Monitoring patients during anaesthesia Flashcards by Hannah Chestnutt

What parameters are assessed to monitor the depth of anaesthesia?

the clinical ones, not equipment

Cranial nerves reflexes (palpebral)
Muscles tone
Cardiovascular parameters
Response to surgery

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What happens to cranial reflexes as anaesthesia becomes deeper?

Cranial reflexes become slow and disappear

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Is the corneal reflex a good indicator of anaesthesia depth?

No, it can still be present after cardiac arrest

And corneal trauma can occur if repeatedly stimulated

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How do the eyes position change as anaesthesia deepens in dogs and cats?

They tend to move ventromedially and become central at a deeper plane

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During which type of anaesthesia is the palpebral reflex maintained?

Ketamine anaesthesia

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What reflex may be useful in assessing depth of anaesthesia in dogs, cats, and small rodents?

Pedal withdrawal reflex

and palpebral

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What cardiovascular parameters are monitored clinically during anaesthesia?

Palpation of the apex beat
Auscultation
Pulse palpation
Mucous membrane colour
CRT

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What can influence cardiovascular and respiratory parameters during anaesthesia?

Drugs, pain, and surgical manipulations

And also inadequate depth but important to know not always this

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What is observed in clinical monitoring of the respiratory system and what can effect it

monitor resorvoir bag and chest for rate depth and pattern.
factors that effect this are drugs, body temp, depth of anasthesia, surgical stimulation and respiratory pathology

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What is the normal range for end-tidal carbon dioxide (ETCO2)?

35mmHg (4.6KPa) < pCO2 < 45mmHg (6KPa)

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What are the phases of a capnogram?

draw

Inspiratory baseline
Expiratory upstroke
Expiratory plateau
Inspiratory downstroke

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What is capnography used to inform/detect during anaesthesia?

Assessment of pulmonary ventilation.
Dectection of oesophageal/confirmation of ET intubation.
Indication of disconnection of the breathing system or ventilator.
Diagnosis of circulatory problems or malignant hyperthermia.

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What is the difference between an mainstream and sidestream capnograpgh

Mainstream sampling chamber is directly interposed between the ET tube and the breathing circuit.
Side stream the samplimg chamber lies withing the rest of the monitoring equipment and a pump aspirates sample from a connector between the ET tube and circuit

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Can you compare and contrast some differences/advantages etc of sidestream and mainstream capnography

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What factors determine end-tidal carbon dioxide (ETCO2)?

Metabolism
Cardiac output
Ventilation

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What causes rebreathing in a capnogram?

Exhausted soda lime or expiratory valve incompetency. Insufficent fresh gas flow when a non- rebreathing circuit is used. Tachypnoea and increased/too much deadspace may also cause

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What could cause the capnograph to flatline

Capnograph disconnected
Respiratory arrest/ No CO,
Airway not patent, check ET tube, suction change, confirm placement.
calibration

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What could cause the abcense of a plateau

leak around the ET tube
octruction, bhroncospasm, secretions kinking
Dilution of sample with high fresh gas flow in non rebreathing.

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What is shown on this trace/why

inspiratory cleft. caused when an spontaneous breath is superimposed on controled ventilation.

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What are some possible causes for lower than expected ETCO2

Hypothermia
Hypotension
bradycardia
Poor cardiac output (often related to one of above.
pulmonary embolism
hyperventilation
ET tube cuff deflated
Fresh gas flow too high

What are the possible causes when ETCO2 is higher than expected

Increased metabolism eg sepsis, SIRS hyperthermia.
Increased CO if tachycardic or hypertension.
HYPOVENTILATION
Insufficent fresh gas flow or exhausted soda lime

What is the formula for calculating arterial oxygen content (CaO2)?

CaO2 = (1.36 x [Hb] x SPO2 or SaO2) + (0.003 x PaO2)

Explain how a pulse oximeter works to produce a reading of SPO2

Light source on one side emits both red and infrared light and photodector on the otherside
Oxygenated hemoglobin absorbs more infrared light while deoxygenated hemoglobin absorbs more red light. The device detects the amount of light absorbed during each pulse and uses the ratio to calculate SpO₂.
dectects pulsatile absorption so it can discount that absorbed by tissue and venous blood

What can affect pulse oximeter readings?

Loosely or tightly applied sensor
Probe applied over thin tissue
Peripheral vasoconstriction
Venous congestion
Severe anaemia
surgical diathermy
Shivering
hypotension, hypovolaemia, anything causing vasoconstriction.
ambient light

What can affect the pulse oximeter reading?

Factors include: * Loosely applied sensor * Tightly applied sensor * Probe applied over a thin layer of tissue * Peripheral vasoconstriction * Venous congestion * Severe anaemia * Bright lights in theatre * Surgical diathermy * Shivering * Abnormal forms of haemoglobin

What is the effect of carboxyhaemoglobin on pulse oximeter readings?

It causes the oximeter to overestimate the saturation.

What happens to pulse oximeter readings in the presence of methaemoglobin?

Readings will tend towards 85%, regardless of the true saturation.

True or False: The pulse oximeter reading is affected by jaundice if haemoglobin is above 5g/100ml.

False.

What are some advantages of using a pulse oximeter?

Advantages include: * Assessment of tissue oxygen delivery * Assessment of peripheral pulse rate * Continuous monitoring * Simple and non-invasive * Early detection of hypoxia

What are the disadvantages of pulse oximetry?

Disadvantages include: * Accuracy can be affected by various conditions * No information about ventilation adequacy * May give a false sense of security * Can distract from good clinical monitoring

What is the formula for calculating cardiac output (CO)?

CO = heart rate (HR) x stroke volume (SV)

How is blood pressure calculated?

Blood pressure = CO x Systemic Vascular Resistance (SVR)

What is pulse pressure?

Pulse pressure is the difference between systolic and diastolic pressure.

What can a weak pulse indicate in a hypovolaemic dog?

It may indicate a small stroke volume, but normal pressure due to vasoconstriction.

What does systolic blood pressure mainly reflect?

It mainly reflects stroke volume.

What does diastolic blood pressure reflect?

It reflects systemic vascular resistance.

How can mean arterial blood pressure be derived?

Mean arterial blood pressure = diastolic + (systolic - diastolic)/3

What are the indirect techniques for measuring blood pressure?

Indirect techniques include: * Oscillometric method * Doppler method

What is the recommended width of the cuff for blood pressure measurement?

The width of the cuff should be about 40% of the circumference of the extremity.

What does the oscillometric method measure? how and which reading is most accurate

It measures the oscillations caused by arterial pulse pressure. cuff inflated to above systolic then slowly deflated whitle a pressure transducer senses changes in oscillations. Its most accurately measures the MAP.

What are the disadvantages of the oscillometric method?

It may not work well with low heart rates, arrhythmias, and small patients. it is affected by movement Accurate reading requires the cuff at the level of the heart. It tends to overestimate systolic pressure at low [ressures and understimate at high.

How does the doppler method work to measure blood pressure

- Using a doppler flow detector. - It emits an ultrasound signal which is reflected and sensed by the probe. - The difference between the emitted and returning frequencies is transformed into an auditory signal. - The blood pressure is read manually by an operator using an aneroid manometer connected to the occulding cuff placed proximal to the probe.

What are some disadvantages of/considerations for doppler BP measurement

- Only determines systolic (mean in an anaethetised cat) - again cuff size important and can alter readings. for an accurate reading cuff should be at the level of the heart.

What are some advantages of direct arterial BP measurement? | What is some additional information that you might get from the waveform

- real time reading of HR, systolic mean and diastolic BP, accurate. - Trace can also tell you stroke volume, SVR and contactility.

What are some potential disadvantages of direct arterial BP measurement

- More expensive equipment and personnel training - risk of bleeding and haematoma formation - risk of cannula infection - Inadvertant drug administration must be avoided

What are possible sites for arterial cannulation in cats and dogs?

Possible sites include: * Metatarsal artery * Palmar artery * Femoral artery

What is the most common reason for a blood pressure monitor not displaying 'zero'?

Incorrect positioning of the 3-way tap.

What is required for a correct reading using a direct technique?

The transducer should be placed at the level of the right atrium.

How is direct arterial BP measured

- Arterial cannula placed andconnected to fluid filled tubing. - Pulse creates a wave that is transported through the tube of heparinised saline to the transducer. - The transducer senses a wave causing a change in resistance in an electrical circuit. - this causes an electrical signal to develop which is transferred to the monitor and displayed as a waveform with calculated pressure values