Anaesthesia 2 Flashcards
Why is monitoring and support required in anaesthesia?
- Influences the outcome
- Ethical and moral obligation
- Maintain oxygen delivery
What physiological parameters are monitored in anaesthesia?
- Oxygen delivery (affected by multiple parameters)
- CaO2 (carriage of oxygen in blood)
- Mean arterial pressure
- Respiratory function
- Cardiovascular function
What affects the carriage of oxygen in the blood?
- Saturation of Hb with oxygen
- Amount of oxygen dissolved in plasma
- Huffner’s constant (1.34)
What is Huffner’s constant?
The number of molecules of oxygen that attach to a haemoglobin molecule
How is respiratory function measured?
- Oesophageal stethoscope
- Capnograph
- Pulse oximeter
How is cardiovascular function measured?
- ECG
- Blood pressure
- Pulse
When is oxygen support delivered to a patient?
- During all anaesthetics
- Pre-induction
- In recovery
How can oxygen be delivered to a patient?
- Mask if tolerated
- Flow by: oxygen source next to nose and allowing them to breathe this
- Intranasal prongs
- Intratracheal tube attached to oxygen
- Tracheostomy
What are the limitations of pulse oximeters?
- Low or high heart rates alter results
- Alpha2 agonists lower heart rate
- Not all probes are designed for veterinary use
- Only shows early warning sign of when patient is about to become cyanotic
- Do not compensate for anaemic or hypovolaemic patients
Explain how pulse oximeters work
- Probe has transmitter and receiver of IR and red light, transilluminates pulsatile arteriolar bed
- Computer software analyses absorption of ight
- Oxyhaemoglobin absorbs more IR and reduced Hb absorbs more red light
- Ratio calculated corresponding to % haemoglobin saturated with oxygen
- Can be pulsatile due to arteriolar flow
Explain how pulseoximeters are used in monitoring anaesthesia
- SPO2% given by pulse oz
- Oxygen content = (1.39xHbxSPO2%) +(0.003xPaO2)
- Used to give early warning signs for potential cyanosis
How can oxygen content in the blood be assessed during anaesthesia?
- Blood gas analysis (pH, HCO3, PCO2, PO2), most accurate
- Capnography
- Oesophageal manometry (rare in veterinary)
Which arteries are commonly used during anaesthesia to assess pulse?
- Femoral
- Dorsal metatarsal
- Lingual
- Auricular
Describe the measurement of pulse during anaesthesia
- Compare dorsal metatarsal artery and femoral
- Femoral will beat even after death, therefore not good for monitoring subtle changes
- Dorsal metatarsal will show changes much sooner, will disappear with hypertension-
How can arterial blood pressure be monitored during anaesthesia?
- Non-invasive pressure monitoring (NIBP) e.g. sphygmomanometry, oscillometry (and HDO), Doppler
- Invasive blood pressure monitoring
- Pulse cannot be used
Outline the use of a Doppler to assess blood pressure during anaesthesia
- Piezoelectric crystal placed over artery (clipped)
- Locate artery with distinct noise of arterial pulse (whoosh)
- Cuff placed proximal to probe
- Give systolic pressure
- Tape in place, leave for length of anaesthetic
Outline the use of oscillometry to assess blood pressure during anaesthesia
- Unreliable in cats and small dogs
- Expensive
- Gives systolic, mean and diastolic pressures
- More accurate methods are available
Give examples of invasive blood pressure monitoring methods
- Artery cannulation
- Central venous pressure
Outline the use of artery cannulation to assess blood pressure during anaesthesia
- Auricular, dorsal pedal, facial arteries most commonly used
- Gives systolic, mean and diastolic arterial pressures, beat to beat wave forms of all 3 values
- Gold standard
Must label catheter, line and flush regularly - Never inject drugs
- Tubing must be narrow bore and non-compliant to amplify signal
- Difficult to place
Outline the use of central venous pressure to assess blood pressure during anaesthesia
- Long jugular catheter
- Indicates filling pressure of heart
- Affected by contractility and circulating blood volume
- Useful for fluid therapy
- Need several readings to discern trend, gives trace
- Normal: 0-10cm H2O in dog, 0-5cm H2O in cat
What is indicated by an increasing central venous pressure?
Failing heart or volume overload
What is indicated by a decreasing central venous pressure?
Haemorrhage, blood pooling, inadequate fluid therapy
How can heart rhythm be assessed during anaesthesia?
- Stethoscope
- Continuous ECG
Outline the use of a continuous ECG during anaesthesia
- Indicates trends, good for spotting changes
- Often distorted due to patient position and placement of electrodes
- Does not give heart rate, indicates electrical activity of heart, not performance