In the study conducted by Wideside et al (17) the onset time for sensory block after 3 ml of intrathecal 0.5% ropivacaine was 5 min and for that of 3 ml of 0.5% bupivacaine was 2 min (pvalue = 0.0046) they attributed the difference to baricity
of the solutions used.
Height of block level is difficult to predict and it depends upon position of patient, site and speed of injection and properties of anaesthetic agent such as baricity
, volume and dose.
The effect of posture and baricity
on the spread of intrathecal bupivacaine for elective caesarean delivery.
Four (0.6%) spinal anesthetics included hyperbaric bupivacaine (3.75-7.5 mg) in an admixture with isobaric mepivacaine for added baricity
of local anesthetic has an important role on spinal blockade effects.
(1,15) Several studies have been undertaken in the past to evaluate the clinical efficacy and toxicology of these local anaesthetics in different dosage and baricity
. Most of these clinical studies suggested that levobupivacaine was slightly less potent than bupivacaine but more potent than ropivacaine.
Thirdly, different baricity
of intrathecal solution of ropivacaine may be another factor.
of the local anaesthetic agent is the major factor that influences the distribution of the local anaesthetic in the subarachnoid space .
a strict unilateral block was achieved by manipulating different factors influencing the spread of anaesthetic agent such as local anaesthetic baricity
, patient's position during and after injection, anaesthetic dose and injection site.
EVE, intrathecal drug baricity
and patient position
Factors affecting the spread of the local anaesthetic solution Factor Mechanism Baricity
of the local Blocks can be better controlled with anaesthetic solution hyperbaric solutions Position of the Level of the block may change if the patient patient's position is altered Concentration of and A higher concentration produces a denser volume injected block; a larger volume produces a block over a larger area Speed of injection Rapid injection produces eddy currents within the CSF and a less predictable spread Increased abdominal Leads to engorgement of the epidural pressure veins and reduction in CSF volume
The majority of previous work did not show any effect of baricity
on the drug spread within the cerebrospinal fluid in the obstetric population.4 This is probably due to gravid uterus that causes general flattening of the spinal column with the loss of thoracic depression.