EPIDURAL-ANESTHESIA AND ACUTELY INCREASED INTRACRANIAL-PRESSURE - LUMBAR EPIDURAL SPACE HYDRODYNAMICS IN A PORCINE MODEL

Background: The effects of epidural injection on Intracranial pressure (ICP), lumbar epidural pressure, cerebral blood flow (CBF), and spina l cord blood flow (SCBF) were studied after acutely increased ICP in s wine. Methods: Twenty pigs, anesthetized with isoflurane and mechanica lly ventilated to maintain normocarbia, had two Tuohy needles placed i n the lumbar epidural space, The ICP, lumbar epidural pressure, heart rate, mean arterial pressure, and central venous pressure were monitor ed. All animals had a Fogarty catheter pieced in the parietal epidural space. Six pigs were randomized to a normal ICP group (group N) and e ight pigs to an increased ICP group by inflation of the Fogarty cathet er balloon (group R). Each pig had 0.33 ml . kg(-1) of 2.0% carbonated lidocaine injected over 20 s via an epidural needle placed at L3. The ICP and lumbar epidural pressure mere then monitored continuously for 30 min. Pressure-time data were fit to traditional compartmental mode ls. Epidural elastance and resistance were calculated using a derivati on of the Windkessel theory. An additional six pigs bad ICP elevated a s in group R and CBF and SCBF measured using radioactive microspheres at five time periods: baseline, 0-60 s, 100-160 s, 200-260 s, and at 3 0 min after epidural injection. Results: The animals did not differ wi th respect to heart rate, central venous pressure, or mean arterial pr essure at baseline. The ICP was 10 +/- 2 mmHg in group N, and 24 +/- 2 mmHg after balloon inflation in group R. After epidural injection, pe ak ICP was significantly greater in group R (76 +/- 22 vs. 54 +/- 17 m mHg) but not different by 30 min (17 +/- 5 vs, 11 +/- 1 mmHg). Epidura l elastance in group N was 8.3 +/- 3.1 mmHg . ml(-1) and 12.8 +/- 5.0 mmHg . ml(-1) in group R (P = 0.045). Epidural resistance was 1,330 +/ - 590 mmHg . s . ml(-1) in group N and 2,220 +/- 600 mmHg . s . ml(-1) in group R (P = 0.038). The CBF and SCBF were less than 10% of baseli ne during the 0- to 60-s time period after epidural injection. Thereaf ter, CBF and SCBF did not differ from baseline values. Conclusions: in this porcine model, epidural injection increased ICP. With increased ICP at baseline, more pronounced increases in ICP followed epidural in jection. With increased baseline ICP, both epidural elastance and resi stance increased compared with controls. The CBF and SCBF were markedl y reduced immediately after local anesthetic injection into the epidur al space.