Hyperbaric Prilocaine 2% for spinal anesthesia 60 or 80 mg: a dosing study in day care patients.

Until recently no short acting spinal local anesthetic was registered in the
Netherlands. Older anesthetics such as articaine were not reregistered by their
manufacturers. Short acting spinal local anesthetics are important in our
practice for day case surgery. Up till now we used articaine based on dutch
legislation enabling use if no registered medication is available.
Recently prilocaine 2% hyperbaric (prilotekal ®) was registered in the
Netherlands for intrathecal use. We plan to switch to prilotekal. Manufacturers
dosing advice is 60 mg with a maximum of 80 mg. However there is only limited
and controversial literature with regard to dosing. For arthroscopy of the knee
dosages of 20 mg with 20 microgram fentanyl up to 60 mg were used with good
results. For bilateral open inguinal hernia repair a dosage of 50 mg was
sufficient, although the level of anesthesia did not extend above the level of
the ninth dermatome. These findings are not in line with our limited
experience. In our practice bilateral open inguinal hernia repair is a
challenging operation in day case surgery. A high anesthetic level up to the
fourth thoracic dermatome is needed for the duration of the surgery. If this is
not achieved manipulation of the peritoneum will be painful. Spinal anesthesia
is most intense and long lasting in the lumboscral segments and will rise to
thoracic levels where it will be short lasting. Our experience with 80 mg so
far is just acceptable. This may be due to longer operation times and a
different technique as suggested in a recent review. This review also notices
that little data are available with regard to anesthetic spread in the elderly.
High dosages will reduce failure rated and reduce the use of rescue medication
or general anesthesia. However lower doses reduce the severity and duration of
adverse effects of spinal anesthesia such as hypotension, bradycardia and high
thoracic block extending above the required level. Low doses will also promote
early discharge.
Instead of a trial and error method to find the right dose in our practice we
aim to perform a proper dose effect study.

To obtain a time effect curve of prilocaine 2% hyperbaric for intrathecal use
in day case surgery

Patients will receive 60 or 80 mg. Block randomisation in blocks of 20 will be
used. Only the anesthetist performing the spinal anesthetic will know the
dosage. Patient and observer are blinded. A copy of the randomisation list is
available in the OR in case of an emergency. If the attending anesthesiologist
has important medical reasons to administer a different dose this will be
recorded. This decision has to be made before randomisation

For every patient these data will be recorded:

height of the anesthetic block (sensibility and motor) every 5 minutes up till
incision. As far as possible during surgery every 15 minutes
height of the anesthetic block (sensibility and motor) on arrival in the
recovery room and then every 15 minutes
height of the anesthetic block (sensibility and motor) on the ward every 30
minutes until discharge or complete resolution of block
amount of fluids ingested up till 6 hours before surgery
the amount of fluid infused during and after surgery and the amount of fluids
taken postoperatively
bladder volume pre and postoperatively and at discharge if the patient did not
urinate yet
time of first urine production. If the patient does not urinate during
admission, he/she will be asked to record the time at home
bladder catheterisation if necessary and volume
additional analgesics per and postoperatively
use of vasopressors
patient satisfaction with the procedure
time of discharge, night admission if necessary and reason for night admission

Use of 60 mg or 80 mg prilocaine 2% hyperbaric for lower limb surgery

Patients do get the same anesthetic as they would have had except the dose is
fixed in advance. They will only have more tests for block height (sensibility
for ice), motor response and measurement of bladder volume with ultrasound.
The risks are thus the same as for patients outside the study.