ANAESTHESIA - Monitoring Flashcards
Which four factors should you monitor to assess anaesthetic depth?
Movement
Eye position
Eye reflexes
Jaw tone
Which two eye reflexes should you monitory to assess anaesthetic depth?
Palpebral reflex
Corneal reflex
What should you assess instead of jaw tone in large animals?
Tension of the strap muscles of the neck
What are three indicators of good anaesthetic depth?
Ventro-medial eye rotation
Absent palpebral reflex
Relaxed jaw tone
What are three indicators of excessive anaesthetic depth?
Central eye rotation
Absent corneal reflex
Mydriasis (pupil dilates)
How can you manually monitor the respiratory system?
Monitor the respiratory rate
Which two methods can you use to manually monitor the respiratory rate?
Take respiratory rate by counting the chest movements or by counting the movements of the resevoir bag
How can you manually monitor the cardiovasular system?
Palpate pulses
Auscultate heart
Assess mucous membrane colour
CRT
Why is palpating pulses preferable to auscultating the chest when a patient in under anaesthesia?
Palpating pulses provides a pulse rate, rhythm and allows you to assess pulse quality/strength which gives some indication as to the levels of peripheral perfusion
Give three examples of arteries you can use to palpate pulses
Femoral artery
Dorsal pedal artery
Metacarpal artery
Why is it better to take pulses from the more peripheral arteries (i.e. dorsal pedal and metacarpal arteries)?
Palpating pulses using the more peripheral arteries gives a better idea of peripheral perfusion
Why should you always compare the pulse rate to the heart rate?
If the pulse rate and heart rate are not the same, this is abnormal (known as an anacrotic pulse)
Which pieces of equipment are used to monitor the respiratory system?
Pulse oximetry
Capnography
What is blood gas analysis?
Blood gas analysis is when you take an arterial blood sample and use this to measure the partial pressure of oxygen and carbon dioxide (PaO2 and PaCO2) in the arterial blood
Why is blood gas analysis less commonly used?
Blood gas analysis is an invasive procedure which requires skill and also doesn’t allow for continuous monitoring
What information do pulse oximeters typically provide?
SpO2
Pulse rate
Signal quality
Which five parts of the body would be appropriate for the placement of a pulse oximetry sensor?
Tongue
Nail bed
Ear tip
Vulva/prepuce
Lip fold
How does the pulse oximetry sensor detect the percentage of arterial haemaglobin saturated with oxygen (SpO2)?
The pulse oximetry sensor is placed onto an appropriate part of the body. The probe transmits, and detects, specific wavelengths of red and infra-red light that are differentially absorbed by oxygenated and de-oxygenated haemoglobin on passage through tissue. Analysis of this differential absorption allows calculation of SpO2
List six possible factors that can result in unreliable pulse oximetry readings
Poor contact between tissue and sensor
Pigmented skin
Movement
Peripheral vasoconstriction
Hypotension
Abnormal haemoglobins
How does peripheral vasoconstriction affect pulse oximetry readings?
Peripheral vasoconstriction reduces blood flow to the peripheral tissues and thus decreases the flow of oxygen to the periphery and the pulse
How does hypotension affect pulse oximetry readings?
Hypotension reduces blood flow to the periphery by lowering the overall pressure being excerted within the arteries, meaning there is less force pushing the blood to the periphery hence reducing the flow of oxygen
What is used to monitor the signal quality of a pulse oximeter?
Plethysmograph
Flashing lights (red/orange/green)
What is a plethysmograph?
A plethysmograph is a graphical display of the pulse oximetry signal over time, with well defined waveforms being indicative of good signal quality
What should the SpO2 be in animals breathing in room air?
SpO2 should be over 90% in animals breathing in room air
What should the SpO2 be in anaesthetised animals breathing in 100% oxygen?
SpO2 should be over 95% in anaesthetised animals breathing in 100% oxygen
What can cause a low SpO2?
Low inspired oxygen
Lung disease
Right to left cardiac shunting
Hypoventilation
What can cause a patient to have low inspired oxygen resulting in a low SpO2?
Disconnection between the patient and the oxygen supply
Kinked endotracheal tube
Airway obstruction/blocked endotracheal tube
What can be a physical indicator of a low SpO2?
Cyanosis
What are the three main limitations of pulse oximetry?
Readings are not always reliable
Doesn’t monitor CO2 levels
Doesn’t tell you about perfusion/blood pressure
What is capnography?
Capnography is the continuous measurement and graphic display of the partial pressure of carbon dioxide in respired gases as the patient breathes in and out
Interpret the different phases of a normal capnograph
PHASE 1: Phase 1 is inhalation and since no carbon dioxide is going out when the patient is breathing in, it is at baseline
PHASE 2: Phase 2 is the beginning of exhalation, carbon dioxide begins to travel from the alveoli through the anatomical dead space of the airway causing a rapid rise in the graph. This part of the graph goes up as the more concentrated CO2 gases from lower in the lungs rise up past the sensor
PHASE 3: Phase 3 is when the sensor is receiving the carbon dioxide rich gas from the alveoli. Because this is a fairly stable amount, the graph levels off into a plateau. The peak measurement at the end of phase three is the EtCO2 reading.
At the end of phase 3, the patient inhales again, bringing clear air past the sensor, dropping the graph back down to baseline to start over again at phase 1
What information is provided by capnography?
Respiratory rate
End-tidal CO2 (EtCO2)
Capnograph waveform shape (traces) can indicate different conditions
Indication of the adequacy of cardiac output
What is end-tidal CO2 (EtCO2)?
End-tidal CO2 (EtCO2) is the level of carbon dioxide that is released at the end of an exhaled breath (EtCO2)
What is the normal range for EtCO2 in dogs?
35 - 45 mmHg
or 4.6 - 6kPa
How does hyperventilation affect the EtCO2 levels?
Hyperventilation increases how much carbon dioxide is eliminated from the body, resulting in hypocapnia and a decreased EtCO2
How does hypoventilation affect the EtCO2 levels?
Hypoventilation decreases how much carbon dioxide is eliminated from the body, resulting in hypercapnia and an increased EtCO2
Hypoventilation is common in animals under anaesthesia
At what EtCO2 level is action required?
EtCO2 of 60mmHg/8.0kPa or above
What is the first thing you should do if the EtCO2 levels are 60mmHg/8.0pKa or above?
Decrease the anaesthetic depth as the most likely cause of the patient’s hypoventilation and high EtCO2 is excessive anaesthetic depth
What should you do if you have decreased anaesthetic depth the patient still has a high EtCO2?
Intermittent positive pressure ventilation (IPPV)
What is indicated by this capnograph waveform (trace)?
Kinked endotracheal tube
Blocked endotracheal tube
Bronchoconstriction
What is indicated by this capnograph waveform (trace)?
Rebreathing of CO2 (i.e. a problem with the anaesthetic breathing system)
What is indicated by this capnograph waveform (trace)?
‘Bucking’ the ventilator
What is indicated by a gradual loss of the capnograph waveform (trace)?
Cardiovascular collapse
What is indicated by a sudden loss of the capnograph waveform (trace)?
Disconnection of the ventilator or the capnograph
How does capnography provide an indication of the adequacy of cardiac output?
The EtCO2 detected by capnography reflects how effectively carbon dioxide is being carried in the blood back to the lungs for exhalation which can indicate the adequacy of cardiac output
What is the main limitation of capnography?
Capnography doesn’t measure oxygenation
Which pieces of equipment are used to monitor the cardiovascular system?
Electrocardiography (ECG)
Blood pressure
What is measured by electrocardiography (ECG)?
ECG measures the electrical activity of the heart as well as provides continuous monitoring of heart rate and rhythm
What are the three key benefits of ECG for monitoring the cardiovascular system?
Detects arryhthmias
Continuously monitors heart rate and rhythm
Useful for identify cardiac rhythm during CPR
What is the main limitation of ECG for monitoring the cadiovascular system?
ECG gives no indication of cardiac output and tissue perfusion
What is blood pressure?
Blood pressure is the force exerted onto the arterial walls by circulating blood
Which calculation can be used to calculate blood pressure?
Blood pressure = Heart rate x Total peripheral resistance
What is systolic blood pressure?
Systolic blood pressure is the force exerted onto the arterial walls when the heart beats and pumps blood (systole)
What should the systolic blood pressure be in a healthy animal?
Systolic blood pressure should be over 90mmHg
What is diastolic blood pressure?
Diastolic blood pressure is the minimal force exerted onto the arterial walls before the next cardiac ejection occurs
What should the diastolic blood pressure be in a healthy animal?
Diastolic blood pressure should be over 40mmHg
What is mean arterial pressure (MAP)?
Mean arterial pressure (MAP) is the average force exerted onto the arterial walls within one cardiac cycle (systole and diastole)
What should the mean arterial pressure (MAP) be in a healthy animal?
Mean arterial pressure (MAP) should be over 60mmHg
How do you measure direct blood pressure?
To measure direct blood pressure you carry out arterial catheterisation and then connect the catheter to a pressure transducer to allow for a direct and continuous measure of blood pressure
Why is measuring direct blood pressure not commonly done?
Measuring direct blood pressure is an invasive procedure which requires a lot of skill
What are the two forms of indirect blood pressure monitoring?
Oscillometric
Doppler
How do you carry out oscillometric blood pressure monitoring?
Place a cuff over a peripheral artery. The cuff will inflate and occlude the blood flow and detect oscillations which will begin as systolic blood pressure, maximise at mean arterial pressure (MAP) and stop at diastolic pressure
How do you carry out doppler blood pressure monitoring?
Place a cuff over a peripheral artery. Apply ultrasound gel and an ultrasound probe distal to the cuff. This will provide a continuous audible signal. Inflate the cuff until the audible signal disappears and then allow the cuff to slowly relax - the sound will return at the systolic blood pressure
How do you choose the correct blood pressure cuff size?
The width of the blood pressure cuff should be within 40-60% of the limb diameter
What can be used to monitor renal perfusion?
Urine production as renal perfusion is required for the production of urine
How can you monitor urine production?
Use a closed collection system - i.e. a urinary catheter attached to a collection bag - to measure urine production
What is the normal urine output?
1 - 2ml/kg/hour
