Chapter 34: Noninvasive Mechanical Ventilation

INTRODUCTION

Noninvasive positive pressure ventilation (NPPV) is a form of mechanical ventilatory support using a mask instead of an invasive airway device such as an endotracheal or tracheostomy tube. Its use has been increasing in frequency in both intensive care and postanesthesia care recovery units.

Successful use of this intervention requires careful patient selection, proper management of the underlying disease necessitating its use, and continuous respiratory monitoring. Noninvasive positive pressure ventilation can be used as first-line therapy in patients with respiratory insufficiency (eg, exacerbation of chronic obstructive pulmonary disease [COPD]), as a form of weaning from ventilator therapy, and as a bridge support after early extubation. After initiation of NPPV, patients must be closely monitored. Lack of improvement within several hours, intolerance to therapy, or signs of clinical deterioration should prompt a decision for endotracheal intubation. Patients intubated after a failed trial of noninvasive ventilation may spend a longer period of time in the intensive care unit (ICU) on the ventilator.

ADVANTAGES AND INDICATIONS

Noninvasive ventilation has a number of advantages over invasive ventilation, the sum of which may contribute to reductions in ICU length of stay and mortality.

• Reduces the need for endotracheal intubation.

• Reduces the risks of artificial airway complications, such as airway trauma due to laryngoscopy and intubation.

• Reduces the rate of nosocomial infections associated with invasive mechanical ventilation: ventilator-acquired pneumonia, sinusitis, and sepsis.

• Causes less patient discomfort.

• Reduces the need for intravenous sedation.

• Serves as an alternative for patients whose advanced directives prohibit endotracheal intubation (ie, DNI—“Do Not Intubate”).

Noninvasive ventilation is best suited as an adjunct to manage pulmonary insufficiency in which the underlying condition responds well to other simultaneous treatments. Randomized controlled clinical trials have shown that the following indications for NPPV can reduce pulmonary complications, improve mortality rates, and decrease length of stay:

• COPD exacerbation.

• Cardiogenic pulmonary edema.

• Respiratory failure of any etiology (hypercapnia or hypoxemic).

• Respiratory distress in immunocompromised (solid organ and bone marrow transplant) patients.

• Respiratory distress immediately after lung resection, gastric bypass, or upper abdominal surgery.

• Preoxygenation of patients in hypoxemic respiratory failure prior to intubation.

Consideration of noninvasive ventilation begins with a patient who has signs of respiratory distress. These signs include moderate-to-severe dyspnea, tachypnea greater than 24 breaths per minute, and evidence of increased work of breathing (such as pursed-lip breathing or use of accessory muscles). Analysis of arterial blood gases shows respiratory acidosis (pH 7.10-7.35) due to hypercapnia (Paco₂ > 40 mm Hg) as well as hypoxemia (Pao₂/Fio₂ < 200 mm Hg). Patients suitable for NPPV must be alert, cooperative, and have an obstructed airway with intact respiratory drive.

DISADVANTAGES AND CONTRAINDICATIONS

Compared to endotracheal intubation, the use of noninvasive modalities for oxygenation and ventilation has several disadvantages:

• May ...