IVC compression and hyperventilation decrease lumbar CSF volume

Tom Archer, MD

Manbit imageshttp://www.manbit.com/OA/f28-1.htm

Lateral position– IVC is not compressed.

http://www.manbit.com/OA/f28-1.htm

Supine position– IVC is compressed and epidural veins are engorged.

Lee RR et al Spine 2001;26:1172–1178

Abdominal compression narrows the IVC in non-pregnant volunteers.

Lee RR et al Spine 2001;26:1172–1178

Hyperventilation (B) decreases lumbar CSF volume.

Lee RR et al Spine 2001;26:1172–1178

Hyperventilation (B) decreases lumbar CSF volume.

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%.

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.

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.