Anaesthetic Machine & Monitoring Equipment Flashcards
What is the primary gas used in anaesthesia?
Oxygen
What percentage of inspired oxygen is required by healthy small animals to maintain oxygen saturation during GA?
33%
What colour coding on a cylinder indicates oxygen?
White
What can cause absorption atelectasis?
High inspired fraction of oxygen
What colour coding on a cylinder indicates medical air?
Black and White
What were the benefits of using nitrous oxide?
Analgesic effects
Reduction in inhalational anaesthetic requirements
What colour coding on a cylinder indicates nitrous oxide?
Blue
What are gas cylinders usually made of?
Molybdenum steel
What pressure and what form is oxygen stored at?
A compressed gas with a pressure of 13700kPa
What pressure and what form is nitrous oxide stored at?
Liquid at a pressure of 4400kPa
What is used to ensure the correct cylinders get connected to the correct outlet on the machine?
Pin Index System
What must be placed between the anaesthetic machine yolk and the cylinder?
Bodok Seal (a compressable sealing washer)
Why are cylinders opened slowly?
To prevent rapid release of pressure and therefore generation of heat
What is present to prevent loss of gas from an empty yoke?
Backflow check valve (a one way valve)
How/where is liquid oxygen stored?
Stored in a vacuum insulated evaporator (VIE) at a very low temperature of -150 to -170 celcius and a high pressure of 500-1000kPa
What can be used to supply oxygen to a single patient?
Oxygen concentrators
What do we need to be careful of when using a circle with an oxygen concentrator?
Build up of argon - not filtered out by zeolite sieves.
What is the pressure of a piped oxygen supply?
400kPa
What two safety features ensure piped gases get connected to the correct outlets?
Schraeder probe - a collar around the hose that has a specific diameter for that pipeline’s terminal.
Non-interchangeable screw thread (NIST) attaches the hose to the anaesthetic machine.
What changes the pressure of oxygen from 13700kPa in the cylinder to 400kPa in the gasline?
Pressure regluator
What is the function of the flow control valve on a flowmeter?
To reduce the pressure of the gas from 400kPa to just to just above atmospheric pressure (1-8kPa)
What happens when the oxygen flush button is used?
flowmeter and vapouriser are by-passed, the oxygen is delivered at a flow rate of 30-70L/minute at a pressure of 400kPa direct from the oxygen source.
What three measures are the in an anaesthetic machine to prevent hypoxic gas being delivered?
- Oxygen Fail safe
- Oxygen failure alarm
- Hypoxic guard
What does an oxygen fail safe do?
Cuts off the delivery of nitrous oxide when oxygen pressure and flow falls.
What is a hypoxic guard?
Prevents the delivery of hypoxic gas mixture with oxygen less than 25%.
What is the difference between a plenum vaporiser and a draw-over vaporiser?
Plenum - or pressurised - vaporiser is where gas is ‘pushed’ through under positive pressure from the FGF. Draw-over vaporisers ‘pull’ the gas over the open jar-type vaporiser.
What are present in the vaporiser to increase surface area and improve efficiency?
Wicks and Baffles
What mechanisms does a vaporiser have to ensure its internal temp is maintained?
- Made from copper and brass which acts as a heat sink
- A bimetallic strip - alters the proportion of gas entering the chamber dependin gon temperature (called the temperature compensation mechanism).
Why should you not tilt the vaporiser?
Can cause inhalant anaesthetic liquid to enter the bypass chamber
What type of vaporiser would be required for desfurane and why?
Electronically controled, as desflurane has boiling point close to room temp.
What mechanisms are in place in the GA machine to stop damage from excessive pressures?
Non-return valve downstream of vaporiser to prevent backflow pressure and damage if gas outlet occluded. Also a pressure relief valve on the back bar that opens when pressure reaches 30-40kPa.
What size is the common gas outlet?
22mm male, 15mm female
What flow/pressure does the oxygen flush supply at?
35-75L/min directly from the oxygem source (usually 400kPa)
What is the maximum accepted waste gas exposure in ther UK for halothane, isoflurane, nitrous oxide and sevoflurane?
H- 10 ppm
I - 50ppm
NO - 100ppm
S - 60ppm
What does a passive scavenging cannister contain?
Charcoal
What pressure does the non-return pressure relief valve open on the back bar?
30kPa
How can oxygen be supplied?
- Compressed gas in cylinders
- Liquid in a vacuum insulated evaporator (VIE)
- generated in an oxygen concentrator
How does a plenum vaporiser ensure the desired percentage of volatile agent is delivered?
Thye have 2 chambers - a pressurised vaporising chamber within which the carrier gas becomes fully saturated with vapour, and a bypass chamber which has no anaesthetic agent in it. The proportion of carrier gas entering each chamber is controlled by the dial.
What factors influence how much volatile agent is vaporised?
- Temperature
- Surface Area
- FGF
- Tilting the vaporiser
Define Dead Space
The volume fo gas that is not involved in gas exchange. Gas exchange only occurs within the alveoli.
Define Tidal Volume
The volume of gas entering the lung with each inspiration
Define Minute volume
Volume of gas entering the lunch in each minute. TV X RR
If the patient is panting, what minute volume can you use?
200mls/kg/minute
Define Metabolic oxygen requirement
Amount of oxygen required each minute for metabolic processes
What are the estimated metabolic oxygen requirement for small animals and large animals?
Small - 10mls/kg/minute
Large - 5mls/kg/minute
Define Rebreathing
When the inspired gases reaching the alveoli contain more carbon dioxide than can be accounted for be mere re-inhalation from the patients dead space gas.
What is the function of an anaesthetic breathing system?
Used to connect the patient to the GA machine. To allow the delivery of oxygen and volatile agent and removal of waste volatile agent and CO2.
Why is removing CO2 from the expiratory breath important?
To prevent hypercapnia, and therefore prevent respiratory acidosis, sympathetic stimulation - tachycardia, hypervolaemia, tachypnoea and possibly cardiac arrthymias.
How do you decide what sized reservoir bag to use on a circuit?
Should be 3-6 times the animal’s tidal volume (10mls/kg)
What safety feature do APL valves have?
A ‘pop-ff’ once maximum pressure reached to prevent barotrauma or volutrauma.
Describe Poiseuille’s Law
Equation showing the resistance to airflow is inversely proportional to the radious of the tubing.
E.g. halving the radius of the tubing increases the resistance 16 fold. Doubling the length only doubles the resistance.
Compare pros and cons of coaxial and parallel tubing
Coaxial in theory allows expired air to wamr inspired air, but probably doesnt have time and also risk of kinking or disconnection of inner tube. Parallel has no warming but damage is more easily detected.
What does soda lime contain?
Hydroxide, sodium hydroxide, water, and an indicator dye.
How do non rebreathing circuits remove CO2?
They rely on relatively high gas flows and co2 is ‘flushed’ into the scavenging system.
What are the advantages of non rebreathing circuits
- facilitate rapid changes in depth of anaesthesia
- can use NO
- Cheap to purchase and maintain
- Lower resistance so better for smaller animals
What are the disadvantages of non rebreathing circuits?
- high fresh gas flows and volatile agent required (environmental and cost implications)
- Heat and Moisture lost
- Flow rates may become impractically high for larger animals.
How do you calculate fres gas flow?
FGF = MV x CF
(MV = TV (10mls/kg) x RR)
CF Bain and Ayres T = 2-3, the magill and lack 0.8-1
How would you prevent diffusion hypoxia at the end of anaesthesia if using NO ?
NO turned off 5 minutes before end of GA and O2 flow increased to 3L/min
Describe the features of a Bain circuit
Weight 8+kg
Can be used for IPPV
Mod resistance, low drag and low dead space
The resservoir bag is on the expiratory limb of the breathing system.
Describe the features of a Ayres T piece circuit
- weight up to 10kg
- Prolonged IPPV
- Low resistance, drag and dead space
- Circuit Factor 2-3
Describe the features of a lack
- Weight over 10kg
No IPPV
CF 1
Resistance lower if parallel than coaxial
Drag and dead space moderate
Reservior bag on INSPIRATORY limb
Describe the features of a magill
Over 5kg weight
NO IPPV
Resistance mod, drag high, dead space mod.
Bag and scavenge next to patients head - inconvienient.
What are the advantages of a rebreathing system?
Lower FGF and volatile agent consumption
Heat and moisture conserved
Easy to change between spontaneous and manual ventilation
What are the disadvantages of a rebreathing system?
Slower change of depth of anaesthesia
NO should not be used at low flow rates
High resistnace nmay be problematic in smaller animals.
May contirbute to hyperthermia
How are FGF rates calculated for rebreathing systems?
By estimating the animals metabloic oxygen consumption (what is used at cellular level)
Approx 5-10mls/kg/minute.
How should the flow be regulated for a rebreathing circuit? i.e. what rates should you eb on?
Start with high FGF for first 15 mins to flush nitrogen from room air out of circuit.
Then reduce to minimum 0.5l/min.
Describe the features of a circle
Can be used for IPPV
More resistance than non-rebreathing
Drag mod-high
How long should you hold pressure in the reservoir bag during testing the circuit for leaks?
10 seconds
What would indicate the APL has been left closed?
- Distention of reservoir bag as pressure builds
- Reduced thoracic movements
- Low ETCO2
- Possible leaking round an uncuffed ETT
- Tachycardia if CO affected
- Possible drop in SPO2
What would indicate that resistance within a circuit was too high for that patient?
- Altered RR - usually low
- Decreased TV
- Hypoventilation and hypercapnia
- Hypoxia
- Light anaesthesia due to reduced alveolar ventilation
- Altered resp pattern - paradoxical or increased effort
Why is IPPV required for thoracotomy?
Entering the thorax abolishes the animal’s ability to generate negative pressure that drives the inflow of gas during inspiration.
Why may IPPV be indicated in patietns with raised ICP?
Hypercapnia increases ICP, as increased PaCO2 causes cerebral vasodilation, potentially increasing the volume within the cranium.
What drugs would mean IPPV is required?
Opioids may temporarily cause anoea.
Neuromuscular blocking agents will cease spontaneous ventilation due to paralysis of respiratory muscles.
What is compliance?
Defined as the volume change per unit pressure change.
What is hysteresis?
When the inspiratory curve is different to the expiratory curve on a graph of lung compliance.
What conditions can reduce compliance?
Pulmonary fibrosis
Pneumothorax
What effects can prolonged IPPV have on the rest of the body?
Increased intrathoracic pressure can reduce venous return, and therefore cardiac output due to compression of vena cava.
Renal plasma flow is reduced during IPPV, and increased production of anti-diuretic hormone (reduces urine production)
What is the difference between barotrauma and volutrauma?
Barotrauma is caused by high airway pressures an is characterised by air outside the alveoli as a consequence of alveolar rupture.
Volutrauma causes alterations in gas exchange and is thought to be caused by repeated stretch and overinflation of alveoli.
What is the difference between a volume controlled and pressure controlled ventilator?
A volume controlled ventilator delivers a constant flow of gas to the animal whereas a pressure controlled ventilator delivers a constant pressure of gas to the aptient
How does a time cycled volume controlled ventilator work? And how can the TV be adjusted?
Deliver constant flow of gas for a defined period of time, once time is up, ecpiration begins. If you increase the inspiratory time or inspiratory flow then TV will increase.
What would result in increased airway pressure when using a ventilator?
Increase in airway resistance or reduction in compliance.
Describe how a volume controlled, volume -cycled ventilator would work?
Deliver a constant flow of gas until the pre-determined tidal volume is delivered. Increase in flow will cause the RR to increase as the TV is pre-set so it will just be achieved quicker.
Describe how volume-controlled pressure cycled ventilators work
A constnat flow of gas delivereed until a pre-set peak airway pressure is reached (usually 10-15 cmH20) , at which point inspiration is terminated. The tidal volume can vary depending on compliance of lungs and airway resistance.
Describe how a pressure-controlled and time cycled ventilator works
During inspiration, the pressure of the gas being delivered is maintained at a consistent pressure. Once the set pressure has been reached, the gas flow reduces to ‘hold’ that pressure int he lungs until the set time has elapsed, then expiration begins.
Desribe the difference between PEEP and CPAP
PEEP is the application of positive end expiratory pressure during IPPV whereas CPAP is the continuous positive airway pressure during spontaneous ventilation.
Both aim to improve functional residual capacity by holding alveoli ‘open’ at the end of a breath.
Describe the role of the nurse during anaesthesia
Monitor patient. Detect changes in physiological variables and recognise trends.
Advocating for the animal and organising the team.
Describe the patient at an ideal depth during GA
- minimal jaw tone
- ventro-medially rotated eye position
- sluggish-no palpebral reflex
- no laryngeal or pharyngeal reflex
- absence of lacrimation
- regular respiratory pattern
What key things should be included in the anaesthetic record?
Date, animal details, procedure, drugs, timing of critical events and physiological parameters including HR RR temp
What can be used to reduce human error during GAs?
Record keeping and safety checklists
What effects can hypothermia have?
- effects on drug metabolism
- prolong recovery
- bradycardia and arrythmias
- reduces MAC of inhalational agents therfore need less
- negative impact on wound healing and infection rates
What conditions would require blood glucose monitoring under GA?
- diabetes mellitus
- Sepsis
- Hepatic dysfunction
- Neonates
Describe the PQRS and the electrical conductivity of the heart
P wave is generated by atria , where the elctrical impulse moves from the SA node to the AV node. The QRS complex occurs when the electrical impulse moves through the ventriclesdown the bundle of HIS and up the purkinje fibres.
Describe the placement of ECG pads in horses
Red - jugluar furrow
Yellow - Sternum
Black - ribcage
What reading do each lead take on an ECG?
Lead 1 - Righ arm to Left arm
Lead 2 - Right arm to Left Leg
Lead 3 -Left arm to elft leg
What is the equation for Blood pressure?
Blood Pressure = CO x SVR
What is the equation for cardiac output?
CO = HR x SV
What factors affect stroke volume?
Preload, afterload and contractility of the heart
What is the formula to calculate MAP
Diastolic pressure + 1/3 (Systolic pressure - Diastolic Pressure)
Discuss the benefits and risks of direct Arterial Blood Pressure measurement
Most accurate
Provides continuous information
Risks include H+, haematoma formation, infection and thrombosis
Cannulation of artery is technically challenging.
How can you determine the correct sized blood pressure cuff?
Cuff width should be 40% of the limb circumference
What is central venous pressure and what is ti affected by?
Pressure measurement of blood in the cranial vena cava. Affected by venous return, blood volume and cardiac output
What is the formula to calculate Partial pressure of oxygen in the aveoli (Pao2)?
PaO2 = FiO2 (Atmospheric Pressure Patm - Water vapour Pressure Ph20) - PaCO2/RQ respiratory quotient
or at sea level 5xFiO2
What is the PaO2 at room air and under 100% oxygen??
Room air - 100mmHg
100% O2 - 500mmHg
What does the oxyhaemaglobin dissociation curve show us?
Relates the Partial pressure of o2 in the blood (PaO2) to the haemaglobin saturation of oxygen
What does the SPO2 measure?
The haemaglobin oxygen saturation in arterial blood of the available red blood cells
Describe the phases of a capnograph waveform
1 ETCO2=0. End of inspiration.
2 ETCO2 starts to increase. Expiration of deadspace gas and alveolar gas.
3 ETCO2 levelling off. Expiration of alveolar gas. Alveolar plateau
How does a capnograph work?
Sines infrared light through sample of expired gas and measures how much is absorbed by the CO2 molecules.
Describe the pros and cons of mainstream vs sidestream capnography
Mainstream - rapid results, sensor adds dead space.
Sidestream - slower results, water trap needs emptying, less dead space, can be used in MRI, scavenge exhaust gases.
What trace would indicate a leak on a capnograph?
Lack of alveolar plateau
What would a shark fin trace indicate on a capnograph?
Resistance within the airway or ETT
What does spirometry measure?
Measures flow, volume and pressure to assess the function of the respiratory tract
What does blood gas analysis measure?
Used to evaluate acid base balance, ventilatory efficiency, and blood oxygenation. Some also measure electrolytes or lactate
List the checks needed when an alarm sounds on the GA machine
- Ausculate heartbeat
- Assess pulses
- Check MM colour
- Assess depth
- Assess respiratory function. ETCO2 and SPO2.
- Measure body temp
- Quantify any blood loss
- Consider what drugs have been administered
- BP measure
How would tachycardia affect CO?
Initially a slight tachycardia would increase cardiac output. However too fast and this will affect diastolic filling time and reduce stroke volume, therefore reducing CO.
What are the common causes of tachycardia under GA?
- Inadequate anaesthesia or analgesia
- Hypotension/ hypovolea
- Hypercapnia
as well as… - Hypoxia
- Hyperthermia
- Anaemia
What are causes of bradycardia under GA?
- Drugs
- Deep anaesthesia
- Hypothermia
as well as… - Hyperkaleamia
- Hypertension can also cause reflex bradycardia
- vagal reflex
List what you should do if an arrythmia is detected?
- Assess the pulse and the abnormalities
- Assess frequency of abnormality
- Are the abnormal complexes to do with an event/manipulation?
- Assess BP
What troubleshooting should be done on a low BP reading under ga?
- Repeat
- Evaluate other factors to determine if its true e.g. HR
- Check pulses
- Check depth, analgesia (so can reduce volatile agent)
- Check HR +/- manage
- Is there any blood loss?
What can be considered under GA to treat low BP?
Fluid boluses or use of inotropes/vasopressors.
What three things should evaluate if you get a low SPO2?
- Oxygen delivery to animal. Check O2 flow, check valves, circuit and ETT.
- Gas exchange within the lungs. Manual IPPV to confirm chest movement. Ensuring no leaks. Check ETCO2 and capno.
- Circulation. Confirm pulses. Measure BP.
Describe troubleshooting re-breathing on a capnograph under GA
- Ensure FGF high enough in non-rebreathing circuit.
- Ensure tubes of circuit are patient (especially a Bain).
- Check soda lime isnt exhausted and no valves are stuck. ona circle.
- Give breath - check chest wall movement, check resistanc, listen for abnormal sounds.
- Evaluate dead space in the breathing system.
List what you should do if an alarm sounds indicating low/no ETCO2
- Check pulse/HR
- Check breathing system connected
- Confirm ETT in trachea.
- Check sampling line for kinks/breakage
- Manual IPPV while assessing compliance, chest wall, leaks , resistance etc.
