Adding Magnesium Sulfate to Bupivacaine in Ultrasound Guided Paravertebral Block for Laparoscopic Cholecystectomy

Patients and Methods

Patients:

This is a blind prospective randomized controlled study that will be conducted for one year in Mansoura university hospitals after approval from the Institutional Research Board (IRB), Faculty of Medicine, Mansoura University, patients will be interviewed and written informed consents will be obtained. This study will include 26 patients of American Society of Anesthesiologists physical status grade I and grade II, of both sexes, aged between 20-60 years who will be scheduled for laparoscopic cholecystectomy.

Sample size calculation A Priori G-power analysis was done to estimate study sample size. A power of 90% was estimated with type I error of 0.05 to get an analgesic duration difference between groups of approximately 30% to yield of total sample size of 50 cases (25cases per group).

Randomization:

Fifty patients (number = 50) had laparoscopic cholecystectomy and bilateral paravertebral block during the study period. These patients were randomly allocated to undergo bilateral ultrasound guided paravertebral block. The groups allocated are concealed in sealed opaque envelopes which were not opened until patient consent was obtained.

The two groups were:

1. Control group: Bupivacaine Group (B group) Number=25 :

   Included patients who received 17 mL of 0.25% bupivacaine + 3 mL mili saline 0.9% in a total volume of 20 ml on each side.

2. Magnesium Group (M group) N=25 :

Included patients who received 17 mL of 0.25% bupivacaine + 3 mL of 75 mg milgram magnesium sulfate diluted in 0.9% saline in a total volume of 20 ml on each side.

All patients were performed by the same anesthetic team with standard procedure.

Methodology:

Anesthetic Management:

Preoperative Management:

All patients will be visited a day prior to surgery and will be assessed preoperatively by History, physical examination and laboratory evaluation (complete blood picture, coagulation profile, liver function and renal function tests). The study protocol and paravertebral block procedure will be explained to all patients. All patients will be familiar with the use of 0-10 visual analogue scale score identifying 0 as no pain and 10 as worst imaginable pain. Patient fast 6-8 hour before the time of surgery.

On arrival of the patient to the operating room routine monitoring will be applied, peripheral intravenous cannula 20 gauge will be inserted and 0.9% saline will be started to be infused. All patients will be premedicated using midazolam 0.03 mg/kg kilo intravenous.

Paravertebral block will be performed before induction of general anesthesia.

Technique of ultrasound guided paravertebral nerve block:

• Standard precautions for the performance of ultrasound-guided nerve blocks will be followed which include continuous routine monitoring, the skin overlying the injection site should be free of signs of infection and prepped with an antiseptic solution.
• Patient will lay in the lateral position, paravertebral block will be done using a 38 mm mile meter broadband linear array ultrasound probe.The probe surface in contact with the skin should be covered with a sterile adhesive dressing.
• A sagittal paramedian view of the paravertebral space will be obtained by applying the probe at a point 2.5 cm centimeter lateral to the tip of the spinous process in a vertical orientation, The fifth thoracic vertebral level will be identified by palpating and counting down from the seventh cervical body.
• The midpoint of the transducer will be aligned midway between the transverse processes of thoracic vertebra T5 and T6, 4 ml of 1 % lidocaine was injected subcutaneously at the puncture site,and 22 gauge spinal needle will be inserted in an in plane approach in a cephalad orientation and will be advanced perpendicularly to all skin planes under direct vision to puncture the superior costotransverse ligament where a click may be appreciated.
• Following negative aspiration, 1-2 ml of study solution will be injected to verify correct position of the needle tip and the rest of study solution will be injected in fractioned doses following intermittent aspiration between the superior costotransverse ligament and the parietal pleura which will be displaced anteriorly by the injectate.
• Similar approach will be used for the paravertebral block on the other side.
• Sensory block over the area of surgical incision will be confirmed by loss of cold sensation using an alcohol swab and pinprick sensation using a 23 G gauge needle every 3 mint until 15 min after injection of the study solutions and before starting general anesthesia.

General Anesthesia:

General Anesthesia will be induced using intravenous propofol (2-3 mg/kg), fentanyl IV (1µ/kg) microgram/kilo and atracurium besylate (0.6 mg/kg) to facilitate intubation. Then patient will be mechanically ventilated using a volume control mode with Tv 6-8ml/kg, respiratory rate 10-14 breath/min and I.E. ratio 1:2 to maintain Etco2 35-40 mmHg mli mercury. Anesthesia will be maintained using minimum alveolar concentration of isoflurane 1.2% and 60% air in O2 mixture with top up dose of atracurium. Intraoperative IV fluids will be given per body weight and according to intraoperative loss.

All patients will be extubated at the end of surgery after neuromuscular reversal with administration of neostigmine (0.05 mg/kg) and IV atropine (0.02 mg/kg) and fulfilling the criteria of extubation. The duration of the surgery will be recorded.

Monitoring:

Intra-operative assessment

• In operating room, monitoring will be achieved by five lead electro cardi gram, oxygen saturation and non-invasive mean arterial blood pressure.
• Base line values of heart rate, oxygen saturation and non-invasive mean arterial blood pressure will be collected before and after paravertebral block, just after induction of anesthesia, at skin incision, then recording will be done every 15 mint till the end of the first hour and then every 30min interval till the end of surgery.
• Sensory block onset will be defined when the patient subjectively evaluate the intensities of both cold and pinprick sensations in the blocked side decrease 75 % or more.
• Duration of surgery will be defined as the time from induction to discharge from the operating room will be recorded.
• In case of increased in intra-operative systolic blood pressure and heart rate of more than 20% of baseline for longer than 5min, incremental doses of fentanyl IV 0.5µ/kg will be given and the case will be excluded.

Postoperative Assessment:

• On admission into the post operative care unit, all vital data \& hemodynamics (non-invasive mean arterial blood pressure, heart rate, and oxygen saturation) will be recorded at 1, 2, 6, 12 and 24 hrs. postoperative
• Post-operative complications will be recorded including post-operative nausea and vomiting treated by metoclopramide, hypotension treated by phenylephrine drops, bradycardia treated by atropine or pneumothorax, respiratory depression and chest pain, respiratory depression is defined as respiratory rate less than 8 per minute or oxygen saturation below 90%.

Statistical analysis The statistical analysis of data will be done by using excel program for figures and Statistical Package for Social Science program version 22. To test the normality of data distribution Kolmogorov- Smirnov test will be done only significant data revealed to be nonparametric. Unpaired student-t test will be used for comparisons of numerical variables between-group, if its assumptions were fulfilled, otherwise for non-parametric; the Mann-Whitney test will be used. The description of data done in the form of mean (±SD) stander division for quantitative data and frequency and proportion for qualitative data. Any difference or change showing probability (P) less than 0.05 will be considered statistically significant at confidence interval 95%.