p.10
Impact of Altitude on Vaporiser Function
What happens to the delivery of desflurane at high altitudes?
The partial pressure of desflurane in the alveoli will be much lower due to lower ambient pressure.
p.3
Definitions of Ventilatory Modes
What are the two levels of pressure set in BiPAP?
The first is the PEEP level, and the second is the positive inspiratory pressure.
p.10
Impact of Altitude on Vaporiser Function
How does Dalton's law apply to the delivery of desflurane at altitude?
It shows that the partial pressure of desflurane decreases at altitude, resulting in a lower effective concentration delivered.
p.12
Neuromuscular Blockade Monitoring Techniques
What is a disadvantage of acceleromyography?
The hand must be splinted and stable, making it fiddly and inconvenient.
p.5
Variable Bypass Vaporisers
What happens when the control dial is turned to zero?
The valve is closed and no fresh gas flows through the vaporising chamber.
p.8
Impact of Altitude on Vaporiser Function
What is the total pressure of a gas mixture?
The sum of the partial pressures of all the gases present.
p.12
Neuromuscular Blockade Monitoring Techniques
What is the main advantage of electromyography?
It is more accurate than visual monitoring and avoids issues with positioning transducers.
p.5
Variable Bypass Vaporisers
How is the problem of high fresh gas flow mitigated?
By using wicks and baffles to increase the surface area of volatile anaesthetic exposed to fresh gas flow.
p.13
Stimulation Patterns in Neuromuscular Monitoring
What does the ratio of twitch height t4:t1 indicate in TOF?
It indicates the degree of receptor occupancy by the NMBD.
p.4
Variable Bypass Vaporisers
What is the purpose of the bypass pathway in variable bypass vaporisers?
To mix vapor-saturated gas with vapor-free bypass gas before delivery to the patient.
p.13
Stimulation Patterns in Neuromuscular Monitoring
What is the simplest stimulation pattern in neuromuscular monitoring?
Single twitch stimulation at a frequency of 1 twitch per second.
p.8
Impact of Altitude on Vaporiser Function
How can the partial pressure of sevoflurane be expressed in different units?
As 4.05 kPa, 30.4 torr, or 30.4 mmHg.
p.2
Definitions of Ventilatory Modes
How does CPAP improve lung compliance?
By preventing alveolar and airway closure during expiration and moving the lungs up the compliance curve.
p.7
Desflurane Vaporiser Design
What is the function of the electronic control unit in the vaporiser?
To couple fresh gas flow to the rate of injection of the anaesthetic agent.
p.2
High-Frequency Oscillating Ventilator (HFOV)
What is a high-frequency oscillating ventilator (HFOV)?
A type of ventilator that employs an 'open lung' strategy using high PEEP and very small tidal volumes at high respiratory rates.
p.3
Definitions of Ventilatory Modes
How does the ventilator respond to patient effort in Pressure Control mode?
Any respiratory effort made by the patient is ignored by the ventilator.
p.2
High-Frequency Oscillating Ventilator (HFOV)
What is the maximum respiratory rate for HFOV?
Up to 15 Hz (i.e., 900 breaths per minute).
p.12
Neuromuscular Blockade Monitoring Techniques
What is a disadvantage of electromyography?
Even small movements of the hand can alter the electrode's response.
p.1
Classification of Ventilators
What is a key difference in leak compensation between pressure and flow-generated ventilation?
Pressure-generated ventilation compensates for leaks, while flow-generated does not.
p.6
Types of Vaporisers in Anaesthesia
What feature helps reduce the risk of over-filling in vaporisers?
Low filling ports and a transparent window with a 'fill line'.
p.9
Impact of Altitude on Vaporiser Function
What does the saturation vapor pressure (SVP) of sevoflurane depend on?
It only changes with temperature, not with ambient pressure.
p.8
Impact of Altitude on Vaporiser Function
What is the partial pressure of sevoflurane delivered as 4% at sea level?
0.04 atm (or 4% of 1 atmosphere).
p.12
Neuromuscular Blockade Monitoring Techniques
What is acceleromyography?
A transducer using piezoelectric crystals secured to the end of a digit to measure muscle contraction force.
p.3
Definitions of Ventilatory Modes
What is the primary use of Pressure Control (PC) mode?
It is used in mechanically ventilated patients to deliver a set tidal volume or pressure.
p.4
Variable Bypass Vaporisers
How do variable bypass plenum vaporisers operate?
They allow fresh gas to flow through either the vaporising chamber or a bypass pathway, mixing saturated gas with bypass gas.
p.6
Types of Vaporisers in Anaesthesia
How does incorrect anaesthetic liquid introduction to a vaporiser get mitigated?
Through standardized colour coding of vaporisers and bottles.
p.9
Impact of Altitude on Vaporiser Function
What happens to the partial pressure of sevoflurane at high altitudes?
It drops by half due to decreased ambient pressure.
p.11
Neuromuscular Blockade Monitoring Techniques
What are the two steps involved in monitoring neuromuscular blockade?
1. Stimulation of a motor nerve 2. Assessment of the muscular response.
p.2
Definitions of Ventilatory Modes
What is the primary function of PEEP?
To prevent alveolar and airway closure during expiration and improve lung compliance.
p.4
Types of Vaporisers in Anaesthesia
What are the main types of vaporisers classified in the text?
Plenum Vaporisers, Desflurane Vaporiser, Direct Injection of Volatile Anaesthetic Vaporiser, Variable Bypass Vaporisers.
p.6
Types of Vaporisers in Anaesthesia
What is the purpose of a non-return valve in a vaporiser?
To prevent gas saturated with vapour from being displaced back into the bypass channel.
p.2
High-Frequency Oscillating Ventilator (HFOV)
What conditions are HFOV recommended for?
Patients requiring a high FiO2 > 0.60 and with high mean airway pressures > 24 cm H2O.
p.4
Variable Bypass Vaporisers
What happens to the gas that enters the vaporising chamber of a variable bypass vaporiser?
It becomes fully saturated with vapour.
p.2
Definitions of Ventilatory Modes
What is CPAP?
Continuous Positive Airway Pressure, a mode where positive pressure is applied to the airway of a spontaneously breathing patient.
p.3
Definitions of Ventilatory Modes
What is the goal of Pressure Regulated Volume Control (PRVC) mode?
To deliver a set tidal volume with the lowest resultant inspiratory pressure to reduce the risk of barotrauma.
p.4
Types of Vaporisers in Anaesthesia
What is an example of a Desflurane Vaporiser?
Aladin Cassette Vaporiser® (GE).
p.9
Impact of Altitude on Vaporiser Function
How does a vaporiser calibrated at sea level behave at high altitudes?
It delivers a higher concentration of sevoflurane, e.g., 8% at 5.5 km instead of 4%.
p.3
Definitions of Ventilatory Modes
How does the BiPAP machine sense when to augment a patient's breath?
It uses a pressure transducer that senses negative pressure in the system.
p.10
Impact of Altitude on Vaporiser Function
What must an anaesthetist do to achieve the same clinical effect at altitude as at sea level?
Dial in a higher percentage of desflurane.
p.10
Desflurane Vaporiser Design
What is the effect of ambient pressure on the Tec 6 vaporiser's output?
The SVP remains constant at altitude, but the effective delivery is affected by lower ambient pressure.
p.7
Desflurane Vaporiser Design
What must be adjusted according to the fresh gas flow when using desflurane?
The rate of injection of desflurane.
p.11
Neuromuscular Blockade Monitoring Techniques
What are the two methods for stimulating a motor nerve clinically?
1. Needle electrodes (e.g., stimuplex needle) 2. Skin electrodes placed over a peripheral nerve.
p.6
Types of Vaporisers in Anaesthesia
Why is a special vaporiser necessary for desflurane?
Due to desflurane's high volatility and low boiling point, which makes it sensitive to ambient temperature changes.
p.7
Desflurane Vaporiser Design
What is the MAC and dial range for sevoflurane?
MAC = 2.10, range 0–8% on dial.
p.10
Desflurane Vaporiser Design
What is the function of the Tec 6 vaporiser?
To heat desflurane to 39 °C to ensure its saturated vapor pressure (SVP) is constant.
p.3
Definitions of Ventilatory Modes
How is BiPAP delivered to the patient?
Via a face mask, usually to a conscious and spontaneously ventilating patient.
p.1
Classification of Ventilators
How can ventilators be classified?
According to the Mapleson classification into 'pressure-generated' or 'flow-generated' ventilation.
p.13
Stimulation Patterns in Neuromuscular Monitoring
What happens to muscle units during single-twitch stimulation?
There is complete recovery between each stimulation, so 'fade' is not observed.
p.3
Definitions of Ventilatory Modes
What distinguishes SIMV from PC and PS modes?
SIMV allows the ventilator to deliver set breaths while also augmenting breaths if the patient makes an inspiratory effort.
p.11
Neuromuscular Blockade Monitoring Techniques
Why is it important to assess the degree of neuromuscular blockade in patients?
To manage various stages of anaesthesia, including tracheal intubation, muscle relaxation, and ensuring safe surgery.
p.4
Variable Bypass Vaporisers
What determines the concentration of the volatile agent in the mixture delivered to the patient?
The amount of fresh gas that flows through each of the pathways.
p.9
Impact of Altitude on Vaporiser Function
What is the relationship between the pressure inside the vaporising chamber and ambient air pressure?
The pressure inside the vaporising chamber is approximately equal to the ambient air pressure.
p.5
Variable Bypass Vaporisers
How does the bimetallic strip help in vaporiser function?
It compensates for fluctuations in output due to temperature changes.
p.7
Desflurane Vaporiser Design
What is the MAC and dial range for isoflurane?
MAC = 1.15, range 0–5% on dial.
p.9
Impact of Altitude on Vaporiser Function
What remains the same for the clinical effect of sevoflurane on the patient at different altitudes?
The partial pressure of sevoflurane remains constant, ensuring the clinical effect is the same.
p.10
Desflurane Vaporiser Design
What is the saturated vapor pressure (SVP) of desflurane inside the Tec 6 vaporising chamber at 39 °C?
2 atmospheres, regardless of ambient pressure.
p.3
Definitions of Ventilatory Modes
What is BiPAP?
A trade name for a type of non-invasive ventilator that provides bi-level positive airway pressure.
p.4
Types of Vaporisers in Anaesthesia
What is the primary function of a vaporiser in inhalational anaesthesia?
To administer a given concentration of a volatile anaesthetic agent.
p.6
Types of Vaporisers in Anaesthesia
What is the 'pumping effect' in vaporisers?
It refers to the intermittent pressure changes caused by positive pressure ventilation, which can displace gas saturated with vapour into the bypass channel.
p.7
Desflurane Vaporiser Design
How does the desflurane vaporiser inject anaesthetic vapour?
Into the free gas flow downstream of the vaporisation chamber.
p.6
Types of Vaporisers in Anaesthesia
What happens if a vaporiser tips past 45°?
Anaesthetic liquid can obstruct the valves, resulting in very high concentrations of vapour being delivered to the patient.
p.11
Neuromuscular Blockade Monitoring Techniques
What is the purpose of using needle electrodes in nerve stimulation?
To identify nerves to block during regional anaesthesia.
p.8
Impact of Altitude on Vaporiser Function
How does altitude affect the use of plenum vaporisers?
There is no clinical difference in using plenum vaporisers at altitude.
p.1
Classification of Ventilators
What is the primary function of a ventilator?
To deliver gas to the lungs.
p.12
Neuromuscular Blockade Monitoring Techniques
What is the main advantage of acceleromyography?
It is more accurate than visual monitoring.
p.13
Stimulation Patterns in Neuromuscular Monitoring
Why should single twitch be used before and after administering neuromuscular blocking drugs (NMBDs)?
To assess the degree of receptor occupancy by comparing the height of the twitch before and after drug administration.
p.8
Impact of Altitude on Vaporiser Function
What is Dalton's law of partial pressures?
Each gas in a mixture exerts a pressure equal to what it would exert if it were the only gas present.
p.13
Stimulation Patterns in Neuromuscular Monitoring
What indicates 75% occupancy of acetylcholine receptors?
The height of the twitch starts to reduce.
p.13
Stimulation Patterns in Neuromuscular Monitoring
What does the disappearance of t4, t3, t2, and t1 indicate in terms of receptor occupancy?
t4 = 75% occupancy, t3 = 80%, t2 = 90%, t1 = 100%.
p.12
Neuromuscular Blockade Monitoring Techniques
What are the main stimulation patterns used in neuromuscular monitoring?
Single twitch, Train of four (TOF), Tetanic stimulation, Post-tetanic count, Double burst stimulation (DBS).
p.8
Impact of Altitude on Vaporiser Function
What determines whether a patient is anaesthetised?
The partial pressure of the volatile agent, not the percentage concentration.
p.14
Neuromuscular Blockade Monitoring Techniques
What does a fade in the train of four (TOF) indicate?
A smaller amount of neuromuscular blocking drug (NMBD) present at receptors.
p.5
Variable Bypass Vaporisers
What is the 'splitting ratio'?
The ratio of fresh gas flowing through the chamber to that flowing via the bypass pathway.
p.3
Definitions of Ventilatory Modes
What is the purpose of Pressure Support (PS) mode?
It is used for weaning patients from the ventilator by augmenting their inspiratory effort.
p.5
Variable Bypass Vaporisers
What problem can high fresh gas flow cause in a vaporiser?
It may result in insufficient vapour being available to fully saturate the fresh gas.
p.5
Variable Bypass Vaporisers
What is the role of the copper casing in plenum vaporisers?
It conducts heat from the environment to the liquid as it cools, mitigating temperature effects.
p.11
Neuromuscular Blockade Monitoring Techniques
What does mechanomyography measure?
The tension generated in the muscle following stimulation, which is inversely proportional to the degree of neuromuscular blockade.
p.5
Variable Bypass Vaporisers
What determines the path of fresh gas flow in a vaporiser?
The 'splitting valve' attached to the control dial.
p.8
Impact of Altitude on Vaporiser Function
What happens to the partial pressure of sevoflurane at an altitude of 5.5 km?
It reduces to 0.02 atm (or 2% of 1 atmosphere).
p.13
Stimulation Patterns in Neuromuscular Monitoring
What occurs when 100% of acetylcholine receptors are occupied?
There are no twitches at all.
p.13
Stimulation Patterns in Neuromuscular Monitoring
What is the frequency and number of twitches in a Train of Four (TOF)?
Frequency is 2 Hz (2 every second) and the number of twitches is 4.
p.14
Neuromuscular Blockade Monitoring Techniques
What does tetanic stimulation assess?
The presence of profound neuromuscular block.
p.12
Neuromuscular Blockade Monitoring Techniques
What is the standard current used for twitches in neuromuscular monitoring?
50 mA (supramaximal stimulus).
p.1
Classification of Ventilators
What is the risk of barotrauma in flow-generated ventilation?
Higher risk, so pressure limits must be set.
p.11
Neuromuscular Blockade Monitoring Techniques
What is the current applied to the nerve when using needle electrodes?
Low amplitude (1–3 mA) initially, reducing to 0.2–0.5 mA as the needle approaches the nerve.
p.11
Neuromuscular Blockade Monitoring Techniques
What are the advantages of visual/tactile assessment of motor response?
Simple, convenient, and cheap.
p.11
Neuromuscular Blockade Monitoring Techniques
What are the advantages of mechanomyography over visual monitoring?
More accurate than visual monitoring.
p.1
Classification of Ventilators
What is the risk associated with pressure-generated ventilation?
Low risk of barotrauma but higher risk of volutrauma.
p.1
Classification of Ventilators
What factors influence inspiratory flow rates and tidal volume in pressure-generated ventilation?
The patient's lung compliance.
p.12
Neuromuscular Blockade Monitoring Techniques
What is electromyography?
A technique where a skin or needle electrode is placed over the adductor pollicis to record muscle action potentials.
p.1
Classification of Ventilators
How does flow-generated ventilation cycle?
It cycles when the set tidal volume has been delivered.
p.7
Desflurane Vaporiser Design
What is the purpose of the DIVA vaporiser?
To provide a measured flow of various anaesthetic agents, including desflurane.
p.11
Neuromuscular Blockade Monitoring Techniques
What is the current delivered by skin electrodes during nerve stimulation?
Supramaximal current (50 mA) to ensure recruitment of all muscle units.
p.1
Classification of Ventilators
What happens to inspiratory pressures in flow-generated ventilation?
They depend on the patient's lung compliance; lower compliance results in higher peak inspiration pressure.
p.6
Types of Vaporisers in Anaesthesia
What can over-filling a vaporiser cause?
Overdose and potential spillage of anaesthetic liquid onto the patient circuit.
p.7
Desflurane Vaporiser Design
What happens to the resistance to the flow of desflurane as the dial setting increases?
Resistance decreases and more desflurane is injected.
p.5
Variable Bypass Vaporisers
What happens to the temperature of the liquid in the chamber as it vaporises?
It absorbs energy, leading to a fall in temperature.
p.2
Definitions of Ventilatory Modes
What is PEEP?
Positive End Expiratory Pressure, a set level of pressure below which the circuit is not allowed to fall at the end of expiration for mechanically ventilated patients.
p.6
Types of Vaporisers in Anaesthesia
What are plenum vaporisers with electronic control?
Vaporisers that use cassettes to deliver anaesthetic and are controlled electronically for precise concentration delivery.
p.11
Neuromuscular Blockade Monitoring Techniques
What are the disadvantages of visual/tactile assessment?
Prone to interpretation error, inaccurate, and crude.
p.11
Neuromuscular Blockade Monitoring Techniques
How is the motor response assessed after nerve stimulation?
1. Visual/tactile observation of 'twitches' 2. Mechanomyography measuring tension generated in the muscle.
p.7
Desflurane Vaporiser Design
What properties of the anaesthetic should be considered when building a vaporiser?
Saturated vapour pressure at room temperature, boiling point at atmospheric pressure, and MAC of the anaesthetic agent.
p.7
Desflurane Vaporiser Design
What is the MAC and dial range for desflurane?
MAC = 6.00, range 0–12% on dial.
p.6
Types of Vaporisers in Anaesthesia
How does the volatility of desflurane affect its delivery?
Small changes in ambient temperature can lead to large changes in its saturated vapour pressure, affecting the concentration delivered.
p.11
Neuromuscular Blockade Monitoring Techniques
What are the disadvantages of mechanomyography?
Hand must be splinted and stable, it is fiddly and inconvenient, mainly used in research.
