58: Patient controlled analgesia use in the ICU

In this episode I’ll discuss using patient controlled analgesia in ICU patients.
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What is PCA?

Patient controlled analgesia (PCA) is when a patient self-administers opioid medication through the use of a programmable IV pump. PCA allows self-dosing up to a predetermined limit set by the clinician.

PCA generally involves a demand dose such as 1 mg morphine every 6 minutes.  Select patients may also receive a continuous or basal rate such as 1 mg/hr of morphine. A lockout period is programmed in the IV pump to prevent excess opioids from being administered.

When used correctly, PCA can allow patients to safely receive opioids while giving the patient a sense of control over their pain.

Patient selection

Proper patient selection is critical to the safe use of PCA.  For patients in the ICU with postoperative or rapidly resolving pain, PCA can be an excellent choice.

Patients must be capable of using PCA correctly. The ISMP in their monograph for PCA use says:

Patients must be cognitively, physically, and psychologically capable of understanding the concepts of PCA and handling the procedure necessary to obtain pain relief. This frequently may rule out the use of PCA in many pediatric and confused elderly patients. Less than ideal candidates also include those at risk for respiratory depression due to co-morbid conditions such as obesity, asthma, or sleep apnea, or use of concurrent drugs that potentiate opiates.

Because the level of nursing care and monitoring is much higher in ICU patients, patient selection for PCA use is different for ICU vs general medical unit patients.

When I think about which patients in the ICU might be good candidates for PCA, I go back to the 3 reasons for ICU admission that I talked about in episode 11:

1. A vital system has failed and we need to support it (for example: respiratory failure or on vasopressors).
2. Something has happened that makes it likely a vital system will fail, and we need to recognize and support it when that happens (for example: tPA for stroke within the last 24 hours, overdose of unknown substances, or high risk surgical procedure).
3. Nonsense.

“Type 2” ICU patients are the ones that are usually most appropriate for PCA use. In my practice this often means thoracic surgery patients who have had a thoracotomy, decortication, lung resection, etc..

Choice of opioid

At my institution IV PCA is available as morphine, hydromorphone, or fentanyl. Morphine is the “gold standard” opioid, but patient factors may indicate another opioid should be considered. In general, hydromorphone and fentanyl cause less itching than morphine. Fentanyl is shorter acting than hydromorphone or morphine.

Patient education

Patients and their families must be taught the relationship between pain, pushing the button, and adequate pain relief. They should understand the benefits of PCA and how it works. They should understand how critical it is for only the patient to push to PCA button. If PCA is planned in the post-operative period, this education should ideally begin in the pre-admission process.

Dangers & pitfalls of PCA use

PCA is an excellent way to allow large doses of opioids to be adminsitered safely to control a patient’s pain. However it is very easy to cross the line between safety and patient harm with a PCA.

PCA by proxy

It is important that only the patient pushes the button on a PCA. Several adverse events, some fatal, have been reported when family members have pushed a PCA button on the patient’s behalf. One of the key safety benefits of PCA is the self-limiting factor of the patient’s mental status. Drowsiness from excessive opioids precedes respiratory depression, and when the patient becomes drowsy they stop self-administering opioids. This prevents respiratory depression. When others press the button on the patient’s behalf this safety feature of PCA is bypassed.

Basal rates in opioid naive patients

Most patients who are opioid naive should not be given a basal rate on their PCA. The continuous administration of opioids can give the same adverse effects as PCA by proxy described above. Opioid naive patients especially are susceptible to over sedation from continous administration rates on PCA.

There are two exceptions that I generally follow regarding my practice of avoiding PCA basal rates in opioid naive patients:

Nighttime basal

Patients who sleep well without pushing their PCA button may awake in severe pain. If this occurs I’ll use a nighttime only basal rate between the hours of 10pm and 6am. I’ll never exceed 1 mg/hr of morphine or equivalent for this nighttime basal.

Unusual circumstances causing severe pain

Occasionally thoracic surgery patients are not candidates for epidural use. When this happens postoperative pain management is usually much more difficult. In this type of scenario I’ll consider using a basal rate at a maximum of 1 mg/hr of morphine or equivalent in an opioid naive patient.

Concentration errors

Concentration errors when switching between opioids have caused harm to many patients. For example if a PCA pump is programmed for morphine 1 mg/mL and is then switched to hydromorphone 1 mg/mL without the pump settings being changed, a 7-fold overdose results.

At my institution we have eliminated the problem by making our PCA concentrations equianalgesic. Our only concentrations are:
Morphine 1 mg / mL (standard bag is 50 mg in 50 mL)
Hydromorphone 0.15mg/mL (standard bag is 7.5mg in 50 mL)
Fentanyl 10mcg/mL (standard bag is 500mcg in 50 mL)

If a patient is receiving a large amount of opioid we will make a bigger bag, but always at the same concentration. In this way we completely eliminate the chance of a concentration-based PCA error.

How to use PCA effectively

Initial bolus

The initial bolus is essential to use when initiating PCA in a patient whose pain is not yet controlled. At my instituion the suggested initial bolus is 40 mcg of fentanyl, 0.6 mg of hydromorphone, or 4 mg of morphine. This bolus should be adjusted based on patient specific factors such as tolerance to opioids and risk of respiratory depression.

Demand dose

For most opioid naive patients, a demand dose of 1 mg morphine or the equivalent (10 mcg fentanyl, 0.15mg hydromorphone) given every 6 to 8 minutes is sufficient. For patients that are tolerant to opioids, a larger dose may be used.

Basal rate

As discussed previously in the section on pitfalls, a basal rate in an opioid naive patient greater raises the risk of respiratory depression and should not be used routinely.

For patients who are tolerant to opioids, a portion of their daily opioid dose can be converted into the basal rate provided by the PCA.

For patients on long-acting opioids such as fentanyl patches or extended release oral opioids, I like to continue their usual long-acting regimen and use the PCA with no basal rate. My institution’s policy is to maintain 1 single source of “demand” or “prn” opioid and 1 single source of long-acting opioid. This means that a fentanyl patch may be left on and a PCA may be used for demand dosing. In my experience it is best to avoid removing a fentanyl patch only to have to place it back on at a later time.

Titration & troubleshooting

PCA allows for rapid titration of the opioid dose. With the typical PCA settings I’ve outlined,the patient is largely in control of the titration.

It is appropriate for a clinician to evaluate the PCA effectiveness within 1 or 2 hours of starting PCA.

Things I look for include:

– Clinically meaningful reductions in pain scores.
– Is the patient satisfied with their level of pain relief?
– Is the patient able to participate in their care (physical therapy, pulmonary toileting, etc…)?

If any of the above items are not satisfactory I’ll troubleshoot & titrate the PCA regimen. Things to look for include:

– Whether the patient appears to be a good candidate for PCA
– The patient’s perception of the effectiveness of PCA
– How many times the patient has pushed the button vs how many doses they have received

Sometimes it becomes clear after starting PCA that the patient is not a good candidate. Perhaps they don’t have the cognition necessary or some other reason is keeping them from using PCA. If this happens, I’ll make an assessment to either provide additional patient education on using the PCA or to discontinue the PCA in favor of nurse administered analgesia.

A significant number of times, the patient will mention that they don’t feel relief from a PCA dose of 1 mg of morphine (or equivalent) every 6 minutes. When this happens I will consider doubling the PCA dose to 2 mg of morphine (or equivalent) and extending the interval to every 12 minutes.

If the patient’s pain is not adequately controlled on PCA and the patient has pushed the PCA button many more times then they have received doses, I’ll increase the total opioid dose available via the PCA by 25-50%.

When optimizing the PCA dose, I’ll avoid increasing the basal rate in almost all circumstances. Increasing the demand dose rather than the basal dose maintains the safety benefits inherent with using PCA.

A note about patient monitoring with PCA:

Being in the ICU, most patients are already on continuous pulse oximetry and are being frequently monitored by their nurse. When titrating PCA doses past the starting dose, I’ll often add continuous pulse oximetry monitoring if it is not being used already.

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If you like this post, check out my book – A Pharmacist’s Guide to Inpatient Medical Emergencies: How to respond to code blue, rapid response calls, and other medical emergencies.

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