Monitoring anaesthesia Flashcards
Why do we monitor patients
To prevent patient response to surgical stimulation (nociception)
To detect abnormalities before they turn into major complications
Helps monitor for worsening of underlying or subclinical diseases
Enables early interventions to keep patient close to their physiological norm
To maintain tissue perfusion & oxygenation so we can improve patient outcome
What is the purpose of anaesthetic monitoring charts?
Serve as legal clinical record
Facilitate handover between clinicians
Help identify trends in patient parameters over time
Guide early interventions to prevent complications
Why is it important to record trends rather than single values in anaesthesia?
Trends provide clearer picture of patient’s condition over time
e.g. Gradual increases in HR, BP, & RR can indicate nociception, prompting intervention (e.g., IV ketamine)
What do the following abbreviations mean in anaesthesia monitoring?
BP
HR
RR
MAP
IPPV
BP: Blood Pressure
HR: Heart Rate
RR: Respiratory Rate
MAP: Mean Arterial Pressure
IPPV: Intermittent Positive Pressure Ventilation
What is tissue perfusion?
Adequate supply of oxygen & nutrients are delivered to tissues & CO2 & other waste products are removed
Requires fully functioning respiratory & cardiovascular system
How do anaesthetic drugs affect tissue perfusion?
Cause cardiac depression, reducing blood flow
Cause respiratory depression, limiting oxygen delivery
Decrease patient’s ability to maintain homeostasis (e.g., temperature control, electrolyte balance)
How does low blood pressure affect tissue perfusion?
Insufficient blood pressure reduces flow of oxygenated blood to tissues, impairing metabolism & waste removal.
What are causes of decreased blood flow that can decrease tissue perfusion?
Reduced heart rate (HR) or cardiac output
Haemorrhaging (blood loss)
Anaemia (low red blood cell count)
Conditions that impair blood flow (e.g., vascular obstructions)
What can cause decreased oxygen delivery to tissues?
Reduced respiratory rate (RR)
Oxygen delivery issues: Equipment failure or low oxygen flow
Pulmonary disease: Reduces oxygen exchange
Obesity in dorsal recumbency: Excess pressure on diaphragm decreases tidal volume, impairing inspiration
What are the 3 problems that are bound to occur to a certain extent during anaesthesia?
Hypotension
Hypothermia
Hypoventilation
How can we establish depth of anaesthesia?
Checking jaw tone
- Ideally nice & loose
Eye position check
Negative palpebral reflex
- Positive palpebral reflex = too light
Other indicators:
- capnography, HR, RR, BP
What are the stages of eye position during anaesthesia?
Picture A (Conscious): Central eye position
Picture B (Early induction): Slight eye rotation
Picture C (Deeper induction): Further rotation, eye points rostrally
Picture D (Ideal for surgery): Eye rotated ventrally, indicating surgical plane
Picture E (Central eye):
- Dilated pupils: Too deep (excess CNS depression)
- Normal or constricted pupils: Too light for surgery.
Why can eye position be unreliable with ketamine?
Ketamine increases muscle tone, preventing normal relaxation of eye muscles that causes eye rotation during anaesthesia
Eye position may not correlate with anaesthetic depth in patients receiving ketamine.
Why is it important to lubricate eyes regularly throughout anaesthesia?
They can’t blink when anasethetised which means eyes can dry out, this could lead to problems such as corneal drying &/or corneal ulceration
How can brachycephalic breeds and ketamine affect jaw tone?
Brachycephalic breeds: Often maintain some jaw tone throughout anaesthesia
Ketamine: Increases muscle tone, making jaw tone unreliable indicator of depth
(remember that not every animal will follow what textbook suggests)
Why is monitoring temperature during anaesthesia important?
Hypothermia is leading cause of slow recoveries & is painful
What are the 2 most common ways of monitoring temperature?
Rectal thermometer: simple & widely available method
Oesophageal temperature probe: Requires multiparameter monitor & provides continuous temperature readings
How do you insert an oesophageal temperature probe?
- Measure probe length from incisors to caudal scapula to determine insertion depth
- Pull patient’s tongue forward
- Slide probe down side of ET tube
- Guide it into oesophagus to required depth
How can you monitor the cardiovascular system?
can assess:
- heart rate & rhythm
- mm colour & CRT
- bleeding
- BP
- heamoglobin oxygen saturation
- arrythmias
Equipment:
- BP monitors
- Pulse oximeters
- ECG
- Stethoscope
What factors influence a normal heart rate under anaesthesia?
Normal HR under anaesthesia is 60-120bpm
Species & size of the animal
Underlying conditions
Stress levels.
Drugs administered during premedication or induction.
Breed-specific phenomena (e.g., Dachshunds may have HR of 50–60 bpm under anaesthesia due to increased vagal tone).
Why is knowing pre-induction HR important?
Helps establish what is normal for individual patient
Guides decisions during anaesthesia monitoring to avoid unnecessary interventions
Why does the presence of a heart beat not always indicate adequate circulation?
beating heart doesn’t guarantee sufficient cardiac output or tissue perfusion
Monitoring should include pulse palpation & blood pressure measurement to assess circulation adequacy
What tools should be used to monitor heart rate and rhythm during anaesthesia?
Stethoscope: To confirm presence & rate of heartbeat
- can also use oesophageal stethoscope which is more reliable & useful if patient is draped
Pulse palpation: To assess peripheral circulation
Blood pressure measurement: To evaluate tissue perfusion
Why is it important to listen to heart while palpating a pulse?
To detect pulse deficits, which occur when peripheral pulse doesn’t match heart rate determined by stethoscope
Pulse deficits may indicate cardiac dysrhythmias, which require ECG evaluation.
What are the commonly used sites for pulse palpation?
Sublingual artery: Ventral aspect of tongue
Mandibular artery: Along mandible
Digital metacarpal artery: Palmar surface of forelimb
Digital metatarsal artery: Plantar surface of hindlimb
Dorsal pedal artery: Dorsum of metatarsal area
Femoral artery: Medial aspect of femur
Coccygeal artery: Ventral surface of tail
What are the common signs of pulse deficits during palpation?
Irregular rhythm
Pauses in the pulse
Pulse rate is less than heart rate determined by stethoscope
What is capillary refill time (CRT)
Assessment of peripheral perfusion and oxygenation
should be <2s
What does this mucous membrane assessment show?
Vasodilation (usually very pink or red with rapid CRT)
examples:
- Sepsis
- Anaesthetic drugs (e.g. anaphylaxis)
- Low MAP (mean arterial blood pressure); this depends on root cause
What does this mucous membrane assessment show?
Healthy = pink & moist
Dry/Tacky = dehydration, hypovolaemia
Wet = over infusion, nausea (risk of regurgitation/gastric reflux, aspiration)
What does this mucous membrane assessment show?
Vasoconstriction (usually very pale with slow CRT)
examples:
- Anaemia
- Inadequate blood flow
- Alpha 2 Agonists
What does this show?
Cyanosis is bluish/purplish discolouration of skin or mucous membranes due to tissues near skin surface having low O2 saturation
Indicates sebere hypoxaemia (very close to death)
(Chow Chows always have blue tongue)
Why is communication between the anaesthetic monitor and the surgeon important during intraoperative bleeding?
Surgeon can alert anaesthetic monitor to suspected bleeding, prompting monitoring for signs like:
- Prolonged CRT.
- Low blood pressure.
Monitor can inform surgeon of any detected issues to help them check surgical site & adjust their approach
How can you estimate the volume of blood lost during surgery?
Weigh blood-soaked surgical swabs
1 mL of blood = ~1 g of weight
What signs might indicate intraoperative bleeding from the monitoring perspective?
Prolonged CRT
Low blood pressure (BP)
Other signs of poor perfusion or hypovolemia
What are the 2 main methods of measuring blood pressure?
Doppler: Portable; measures systolic BP in dogs & mean arterial pressure (MAP) in cats & animals <10 kg
Oscillometric: Usually part of multiparameter monitor; measures systolic, diastolic & MAP
How do you select correct cuff size for measuring blood pressure?
cuff width should be 40% of circumference of limb where it is placed
Too large cuff: Underestimates BP
Too small cuff: Overestimates BP
What are the normal BP ranges for healthy animals?
Systolic BP: 100–160 mmHg.
Diastolic BP: 80–120 mmHg.
Mean arterial pressure (MAP): 60–100 mmHg
What can an MAP <60mmHG for <30min lead to?
MAP of 60mmHg (systolic >90mmHg) needed to properly perfuse heart, brain & kidneys
Can lead to:
- Renal failure.
- Delayed recovery
- Neuromuscular complications
- Decreased hepatic metabolism of drugs
- CNS abnormalities such as blindness
What do these 3 values show?
Reading to left (127) is systolic Bp, one next to that (92) is diastolic & one in brackets (105) is mean arterial pressure.
How is a Doppler device used to measure BP?
- Place pressure cuff proximal to Doppler probe & connect it to sphygmomanometer
- Inflate cuff until Doppler sounds are no longer audible (artery is occluded)
- Slowly deflate cuff while observing sphygmomanometer
- Record pressure at which first audible arterial pulse is heard:
- Dogs: Closest to systolic BP.
- Cats: Closest to MAP.
Why should multiple measurements be taken in conscious patients using a Doppler?
Variability between readings is common
Take several readings & average the middle 3 measurements.
What is the ideal patient position for Doppler BP measurement?
Patient should lie in lateral recumbency
cuff should be positioned on limb at level of right atrium
What does a pulse oximeter measure?
percentage of haemoglobin saturated with oxygen (SpO₂)
Displays pulse rate & waveform called plethysmograph (“pleth” for short)
Waveform indicates strength & consistency of pulse, helping assess peripheral perfusion.
What do these arrows show?
What does a change in EtCO2 suggest?
What is this?
What do these lines show?
What is the most commonly used capnography system in veterinary practice?
Side-stream systems, where capnograph line is attached to connector between breathing system & endotracheal tube
Cockerpoo, castrate, ASA 1, HR 108 bpm prior to surgery
Premed: dexmedetomidine & methadone
Induction: alfaxalone to effect
Maintenance: isoflurane in oxygen, 5 mins after induction you see this
What do you think? What do you do?
Bradycardia (HR: 60 bpm):
- Likely due to dexmedetomidine (alpha-2 agonist), which reduces sympathetic tone
Perfusion & oxygenation:
- Normal MAP (91 mmHg) & SpO2 (100%) indicate no immediate compromise in perfusion or oxygen delivery
Response:
- Monitor closely: Since perfusion (MAP) & oxygenation (SpO2) are adequate, immediate intervention may not be required
- Reverse alpha-2 effects if needed: If bradycardia worsens or perfusion is compromised, administer atipamezole to reverse dexmedetomidine
- Check anaesthetic depth: Ensure anaesthesia is not excessively deep
- Administer anticholinergics if needed: Consider atropine or glycopyrrolate if perfusion deteriorates
GSD X, TPLO, ASA 2, HR 96bpm prior to surgery
Premed: acepromazine & buprenorphine
Induction: propofol to effect
Maintenance: isoflurane in oxygen, during anaesthesia gradual decline in HR & ABP
What do you think? What do you do?
Bradycardia:
- Likely due to acepromazine (vasodilation) & buprenorphine (opioid effects), combined with propofol & isoflurane, which depress cardiovascular system
Hypotension (MAP 57 mmHg):
- Suggests compromised tissue perfusion & requires intervention to prevent further complications
Response:
- Address bradycardia:
- If perfusion is compromised, consider atropine or glycopyrrolate to increase HR - Manage hypotension:
- Reduce isoflurane vaporiser settings if anaesthetic depth is excessive
- Administer IV fluids to improve circulating volume.
- If needed, use inotropes like dobutamine or vasopressors like norepinephrine to support blood pressure - Monitor closely:
- Continuously assess ABP, HR, & SpO2 to ensure interventions are effective
TBx, ASA 1, HR 40 bpm prior to surgery, bilat hock arthroscopy
Premed: acepromazine, morphine
Induction: romifidine, ketamine, midazolam
Maintenance: sevoflurane in oxygen 3.1% (ET), 30 minutes later during prepping of leg, this is the situation
What do you think? What do you do?
What’s happening:
- Severe bradycardia likely caused by romifidine (alpha-2 agonist) & morphine effects.
- Hypercapnia (EtCO2 67 mmHg) due to hypoventilation caused by respiratory depression from sevoflurane & sedatives.
- MAP (76 mmHg) acceptable, indicating perfusion is not yet critically compromised
Response:
- Reverse romifidine with atipamezole if needed or use atropine/glycopyrrolate for bradycardia if perfusion worsens
- Ventilate manually or mechanically to address hypercapnia.
- Reduce sevoflurane vaporiser setting to decrease respiratory depression
- Monitor HR, EtCO2 & MAP to ensure stability
Male 6y DSH, HR 90bpm prior to sedation, v large bladder
Premed: methadone
Induction: ketamine, midazolam
Maintenance: isoflurane in oxygen, 0.8% (ET)
What do you think? What do you do?
What is happening:
- Bradycardia (HR 75 bpm): Not critical but may be influenced by methadone (opioid) & midazolam, with no immediate compromise to perfusion or oxygen delivery
- Hypocapnia (EtCO2 30 mmHg): Likely caused by hyperventilation (RR 24) & shallow ventilation
- MAP (77 mmHg): Within acceptable range for perfusion.
- SpO2 (92%): Indicates borderline hypoxaemia; possible ventilation-perfusion mismatch
Response:
- Address hypocapnia: Reduce RR if manually ventilating & evaluate anaesthetic depth.
- Improve oxygenation: Adjust fresh gas flow & ensure proper ETT placement.
- Monitor closely: Observe for any further changes in HR, MAP, SpO2 & EtCO2 to maintain stability
- Support perfusion: Administer fluids if indicated to sustain MAP & oxygen delivery
2 yr old Bassett ASA 1, HR 96 bpm prior to surgery for lumpectomy
Premed: dexmedetomidine, methadone
Induction: propofol, local block
Maintenance: isoflurane
2 mins after incision, HR increased
What do you think? What do you do?
What’s happening:
- Tachycardia: due to pain or insufficient anaesthetic depth
- Hypotension: Compromised perfusion from vasodilation or sympathetic overdrive.
- SpO2 92%: Borderline hypoxaemia
Response:
- Increase anaesthetic depth or provide additional analgesia (e.g., fentanyl).
- Administer IV fluids & consider vasopressors (e.g. norepinephrine) if hypotension persists
- Verify oxygen delivery & adjust fresh gas flow or ETT placement
- Monitor HR, MAP & SpO2 to ensure stabilisation
14yr old DSH cat chronic renal insufficiency, ASA 3, dental
Premed: midazolam & methadone
Induction: alfaxalone to effect
Maintenance: isoflurane in oxygen
What do you think? What do you do?
What’s happening:
- Tachycardia (HR 231 bpm): due to pain, stress, or hypoxia, exacerbated by renal insufficiency
- Hypotension (MAP 56 mmHg): Compromised perfusion from vasodilation or poor cardiac output
- Hypocapnia (EtCO2 24 mmHg): Indicates hyperventilation or poor perfusion
- SpO2 90%: Borderline hypoxaemia, needs addressing.
Response:
- Administer analgesia (e.g., fentanyl) & reassess depth of anaesthesia
- Provide IV fluids & consider vasopressors (e.g. norepinephrine) to improve BP.
- Ensure proper oxygen delivery by adjusting ETT placement or increasing oxygen flow.
- Monitor HR, MAP, SpO2 & EtCO2 for stabilization.
1 year old 2.2kg Dutch rabbit for castration
Premed: buprenorphine SC
Induction: Medetomidine, ketamine SC
What do you think? What do you do?
What’s happening:
- Tachycardia (HR 209 bpm): stress or pain response from insufficient analgesia or light anaesthesia.
- Hypocapnia (EtCO2 24 mmHg): due to hyperventilation or poor cardiac output.
- MAP 94 mmHg & SpO2 97%: Perfusion & oxygenation adequate
Response:
- Administer additional analgesia (e.g., fentanyl) to manage pain
- Assess & adjust anaesthetic depth to address potential stress or sympathetic stimulation
- Monitor ventilation to ensure hyperventilation resolves & EtCO2 normalises.
- close monitoring of HR, EtCO2, & MAP for stability.
What’s happening:
- Initial tachycardia progressing to bradycardia: due to prolonged anaesthesia, inadequate ventilation, or cardiac strain
- Hypotension (MAP 56 mmHg): decreased perfusion from vasodilation or inadequate cardiac output
- Hypercapnia (EtCO2 54 mmHg): Due to hypoventilation or insufficient respiratory support
Response:
- Address hypotension: Increase IV fluids, consider inotropes (e.g., dobutamine) to support cardiac output.
- Improve ventilation: Increase intermittent positive pressure ventilation (IPPV) to reduce EtCO2 & support oxygenation.
- Adjust anaesthetic depth: Reduce isoflurane concentration to minimize cardiovascular depression.
- Monitor HR, MAP & EtCO2 continuously to ensure stabilisation
What are common causes of ventricular ectopic beats?
Circulating catecholamines (stress)
hypoxia
hypercapnia
hypovolaemia
anaesthetic drugs
myocardial irritation
major organ disease
How do you manage ventricular ectopic beats?
- Assess if perfusion is compromised (check ABP & SpO2%)
- Identify cause (depth of anaesthesia, CO2 levels, etc.)
- Administer lidocaine or beta-blockers (propranolol/esmolol) if needed
- Monitor for progression to ventricular fibrillation.
What are common causes of hypotension during anaesthesia?
Anaesthetic drugs, hypovolaemia, haemorrhage, or cardiac insufficiency
How do you treat hypotension?
- Reduce inhalant agent (TIVA or PIVA may be used).
- Increase IV fluids to restore circulating volume.
- Administer inotropes (e.g. dobutamine) or vasopressors (e.g. norepinephrine) if required
- Monitor urine output to ensure perfusion
What are common reasons for falling ET CO2 values during anaesthesia?
Obstruction: Partial airway blockage
Hyperventilation: Exhaling CO2 too quickly
Circulatory failure: Reduced blood flow to lungs
Hypotension: Poor perfusion affecting gas exchange
Cardiac arrest: Cessation of circulation
No, they are typically benign finding & don’t indicate clinical issue
How do you identify hypoxaemia?
