Modeling Spinal Intrathecal Drug Distribution

Severe altered mentation due to cervicothoracic intrathecal pump after correction of cervical stenosis: a case report

BACKGROUND

Cerebral spinal fluid (CSF) dynamics are complex and changes in spinal anatomy may influence the rostrocaudal movement of intrathecal medications. We present the first reported case demonstrating that acute cervical spinal stenosis may impede the distribution of adjacent intrathecal medications, and that correction of such stenosis and the resulting changes in CSF flow may necessitate significant adjustments in the intrathecal infusates.

CASE PRESENTATION

We present a case of a 60-year-old male patient with a cervicothoracic intrathecal pump (ITP) infusing morphine, bupivacaine, and baclofen for chronic neck pain. The alert and oriented patient had a recent fall resulting in an acute severe cervical stenosis and cord compression which required urgent surgical decompression. Postoperatively, after the cervical decompression, the patient had significant altered mental status requiring a naloxone infusion. Multiple attempts to reduce the naloxone infusion were initially not successful due to worsened somnolence. The previously tolerated ITP medications were continuously reduced over the next 14 days, allowing concomitant decrease and eventual cessation of the naloxone infusion while maintaining patient mental status. The only opioids the patient received during this period were from the ITP.

CONCLUSIONS

This case presents clinical evidence that severe spinal stenosis may impede the rostral CSF distribution of intrathecal medications. Intrathecal medications previously tolerated by patients prior to decompression may need to be significantly reduced in the postoperative period.

Oxycodone concentrations in the central nervous system and cerebrospinal fluid after epidural administration to the pregnant ewe

The main sites of the analgesic action of oxycodone are the brain and spinal cord. The present study describes the concentrations of oxycodone and its metabolites in the brain and spinal cord after epidural administration to the ewe. Twenty pregnant ewes undergoing laparotomy were randomized into two groups to receive epidural oxycodone: infusion group (n = 10, 0.1 mg·kg^-1 bolus followed by continuous infusion of 0.05 mg·kg^-1 ·h^-1 for five days) or repeated boluses group (n = 10, 0.2 + 2x0.1 mg·kg^-1 bolus followed by a 0.2 mg·kg^-1 bolus every 12 hours for five days). After five days of oxycodone administration, arterial blood samples were collected, the sheep were killed, and a CSF sample and tissue samples from the cortex, thalamus, cerebellum and spinal cord were obtained for the quantification of oxycodone and its main metabolites. The median plasma and CSF concentrations of oxycodone were 9.0 and 14.2 ng·mL^-1 after infusion and 0.4 and 1.1 ng·mL^-1 after repeated boluses. In the infusion group, the cortex, thalamus and cerebellum oxycodone concentrations were 4-8 times higher and in the spinal cord 1310 times higher than in plasma. In the repeated boluses group, brain tissue concentrations were similar in the three areas, and in the spinal cord were 720 times higher than in plasma. Oxymorphone was the main metabolite detected, which accumulated in the brain and spinal cord tissue. In conclusion, first, accumulation of oxycodone and oxymorphone in the CNS was observed, and second, high spinal cord concentrations suggest that epidural oxycodone may provide segmental analgesia.

Characterization of intrathecal cerebrospinal fluid geometry and dynamics in cynomolgus monkeys (macaca fascicularis) by magnetic resonance imaging

Recent advancements have been made toward understanding the diagnostic and therapeutic potential of cerebrospinal fluid (CSF) and related hydrodynamics. Increased understanding of CSF dynamics may lead to improved detection of central nervous system (CNS) diseases and optimized delivery of CSF based CNS therapeutics, with many proposed therapeutics hoping to successfully treat or cure debilitating neurological conditions. Before significant strides can be made toward the research and development of interventions designed for human use, additional research must be carried out with representative subjects such as non-human primates (NHP). This study presents a geometric and hydrodynamic characterization of CSF in eight cynomolgus monkeys (Macaca fascicularis) at baseline and two-week follow-up.

Results showed that CSF flow along the entire spine was laminar with a Reynolds number ranging up to 80 and average Womersley number ranging from 4.1–7.7. Maximum CSF flow rate occurred ~25 mm caudal to the foramen magnum. Peak CSF flow rate ranged from 0.3–0.6 ml/s at the C3-C4 level. Geometric analysis indicated that average intrathecal CSF volume below the foramen magnum was 7.4 ml. The average surface area of the spinal cord and dura was 44.7 and 66.7 cm² respectively. Subarachnoid space cross-sectional area and hydraulic diameter ranged from 7–75 mm² and 2–3.7 mm, respectively. Stroke volume had the greatest value of 0.14 ml at an axial location corresponding to C3-C4.

Lumbosacral and thoracolumbosacral cerebrospinal fluid volume changes in neonates, infants, children, and adolescents: A retrospective magnetic resonance imaging study

BACKGROUND

The volume of cerebrospinal fluid can affect the pharmacokinetics and pharmacodynamics of local anesthetics for spinal anesthesia and other intrathecal medications.

AIMS

The objective of this study was to estimate the lumbosacral cerebrospinal fluid volume and thoracolumbosacral cerebrospinal fluid volume using magnetic resonance images in pediatric patients from neonates and infants to adolescents.

METHODS

Spinal magnetic resonance images of 500 pediatric patients (age <18 years) were reviewed. The lumbosacral cerebrospinal fluid volumes of 418 patients and thoracolumbosacral cerebrospinal fluid volumes of 248 patients were measured. The relationship between cerebrospinal fluid volumes and age, height, and weight were evaluated. The lumbosacral and thoracolumbosacral cerebrospinal fluid volumes per weight were calculated to elucidate developmental changes.

RESULTS

The lumbosacral and thoracolumbosacral cerebrospinal fluid volumes showed linear correlations with height (r²  = 0.730 and r²  = 0.661, respectively), whereas they showed curvilinear correlations with age (r²  = 0.752 and r²  = 0.717, respectively) and weight (r²  = 0.734 and r²  = 0.734, respectively). The mean lumbosacral cerebrospinal fluid volume per weight (mL/kg) was 0.85 (standard deviation [SD]: 0.19, 95% confidence interval [CI]: 0.81-0.90) in neonates and infants, 0.86 (SD: 0.22, 95% CI: 0.83-0.89) in toddlers and preschoolers, 0.71 (SD: 0.26, 95% CI: 0.66-0.76) in schoolers, and 0.54 (SD: 0.20, 95% CI: 0.49-0.60) in adolescents. The mean thoracolumbosacral cerebrospinal fluid volume per weight (mL/kg) was 1.95 (SD: 0.37, 95% CI: 1.86-2.04) in neonates and infants, 1.82 (SD: 0.41, 95% CI: 1.75-1.88) in toddlers and preschoolers, 1.38 (SD: 0.40, 95% CI: 1.23-1.52) in schoolers, and 0.99 (SD: 0.34, 95% CI: 0.45-1.53) in adolescents.

CONCLUSION

The lumbosacral and thoracolumbosacral cerebrospinal fluid volumes in pediatric patients were much smaller than previously presented values, showing linear correlations with height, and demonstrate curvilinear correlations with age and weight.