You might say I'm biased, but don't we have the best field in medicine?
The core business of critical care is mechanical ventilation. This page gives you an overview of the various articles I've written on the subject. So consider this a work in progress. The end goal? This should become a basic to advanced course in mechanical ventilation. See the roadmap below for the plans I have. I'm making this public so you can hold me accountable when I've slacked off ;)
Stay tuned for: terminology, modes, physiology of positive pressure ventilation, PEEP, MV in ARDS, MV in COPD, basic trouble shooting, etc. …
So we've talked about the importance of safe mechanical ventilation and one way of quantifying safe mechanical ventilation during pressure support. We've also discussed driving pressure as an important parameter during mechanical ventilation, as it is directly related to mortality. Now get this, it's possible to measure driving pressure during pressure support! Sure, there are some caveats and considerations, but why am I so excited about this?
During COVID-19 we've obviously had a tremendous influx of patients with ARDS. A lot of these patients require mechanical ventilation for weeks. In early ICU admission phases, these patients are usually ventilated with a controlled mode, which makes it easy to guide safe mechanical ventilation and also measure driving pressure and compliance. Static compliance can be used as a decent way of quantifying “how sick their lungs are”. …
This article covers triggering, cycling and basic ventilator modes and settings.
Consider a patient's respiratory rate of, for instance, 20 breaths per minute. One breath consists of an inhalation and exhalation. The ratio of inspiration to expiration is typically 1:2. This means that for 20 breaths per minute (i.e. 60 seconds), one breath cycle takes 60/20 = 3 seconds. Of these 3 seconds 1 second is used for inspiration (inspiratory time), and 2 seconds is used for expiration. These settings are available on your ventilator; we'll get back to that in a minute.
Our lungs have 23 generations of airway branches. Surface area increases as we travel deeper within the lung. The functional unit of the lungs are the alveoli, responsible for oxygenation and ventilation, which together have a surface area of around 70 m².
For healthy individuals, total lung capacity (TLC, after maximal inspiration) is 6–8 liters. Residual volume (RV, after maximal expiration) is 2–2.5L. The difference between the two is called the vital capacity (VC), 4–6L. Functional residual capacity (FRC, after normal expiration) is 3–4L, which decreases when lying down, during anesthesia, etc. In short, everything that causes atelectasis. Anatomical dead space (Vd) is around 100–150ml, does not contribute to ventilation and is about 30% of tidal volume (Vd/Vt = 0.3). This obviously increases when we add stuff that does not contribute to ventilation, like an endotracheal tube, ventilator tubing, etc. …
An important parameter to guide safe mechanical ventilation is driving pressure. In this article, we learn how to calculate driving pressure, its origin, and most importantly, how to use it in clinical practice.
Driving pressure (DP or ΔP) is calculated by taking the difference between the pressure at end inspiration (when flow is 0) and the pressure at end expiration (when flow is 0). This means that during volume controlled ventilation, driving pressure is the difference between plateau pressure (Pplat) and total PEEP. Measurement thus requires an inspiratory and expiratory hold.
Patient Self Inflicted Lung Injury (PSILI) is a relatively new concept within mechanical ventilation. It implies that a patient can cause harm to their own lungs, creating barotrauma due to excessive transpulmonary pressure as a result of increased patient respiratory effort.
In Pressure Support mechanical ventilation it's not always easy to identify patients at risk of PSILI. This page will attempt to show you how.
Intensivist Dr. Bertoni proposed a method to estimate respiratory effort: he proposed that by performing an expiratory hold and determining the nadir of the pressure curve, you could determine the force that the patient is applying to the ventilator in order to receive an inspiration, i.e. the predicted muscular pressure or Pmus. Despite seemingly adequate respiratory support by the ventilator, some patients still show signs of increased respiratory effort. The predicted force applied specifically to the lungs, i.e. …
Dyssynchronies between inspiratory attempts of the patient and the inspiration by the ventilator could cause ventilator-induced lung injury (VILI). It is therefore important to recognize these dyssynchronies and act accordingly. On this page, you’ll find a quick overview of common dyssynchronies and how to treat them.