The Fundamentals of Gases and Vapors Course is Now Complete!

In this tutorial I explain the fundamental principles behind modern anaesthetic vaporizers. I begin by exploring why volatile anaesthetic agents are stored as liquids, why saturated vapour pressure is central to vaporizer design, and the three key problems every vaporizer must solve.

I then compare traditional draw-over vaporizers with modern variable bypass (plenum) vaporizers before examining how contemporary vaporizers achieve accurate and reliable delivery using flow splitting, wicks, baffles and temperature compensation. Finally, I discuss tipping, overfilling and the position of the vaporizer within the circle breathing system.

Volatile Anesthetics

Posted on July 22, 2026 by Pat Neligan

In this tutorial we review the modern volatile anesthetic agents used in everyday anesthesia practice: sevoflurane, desflurane and isoflurane. We begin by explaining the key pharmacological concepts that every anesthesia trainee should understand, including blood-gas partition coefficient, oil-gas partition coefficient, tissue-blood partition coefficient, potency, onset of action, emergence, and minimum alveolar concentration (MAC). We also show how MAC is applied in routine clinical practice to achieve and maintain an appropriate depth of anesthesia.

The tutorial then compares the three commonly used volatile agents, highlighting their individual advantages and limitations, including speed of induction and recovery, metabolism, pungency, suitability for inhalational induction, and low-flow anesthesia. Finally, we examine their physiological effects on the brain, spinal cord, respiratory system, cardiovascular system, and other organ systems, explaining why these effects matter during routine anesthesia.

Nitrous Oxide

Posted on July 15, 2026 by Pat Neligan

In this tutorial we take a practical, evidence-based look at nitrous oxide—one of the oldest drugs in anaesthesia and still the only anaesthetic gas in routine clinical use. We explore its unique pharmacology, including the concentration effect, second gas effect and reverse second gas effect, explain why it remains useful during inhalational induction, and examine its true contribution to anaesthesia. The tutorial also reviews the evidence from major clinical trials, dispels common misconceptions, and discusses the important complications of nitrous oxide, including expansion of closed gas spaces, diffusion hypoxia, postoperative nausea and vomiting, vitamin B₁₂-related toxicity, and its environmental impact. By the end, you’ll understand when nitrous oxide adds real value to modern anaesthetic practice—and when it is better avoided.

Emergence From Anesthesia – Tissue Blood Partition Co-Efficient and Other Factors (2 tutorials)

Posted on April 2, 2026 by Pat Neligan

Part 1 – Tissue Blood Partition Co-Efficients

This tutorial explains why emergence from volatile anesthesia depends on more than simply turning off the vaporizer. It reviews how blood gas partition coefficients influence onset, how oil gas partition coefficients relate to potency and MAC, and then focuses on tissue blood partition coefficients as a key determinant of recovery. The tutorial describes anesthetic uptake into blood, muscle, and fat during short, intermediate, and long cases, showing how tissue storage increases with time and with agent solubility. It also explains tissue back diffusion, where anesthetic stored in tissues continues to return to the blood and brain after the vaporizer is turned off, delaying wake-up. Finally, it compares volatile agents such as nitrous oxide, desflurane, sevoflurane, isoflurane, halothane, and methoxyflurane, emphasizing how lower tissue solubility produces faster, more predictable emergence.

Part 2 – Other Factors that Impact Emergence from Anesthesia

This tutorial examines the additional factors that determine how quickly a patient wakes after volatile anesthesia. It covers the concentration-flow ramp, fresh gas flow, alveolar ventilation, and cardiac output, explaining how these influence washout of anesthetic from the lungs and circulation. It discusses the effects of poor gas exchange, atelectasis, duration of surgery, higher inspired concentrations, and obesity on tissue loading and delayed emergence. The tutorial also reviews hysteresis and MAC awake, showing why patients can remain asleep at concentrations lower than those required for induction. Other important contributors such as hypothermia, opioids, benzodiazepines, propofol, dexmedetomidine, clonidine, ketamine, and nitrous oxide are included, along with a discussion of spontaneous ventilation versus intermittent positive pressure ventilation. The overall message is that emergence depends on both how efficiently the lungs clear anesthetic and how much anesthetic the body gives back

Gases and Vapors – Anesthesiology Tutorials

Posted on March 19, 2026 by Pat Neligan

Here is the first part of the anesthesia specific tutorials on gases and vapors. Some of these are in the “beta” phase and are not published on my @ccmtutorials main channel. So, if you spot any glaring mistakes, don’t hesitate to contact me.

Blood Gas Partition Co-Efficient (speed of onset)

Oil Gas Partition Co-Efficient (potency)

MAC (Minimum/Median Alveolar Concentration) – The History of MAC

MAC – Part 2 – MAC Variants (MAC EI, MAC BAR, MAC Awake, MAC Amnesia)

MAC Part 3 – How to Use MAC in Clinical Practice

Volatile Anesthetics – How We Got to Here

Posted on February 4, 2026 by Pat Neligan

We are now moving to phase 2 of the course on Gases and Vapors – and this is principally directed to anesthesiologists.

General anesthesia is not simply unconsciousness; it requires hypnosis, amnesia, immobility, autonomic stability, and analgesia.
There is no universally agreed quantitative definition of anesthetic depth; practical clinical endpoints guide real-world anesthesia.
Ether ushered in modern anesthesia but was limited by high blood and tissue solubility and flammability, leading to slow induction and emergence.
Safety concerns, particularly flammability, led to the abandonment of agents such as cyclopropane despite favorable pharmacology.
Methoxyflurane represented a major advance but fell out of routine use due to extensive metabolism and fluoride-related toxicity.
Progressive halogenation of ether derivatives produced agents with greater stability, lower solubility, and reduced metabolism.
Isoflurane marked a major milestone due to its minimal metabolism and predictable pharmacology.
Desflurane offers extremely rapid onset and emergence but is limited by pungency and airway irritation.
Sevoflurane became dominant primarily because it is non-pungent and universally applicable, allowing inhalational induction and use across all patient groups.
Nitrous oxide historically reduced volatile requirements in high-flow systems but is less essential in modern low-flow anesthesia.
Understanding volatile anesthetics requires grasping blood–gas solubility, lipid solubility, tissue uptake, and their effects on onset, potency, and emergence.

These principles set the foundation for understanding MAC, its utility, and its limitations.

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 CAPNOMETRY AND CAPNOGRAPHY

Posted on December 12, 2025 by Pat Neligan

Here are three tutorials on inspiratory and expiratory CO2 gas analysis. Tutorial 1 looks at Capnometry and the process behind measuring CO2 in exhaled gas. I cover mainstream CO2 analysis and explain why the end tidal CO2 (EtCO2) may be high or low. Tutorial 2 addresses the Capnograph, the trace and anomalies of the Capnograph at the time of intubation. I also explain Sidestream and Microstream CO2 and gas analysis. The final tutorial will be very helpful to anesthesiologists, particularly those taking exams: I go through a series of abnormal Capnographs, explaining why they are abnormal. I guarantee that you will learn something.

ORtoICU

Tutorials in Anesthesiology & Intensive Care