1. IVC compression and hyperventilation decrease lumbar CSF volume Tom Archer, MD

2. Manbit images http://www.manbit.com/OA/f28-1.htm Lateral position– IVC is not compressed.

3. http://www.manbit.com/OA/f28-1.htm Supine position– IVC is compressed and epidural veins are engorged.

4. Lee RR et al Spine 2001;26:1172–1178 Abdominal compression narrows the IVC in non-pregnant volunteers.

5. Lee RR et al Spine 2001;26:1172–1178 Hyperventilation (B) decreases lumbar CSF volume.

6. Lee RR et al Spine 2001;26:1172–1178 Hyperventilation (B) decreases lumbar CSF volume.

7. Lee RR et al Spine 2001;26:1172–1178 Hyperventilation alone decreases lumbar CSF volume by 10%, abdominal compression alone decreases it by 28 %. Both together decrease CSF volume by 41%.

8. Summary Volume of lumbar thecal sac and lumbar epidural blood is dynamic and respond to: 1) IVC compression and 2) hyperventilation– perhaps d/t decrease in intracranial blood volume with shift of CSF into the head.

9. Summary IVC compression in pregnancy, with engorgement of epidural veins and decrease in lumbar CSF volume, probably explains 30% decrease in local anesthetic required for spinal anesthesia in pregnancy. Rare instances may occur, as in this case, of a “tight” lumbar epidural space with nerve compression and ischemia with epidural medication injection.