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.

Upcoming Activity

Posted on September 25, 2025 by Pat Neligan

The next 3 tutorials will be on the impact of Carbon Dioxide in Acid Base. This is different from the tutorials in the Acid Base series – and is complementary – but you don’t have to review that series to follow the tutorials. The tutorials follow directly on from those in the Vapors and Gases series.

I will be speaking at the ASA in San Antonio – on Stewart Acid Base on Oct 11th at 4pm. My updated chapter on that topic in the new edition of Miller should be available shortly. Drop by and say hello if you are in Texas.

I will be instructing on the JFICMI Mechanical Ventilation course in Galway on October 24th.

I will also be co-hosting this year’s Hi-Impact Critical Care Conference 6.0 Sepsis in Galway, at the Clayton Hotel, on November 7th.

I am organizing next year’s Western Anaesthesia Symposium at the Lake House Glasson, near Athlone, Ireland, on April 17th and 18th. It will be an awsome – fully interactive highly clinical meeting in a great location.

I am the co-convenor of the College of Anaesthesiologists Annual Congress, and organizer of the ICSI (Intensive Care Society of Ireland) ASM (at the same conference) on May 21st and 22nd 2026. This will be a really useful meeting for Anaesthesiologists and Intensive Care Specialists, and we (the CAI Council) hope you will be able to attend.

I am delighted to receive feedback on the tutorials and videos that I have posted, so if you come across me at any of those conferences – please tap me on the shoulder and we will have a chat over coffee, beer or wine.

Finally, the Eagle eyed of you will note that I am posting videos on @or2icu and @ccmtutorials. The or2icu channel will be used for rough cuts of videos (to get them out earlier – but there may be some mistakes), and random thoughts and (sometimes unedited) short videos that I will not be posting on the main channel. I will use it for audio only podcasts. On occasion I will post clips from other long videos that I think are worth watching. So, it is worth subscribing to both channels.

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.

A SHORT COURSE ON LOCAL ANESTHETICS

Posted on May 28, 2025 by Pat Neligan

I published 3 tutorials on Local Anesthetics this Month. These are part of a new series of Anesthesiology Tutorials.

Tutorial 1 looks at the basic pharmacology of local anesthetics

Tutorial 2 looks at the various different drugs that we use, the volume and concentration. I discuss the maximum safe doses at the end of the tutorial.

Tutorial 3 looks at the history of, the diagnosis of and the treatment of Local Anesthetic Systemic Toxicity (LAST)

Anaphylactic Shock

Posted on April 3, 2025 by Pat Neligan

This tutorial, from the Introduction to Critical Care Series, looks at perioperative anaphylaxis. It covers topics that are relevant to practitioners in the OR, ICU, ED and wards.

Nutrition 3 – Timing and Route of Nutrition in ICU

Posted on March 19, 2025 by Pat Neligan

This HI-Impact tutorial looks at the common questions relating to commencement and route of nutrition in critical care. Is TPN good, bad or indifferent. Is enteral feed better than parenteral? When should we start feeding? Is it useful to add parenteral feed to enteral if the patients’ caloric goals have not been met? When should patients achieve their isocaloric goals. I guarantee you’ll learn something.

Cardiovascular Assessment 1: The Heart Rate

Posted on September 4, 2024 by Pat Neligan

This is the first tutorial in the cardiovascular assessment module. In the tutorial I discuss heart rate, how it originates and how it is controlled. This is principally a discussion about sinus bradycardia and sinus tachycardia. I go on to discuss the parasympathetic nervous system and the sympathetic nervous system, how they function physiologically and how they are impacted by drugs that we administer and disease processes. I provide a detailed discussion of adrenoceptor agonists and antagonists.

At Last – CHEST DRAINS!

Posted on August 21, 2024 by Pat Neligan

I feel like I have been working on this tutorial for several years. I actually have. When one encounters a modern chest drain unit in ICU for the first time or the 50th time it can be quite daunting. How much is draining? Is it oscillating? What does “bubbling” imply? When do you use suction? Why do some nurses leave a meniscus of fluid in the tubing but others don’t? What is the little red cap supposed to do?

This tutorial starts with a discussion of the physiology of pneumothorax and hemothorax, and then progressively visits one bottle, two bottle and three bottle systems. I then go on to explain how relatively modern chest drainage systems work, and how they need to be modified to apply suction – wet and dry. Finally I explain how very modern digital chest drainage systems work.

If you have struggled with understanding chest drains, I guarantee you’ll learn something.

ORtoICU

Tutorials in Anesthesiology & Intensive Care

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