If you go into most ICUs today, the most commonly used mode of ventilation is Pressure Support. There are many reasons for this: it is widely believed that supporting spontaneous breathing results in less muscular – and in particular diaphragmatic – atrophy; patients require minimum sedation and can be gradually weaned and, because it is a pressure targeted mode, there is biologically variable ventilation. Although not every ICU uses Pressure Support as part of its invasive ventilation strategy, virtually all units use it for non invasive ventilation. If you work in ICU you MUST understand Pressure Support. In my view it is the MOST important mode of ventilation. It is also the easiest mode to get started with and one of the most difficult to master.
These are four tutorials on Pressure Support Ventilation – starting with Triggering, then Breath Initiation, then Setting the Level and, finally, Expiration. The first tutorial introduces the concept of Assisted Spontaneous Breathing and Pressure Support and revisits Triggering – Flow and Pressure Triggering. Although I covered this in the introductory tutorials, I go into much greater detail here. In particular I cover Undertriggering and Overtriggering. I guarantee you will learn something.
I decided to do a tutorial on end tidal CO2 as there has been a lot of discussion about it’s merits and limitations in our practice. It is fairly long and can be broken into sections at 20 minutes and 37 minutes if you have a short attention span (I will split it up into smaller segments at some stage in the future).
The content is absolutely essential for doctors and nurses working in anesthesiology and intensive care. In my opinion measuring expiratory CO2 from the ventilator circuit is the most useful clinical measurement tool that we have. It gives us information about cellular metabolic activity, blood flow, venous return, lung unit perfusion, gas exchange and alveolar ventilation. The tutorial commences with a discussion of CO2 as a gas and discusses Henry’s and Daltons’ laws. I then discuss the various different CO2 moieties, particularly bicarbonate. Subsequently I go on to discuss the impact of alveolar ventilation on PaCO2. After 20 minutes I move on to discuss capnometry – the measurement of the presence and quantity of CO2 emerging from the lung at end expiration. I discuss why the etCO2 may rise of fall. I then look at a specific clinical scenario where the etCO2 falls precipitously. After 37 minutes I discuss capnography – initially the normal capnograph and then a series of different capnography traces that you should be able to recognize. As a final thought I mention that CO2 is not the only waste produce or metabolic intermediary that we measure, routinely, in clinical practice.
Clinicians who work in anesthesiology, intensive care or emergency medicine who are involved in the management of respiratory failure must understand the problem of failure to ventilate: “can’t breathe, won’t breathe.” This long tutorial covers a lot of ground and could be viewed in split sessions.
My principle goal is to give you the tools to work the problem of respiratory failure. Along the way I introduce the alveolar gas equation, ventilation perfusion matching and lung volumes; particularly functional residual capacity. In the second half (from 28:20 onwards), I discuss anatomical and physiological dead space, calculate out the dead space to tidal volume ratio and show how you can be inadvertently increasing physiologic dead space by applying PEEP or neglecting auto-PEEP.
Even if you think you know a lot about this subject, I guarantee that you will learn something.
This is the second tutorial on Volume Controlled Ventilation. I discuss the evolution of ventilators from pure controlled mechanical ventilation, to intermittent mandatory ventilation – with spontaneous breathing to synchronized IMV with Pressure Support. This mode remains robustly popular around the world and critical care practitioners and anesthesiologists should be familiar with the mode, along with its advantages and disadvantages. I guarantee you will learn something. @ccmtutorials
I am now moving on to the “meat” of the mechanical ventilation course, starting with volume controlled ventilation. The first of these tutorials is on volume assist control. Even if you think you know a lot about this mode – stick with me, there is a lot of information packed in and I guarantee that you will learn something. Comments always welcome.
This is the last tutorial in the introductory module – “setting up a mechanical ventilator.” In this tutorial I will discuss how the ventilator cycles from inspiration to expiration. In controlled modes this is usually time cycling. However, traditionally volume cycling of volume control was used. On occasion the ventilator pressure cycles – and you must be aware of this as it may cause problems. Finally I will introduce the concept of flow cycling: it is imperative that you understand this process if you use pressure support ventilation. I guarantee you will learn something in this tutorial.
Next week we will be moving on to Volume Controlled Ventilation – specifically Volume Assist Control.
Plan For Upcoming Tutorials (Available Wednesdays – 09.00 GMT)
March 1st 2023 Tutorial 5: Volume Assist Control Ventilation
March 8th 2023 Tutorial 6: Synchronized Intermittent Mandatory Ventilation
March 15th 2023 Tutorial 7: Understanding Ventilation & CO2 Clearance
March 22nd 2023 Tutorial 8: Pressure Support Part 1 – Triggering the Breath
March 29th 2023 Tutorial 9: Pressure Support Part 2: Controlling the Initial Flow (the rise time)
April 5th 2023 Tutorial 10: Pressure Support Part 3: Setting the Pressure Support Level
April 12th 2023 Tutorial 11: Pressure Support Part 4: Controlling Exhalation (the EXPsens)
April 19th 2023 Tutorial 12: Measuring Oxygenation
April 26th 2023 Tutorial 13: Understanding Hypoxia and Oxygen Therapy Part 1
May 3rd 2023 Tutorial 14: Why Low Lung Volumes are Bad
May 10th 2023 Tutorial 15: Why we use PEEP and CPAP
May 17th 2023 Tutorial 16: Non Invasive Ventilation
May 24th 2023 Tutorial 17: Pressure Controlled Ventilation – Part 1 Assist Control
May 31st 2023 Tutorial 18: Pressure Controlled Ventilation – Part 2 Bilevel PC and Volume Guaranteed Pressure Control
June 7th 2023 Tutorial 19: How To Read A Blood Gas – Part 1 – Carbon Dioxide
June 14th 2023 Tutorial 20: How To Read A Blood Gas – Part 2 – Metabolic Disorders
June 21st 2023 Tutorial 21: The Patient with High Airway Pressures – Part 1 – Airway Pressure Monitoring and Flow Volume Loops
June 28th 2023 Tutorial 22: The Patient with High Airway Pressures – Part 2 – Treating the Problerm
July 5th 2023 Tutorial 23: The Patient is Fighting the Ventilator – Part 1
July 12th 2023 Tutorial 24: The Patient is Fighting the Ventilator – Part 2
July 19th 2023 Tutorial 25: ARDS – Part 1 – Understanding the Disease
July 26th 2023 Tutorial 26: ARDS – Part 2 – Treating the Patient with ARDS
Subsequently: Ventilator Weaning and Liberation Failure to Wean Tracheostomy Advanced Modes of Ventilation
How does the ventilator know that it needs to deliver a breath? The term to describe this is “Triggering.” In this tutorial I will cover time triggering, pressure triggering and the relentlessly confusing concept of flow triggering. I guarantee that you will learn something in this 12.5 minute tutorial.
Most bedside practitioners pay little attention to ventilator waveforms – usually just the tidal volume and, occasionally, the pressure waveform. However, mechanical ventilation is all about flow – if there is no flow there is no breath. In this tutorial I will look at flow patterns in patients attached to a ventilator. Patients who breathe spontaneously, without assistance, draw flow from the ventilator, the positive flow in inspiration is hemispheric in appearance, exhalation is a v shape – reflecting elastic recoil. Volume controlled ventilation may be delivered by either constant or decelerating flow, with or without an inspiratory hold (also known as a pause). The flow pattern in pressure control is always decelerating – as airway pressure rises, flow falls. Tidal volumes are variable in pressure control, as the negative pressure deflection during inspiration increases the inspiratory ramp and and hence the tidal volume.
I guarantee you will learn something from this tutorial and will never look at a ventilator the same way again.
As promised – here is the first tutorial from Module 1 (“Setting Up a Mechanical Ventilator”) of the course on Mechanical Ventilation. I discuss the difference between Volume Control and Pressure Control and Dual Control – including the advantages and disadvantages associated with each mode.
I have received quite a lot of feedback over the years regarding the original ccmtutorials website and what is apparent to me is that the Mechanical Ventilation Tutorials were unfailingly popular. Fortunately I have delivered quite a few Mechanical Ventilation lectures and tutorials over the past few years. I have redone, reworked and rethought all of this material through and now I am announcing a new version of the Mechanical Ventilation Tutorials for the 2020s. The tutorials will start to stream this week.
The first part of the course is titled: “Setting Up A Mechanical Ventilator” and this contains four tutorials. 1. Ventilator Control: Volume Control and Pressure Control 2. Flow Patterns 3. Triggering 4. Cycling Please follow these tutorials sequentially – you might think you know a lot about mechanical ventilation; you do not. Here is the intro spiel to the first module of the course: If you have ever sat into an unfamiliar car – a rental car or a new car for example – you need to take some time to figure out the controls. How does it start ? Manual or Automatic? Left or right sided drive? Where is the hand break – lever or button? The lights? The wipers? The de-mister? The radio? How you connect your phone etc. Before you ever put a patient onto a ventilator you need to understand how the machine works and how to set it up. This tutorial will look at the basics of setting up a ventilator – and this is essential material. Do not skip onto the next tutorial until you have learned this material.
(note I haven’t forgotten the fluid course – Hyponatremia and Hypernatremia to feature soon).