INTRODUCTIONSpinal anaesthesia is the most common technique of regional anaesthesia used for lower abdominal and lower limb surgeries. First spinal anaesthesia was performed by August Bier in 1898 by using 0.
5% cocaine. Subarachnoid block provides effective sensory and motor blockade. A wide variety of local anaesthetic drugs are available for spinal anaesthesia namely Lidocaine, Bupivacaine.
.Lignocaine was the local anaesthetic of choice for decades due to its rapid onset of action and good motor block. But its use was limited by its short duration of action and its implication in causation of transient neurological symptoms and cauda equina syndrome following intrathecal injection(1, 2).Bupivacaine is one of the commonest local anaesthetics used which has longer duration of action and its potency is higher than lignocaine(3). But it can cause profound myocardial depression and even cardiac arrest when used in higher concentration or when accidentally administered intravascularly(4).Ropivacaine, is a long acting amino amide local anaesthetic structurally similar to bupivacaine.
It produces effects similar to other local anaesthetics via reversible inhibition of sodium ion influx in nerve fibres. It is a racemate, pure S(-) enantiomer, developed for the purpose of reducing potential toxicity and improving sensory and motor block.(5)Ropivacaine is less lipophilic than bupivacaine and is less likely to penetrate large myelinated motor fibres. The reduced lipophilicty is associated with decreased potential for central nervous system toxicity and cardiotoxicity(5). It produces similar sensory block and reduced motor block to that of an equivalent dose of bupivacaine due to its less lipophilicity(5).Various factors can affect the distribution of local anaesthetic solutions in CSF.
These include patient’s age, height, anatomical configuration of spinal column, site of injection, direction of needle during injection and density of CSF, baricity(6), density and volume of local anaesthetic solution and position of the patient.Higher concentration of glucose free isobaric ropivacaine solutions results in variable spread of analgesia but with good quality of motor block with higher concentration, adequate for the proposed surgery(7, 8, 10). However in comparison with bupivacaine, plain ropivacaine produces rapid postoperative recovery of sensory and motor blockade(10).Previous studies had shown that, hyperbaric solution of ropivacaine produces predictable and consistent anaesthesia for surgery than plain one(10, 11), but with a duration shorter than bupivacaine(12, 22).
Although several studies have examined the effects of intrathecal ropivacaine in both women in labor(23) and patients undergoing minor surgery. Less number of studies have evaluated its use in anaesthesia for major surgery.Hence this study is undertaken to compare plain and hyperbaric solutions of ropivacaine in spinal anaesthesia in patients undergoing elective lower abdominal and lower limb surgeries.