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Analysis of human epidural pressures
P S Thomas1, J I Gerson, G Strong
1Department of Anesthesiology, SUNY Health Science Center, Syracuse 13210.
Regional Anesthesia
|July 1, 1992
Summary
Lumbar epidural pressure is typically above atmospheric pressure, not negative as previously thought. Baseline epidural pressure varies, especially in patients with prior back surgery, and returns to baseline after small local anesthetic injections.
Area of Science:
- Anesthesiology
- Pain Management
- Neurosurgery
Background:
- Traditional methods for identifying epidural space entry rely on indirect pressure measurements.
- Literature presents confusion regarding epidural entry pressures versus baseline pressures.
- Zero reference pressure in epidural studies is often inconsistently applied.
Purpose of the Study:
- To examine baseline epidural pressure changes in patients undergoing epidural injections.
- To investigate the relationship between epidural pressure waves and arterial/venous waveforms.
- To clarify epidural pressure dynamics relative to atmospheric pressure.
Main Methods:
- Measured baseline epidural pressure in 39 patients using a closed system zeroed to the dorsal spine.
- Monitored epidural pressure changes during and after local anesthetic injection.
- Analyzed temporal relation of epidural pressure waves to arterial and venous waveforms.
Main Results:
- Subatmospheric epidural pressure was rare; baseline pressure averaged 7.7 +/- 3.9 mmHg.
- Patients with prior back surgery exhibited significantly higher baseline epidural pressure (11.8 +/- 3.4 mmHg) than those without (7.0 +/- 3.5 mmHg).
- Epidural pressure returned to baseline within 3 minutes after a 2-ml injection, but remained elevated after a 6-ml injection. Epidural pressure waveforms mimicked radial artery waveforms more closely than central venous pressure.
Conclusions:
- Lumbar epidural pressure, when referenced to zero at the dorsal spine, is consistently positive (greater than atmospheric pressure).
- Baseline epidural pressure is influenced by surgical history.
- Injection volume affects the duration of elevated epidural pressure.