PATIENT CONTROLLED ANALGESIA (PCA)

SUMMARY: Patient Controlled Analgesia (PCA) provides continuous relief of post-operative pain.  Medical errors in delivering PCA sometimes result in death or permanent brain injury.  Medical error may contribute to other causes of Adverse Outcome.  The effectiveness of pain relief may result in missed diagnosis. 

Concepts

Individual variation

Dose-response

In any given patient, increasing doses of narcotic give very little pain relief until close-to-optimal dosage (Minimum Effective Analgesic Concentration, MEAC) is reached.  Beyond close-to-optimal dosage, small increases give disproportionately large increases in pain relief for a narrow range, then cause rapidly increasing side-effects: 

Patient Controlled Analgesia (PCA) solves these therapeutic dilemmas by placing adjustment of dosage in the hands of the patient - with important safeguards. Guided by need for analgesia, the patient repeatedly triggers the injection of a small dose of narcotic with a minimum lock-out period of 5-12 minutes. 

Litigators should be aware that, popular as this method of post-operative pain control is, the empirical evidence for its superiority over more traditional methods is limited^{2 []}. 

Adverse Effects

Medical Errors

Medical errors in delivering PCA sometimes result in death or permanent brain injury. 

The principal danger of PCA is inadvertent over-dosage that causes respiratory depression and a potential for brain-damage or death³.  Respiratory depression is seen in about 1 in 200 patients.  The nursing monitoring standard for prompt detection is hourly determination of respiratory rate and aroused level of consciousness. 

Medication errors may include drug interactions, wrong narcotic prescribed, concentration, unit dose and lock-out period.  Routine use of a "background" intravenous delivery of narcotic is accompanied by increase in the occurrence of respiratory depression to 1 in 50 patients¹.   

Depending on severity, pre-existing respiratory compromise may contraindicate PCA.  Advanced age and co-morbid medical conditions make some patients unsuitable for this method of post-operative pain relief. 

Programming errors are generally in unit volume of drug and lock-out period.  The commonest cause of litigated Adverse Effects after PCA is programming error after a change in narcotic concentration⁴.

Giving nurses the discretion to vary unit dose and lock-out period or add a "background" infusion requires greater than standard nursing education and training. 

Other Safeguard Failures

Medical error may contribute to other causes of Adverse Outcome. 

Medical error may cause or contribute to other causes of Adverse Effects during PCA.  Device malfunction is more likely to arise from improper maintenance than design error. 

PCA by proxy means that the medication is administered other than by the patient - usually by family member, friend, nurse or physician³.  This intervention removes the built-in safeguard against over-narcosis. 

Contributory caregiver factors in unauthorised PCA by proxy errors include inadequate patient and caregiver education, improper patient selection, inadequate patient monitoring, and inexperience with the selection of drugs, dosing, lock-out periods and infusion devices^{5 []}

Arising from Effective PCA

The effectiveness of pain relief may result in missed diagnosis.

The superiority of PCA in providing continuous pain relief postoperatively is the very reason for one of its dangers, that of masking^{2 []} postoperative complications. Postoperative conditions that have consequently been missed during PCA include compartment syndrome, urinary retention⁶ pulmonary embolism⁷ and  myocardial infarction⁸

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