Chapter 15: Perioperative Inhalation Therapy & Mechanical Ventilation

INTRODUCTION

Supplemental oxygen is indicated for adults, children, and infants (older than 1 month) when PaO₂ is less than 60 mm Hg (8 kPa) or SaO₂ or SpO₂ is less than 90% while breathing room air. In neonates, therapy is recommended if PaO₂ is less than 50 mm Hg (6.7 kPa) or SaO₂ is less than 88% (or capillary PO₂ is less than 40 mm Hg [5.3 kPa]). Supplemental oxygen is given during the perioperative period because general anesthesia commonly causes a decrease in PaO₂ secondary to increased pulmonary ventilation/perfusion mismatching and decreased functional residual capacity (FRC).

AMBIENT OXYGEN THERAPY EQUIPMENT

Classifying Oxygen Therapy Equipment

Oxygen given alone or in a gas can be mixed with air as a partial supplement to patients’ tidal volume or serve as the entire source of the inspired volume. The devices or systems used for this are classified based on their maximal flow rates and a range of fractions of inspired oxygen (FIO₂) (Table 15–1). Other considerations in selecting an oxygen delivery technique include patient compliance, the presence and type of artificial airway, and the need for humidification or an aerosol delivery system.

A. LOW-FLOW OR VARIABLE-PERFORMANCE EQUIPMENT

Oxygen (usually 100%) is supplied at a fixed flow that is only a portion of inspired gas. Such devices (eg, nasal “prongs”) are usually intended for patients with stable breathing patterns. As ventilatory demands change, variable amounts of room air will dilute the oxygen flow. Low-flow systems are adequate for patients with:

• Minute ventilation less than or equal to 8–10 L/min

• Breathing frequencies greater than or equal to 20 breaths/min

• Tidal volumes (VT) less than or equal to 0.8 L

• Normal inspiratory flow (10–30 L/min)

B. HIGH-FLOW OR FIXED-PERFORMANCE EQUIPMENT

Inspired gas at a ...