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

Question 24

What are the stages of wound healing?

Answer 24

haemostasis
inflammation
regeneration
remodelling

Question 25

What is the cause of a hypertrophic scar?

Answer 25

Excessive amounts of collagen within a scar

Question 26

What is the cause of a keloid scar?

Answer 26

Excessive amounts of collagen within a scar. Typically a keloid scar will pass beyond the boundaries of the original injury. They do not contain nodules and may occur following even trivial injury. shiny dark scar bigger than the wound injury

Question 27

What are the early causes of post-op pyrexia (0-5 days)?

Answer 27

``` Blood transfusion Cellulitis Urinary tract infection physiological systemic inflammatory reaction Pulmonary atelectasis ``` Day 1-2: 'Wind' - Pneumonia, aspiration, pulmonary embolism Day 3-5: 'Water' - Urinary tract infection (especially if the patient was catheterised) Day 5-7: 'Wound' - Infection at the surgical site or abscess formation

Question 28

What are the late causes of post-operative pyrexia? >5 days

Answer 28

VTE pneumonia wound infection anastomotic leak Day 5+: 'Walking' - Deep vein thrombosis or pulmonary embolism Any time: Drugs, transfusion reactions, sepsis, line contamination

Question 29

What is the management of post-operative ileus?

Answer 29

NBM + NG tube insertion

Question 30

What drug should patients taking prednisolone be prescribed before surgery?

Answer 30

Hydrocortisone

Question 31

When is thromboprophylaxis given post-surgery?

Answer 31

6 hours post surgery