Side Effects of a Single Shot Intrathecal Morphine in Clinical Practice, a Retrospective Analysis

Most patients undergoing invasive procedures experience postoperative pain. The definition of pain is described as an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage. Postoperative incisional pain is a unique and common form of acute pain. Recent studies demonstrate that about 50-70% of patients experience moderate to severe pain after surgery indicating that postoperative pain remains poorly treated.

Mismanagement of acute postoperative pain compromises patient recovery by increasing morbidity and delaying recovery. Therefore, adequate pain treatment is crucial. Steps for formulating a multimodal regimen consider both non pharmacologic and pharmacologic therapies. Opioids are considered a staple in the management of acute postoperative pain. Opioid analgesics embody a wide range of medicinal products that share the ability to relieve acute severe pain by acting on the opioid receptors. There has been a significant increase in the number of opioid analgesics, and they differ in their chemical composition and route of administration (oral, intravenous, subcutaneous, intramuscular, topical, transmucosal, transdermal, neuraxial). Despite their effectiveness in pain relief, opioids are also associated with side effects, including physical dependence and respiratory depression. Consequently, researchers have been exploring alternative methods of opioid administration to minimise the risk of these side effects, one of which is intrathecal opioid delivery.

Since their introduction in the 1970s, intrathecal opioids have been extensively utilised and have gained significant popularity for their efficacy in the management of postoperative pain. Intrathecal morphine (ITM) refers to the single injection of morphine into the subarachnoid space between two lumbar vertebrae. It can be used in combination with general anaesthesia, as adjuncts to intrathecal local anaesthetics or alone. It is rather easy to administer and when used as a single shot technique, it can provide long-lasting effective postoperative analgesia. Moreover, it can decrease systemic opioid consumption and potentially facilitates enhanced recovery due to optimised pain management and faster mobilisation.

Despite its potential, the use of ITM is restrained in daily clinical practice due to the concerns about the potential side effects, including postoperative nausea and vomiting (PONV), pruritus, urinary retention, sedation and respiratory depression. Especially the latter is a reason for clinicians to be reluctant to the use of ITM. At present, data regarding the incidence and severity of side effects following ITM is relatively limited. Respiratory depression is one of the most serious side effects and appears to be dose dependent. Since lower doses of ITM are currently being used, it occurs less frequently than in the past. Respiratory depression has no clear definition in the literature and can be caused by several factors, which makes it challenging to investigate. Studies report an incidence ranging from 0 to 3.4%, depending on the dose of ITM. A single shot up to 150µg seems to be safe and the risk of respiratory depression equals that of systemic opioids in this dosage. A higher amount of ITM may increase the risk of respiratory depression, without necessarily improving analgesia.

Inclusion criteria

• Patients undergoing surgery and receiving general anaesthesia with preoperative administration of a single shot of ITM.

Exclusion criteria

• Patients who are less than 18 years old.