7. Intraoperative complications continued

Question 1

What is Hypoxaemia

What species are we most concerned about this in?

Answer 1

• Reduced level of O2 in blood

Most concerned in horses. Less common in SA, hypercapnoae is more worried in SA!

Question 2

How do we measure O2 levels?

Answer 2

– Sampling arterial blood (PaO2) measure how much O2 dissolved in blood
– Via pulse oximeter (SpO2) – how saturated Hb is with O2

Question 3

What should SpO2 be? and when do we treat?

Answer 3

• Sp02 should be greater than 95% but we treat is less than 90
• Treatment if SpO2 < 90 % or (dissolved oxygen) PaO2 < 60 mmHg

Question 4

What are causes of hypozaemia?

Answer 4

1. Not enough oxygen delivered
   • Run out of O2 and didn’t notice?! Should be alarm!!)
   • Not connected to breathing system properly
2. Profound hypoventilation
   • Mainly large breath one breath a minute under anaesthesia
3. Impaired gas exchange
   • Disease (e.g. pneumonia)
   • Positional compression (dorsal recumbency impairs gas exchange)
4. Airway obstruction
   • ET tube full of mucous
   • Brachy dog, soft tissue palette can obstruct
5. Severe hypovolaemia, ‘Shock’
   • Not enough blood around body to provide enough O2 and perfuse lungs
   • V rare

Question 5

How do we treat Hypoxaemia?

Answer 5

Increase oxygen delivery (up to 100%)
2. Start mechanical ventilation ( can make it worse)
3. Increase gas exchange (if think impaired) particularly for large animals
• Bronchodilation
• Not dorsal, head elevated slightly which helps intestines fall away from table (c section dog same issue as large animal),
• recruitment manoeuver  give bigger than normal breath and hold for few seconds. This tries to open any alveoli who are closed due to being squashed
• PEEP – need fancy ventilator!
4. Check ET tube for mucus/blood clots, change or suction airway to remove mucous and clots
• Extubate, mucousy, put clean
5. Restore circulating volume – fluids, vasopressors
• Severe hypovolaemic shock  lot of fluids and drugs to cause vasoconstriction, can improve circulating volume and improve delivery of O2 to tissues and within blood

Question 6

What arrhythmias can arise under GA?

Answer 6

Tachycardia and bradycardia

Question 7

Bradycardia caused

Answer 7

– Increased parasympathetic system activation
• Drugs (opioids, alpha 2 agonists, propofol induction agent)
• Vagal response – vagus nerve is stimulated by something doing in surgery, para sympathetic nervous system stimulated and HR DROPS. Solve by stop pulling on organ and give drugs.
– Hypothermia
• Severe enough = arrhythmias called bradyarrthymias.
– Disease e.g.
• So may be unrelated to anaesthesia but actually a disease the animal already has
• Hyperkalaemia
• Raised intra cranial pressure (ICP)

Question 8

Consequences of bradycardia?

Answer 8

Reduced HR
•	Reduced cardiac output = 
•	Reduced blood pressure = 
•	Reduced perfusion vital organs = 
•	Organ/tissue damage as a consequence

Question 9

How does bradycardia affect neonates differently to adults?

Answer 9

More severe issue in neonates
Cardiac output is determined by HR and SV so…
• If Heart rate drops, heart compensated by inc SV to maintain CO (stretch more, fill with blood)
• Neonates are NOT very good at doing above. CO entirely relies on HR. Heart not able to pump more out if needs to, not v stretchy. So maintain CO by keeping HR relatively high
• Adults more able to cope with bradycardia

Question 10

How do we treat bradycardia?

Answer 10

• If due to disease, treat this
• Not due to disease, depends on blood pressure
• If (mean arterial pressure) MAP > 60 mmHg no need to treat
– Animal coping
– CO best as adequate
– Pefusion to vital organs is fine
• If MAP < 60 mmHg
– Antagonise drugs
– Give parasympatholytics (inc HR e.g. atropine)
– Warm up
• Due to disease
– Treat underlying diseases e.g. hyperkalaemia, ICP

Question 11

Arrhythmias - tachycardia causes

Answer 11

–	Increased sympathetic tone (fight or flight response)
•	Pain
–	Hypovolaemia 
–	Hyperthermia
•	Relatively uncommon but not impossible
–	Hypercapnia
•	CO2 above 60

Question 12

Consequences of tachycardia

Answer 12

Tachy = inc HR
cardiac muscle perfused in diastole
however inc HR reduces time for diastole and increases myocardial oxygen demand
Heart muscle needs more oxygen but isn’t receiving it = cardiac dysfunction

Cardiac dysfunction
– Heart failure (if HR vvvv fast)
– Malignant arrhythmias which can lead to death if untreated for a length of time
– Death

Question 13

Treatment of tachycardia =

Answer 13

• Treat underlying cause
– Painful? = analgesics
– Hypovolaemia? = restore circulating volume with fluids
– Hyperthermia? = cool
– Hypercapnia = reduce anaesthetic plane, start ventilation
• If severe can give drug therapy also,
– Beta blockers, lidocaine etc