Now that we have introduced the concept of the pain ladder, this section will concentrate on the different classifications of analgesia that you might use in the perioperative period.

Step 1: Non-opioid

Paracetamol

As you have just seen, paracetamol is one of the most commonly prescribed and administered analgesics in the hospital setting.

Paracetamol tablets. (Photo credit: Alexandra Constantin)

How does it work?

Despite being one of the most widely used and safest analgesic agents, how it works is not completely understood.

It is thought to be similar to the NSAIDs and inhibit COX enzymes at the site of inflammation. It probably also has actions at a number of other pathways/receptors such as serotonin, cannabinoid, nitric oxide, and TNF-α.

When can’t you give it?

There are very few contraindications to paracetamol. Although it causes liver failure in overdose, normal doses are safe to use in both renal and liver disease.

How can you give it?

Paracetamol can be administered intravenously, orally or rectally. As mentioned previously, you will need to adjust the dose if the patient weighs less than 50kg to 15mg/kg which can be given every 4-6 hours.

What are the side effects?

Rarely gastrointestinal disturbances, skin reactions and a reduction in platelets can occur.

Non-Steroidal Anti-Inflammatory Drugs (NSAIDS)

Non-Steroidal Anti-Inflammatory Drugs, often abbreviated to NSAIDs, include ibuprofen, diclofenac and naproxen.

A box of Ibuprofen. (Photo credit: Alexandra Constantin)

How do they work?

Prostaglandins (lipid messengers) are released at sites of injury and inflammation. They are very important in pain transmission. They are made by an enzyme called cyclooxygenase or COX. NSAIDs prevent prostaglandin synthesis in the tissues, nerves, and the CNS by inhibiting COX.

How can you give it?

• NSAIDS can be administered intravenously, orally, rectally or topically.
• Caution is needed if the patient is at risk of impaired renal function or has evidence of renal injury, renal impairment or transplant.
• International consensus recommends that if the eGFR <30, NSAIDS are to be avoided.
• Caution to be taken if the patient has a history of peptic/duodenal ulcers or is taking blood thinning medication.
• Many units caution against NSAIDS immediately after surgery as patients may still be hypovolaemic, which may exacerbate their potential for renal injury.

What are the side effects?

Prostaglandins have beneficial effects and are present in a number of tissues. Many adverse effects of NSAIDs occur when COX1 cannot produce protective prostaglandins – have a look at the table below.

When taken for a long time, NSAIDs also cause a rise in blood pressure and increase the risk of myocardial infarction. 10-15% of asthmatics are NSAID sensitive and may develop wheeze if they take NSAIDs. Allergic reactions and rashes to NSAIDs are common.

Step 2 & 3: Opioids

Opioids are drugs that act at opioid receptors. Morphine is the most well known drug in this family but there are many more.

Forms of Opioids. (Photo credit: Alexandra Constantin)

How do they work?

Opioid receptors are found throughout the CNS, at all levels of pain transmission. Activation of opioid receptors inhibits pain transmission and perception both centrally and peripherally.

How can you give it?

Opioid drugs can be given by oral, intravenous, intramuscular, subcutaneous, transdermal, intrathecal (in a spinal), epidural and inhalation routes.

How are they classified?

Opioids can be classified according to their potency (strength) or duration of action:

Other things to we should think about prescribing for strong opioids:

• Oxygen
• Laxatives
• Antiemetics
• Naloxone

Hear Dr Rob Stephens briefly describe some cautions around using opioids.