Monitoring Anaesthesia Flashcards
What are the aims of monitoring anaesthesia?
Ensure adequate depth of anaesthesia
Ensure adequate perfusion and oxygenation of tissues
Monitor: \+ CNA \+ Respiratory system \+ CVS system \+ Body temperatures
How do you monitor the CNS?
Cranial nerve reflexes
Palpebral reflex Occular position (central or ventral) Pupil diameter Jaw tone Other signs Corneal reflex Lacrimation Salivation Tongue curl
Autonomic responses
Cardiovascular indicators
+ HR
+ Capillary refill time
+ Arterial blood pressure
Respiratory indicators
+ Resp rate, depth, pattern
Sites for peripheral vs central pulse during anaesthesia?
Peripheral
Dorsal pedal
Auricular
Digital
Central
Femoral
How is an ECG used to monitor CVS function?
Electrical activity of heart
Diagnosis of arrhythmias
NOT cardiac output
Normal conscious arterial blood pressure (systolic, diastolic, mean)
a. Dog
b. Cat
a. Dog:
Systolic = 140mmHg
Mean = 100mmHg
Diastolic = 75mmHg
b. Cat:
Systolic = 180mmHg
Mean = 135mmHg
Diastolic = 100mmHg
Why is monitoring arterial blood pressure important in anaesthesia?
Important for maintenance of autoregulation of organ function (brain, heart, kidneys, liver, muscles)
Indirect indicator of cardiac output
Name the non-invasive methods of monitoring arterial blood pressure
Doppler flow detection
Oscillometric method
Pros/cons of doppler for monitoring ABP in anaesthesia…
Pros: Can use on conscious patients Useful in hypotensive patients Good in small animals Cheap
Cons:
Not reliable in horses
Underestimates systolic ABP in cats about 10-14mmHg
Pros/cons of oscillometric methods for monitoring ABP in anaesthesia…
Pros
Automatic
Good for dogs
Cons
Less reliable in small cats and during hypotension
Expensive
Describe direct method for monitoring arterial blood pressure
Arterial catheter in peripheral artery
Continuous monitor
Allows blood gas samples
Transducer needs to be zeroed at level of heart
What is a spirometer?
Measures ventilation and the movement of air into and out of the lungs
Identifies obstructive and restrictive ventilation (eg. kinked ET tube)
What does a capnograph measure?
End-tidal carbon dioxide (ETCO2)
CO2 produced at the end of respiration
What does capnography indicate?
Adequacy of ventilation/gas exchange
Indirect indicator of arterial CO2
Heart pumping blood to lungs (CVS peformance)
Metabolic level (CO2 production)
Indicates airway obstruction (ET tube blockage)
Shows patient disconnection/adequacy of resuscitation/rebreathing of CO2
Capnography
a. Normal ETCO2
b. ETCO2 seen with hyperventilation
c. ETCO2 seen with hypoventilation
a. 35-45mmHg
b. Decreased
c. Increased
What does capnograph look like if ET tube is blocked?
Shark fin shape rather than normal square
What does pulse oximetry indicate?
Measures haemoglobin oxygen saturation
Oxygenation of tissues not ventilation
Heart rate
Pressure wave form (peripheral circulation)
Pulse
Normal O2 saturation for pulse oximetry is…
> 95% O2 saturation
What is arterial blood gas analysis used for in anaesthesia?
Definitive information on ventilation
Information on metabolic status
Measured parameters
+ Oxygen
+ Carbon dioxide
+ pH (metabolic/respiratory alkalosis/acidosis)
Arterial samples = efficiency of ventilation
Venous samples = acid-base status
What does arterial O2 tension (PaO2) indicate? Normal range?
How well the lungs can oxygenate the blood.
+ Normal = >80mmHg
+ Serious hypoxaemia = <60mmHg
+ Critical hypoxaemia = <40mmHg
What does arterial CO2 tension (PaCO2) indicate? Normal range?
Measure of alveolar ventilation (similar to ETCO2 in healthy animals).
Normal = 35-45mmHg Hypoventilation = >45mmHg Hyperventilation = <35mmHg
What does hypothermia during anaesthetic lead to?
+ Reduced anaesthetic requirements
+ Slowed drug metabolism
+ Prolonged recovery
Drop in 2 degrees leads to vessel shut down = be aggressive in keeping animal warm from the start.
What leads to hyperthermia during anaesthetic?
Malignant hyperthermia (genetics)
Pyrexia
Rebreathing circuits on a warm day
Can be fatal
