metered dose inhalers (MDIs) in mechanically ventilated patients.

4. Select an appropriate aerosol delivery device for use during mechanical ventilation.

Oxygen and air are mixed to provide the prescribed Fio2. Rarely, nitric oxide, helium, or volatile anesthetics are added to the inspired gas. Aerosol medication can also be added to the inspired gas. This chapter covers aspects of inhaled gas and aerosol administration.

### Inhaled Gases

#### Nitric Oxide

Inhaled nitric oxide (iNO) is a selective pulmonary vasodilator. As such, improved blood flow in ventilated lung units may occur, often resulting in improved ventilation-perfusion mismatch, better oxygenation, and lower pulmonary arterial pressure. In adults with acute respiratory distress syndrome (ARDS), iNO is associated with a transient improvement in oxygenation. However, no survival benefit or reduction in ventilator-free days has been reported with use of iNO for ARDS. With iNO, there is an increased risk of developing renal dysfunction. Although iNO may result in systemic methemoglobinemia or in generation of inhaled nitrogen dioxide, these effects are rare unless high doses are used. Oxygenation benefit typically occurs with an iNO dose of 20 ppm or less. Rebound hypoxemia can occur when iNO is discontinued. Despite the lack of evidence that iNO improves important outcomes, it is used as rescue therapy for refractory hypoxemia. The cost of iNO in the United States is very high and is not offset by third-party reimbursement or in cost savings from fewer days on the ventilator.

#### Heliox

Heliox is a mixture of helium (60%-80%) with oxygen (20%-40%). The use of heliox in severe asthma can improve gas exchange and decrease the work-of-breathing. Heliox has also been used with invasive and noninvasive ventilation (NIV) in patients with chronic obstructive pulmonary disease (COPD) exacerbation. The low density of helium reduces the pressure required for flow through a partially obstructed airway. Ideally, a gas mixture containing 80% helium is preferred, but improved clinical status may occur with as low as 40% helium. Heliox can be administered through some mechanical ventilators, but it adversely affects the function of others. High-level evidence is lacking to support improved outcome in patients with obstructive lung disease (eg, asthma and COPD). There is contradictory evidence related to the benefit of heliox to improve aerosol delivery; heliox may improve aerosol delivery, but it is unclear whether this improves patient outcomes. Heliox might be considered in patients who develop postextubation stridor, but there is concern that the heliox will mask the symptoms with progression to life-threatening airway obstruction.

#### Volatile Anesthetics

Inhaled anesthetic agents have been used to achieve improved gas exchange in patients with severe acute asthma. Inhaled anesthetics ...

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