Anaesthesia: Essentials of Monitoring and Intraoperative Complications Flashcards
What is the aim of monitoring?
To have the triad of:
Unconsciousness
Analgesia
Muscle relaxation
Also to maintain physiology, anaesthetic depth, prevent suffering and there are legal implications
Why is monitoring essential?
There is a risk of anaesthetic related mortality
Too light and the animal might climb off the table
Too deep leads to deteriorating function and possibly death
How can a patient be monitored using minimal technology?
Using our senses
- Touch- pulse, thoracic excursions
- Smell- smell of isoflurane
- Hear changes in breathing pattern
- Monitoring versus measuring
How can the CNS me monitored with minimal technology?
Reflexes- palpebral, corneal
Anal tone
Eye position and movement
Lacrimation
Changes in autonomic tone: sweating/CV changes
Muscle tone- tension un muscles
Movement- light- could be about to die
Response to surgical stimulation
How can the CV system be monitored with minimal technology?
Auscultate, palpate and observe
Pulse/HR- dogs 50-100, horse 20-40, cat 80-160
Pulse quality- subjective
MM: colour indication of oxygenation and perfusion
CRT- indicator of blood volume and capillary tone
Haemorrhage
How can the respiratory system be monitored with minimal technology?
Listen, observe, touch and smell
Rate- horse 4-10, Dog 10-20, Cat 15-30
Rhythm
Ausultation
Reservoir bag movement
MM colour
Name some every day equipment that can be used for monitoring
Stethoscope- oesophageal stephoscope for auscultation of the heart and lung sounds even with drapes
Thermometer- rectal- avoid hypo/hyperthermia
ECG- no information about cardiac input
Arterial blood pressure
What is normal arterial systollic pressure, diastollic pressure and mean pressure?
Systollic- 80-140mmHg
Diastollic- 50-90mmHg
Mean- 60-90mmHg
What is the gold standard for arterial blood pressure?
Invasive blood pressure
Gold standard, continuous readings
Takes time to place indwelling arterial cannula
Expensive equipment
//What is pulse oximetry and what are its limitations
SpO2
Measures % saturation of haemoglobin
Normal is above 95%
Limitations: Hypoperfusion/vasoconstriction, bright lights, movement, anaemia
What species can the dopples be useful for?
Exotics
What is capnography, what are its uses and limitations?
Measures end tidal CO2
Normal is 35-45mmHg, inspired CO2 should be 0
Other uses- correct ETT placement, confirms cardiac output, indicates problems with breathing systems
Limitations- can become kinked/clogged, delay in reading
What is blood gas analysis?
Arterial (or venous) sample of blood
The gold standard for gas analysis
High cost of equipment
What are the common factors that cause complications during anaesthesia?
Patient factors- species, breed, weight and age
Anaesthetisa factors
Procedure factors
Systems affected- CNS, CV, Resp, renal and hepatic
What are the common complications of anaesthesia?
Three Hs
Hypotension
Hypothermia
Hypoventilation- hypercapnia, hypoxaemia
Others- bradycardia, tachycardia
What is the mean arterial pressure and what would it be if the patient was in hypotension?
MAP >60 to maintain vital organ perfusion
Hypotension- MAP <60 or Systolic AP <90
What are the causes of hypotension during anaesthesia?
Reduced cardiac output- reduced stroke volum/HR
Reduced systemic vascular resistance
How should hypotension be treated during GA?
- Check cuff- repeat reading
- Check plane of anaesthesia and reduce
- Check HR- treat if low
- Give fluid therapy- crystalloids 10ml/kg over 10-15 mins
- Drugs- vasopressors, positive inotropes
- Change position
- Stop ventilation
What are the potential consequences of hypotension?
Organ/tissue damage- acute kidnet injury and myopathy
Severe hypotension- poor perfusion of the heart- arrhythmias, death
What patients are more prone to hypothermia and what are the causes during GA?
Small patients are more prone
Causes: increased heat loss, reduced heat production, abolished behavioural responses, alterations in hypothalamic function
How can hypothermiabe prevented?
Pre-op warming
Blankets
Bubble wrap
Warm air
Heated mats
Heat and moisture exchanger
most effective if started before anaesthesia
What are the consequences of hypothermia?
Cardiovascular and haematological:
Arrythmias can be fatal, coagulopathies, reduced immine function- post op infection
Metabolic:
Reduced drug metabolism- prolonged effects and delayed recoveries
Shivering increases O2 demand
What can hypoventilation lead to?
Hypercapnia- increased CO2
Hypoxaemia- Hypoxaemia
What are the causes of hypoventilation?
Effects of drugs on CNS and respiratory muscles
Positional changes- Dorsal v sternal recumbancy
What is hypercapnia?
How can it be confirmed?
At what level should treatment be supplied?
Increased CO2 in blood
Measured either- sampling arterial blood or via capnography
Normal 35-40, Hypercapnia is >45mmHg
Treatment if >60mmHg
What are the causes of hypercapnia?
Hypoventilation- main cause
Breathing systems- non-rebreathing, not enough FGF, exhausted soda lime
How is hypercapnia treated?
Increase minute ventilation- MV
Lighten plane of anaesthesia- reduce vaporiser setting, reduce drug administration
Mechanical ventilation- squeezing of reservoir bag- IPPV
What is hypoxaemia?
How is it diagnosed?
When is treatment needed?
Reduced O2in the blood
Measured by sampling arterial blood or pulse oximiter
Treatment if SpO2 <90mmHg or PaO2 <60
What causes hypoxaemia during anaesthesia?
Not enough O2 delivery
Profound hypoventilation
Impaired gas exchange- disease, positional compression
Airway obstruction
Severe hypovolaemia ‘shock’
How is hypoxaemia treated?
Increase O2 delivery to 100%
Start mechanical ventilaiton
Increase gas exchange- bronchodilation, nor dorsal, head up
Check ET tube for mucus/blood clots
Restore circulating volume- fluids, vasopressors
What are the causes of bradycardia during anaesthesia?
Increased parasympathetic activation- drugs, vagal response
Hypothermia
Disease- hyperkalaemia, raised inta cranial pressure
What are the consequences of bradycardia?
Reduced cardiac output
Reduced blood pressure
Reduced perfusion- organ/tissue damage
How is bradycardia during anaesthesia treated?
Not due to disease, depends on blood pressure
If MAP >60 no need
If below 60- atagonise drugs, give parastympatholytics
If due to disease- treat underlying disease
What casues tachycardia during anaesthesia?
Increased sympathetic tone- pain
Hypovolaemia
Hyperthermia
Hypercapnia
What are the consequences of tachycardia?
Cardiac dysfunction- heart failure, malignant arryhtmias, death
How is tachycardia during GA treated?
Pain= analgesics
Hypovolaeamia- restore circulating volume
Hyperthermia- cool
Hypercapnia- reduce anaesthetic plane, start ventilation
If severe can use beta blockers and lidocaine
