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Acute pain and the anaesthetist

Postoperative pain:

This is best dealt with by preventing it happening in the first place
The patient who wakes up in severe pain following surgery can be a difficult problem and the mainstay of dealing with this sort of occurrence is the IV administration of opioid drugs (e.g. morphine), larger doses of which may be necessary

Trauma pain:

Anaesthetists are most likely to encounter a trauma patient in pain when in the process of resuscitation or in preparation for theatre
It is important that analgesia in these circumstances does not interfere with the resuscitation process or mask important diagnostic signs in the patient
For example, the use of IV morphine to treat a man with a fractured femur, shock and head injury may lower his BP further, depress his level of consciousness, interfere with neurological observations and increase the risk of regurgitation and aspiration of gastric contents
It is still important to treat pain in these circumstances, however, and a nerve block with local anaesthetics is often the technique of choice

Labour pain:

The pain of childbirth is, at its worst, one of the most severe pains that can be experienced, and very few mothers are lucky enough to go through labour without the need for some form of analgesia
Several features distinguish the pain of labour from the other forms of pain:

It gets worse, not better, with time
It is non-pathological
Is associated with a happy outcome
Its relief must not result in compromise to the baby
Its relief should not interfere with the ability of the mother to share in the birth experience

This means that the ideal pain relief in labour must be very potent, very safe and not have any depressant effect upon the CNS
This is where regional block, in the form of epidural or spinal anaesthesia, comes into its own

Simple analgesic drugs:

E.g. aspirin and paracetamol
Are of little use when dealing with severe pain
They are not strong enough and they can usually only be administered orally, a route which is certainly not practical following major surgery
However, it is important not to forget these drugs in the postoperative period; while recovery from painful surgery, most patients need a ‘halfway’ drug to tide them over the period between opioid usage and total freedom from pain

Non-steroidal anti-inflammatory drugs (NSAIDs):

This wide-ranging group of drugs (used for many years to treat arthritis and other musculoskeletal disorders) is now finding a role in the management of postoperative pain
Recent additions to the range (e.g. diclofenac and ketorolac) have more powerful analgesic properties than their ancestors
Can be administered by a variety of routes, including:

IV
IM
Rectal

Have well recognised side-effects, the most notorious being GI irritation and haemorrhage. They also interfere with platelet function and may exacerbate asthma and renal failure

Opioids:

Of the drugs available, morphine is the most commonly prescribed in the UK. It has a duration of action of ~3-4 hours following a single IM dose
Diamorphine (heroin) is a powerful analgesic with some advantages over morphine. However, its association with addiction and abuse have, probably unfairly, somewhat restricted its use
Pethidine, used especially in labour, is slightly shorter-acting and has atropine-like properties:

Bronchodilation
Tachycardia
Reduction in secretions

Pethidine derivatives (e.g. fentanyl and alfentanil) are very potent, short-acting opioids that tend to be used intraoperatively , although they can be used postoperatively via the epidural/spinal route

Opioid drugs may be administered via a variety of routes:

Painful
Lag time of ~20 minutes
Only effective if the muscle is well perfused

No lag time
Can be painlessly via an indwelling cannula
The dose can be accurately titrated
No reliance on adequate tissue perfusion

Infusions:

Designed to maintain a constant blood level of analgesia

Patient-controlled analgesia (PCA):

A syringe is filled with a large quantity of morphine and connected to the patient via an indwelling cannula
The patient is given a button which, when pressed, delivers a fixed small dose of morphine
The machine ‘locks out’ for a short period of time to give the dose a chance to achieve its effect (usually 5 minutes), and then the patient may take another dose if needed
A typical prescription would allow 1mg of morphine to be taken every 5 minutes, thus allowing the patient up to 12mg/hour

Epidural/spinal:

Receptors for opioids are found in high concentrations in the spinal cord, and small doses of these drugs can have profound analgesic effects when administered into the epidural or intrathecal (spinal) regions
A dose of morphine as small as 0.2mg (1/50^th of the IM dose) can produce highly effective pain relief for 24 hours following lower abdominal surgery

Side-effects of opioids:

Sedation
Respiratory depression
Nausea and vomiting
Dysphoria
Itching
Urinary retention
Histamine release
Miosis


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	Acute pain and the anaesthetist Postoperative pain: This is best dealt with by preventing it happening in the first place The patient who wakes up in severe pain following surgery can be a difficult problem and the mainstay of dealing with this sort of occurrence is the IV administration of opioid drugs (e.g. morphine), larger doses of which may be necessary Trauma pain: Anaesthetists are most likely to encounter a trauma patient in pain when in the process of resuscitation or in preparation for theatre It is important that analgesia in these circumstances does not interfere with the resuscitation process or mask important diagnostic signs in the patient For example, the use of IV morphine to treat a man with a fractured femur, shock and head injury may lower his BP further, depress his level of consciousness, interfere with neurological observations and increase the risk of regurgitation and aspiration of gastric contents It is still important to treat pain in these circumstances, however, and a nerve block with local anaesthetics is often the technique of choice Labour pain: The pain of childbirth is, at its worst, one of the most severe pains that can be experienced, and very few mothers are lucky enough to go through labour without the need for some form of analgesia Several features distinguish the pain of labour from the other forms of pain: It gets worse, not better, with time It is non-pathological Is associated with a happy outcome Its relief must not result in compromise to the baby Its relief should not interfere with the ability of the mother to share in the birth experience This means that the ideal pain relief in labour must be very potent, very safe and not have any depressant effect upon the CNS This is where regional block, in the form of epidural or spinal anaesthesia, comes into its own Simple analgesic drugs: E.g. aspirin and paracetamol Are of little use when dealing with severe pain They are not strong enough and they can usually only be administered orally, a route which is certainly not practical following major surgery However, it is important not to forget these drugs in the postoperative period; while recovery from painful surgery, most patients need a ‘halfway’ drug to tide them over the period between opioid usage and total freedom from pain Non-steroidal anti-inflammatory drugs (NSAIDs): This wide-ranging group of drugs (used for many years to treat arthritis and other musculoskeletal disorders) is now finding a role in the management of postoperative pain Recent additions to the range (e.g. diclofenac and ketorolac) have more powerful analgesic properties than their ancestors Can be administered by a variety of routes, including: IV IM Rectal Have well recognised side-effects, the most notorious being GI irritation and haemorrhage. They also interfere with platelet function and may exacerbate asthma and renal failure Opioids: Of the drugs available, morphine is the most commonly prescribed in the UK. It has a duration of action of ~3-4 hours following a single IM dose Diamorphine (heroin) is a powerful analgesic with some advantages over morphine. However, its association with addiction and abuse have, probably unfairly, somewhat restricted its use Pethidine, used especially in labour, is slightly shorter-acting and has atropine-like properties: Bronchodilation Tachycardia Reduction in secretions Pethidine derivatives (e.g. fentanyl and alfentanil) are very potent, short-acting opioids that tend to be used intraoperatively , although they can be used postoperatively via the epidural/spinal route Opioid drugs may be administered via a variety of routes: IM: Painful Lag time of ~20 minutes Only effective if the muscle is well perfused IV: No lag time Can be painlessly via an indwelling cannula The dose can be accurately titrated No reliance on adequate tissue perfusion Infusions: Designed to maintain a constant blood level of analgesia Patient-controlled analgesia (PCA): A syringe is filled with a large quantity of morphine and connected to the patient via an indwelling cannula The patient is given a button which, when pressed, delivers a fixed small dose of morphine The machine ‘locks out’ for a short period of time to give the dose a chance to achieve its effect (usually 5 minutes), and then the patient may take another dose if needed A typical prescription would allow 1mg of morphine to be taken every 5 minutes, thus allowing the patient up to 12mg/hour Epidural/spinal: Receptors for opioids are found in high concentrations in the spinal cord, and small doses of these drugs can have profound analgesic effects when administered into the epidural or intrathecal (spinal) regions A dose of morphine as small as 0.2mg (1/50^th of the IM dose) can produce highly effective pain relief for 24 hours following lower abdominal surgery Side-effects of opioids: Sedation Respiratory depression Nausea and vomiting Dysphoria Itching Urinary retention Histamine release Miosis
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