Doctoral Degrees (Neurosurgery)

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    Comparison of intrathecal and intravenous morphine for post-operative analgesia after single level spinal fusion surgery
    (Stellenbosch : Stellenbosch University, 2020-12) Vlok, Adriaan Johannes; Coetzee, Andre; Stellenbosch University. Faculty of Health Sciences. Dept. of Surgical Sciences: Neurosurgery.
    ENGLISH ABSTRACT: The purpose of this study was to evaluate the efficacy, safety and cost effectiveness of a 0.005mg/kg, up to a maximum of 0.45mg, dose of intrathecal morphine in first-time single level spinal surgery. The study was conducted, and results apply, to a tertiary care public service hospital in South Africa. This experimental intervention was compared to the institutional standard of care being the use of intravenous morphine via a patient-controlled device, administering 1mg of morphine intravenously every 7 minutes as required. Efficacy was measured with reference to validated scoring systems which included the Oswestry disability index, Roland Morris questionnaire, EQ-5 score and visual analogue scale (VAS) to assess pain, analgesia and disability in the post-operative phase and subsequent follow up. A standardised physiotherapy regime was used to mobilize patients and the patients was discharged directly to their homes, specifically skipping a step-down facility. Safety was assessed by monitoring the known side-effects of morphine (nausea, vomiting, pruritis), oxygen saturation, respiratory rate and sedation during the stay in the ICU. Inter alia, blood gases were analysed on 11 occasions within the first 24 hours. General patient follow-up occurred at 6 weeks, 3 and 6 months. The study was conducted in a prospective double-blind, randomized placebo controlled fashion. 40 patients were enrolled (20 per group). The time to discharge for the intrathecal morphine group (IT) was statistically significantly shorter (3.68 days) compared to 5.61 days for the patient-controlled analgesia (PCA) group. This translated into a 43.5% saving for general ward stay costs. VAS was assessed when lying still and moving and the difference between these values was used to quantify the intensity of pain. A significant difference was noted at 24 hours favouring the IT group. Significantly less supplemental analgesia was used in the IT group during the first 24 post-operative hours. No significant difference in side-effects were noted between the groups. The initially elevated mean PaCO2 in the IT group demonstrated a significant decrease from 4 hours up to 24 hours. An increase in mean respiratory rate was demonstrated from 10 hours onwards in both groups. Seven incidents of hypoxia (PaO2 < 8kPa) were observed (IT=4, PCA=3). The 7 incidents were explained by either a low FiO2 or a decrease in functional residual capacity (FRC) as proven by the A-a gradient. No overt sedation was clinically demonstrated at the time the PaO2 was less than 8.0 kPa. Six week, 3-month and 6-month follow-up demonstrated significant improvement in all scoring modalities in both groups. The intrathecal use of morphine had a direct effect on the μ-receptors in the spinal cord resulting in segmental analgesia allowing the patients to mobilize faster compared to the more central acting analgesic effects offered by intravenous morphine. The proposed dose proved to be safe with minimal side-effects, all of which were comparable to the PCA group. The application will be particularly useful in obese patients where the calculation of a safe intravenous dose can be challenging because of excess adipose tissue. When using IT or PCA morphine, supplemental oxygen is suggested for the first 4 hours post-operatively and continuous monitoring of respiratory rate, saturation and sedation should be done. Finally, it is recommended that it will be safer practice to reset the minimum cut-off value for saturation at a higher value than the conventional 90% level.