Spinal Morphine administration is a well-established anesthetic technique for postoperative analgesia due to its efficacy, safety and low cost. Excessive doses of morphine can be associated with several adverse events such as nausea, vomiting, pruritus, urinary retention and respiratory depression. We present a 59-year-old female presented with paraparesis, urinary incontinence and chronic pain due to lumbar osteomyelitis and vertebrae instability. The patient underwent T10-L3 spinal fusion and Laminectomy L3-S1 with combined general and spinal anesthesia. Mistakenly, a 0.1 mg/kg of morphine was administered (5 mg in total) instead of 0.1 mg total dose, the standard dose used as per our protocol. At the post anesthesia care unit and under continuous infusion of Naloxone 1 mcg/kg/min, the patient regained consciousness and spontaneous ventilation 12 hours after the spinal administration but remained ventilated for 8 hours more due to hypoventilation and low Minute Volume. To conclude, accidental overdose of spinal morphine administration may happen and is associated with prolonged unconsciousness and hypoventilation. It is important to report and discuss errors with colleagues in order to learn from mistakes and improve clinical practice.

Spinal Morphine (SM) is a well-established anesthetic technique for postoperative analgesia due to its efficacy, safety and low cost. SM effect peaks at approximately 6 hours after injection and can last for 18-24 hours, due to its lipophilic properties [1- 3]. Excessive doses of morphine can cause several complications: (Depending on the route of administration) such as nausea, vomiting, pruritus, urinary retention and respiratory depression [4].

Generally the dose used for major orthopedic spine surgery is 200 -300 mcg, in association with general anesthesia (GA) [1].

We present a case of an accidental injection of extremely high dose of SM in a patient underwent an elective spinal. There are few reports in the literature describing the perioperative course of an opioid intrathecal overdose. [2,5,6]. These previous cases occurred in patients undergoing orthopaedic surgery and where cerebrospinal fluid removal, or mechanical ventilation, or both were performed. Our report details the successful treatment of intrathecal morphine 5 mg overdose that did not require prolonged mechanical ventilation.

A 59 year-old female with a BMI of 19 presented to our hospital with paraparesis, urinary incontinence and chronic pain due to lumbar osteomyelitis and vertebrae instability. She reported a history of heavy smoking, blood hypertention, hyperlipidemia, asthma and schizophrenia. The patient underwent T10-L3 spinal fusion and Laminectomy L3-S1 with combined general and spinal anesthesia. Spinal morphine was administered at L3-L4 level and was done after general anesthesia. Mistakenly, a 0.1 mg/kg of morphine was administered (5 mg in total) instead of 0.1 mg total dose, the intended dose. This mistake occurred secondary to a human error; a junior resident in anesthesia who prepared the syringe and aspirated the morphine from the ampule, handed it to a senior anesthesiologist, without any information regarding the exact dose of the morphine, consequently a 5 ml syringe containing 5 mg of morphine was administered intrathecally.

Throughout the operation patient received only 0.1 mg of fentanyl, upon intubation.

PACU – Management

Mechanically ventilated, the patient was transferred to the post anesthesia care unit (PACU) and stayed there 21 hours for surveillance. At the PACU and under continuous infusion of Naloxone (1 mcg/kg/min), she gradually regained consciousness and spontaneous ventilation 12 hours after the spinal administration but remained ventilated for 8 hours more due to hypoventilation and low Minute Volume. With intravenous acetaminophen 1 gram PRN her pain was well controlled with mean VAS scores of 0 and 3 in POD 0 and POD 1, respectively. Naloxone infusion stopped after 24h of SM injection. No sedation or hypoventilation occurred following extubation, which was performed 21 hours after the spinal injection.

Accidental massive overdose administration of opioids has been reported in various settings including dysfunctional patient-controlled analgesia (PCA) device, during epidural and intrathecal anesthesia [6].

Common causes for opioids administration error include accidental switching of drug vial or syringe, mistakes in recognizing drug vial and injection performed by inexperienced person [6].

The accidental massive overdose in our patient was injected by an unexperienced junior anesthesiology resident, who was not familiar with the standard dose of morphine routinely administered intrathecally. 

To manage spinal opioids overdose, patient should preferably be admitted to PACU or intensive care unit (ICU) and should be given an intravenous continuous naloxone infusion 0.3-1 mcg/ kg/min for at least 24 hours. Other recommended measures include vital signs monitoring, anti-emetics, urinary catheter and urinary output monitoring, respiratory support, anti-convulsant and CSF drainage should be considered in extremely high doses and severe adverse events.

To conclude, overdose spinal morphine might be associated with life – threatening side effects, such as, prolonged unconsciousness and hypoventilation. It is important to report and discuss errors with colleagues in order to learn from mistakes and improve clinical practice.

1. James P. Rathmell, MD, Timothy R. Lair, MD, and Bushra Nauman, MD, The Role of Intrathecal Drugs in the Treatment of Acute Pain. Anesth Analg. 2005 Nov;101(5 Suppl):S30-43.
2. Perrot G, Muller A, Laugner B, Accidental overdose of intrathecal morphine. Treatment with intravenous naloxone alone. Ann Fr Anesth Reanim. 1983; 2: 412-414
3. Mindy Cohen 1, Jeannie Zuk, Nancy McKay, MarkErickson, Zhaoxing Pan, Jeffrey Galinkin, IntrathecalMorphine Versus Extended-Release Epidural Morphine forPostoperative Pain Control in Pediatric Patients UndergoingPosterior Spinal Fusion, Anesth Analg. 2017 Jun;124(6):2030-2037.
4. M. Gehling, M. Tryba, Risks and side-effects of intrathcal morphine combined with spinal anesthesia: a meta-analysis. Anaesthesia. Volume64, Issue6, June 2009, Pages 643-651
5. Pomonis SP, Economacos G, Costopanajiocoy SP, Overdose ofintrathecal morphine. Anesthesia. 1986; 41: 670
6. M. Cannesson, N. Nargues, B. bryssine, R. Debon, E. Boselli,D. Chassard, Intrathecal morphine overdose during combinedspinal- epidural block for caesarean delivery – case report.BJA Volume 89, Issue 6, p925-927, DEB. 2002
7. M. Cannesson, N. Nargues, B. Bryssine, R. Debon, E. Boselliand D. Chassard, Intrathecal morphine overdose duringcombined spinal±epidural block for Caesarean delivery, Br JAnaesth 2002; 89: 925±7.