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Monday, June 19, 2017

SAQ Physiology Discussion with Dr. Tan HS

Hi all, Dr Tan has put forward a few good SAQ physiology for discussion. I do hope you guys utilise this masters blog to enrich both yourself and others in training.

SAQ

1) Describe the ionic basis for automaticity of cardiac pacemaker.

2) Classify the cause of hypotension in the early postoperative period, giving relevant examples (divide answer into preload, afterload and myocardial contractility).

3) Describe the determinants of venous return and the effect of general anaesthesia would have on these.

4) Draw a pressure volume loop for the left ventricle in a normal adult. Outline the information that can be obtained from such a loop.

5) Explain the physiological processes involved in the development of interstitial edema.

link to answers:
https://docs.google.com/viewer?a=v&pid=sites&srcid=ZGVmYXVsdGRvbWFpbnxiaXVzcWVofGd4OmVhMDVmODJkZDE0ZjAzNA

Monday, July 14, 2014

Pharmacology SAQ - Pharmacodynamics

1. Using opioids as examples describe and illustrate with graphs what you understand by the terms "potency", "efficacy", "partial agonist", "competitive antagonist", and "therapeutic index".

2. Briefly describe how drugs produce their pharmacological effects. Illustrate each mechanism with examples.

3. Define the terms “tolerance” and “tachyphylaxis”. Discuss the different mechanisms by which tolerance can develop, giving examples where appropriate.

Saturday, July 12, 2014

QEH Masters Teaching Roster

This is our teaching roster -- some topics are overlapped with Dr Johnny's and Dr Foo's classes - so those I put them way to the end -- in 2015.

All are welcome to these sessions - including those who are not in the Masters programme yet.

Our sessions for now will be Tuesdays and Fridays 3-5pm. And our venue ... is kinda small. Maybe use the pantry beside Dr Lily's room? Do adjust your day and time according to your needs as well.

https://docs.google.com/document/d/1e0_ahHcxVHuYReSIiuB2dUugLXHneRSuToZXuyg9hS4/edit?usp=sharing

Do add in your names on this document via Google Docs -- presenters and moderators. Thank you very much - Dr Lily reminded us to use this roster and our attendance to claim CPD points :) hehe.

Note: Presenters -- do contact your moderator early and do prepare early if possible.

Thursday, July 10, 2014

Some recommended books to read and help us through the primary exam

Hi... Just some recommended books and websites that are useful for readings and references:

CVS:


  1. Guyton and Hall Medical Physiology - the few chapters on CVS are excellent and everything is explained in details. Guyton and Hall
  2. Ganong Medical Physiology - concise and power packed. But the American English may put some people off. Ganong
  3. LANGE Cardiovascular Physiology series - very comprehensive review on CVS. Strongly recommended if you havent had any CVS reference with you. Lange


Respiratory:


  1. Respiratory Physiology JB West - THE book of choice for respiratory system. Simple and concise, written in grandfather story-telling style. Jb West
  2. Pulmonary Physiology By M Levitzsky - an alternative to the JB west. Written by American. So no grandfather stories and in certain chapters, more detailed than JB West. Levitzsky
  3. Nunn's Respiratory Physiology - This is THE BIBLE of respiratory physiology. Most people will use it as reference rather than core textbook. But if you are dying to impress the examiners, go ahead. Nunn
  4. Guyton Medical Physiology and Ganong and any other physiology textbooks can be used. But the above 3 were written mainly related to anaesthesia and hence very attuned to matters related to anaesthesia. Therefore, it would be better to have those books than the pure physiology books per se. 


CNS:
  1. Principle of Physiology for Anaesthetist by Peter Kam - This legendary author is actually a Malaysian born Australian currently residing in you-know-where. He comes to the masters intensive course or as examiners. His book's chapter in CNS physiology is concise and simple to understand. But additional information may need to be obtained from other sources. Peter Kam
  2. Ganong Medical Physiology
  3. Guyton Medical Phsyiology

GIT / Hepatobiliary 
  1. Principle of Physiology for Anaesthetist by Peter Kam. This book is quite sufficient for the GIT and liver system. But for liver system, especially when you read on drug metabolism by liver, there will be a section on calculating liver blood flow. For this, recommended textbook will be Ganong Medical Physiology.

Maternal-Neonatal Physiology
  1. Principle of Physiology for Anaesthetist by Peter Kam. This is the only recommended book, and it is very well written. 

Pharmacology:
  1. Principles and Practice of Pharmacology for Anaesthetists by Norman and Norton. A very comprehensive and concise book for pharmacology. A must have I would say. Unfortunately, I only discovered this book after I had passed the part 1. Norman and Norton.
  2. Pharmacology for Anaesthesia and Intensive Care by Peck and Hill - This is a good book to read as a start if you are really new to pharmacology. It covers superficially of all the pharmacological topics in the primary exam. But it is NOT sufficient to use this book to pass the primary exam, I am very sure about it. So, use this book to grasp a basic understanding or an overview of the pharmacology topics before reading them in details. Peck & Hill
  3. Pharmacology and Physiology in Anaesthetic Practice by Robert Stoelting - This is considered the BIBLE of pharmacology for anaesthesia and most will use it as reference. But it is more than welcome to have the entire pharmacology section in your brain before the exam. Start reading early and you will be able to finish them. Stoelting


Clinical Measurement:
  1. Basic Physics & Measurement in Anaesthesia, by Prabook - Although it is written as BASIC physics, it is actually quite detailed when you read through. Furthermore, on the cover of the book, you will not find the author Prabook on it because this author died after the first edition was published. You will only find his name in the foreword of the book. Basic physics and measurement
  2. Essentials of Anaesthetic Equipments by Baha Al-Sheikh - This book mainly for part 2 of the exam but some of the info are still relevant for part 1. Have a look if you have the time. Baha Al-Sheikh
Above all, Kerry Brandis Viva of Physiology is a MUST have. Please get a copy if you havent had one.
Other recommended books include the following:
  1. Fundamentals of Anaesthesia by Tim Smith and Pinnock. It is a decent book to read on all aspects about physiology and pharmacology. For the pre-master, you can use this book for the entire physiology and pharmacology. Pinnock
  2. Clinical Anesthesiology by Morgan and Mikhail- Although this book has always been lauded as a MUST have for part 2 exam, it actually contains alot of information for primary exams, because the first few chapters is always on organ system based reviews. Usually it comes in 2 chapters - First chapter will be physiology of an organ, e,g, respiratory system, and implication to anaesthesia, followed by another chapter about anaesthesia for patients with respiratory problems. The pharmacology part is very interesting to read also because it incorporates clinical practice into pharmacology. Morgan Mikhail
  3. Drugs in Anaesthesia and Intensive Care by Sasada - This booklet helps alot in answering MCQs because it has all indication and contraindications and side effects and etc etc for all the drugs. So, can swallow the book just before the MCQs. Sasada
  4. Anaesthesia and Intensive Care A to Z by Gary Smith. This is actually more of a dictionary but alot of useful information regarding definitions and formulas included. A-Z 

Online resources:
  1. Anaesthesia MCQ - An online resources of MCQs, SAQs and etc.
  2. Mark Finnis Notes - Mark Finnis is an anaesthetist working at Adelaide Hospital.He has written quite a lot of notes pertaining to Anaesthesia. For the primary exam, just check on primary ANZCA examination notes.
  3.  ANZCA primary notes  - Relatively new website but contains alot of recent / latest questions from the ANZCA exams.
  4. FRCA primary exam recommended books - This website contains some recommended books for primary exam of FRCA.

That's all I could think of. Feel free to add in if you have come across other useful books or links. Sharing is caring. Dont be shy and dont be selfish.

Saturday, July 5, 2014

Some tips for answering SAQ

1. These are short answer questions -- so short notes or point form are allowed.
2. Be precise AND complete. Do not assume your examiner will understand your arrows, short forms, symbols and abbreviations.
3. Use tables / diagrams / graphs to save time and to provide structure to your answers whenever possible.
4. Read the questions carefully and plan your answer -- don't answer part B questions in part A and then you'll have to double write.
5. Practice LEGIBLE handwriting.
6. Time management is VERY important - do not answer BEYOND your 20 minutes for each question. I can't stress this enough -- most candidates will complain of inadequate time and it is perfectly normal NOT to have enough time. That's the way the exam is. Just write all you can within 20 minutes and go to the next question. 
7. GO straight to the point -- lengthy introductions will not give you marks -- this is not a viva.

Pharmacology SAQ - Pharmacokinetics

Instructions : Do read up on these topics, then give yourselves 20 minutes to answer each question. It is very useful to be able to practice answering within a limited time period -- so that your answers are concise and you don't run out of time before answering all questions.

Bioavailability
a. What is bioavailablity and how is it measured? (4 marks)
b. What are the factors that influence bioavailability of an orally administered drug? (6 marks)

a.
Bioavailability – the fraction of administered dose that reaches the systemic circulation unchanged.

Bioavalability = fraction absorbed x (1 – extraction ratio)

b.
Uptake – depends on the unionised, lipid soluble portion moving down a concentration gradient.

Ficks law of diffusion
Diffusion rate is proportional to the area, but inversely proportional to the thickness.
Diffusion rate is proportional to concentration gradient.
Diffusion rate is proportional to the solubility of the drug in the tissue, but inversely proportional to the square root of the molecular weight.

Drug factors
1. Formulation & dissolution – particle size & form (liquid, solid, sustained release, enteric coated)
2. PKa & ionisation - changes that favour the presence of the drug in its nonionized (lipid soluble) form increase absorption. Weak acids (aspirin) become highly ionized in the alkaline environment of the small intestine, but absorption is still good due to the large SA.
3. Ability to resist degradation – stability at different pHs, chemical or microbiological contents of GIT

Patient factors – position, age, pregnancy, gender, size.
1. Surface area - principle site of absorption is the small intestine, due to large SA. ↓bowel resections/disease.
2. Blood flow to mucosa
3. Gastric motility - gastric emptying rate, intestinal motility + transit time – affected by food, drugs & disease
4. Effects of disease
5. Drug interactions in the GIT lumen – food interactions, complexation (tetracyclines with divalent metal cations)
6. Passage through the GIT wall – metabolism by enzymes in intestinal endothelium
7. Compliance

Carrier mediated – levodopa, iron, calcium

Systemic availability post uptake
First Pass Hepatic Effect – drugs absorbed from the GIT enter the portal venous blood and pass through the liver before entering the systemic circulation. Hepatic extraction & metabolism can greatly diminish the systemic effect (e.g. propranolol, lignocaine).

Clearance
a. Define clearance. (2 marks)
b. Describe the clearance of drugs by the kidney and the factors that influence renal clearance of drugs. (8 marks)

a.
Clearance – the volume of plasma completely cleared of drug per unit time (L/hr or mL/min)
Clearance = rate of elimination from plasma  / plasma [drug]

b.
Renal Clearance   = rate of elimination urine / plasma drug concentration
                        = [urine] x urine volume / [plasma]

The kidneys are the most important organs for elimination of unchanged drugs or metabolites.
Water soluble compounds are excreted more efficiently than lipid soluble compounds. \metabolism to convert highly lipid soluble compounds to water soluble metabolites is important.
Drugs eliminated by the kidneys are correlated with endogenous creatinine clearance or serum creatinine concentration. The increase in these indices allows for an estimate of dosage reduction.

Renal excretion involves…
  1. Glomerular filtration – depends on protein binding, water/lipid solubility & glomerular filtration rate.
  2. Active tubular secretion – involves selective active transport processes. E.g. organic anions (PAH, urate, thiazides) & cations (A/NA, creatinine, morphine, atropine, LA).
  3. Passive tubular reabsorption – removes drugs from the lumen that has entered by the above 2 methods. Most predominant in lipid soluble drugs that can readily cross renal tubular cell membranes e.g. thiopental. Water solubility facilitates excretion. Influenced by rate of urine flow & pH (weak acids are excreted more rapidly in alkaline urine – more crosses, is ionized & \less able to be reabsorbed).


Context Sensitive Half Time
a. Define context sensitive half time. (2 marks)
b. Compare the CSHT of Propofol, Thiopentone, Fentanyl and Remifentanil. How does their CSHT differ and what are the factors that influence their CSHT? Illustrate and explain. (8 marks)

a.
Context-Sensitive Half Time – the time necessary for the plasma drug concentration to decrease by 50% after discontinuing a continuous infusion designed to maintain constant plasma concentration

b.
Context sensitive t½ - is a function of elimination t½ but also considers the combined effects of…
  1. Distribution - peripheral tissue uptake will decrease with infusion duration as the tissues reach equilibrium with plasma
  2. Rate of equilibration between plasma & effector site
  3. Elimination
  4. Duration of drug infusion
  5. Method of administration – bolus or infusion


Notes:
When drawing these diagrams - make sure some key-points are accurate
- propofol CSHT at 8 hours is 40 minutes
- fentanyl shoots up after 2 hours
- remifentanil remains at 4 minutes no matter how long the infusion time is

Thiopentone – highly protein bound & lipid soluble. Offset of action is by redistribution to inactive tissue sites. Context sensitive t½ becomes prolonged after »15mins due to return from peripheral compartments on infusion cessation, which slows the rate of plasma [thiopentone] decline. \poorly suitable for infusions. (t½ 11.6 hrs)

Propofol – rapid ESET & short context sensitive T½. Context sensitive T½  - for infusions up to 8hrs <40mins. The rapid metabolic clearance is so great that when infusions are ceased drug returning from tissue storage sites is not able to retard the decrease in plasma concentration. Excellent for infusions. (t½ 0.5-1.5hrs)

Fentanyl – fentanyl's context sensitive t½ is larger than other (al/su/remi-fentanils) if continuous infusion occurs beyond 2hours. This reflects large Vd, ­fat solubility & saturation of inactive tissue sites & return of opioid from peripheral compartments on infusion cessation, which slows the rate of plasma [fentanyl] decline. (»3-6hrs).

Remifentanyl~4mins & independent of infusion duration because of small Vd & extremely rapid clearance. (t½ 99.8% cleared in 6mins or less). Ideal drug for infusions.
Alfentanyl – some accumulation occurs, but is more predictable than fentanyl because it levels off at about 60mins after a 3+hr infusion \longer infusions make little difference. Vd is low & is not widely distributed \less is required to produce an adequate effective concentration, hence its rapid excretion. (t½ 96% cleared in 60mins).


With prolonged infusions the context sensitive t½  approaches the elimination t½.