Anaesthetics - Peri-Operative Care

Question 1

How common is post-op nausea/vomiting (PONV)?

Answer 1

25% surgical pts

-delayed discharge & recovery

Question 2

What is the pathophysiology underlying PONV?

Answer 2

Input to vomiting centre from

• higher cortical centres (memory/fear)
• stomach/SI (direct surgical effects)
• chemoreceptor trigger zone (anaesthetic drugs/opioids)

Question 3

What are the risk factors for PONV?

Answer 3

Pt = F>M, obesity, non-smoker, prev hx of PONV
Procedure = abdo, gynae, ENT
Anaesthetic = long duration, GA, inhalation agents
Post-op = pain, opioid analgesia, dehydration, hypotension

Question 4

What are the common treatments for PONV?

Answer 4

Cyclizine (50mg/8h IV/IM/PO)
Prochlorperazine (12.5mg/6h IM)
Ondansetron (4mg/8h IV/PO)

Question 5

When is Dexamethasone added to manage PONV?

Answer 5

At any stage if nausea not controlled

-often added w/ Cyclizine

Question 6

What is Cyclizine?

Answer 6

Anti-histamine useful in middle ear surgery/motion sickness

Question 7

When is Cyclizine contraindicated?

Answer 7

Heart failure
BPH
Hepatic/renal disease

Question 8

What is Prochlorperazine?

Answer 8

Dopamine antagonist stabilizing the CTZ & having prokinetic effects
-also Metoclopramide/Domperidone

Question 9

When is Metoclopramide ineffective?

Answer 9

PONV

Question 10

When is Prochlorperazine contraindicated?

Answer 10

Parkinson’s

Question 11

What is Ondansetron?

Answer 11

5-HT3 antagonist that blocks vagal afferents from gut/CTZ

• most effective agent
• can be given prophylactically

Question 12

When is use of Ondansetron cautioned?

Answer 12

Hepatic impairment
QT prolongation
Pregnancy/breast feeding

Question 13

What is Dexamethasone?

Answer 13

Glucocorticoid w/ unknown MoA augmenting other medications

-used early on

Question 14

How long should supplementary O2 be given for post-op?

Answer 14

At least 72hrs

Question 15

Why should supplementary O2 be given post-op?

Answer 15

Dose-dependant depression on sensitivity of central chemoreceptors to stimulatory effect on CO2

Question 16

What are the methods of O2 delivery used post-op?

Answer 16

Nasal cannulae
Simple (Hudson) facemask
Venturi masks

Question 17

How much O2 do nasal cannulae deliver?

Answer 17

2-4 L/min + plus room air

Question 18

How much O2 do simple (Hudson) facemasks deliver?

Answer 18

5-10 L/min

Question 19

How much O2 do venture masks deliver?

Answer 19

Blue = 24% inspired O2, 2-4 L/min
White = 28% inspired O2, 4-6 L/min
Yellow = 35% inspired, 8-10 L/min
Red = 40% inspired, 10-12 L/min
Green = 60% inspired, 12-15 L/min

Question 20

What are the limitations of pulse oximetry?

Answer 20

Cannot distinguish b/w CO & O
-inaccurate after smoke inhalation, CO poisoning, smokers
Does not reflect O2 carrying capacity
Hypovolaemia makes getting a reading difficult
Venous pulsations can produce a venous reading
Nail polish affects SpO2

Question 21

How should Warfarin be managed pre- & post-op?

Answer 21

Stop 10 days before surgery
-if INR <1.5 surgery can go ahead
Generally substituted w/ LMWH
-withheld evening before surgery

Question 22

How should Clopidogrel be managed pre-op?

Answer 22

Stop 7 days before surgery

Question 23

How should COCP be managed pre- & post-op?

Answer 23

Stop 4wks before major ops
-switching to POP acceptable
Restart at first menses
->2 wks after mobilisation