Oxygen Delivery Systems

Plan to spend at least 20 minutes preparing for this talk by using the interactive board, clicking through the graphic, and becoming familiar with the order of the content that appears on the graphic. The teaching script below details how to walk through the talk. Every interactive or “clickable” element is denoted with a rounded box and cursor icon.

Anticipated time to deliver the talk with and without cases or other features:

• Without cases 20-25 min
• With cases 35-40 min

Objective 1 (The Basics): Name factors that impact oxygenation and ventilation

• Oxygenation is affected by inspired FiO2 and positive end expiratory pressure (or PEEP). Click on each button to reveal how they impact oxygenation.
• Ventilation is impacted by tidal volume (Vt) and respiratory rate (RR). Minute ventilation = Vt x RR.

Objective 2 (Oxygen delivery systems): Identify commonly used oxygen delivery devices and differentiate between them

Oxygen delivery devices used on acute care floors are largely limited to adjustments in FiO2. Non-invasive positive pressure ventilation (NIPPV), such as CPAP (continuous positive airway pressure) or BiPAP (bilevel positive airway pressure), provide PEEP to further support oxygenation.

In addition to PEEP and FiO2, oxygen flow rate (as compared to a patient’s inspiratory flow rate) can have an indirect effect on a patient’s oxygenation. It is important to recognize that the most commonly used oxygen devices on acute care floors (nasal cannula, simple face mask) deliver 100% FiO2 oxygen at an adjustable flow rate. This oxygen intermixes with ambient air (21% FiO2) which dilutes the oxygen to produce an “effective FiO2”. With respiratory distress, a patient’s inspiratory flow rate can range from 30 – 120 L/min, which far exceeds the flow rate provided by some oxygen delivery devices and as a result, further dilutes the inspired oxygen. 

Only more advanced oxygen delivery systems (Venturi mask, high flow nasal cannula) allow fine tune control over the delivered FiO2.

Click on each type of oxygen delivery device to learn more. For this section, we recommend only choosing 4 of the modalities of oxygen delivery to focus on. Choose oxygen devices most relevant at your institution. Click on the numbered buttons in order to reveal additional information. Navigate back to the “O2 Devices” page using the table of contents in the left upper corner. 

• Nasal cannula– the most commonly used form of oxygen delivery on the medical wards. It is most effective between 2-6L/min. Effective FiO2 is impacted by work of breathing and mouth breathing.
• Simple face mask – another commonly used form of oxygen delivery on the medical wards. More effective for patients who are mouth breathers and can deliver higher maximum FiO2 than nasal cannula. It creates a small reservoir of 100% FiO2 oxygen in the mask, which dilutes out the inspired ambient air. With nasal cannula, the reservoir is our nasopharynx (~50 mL).  The larger the reservoir, the less ambient air is entrained with every breath.  Limitations include preclusion of eating,  potential rebreathing of CO₂.
• Venturi mask – the Venturi device entrains ambient air and mixes with 100%  FiO₂. to deliver a fixed FiO₂. It can deliver higher max FiO₂ than nasal cannula and is ideal for delivering a set FiO₂ to patients with a variable breathing pattern. 
• Oxymizer – contains a small reservoir that allows higher flow rates and higher effective FiO₂ to be delivered compared to nasal cannula. It also contains thicker nasal prongs which reduces entrainment of ambient air. 
• Non-rebreather (NRB) – this is a rescue form of oxygen only! NRB masks contain a larger reservoir bag that is filled with 100% FiO₂ oxygen. A set of one way valves ensures the patient breathes in only from the reservoir bag, effectively delivering near 100% FiO₂. This is a quick way to improve a patient's oxygenation but should be de-escalated to another form of oxygen delivery such as nasal cannula, face mask, oxymizer, Venturi mask, or high flow nasal cannula. 
• High flow nasal cannula (HFNC) – HFNC is a newer form of oxygen delivery device that allows for delivery of high flow rates that can more closely match a patient’s inspiratory flow rate and high FiO₂. HFNC has been shown to not only improve oxygenation, but also to improves work of breathing and minute ventilation (V_E). This is also the only form of delivery device that delivers a small amount of PEEP, though it is not readily measurable or adjustable.
  • Bonus: A number of studies have shown the benefit of HFNC compared to traditional oxygen therapy in patients with acute hypoxemic respiratory failure. The FLORALI study (NEJM, 2015) was a multicenter study that randomized 313 patients with acute hypoxemic respiratory to receive HFNC, standard oxygen therapy (continuous NRB face mask) or NIPPV and evaluated intubation rates and mortality. The study found there was no statistically significant difference in intubation rates between the 3 groups at 28 days. However, there was a statistically significant difference in all cause mortality at 90 days and in ventilator free days at 28 days. Subgroup analysis did show that in patients with more severe hypoxemia (PaO₂/FiO₂ ratio < 200), there was a statistically significant difference in intubation rates at 28 days.
  • HFNC also potentially lowers risk for reintubation. Hernandez, et al. in 2016 in JAMA randomized 527 patients to HFNC or conventional oxygen therapy (nasal cannula or NRB) after extubation. At 72 hours, reintubation rates were 4.9% in the HFNC group compared to 12.2% in the conventional group (p = 0.004). Subsequent studies⁹ looking at patients at higher risk for extubation failure have not demonstrated statistically significant difference.

Objective 3 (NIPPV): Differentiate between CPAP and BiPAP and their impact on respiratory and cardiac physiology

Both CPAP and BiPAP allow for titration of FiO₂ and PEEP.  Click on CPAP and BiPAP in the chart to learn more about their differences.

• CPAP – CPAP provides a continuous pressure throughout inspiration and expiration. The positive pressure applied at end expiration is effectively PEEP.  CPAP only affects oxygenation and should only be used with patients with hypoxemic respiratory failure.
• BiPAP – BiPAP provides an inspiratory positive airway pressures (IPAP) and expiratory positive airway pressure (EPAP). The EPAP is effectively PEEP. The IPAP additionally recruits alveoli during inspiration and effectively increases the Vt, affecting ventilation. Thus, BiPAP can be used for both hypoxemic and ventilatory (hypercapnic) respiratory failure. The degree to which Vt is increased is determined by the difference between the IPAP and EPAP. 
• Effects on respiratory physiology – positive pressure ventilation has several effects on our cardiac physiology. It decreases RV preload, decreases LV preload, and decreases LV afterload – all of which is beneficial in acute cardiac pulmonary edema. Click on the numbered buttons for additional information. 

Objective 4 (Indications for NIPPV): Name indications for NIPPV

• Indications
  • The strongest evidence for use in acute respiratory failure is in acute cardiogenic pulmonary edema (both CPAP and BiPAP) and hypercapnic respiratory failure in patients with COPD exacerbations (BiPAP only).
  • Use in immunocompromised patients is driven by the rationale that endotracheal intubation and presence of indwelling tube increases the risk of infection.
  • Use of NIPPV has not been well studied and is not recommended in hypoxemic respiratory failure from ARDS (acute respiratory distress syndrome)10. In pneumonia, there is stronger evidence to support the use of NIPPV in patients with concurrent COPD¹⁰.
• Contraindications
  • Anything that prevents the patient’s ability to remove the mask – significant AMS, paralysis
  • Anything “coming out of the patient” – active nausea/vomiting, increased secretions
  • Inability to wear the mask – facial trauma
  • Recent esophageal/tracheal surgery (surgical anastomosis/healing at risk from increased pressure