The Blood Gas Machine – Measuring Oxygen, pH, Carbon Dioxide, Tips and Tricks and Derived Variables

Posted on December 18, 2025 by Pat Neligan

To round out the year, here are three tutorials on the blood gas machine, blood gas analysis and the blood gas printout.

The first tutorial looks at how oxygen is measured using the Clark Electrode on the blood gas analyser and demonstrates the importance of co-oximetry in modern blood analysis. From that the fractional saturation of hemoglobin with oxygen is derived.

The second tutorial explains the Glass Electrode that measures pH and PCO2. Subsequently I cover problems you might encounter with blood gas sampling. If you don’t want to watch the technical stuff, I strongly recommend you scroll to the middle of the tutorial (12 minutes in) as it covers information that all healthcare practitioners must know.

The final tutorial looks at all of that other data that appears on blood gas printouts that you may never have understood – and it can be really confusing – DERIVED or calculated variables (bicarbonate, temperature correction, TCO2, O2 content, Base Excess, Standard Bicarbonate, Anion Gap etc.). I cover both the Radiometer ABL machines and the GEM 5000. I guarantee you’ll learn something.

Tutorials on Pulse Oximetry

Posted on November 5, 2025 by Pat Neligan

There are two tutorials on pulse oximetry. The first looks at the SpO2 and how it is measured. The second looks at the pleth waveform and problems that we commonly encounter with pulse oximetry in general. I guarantee you’ll learn something.

New Series – Fundamental of Anesthesiology – Gases and Vapors

Posted on July 24, 2025 by Pat Neligan

This is a new series on the Fundamentals of Anesthesiology – the first course is on Gases and Vapors. It should serve as a good introduction to the topic for early stage residents in Anesthesiology – but is also applicable in critical care and emergency medicine and nursing. For experienced practitioners it will be a straightforward refresher course – but I guarantee you’ll learn something.

First up I discuss the forgotten gas – water vapor – and why it is really important in our practice. The main concept that you must learn is the Saturated Vapor Pressure.

Metabolic Acidosis in 2025 – More Important than Ever!

Posted on May 28, 2025 by Pat Neligan

This is a longer version of the lecture that I delivered at the 2025 College of Anaesthesiologists of Ireland Annual Scientific Meeting.

Mechanical Ventilation – Setting Up a Ventilator – Flow Patterns

Posted on February 8, 2023 by Pat Neligan

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.

ORtoICU

Tutorials in Anesthesiology & Intensive Care

Tag Archives: anesthesiology