Everything You Need to Know About Pre-operative Use of Acetaminophen for Pain

Updated: Sep 22

The proper management of acute pain after a surgical procedure, physical trauma, or in those with an acute painful medical condition is imperative. I feel as if we are in the midst of a public health crisis when a systematic approach to pain management is not held to the position of the 'gold standard' of care. While some institutions and individuals do pay attention to the variety of medications and strategies available for optimal pain management, there remains a great opportunity to improve quality of life, patient-provider communication, and functionality with a more widespread attention to acute pain management.

The World Health Organization principles suggest that safer, non-opioid medications should be the first-line agents for all types of pain: mild, moderate, or intense. As such, many providers consider acetaminophen as the foundation of a pain management plan while taking into consideration the need for other agents as the expected intensity of pain increase as associated with various surgical procedures.

In this blog post, I will review the evidence for the use of acetaminophen in the pre-operative period, specifically using acetaminophen in a proactive manner. For your reference, you can see the journal article from JAMA here and from the journal Pain.

The first paper I will discuss is titled 'Postoperative Multimodal Analgesia Pain Management with Nonopioid Analgesics and Techniques: A Review' published in JAMA. While Dr Wick describes the various multimodal techniques part of the enhanced recovery after surgery pathway (ERAS), this post will focus on the use of acetaminophen only. This is an excellent paper and the interested reader should read the entirety of the journal article. Rather than using this strategy (ERAS) for individuals undergoing a select procedure, I believe this philosophy should be applied to all surgical patients, using the strategies appropriately weighing the risks and the benefits, based on the expected intensity associated with the procedure or medical condition.

Wick advocates for the use of acetaminophen on a scheduled rather than on a PRN (as needed) basis. Perhaps if an individual is having a procedure associated with only mild pain, it might be reasonable to offer acetaminophen on a PRN basis. However, instrumental to good pain management is being proactive and anticipating potential increases in pain, and this is were the PRN dosing can fall short. Particularly when an individual is expected to increase their functioning a day after a surgical procedure, maintaining adequate pain management is an important component of healing. Acetaminophen can be an effective pain reliever and, when added to opioids, produces superior analgesia and can have an opioid-sparing effect. This in turn may result in fewer side effects commonly experienced with opioids, including nausea, vomiting, or sedation.

Acetaminophen can also be co-administered with a non-steroidal anti-inflammatory drug (NSAID) for even greater efficacy. Depending upon the perceived burden an individual experiences with taking medications, one can administer acetaminophen and NSAIDs at the same time or consider administration at different times. If providing both medications on a scheduled basis, the blood stream concentration will stay relatively stable. The maximum dosage of acetaminophen should not exceed 3 - 4 grams / day for any patient.

The second article I will discuss is titled 'Intravenous acetaminophen reduces postoperative nausea and vomiting: A systematic review and meta-analysis' by Christian Apfel et al published in the journal Pain . Addressing nausea and vomiting associated with pain or anesthetic technique is imperative when considering the patient experience and recovery after a surgical procedure. While it is known that acetaminophen reduces opioid requirements, data is now becoming available to suggest that nausea and vomiting may be reduced as an additional benefit.

Prophylactic IV acetaminophen reduced postoperative nausea and vomiting (PONV) and was most effective when given before surgery and intraoperatively, but not when treatment was initiated after onset of pain. The reduction of PONV correlated with the reported reduction of pain, but not postoperative opioid consumption. In addition, it was determined that a single dose of prophylactic IV acetaminophen is at least as effective as repeated doses or as antiemetics.

Dosing Considerations

Dosing for acetaminophen is as follows:

Children: 10 mg / kg q 4 hours

15 mg / kg q 6 hours

Adults: 650 mg q 4 hours

1000 mg q 6 hours

Screenshots from the PreEmpt Pain smartphone app

How does one decide if dosing should be every 4 or 6 hours? Generally we need to acknowledge the burden of taking medication. Particularly in children whom might find it difficult and traumatic to receive medication, dosing acetaminophen every six hours would seem reasonable. Alternatively, there could be a benefit for some individuals of knowing they are receiving medication more frequently, thus every four hour dosing would seem reasonable.

Regarding the scheduled versus as-needed dosing for acetaminophen, I am a strong advocate for scheduled dosing for those patients undergoing procedures associated with moderate or intense pain, especially if they are receiving concurrent opioid medications for pain. Those patients with mild pain can receive as-needed acetaminophen; scheduled acetaminophen should be considered if pain is ongoing. It is reasonable to reassess the pain management plan on a regular basis, at least once daily if not more frequently. If the medication is administered on a scheduled basis, the plasma level will be relatively the same regardless of receiving the medication every four or six hours.

Contraindications to acetaminophen include allergy to acetaminophen, elevated liver function tests, or concurrent administration of other acetaminophen-containing medications.

Take Away Points

- Administer acetaminophen as a first-line agent based on the expected intensity of pain

- mild expected pain - scheduled or as-needed (PRN) acetaminophen

- moderate expected pain - scheduled acetaminophen

- intense expected pain - scheduled acetaminophen

- Administer acetaminophen along with an NSAID (such as ibuprofen) if no contraindications for improved efficacy

- Do not exceed 3 g / day total dose of acetaminophen

- Preemptive IV acetaminophen can be helpful to decrease the incidence of nausea and vomiting; administer in preop area or during anesthesia. Effect is minimized when administered after the onset of pain

- Reassess efficacy at least once daily