L29: Monitoring the anaesthetised patient

what should an anaesthetist be

• Present at all times

• Record keeping

• Good understanding of

  • physiology

  • Pharmacology

  • Physics

  • Equipment

  • clinical information available

What is the anaesthetic record

Legal document of

• Patients signalment

• Drugs administered

• Fluid therapy

• Parameters every 5-10 minutes

• important events

• complications

• Vital parameters of the animal in recovery

Why do we monitor patients

• To maintain the body as close as possible to physiologically normality

• To maintain adequate depth of anaesthesia

• To promote patient and personnel safety

• Legal requirement

What do you monitor when in anaesthesia

• CNS

• CVS

• Respiratory system

• Temperature

• Neuromuscular function

• renal function

• Metabolic status

How do you monitor anaesthesia

Listen→ Ventilation sounds, alarms, gas leaks

Look → eye position, chest movements, mucous membrane colour

Feel → Pulse quality, rate rhythm, jaw tone, reflexes

Small → That volatile agent- is it a leak, a disconnection?

How do you monitor the CNS

Depth of anaesthesia → assessment of reflexes

• Palpebral reflex

• Corneal reflex

• Gag reflex and jaw tone

• Limb withdrawal reflexes

• Perineal reflex (anal tone)

• Righting reflex

• Eye postioin

• Movement of the globe

• Lacrimation

• Pupil size

• ECG

• BIS

what can alter cardiac output

Why is it important to monitor the CVS

• Factors determining tissue perfusion and oxygen delivery

How can blood pressure affect the CVS

What are some normal blood pressures

How can you measure arterial blood pressure

• non invasive monitoring (NIBP)

  • Oscillometry

  • Doppler

• Invasive (IBP) monitoring

  • Direct arterial blood pressure

What is oscillometry

• Accuracy depends on the cuff (40% circumference limb)

• Cuff levelled with the heart

• Gives SAP, MAP, DAP

• MAP is the most accurate value

• Tendency of under-estimation

What is a doppler and how does it work

• Gives only one value → SAP

• In cats value is between SAP and MAP

What is an IBP

• Gold standard

• Arterial catheter

• Transducer at level of the heart

• Heparinized saline to flush

What do you look at in IBP

• Arterial blood gas

  • Acid base status

  • Efficiency of ventilation

• pH

• PaO2

• PCO2

• HCO3

• Electrolytes

How do you troubleshoot low blood pressure

MAP= cardiac output x systemic vascular resistance

• Assess depth of anaesthesia and reduce if possible

• Intravenous fluid therapy (bolus 5-10 mL/kg)

• Vasopressors

  • Positive inotropes (dobutamine)

  • Vasoconstrictors (ephedrine, phenylephrine, noradrenaline)

• Avoid NSAIDS during hypotension

How do you monitor the cardiovascular system using electrocardiography

• Heart rate

• Heart rhythm

• P waves

• PR interval

• QRS complex

• ST segment

• T waves

What types of stethoscopes are there

• traditional stethoscope

• Oesophageal stethoscope

  • Heart sounds

  • Heart rhythm

  • Lung sounds

What do you look for when monitoring the respiratory system by observing

• Breathing rate (RR)

• Breathing rhythm

• Tidal volume (TV)/depth of each breath

• Mucous membrane

Minute ventilation (MV)=TV x RR

What do different mucous membrane colours show

White→ anaemia, intense vasoconstriction

Yellow → Jaundice, carotens

Grey/purple/cyanotic → Poor tissue oxygen delivery (not observed at least 5 g/dL of deoxyhaemoglobin

Navy blue→ Excess of nitrous oxide (severe cyanosis)

Cherry red → Carbon monoxide poisoning

Muddy brown → metaHb (nitrate, paracetamol poisoning)

Brick red/brown → Systemic inflammatory response, sepsis

How do you assess ventilation with capnography

• CO2 in respiratory gases

• End-tidal (ET) and inspiratory (Fi) CO2

• Continuous

• Non-invasive

• Et-CO2 tension reflects the systemic arterial CO2 tension

• EtCO2 = PACO2 = PaCO2

What is capnography

• Measures how well the animal is ventilating

• Normal range 35-45 mmHg (4.5-6 kPa)

• Values > 60 mmHg (>8kPa) may require mechanical ventilation

What are types of capnography

• sidestream technology

• Mainstream technology

what are the phases of capnography

What do different capnograms look like

What does an increase in CO2 show

increase CO2 = hypercapina

• alveolar hypoventilation

• increased cardiac output

• Hyperthermia

• Bicarbonate administration

What does a decrease in CO2 show

Decrease in CO2=hypocapnia

• Decreased cardiac output (shock, cardiac arrest)

• Hypothermia

• Hyperventilation/panting

• Pulmonary thromboembolism

How do you assess ventilation with spirometry

• Connected to the ET tube

• Continuous

• Non-invasive

• Tidal volume

• Airway pressures

• Compliance

How do you monitor anaesthetic gas concentration

• Continuous

• Non invasive

• Measures Et and FI concentration of gases

• Helps in assessing depth of anaesthesia

  • Need to know the MAC of the agent in a certain species

• Useful during “low flow anaesthesia “

How do you want to monitor the respiratory system with oxygenation

• Observe- mucous membranes

• Pulse oximetry

  • Non-invasive, continuous, measured at the level of arterioles

• Arterial blood gas analysis

  • Invasive, Intermittent results, possible complications

What is pulse oximetry

• Measures oxyhaemoglobin (HbO) as a % of the total haemoglobin in the arterial blood

• SpO2%

• Pulse rate

• Adequacy of tissue perfusion

How does pulse oximetry work

• Majority of oxygen in the blood is carried by Hb

• SpO2 %

• Measurement of saturation enables estimation of oxygen content and oxygen delivery to tissues

what is the equation for rate of oxygen delivery (ml per minute)

What is normal pulse oximetry

when is pulse oximetry not a good measurement

• animals under anaesthesia breathing 100% O2

• Room air has only 21% O2

• Good to check in recovery when animal is back on breathing room air

What do you do if SpO2 is less than 95%

• Check probe position

• Check oxygen supply and FiO2

• check perfusion

  • BP

  • Use of alpha2-agonist

• Hypoxaemia

  • right to left shunting

    • anatomical: tetralogy of fallot

    • Intrapulmonary: Perfusion of unventilated alveoli

  • Ventilation/perfusion mismatch

  • impaired diffusion

  • hypoventilation

How do you use a thermistor

• Probe placed in oesophagus or rectum

• Non invasive

• continuous

Are larger or smaller animals more at risk of hypothermia

smaller due to increased surface area to body mass ratio

what are the stages of hypothermia

Label this machine