Sequential and Mixture Injection of Opioids and Hyperbaric Bupivacaine
Status:
Completed
Trial end date:
2021-03-17
Target enrollment:
Participant gender:
Summary
Neuraxial anesthesia, especially the subarachnoid block, is the preferred method for LSCS.
The intrathecal spread of local anesthetic drugs is unpredictable. However, Baricity, which
is the relative density of local anesthetics to that of CSF, is a key determinant of the
local anesthetic spread within the subarachnoid space. Alterations in the baricity of a
solution to the extent of 0.0006 g/ml-1 can alter the spread of local anesthetic solution in
CSF. Patients features such as position, weight, height, and age, and local anaesthetic
characteristics such as density, PH, and temperature may play a role as well.
Bupivacaine is the main local anaesthetic used frequently for the subarachnoid block.
Hyperbaric bupivacaine has dextrose added at a concentration of 80 g/ml to increase its
density to 1.0262 which is higher than that of cerebrospinal fluid (CSF), leading to a more
predictable spread after intrathecal injection.
Opioids such as morphine and fentanyl are commonly injected as adjuvants to hyperbaric
bupivacaine. Their synergistic role leads to satisfactory block at smaller subtherapeutic
doses of bupivacaine which minimizes the associated side effects. The combination of fentanyl
which is lipophilic opioid and morphine which is hydrophilic opioid results in rapid onset
and prolonged course of perioperative analgesia. In an in vitro study, the mean densities of
fentanyl and morphine were found to be 0.9957 and 1.0013 respectively while the mean density
of CSF in term pregnant woman is 1.000306. Thus, opioids spread freely within the CSF
interacting on the spinal and supraspinal opioid receptors. They have a synergistic effect to
bupivacaine leading to adequate sensory blockade with lesser hemodynamic adverse effects.
Nevertheless, opioids are commonly mixed with hyperbaric bupivacaine in a single syringe
before intrathecal injection. This practice alters the density and PH of the mixture which
may impact the pharmacokinetics of each individual drug. Therefore, we hypothesize in this
study that separate injection of opioids and hyperbaric bupivacaine may improve their
intrathecal spread. This will not only improve the quality of anesthesia, but it will also
decrease the associated hemodynamic adverse events and the incidence of undesired high
sensory block levels, which all will increase the perioperative patient satisfaction.