Hyperbaric 0.75% Ropivacaine versus hyperbaric 0.5% Bupivacaine for spinal anesthesia in adults undergoing lower limb orthopedic surgeries

Background

Spinal anesthesia is one of the commonest anesthetic procedures. It is a neuraxial anesthesia technique in which local anesthetic is placed directly in the intrathecal (subarachnoid) space. The first case of spinal anesthesia in humans was performed by August Bier in 1898 using the local anesthetic cocaine. Since then it has become a choice of anesthetic procedure for a variety of surgical procedures including gynecological, orthopedic, plastic, vascular and general surgeries. There are two forms of commercially available spinal anesthetic drugs: isobaric, with a density equal to that of cerebrospinal fluid (CSF), and hyperbaric with a density heavier than CSF which is prepared by adding dextrose to the local anesthetic. The difference in densities affects their diffusion patterns and thus determine the effectiveness, speed of onset, block height and side-effect profile of the drug; hyperbaric solutions provide a rapid motor block.[1,2] In the past, various local anesthetics like procaine, mepivacaine, lignocaine, Bupivacaine and Ropivacaine have been used to provide spinal anesthesia. Of these, hyperbaric Bupivacaine has been the undisputed drug of choice for many decades. Quite recently, hyperbaric Ropivacaine (0.75%) has been launched in the Indian market for use in spinal anesthesia as an alternative. Ropivacaine is a pure S(-) enantiomer and compared to a racemic Bupivacaine and is less lipophilic. This accounts for Ropivacaine being less cardiotoxic and neurotoxic.[3,4] Isobaric Ropivacaine has been extensively used and proven to be a good local anesthetic in peripheral nerve blocks and epidural anesthesia. It has also been tried in spinal anesthesia. Being less lipophilic, Ropivacaine penetrates less into large myelinated Aβ motor fibers than pain-transmitting Aδ and C nerves. This provides a more selective sensory block and a Quicker regression of motor blockade which is an advantage as it allows early postoperative mobility which in turn increases recovery and overall patient satisfaction.[4]

Rationale For The Study

Isobaric Ropivacaine has been in use for a few decades and many studies pertaining to its use in epidural and peripheral nerve blocks have been published. Comparative studies of the same intrathecal doses of Ropivacaine and Bupivacaine have found that Ropivacaine is well tolerated and provides an adequate block for total hip arthroplasty. A more rapid postoperative recovery of sensory and motor function has been observed with Ropivacaine.[5] Although use in spinal anesthesia has been limited due to non availability of the hyperbaric formulation of the drug in the market till now, still studies including hyperbaric Ropivacaine have been performed by preparing a 0.5% Ropivacaine mixture using a 0.75% drug and mixing it with 25% Dextrose. We have not come across any studies involving 0.75% hyperbaric Ropivacaine for spinal anesthesia in any surgeries. So we plan to conduct a study to find out the efficacy and safety of intrathecal hyperbaric 0.75% ropivacaine in comparison to hyperbaric 0.5% bupivacaine in adults undergoing lower limb surgeries.

AIMS AND OBJECTIVES

Aim: To compare the efficacy and safety of 0.75% hyperbaric Ropivacaine versus 0.5% hyperbaric Bupivacaine for spinal anesthesia in patients undergoing lower limb orthopedic surgeries

Objectives:

1. To compare the time taken to achieve and total duration of adequate sensory blockade (level of block upto T10) achieved in spinal anesthesia with hyperbaric 0.75% Ropivacaine and hyperbaric 0.5% Bupivacaine in patients undergoing lower limb orthopedic surgeries.

2. To compare the motor block achieved with both the study drugs and time taken for full regression of the motor block.

3. To compare both the study groups for time for first analgesic demand postoperatively.

4. To compare perioperative blood pressure, SpO2 and heart rate among the study groups.

5. To compare the incidence of adverse effects ( bradycardia, hypotension, failed spinal anesthesia) among both the study groups.

MATERIALS AND METHODS

Place of Study: Dr Susheela Tiwari Hospital, Haldwani

Duration of study: Six months

Study Design: This will be a prospective randomized single blinded study

Study Population: Patients male or females 18 to 70 years old admitted to the institute for lower limb orthopedic procedures requiring spinal anesthesia.

Sample size: Assuming a marginal error of 12.06 % according to the study by Mc Namee, confidence interval of 95%, the minimum sample required comes to be 67. So we will take a sample size of 70 equally divided into the two groups.

Inclusion Criteria :

Males or females

18-70 years of age

American society of anesthesiologists (ASA) grade 1 or 2

Orthopedic lower limb surgeries

Spinal anesthesia

Exclusion Criteria :

Patients not in the desired age group

ASA grade >2

Coagulopathy

Patients with known allergy to study drugs

Patient refusal for spinal anesthesia

Patient who require epidural along with spinal anesthesia

Patient requiring conversion of spinal to general anesthesia

Expected duration of surgery more than 3 hours

Methodology:

Patients enrolled in the study will be posted for surgery after preoperative anesthetic evaluation as per existing protocols. The anesthetic procedure and the study will be thoroughly explained to the patients and consent for anesthesia and participation in the study will be taken. All patients will be kept for preoperative fasting according to the standard protocols and on the morning of surgery, they will be given tablet Clonazepam 0.5 mg orally. The enrolled patients will be randomly allotted to two groups using online software. Group B will receive spinal anesthesia with 3.2 ml of inj. Bupivacaine (0.5%) heavy and group R will receive spinal anesthesia with 3.2 ml of inj. Ropivacaine (0.75 %) heavy.

After taking a patient to the operation room, standard ASA monitoring will be attached and iv cannula accessed. The patients will be placed in sitting position and the back area will be sterilized using povidone iodine and spirit and draped using a sterile sheet as per existing protocols. Using a 25 or 26 G spinal needle, spinal anesthesia will be provided to the patient using either Bupivacaine heavy or Ropivacaine heavy as per the allotted group.

The patient will be placed supine and the patient be monitored for level of sensory block, motor block, blood pressure, heart rate, SpO2. Surgery will be started when the sensory level of block is at least T10. Time of requirement of first rescue analgesic will be noted Any adverse effects seen during the study period will be noted.

Statistical analysis: The data collected from the study will be filled in spreadsheet format and analyzed using appropriate statistical tools.

REFERENCES

1. Greene NM. Distribution of local anesthetic solutions within the subarachnoid space. Anesth Analg. 1985;64:715–730.

2. Uppal V, Retter S, Shanthanna H, Prabhakar C, McKeen DM. Hyperbaric Versus Isobaric Bupivacaine for Spinal Anesthesia: Systematic Review and Meta-analysis for Adult Patients Undergoing Noncesarean Delivery Surgery. Anesth Analg 2017;125(5):1627–37.

3. Simpson, D., Curran, M.P., Oldfield, V. et al. Ropivacaine. Drugs 65, 2675–2717 (2005).

4. Gaurav Kuthiala and Geeta Chaudhary. Ropivacaine: A review of its pharmacology and clinical use. Indian J Anaesth. 2011 Mar-Apr; 55(2): 104–110.

5. D. A. McNamee, A. M. McClelland, S. Scott, K. R. Milligan, L. Westman, U. Gustafsson, Spinal anaesthesia: comparison of plain ropivacaine 5 mg ml–1 with bupivacaine 5 mg ml–1 for major orthopaedic surgery, BJA: British Journal of Anaesthesia, Volume 89, Issue 5, November 2002, Pages 702–706.