PEMS LOs

Question 1

What is the MOA of amitriptyline?

Answer 1

Competitive inhibition of neuronal uptake of noradrenaline and serotonin to increase neurotransmitter in synapse.

Also acts on muscarinic, histamine, a-adrenoceptors.

Question 2

How do drugs interact with amitryptyline?

Answer 2

Hyosine, chlorpromazine and prochlorperazine displace TCA from their binding sites on plasma proteins and increase TCA activity

Thiopentone increases the hepatic metabolism of TCAs

TCA toxicity may occur in the presence of Cimetidine due to CYP450 inhibition

Question 3

Why do we use assisted mechanical ventilation?

Answer 3

Types include pressure support and SIMV

Preserves diaphragmatic activity which

• Reduces need for sedation and paralysis
• prevents disuse atrophy
• Minimises the CV effects of mechanical ventilation

Improves V/Q mismatch

Question 4

What is the capillary hydrostatic pressure (A+V) and interstitial hydrostatic pressure (A+V)

Answer 4

Cap arterial - 32 mmHg venous 15mmHg

Inter arterial - 0 venous 3

Question 5

What is the oncotic pressure of systemic capillary and interstitium

Answer 5

Systemic - 25mmHg due to albumin, globulin, fibrinogen

Interstitial - 3mmHg

Question 6

Mathematically explain why pulmonary capillaries favour net movement into capillaries from interstitial space.

Answer 6

Starling’s forces
Fluid movement = Hydrostatic pressure of (cap - interstitial space) - Oncotic pressure of (cap - inter)

= 10 - 0 - (25 - 10) = 10 - 15 = -5

Question 7

For glomerular membrane, what are the values for

• Capillary hydrostatic pressure
• Tubular hydrostatic pressure
• Capillary oncotic pressure
• Tubular oncotic pressure

Answer 7

• 60mmHg, much high than systemic / pulmonary cap
• 15 mmHg
• 25 mmHg
• 0 mmHg

Favours movement into tubule

Question 8

What are the chemical reactions for phase 1 liver metabolism?

Answer 8

HOR
Hydrolysis
oxidation
reduction

Question 9

List some drugs metabolised by CYP 2D6

Answer 9

Tramadol
Codeine
Metoprolol
Oxycodone

Question 10

List some drugs metabolised by CYP 2C9

Answer 10

Propofol
warfarin
Parecoxib
Losartan

Question 11

List some drugs metabolised by CYP 3A4

Answer 11

diazepam, midazolam
fentanyl, Alfentanil 
Lignocaine, amide LA 
Vecuronium 
Oxycodone

Question 12

List some CYP inhibitors

Answer 12

CAGE

Cimetidine
Amiodarone
Grapefruit
Ethanol / erythromycin

Question 13

List some CYP inducers

Answer 13

SCRAP

Smoking / steroids 
Carbamazepine 
Rifampicin 
Alcohol 
Phenytoin

Question 14

What is

• Humidity
• Absolute humidity
• Relative humidity

Answer 14

Measure of moisture or dampness of a gas, usually air

Absolute - mass of water vapour present per unit volume of air

Relative - amount of water vapour present / amount of water necessary for saturation at the same temp and pressure

Question 15

What is the principle of a hair hydrometer

Answer 15

Hair gets longer as the humidity rises and the hair controls a pointer moving over a scale.

Gives direct reading of relative humidity

Question 16

What is the principle of a wet and dry bulb hygrometer

Answer 16

Consists of two thermometers

• One measures true ambient temperature
• The other measures lower temperature due to the cooling effect of evaporation of water from the wick surrounding the bulb.
• The difference in temp is related to the rate of evaporation of water which in turns depends on ambient humidity.

Use a set table and obtain relative humidity from the temperature difference.

Question 17

What is the principle of a dew point hydrometer

Answer 17

Consists of a silver tube which contains diethyl ether.

• Silver has high thermal conductivity so the temp outside the tube is the same as the temp in contact with ether.
• Temp of ether is monitored with a thermometer

Gas flow over the top of the tube leads to continued evaporation of the ether causing cooling

Temp of the silver tube continues to drop as ether evaporates

A dew appears on the outside of the tube. The temp at which this dew first appears is the dew point.

At this dew point the air layer on the outside of the tube has just become fully saturated with water vapour and dew now forms

Can then mathematically derive the relative humidity.