• The primary outcome variables are the correlation between the ratio of CSF/plasma morphine , morphine-3-glucuronide (M3G), and morphine-6-glucuronide (M6G) levels and the plasma concentration of IL-6 over time. [ Time Frame: CSF and Blood samples will be taken in the OR, post operatively ( every 6 hrs until POD 5 if CSF drain still in place) ] [ Designated as safety issue: No ]
  

• Correlation between CSF/Plasma ratios of morphine, M3G, M6G and plasma concentration of TNFα and ET-1 over time. [ Time Frame: CSF and Blood samples will be taken in the OR, post operatively ( every 6 hrs until POD 5 if CSF drain still in place) ] [ Designated as safety issue: No ]
  
• Correlation between CSF/plasma ratios for morphine, M3G, M6G and CSF/Plasma ratios for albumin and S-100β over time. [ Time Frame: CSF and Blood samples will be taken in the OR, post operatively ( every 6 hrs until POD 5 if CSF drain still in place) ] [ Designated as safety issue: No ]
  

Procedure: Repair of descending thoracic aneurysm and morphine
Elective surgical patients undergoing repair of a descending thoracic aortic aneurysm, requiring insertion of a cerebral spinal fluid (CSF) drain and receiving Morphine as their primary analgesic agent can be enrolled

Study Objectives: To determine the role of surgery-induced inflammation on the transport of morphine and its metabolites, M3G and M6G, across the blood-brain barrier.

Study phase: IV Study Design: This is a sequential enrolment study design in which elective surgical patients presenting for repair of an ascending thoracic aneurysm and fitted with a CSF drain as part of their standard of care will be approached for permission to draw blood samples at specified times during their hospital course. Concomitantly, samples of CSF will be collected from the CSF drainage system (CSF is normally wasted).

Morphine will be used as the primary analgesic agent (this is within the standard of care). Samples will be collected at specified time intervals for 5 days or until the CSF drain is removed (whichever comes first). Samples collected will be analysed for morphine, its 3- and 6- glucuronide metabolites, inflammatory cytokines, markers of CNS injury and anatomical integrity of the BBB. Area under the concentration vs. time curve will be calculated and the effect on morphine metabolism and penetration across the BBB will be determined using a repeated measures analysis of variance technique (as used in our previous study).