Anaesthesia: Essentials of Monitoring and Intraoperative Complications

Question 1

What is the aim of monitoring?

Answer 1

To have the triad of:
Unconsciousness
Analgesia
Muscle relaxation

Also to maintain physiology, anaesthetic depth, prevent suffering and there are legal implications

Question 2

Why is monitoring essential?

Answer 2

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

Question 3

How can a patient be monitored using minimal technology?

Answer 3

Using our senses

• Touch- pulse, thoracic excursions
• Smell- smell of isoflurane
• Hear changes in breathing pattern
• Monitoring versus measuring

Question 4

How can the CNS me monitored with minimal technology?

Answer 4

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

Question 5

How can the CV system be monitored with minimal technology?

Answer 5

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

Question 6

How can the respiratory system be monitored with minimal technology?

Answer 6

Listen, observe, touch and smell

Rate- horse 4-10, Dog 10-20, Cat 15-30

Rhythm

Ausultation

Reservoir bag movement

MM colour

Question 7

Name some every day equipment that can be used for monitoring

Answer 7

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

Question 9

What is normal arterial systollic pressure, diastollic pressure and mean pressure?

Answer 9

Systollic- 80-140mmHg

Diastollic- 50-90mmHg

Mean- 60-90mmHg

Question 10

What is the gold standard for arterial blood pressure?

Answer 10

Invasive blood pressure

Gold standard, continuous readings

Takes time to place indwelling arterial cannula

Expensive equipment

Question 11

//What is pulse oximetry and what are its limitations

Answer 11

SpO2

Measures % saturation of haemoglobin

Normal is above 95%

Limitations: Hypoperfusion/vasoconstriction, bright lights, movement, anaemia

Question 12

What species can the dopples be useful for?

Answer 12

Exotics

Question 13

What is capnography, what are its uses and limitations?

Answer 13

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

Question 14

What is blood gas analysis?

Answer 14

Arterial (or venous) sample of blood

The gold standard for gas analysis

High cost of equipment

Question 15

What are the common factors that cause complications during anaesthesia?

Answer 15

Patient factors- species, breed, weight and age

Anaesthetisa factors

Procedure factors

Systems affected- CNS, CV, Resp, renal and hepatic

Question 16

What are the common complications of anaesthesia?

Answer 16

Three Hs

Hypotension

Hypothermia

Hypoventilation- hypercapnia, hypoxaemia

Others- bradycardia, tachycardia

Question 17

What is the mean arterial pressure and what would it be if the patient was in hypotension?

Answer 17

MAP >60 to maintain vital organ perfusion

Hypotension- MAP <60 or Systolic AP <90

Question 18

What are the causes of hypotension during anaesthesia?

Answer 18

Reduced cardiac output- reduced stroke volum/HR

Reduced systemic vascular resistance

Question 19

How should hypotension be treated during GA?

Answer 19

1. Check cuff- repeat reading
2. Check plane of anaesthesia and reduce
3. Check HR- treat if low
4. Give fluid therapy- crystalloids 10ml/kg over 10-15 mins
5. Drugs- vasopressors, positive inotropes
6. Change position
7. Stop ventilation

Question 20

What are the potential consequences of hypotension?

Answer 20

Organ/tissue damage- acute kidnet injury and myopathy

Severe hypotension- poor perfusion of the heart- arrhythmias, death

Question 21

What patients are more prone to hypothermia and what are the causes during GA?

Answer 21

Small patients are more prone

Causes: increased heat loss, reduced heat production, abolished behavioural responses, alterations in hypothalamic function

Question 22

How can hypothermiabe prevented?

Answer 22

Pre-op warming

Blankets

Bubble wrap

Warm air

Heated mats

Heat and moisture exchanger

most effective if started before anaesthesia

Question 23

What are the consequences of hypothermia?

Answer 23

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

Question 24

What can hypoventilation lead to?

Answer 24

Hypercapnia- increased CO2

Hypoxaemia- Hypoxaemia

Question 25

What are the causes of hypoventilation?

Answer 25

Effects of drugs on CNS and respiratory muscles Positional changes- Dorsal v sternal recumbancy

Question 26

What is hypercapnia? How can it be confirmed? At what level should treatment be supplied?

Answer 26

Increased CO2 in blood Measured either- sampling arterial blood or via capnography Normal 35-40, Hypercapnia is \>45mmHg Treatment if \>60mmHg

Question 27

What are the causes of hypercapnia?

Answer 27

Hypoventilation- main cause Breathing systems- non-rebreathing, not enough FGF, exhausted soda lime

Question 28

How is hypercapnia treated?

Answer 28

Increase minute ventilation- MV Lighten plane of anaesthesia- reduce vaporiser setting, reduce drug administration Mechanical ventilation- squeezing of reservoir bag- IPPV

Question 29

What is hypoxaemia? How is it diagnosed? When is treatment needed?

Answer 29

Reduced O2in the blood Measured by sampling arterial blood or pulse oximiter Treatment if SpO2 \<90mmHg or PaO2 \<60

Question 30

What causes hypoxaemia during anaesthesia?

Answer 30

Not enough O2 delivery Profound hypoventilation Impaired gas exchange- disease, positional compression Airway obstruction Severe hypovolaemia 'shock'

Question 31

How is hypoxaemia treated?

Answer 31

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

Question 32

What are the causes of bradycardia during anaesthesia?

Answer 32

Increased parasympathetic activation- drugs, vagal response Hypothermia Disease- hyperkalaemia, raised inta cranial pressure

Question 33

What are the consequences of bradycardia?

Answer 33

Reduced cardiac output Reduced blood pressure Reduced perfusion- organ/tissue damage

Question 34

How is bradycardia during anaesthesia treated?

Answer 34

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

Question 35

What casues tachycardia during anaesthesia?

Answer 35

Increased sympathetic tone- pain Hypovolaemia Hyperthermia Hypercapnia

Question 36

What are the consequences of tachycardia?

Answer 36

Cardiac dysfunction- heart failure, malignant arryhtmias, death

Question 37

How is tachycardia during GA treated?

Answer 37

Pain= analgesics Hypovolaeamia- restore circulating volume Hyperthermia- cool Hypercapnia- reduce anaesthetic plane, start ventilation If severe can use beta blockers and lidocaine