Problem 10: Post-Operative Pain Management

Question 1

Explain why it is important to manage pain post-operatively?

Answer 1

Surgical tissue damage causes local release of algesic substances, such as bradykinin, arachidonic acid, histamine, 5-hydroxytryptamine (5HT), substance P and prostaglandin. These chemicals stimulate peripheral pain receptors (nociceptors), which transmit impulses via afferent nerve fibres to the spinal cord.

Post-operative pain is usually acute, and should decrease over a few days. However, pain can become chronic and persist as a result of disease progression or inadequate control of early nociceptor or nerve discharge.

Inadequately controlled pain causes morbidity. The cellular response to pain and surgical
tissue damage causes proteins to break down, platelets to aggregate and the immune system to be suppressed. Pain can also cause ileus, nausea and vomiting. Tachycardia and hypertension occur with the release of catecholamines and this can lead to myocardial ischaemia or infarction.

For operations replacing joints as in a total hip replacement, there is a balance between pain control and mobility so that rehabilitation of the joint is not too painful and therefore delayed, but over analgesia does not prolong hospitalisation.

Question 2

Describe the advantages and disadvantages of PCA

Answer 2

+ allows patients to titrate their own opioid analgesic via infusion pump according to their needs, dose limits can be personalised to the patient and lock out times avoid overdose, background infusion can be used with a PCA for breakthrough pain. Empowers patients to have some degree of control. Quick immediate dose that doesn’t have delay in administration. More positive perception of hospital stay.

• monitoring is essential to pick up signs of excessive opioid administration.
• patients rely heavily on regularly pressing the PCA
• not acceptable for patients who are confused or have learning difficulties, with poor manual dexterity, critically ill.

Question 3

Explain the terms “loading dose” “bolus dose” “lockout interval” and “background infusion”

Answer 3

Loading dose is the total opioid dose which is initially required to provide analgesia. It is administered either by pre-setting PCA pump and allowing automatic administration or by nurse administration in a recovery setting.
Bolus dose is the quantitiy of analgesia given to a patient at each self-administration demand. It is assumed that patients demand doses of analgesia until the pain has been relieved but the size of the dose influences how effective the treatment has been.
Lockout interval is the time period between patient demands during which the machine will not administer a further dose despite any further demands made by the patient. The lockout interval is determined by the size of the bolus dose, the pharmacokinetics of the drug. or morphine, peak concentration after intravenous bolus is achieved after about 4 minutes. It would be inappropriate to set a lockout time shorter than this time to peak plasma concentration.
Background infusion; the basis of PCA meaning tat patient experiences pain before demanding relief or in anticipation of pain. If a drug has a short half life then analgesia is rapidly achieved but a high demand frequency is necessary. If the patient falls asleep they would frequently wake up in pain. Backfround infusion therefore allows for constant rate of opioids such as morphine to be infused then the PCA used only for breakthrough pain. Some studies show that respiratory depression can occer when an infusion is used.

Question 4

Explain why naloxone is prescribed for this patient?

Is it appropriate?

Answer 4

Naloxone: indicated for the treatment of opioid toxicity associated with respiratory or neurological depression. Competitive antagonist at opioid receptors (particularly u). Naloxone displaces opioid from its receptors and in doing so, reverses its effects. Written normally in the once only section (normally administered in an emergency so the prescription can be completed at a later date. If opioid toxicity develops in a patient on chronic use then incremental addition of naloxone is sufficient compared to large immediate doses in acute overdose.

Question 5

Describe the signs and symptoms of opioid toxicity?

Answer 5

Opioids cause respiratory depression by reducing respiratory drive. Neurological depression can follow euphoria. Nausea and vomiting as result of CTZ stimulation. Pupillary constriction. Constipation
Itching

Tolerance can develop after extended use and dependence. Withdrawal reaction upon cessation indicates opioid dependency.

Question 6

Explain how dosing errors with opioid medicines can be reduced

Answer 6

Often the safety concern comes from the unsafe doses of opioid medicines where dose or formulation was incorrect based on patients previous doses. Knowledge of previous opioid dose is crucial to patient safety.

Safety precautions that should be taken are:

1. confirm any recent opioid dose, formulation, frequency of administration in anything other than acute emergencies
2. ensure where dose increase is intended that the calculated dose is safe for the patient (e.g. for oral morphine or oxycodone, not normally more than 50% higher than previous doses
3. ensure they are familiar with the following characteristics of that medicine and formulation i.e. usual starting dose, frequency of administration, standard dosing increments, symptoms of overdose and common side effects.

Question 7

Give the rationale for any other medicines that you might recommend for this patient, alongside opioids?

Answer 7

Anti-emetics

Stimulant laxative