Entrainment Ratios in Oxygen Therapy

This tutorial is best experience with a pencil and paper. Before I get into a discussion about high flow oxygen therapy you really need to understand flow. Conventional facemasks, Venturis and nasal cannula deliver modest flows of oxygen to the patient, but to ensure a correct FiO2, oxygen must be blended with air - in the airway or in the device. That air is drawn into the system by entrainment either from the room via the mask or mouth or injected in the case of Venturis into the breathing system. In any case - the inward flow of gas is determined, principally by the patient's inspiratory effort and the concentration of oxygen during peak inspiratory flow is, hopefully, kept constant.
In general, to keep FiO2 constant - a gas flow of at least 30L/min is required. Most devices deliver 40 liters or more, but only at lower FiO2 levels. It is essential to understand that, in this case, the 30 to 40L is NOT high flow - because it is "draw over" flow generated by the patient. High flow, as we will see in the next tutorial is delivered to the patient. For example - when delivering 24% and 28% oxygen to a patient - the total flow may be 44L but the fresh gas flow is only 2 to 4L. The remainder is entrained.
This tutorial explains the concept of gas entrainment and how to calculate entrainment ratios and flow rates. If you have never encountered this concept before, I guarantee that you will learn something!
@ccmtutorials. www.ccmtutorials.org
Description
00:00 Beginning and Introduction
00.47 Review of Previous Tutorial
01:45 Contents of This Tutorial
02:10 Clinical Scenario Oscar - Emergency Laparotomy
02:40 Oxygen and Air Blending
04:05 The Problem of Peak Flow Revisited
04:30 Problem - Manually Blending Oxygen And Air For A Desired FiO2
05:20 Old Fashioned Anesthetic Flowmeters
10:00 If I Deliver 7L of Air and 3L of Oxygen - What is the FiO2?
11:45 The FiO2 vs Flow Equation FiO2 = (Air Flow x 0.21) + (O2 Flow) / Total Flow
12:15 What is the FiO2 if I Deliver 3L of Air and 1L of Oxygen?
13:00 How Do I Figure Out How To Deliver 30% Oxygen With 4L of Flow?
13:13 The Air:Oxygen Equation: Air/Oxygen = (100% -FiO2)/(FiO2 - 21%)
14:30 I am delivering 30L of Flow and I want to give 35% Oxygen?
15:34 I am Using a FiO2 40% Venturi Device (Red) With 10L Oxygen Flow - What is the Total Flow?
16:35 The Magic Box Approach to Air / Oxygen Ratios
18:15 The Magic Box to Calculate Total Flow from 24% Blue Venturi (and other Venturis)
20:00 Calculating Out Total Flow From 60% Venturi (15L Oxygen)
20:48 Summary Of Entrainment Ratios For Different Venturi Devices
22:45 Why Patient Run into Problems with Flow at FiO2 of Greater Than 40%
23:00 What Oxygen Flow Rate Should Be Delivered To Obtain an FiO2 of 0.5 (50%) with a Total Flow of 70l/min?
23:24 Oxygen Flow Equation: (Total Flow x (FiO2 -21))/79
24:24 Why High Flow Devices Are Needed
25:20 Review Of This Tutorial
25:45 Preview of Next Tutorial