Gastro-intestinal changes in pregnancy

 

SS_OB 1.1

Describe the physiological changes and their implications for anaesthesia that occur during pregnancy, labour and delivery, in particular the respiratory, cardiovascular, haematological and gastrointestinal changes.

There is delayed gastric emptying for 12 weeks gestation. TRUE/FALSE/CONTROVERSIAL

During pregnancy, liver blood flow remains unaltered. TRUE/FALSE

The lower oesophageal sphincter becomes incompetent in pregnancy solely due to the loss in the angle of the gastro-oesophageal angle. TRUE/FALSE

Epidural analgesia using local anaesthetics and no opioids can reduce gastric emptying. TRUE/FALSE

Gastrin from the foetus may slow gastric emptying TRUE/FALSE

 

 

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).

Corpus Curare Spiritumque

There have been some really good study / exam tips lately, so I thought I’d post something with a motivational flavour. (Also, I resisted doing a history post because it’s too close to the exam to risk taking you on a procrastination tangent).

 

ANZCA motto

 

“Corpus Curare Spiritumque” is the Latin motto which appears on the ANZCA coat of arms.

It translates as “To care for the body and its breath of life”. I think this encapsulates really well, so much of what anaesthetists do.

Whether we are in theatre, attending a trauma, in pre-admission clinic, or on a ward round, we are always focused on the whole patient. Especially in theatre, sometimes we are the only doctors who seem to have a handle on the big picture!

We are doctors who are good at keeping people alive. However, the full meaning of the “breath of life” can extend to include every aspect of homeostasis.

In order to live up to the lofty motto chosen by the Founding Fellows of the College, anaesthetists need a solid grounding in basic sciences.  That’s because we are surrounded every day by pharmacology, altered physiology, and technology.

At the end of the day, I hope that you can see the value and impact of all your study for the primary exam, in terms of your ability as an anaesthetist to “care for the body and its breath of life”.

 

 

Thiopentone

BT_GS 1.30 Describe and compare the pharmacokinetics of intravenous induction agents …

BT_GS 1.31 Describe and compare the pharmacodynamics of intravenous induction agents …

Thiopentone is a terrific drug. Unfortunately, the current generation of trainees lack familiarity and confidence with it. 

T / F  compared with propofol, a standard induction dose of thiopentone causes less vasodilation and less hypotension

T / F  when diluted with 20 mL water, 500 mg thiopentone makes a 2.5% solution, with a pH of 11  (regarding the pH, can you explain why you think this is true or false? Why is this pH necessary / not necessary?)

T / F  in plasma, thiopentone is 80% bound to albumin

T / F  thiopentone is a weak base with pKa 7.6 – therefore, 12% of an injected dose will be available to cross the blood brain barrier

T / F  the majority of thiopentone is metabolised to inactive metabolites

T / F  thiopentone effectively blunts the upper airway reflexes

♦♦♦♦♦

Now that you’ve become fascinated by thiopentone, it would be useful to use this knowledge to answer some SAQ’s.

  1. Write short notes on the pharmacology of thiopentone.
  2. Compare and contrast the pharmacology of propofol and thiopentone.
  3. Explain the advantages and disadvantages of propofol and thiopentone for induction of general anaesthesia.

These 3 SAQ’s are in ascending order of complexity, in terms of the level of understanding they are testing. Regurgitating your summary notes (Q1) is low level knowledge – a candidate may score highly without really understanding what they are writing. But Q3 requires not only the application of PK and PD data – this information must be further organised to address the advantages and disadvantages. Scoring well on this question would demonstrate a high level of understanding (appropriate given the “core” nature of the drugs in question).

Have a go at answering the 3 SAQ’s above. While the 3 answers will each contain some of the same information, the final answers will be quite different. Hopefully this will help you reflect on the importance of reading the question!!

 

 

Calcium

BT_PO 1.88 Outline the regulation of plasma calcium including the actions and control of vitamin D, parathyroid hormone and calcitonin

T / F  of the total calcium in plasma, 20% is present in the free ionised form

T / F  a decrease in plasma calcium causes the release of parathyroid hormone

T / F  PTH acts by directly (i) releasing calcium from bone, (ii) increasing calcium absorption from the GIT, and (iii) decreasing renal calcium excretion

T / F  vitamin D is converted to 1,25-dihydroxy cholecalciferol by UV light, which then acts to increase calcium absorption from the GIT

T / F  hypocalcaemia can prolong the QT interval

T / F  10 mL of 10% calcium chloride contains 6.8 mmol Ca++, and 10 mL of 10% calcium gluconate contains 2.2 mmol Ca++

Extra discussion questions:

  1. Following a total thyroidectomy, patients can develop hypocalcaemia. Can you explain why? What symptoms would develop, and what physiology explains these?
  2. Patients with bony metastases can develop hypercalcaemia. What is the mechanism of this? What symptoms would develop, and what physiology explains these?

Insulin

BT_PO 1.90 Describe the pharmacology of insulin preparations …
BT_PO 1.85 Describe the control of blood glucose

T / F  the beta cells of the islets of Langerhans secrete proinsulin, which is then cleaved in the plasma to insulin

T / F  soluble insulin (Actrapid) starts working 30 minutes after S/C injection

T / F  insulin aspart (Novorapid) is more rapidly absorbed than Actrapid because it consists of only the A chain of amino acids

T / F  insulin glargine (Lantus) is slowly absorbed because the insulin is complexed with zinc and protamine

T / F  biguanides act by increasing cellular sensitivity to insulin

T / F  insulin increases the uptake of glucose into the liver, by upregulating the number of GLUT-4 transporters

ETCO2

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

 

Study tip: Answering SAQs – make the most of your unconscious brain, but don’t let it fool you….

Ok, that title is a little cryptic, but bear with me….

We have probably all had experiences when we are asked to recall something which we are sure that we know (for me this is often a person’s name), but seems impossible to drag up from the depths of our brain. We give up and then the answer just pops into our consciousness. Perhaps this is your unconscious brain at work.

How can you use unconscious brain to your advantage during the SAQs? As soon as you read the questions your brain will start working on them. Make sure that you read all of the questions carefully in the first 10 minutes. Spend a bit of time carefully checking to see exactly what the question is asking, as you want to set your brain off on the right track. I will assume that you have studied well and have a good knowledge base. In spite of this, some questions may initially seem tricky: perhaps the information doesn’t spring to mind; you may not be sure how to structure the answer. That’s ok – don’t panic! Panic is shocking for your memory. Send these questions to the unconscious mind and get on with answering the questions you feel more confident with. When the time comes to answer the questions that you have set aside, hopefully your mind will have worked on them in the background and that knowledge will be easier to access.

Now for your second part – don’t let the unconscious brain fool you. This part applies to your SAQ practice. I suspect, and hope, that all of you are practising past SAQs. How do you do this? Here are some options:

  1. Do you select 6 questions at the start of your study session to write at the end?
  2. Do you choose some questions the day before to attack the following day?
  3. Have you put a whole lot of individual past SAQs in a box, from which you randomly pick a selection to look at and answer straight away?
  4. Do you have a friend/colleague put a set of questions in a sealed envelope to open and answer under exam conditions?

If you picked 3 or 4 – perfect! You are receiving a true reflection of how you could answer that question in the exam. The results may be confronting, but it will show your where a brush up is needed.

If you picked 1 or 2, I would contend that you are giving yourself an advantage that you will not have in the exam. You are giving your brain extra time to work on these questions even if you consciously try not to think about them.

There are still a couple of weeks until the next written exam. It’s not too late to give yourself some good quality SAQ practise. Any holes that you find in your knowledge should be easier to learn as this information is likely to have meaning for you.

Good luck everyone!! I am not sure that I will be back on the blog until after the written, but I wish you all of the best…..

….and just to finish, I couldn’t leave you photo free.

IMG_0692

“Brain” jellyfish, Mljet, Croatia

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….

P1020218

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 1.41 Nitric Oxide

Staying on a vaguely respiratory topic….

This little molecule is actually mentioned in two LOs, so double bang for your buck today.

Amix-Nutrition-Nitric-Oxide-120-kapslí

But perhaps Nitric Oxide itself will give you the most bang!!

BT_PO 1.41 Outline the pharmacology of drugs used to treat pulmonary hypertension including nitric oxide

BT_PO 1.58 Describe the pharmacology of anti-hypertensive agents and their clinical application, including the following agents:

  • nitric oxide
  • plus lots of others….

 

Nitric oxide is synthesised from l -arginine                                   TRUE/FALSE

Nitric oxide for inhalation is stored in cylinders diluted with nitrogen   TRUE/FALSE

Nitric oxide inhibits platelet activation                                           TRUE/FALSE

Inhaled nitric oxide improves oxygenation by reducing V/Q mismatch   TRUE/FALSE

Effects of NO on the immune system are beneficial                     TRUE/FALSE