Draw and explain the characteristics of a quantal dose-response curve that describes the major clinical effects of rocuronium. Outline medications and medical conditions that shift the curve to the left or the right.
Neuromuscular blockers and opioids can be used as clinical examples to test candidates’ understanding of the various types of dose response curves. Why do we recommend 2 to 3 times the “ED95” as the intubating dose for muscle relaxants?
T / F a quantal dose-response curve is semi-logarithmic
T / F the y-axis shows % twitch height reduction, from 0 to 100%
T / F for the specific case of muscle relaxants, the ED50 refers to 50% of the population achieving a 95% reduction in twitch height, and is also referred to as the ED95, or ED50(95%)
T / F a right shift in the curve reflects reduced potency, and could be caused by a recent dose of neostigmine, or one week of bed rest
T / F hypothermia increases the potency of rocuronium
T / F patients with myasthenia gravis would have a left shifted curve
If I want to check a registrar’s understanding of a certain topic, I will often ask about the basic physiology or pharmacology and then add a complication. This might be a disease process, a drug or an altered state of physiology. Those who have memorised an answer soon come unstuck when they are asked to apply their knowledge.
When you look through the ANZCA Primary Syllabus, such that it is, you will find a number of LOs related to these “complications”, including this one…..
BT_PO 1.108 Describe alterations to drug response due to hepatic disease
This little guy was in the case with the bears from yesterday’s photo (oh, how times have changed….)
The clearance of propofol is minimally affected by hepatic disease TRUE/FALSE
Patients with hepatic failure have a hyper-dynamic circulation, which will protect them from the cardiac depression effects of an induction dose of propofol TRUE/FALSE
Reduced plasma protein levels may result in a longer than expected duration of action for highly protein bound drugs TRUE/FALSE
All volatile anaesthetic agents have been shown to decrease hepatic blood flow independent of a reduction in mean arterial pressure TRUE/FALSE
Oral bioavailability of drug with a high extraction ratio, such as morphine, may be markedly reduced in patients with severe liver disease TRUE/FALSE
Ok, I’ve paraphrased that LO a bit, so that we can stay with the topic for one more day.
We give drugs to people with a high BMI on a daily basis (at least at the institution I work in..), so it is important that we know what the implications of a larger lipid load are and how to adjust our dosing…
For today’s picture I have chosen another one of Andy Paiko’s amazing glass works.
BT_PO 1.16 Describe alterations to drug response due to pathological disturbance with particular reference to cardiac, respiratory, renal and hepatic disease
This is a complicated issue [I’m giving you a free true statement]
It is appropriate to dose muscle relaxants, such as vecuronium and rocuronium, based on ideal body weight (IBW) TRUE/FALSE
When using propofol for maintenance of anaesthesia, calculate the infusion rate based on total body weight (TBW) TRUE/FALSE
The increased cardiac output seen in morbid obesity, will hasten recovery from volatile anaesthesia TRUE/FALSE
Plasma levels of pseudocholinesterase are increased with morbid obesity TRUE/FALSE
Suxamethonium doses should be based on TBW TRUE/FALSE
Outline the genetic variations in the cytochrome P450 2D6 enzyme and discuss the clinical relevance for drugs used in the perioperative period.
This enzyme is responsible for much of the variation in efficacy and toxicity of some commonly used drugs.
This enzyme metabolises tramadol into a more active metabolite TRUE/FALSE
Ondansetron may be ineffective with poor metabolisers TRUE/FALSE
Patients from the middle east are more likely to be ultrarapid metabolisers TRUE/FALSE
Approximately 90% of caucasians are poor metabolisers TRUE/FALSE
This enzyme metabolises codeine into a more active metabolite TRUE/FALSE
SS_OB 1.9 Describe the influence of pregnancy on the pharmacokinetics and pharmacodynamics of drugs commonly used in anaesthesia and analgesia
TRUE/FALSE In pregnancy the average gain of 8 litres of total body water significantly increases the volume of distribution of hydrophilic drugs.
TRUE/FALSE Foetal and placental tissues provide another compartment for drug distribution.
TRUE/FALSE Pseudocholinesterase activity is decreased in pregnancy causing prolongation of succinylcholine block.
TRUE/FALSE Pregnancy reduces MAC by 25-30%.
TRUE/FALSE Nociceptive response thresholds are elevated in pregnancy.