Louise's SAQ feedback

Question 1

What are some of the characteristics of left coronary blood flow?

Mention graph of flow vs. time

Answer 1

perfusion during diastole.

Graph of flow vs. time
Systole
- Initial reversal of flow during isovolumetric contraction.
- Flow increases and peaks at peak aortic systolic pressure then drops

Diastole
- Flow rapidly increases during diastole and peaks at mid diastole.

Question 2

What is the definition of Starling resistor?

Answer 2

a conduit where resistance to flow increases as its transmural pressure
decreases

Question 3

What are the factors that govern the resistance of coronary arteries?

Answer 3

Poiseuille’s Law
Blood viscosity
Metabolic auto regulation - vasodilator release triggered by local metabolites

Myogenic autoregulation - smooth muscle stretch results in contraction

Autonomic control - mild effect. SNS directly vasoconstrict coronary vessels (via a1 receptors), but also causes indirect SNS stimulation of heart -> metabolic auto regulation to vasodilator.

Question 4

What is the chemical structure of dantrolene?

Answer 4

a hydantoin derivative related to phenytoin

Question 5

Where is the action of dantrolene?

Answer 5

acts at the level of the dihydropyridine receptor to block electrical transmission to RYR1 receptors.

Question 6

What are the adverse effects of dantrolene?

Answer 6

irritant if extravasated / thrombophlebitis (pH 9-10)
Generalised muscle weakness
Sedation
Diuresis due to addition of mannitol
N / V /D
Hepatitis or pleural effusion from chronic use

Question 7

Dantrolene

• Metabolism?
• Half life?

Answer 7

Liver metabolism to active metabolite

3-12 hours

Question 8

What is the nerve supplying the nasal cavity?

Answer 8

Branches of trigeminal nerve mainly

Question 9

What does the glossopharyngeal nerve supply in the oropharynx?

Answer 9

posterior 1/3 of tongue
oropharynx
valleculae
Superperior surface of epiglottis

Question 10

What does the superior laryngeal nerve supply?

Answer 10

Divides into internal and external branches

Internal: sensation from epiglottis to above vocal cord
External: cricothyroid muscle

Question 11

What does the recurrent laryngeal nerve supply?

Answer 11

loops around ligaments arteriosum on left and around subclavian artery on right.

Inferior laryngeal nerve - sensation to larynx below and including vocal cords + trachea. Motor to all intrinsic muscles except for circothyroid

Question 12

Calculate the O2 content of an awake supine person breathing room air

Answer 12

PAO2 = FiO2 x (Patm - SVP of water) - PCO2/0.8

= 0.21 (760 - 47) - 40/0.8 = 100 mmHg

As a % of alveolar pressure, 100/760 = 13%, so 13% of FRC is oxygen

FRC = 30ml x 70kg = ~2000L

2000 x 0.13 = 260ml

Question 13

What are the benefits of THRIVE?

Answer 13

apnoeix oxygenation
Continuous positive airway pressure of 7cmH2O
apnoeic ventilation - continuous insufflation to facilitate oxygenation and CO2 clearance through gaseous mixing and flushing of the headspace.

Question 14

What is the effect of liver failure on volume of distribution?

Answer 14

Decrease plastic protein concentration

• Significant effect on highly protein bound drugs
• Increased free fraction -> increased effect and potential toxicity

Question 15

Why is there is drop in BP and rise in HR on phase 3, release of Valsalva maenuvre?

Answer 15

Phase 3 - release of breath
- Release of force against preload -> increase RV preload -> inter ventricular dependence -> further reduce LV preload -> reduce LV CO

• person usually takes a deep breath here, which exaggerates the preload response
• Low CO triggers baroreceptor reflex to increase HR

Question 16

In phase 4 of Valsalva, why is there an overshoot of blood pressure?

Answer 16

The systemic vascular resistance remains high after the period of increased intrathoracic pressure.

HR here can also return to lower than baseline level due to baroreceptor reflex.

Question 17

What does the valsalva manoeuvre indicate?

Answer 17

Autonomic function 
Cardiac function (less response in people in heart failure)
B-blocked: less phase 4 overshoot, less fluctuation in heart rate.

Question 18

Why is there a greater risk of hepatotoxicity with des over servo?

Answer 18

Des - minimal hepatic metabolism of 0.02%

Metabolised to trifluoroacetyl adducts which have the potential to cause hepatotoxicity via immune mediate mechanisms

Question 19

What is the dose of intralipid in LAST?

Answer 19

use 20% intralipid
Initial bolus of 1.5ml/kg 
followed by 0.25ml/kg infusion
If sign of LAST not stopping, bolus another 0.5ml/kg 
Safety limit up to 10ml/kg