Analgesia and antiemetics

Question 1

What’s important to assess in a patient presenting with post-op pain?

Answer 1

It is important to assess the site of pain to be sure that it is incisional wound pain

Question 2

What other causes of pain (other from wound pain) may be present in a post-operative patient?

Answer 2

• Musculoskeletal pain
• Bladder distension
• Intra-peritoneal bleeding

Question 3

What to measure if a patient is not in pain at rest?

Answer 3

To assess pain on movement

Question 4

How to assess post-op pain?

Answer 4

Question 5

First-line treatment for severe pain

Answer 5

opioids

Question 6

What’s the greatest concern in terms of opioid side effect after IV administration?

Answer 6

After intravenous (IV) administration is respiratory depression

An opioid antagonist (naloxone) and the facility to provide ventilatory support (bag-valve-mask) should be available where IV bolus doses of opioids are administered

Question 7

What opioid and at what dose is the most commonly used for a severe pain post-op?

Answer 7

Morphine

• adult patient (who has not received a recent dose of an opioid) → typically require an IV bolus dose of 0.1–0.2 mg/kg
• elderly patients require significantly lower doses

Question 8

What’s Morphine’s onset of action?

Answer 8

• Morphine has a slow onset of action → due to its low lipid solubility
• peak effect occurs 10-15 min after IV administration
• It should therefore be titrated by administering small doses (e.g. 2 mg) at set intervals (e.g. 5 min)

Question 9

What should be monitored after administration of Morphine?

Answer 9

Observations of respiratory rate should continue for at least 15 min after the last dose (check hospital protocol)

Question 10

What’s the onset of action of Fentanyl?

Answer 10

Fentanyl is highly lipid-soluble, and has a rapid onset of action

Question 11

What’s the dose of Fentanyl that we should administer to the patient?

Answer 11

A bolus dose of 20-25 µ g (micrograms) IV may be administered to an adult, and repeated to a total of 100 µ g.

*It has a short duration of action, so its offset should be anticipated, and a longer-acting agent such as morphine administered, before its effect wears off

Question 12

What’s meant by a ‘morphine sparing’ effect?

Answer 12

Drugs which if administered contemporaneously with opioids, they improve the quality of analgesia and decrease opioid requirements

Question 13

Examples of drugs with ‘morphine sparing’ effect

Answer 13

• NSAIDs
• COX-2 inhibitors
• paracetamol

*if administered contemporaneously with opioids, they improve the quality of analgesia and decrease opioid requirements

Question 14

What’s the most commonly used NSAID for post-op pain and what’s its administration route and dose?

Answer 14

Diclofenac

• IV dose of 75 mg
• subsequent doses may be administered orally or rectally

Question 15

Side effects of NSAIDs

Answer 15

• bleeding
• renal impairment
• peptic ulceration

*The risk of adverse effects on renal function are increased by hypovolaemia, hypotension, pre-existing renal impairment, ACE inhibitors and nephrotoxic drugs such as aminoglycosides

Question 16

What factors increase the risk of renal impairment while being on NSAIDs?

Answer 16

The risk of adverse effects on renal function are increased by:

• hypovolaemia
• hypotension
• pre-existing renal impairment
• ACE inhibitors
• nephrotoxic drugs (e.g. aminoglycosides)

Question 17

What drugs (and doeses) is a suitable adjunct to opioid analgesia in an adult? (2)

Answer 17

• Parecoxib 40 mg IV →COX -2 inhibitor
• Paracetamol 1 g infused IV over 20 minutes

*A reduced dose of Paracetamol should be used in patients with liver disease

Question 18

What’s the most common way of post-op analgesia provision following a major surgery?

Answer 18

Regional technique e.g. epidural catether

Question 19

How to check the position of an epidural catheter?

Answer 19

The position of the epidural catheter should be checked → to ensure it has not been removed accidentally

In order to do so, the patient must be moved to either lateral or sitting position. This may in turn require the administration of systemic analgesia

The mark on the catheter at the skin, and depth to or length of catheter in the epidural space, should be recorded on the anaesthetic chart or epidural prescription chart.

Via examination of the epidural entry site, it should then be possible to determine whether the catheter is still in place

Question 20

What must be determined when topping up epidural analgesia?

Answer 20

Initially, it needs to be determined whether there is:

• An effective epidural block, but the block height is inadequate
• There is inadequate block density
• No demonstrable block

This can be done by checking sensation to cold, with ice or cold spray. Sterilizing solution containing alcohol, which is volatile and takes its latent heat of vaporization from the skin, can be used

Question 21

What to check and how before administrating a top-up of epidural analgesia?

Answer 21

• to check if a patient is normovolemic⇒ administration of a top-up local anaesthetic can cause hypotension
• BP should not be relied upon, as this may be increased by catecholamines produced in response to pain
• Capillary refill time (CRT), core-peripheral temperature gradient and urine output assist us in assessing whether a patient is normovolaemic

Question 22

What are suitable drugs to administer via topping-up epidural anaesthesia?

Answer 22

• Bupivacaine 0.25 % or levobupivacaine 2.5 mg/ml
• Ropivacaine 5 mg/ml
• Fentanyl 100 μg may be added

A suitable dose of the above local anaesthetics is 5 ml, repeated once if necessary

Question 23

What’s the location (on the catheter) where a top-up of epidural anaelgesia should be administered?

Answer 23

Administration set should be disconnected between the pump and the bacterial filter, not between the filter and the patient

Question 25

How often to monitor BP after administration of epidural analgesia?

Answer 25

• monitor the patient’s BP at 5 min intervals for at least 20 min
• treat hypotension with vasopressor

Question 26

What to do if epidural analgesia failed to achieve its effects within 30 min?

Answer 26

If adequate analgesia is not achieved within 30 min, the epidural has failed:

• systemic analgesia should be administered
• the epidural catheter may be removed provided that low molecular weight heparin (LMWH) has not been administered within the preceding 10 h

Question 27

What causes post-op nausea and vomiting (PONV)?

Answer 27

PONV is caused by a number of factors including:

• hypotension
• dehydration
• hypoxia
• pain

Question 28

What anaesthetic agents can cause PONV?

Answer 28

Anaesthetic agents such as:

• opioids
• volatile agents
• N2O
• *treatment with antiemetics.

Question 29

General modes of treatment of PONV (4)

Answer 29

• fluids and/or vasopressors
• oxygen therapy
• anti-emetics

Question 30

What classes of drugs (4) are used to treat PONV?

Answer 30

• 5HT3 antagonists
• H1 antagonists
• Dopamine (D2) antagonists
• Dexamethasone

Question 31

What class of antiemetics is the most commonly used an why?

Answer 31

5HT3 antagonists

• have minimal side-effects
• can be given IV
• have rapid onset of action.

Ondansetron is the most commonly used, in a dose of 4 mg IV.

Question 32

What’s the dose and name of the most commonly used anti-emetic?

Answer 32

Ondansetron 4 mg IV

Question 33

H1 antagonists in the treatment of PONV

• side effects
• monitoring
• drug and dose used

Answer 33

H1 antagonists

• Cyclizine 50 mg IV
• significant anticholinergic side-effects and can cause tachyarrhythmias
• it should be given by slow IV injection
• ECG monitoring

Question 34

Use of Dopamine Antagonists in treatment of PONV

• dose and administration route
• main disadvantage

Answer 34

Dopamine (D2) antagonists

Prochlorperazine 12.5 mg IM

• relatively slow onset of action

Question 35

Is Metoclopramide useful in management of PONV?

Answer 35

Metoclopramide (a weak D2 antagonist)

• shown to have little benefit in treating PONV

Question 36

Use of Dexamethasone in PONV treatment

• dose
• advantage (1)
• disadvantage (1

Answer 36

Dexamethasone 4-8 mg

• long half-life
• it has a slow onset of action → most appropriately used for prophylaxis, rather than rescue

Question 37

Are Neurokinin (NK1) antagonists useful in the treatment of PONV?

Answer 37

Neurokinin (NK1) antagonists:

• currently only available for oral administration → not suited to the treatment of PONV

Question 38

What to do if a prophylactic dose of anti-emetic been given?

Answer 38

When treating PONV:

• check whether prophylactic antiemetics have been administered
• If so →use a drug from a different group, with a different mode of action, starting with a rapidly-acting drug that can be given IV