BT_PO 1.54 Pharmacology of beta receptor blocking agents

jan 2006 156

I asked about these drugs in the recent in exams and was fascinated (read horrified and astounded) that only one person had a plausible explanation as to how these little chaps cause hypotension…..

These drugs are actually mentioned in 5 LOs BT_PO 1.54 and BT_PO 1.57-1.60

We see a lot of patients on these drugs, partly because they have been shown to confer a survival advantage in people with heart failure, so it is probably a good idea to know a bit about them…

BT_PO 1.54 Describe the pharmacology of commonly used alpha and beta receptor blocking agents, their clinical use, adverse effects and use in the perioperative period


Metoprolol is metabolised by the CPY2D6, and hence prone to large inter individual variation in response   TRUE/FALSE

Beta1 selective blockers produce a significant reduction in blood pressure when given to normotensive individuals     TRUE/FALSE

Hypotension with beta blockers is mediated by the dilation of vessels in skeletal smooth muscle   TRUE/FALSE

Beta blockers cause a reduction in the release of renin TRUE/FALSE

Some beta blockers have an alpha agonist effect TRUE/FALSE

Another structure quiz

This seemed to be popular last time.

As with the structures shown previously, you are unlikely to have to draw these in the exam. Some of them, you wouldn’t be expected recognise. If you don’t recognise the molecule, have a look at its structure and see what clues that gives you to its function. Several of the molecules are related to each other. All of these molecules are, or have been, used in anaesthetic practice.

I have included a couple of historic interest

























The Lower Oesophageal Sphincter

One of the body’s most under-rated sphincters…

BT_PO 1.107

Explain the:

  •   Physiology of swallowing
  •   Factors preventing reflux of gastric contents into the oesophagus
  •   Control of gastric motility and emptying
  •   Composition of gastric fluid
  •   Physiology of nausea and vomiting

General anaesthesia reduces lower oesophageal sphincter tone. TRUE/FALSE

Cricoid pressure reduces lower oesophageal sphincter tone. TRUE/FALSE

Suxamethonium reduces lower oesophageal sphincter tone. TRUE/FALSE

The lower oesophageal sphincter is a physiological sphincter, primarily due to the oblique gastro-oesophageal angle. TRUE/FALSE

Relaxation of the lower oesophageal sphincter after swallowing is neurally mediated. TRUE/FALSE



BT_PM 1.9

Describe the pharmacology of the following agents applicable to pain management, including:

  •   Opioids
  •   Tramadol
  •   Local anaesthetic agents (also refer to the Regional and local anaesthesia clinical fundamental)
  •   NSAIDs
  •   Paracetamol
  •   NMDA antagonists
  •   Anticonvulsants
  •   Antidepressants
  •   Corticosteroids
  •   Inhalational analgesics – nitrous oxide, methoxyflurane

Methoxyflurane has a risk of nephrotoxicity and hepatotoxicity TRUE/FALSE

Methoxyflurane can be used in paediatric practice TRUE/FALSE

Methoxyflurane is safe in patients with Malignant Hyperpyrexia. TRUE/FALSE

The “Penthrox” inhaler dispenses 2-4% methoxyflurane. TRUE/FALSE

A large proportion of the inhaled methoxyflurane that is taken up by the body is removed from the body by exhalation. TRUE/FALSE

Labour physiology and pharmacology

SB_OB 1.9 and SB_OB 1.8

Describe the influence of pregnancy on the pharmacokinetics and pharmacodynamics of drugs commonly used in anaesthesia and analgesia

Describe the anatomy and physiology of pain in labour and childbirth


Paracetamol is a category A drug in pregnancy, but care should still be taken in patients with pre-eclampsia. TRUE/FALSE

The addition of lipid-soluble opioids to lumbar epidurals allows a reduction of local anaesthetic concentration. TRUE/FALSE

Visceral pain receptors located in the lower uterine segment and cervix extend to the spinal segments of S2-S4. TRUE/FALSE

Oxygen consumption increases by 40% during the first stage of labour. TRUE/FALSE


Entonox side effects include maternal sedation. TRUE/FALSE.

Wednesday is always a good day for primary revision.

SS_OB 1.4 … again.

Describe the utero-placental circulation and the principles of placental physiology as related to placental gas exchange and regulation of placental blood flow.

The primary limitation to carbon dioxide transfer across the placenta is blood flow. TRUE/FALSE

Maternal-fetal exchange of most drugs and other substances occurs primarily by diffusion TRUE/FALSE

Foetal O 2 saturation does not exceed 40% even with 100% O 2 delivery to the mother. TRUE/FALSE

The placenta synthesises progesterone from cholesterol. TRUE/FALSE

O 2 delivery to the fetus is facilitated primarily because the fetal oxyhemoglobin dissociation curve is righ-shifted. TRUE/FALSE.

Obstetric Week

SS_OB 1.4

Describe the utero-placental circulation and the principles of placental physiology as related to placental gas exchange and regulation of placental blood flow.

Pregnant women have normal peripheral sympathetic nervous system activity. TRUE/FALSE

Uterine blood flow in the non pregnant state is 700mL/min. TRUE/FALSE

Increased maternal systemic resistance can lead to increased placental blood flow at term. TRUE/FALSE

A “normal” blood pressure reading in a supine (term) pregnant woman’s arm is a reliable indicator of uterine perfusion pressure. TRUE/FALSE

If there is no maternal hypotension then neuraxial blockade does not alter uterine blood flow. TRUE/FALSE

BT_PO 1.46 Myocardial oxygen balance

This LO is a fertile source of SAQ questions.


And above, not really a fertile source for anything, but an appropriately shaped piece of rock left over from the burning of coal, at the Coal Mines Historic Site, operated by convicts from 1838-1848, near Port Arthur, Tasmania.

BT_PO 1.46  Describe the factors determining myocardial oxygen supply and demand and their clinical implications

Oxygen supply to the myocardium is flow limited TRUE/FALSE

In the normal heart, coronary blood flow and the metabolic activity of the myocardium move in parallel with each other TRUE/FALSE

Neural factors exert the dominant influence on myocardial blood flow TRUE/FALSE

For a given percentage change, pressure work by the heart increases oxygen consumption more than volume work does TRUE/FALSE

Reduction in heart rate often improves myocardial oxygen supply and reduces myocardial oxygen demand TRUE/FALSE