Monitoring Anaesthesia Flashcards
What should be observed during anaesthesia? What can be monitored using equipment?
- depth
- mucous membranes
- pulse
- chest movement
- pupil size
- responses to surgery
- blood loss
- urine output?
machines
> respiratory gases
> pulse ox
> blood pressures
> ECG
> thermometer
> blood gases
What can be used to assess depth of anaesthesia?
- eye position
- presence of nystagmus
- lacrimation
- pupil size and response to light
- nuero responses (eg. cranial nerve reflexes)
- muscle relaxation (jaw, neck)
- EEG changes (people)
What does capnography measure? How can arterial CO2 be estimated?
- CO2 in resp gases
- end-tidal and inspired CO2
- End tidal = Alveolar = Arterial CO2
Normal PaCO2?
35-45mmHg
How can kPa be calculated from hhMg?
divide mmHg by 7.5 to give kPA
At waht PaCo2 is IPPV warranted?
> 60mmHg
Causes of hypercapnia?
- alveolar hypoventilation
- ^ CO
- hyperthermia
- bicarbonate administration
Causes of hypocapnia?
- v CO (eg. shock)
- hyperventilation/shallow breaths
- artefact
- hypothermia
What shape is the normal capnogram?
- log increase from baseline, alveolar plateaux phase, sharp drop to baseline (where end tidal values measured)
What can changes in the capnograph indicate?
- rebreathing
- asthma
- cardiogenic oscillations -> ripple effect
- VQ mismatch
- tachypnoea
What is FI/ET anaesthetic agent concentration useful for?
- helps assess depth
- need to know MAC for this to be useful
- useful when using v low flows in circle system
How can oxygenation be assessed?
- cyanosis
- pulse ox
- blood gases
What does pulse ox tell you? What does it not tell you?
Saturation of Hbg (SpO2%)
pulse rate
adequate tissue perfusion? (be aware may squash underlying vessels and give false reading)
- does NOT measure ventilation
How is oxygen delivery calculated?
Oxygen content x CO
Normal SpO2 range? What do low number indicate?
95-100%
<60mmHg = hypoxaemia
What is spirometry similar to?
Peto tube measuring airspeed in planes
Causes of low SpO2 on 100% oxygen?
- oxygen supply, probe position, BP may be affected reading, alpha 2 agonist given??
> R->L shunt - anatomical shunt
- intrapulmonary shunt (VQ mismatch) esp horses
> diffusion impaired (rare)
What effect does 2,3 DPG have on the O2 dissociation curve?
shifts it right
2,3-DPG produced in chronic anaemia
What does ECG not tell you?
- cardiac output
- blood pressure
- mechanical activity of the heart
What methods of measuring blood pressure are there?
- Invasive (direct, IBP)
- Non-invasive (NIBP) > doppler (cats true value between mean and systole) and oscillometry (tends to under read, MAP value most accurate)
Normal BP systole, diastole and mean?
- 100-160mmHg systole
- 60-100mmHg diastole
- 80-120mmHg mean
- mean must stay above 60 or renal perfusion will fall
Where does the transducer of invasive blood pressure probes need to be positioned?
- point of shoulder in dorsal recumbency
- manubrium sternea in lateral
> at level of the heart
Tx for blood pressure dropping < 60-70mmHg?
- reduce depth
- fluid bolus (5-10ml/kg)
- inotropes (dopamine, dobutamine)
- AVOID NSAIDs
Which blood gases are analysed for which parameters?
- arterial = ventilation
- venous = acid/base balance
How can PaO2 be calculated from inspired O2?
PaO2 = 5 x FiO2
How are serious hypoxaemia and critical hypoxaemia defined?
Normal PaO2 >80mmHg
Serious hypox PaO2 <40mmHg
What should the PaO2/FiO2 be greater than?
300
What does PaO2 tell you?
How well the lungs can oxygenate blood
What does the arterial CO2 tension (PaCO2) tell you?
Measure of alveolar ventilation
- normally similar to ETCO2 in healthy animals
- Arterial - alveolar PCO2 may be larger if lungs diseased or during thoracotomy
How are hypo and hyper ventilation defined by PaCO2 parameters?
normal 35-45
hypo >45
hyper <35mmHg
Where is core temperature most accurately measured from?
rectum or oesophagus
Which patients are at greatest risk of developing hypothermia?
small
Which animals are very susceptible to hypoxaemia?
Horses (when breathing 100% oxygen PaO2 should be ~500mmHg, may be ~60mmHg!!)
What level of PaO2 = risk of cardiac arrest?
<40mmHg
