Anaesthetic monitoring Flashcards
What are the goals of anaesthetic monitoring?
Provide an appropriate depth of anaesthesia for the procedure required;
Whilst maintaining normal physiological function
How often is anaesthetic monitoring carried out?
Patients monitored continuously, parameters recorded every 5 min
Allows for action
Chances of surviving slim if not checked at least every 5 minutes
Describe monitoring charts
Must be completed for all cases.
Legal document
Don’t become so focused on completing this form that you are neglecting your monitoring.
What should be monitored?
- Anaesthetic depth
- Circulation
- Respiratory system
- Temperature
What cranial nerve reflexes can be checked to aid in anaesthetic monitoring?
Palpebral Reflex
Corneal reflex
Pedal reflex
(Jaw tone)
Avoid doing too often or can become refractory (palpebral)
Describe eye position and pupil diameter
Observe both eyes
Surgical plane of anaesthesia eye ventromedial position with some sclera visible
Depth increases
-the eye becomes central again
The use of ketamine will affect this pattern
As the depth of anaesthetic increases the pupil becomes more dilated
What might salivation indicate?
Excessive with an inadequate anaesthetic depth/pain
Note breed variation
Describe indications from mucous membranes and capillary refill times
Mucous membrane colour should be pink
Capillary refill time (CRT) is measured by pressing on a non-pigmented area of gingiva. This will cause it to blanch
The time for the colour to return is the CRT
Should be ~2seconds
How can the response to surgical stimulation aid in monitoring?
Lost during surgical planes
If present increase in heart rate, respiratory rate and muscle tone
Describe the heart rate and pulse quality
Check every 5 minutes.
Rapid when
-the patient is light
Slows in surgical planes
Will slow further
-as anaesthetic depth increases
Describe the respiratory rate and pattern
Check every 5 minutes
Rapid and irregular
-patient is too lightly anaesthetised
Slower and regular at surgical planes
Shallower and slower when
-too deep until irregular jerky breathing movements are seen, eventual apnoea.
How might temperature aid in anaesthetic monitoring?
Hypothermia is common
Temperature should be monitored regularly
-Every 5-30mins
Frequency of measurement depends on the case details
What is the purpose of monitoring aids?
To provide additional information about the physiological status of the patient. They should never replace the basic hands on monitoring detailed previously
Describe the advantages/disadvantages regarding mechanical aids
Allows a more precise picture of the patients health status
May detect early changes in patients’ health status allowing early intervention
Allow closer control over anaesthetised patients
Must be monitored to ensure information provided is correct
Should never take the place of routine, basic monitoring procedures i.e. observations, listening and touching the patient
Describe the oesophageal stethoscope
Often overlooked
Simple and effective
Allows VN to hear heart beat reliably
Describe the pulse oximeter
Non-invasive method of measuring arterial oxygen saturation
Gives information about gas exchange and arterial oxygenation
Provision of an audible indicator of heart rate is reassuring
but the remaining information is limited- when breathing oxygen, the saturation will not fall unless your patient is in serious trouble
The oxygen saturation of a patient receiving 100% oxygen should always be above 95%.
How do pulse oximeters work?
Two sources of light originate from the probe at different wavelengths (red and infra-red)
Absorbed by the red blood cells differently depending on how well the RBCs are saturated with oxygen
The device recognises the pulsatile flow of the arteries and can display both the oxygen saturation and the pulse rate.
Where is the probe of the pulse oximeter usually placed?
Usually the probe is placed on the tongue
Can be placed on other non-pigmented areas of skin
- Prepuce
- Vulva
- Between the toes
- Ear pinna
- Lip
When might a pulse oximeter fail?
f there is peripheral vasoconstriction, or low blood pressure
In smaller patients the heart rate may be too high for a standard machine to register
Diathermy and bright operating lights can both disrupt the signal
Can be misleading in the anaemic patient
Define systolic blood pressure
This is the peak pressure within the arteries that occurs towards the end of the cardiac cycle, when the ventricles are contracting. It is determined by a combination of peripheral vascular resistance, stoke volume and intravascular volume.
The normal range in dogs, cats and horse is 90-120mmHg
Define diastolic blood pressure
This is the minimum pressure within the arteries that occurs towards the beginning of the cardiac cycle. This is when the ventricles are filled with blood and is predominately determined by the peripheral vascular resistance.
The normal range for dogs, cats and horses is 55-90mmHg
Define mean blood pressure
This is the average blood pressure during the cardiac cycle. It provides information about tissue perfusion. The normal range for dogs, cats and horses is 60-85mmHg.
It is important to maintain a mean blood pressure > 60 mmHg to ensure adequate organ perfusion
Why would you use blood pressure monitoring?
Gives more direct information about the peripheral circulation than palpating a pulse
Useful measure of cardiovascular function specifically in patients with significant cardiovascular disease or those undergoing major surgery
It provides information of the heart’s ability to pump blood around the body and the fluid balance of the patient
Fluid therapy supports blood pressure, would be useful to know we are using an adequate flow rate
What might high blood pressure indicate?
A low blood pressure may indicate that vital organs are not being sufficiently perfused and/or the patient is under deep anaesthesia
What might low blood pressure indicate?
High blood pressure may indicate that an animal is only lightly anaesthetised or that there is sympathetic stimulation
Describe doppler ultrasonography
This method provides intermittent readings of blood pressure.
A cuff tourniquet is applied proximal to the artery (cuff width = 40% circumference of the limb)
The area where the Doppler is to be applied; normally over the carpal pulse is clipped and contact gel applied
The Doppler is then used to detect the pulse
Once detected the cuff is inflated using the sphygmomanometer until the sound disappears, then slowly deflated until the first sound is heard
The pressure at which the flow recommences is taken as the systolic blood pressure.
Describe oscillometric blood pressure
Measures the magnitude of arterial pulsations produced within an air filled cuff. It detects movement of the artery wall vibrating against the cuff
Inaccurate results can be given when there is patient movement (Shivering), dysrhythmia, hypotension and bradycardia
These monitors can be set up to take repeated measurements
Systolic, diastolic and mean blood pressure is recorded
Describe a capnograph
Provides information of both respiratory and cardiovascular function
Measures adequacy of ventilation (hyper or hypoventilation)
Provides measurement of carbon dioxide in each breath of the respiratory cycle
Describe capnography
Gas breathed out a mixture of anatomical dead space gas followed by increasing levels of CO2 rich gas
When the animal breathes in the level of CO2 will return to zero (if breathing system working correctly)
What can affect capnography?
Problems with either the circulation or respiratory system will affect amount of CO2 breathed out
Skill needed to interpret the trace
When will a capnography graph never return to the base line?
Rebreathing CO2
When will the end tidal CO2 rise?
Breathing too shallow or slowly and CO2 building up in the lungs
What can lead to a reduction in ETCO2?
Hyperventilation
Why would you use an ECG?
Can provide useful information on -
Heart rate
Assessment of heart rhythm
Does not indicate the mechanical output of the heart – tracing can continue many minutes after the heart has ceased to be an effective pump
What parameters would class as bradycardia in dogs and cats?
dogs < 60, cats <90
What parameters would class as tachycardia in dogs and cats?
dogs >200, cats >250
Describe an ECG
Electrical equipment can interfere with the signal, as can movement.
An audible beep is usually given
Rate displayed on the screen or on a paper output
Abnormal rhythms are easily visible (but could also be heard using a stethoscope)
What do you check on an ecg to determine if it is normal?
HR
P for every QRS
QRS for every P
QRS and P’s all the same
Rhythm regular
How may an ECG indicate an issue?
Abnormal complex shapes, or missing p waves can indicate impending problems before the abnormal pumping action actually occurs
If there is no audible heart beat the ECG will tell us whether fibrillation is present and allow more effective treatment
Unlikely to be used for every operation, but in high risk cases it can be a valuable aid
Describe arterial blood gas
Only way of truly knowing how much O2 and CO2 are in the blood
Considered gold standard of monitoring
Blood sample taken from an artery and analysed
Not commonly used in small animal general practice
What are the two methods of temperature support?
Passive
Active
Name types of circulatory support
Intravenous fluid therapy
Blood pressure monitoring
Chest auscultation
Name types of breathing support
IPPV
Manual
Mechanical
What can effect the speed of recovery?
Breed
Existing illness- renal, hepatic, respiratory, cardiac
Temperature
Duration and type of anaesthesia
Route of drug administration
In what cases should you extubate early?
Risks inhalation of FBs
Best for cats
Not for brachycephalic dogs
Allows pollution of atmosphere
In what cases should you extubate late?
Airway protected until gag response returns
Best for potential airway obstruction
Risk of laryngeal spasm in cats
Less pollution of atmosphere
Prolonged O2 breathing
What should you monitor during recovery?
Position of patient
Pulse
Respiratory rate and pattern
MM colour and CRT
What is indicated by
- pale mms?
- cyanosis?
- red mms?
Temperature
Pain
Hydration
Wound management
Drug therapy
Nutrition
How can supplemental oxygen be given?
Flow-past
Oxygen tent
Mask
Intranasal catheter
What are the advantages and disadvantages of a flow-past?
A- Easy to do
D- Inspired oxygen levels lower than with other methods
What are the advantages and disadvantages of an oxygen tent?
A- Easy to do provided equipment is available
D- Only for small patients.
Requires high flow rates so is expensive
What are the advantages and disadvantages of a mask?
A- Can achieve good levels of O2 with low flow rates in ideal situation
D- Patient distress and interference
What are the advantages and disadvantages of an intranasal catheter?
A- Good oxygen levels with low flow rates.
Well tolerated.
Can be used for a prolonged period
D- Not difficult to place, but maybe a bit scary if you haven’t done it before!
Placement takes time so unsuitable for short periods
