Accidental intrathecal injection of high-dose magnesium sulphate with conventional-dose bupivacaine: a case report
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Key findings
• Clinical data on the intrathecal use of high-dose magnesium sulphate combined with standard-dose bupivacaine are limited. In this case, after symptomatic treatment, the patient recovered completely without neurological complications.
What is known and what is new?
• Magnesium sulphate at doses below 100 mg effectively augments analgesia as an adjuvant to spinal anaesthesia without adverse effects. Clinical reports on the intrathecal administration of high-dose magnesium sulphate combined with bupivacaine are relatively limited.
• In this case, significant prolongation of the spinal anaesthesia duration was observed following administration, accompanied by adverse effects such as hypotension and altered mental status.
What is the implication, and what should change now?
• This case highlights the importance of standardized drug administration and the need for medication verification prior to use. When utilized as an adjuvant in spinal anaesthesia, the magnesium sulphate dosage must be strictly maintained within established safety parameters.
Introduction
Magnesium sulphate acts as a calcium channel blocker and an N-methyl-d-aspartate (NMDA) receptor antagonist. It exerts its clinical effects by inhibiting the central nervous system, blocking acetylcholine release at the neuromuscular junction, and relaxing vascular smooth muscle. Therefore, it is primarily used for the treatment of eclampsia and gestational hypertension (1). Previous studies have reported that high-dose intrathecal injection of magnesium sulphate may lead to severe adverse consequences, including paraplegia, sensory loss, and respiratory failure (2,3).
This case describes an orthopaedic patient who developed clinical manifestations, including refractory hypotension, altered mental status, and transient neurological dysfunction following inadvertent intrathecal administration of a high dose of magnesium sulphate combined with a local anaesthetic. We present this article in accordance with the CARE reporting checklist (available at https://acr.amegroups.com/article/view/10.21037/acr-2026-0042/rc).
Case presentation
An 80-year-old female patient with a medical history of well-controlled hypertension and coronary artery disease, who had undergone colostomy followed by standard chemoradiotherapy for an intestinal tumour three years prior, was admitted for emergency left hemiarthroplasty due to a left femoral neck fracture following a fall. Upon arrival in the operating room, her blood pressure was 108/42 mmHg, with a heart rate of 65 beats/min. The anaesthesiologist opted for unilateral hypobaric spinal anaesthesia. During initial positioning, intravenous midazolam 1 mg and nalbuphine 10 mg were administered for sedation and analgesia. In the right lateral decubitus position, single-shot spinal anaesthesia was performed at the L3–4 interspace. The anaesthetic solution was prepared by sequentially drawing 2 mL of 0.75% bupivacaine hydrochloride and 1 mL of sterile water into a 3 mL syringe. After confirming free cerebrospinal fluid flow, the 3 mL solution was injected. The patient remained in the right lateral position for 5 minutes, achieving a sensory block up to T10. Surgical positioning was then established, and right radial arterial cannulation was performed for invasive blood pressure monitoring. Ten minutes after anaesthesia induction, the patient’s blood pressure dropped to 88/34 mmHg with a heart rate of 47 beats/min. Reassessment confirmed the sensory block remained below T10. Despite fluid resuscitation with Ringer’s solution and intravenous ephedrine 10 mg, hemodynamic parameters failed to improve significantly. Subsequently, norepinephrine infusion was initiated to maintain blood pressure within ±10% of the baseline value. The initial infusion rate was 0.08 µg/kg/min; this was gradually titrated down to 0.03 µg/kg/min. Intraoperative sedation was maintained with 1% propofol at 6 mL/h and dexmedetomidine (4 µg/mL) at 3 mL/h. All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Helsinki Declaration and its subsequent amendments. Written informed consent was obtained from the patient for publication of this case report and the accompanying image. A copy of the written consent is available for review by the editorial office of this journal.
The remainder of the surgery proceeded without further complications. Following discontinuation of sedatives at the conclusion of surgery, the patient exhibited eye-opening to verbal commands with preserved but weakened upper limb movement [Medical Research Council (MRC) grade 2]. Complete motor and sensory loss were observed in both lower extremities, maintaining a sensory block below T10. Hemodynamic stability was sustained with norepinephrine infusion during transfer to the intensive care unit. The medication error was not recognized intraoperatively; it was discovered by the anaesthesiologist after the patient had returned to the ward, when reviewing the medications administered. It was found that 1 mL of 50% magnesium sulphate (500 mg) had been erroneously administered instead of sterile water (Figure 1).
Subsequent evaluations were as follows: four hours post-anaesthesia—the patient developed drowsiness with progressive deterioration of upper limb strength (MRC grade 2) and persistent areflexic paralysis (MRC grade 0) in the lower limbs, accompanied by complete loss of pain and tactile sensations. Six and a half hours post-anaesthesia: no recovery of lower extremity motor/sensory function was noted, with the patient progressing to stupor. Serum electrolyte analysis, performed 4.5 hours after the intrathecal injection, showed calcium at 1.91 mmol/L and magnesium at 0.85 mmol/L (both within normal ranges). Empiric intravenous calcium gluconate 1 g was administered as a precautionary measure. Fifteen hours post-anaesthesia: the patient developed pyrexia (38.3 °C) responsive to physical cooling. Sixteen hours post-anaesthesia: faint toe movements were first detected. Twenty-four hours post-anaesthesia: hemodynamic stability was achieved, permitting norepinephrine discontinuation. Thirty-nine hours post-anaesthesia: full recovery of consciousness occurred with complete return of motor/sensory function to preoperative baseline (time points and laboratory data are shown in Table 1; the recovery timeline of relevant parameters is presented in Table 2). The patient was discharged on postoperative Day 8. Two-week telephone follow-up confirmed an absence of neurological sequelae or other complications.
Table 1
| Time point | Event | Lab tests & results |
|---|---|---|
| 11:00† | Entry into the operating room | No laboratory tests were performed |
| 11:30† | Initiation of neuraxial anesthesia (lateral position with the involved side upward) | No laboratory tests were performed |
| 11:40† | Hypotension (managed with fluid resuscitation, ephedrine, and norepinephrine) | No laboratory tests were performed |
| 11:45† | Arterial blood gas‡ | pH 7.378, PaCO2 41.4 mmHg, BE− 1.3 mmol/L, k+ 4.04 mmol/L, Ca2+ 1.21 mmol/L, Na+ 140.5 mmol/L, Lac 1 mmol/L, BG 6.1 mmol/L, FiO2 30% |
| 12:15† | Start of surgery | No laboratory tests were performed |
| 13:40† | End of surgery | No laboratory tests were performed |
| 13:50† | The medication error was discovered | No laboratory tests were performed |
| 21:30† | Calcium gluconate 1 g was administered by slow intravenous infusion | Ca2+ 1.91 mmol/L, Mg2+ 0.85 mmol/L, k+ 4.88 mmol/L, Na+ 137.5 mmol/L |
| Postoperative Day 8 | The patient returned to his preoperative status | Ca2+ 2.11 mmol/L, Mg2+ 0.84 mmol/L, k+ 3.75 mmol/L, Na+ 141 mmol/L |
†, day of surgery. ‡, oxygen partial pressure was not recorded at that time due to equipment failure. BE, base excess; BG, blood glucose; Lac, lactate.
Table 2
| Parameters | Intraoperative | Post-anaesthesia hour 4 | Post-anaesthesia hour 6.5 | Post-anaesthesia hour 16 | Post-anaesthesia hour 24 | Post-anaesthesia hour 39 |
|---|---|---|---|---|---|---|
| Bilateral lower extremity sensation | Anaesthesia | Anaesthesia | Thermal sensation | Light touch/pressure sensation | Light touch/pressure sensation | Full sensory recovery |
| SPO2 (%)/RR (breaths/min) (FiO2 0.3) | 97/13 | 100/15 | 100/15 | 100/17 | 100/20 | 100/23 |
| Lower limb of MRC | 0 | 0 | 0 | 1 | 1 | 5 |
| Upper limb of MRC | 5 | 3 | 2 | 3 | 3 | 5 |
| Consciousness | Sedated | Somnolent | Stupor | Somnolent | Somnolent | Alert |
| Norepinephrine, μg/kg/min† | 0.03–0.08 | 0.03 | 0.03 | 0.03 | Stopped | Stopped |
| Surface temperature, ℃ | 36.4 | 36.4 | 38 | 38.3 | 37.3 | 36.3–36.5 |
†, continuous infusion of norepinephrine was administered to maintain the patient’s mean arterial pressure within ±10% of the baseline value. min, minute; MRC, Medical Research Council; RR, respiratory rate.
Discussion
Previous reports of high-dose intrathecal magnesium sulphate injection have mostly involved the agent alone (4), whereas the present case involved the intrathecal injection of a local anaesthetic mixed with a high dose of magnesium sulphate. This medication error led to clinical manifestations including a prolonged altered mental status, hypotension, and an extended duration of spinal anaesthesia.
Magnesium sulphate produces a general anaesthetic effect by inhibiting NMDA receptors and calcium influx (5,6). In this case, due to the combined use of sedative drugs, the two effects were superimposed, resulting in the patient experiencing a long-term disturbance of consciousness. At the same time, magnesium sulphate can reduce the effect of angiotensin II (7) and inhibit the release of norepinephrine (8). Thus, exerting an antihypertensive effect. In addition to the above mechanisms, the prolonged hypotension in this case may also be related to the prolonged sympathetic nerve block time as an adjuvant.
The combination of magnesium sulphate and local anaesthetics can prolong the duration of anaesthesia; the mechanism may involve a synergistic effect with NMDA antagonists (9), or changes in the pH value of the injection (10). After intrathecal injection of 500 mg magnesium sulphate combined with a local anaesthetic, the sensory and motor block times were significantly prolonged, reaching 39 hours and 16 hours, respectively. Compared with previous studies (11), this result further suggests that there may be a positive correlation between the dose of magnesium sulphate and the duration of block, but this conclusion needs to be further verified.
Studies have confirmed that intrathecal injection of magnesium sulphate has no significant effect on electrolyte homeostasis (12). In the present case, the administration of calcium gluconate, given out of an abundance of caution, was likely limited to a placebo effect. Previous reports of inadvertent high-dose intrathecal magnesium sulphate injection did not employ specific antagonists (3,13); this is consistent with the management strategy adopted in this case, namely, supportive care focused on maintaining vital signs.
The causes of medication errors related to epidural and intrathecal injection of magnesium sulphate can be categorised into the following four aspects (2): organisational influences [look-alike packaging, same-batch dispensing, similar labels (3), no prior corrective action]; supervisory factors [prolonged epidural magnesium infusion, undertrained trainee, unclear nurse-resident handover (14)]; preconditions for unsafe acts (night fatigue, tubing change, multiple ports, poor labels); unsafe acts [skill errors (13), perceptual misidentification, failure to link drug error to inadequate anaesthesia]. The contributing factors to the medication error in this case were as follows: first, the double-check protocol was not strictly enforced, as the anaesthesiologist was negligent in verifying the drug label, and the assisting nurse was a newly recruited intern who had not received systematic training; second, look-alike ampoules were placed adjacent to one another, leading to a selection error; third, high-risk drugs intended for intrathecal use were stored together with other routine medications, without proper segregation.
To prevent similar errors, we recommend the following: strict enforcement of the double-check protocol with independent verification by two providers; systematic training for new staff, especially on high-risk drug identification and administration; separate storage of look-alike drugs with prominent labelling; and segregated management of high-risk intrathecal medications to avoid mixing with routine drugs. These multi-level interventions are effective in reducing the risk of medication errors.
Several limitations should be acknowledged in this case. First, cerebrospinal fluid magnesium levels were not measured after the inadvertent intrathecal administration. Second, the use of propofol and dexmedetomidine for sedation may have interfered with serial assessments of consciousness.
Conclusions
This case report reveals severe complications from accidental intrathecal magnesium sulphate injection during anaesthesia. Accordingly, systemic strategies, including modifying ampoule appearance, optimizing risk-based segregation of high-risk drugs, and strengthening double-check protocol training and enforcement, are recommended to effectively prevent future life-threatening medication errors in anaesthetic practice.
Acknowledgments
None.
Footnote
Reporting Checklist: The authors have completed the CARE reporting checklist. Available at https://acr.amegroups.com/article/view/10.21037/acr-2026-0042/rc
Peer Review File: Available at https://acr.amegroups.com/article/view/10.21037/acr-2026-0042/prf
Funding: None.
Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://acr.amegroups.com/article/view/10.21037/acr-2026-0042/coif). The authors have no conflicts of interest to declare.
Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Helsinki Declaration and its subsequent amendments. Written informed consent was obtained from the patient for publication of this case report and the accompanying image. A copy of the written consent is available for review by the editorial office of this journal.
Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.
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Cite this article as: Huang Y, Dai SY, Zhang TT, Lyu LP, Xue YN, Chen TF. Accidental intrathecal injection of high-dose magnesium sulphate with conventional-dose bupivacaine: a case report. AME Case Rep 2026;10:120.
