Anaesthetic monitoring Flashcards by Josie Campbell

Basic monitoring of cardiovascular function

Clinical monitoring (pulse, MM, CRT, heart ausculation)

Arterial blood pressure measurement

Pulse oximetry (pulse frequency)

Electrocardiography

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Advanced monitoring of cardiovascular function

Cardiac output measurement

Perfusion indexes

New generation pulse oximetry (Masimo technology)

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Clinical monitoring of CV function

Quality, rhythm, and frequency of peripheral pulse to assess volume status and detect arrhythmias

Auscultation of heart sounds

MM colour and CRT as indicators of tissue perfusion

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Mean arterial blood pressure calculation

MAP = CO (cardiac output) x SVR (systemic vascular resistances)

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What is MAP an indicator of?

Parenchymal/muscle perfusion (>70-80mmHg)

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What is SAP an indicator of?

Ejection volume (>90-100mmHg)

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What is DAP an indicator of?

Coronary perfusion (>40mmHg)

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Methods of measurement of arterial blood pressure

Sphygmomanometry (Riva-Rocci cuff)

Oscillometry (standard and high definition)

Doppler

Invasive method (via arterial catheterisation

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Oscillometry - principles of measurement

Reasds SAP, MAP, and DAP

Needs appropriate sized inflatable cuff

Flow restoration generates oscillations whose frequency is proportional to the MAP

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Advantages of oscillometry

Relatively cheap and easy to use

Non-invasive

Usually incorporated in multiparametric modules

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Disadvantages of oscillometry

Reliability decreases in case of arrhythmias or extreme values (hyper/hypo-tension)

Measurement is intermittent

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Prinicples of doppler measurement

Flow sensor equipped with piezoelectric crystal, and an inflatable cuff connected to a manual manometer

Cuff inflation occludes artery

Flow restoration results in audible signal from flow sensor

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Advantages of doppler

Monitor in real time of pulse (audible signal)

Useful and reliable in dogs, cats, and rabbits

Not affected by pulse/heart rhythm

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Disadvantages of doppler

Flow sensor is easy to break/damage

Reads MAP in cats, SAP in other species (less reliable in cats)

Electric noise/interference

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Principles of invasive blood pressure measurement

Based on pressure transducer, converts mechanical energy to electrical signal

Gives pressure reading and pulse wave

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Advantages of invasive blood pressure monitoring

Gold standard

Reliable in all species

Allows measurement of arterial blood gases (respiratory and acid-base assessment)

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Disadvantages of invasive blood pressure measurement

Invasive (requires catheterisation of a peripheral arttery)

Potential complications: vasculitis, haemorrhage

Expensive

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Principles of pulse oximetry

Percentage of saturation of haemoglobin with oxygen <97% when breathing room air)

Pulse frequency (audible signal)

Pulse waveform (amplitude and morphology)

Advantages of pulse oximetry

Easy to use

Allows monitoring of cardiovascular and also respiratory variables

Disadvantages of pulse oximetry

Inaccurate in case of severe anaemia, pigmented MM and carbon monoxide intoxication

False sense of security

Data/reading misinterpretation is common

Common arrhythmias during anaesthesia

Vagal stimulation (drug induced- opioids, intestinal/oesophageal/ocular manipulation)

Hypothermia (bradyarrhythmias)

Electrical currents applied in proximity of the heart

Mechanical stimulation of heart and vessels (thoracotomies, heart surgery)

Hypoxaemia and hypercapnia

Basic monitoring of respiratory function

Clinical monitoring (resp rate, breathing patter, lung ausculation)

Capnography

Pulse oximetry

Advanced monitoring of respiratory function

Spirometry

Arterial blood gases analysis

Why is CO2 so important?

Metabolism

Cardio-circulatory system

Respiratory system

CO2 and metabolism

Produced during cellular metabolism Its production increases during high metabolic states (e.g. fever, exercise) and decreases during phases of low metabolism (e.g. hypothermia, sleep)

Co2 and cardiocirculation

Produced by cellular metabolism Taken up by venous blood and transported through CV system to the lungs (where its removed)

CO2 and respiration

Rate of elimination of CO2 from the lungs (parameter measured by capnography) ultimately tells about the efficiency of ventilation A decrease is one of the first signs of cardiac arrest

Methods of capnography measurement

Laser Spectrography Gas-chromatography Colorimetric technique

Sidestream method of capnography measurement

Exhaled gases are sampled at patient's airways and analysed in the control unit (diverted by a sampling line) Sampling rate: 70-200ml/min (technical problems if used in patients with small tidal volumes) No dead space

Mainstream method of capnography measurement

Analysis of exhaled gases occurs directly at patient airways Considerable dead space No sampling rate Generates heat (burns are possible)

Clinical use of capnography

CO2 value should be 35-45 mmHg Lower values = hyperventilation (hypocapnia) Higher values = hypoventilation (hypercapnia)

What does a rebreathing capnography waveform look like?

Elevated baseline

What does an upper airway obstruction capnography waveform look like?

Shark fin shaped curve

What does an abnormal plateau on a capnography waveform look like?

Gas sampling issues- technical problem of device

Clinical significance of spirometry

Allows evaluation of lung volumes and pressures and their relationship

What do low pressures applied to the airway, generating high lung volumes indicate on spirometry?

Good/high compliance (distensibility) of the lung parenchyma

What do high pressures applied to the airway, generating low lung volumes indicate on spirometry?

High resistance to flow or poor lung compliance (e.g. elderly, pneumonia)

What can result in hypothermia during anaesthesia?

Decreased liver perfusion and metabolism (liver metabolism generates heat) Myorelaxation (muscles generate heat) Decreased cellular metabolism (sleep mode) Drug-induced impaired thermoregulation (e.g. opioids) Surgical preparation (clipping and disinfection) Opening of body cavities (laparotomies, thoracotomies)

Consequences of hypothermia

Increased morbidity Increased rate of infections Impaired coagulation Cardiac arrhythmias Seizures Pain Death

Prevention of hypothermia

Active warming devices (hot-dog, bari-hugger) Heat and moisture exchanger filters (HME) Passive warming devices (blankets) Use of warm fluids for lavage of body cavities Decrease the fresh gas flow of breathing gases When possible limit the duration of anaesthesia

Ventrally rotated eye with slow pupillary reflex and mild palpebral reflex

Surgical anaesthesia achieved

Centrally positioned eye with mydriasis, absent pupillary and palpebral reflexes

Anaesthesia level is too deep

Centrally positioned eye with normal pupillary and palpebral reflexes, swallowing possibly observed

Too superficial anaesthetic plane

Nociception to determine plane of anaesthesia

Deep pain can be used to evaluate opioid induced analgesia Autonomic reflexes more commonly used in clinical practice (e.g. increased heart rate and blood pressure following surgical stimulation)