Hepatic metabolism of drugs

BT_PO 1.108

Describe the alteration to drug response due to hepatic disease.

Metabolic clearance is usually constant and independent of dose. TRUE/FALSE

For drugs with an extraction ratio of nearly 0, a change in liver blood flow produces a nearly proportional change in clearance. TRUE/FALSE

Alfentanil is an example of a drug whose hepatic metabolism is capacity-limited. TRUE/FALSE

In cirrhosis, hepatic drug clearance is usually reduced. TRUE/FALSE

CYP3A4 is responsible for nearly half of all drug metabolism. TRUE/FALSE. Hint…this is the enzyme system affected by grapefruit juice (and interestingly, propofol).


BT_SQ 1.6 Describe methods of measurement (including) … gas analysis, including capnography
BT_PO 1.29 Discuss regional ventilation-perfusion inequalities

Each of the following T/F statements applies to a cardiac arrest with CPR being performed

T / F  an ETCO2 of 15 mmHg would indicate good CPR

T / F  the PaCO2 will correlate with the ETCO2

T / F  the lower ETCO2 is due to a reduced venous CO2 content

T / F  the lower ETCO2 is due to absent aerobic cellular respiration

T / F  the lower ETCO2 is due to increased alveolar dead space

Can you provide a rationale for the correct statements above, from first principles? Hint… this blog relates to learning outcome BT_PO 1.29


BT_PO 1.36 Discuss the physiological effects of hypoxaemia

Keeping with a similar theme….

I have to admit I was feeling a bit low on inspiration as I was writing this post and was wondering which LOs would be of specific interest to you, the reader.

If you have any LOs which you would  like to see a post on, please leave a comment and I will write on them at a future date. A full list of the more than 300 options can be found here

I have updated the Oxygen Cascade post to include quite a nice little article from BJA education…

…and here is another photo from the Plitvice Lakes….


BT_PO 1.36 Discuss the physiological effects of hypoxaemia, hyper and hypocapnia, and carbon monoxide poisoning

Hypoxaemia causes activation of the sympathetic nervous system  TRUE/FALSE

Hypoxaemia causes vasodilation in all tissue beds    TRUE/FALSE

Hb concentration rises acutely with hypoxia due to auto transfusion from the spleen TRUE/FALSE

Alveolar ventilation increases linearly as PaO2 falls below normal levels    TRUE/FALSE

In response to significant hypoxia, neuronal tissue initially becomes hyperpolarised TRUE/FALSE

BT_PO 1.23 Oxygen Cascade


This may seem like a pretty easy topic and, I agree, it is easy to memorise the step wise decreases in oxygen tension as you move from the atmosphere to the the tissue.

Why to these changes occur? Have you thought about the implications, on the oxygen cascade, of environmental and patient factors and how they may exacerbate the natural fall in oxygen partial pressure? Ask yourself these questions and, if you have a patient who is hypoxaemic, look to the oxygen cascade to give you an answer…

There is an great diagram, and accompanying text, in Ch 10 Nunn’s Applied Respiratory Physiology which will help you with your exploration of this topic. This article from BJA Education also contains some good information.


The most amazing cascades I have seen, even in the pouring rain,  – Plitvice Lakes National Park, Croatia….

BT_PO 1.23  Describe the oxygen cascade

Increasing alveolar ventilation will generally increase PAO2     TRUE/FALSE

The effect of a low inspired oxygen concentration can be offset by increased alveolar ventilation TRUE/FALSE

Hypoxaemia caused by increased shunt can be overcome by increasing FiO2  TRUE/FALSE

A sudden reduction in cardiac output will cause an immediate decrease in PAO2 TRUE/FALSE

Diffusion capacity limits oxygen uptake at the the pulmonary capillary in the healthy subject at rest   TRUE/FALSE

Proximal Convoluted Tubule

BT_PO 1.63 Describe glomerular filtration and tubular function

Regarding the proximal convoluted tubule:

Q. It reabsorbs 65% of filtered sodium and water.  TRUE/ FALSE

Q. It reabsorbs 65% filtered chloride.  TRUE/ FALSE

Q. Aquaporin channels are found on the luminal surface of the tubule cells.  TRUE/ FALSE

Q. Most of the glucose is reabsorbed via the paracellular route.  TRUE/ FALSE

Q. This is the principal site of urea secretion.  TRUE/ FALSE



IT_GS 1.8 Physiological changes associated with pneumoperitoneum and their implications for anaesthesia

Another practical LO for today. Miller’s Anaesthesia used to have a chapter devoted to this topic, but unfortunately it has vanished from the current edition. There is however a quite nice little section at the end of Chapter 21

Here is another brief overview of anaesthesia for laparoscopy. In the middle there is a section on the physiological changes. It is worth remembering that a number of the effects are worsened as the intra-abdominal pressure generated increases (one of the reasons for the alarm on the gas insufflation machine).

This chap (a male frigate bird) doesn’t have a pneumoperitoneum, but rather an inflated gular pouch – apparently irresistible if you are a female frigate bird. They can fly with that pouch inflated (I’ll show you a photo of that tomorrow)


IT_1.8  Outline the physiological changes that occur with and the implications for anaesthetic management of pneumoperitoneum

Harking back to yesterday’s post what do you think the effect of pneumoperitoneum is likely to be on renal function?

A pneumoperitoneum causes activation of the sympathetic nervous system TRUE/FALSE

Release of a pneumoperitoneum may be associated the ischaemia-reperfusion injury TRUE/FALSE

Pneumoperitoneum may be associated with abdominal compartment syndrome TRUE/FALSE

Trendelenberg positioning can reverse some of the haemodynamic effects of pneumoperitoneum  TRUE/FALSE (what effect will it have on the respiratory consequences?)

Pnemoperitoneum reduces respiratory system compliance TRUE/FALSE

BT_PO 1.71 Explain the effects on anaesthesia on renal function

I didn’t realise that this LO existed – found it when I was looking for a renal topic to post on, as there seem to be a dearth of renal posts on this site.

This is actually an important topic as relatively minor reductions in renal function are associated with worse peri-operative outcome.

I don’t have any kidney photos. Below is the best I could do for the genitourinary system. There are a whole series of these (some much more X rated) on view at MONA


BT_PO 1.71  Explain the effects on anaesthesia on renal function

Any anaesthetic agent which results in a reduction of blood pressure is likely to reduce GFR   TRUE/FALSE

Attenuation of the stress response to surgery is renal protective   TRUE/FALSE

Volatile anaesthetic agents may provide protection against ischaemia- reperfusion injury of the kidney TRUE/FALSE

IPPV improves renal blood flow TRUE/FALSE

Metabolic acidosis increases the kidneys’ vulnerability to nephrotoxins TRUE/FALSE

BT_PO 1.37 Describe the effect of morbid obesity on ventilation

Sticking with the topic of obesity.. The reference sources from  yesterday  will be valuable…

Look at that dessert (and the look of glee on my daughter’s face!). I can’t remember what it was called – obscene? -but just looking at it makes me put on weight 😊



BT_PO 1.37 Discuss the effect of the following on ventilation:

  • Changes in posture
  • Exercise
  • Altitude
  • Anaesthesia
  • Ageing
  • Morbid obesity

Morbid obesity is associated with decreased compliance of the respiratory system    TRUE/FALSE

FRC is 25% lower in a person with a BMI of 30kg/m2 compared with a person with a BMI of 20kg/m2    TRUE/FALSE

Resting  respiratory rate is increased by morbid obesity      TRUE/FALSE

The alveolar to arterial gradient (A-a gradient) of oxygen is increased with morbid obesity      TRUE/FASLE

The effects of obesity on the respiratory system are improved by lying down TRUE/FALSE

Are your patients talking about this…..

Two posts in one day!! Thought I might as well post about this whilst it was back in my brain.

On June 7 Richard Fidler conducted an interview on ABC local radio, on the topic of consciousness and anaesthesia.

Two patients asked me about it within 24 hrs of it airing……

One, who had listened to it on the day of his procedure, was mildly terrified by the interview ( I hadn’t heard it at that stage, but did my best to reassure him).

I listened to the interview on my walk in to work the following morning.

The first patient of the day mentioned the interview to me. She was fascinated! She had me repeat a random word to her throughout the case to see if she could recall it after the event – she couldn’t! [although I didn’t hypnotise her]

It came to mind today as I was listening to one of my favourite podcasts, Chat10Looks3 , where the interview is discussed again.

It is worth listening to. Make up your own minds about it. It is always good to be cognisant of the information out patients are receiving about our specialty – the information doesn’t always come from us…..

BT_PO 1.50 Describe the cardiovascular changes that occur with morbid obesity


I know those guys guys above are highly trained athletes, but…..

BT_PO 1.50  Describe the cardiovascular changes that occur with morbid obesity

This topic is not well covered in the standard primary exam texts. A textbook previously on the primary examination reading list, Foundations of Anaesthesia , had a whole chapter (Ch 71) devoted to the topic. Unfortunately, the new iteration of the book, Pharmacology and Physiology for Anaesthesia by Hemmings and Egan (a great book to look at), has dispensed with the subject – drats!!

The ANZCA library has three ebooks devoted to the peri-operative management of the morbidly obese. Each of these books has sections detailing the basic alterations of physiology associated with obesity. The most comprehensive of these is Morbid obesity: perioperative management 2e edited by Alvarez et al.

For those of you without access to the ANZCA library, here is a overview of some of the issues, from the little CME journal produced by the same group as the BJA.

Cardiac output increases linearly in proportion to free fat mass          TRUE/FALSE

Blood volume on a mL/kg bases is increased in the morbidly obese    TRUE/FASLE

Left ventricular hypertrophy (LVH) is common in morbid obesity, even in the absence of hypertension      TRUE/FALSE

Standard ECG criteria for diagnosing LVH are valid in morbid obesity   TRUE/FALSE

Angiotensinogen is produced by visceral adipocytes resulting in excessive angiotensin II TRUE/FALSE