Dare I assume only anesthesia folks have a knowledge of spinal anatomy? And I'm a "guy", but the MD puts me on the same ground as you. The role of Asst Program Director of an ACGME Pain Fellowship probably put me ahead of you when it comes to spinal anatomy. And your lack of understanding regarding SPINAL (extracranial) CSF volume as it relates to dehydration as well as your pointing out that I do not have experience in blindly putting a needle into the thecal sac has what to do with the price of tea in China?
Titre du document / Document title
Cerebrospinal fluid formation and absorption in dehydrated sheep
Auteur(s) / Author(s)
CHODOBSKI A. (1) ; SZMYDYNGER-CHODOBSKA J. (1) ; MCKINLEY M. J. (1) ;
Affiliation(s) du ou des auteurs / Author(s) Affiliation(s)
(1) Howard Florey Institute of Experimental Physiology and Medicine, University of Melbourne, Parkville, Victoria 3052, AUSTRALIE
Résumé / Abstract
Cerebrospinal fluid (CSF) plays an important role in the brain's adaptive response to acute osmotic disturbances. In the present experiments, the effect of 48-h dehydration on CSF formation and absorption rates was studied in conscious adult sheep. Animals had cannulas chronically implanted into the lateral cerebral ventricles and cisterna magna to enable the ventriculocisternal perfusion. A 48-h water deprivation altered neither CSF production nor resistance to CSF absorption. However, in the water-depleted sheep, intraventricular pressure tended to be lower than that found under control conditions. This likely resulted from decreased extracellular fluid volume and a subsequent drop in central venous pressure occurring in dehydrated animals. In conclusion, our findings provide evidence for the maintenance of CSF production during mild dehydration, which may play a role in the regulation of fluid balance in the brain during chronic hyperosmotic stress.
Revue / Journal Title
American journal of physiology. Renal physiology ISSN 1931-857X
Source / Source
1998, vol. 44, no2, pp. F235-F238 (22 ref.)
Granted their sheep, and I'm sure you have more experience putting things in sheep than I do, but still.
If you cannot get fluid to flow, you cannot be certain your needle tip is where you think it is.
http://www.cerebrospinalfluidresearch.com/content/5/1/11
I have never (outside of LP's during med school and Baclofen trials for Peds PM&R) thought about putting my MSO4 or Dilaudid test dose, or the Medtronic catheter into a space that I could not verify both with clear CSF flowing and with a myelogram on my fluoro. I also have no problem dumping in 50-70mg lidocaine w/o epi and MPF to allow a more comfortable tunneling of my catheter and pump placement. And I have an Anesthesiologist at the head of the bed for MAC.
Also, reading is Fun. SO is busting your balls knowing you take it so hard.
Dry tap and spinal anesthesia
Krishna Ramachandran, FRCA and Nandakumar Ponnusamy, DA
University Hospitals Coventry and Warwickshire, Coventry
To the Editor:
A major advantage of spinal anesthesia is its definitive endpoint i.e., the free flow of cerebrospinal fluid (CSF).1 Occasionally the needle is felt to be in the correct space, but on withdrawing the stylet there is no CSF flow (dry tap). Common sense dictates that the procedure be repeated, but if the outcome remains the same and the patient refuses general anesthesia the options are limited. Consent was obtained from the hospitals Research and Development Committee and the patient was informed of our intention to publish this case history.
A 60-yr-old obese (120 kg) male with a fear of general anesthesia, was admitted for removal of an infect-ed pin and plate from his tibia. Past history included a cervical laminectomy four years previously. He had been admitted for the same procedure (removal of pin and plate) a few months earlier. Spinal anesthesia was attempted, but abandoned after seven attempts, with no notation as to the nature of the difficulty experienced. As the patient refused a general anesthetic, surgery was postponed. On the current admission he remained adamant that he would only consent to regional anesthesia. A 24G Sprotte needle (Pajunk, Geisingen, Germany) was introduced into the L34 interspace in the sitting position and although a give was felt, no CSF was seen. The procedure was repeated at the L23 interspace with the same result. Aspiration using a 2-mL syringe also failed to produce any CSF. At this point we injected 3 mL of heavy bupivacaine 0.5% in the L23 space and, within ten minutes he had a sensory block up to T12. Surgery proceeded uneventfully.
Causes of dry tap include a blocked needle, needle in the wrong space, spinal surgery and low CSF pressures. It is possible that in patients with absent CSF or very low CSF pressure, the subarachnoid space is obliterated as the arachnoid "collapses" on the pia. This increases the volume of the subdural space and may explain the absence of CSF. In this setting an epidural may be considered, but is not without potential drawbacks as a dural tap may go unrecognized. A final block would not have subjected the patient to any undue risk because of the small volume of local anesthetic involved. While it is not our intention to advocate this practice in every patient who has a dry tap, we share this experience due to its infrequent clinical presentation.
Man this is fun.
