Equipment in Anaesthesia: Part 3 Flashcards
Which patient factors lead to an increased risk of anaesthetic awareness
- younger patients
- chronic opioid and alcohol users
- previous experience of awareness
- risk of haemodynamic instability
- co-morbidities
Which patient factors lead to an increased risk of excessive anaesthesia
- patients with hepatic disease
- high BMI
- older patients
- poor cardiovascular function
Which anaesthetic factors lead to an increased risk of anaesthetic awareness
- use of NMB
- use of TIVA
- difficult intubation
- unrecognised equipment failure
Which surgical factors lead to an increased risk of anaesthetic awareness
- cardiac surgery
- obstetric surgery with GA
- emergency/trauma surgery
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
- 0
- 85-100
- 60-85
- 40-60
- <40
Which anaesthetic drugs provide inaccurate BIS scores
Nitrous Oxide
Ketamine
Uses of ultrasound
regional anaesthesia
intravenous and arterial cannulae
haemodynamics
echocardiography
What is the range of human hearing
20 Hz to 20 kHz
In what frequency range is ultrasound waves
1-10 MHz
What are piezoelectric elements
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.
What is an acoustic window
a gap through which an ultrasound beam can pass
What is the propagation velocity of sound in tissue
1,540 m/s
Define acoustic impedance
The resistance to the propagation of ultrasound waves through tissues
What is the reflection coefficient
The difference between the impedences of two tissues. The magnitude of the difference determines the amount of reflection.
What is a specular reflector
Smooth objects or interfaces
larger than 1 wavelength in the lateral dimension;
they reflect ultrasound as a mirror;
example vessels, nerves, needles
What is the concept of attenuation in ultrasound technology
Returning beams are weaker than incident beams, due to loss of energy via friction, as heat.
Which factors affect attenuation of ultrasound beams
- amplitude
- absorption
- reflection/scatter
- acoustic impedence
- refraction
- diffraction/divergence
Which ultrasound factors most affect the quality of the image obtained
- amplification
- resolution
Define ultrasound resolution
The ability of the machine to resolve structures into meaningful images
What is the pulse length of ultrasound
the wavelength multiplied by the number of cycles in each ultrasound pulse
What patients factors affect ultrasound image quality
- obesity
- oedema
- muscle mass/lack thereof
What kinds of resolution are there in ultrasound technology
- axial resolution
- lateral resolution
- elevation resolution
- temporal resolution
What is axial resolution
how well the ultrasound probe distinguishes structures parallel to the scanning probe. Requires high frequencies.
What is lateral resolution
the ability of the ultrasound probe to resolve two signals side by side in the field. Best in the near field zone.
What is elevation resolution
the ability of the ultrasound image to tell apart objects which are out of plane with each other.
What is temporal resolution
the ability of the ultrasound to display sequential images in real time. Can be compared to frame rate.
What is the equation for the near field length
NFL = (diameter of piezoelectric crystals)^2 / 4(wavelength)
What is the equation to predict the observed frequency of a moving wave (doppler)
fâ = [(V + Vo) / (V - Vs)] x f
where
fâ is observed frequency
V is velocity of waves
Vo is velocity of observer
Vs is velocity of source
f is actual frequency
What is the Doppler effect
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.
