Monitoring during anaesthesia Flashcards
what to monitor
Depth of Anaesthesia
Respiratory system
Cardiovascular system
Body temperature
written anaesthetic record - why
Helps identify trends during anaesthesia
Focuses the person on patient monitoring
Invaluable for personnel changeover
Legal record
Monitoring of the CNS
to ensure correct depth
Cranial nerve reflexes – Palpebral reflex, Ocular position, Pupil diameter, Jaw tone
Corneal reflex
Lacrimation
Salivation
Tongue curl
Cardiovascular indicators - HR, Capillary refill time, Arterial blood pressure
Respiratory indicators - Respiratory rate, depth and pattern
Monitoring of CVS Function - heart rate
Relative rate
Increase in rate – Surgical stimulation /Hypovolaemia
Decrease in rate – Increased depth of anaesthesia, Vagal activity
Monitoring of CVS Function - pulse
Heart rate
Quality – strength, relates to cardiac contractility
Rhythm – indicative of arrhythmias
Sites - Peripheral versus central pulse - Femoral, Lingual, Dorsal Pedal, Mandibular, Auricular
pale mucous membrane colour - cause
Alpha2 agonist administration
Anaemia
Vasoconstriction
Monitoring of CVS Function - Mucous membrane colour
Haemoglobin quantity
Peripheral blood flow
Respiratory adequacy
Toxaemia
Monitoring of CVS Function - Capillary refill time
Peripheral circulation
Normal < 2 seconds
oesophageal stethoscope
Useful if patient inaccessible
Information - Heart + Respiratory rate
Arterial Blood Pressure (ABP)
ABP = Cardiac Output x Systemic Vascular Resistance
Indirect indicator of cardiac output
Methods of monitoring - Non-invasive or indirect methods, Invasive or direct measurement
ABP – Doppler Flow Detection
Ultrasound Sensor distal to cuff - Piezo-electric crystal, Detect audible ‘swooshing’
Place pressure cuff around extremity Distal limb /tail
Advantages - Can use on conscious patients, Useful in hypotensive patients, Good in small animals, NOT horses, Underestimates sABP in cats 10 - 14 mmHg
Inflate cuff until no sound
Release cuff slowly until hear ‘swooshing’ sound - Indicates systolic pressure
ABP – Oscillometric Method
Automatic Good for dogs Less reliable – Small cats. During hypotension HDO (High Definition Oscillometry) Expensive
central venous pressure - indicator of
Volume load / deficit
Adequacy of fluid therapy
Heart performance / failure
respiratory monitors
observation of chest wall / rebreathing bag
Heated probe monitors – sense expired gas
Respirometer – minute ventilation, e.g. Wright’s
End-tidal carbon dioxide – capnography
pulse oximetry
Non-invasive continuous method Haemoglobin oxygen saturation Oxygenation of tissues NOT ventilation Normal > 95% O2 saturation During + after anaesthesia
pulse oximetry - indicator of
Arterial oxygen saturation
Heart rate
Pressure wave form – peripheral circulation
pulse oximetry - method
Sensor – (LED) - Red + Infrared
Photodetector - detects PULSATILE signal = arterial blood
Differential absorption of red + infrared - Oxyhaemoglobin, `Reduced haemoglobin
Pulse oximetry - Limitations
NOT adequacy of ventilation
Poor function if - Compromised circulation, Movement + Light sensitive, Extremes of heart rate
Anaemia – underestimates oxygen saturation
Carboxyheamoglobin – misreads as oxyHB > 100%
Methaemoglobin – absorbs both red and infrared light > 85%
Capnography
Measures - End-tidal carbon dioxide (ET CO2)
Infrared light absorption – proportional to CO2 in gas, mass spectrometry
capnography - indicator of
Gas exchange - Adequacy of ventilation
Indirect indicator of arterial carbon dioxide – Heart pumping blood to lungs - Cardiovascular performance
Metabolic level – CO2 production
capnography - Hyperventilation
decreased ETCO2
capnography – Hypoventilation
Increased ETCO2
capnography - limitations
Sampling error – falsely low ETCO2
Tachypnoea - Incomplete exhalation of alveolar gas, Dilution of alveolar gas by physiologic dead space gas
Equipment delay in response time
High fresh gas flow rates - Wash out end-tidal gas
Hypoventilation - Aspirate gas without CO2 in expiratory pause
arterial blood gas supply
Definitive information on ventilation
Information on metabolic status
Measures - Oxygen, Carbon dioxide, pH
hypothermia
Reduced anaesthetic requirements Slowed drug metabolism Prolonged recovery Shivering in recovery Greater risk of complications
hyperthermia
Malignant hyperthermia
Pyrexia
Rebreathing circuits on a warm day