p.6
Laser Technology and Applications
Why are anaesthetised patients at risk of laser burns?
Self-protecting maneuvers do not come into play.
p.1
Tetany and Post-Tetanic Count
What does a post-tetanic count (PTC) greater than 15 indicate?
Equivalent to two twitches on to fade.
p.9
Ultrasound Principles and Applications
How is the aortic cross-sectional area estimated in Transoesophageal Doppler?
From a nomogram based on age, height, and weight, or measured in some devices.
p.9
Ultrasound Principles and Applications
What is a clinical example of a device utilizing ultrasound?
Transoesophageal Doppler.
p.1
Tetany and Post-Tetanic Count
What does post-tetanic facilitation do?
Mobilizes presynaptic acetylcholine, making it available for contractions in response to post-tetanic count.
p.13
Clinical Monitoring of Nerves
What is a pulse oximeter used for?
To measure the percentage of arterial hemoglobin in the blood that is saturated with oxygen.
p.8
Ultrasound Principles and Applications
What is A (Amplitude) Mode in ultrasound?
The simplest form of ultrasound imaging that emits a single ultrasound wave to scan a line through the body, plotting echoes as a function of depth.
p.2
Neuromuscular Blockade Monitoring
How many acetylcholine (ACh) molecules are contained in each vesicle at the neuromuscular junction?
Over 10,000 ACh molecules.
p.13
Clinical Monitoring of Nerves
What wavelengths of light do the LEDs in a pulse oximeter emit?
660 nm (red light) and 940 nm (infrared light).
p.3
Phase I and Phase II Blocks
What are the characteristics of a phase I block?
Reduced twitch height, no post-tetanic facilitation, and TOF ratio >70%.
p.4
Laser Technology and Applications
What does the acronym 'laser' stand for?
Light amplification by the stimulated emission of radiation.
p.8
Ultrasound Principles and Applications
What is the Doppler effect?
A phenomenon where sound waves reflected from a moving target have a different frequency than the incident sound wave, commonly observed with moving vehicles.
p.7
Ultrasound Principles and Applications
What are the advantages of using ultrasound?
Relatively inexpensive, widely available, non-invasive, and safe in children and pregnancy due to no ionizing radiation.
p.7
Ultrasound Principles and Applications
What are the disadvantages of ultrasound?
Operator dependent, cannot image lung, bone, or deep structures.
p.15
Clinical Monitoring of Nerves
Do fetal hemoglobin and Hb S (sickle) affect oxygen saturation readings?
No, they do not affect readings.
p.1
Tetany and Post-Tetanic Count
What is the relationship between the number of twitches and receptor blockade?
The number of twitches is inversely proportional to the degree of receptor blockade.
What type of infusion pumps should ideally be used for the delivery of anaesthesia in an MRI environment?
'MR conditional' infusion pumps.
p.10
CT and MRI Principles
What is the difference between 'shoot and step' and 'spiral' CT scanning?
'Spiral' scanning is quicker and reduces motion artefact.
What does 'MR Conditional' indicate?
Items are safe under certain tested magnetic conditions, which are specified on the product.
p.14
Clinical Monitoring of Nerves
What can cause falsely high readings in pulse oximetry?
Carbon monoxide poisoning and cyanide poisoning.
p.14
Clinical Monitoring of Nerves
How does carbon monoxide affect pulse oximetry readings?
It irreversibly binds to haemoglobin, leading to falsely high saturation readings.
p.5
Laser Technology and Applications
What tissues do argon lasers penetrate well?
Transparent tissues like aqueous humour, vitreous humour, and lens of the eye.
p.9
Ultrasound Principles and Applications
How does the Transoesophageal Doppler monitor cardiac output?
By measuring red blood cell velocity in the descending thoracic aorta.
p.2
Fade Phenomenon in NMBDs
What does 'fade' refer to in neuromuscular blockade?
The phenomenon of decreasing twitch height when competitive neuromuscular blocking drugs are present at the neuromuscular junction.
p.5
Laser Technology and Applications
What is the wavelength of light produced by carbon dioxide lasers?
10.6 μm (infrared region).
p.10
CT and MRI Principles
What happens to protons in an MRI when exposed to a magnetic field?
They align in the direction of the field.
p.13
Clinical Monitoring of Nerves
What factors does the Beer-Lambert law state affect absorbance?
The concentration of the solution and the path-length of light traveling through the solution.
p.10
CT and MRI Principles
How does a CT scanner capture images?
By taking a series of X-ray images around a central axis.
p.8
Ultrasound Principles and Applications
What is B (Brightness) Mode in ultrasound?
Also known as 2D mode, it emits a linear array of ultrasound waves to produce a two-dimensional cross-sectional view, with echo intensity determining the brightness of the image.
p.2
Tetany and Post-Tetanic Count
What is post-tetanic potentiation?
A substantial increase in ACh release following tetanic stimulation, which helps overcome competition from NMBDs.
p.11
MRI Principles and Applications
What are the two types of MRI images based on relaxation time?
T1 and T2 weighted images.
p.13
Clinical Monitoring of Nerves
How does a pulse oximeter measure oxygen saturation?
By shining light through the patient and detecting the amount of light absorbed by oxyhemoglobin and deoxyhemoglobin.
p.8
Ultrasound Principles and Applications
What is M (Motion) Mode in ultrasound?
A mode that emits a rapid sequence of ultrasound waves to visualize real-time movement of structures, commonly used in echocardiography.
p.5
Laser Technology and Applications
In what types of procedures are carbon dioxide lasers typically used?
Superficial surgery, such as dermabrasion and laser facelifts.
p.10
CT and MRI Principles
What is the role of the radiofrequency coil in MRI?
It generates a second current that disrupts the alignment of protons.
p.10
CT and MRI Principles
What is resonance in the context of MRI?
The exchange of energy between spin states of protons.
p.1
Fade Phenomenon in NMBDs
What happens to twitch height when NMBD is present at the receptor?
Twitch height decreases, indicating a fade phenomenon.
p.7
Ultrasound Principles and Applications
What types of structures are ultrasound good for examining?
Fluid-filled structures (e.g., vessels) and soft tissues.
p.8
Ultrasound Principles and Applications
What correction factor is used when the ultrasound beam is not parallel to the direction of flow?
A correction factor involving the cosine of the angle of incidence (θ) is used.
p.14
Clinical Monitoring of Nerves
What does a lower intensity (I) compared to the original intensity (I0) indicate?
A proportion of the original light has been absorbed by the solution.
p.13
Clinical Monitoring of Nerves
Why does arterial blood appear brighter red than venous blood?
Because oxyhemoglobin absorbs more infrared light and allows more red light to pass through compared to deoxyhemoglobin.
p.11
MRI Principles and Applications
What risks do ferrous implants pose in an MRI scanner?
They can be displaced or experience torque forces, leading to serious injury.
p.8
Ultrasound Principles and Applications
What is Duplex Doppler?
A mode that combines real-time Doppler with real-time ultrasound to assess vasculature.
p.11
Clinical Monitoring of Nerves
What is a common injury associated with MRI?
Burns caused by magnetically induced currents in ECG leads.
p.11
MRI Principles and Applications
In T1 images, how do fat and water appear?
Fat is bright and water is black.
p.10
CT and MRI Principles
What is the primary advantage of MRI over CT?
MRI visualizes soft tissues much better than CT.
p.14
Clinical Monitoring of Nerves
What factors can cause erroneously low readings in pulse oximetry?
Poor perfusion, movement artefact, electrical interference, calloused skin, nail varnish, severe anaemia, cardiac arrhythmias, methaemoglobinaemia, increased venous pulsation, and methylene blue dye.
p.3
Phase I and Phase II Blocks
How does anticholinesterase affect a phase I block?
It potentiates the block by decreasing the rate of suxamethonium breakdown.
p.7
Ultrasound Principles and Applications
What role does ultrasound gel play in imaging?
It acts as a coupling medium to reduce attenuation of the ultrasound waveform and improve image quality.
p.5
Laser Technology and Applications
What is the primary application of argon lasers?
Typically used in eye surgery and dermatological procedures.
p.2
Tetany and Post-Tetanic Count
What is the effect of tetanic stimulation on ACh release?
It produces a substantial increase in ACh release, sufficient to overcome NMBD competition.
p.3
Neuromuscular Blockade Monitoring
Why is it traditional to wait until a patient can lift their head before extubation?
Muscle function returns in reverse order of sensitivity, indicating recovery from NMBDs.
p.5
Laser Technology and Applications
What is the primary use of carbon dioxide lasers?
Used as a lasing medium in gas-state lasers for cutting, welding, and engraving.
p.11
MRI Principles and Applications
What is the purpose of the Faraday cage in an MRI scanner?
To house the entire scanner and shield it from external electromagnetic interference.
What does 'MR Safe' mean?
Items are completely free of all metallic components and pose no hazard in any MR environment.
p.7
Ultrasound Principles and Applications
How is ultrasound used in critical care settings?
For vascular line insertion, cardiac output monitoring, echocardiography, transcranial Doppler, pleural aspiration, ascitic drainage, assessment of hepatic portal vein flow, and detection of venous thromboembolism.
p.8
Ultrasound Principles and Applications
What is the Doppler Mode in ultrasound?
Utilizes the Doppler effect to detect and quantify the velocity of flow, with frequency shifts indicating the speed of moving targets like blood.
p.1
Double Burst Stimulation
How many twitches are involved in double burst stimulation?
3 twitches followed by a break of 750 ms, then 3 more twitches.
p.14
Clinical Monitoring of Nerves
What is the effect of cyanide on oxygen saturation readings?
It prevents oxygen utilization in respiration, causing saturation readings to appear high.
p.8
Ultrasound Principles and Applications
How is velocity calculated in clinical ultrasonography using the Doppler effect?
Velocity = (Speed of sound wave × change in frequency) / (2 × emitted frequency).
p.4
Laser Technology and Applications
What is the role of the external energy source in a laser?
It stimulates the electrons in the laser medium, raising them from a ground state to an excited state.
p.2
Neuromuscular Blockade Monitoring
What is double burst stimulation (DBS) used for?
To improve the ability to detect fade clinically.
p.11
MRI Principles and Applications
In T2 images, how do fat and water appear?
Fat is black and water is bright.
p.7
Ultrasound Principles and Applications
What are some clinical uses of ultrasound in anaesthetics?
Vascular line insertion, guiding peripheral nerve blockade, and catheter placement within the epidural space.
p.3
Phase I and Phase II Blocks
What causes the disorganized muscle contraction in a phase I block?
Suxamethonium binds to the ACH receptor, causing sodium channel opening and membrane depolarization.
p.2
Fade Phenomenon in NMBDs
What happens when neuromuscular blocking drugs (NMBDs) bind to post-synaptic ACh receptors?
It leaves fewer receptors available for ACh to bind to, leading to fade.
What are 'MR Unsafe' items?
Items that pose a hazard in any MR environment.
What is the standard international unit of magnetic strength?
Weber (Wb) for magnetic flux and Tesla (T) for magnetic flux density.
p.11
Clinical Monitoring of Nerves
What type of monitoring equipment is required for MRI?
MR safe ECG electrodes, BP cuffs, and pulse oximeters.
p.3
Neuromuscular Blockade Monitoring
What is the order of sensitivity for muscle paralysis caused by NMBDs?
Eyes, facial muscles, neck, extremities, limbs, abdominal muscles, glottis, intercostal muscles.
p.4
Laser Technology and Applications
What happens when excited electrons return to their ground state in a laser?
They emit energy in the form of light or radiation, which can stimulate further electrons and amplify the process.
p.13
Clinical Monitoring of Nerves
What are the main components of a pulse oximeter?
An electronic processor, two light-emitting diodes (LEDs), and a photodiode.
p.3
Phase I and Phase II Blocks
What is a phase I block in neuromuscular blockade?
A block seen after a single dose of suxamethonium, characterized by reduced twitch height and sustained response to tetanic stimulation.
p.5
Laser Technology and Applications
What is a significant limitation of carbon dioxide lasers in tissue penetration?
Poor tissue penetration of <200 μm due to absorption by water.
p.5
Laser Technology and Applications
What is the wavelength range of light produced by argon lasers?
Between 400 and 700 nm (blue-green region of the visible spectrum).
p.13
Clinical Monitoring of Nerves
What does the microprocessor in a pulse oximeter correct for?
Ambient light and the difference between arterial and venous saturations.
p.6
Laser Technology and Applications
What should the cuffs of the endotracheal tube be filled with?
Saline, to prevent ignition from the laser.
p.6
Laser Technology and Applications
What is the recommended FiO2 level during upper airway laser surgery?
Less than 0.25 if tolerated.
p.14
Clinical Monitoring of Nerves
What is the formula for absorbance in pulse oximetry?
A = εlc, where A is absorbance, ε is the molar absorption coefficient, l is the path length, and c is the concentration.
What classification system has replaced the term 'MR compatible'?
MR Safe, MR Conditional, and MR Unsafe.
p.11
Clinical Monitoring of Nerves
What generic problems are associated with anaesthesia in the scanning department?
Remote location, cold and noisy environment, claustrophobic space, limited space for anaesthetic equipment, and limited access to the patient.
p.8
Ultrasound Principles and Applications
What is Colour Flow Doppler?
A mode that color codes the velocity and direction of blood flow, superimposing it onto a grey-scale 2D image.
p.3
Phase I and Phase II Blocks
What is a phase II block?
A block that occurs after repeated administration of suxamethonium, leading to receptor desensitization.
p.4
Laser Technology and Applications
What are the three key characteristics of the light produced by lasers?
Monochromatic, coherent, and collimated.
p.5
Laser Technology and Applications
What are the hazards associated with laser surgery?
High-energy intensities can cause fire, explosions, and permanent eye damage.
p.11
Clinical Monitoring of Nerves
What are some indications for general anaesthesia in an MRI scanner?
Unstable patients, young children, patients with learning difficulties, very anxious or claustrophobic patients, and patients with movement disorders.
p.7
Ultrasound Principles and Applications
How are ultrasound waves generated?
By applying an electric field to a piezoelectric crystal in the transducer, causing it to vibrate.
p.11
MRI Principles and Applications
What should be done with ferrous-containing equipment in the MRI scanner?
It should not be taken beyond the 50 gauss line unless securely fastened.
p.10
CT and MRI Principles
What is the purpose of the gradient magnet in an MRI scanner?
To allow fine-tuning and focusing of the image.
p.3
Clinical Monitoring of Nerves
Which nerves are commonly monitored in clinical settings?
Facial nerve, ulnar nerve, and posterior tibial nerve.
p.2
Neuromuscular Blockade Monitoring
What role do pre-junctional receptors play in neuromuscular transmission?
They are stimulated by ACh release and help increase ACh production through positive feedback mechanisms.
p.4
Laser Technology and Applications
What does quantum theory state about electrons in a laser?
Electrons are confined to certain energy states and can move between these states by absorbing or emitting energy.
p.5
Laser Technology and Applications
What is the classification of lasers based on power and exposure?
Class 1, Class 2, Class 3a, Class 3b, and Class 4.
p.5
Laser Technology and Applications
What can happen if the laser beam hits the retina?
A permanent blind spot can develop, or permanent blindness if it hits the optic nerve.
p.3
Phase I and Phase II Blocks
What are the characteristics of a phase II block?
Exhibits fade on tetanic stimulation, post-tetanic facilitation, and TOF ratio <0.3.
What is the typical magnetic strength produced by an average MR scanner?
Between 1 and 1.5 T, with newer machines generating up to 3–5 T.
p.7
Ultrasound Principles and Applications
How does the resolution of an ultrasound image relate to depth of penetration?
Resolution is inversely proportional to depth of penetration; deeper structures have lower resolution.
p.6
Laser Technology and Applications
What precautions are taken to minimize laser hazards in the operating theatre?
Designated laser protection supervisor, trained staff, locked doors, closed windows, and warning signs.
p.6
Laser Technology and Applications
What should be used to ventilate the patient if necessary during an airway fire?
A bag-valve-mask circuit.
p.2
Fade Phenomenon in NMBDs
What occurs when 75% of receptor sites at the neuromuscular junction are occupied by NMBDs?
There will be no discernible weakness until this threshold is reached.
p.10
CT and MRI Principles
What causes the banging noise in an MRI machine?
The turning on and off of the gradient magnets.
p.4
Laser Technology and Applications
How does Einstein's theory relate to laser operation?
Stimulated atoms emit photons of equivalent energy, creating a chain reaction that amplifies the light.
p.6
Laser Technology and Applications
What are the main laser hazards affecting anaesthetised patients?
Eye damage, skin burns, and airway fire.
p.4
Laser Technology and Applications
What is the wavelength of light produced by Nd-YAG lasers?
1064 nm (near infrared region).
p.4
Laser Technology and Applications
What is a clinical application of Nd-YAG lasers?
Used typically for endoscopic surgery.
p.4
Laser Technology and Applications
Why is Nd-YAG laser effective in tissue penetration?
It is not absorbed by water, allowing good tissue penetration.
p.6
Laser Technology and Applications
What is the first step in managing an airway fire during surgery?
Call for help and inform the immediate theatre team.
p.4
Laser Technology and Applications
What are the fundamental components of a laser device?
External energy source, laser medium, chamber, system of mirrors, partially reflective mirror, and windows at Brewster's angle.
p.6
Laser Technology and Applications
What should be done after managing an airway fire?
Inspect the airway with a rigid bronchoscope.
p.6
Laser Technology and Applications
What type of eye protection is required during laser surgery?
Laser beam wavelength-specific goggles for both staff and patients.
p.6
Laser Technology and Applications
What type of endotracheal tube is recommended for upper airway laser surgery?
Double-cuffed, laser-resistant endotracheal tube.
p.6
Laser Technology and Applications
What should the surgeon do immediately after an airway fire is detected?
Switch off the laser and flood the operation site with water.
