Equipment in Anaesthesia: Part 3

Question 1

Which patient factors lead to an increased risk of anaesthetic awareness

Answer 1

• younger patients
• chronic opioid and alcohol users
• previous experience of awareness
• risk of haemodynamic instability
• co-morbidities

Question 2

Which patient factors lead to an increased risk of excessive anaesthesia

Answer 2

• patients with hepatic disease
• high BMI
• older patients
• poor cardiovascular function

Question 3

Which anaesthetic factors lead to an increased risk of anaesthetic awareness

Answer 3

• use of NMB
• use of TIVA
• difficult intubation
• unrecognised equipment failure

Question 4

Which surgical factors lead to an increased risk of anaesthetic awareness

Answer 4

• cardiac surgery
• obstetric surgery with GA
• emergency/trauma surgery

Question 5

What is the BIS score if:
1. the EEG is isoelectric
2. the patient is fully awake
3. the patient is sedated
4. the patient is appropriately anaesthetised
5. the anaesthetic is too deep

Answer 5

1. 0
2. 85-100
3. 60-85
4. 40-60
5. <40

Question 6

Which anaesthetic drugs provide inaccurate BIS scores

Answer 6

Nitrous Oxide
Ketamine

Question 7

Uses of ultrasound

Answer 7

regional anaesthesia
intravenous and arterial cannulae
haemodynamics
echocardiography

Question 8

What is the range of human hearing

Answer 8

20 Hz to 20 kHz

Question 9

In what frequency range is ultrasound waves

Answer 9

1-10 MHz

Question 10

What are piezoelectric elements

Answer 10

Crystals that vibrate and generate a sound wave when an electric current is applied to them. They create an electric current if a force is applied to them.

Question 11

What is an acoustic window

Answer 11

a gap through which an ultrasound beam can pass

Question 12

What is the propagation velocity of sound in tissue

Answer 12

1,540 m/s

Question 13

Define acoustic impedance

Answer 13

The resistance to the propagation of ultrasound waves through tissues

Question 14

What is the reflection coefficient

Answer 14

The difference between the impedences of two tissues. The magnitude of the difference determines the amount of reflection.

Question 15

What is a specular reflector

Answer 15

Smooth objects or interfaces
larger than 1 wavelength in the lateral dimension;
they reflect ultrasound as a mirror;
example vessels, nerves, needles

Question 16

What is the concept of attenuation in ultrasound technology

Answer 16

Returning beams are weaker than incident beams, due to loss of energy via friction, as heat.

Question 17

Which factors affect attenuation of ultrasound beams

Answer 17

1. amplitude
2. absorption
3. reflection/scatter
4. acoustic impedence
5. refraction
6. diffraction/divergence

Question 18

Which ultrasound factors most affect the quality of the image obtained

Answer 18

1. amplification
2. resolution

Question 19

Define ultrasound resolution

Answer 19

The ability of the machine to resolve structures into meaningful images

Question 20

What is the pulse length of ultrasound

Answer 20

the wavelength multiplied by the number of cycles in each ultrasound pulse

Question 21

What patients factors affect ultrasound image quality

Answer 21

1. obesity
2. oedema
3. muscle mass/lack thereof

Question 22

What kinds of resolution are there in ultrasound technology

Answer 22

1. axial resolution
2. lateral resolution
3. elevation resolution
4. temporal resolution

Question 23

What is axial resolution

Answer 23

how well the ultrasound probe distinguishes structures parallel to the scanning probe. Requires high frequencies.

Question 24

What is lateral resolution

Answer 24

the ability of the ultrasound probe to resolve two signals side by side in the field. Best in the near field zone.

Question 25

What is elevation resolution

Answer 25

the ability of the ultrasound image to tell apart objects which are out of plane with each other.

Question 26

What is temporal resolution

Answer 26

the ability of the ultrasound to display sequential images in real time. Can be compared to frame rate.

Question 27

What is the equation for the near field length

Answer 27

NFL = (diameter of piezoelectric crystals)^2 / 4(wavelength)

Question 28

What is the equation to predict the observed frequency of a moving wave (doppler)

Answer 28

f’ = [(V + Vo) / (V - Vs)] x f

where
f’ is observed frequency
V is velocity of waves
Vo is velocity of observer
Vs is velocity of source
f is actual frequency

Question 29

What is the Doppler effect

Answer 29

It describes the phenomenon of sound waves emitted from or reflected off a moving object, to vary the apparent wavelength according to the velocity and direction of the object.