Monitoring anaesthesia Flashcards
3 components of balances anaesthesia
unconsciousness, analgesia and adequate mm relaxation
Goals of anaesthetic monitoring - 4
- ensure all components of balanced anaesthesia are provided
- maintain homeostasis
- detect any adverse effects of anaesthesia and correct immediately
Other than the patient, what else should the anaesthetist also monitor? 3
(Patient first)
Anaesthetic machine
Breathing system (+/- ventilator)
IV fluids
When do most anaesthetic deaths occur?
within 3 hours of the end of the procedure
What determines the level of monitoring?
Physical condition (animal) Surgical procedure planned (intense then use both invasive and non-invasive measures)
What is the anaesthetic record?
What should it include? 7
legal document
shows trends
reference for future anaesthetics
Should include:
Drugs (time, dose, route)
All intra-operative monitoring (blood tests, blood loss and urine output)
IV fluids (rate, type)
All procedures (intubation, invasive monitors)
Time of important events (induction, position, timing, extubation)
Unusual events/complications
Condition of animal at end of procedure.
What is the blood volume of dogs and cats?
Why is this important?
Dogs = 80ml/kg Cats = 60ml/kg
(useful to calculate and note the values for blood loss equal to 10%, 15% and 20% of blood volume to help in decision making as to whether to give crystalloids, colloids or blood)
What should you do if an anaesthetic machine doesn’t have low oxygen warning alarms fitted?
check cylinder (or pipeline) pressure and oxygen flowmeters constantly. If using NO2 on older machines without anti-hypoxic devices, it is also essential to check the O2:NO2 ratio regularly to ensure you aren’t delivering a hypoxic mixture to the patient.
What other machine checks should be made?
- Vaporiser settings and level of volatile anaesthetic in vaporiser
- Breathing system (+/- mechanical ventilator) for operation adn disconnedtion
- Fluid administration (rate, contents)
What 2 readings need to be measured by equipment during anaesthesia?
Arterial BP
End-tidal CO2
What can you listen for when monitoring anaesthesia? 5
Ventilation sounds Leaks (ETT or breathing system) Low oxygen pressure warning alarms Malfunctioning equipment Communications
What can you look for when monitoring anaesthesia? 3
Eye position
Chest movements
Colour of MMs
What can you feel for when monitoring anaesthesia?
Pulses - quality, rate, rhythm CRT Jaw tone Palpebral reflex Relaxation - limbs and reflexes
What can you smell for when monitoring anaesthesia?
Detecting volatile anaesthetic agent which would indicate leaks or disconnections
What is the anaesthetist’s first priority when anaesthesia is induced?
ABC assessment:
AIRWAY - placement of ETT, secured, cuff inflated
BREATHING - rapid, slow, regular/irregular
PULSE - strong, weak, thready, absent
Then once you are confident in the patient’s condition, make a quick assessment of the patient’s depth
How do you assess patient’s depth under anaesthesia? 4
- Eye position, nystagmus (species and drug dependent) lacrimation, pupil size and response to light
- Palpebral reflex - absent/present, brisk/sluggish, other CN reflexes.
- Muscular relaxation - jaw tone etc.
- EEG changes
What physiological parameters need to be monitored during anaesthesia?
HR
Pulse rate
RR, depth, quality
What can be used in small animals for physiological parameter monitoring?
oseophageal stethoscope - for heart and respiratory sounds.
What clinical observations should be monitored? 8
Depth of anaesthesia MMs Pulse Chest movements Pupil size Response to surgery Blood loss (Urine output)
What equipment observation should be monitored? 6
Respiratory gases Pulse oximeter Blood pressures ECG Thermometer Blood gases
What does an ECG inform you of?
electrical activity of the heart
What does an ECG not inform you of?
mechanical activity of heart
CO
BP
T/F: after a patient has been euthanased under GA, a normal ECG trace may remain for several minutes
True
Why is ECG monitoring recommended under GA?
cardiac arrhythmias occur in over 80% anaesthetised patients, most not clinically significant. most familiar departure from normal is sinus arrhythmia (so common it cannot be considered an abnormality, CO should be unaffected). abnormal ECGs have more significance if they indicate atrial contraction isn’t followed by ventricular contraction (2nd degree AV block) or ventricular activity is not preceded by atrial contraction (3rd degree AV block).
When might AV blocks be seen under GA? 2
- bradycardic patients
- if sedated with an alpha-2-agonist
= so long as arterial BP is satisfactory,it may not be significant
What might VPCs be a warning of? 5
hypoxia hypercapnia acidosis underlying heart disease others - surgery to remove splenic tumours
Why should VPCs be monitored closely?
worsening can progress to ventricular fibrillation (VF)
What is the most common cause of delayed recovery from anaesthesia?
Hypothermia - can also cause other problems (bradycardia, increased susceptibility to infection, risks increasing the anaesthetic depth inadvertantly). Smaller the patient, the greater the risk (increased surface area to mass ratio)
What is malignant hyperthermia (MH)?
very rare, genetic condition
triggered by used of older anaesthetics (halothane, suxamethonium)
What is core temp. most effectively measured by?
thermistor probe in oesophagus (slightly more reliable) or rectum (slightly less reliable)
When does heat loss occur?
after pre-med
preparation (especially alcohol-based scrubs)
surgery (especially opening of body cavity)
List examples of warming devices
bubble wrap blankets (reflective) hot air blankets water blankets warmed IV fluids warmed fluids for flushing
Why be careful applying direct heat?
burning risk
increased vasodilation (further reduces core temperature)
hypotension
How can respiratory gases be monitored? 3
Inspired oxygen concentration
Capnography
Anaesthetic agent concentration.
What information does inspired oxygen concentration inform you of?
Method?
early warning that hypoxic gas mixtures are being delivered
METHOD = fuel cell fitted at the common gas outlet with a machine that measures % of oxygen OR can be measured at the end of the ETT via sidestream analysis (usually capnography) which allows measurement on a breath-by-breath basis (gives values for both inspired and end-tidal oxygen concentration, as a %).
What is the minimum concentration of oxygen that is usually provided during anaesthesia to small animals and large animals?
Smallies - minimum 30% inspired oxygen concentration
Large animals - minimum of 60% oxygen normally used.
This ensures that hypovetilation alone is unlikely to cause hypoxaemia.
Define capnography
measure of CO2 concentrations in respiratory gases - arguably the most useful monitoring equipment during anaesthesia - provides information on Resp, CVs and anaesthetic breathing systems
How can CO2 concentrations in respiratory gases be measured (capnography)?
- ) most commonly involves sidestream technology - gases are continuously suctioned from the breathing system (rate of about 150ml/min) into a sample cell within monitor (this effectively creates a leak in the breathing system).
- ) mainstream techology
* always remember to scavenge on a capnograph*
What are the normal components of a capnogram?
Phase 1 = inspiratory baseline
Phase 2 = Expiratory upstroke (mix of dead space and alveolar gas)
Phase 3 = alveolar plateau (not horizontal line but continues to rise gradually. End-tidal value for CO2 is taken at the peak of phase 3)
Phase 4 = inspiratory downstroke