Oxygen Therapy Fundamentals
Oxygen is the most commonly administered medication in EMS. Understanding which delivery device to use, at what flow rate, and for which patient is fundamental to EMT practice. The goal of oxygen therapy is to maintain adequate tissue oxygenation, typically targeting a pulse oximetry reading of 94% or higher for most patients (88 to 92% for patients with chronic obstructive pulmonary disease who rely on hypoxic drive).
Room air contains approximately 21% oxygen. Supplemental oxygen delivery devices increase the fraction of inspired oxygen (FiO2) above 21%. The actual FiO2 delivered depends on the device, the flow rate, and the patient's breathing pattern. Higher flow rates generally deliver higher FiO2, but each device has an optimal range.
Low-Flow Oxygen Devices
Nasal Cannula
The nasal cannula is the most comfortable and best-tolerated oxygen delivery device. It delivers low to moderate concentrations of oxygen through two prongs placed in the nostrils. Flow rates range from 1 to 6 liters per minute (LPM), delivering approximately 24% to 44% FiO2. Each liter per minute adds roughly 4% to the FiO2. The nasal cannula is appropriate for patients with mild hypoxia (SpO2 90 to 94%), patients who need supplemental oxygen during transport, and patients who cannot tolerate a mask. It allows the patient to talk, eat, and drink while receiving oxygen.
Simple Face Mask
The simple face mask covers the nose and mouth and delivers moderate oxygen concentrations. Flow rates range from 6 to 10 LPM, delivering approximately 35% to 60% FiO2. The minimum flow rate is 6 LPM to prevent CO2 rebreathing within the mask. The simple face mask is appropriate for patients requiring moderate oxygen supplementation who do not need high-flow oxygen.
High-Flow Oxygen Devices
Nonrebreather Mask (NRB)
The nonrebreather mask is the primary high-concentration oxygen delivery device in EMS. It features a reservoir bag that fills with oxygen and one-way valves that prevent exhaled air from entering the reservoir. Flow rate should be set at 10 to 15 LPM, and the reservoir bag must be fully inflated before placing the mask on the patient. The NRB delivers approximately 60% to 90% FiO2. Indications include significant hypoxia (SpO2 below 90%), shock, major trauma, carbon monoxide poisoning, and any patient requiring maximum oxygen supplementation without positive pressure ventilation.
Bag-Valve Mask (BVM)
The BVM can be used with or without supplemental oxygen. Without oxygen, it delivers room air (21% FiO2). Connected to oxygen at 15 LPM with a reservoir, it delivers close to 100% FiO2. The BVM is used for patients who are not breathing adequately (respiratory failure or arrest) and require positive pressure ventilation. Deliver ventilations over 1 second with just enough volume to produce visible chest rise. Avoid excessive volumes, which cause gastric distension and increase aspiration risk.
Venturi Mask
The Venturi mask delivers precise, fixed oxygen concentrations using interchangeable color-coded adapters (typically 24%, 28%, 31%, 35%, 40%, and 50%). It is primarily used for COPD patients who require precise low-flow oxygen to avoid suppressing their hypoxic respiratory drive. While less common in EMS than in hospital settings, understanding the Venturi mask is important for the NREMT exam.