Physics

Question 1

What is flow?

Answer 1

The amount of a substance passing a point per unit time (F = Q/t)
The two main types of flow are laminar and turbulent

Question 2

What determines flow?

Answer 2

Hagen Poiseuille equation:
Pi x r4 x dP
—————
8 x n x L

(n = Viscosity)

Question 3

What is temperature?

Answer 3

Temperature is the thermal state of a substance. Its SI unit is the Kelvin which is based on the thermodynamic triple point of water

Question 4

What are the components of a scavenging system?

Answer 4

Scavenging systems can be active or passive and will comprise of:
—Collecting system
—Transfer system
—Receiving system
—Disposal system
(—Exterior)

Question 5

How can oxygen be measured?

Answer 5

Oxygen can be measured in a gas mixture or in a solution

Gas:
—Fuel cell (lead & gold) (KOH)
—Paramagnetic analyser

Liquid:
—Clark electrode (Silver/silver chloride & Platinum)(KCl)

Question 6

How can CO2 be measured?

Answer 6

CO2 can be measured either as a gas or dissolved in a liquid.
Common ways to measure include:
Gas:
—Capnograph
—Infrared (2 or more different elements)

Liquid:
—Severinghaus electrode (modified pH electrode)

Question 7

How is cardiac output measured?

Answer 7

Invasively:
—PA catheter
—PiCCO
—LiDCO (rapid)
Non-invasively:
—Oesophageal Doppler
—Bioimpedance

Question 8

What measurements can be obtained from an Oesophageal Doppler?

Answer 8

Cardiac Output

—Stroke Volume Index
—Flow Time corrected (FTc) = preload
—Peak velocity = contractility
—SVR/afterload (FTc & PV interpretation)

Question 9

What is LASER?

Answer 9

LASER stands for Light Amplification by Stimulated Emission of Radiation

Question 10

What information can be obtained from a capnograph?

Answer 10

—Presence of CO2 to confirm endotracheal intubation
—Cardiac output (presence of)
—Bronchospasm
—Breathing pattern/loss of neuromuscular blockade
—Hypo/hyperventilation

Question 11

What do we mean by MRI?

Answer 11

Magnetic Resonance Imaging:
—using strong magnetic fields to create images

A static magnetic field aligns the H+ ions in the body
Pulses of radiofrequency energy are applied to flip these ions out of alignment
As they fall back into their initial alignment, energy is released

Question 12

What is risk? What tools do we use to score it?

Answer 12

Risk is the possibility of suffering harm

Scoring systems:
—NELA
—P-POSSUM
—Cardiac:
-Lee’s revised cardiac risk
-Euroscore
—Thoracoscore

Question 13

What is the number needed to treat?

Answer 13

Describes the number of people who need to receive treatment before 1 person gets benefit.
For anti-emetics = ~5
For some analgesics in chronic pain =~5

NNT = 1/ARR (absolute risk reduction)
ARR = Control Event Rate - Experimental Event Rate

Question 14

When using depth of anaesthesia monitoring, what are the EEG waveforms that indicate surgical anaesthesia?

Answer 14

Beta waves = awake; >12Hz
Alpha waves = sedation/light GA; 8-12Hz
Theta waves = surgical anaesthesia; 4-8Hz
Delta waves = deep anaesthesia; <4Hz
Burst suppression = too deep

Question 15

What is the equation for SVR?

Answer 15

SVR = (MAP - CVP) / CO x 80

In dynes/sec/cm-5

Question 16

What are the key considerations of a vaporiser?

Answer 16

Plenum vs injected

—SVP
—Splitting ratio
—Wicks/baffles/high internal resistance - fully saturate the gas with vapour
—Latent heat of vapourisation = temp falls as liquid vaporises so requires compensation: heat sink and use of bimetallic strip to adjust flow of splitting ratio
—Calibration to individual volatiles

Problems:
—Overfilling
—‘Pumping’ effect
—‘Pressurising’ effect

Question 17

How can we measure stroke volume?

Answer 17

Direct measurement of cardiac output (and working back from that)

Indirect by using Echo or Oesophageal Doppler
(Area under the systolic curve)

Question 18

What are the safety features of an anaesthetic machine?

Answer 18

Power supply:
—Plug in & battery - alarms for failure
Gas supply:
—Pipeline (colour coded, Shrader valves, NIST)
—Cylinders (colour coded, Bodek seal, pin index system)
—Pressure regulators & gauges
Gas flow:
—Pressure regulators
—Flowmeters (mechanical vs electrical; O2 last; hypoxic guard)
—O2 alarm (Ritchie whistle)
—O2 flush
—APL
Vaporisers:
—Colour coding
—Agent specific, filling devices, non-spill

Question 19

How can you measure BP?

Answer 19

Invasively:
—Arterial line

Non-invasively:
—Occlusive cuff method (manual/electronic) - oscillotonometer principle
—Von Recklinghausen oscillotonometer
—Penaz technique (continuous) - infrared
—Doppler US

Question 20

How do we measure temperature?

Answer 20

Non-electric:
—Liquid expansion thermometers (mercury, alcohol)(Bourdon gauge measures pressure change from gas expansion)
—Bimetallic strip dial thermometer (2 different metals with different expansion coefficients)
—Chemical thermometer - crystals

Electric:
—Thermocouple (2 dissimilar metals, voltage difference = proportional to temp) Seebeck effect
—Resistance thermometer (platinum)
—Thermistor (semiconductor; negative exponential)
Infrared (all objects emit em radiation)