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18/7 Week LOs > Louise's SAQs > Flashcards

Louise's SAQs Flashcards

1
Q

How does a strain gauge produce electrical signal?

A

Deflection of the diaphragm introduces strain in the resistance wire.

Change in tension causes a change in resistance which can be measured and recorded.

Increase stretch of resistor = increased resistance

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2
Q

What is a Wheatstone bridge?

A

pressure transducer with 4 strain gauges which form the 4 resistances in the bridge.

  • Increases sensitivity of the pressure gauge
  • Allows the determination of an unknown resistance in terms of a known resistance
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3
Q

What does damping prevent?

A

Damping prevents a system from overshooting after responding to a change, particularly at frequencies close to the natural frequency of the system

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4
Q

What does underdamping cause? what is it caused by?

A

Co-efficient < 0.64, produces exaggerated peaks and troughs in the waveform.

Due to small tubing, or catheter occluding the vessel.

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5
Q

Pressure units

1 atm = ?mmHg = ?kPa = ?cmH2O = ?Bar

A

760 mmHg
101.3 kPa
1033cmH2O
1.013 BAR

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6
Q

What is vomiting?

A

Involuntary, forceful, rapid expulsion of gastric contents through the mouth.

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7
Q

What receptors are found at CTZ?

A

Ach, 5HT3, D2, H1, opioid

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8
Q

What class of drug is metoclopramide, and what are the mechanisms of action?

A

Benzamide
Anti-D2
some 5HT4 agonist activity
Cholinergic effect

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9
Q

What is an example of NK-1 antagonist?

A

Aprepitant

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10
Q

What’s the difference in MOA for promethazine vs. prochloperazine

A

Prochloperazine (stematil) - mainly anti-D2, some mAchR antagonism

Promethazine - mainly an anti-H1, especially useful for vestibular type N/V

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11
Q

Briefly describe the venous drainage of spinal column

A

Internal vertebral venous plexus, divided into anterior and posterior vessels within the epidural space
- Drain into vertebral veins

External vertebral venous plexus, anterior and posterior.
- Drain into azygos, lumbar and deep cervical veins

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12
Q

What’s the significance of Batson’s plexus?

A

Valveless veins from internal vertebral venous plexus. Responsible for cancer metastasis

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13
Q

Which drugs are broken down by plasma pseudocholinesterase?

A

sux, miva, ester LA

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14
Q

Which drugs are broken down by non-specific plasma esterases

A

remi
atracurium / cisatracurium
neostigmine

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15
Q

Why would pneumoperitoneum cause increased PVR?

A

reduced blood flow -> reduced PAP

Increased PCO2 -> increased V/Q mismatch via pulmonary vasoconstriction

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16
Q

How is renal blood flow affected by pneumoperitoneum?

A

Significantly reduced when pressure >20mmHg.
Due to high renal vascular resistance
Only 5% of GFR at > 20mmHG

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17
Q

Describe the MoA of unfractionated heparin

A

Heparin binds to ATIII, increases the activity by 1000x by a conformational change in the ATIII, exposing its active site for more rapid interaction with the activated clotting factors.

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18
Q

What are the factors the heparin inhibit?

A

IIa, IXa, Xa, XIa, XIIa

Mainly internal cascade

19
Q

Aside from clotting factors, what other effects does heparin have?

A

inhibit platelet function
Increases the permeability of vessel angiogenesis
Accelerates the clearing of post-prandial lipoprotein lipase from tissues

20
Q

Define 1 unit of heparin

A

Volume of heparin containing solution that prevents 1ml of citrated sheep blood from clotting for 1 hours after administration of 0.2ml of 1:100 calcium chloride

21
Q

What’s HITTS?

A

heparin inducted thrombocytopenia and thrombosis syndrome

22
Q

Features of type I HIT?

A

mild transient thrombocytopenia, PLT > 100
Totally reversed by heparin cessation
occurs in 10% of patients
Not associated with increased risk of thrombosis
Non-immune mediated, caused by drug induced platelet aggregation

23
Q

Features of type II HIT?

A

severe thrombocytopenia PLT approaching 0
occurs in 1% of patients
Associated with thrombosis in 30% of cases
Requires anticoagulation
IgG mediated, antibodies form within 5-10 days (can be more rapid with recurrent heparin exposure)
Can continue to worsen after heparin cessation

24
Q

Heparin side effects aside from HITTS and bleeding?

A 
osteoporosis 
allergy 
reduced TPR -> reduced BP 
alopecia 
local skin reaction / fat necrosis at injection site
25
Q

Soda lime equation

A

CO2 + H2O = H2CO3 (carbonic acid)
H2CO3 + 2 NaOH = Na2CO3 + 2H2O (sodium carbonate)

Na2CO3 + Ca(OH)2 = CaCO3 + 2 NaOH

Remember that hydroxide is the material, carbonate is the end product

26
Q

What factors would exacerbate carbon monoxide production in soda lime?

A

CO production driven by volatile agent interaction with strong bases of absorber.

Hot and dry environment increase production
Des > enf > iso
Bara-lyme worse
high fresh gas flow which dries the material -> absorbent becomes desiccated

27
Q

Respiratory centre components?

A

DIVE

  • DRG -> inspiration via diaphragm control
  • VRG -> expiration via intercostal muscles
  • Apneustic centre, modulates DRG, prevent over-expansion
  • Pneumotaxic centre, fine tune Resp system
28
Q

What is the function of Pre-Botzinger complex?

A

group of cells that generate respiratory pattern

29
Q

What is the neonatal lung reflex that prevents over-inflation?

A

Hering- Breuer reflex

30
Q

How does NAC work?

A

N-acetylcysteine is a glutathione substitute which conjugates NAPQI.

31
Q

Fick’s method of CO measurement equation

A

Flow = amount of substance uptaken per minute / different AV gradient.

CO = VO2 / (CaO2 - CvO2)

note its C for oxygen content

VO2 is measured by comparing amount of inhaled vs. exhaled O2 from collection bag. Arterial and venous O2 content measured directly .

32
Q

What is indirect Fick’s method?

A

Substitute inconvenient measurements with estimated values.

VO2 can be estimated based on weight, sex, nomograms
mixed venous O2 content estimated from central venous samples
Arterial O2 content estimated from pulse oximetry

33
Q

How does dilution method for CO work? What are some examples?

A

CO = dose / concentration over time (AUC)

Thermodilution 
Lithium dilution (LiDCO) 
Indocyanine green
34
Q

What is pulse contour analysis?

A

continuously monitoring cardiac output by using the shape of the arterial pressure waveform.

  • Arterial waveform (pressure) can be converted to volume via calibration factor.
  • Calibration factor derived using indictor dilution measurement or thermodilution.
  • Then allows continuous monitoring
35
Q

How is flow derived from TOE / TTE?

A

via velocity time integral (VTI) cross sectional area of LVOT.

Oesophageal doppler less accurate than LVOT

36
Q

What is the Stewart-Hamilton principle?

A

uses principle of conservation of heat

measures the RV CO and assumes this is the same as LV output

37
Q

What is the Stewart-Hamilton equation

A

Flow is inversely proportional to the area under the concentration time curve and be calculated from that area if the amount of indicator injected is known.

38
Q

What is required of the gas particle for infra-red absorption method to work?

A

gases with 2 or more different atoms will absorb infra-red radiation.

Each gas will absorb a particularly wavelength

39
Q

What is the absorption wavelength of

  • CO2
  • N2O
  • Volatiles
A

CO2 - 4.3 micro m
N2O - 4.5 micro m
volatile - 3.3 micro m

40
Q

How does water cause error in CO2 measurement?

A

clog in the sample line

condense on the window of sensor cell and absorb infrared light to produce falsely high CO2 readings

41
Q

What does the detector of captometry measure?

A

amount of radiation that has passed through the sample and reference chamber.

  • More CO2 -> more light absorbed -> less passed through
42
Q

What is the Ramgas effect?

A

pressure drop across the sampling line to cause drop in CO2 reading

43
Q

How does mass spectroscopy work?

A

relies on the concept that the mass and charge of particles cause them to move in different ways within an electromagnetic field.

Different movement -> allows separating into distinct streams within a body of gas.

44
Q

How does Raman spectroscopy work?

A

Raman Scattering - when a gas sample is exposed to a high intensity light source, the molecules of gas become excited into unstable energy states.

Upon collapse into lower energy state -> light is emitted (Raman scatter radiation)

Measure the low-intensity radiation.

18/7 Week LOs (4 decks)

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