Background: The antiinflammatory and antinociceptive properties of magnesium by inhibiting calcium entry into the cell and N-methyl-D-aspartate-type (NMDA) glutamate receptors may have a potential role in reducing post operative sore throat (POST).^[1] Several studies also demonstrated efficacy of magnesium sulfate to reduce incidence and severity of POST.^[2,3]

On the other hand, recent studies with topical zinc has shown that it directly activates receptors that promote epithelial repair and high dose of oral zinc sulfate decreases the intensity of mucositis, xerostomia and pain in individuals undergoing chemotherapy or radiotherapy treatments.^[4,5] Recently in 2018, one study has observed significant reduction in the incidence and severity of POST compared to placebo when zinc sulfate lozenges were used preoperatively before endotracheal intubation.^[6]

Thus, in the present study we have compared the incidence and severity of post operative sore throat following endotracheal intubation in patient undergoing laparoscopic cholecystectomy after pre operative magnesium sulfate and zinc sulfate gargle.

Methodology: After obtaining permission from Institutional Ethics Committee and written informed consent from patients, 132 adult patients who met inclusion and exclusion criteria will be randomly allocated to three equal groups (n = 44 in each group) using computer generated random number list.

Patients in Group A will receive magnesium sulfate solution 20 mg/kg dissolved into 20 ml of 5% dextrose solution, group B will receive zinc sulfate 170 mg dissolved into 20 ml of 5% dextrose solution , group C will receive 20 ml of 5% dextrose.

Patients will be asked to gurgle slowly with the solution as per allotment of the group and drug for 30 sec, 15 min before induction of anesthesia. The solution for gargle will be wrapped in colored nontransparent glasses to ensure blinding. The anesthesiologist distributing the solution for gargling will be unaware of the constituent of the drug and allotment of the group and similarly resident doctors keeping records of different parameters will also be unaware of the group allotment.

Trachea will be intubated with a soft seal cuffed sterile polyvinyl chloride ETT with a standard cuff and an internal diameter of 7 mm for women and 8 mm for men. Laryngoscopy and tracheal intubation will be performed by an experienced anesthesiologist after ensuring maximum neuromuscular blocking effect as assessed by train‑of‑four (TOF) guard. Tracheal tube cuff will be inflated with sterile water until no air leakage could be heard with a peak airway pressure at 20 cm H₂O. Those patients who required more than one attempt for passage of the tube will be excluded from the study.

The patients will be interviewed in a standard fashion by an anesthesiologist (blinded investigator) who is unaware of the group allocation. On arrival in the postanesthesia care unit (0 h), and then at half hourly interval for 2 hours POST will be graded on a four point scale (0–3).^[25] After 2 hour POST score will be assessed at 4 hr, 6 hr, 12 hr and 24 hr after extubation. Vital signs, oxygen saturation (SpO₂), visual analogue score and sedation score will be recorded at the same time.

Results will be analyzed by unpaired Student’s t-test for parametric data and Mann-Whitney U-test for nonparametric data when two groups will be compared. One-way ANOVA for parametric data and Kruskal-Wallis test for nonparametric data will be used while comparing three groups. Fisher’s exact test and Chi-square test will be used for categorical data as appropriate. P < 0.05 will be considered statistically significant. All statistical tests will be done by "STATISTICA" version 9 (StatSoft, Inc. Tulsa, OK, USA).

Expected outcome: We expect that both of the drugs will reduce the POST following laryngoscopy and endotracheal intubation but which one is superior will only be known after the completion of study.

References:

1) Fawcett WJ, Haxby EJ, Male DA. Magnesium: Physiology and pharmacology. Br J Anaesth 1999; 83:302–20.

2) Borazan H, Kececioglu A, Okesli S, Otelcioglu S. Oral Magnesium Lozenge Reduces Postoperative Sore Throat: A Randomized, Prospective, Placebo-controlled Study.  Anesthesiology 2012;117(3):512-518.

3) Teymourian H, Mohajerani SA, Farahbod A. Magnesium and Ketamine Gargle and Postoperative Sore Throat. Anesth Pain Med. 2015;5(3):e22367.

4) Arbabi-kalati F, Arbabi-kalati F, Deghatipour M, Ansari Moghadam A. Evaluation of the efficacy of zinc sulfate in the prevention of chemotherapy-induced mucositis: a double-blind randomized clinical trial. Arch Iran Med. 2012 Jul;15(7):413-7.

5) Sharir H, Zinger A, Nevo A, Sekler I, Hershfinkel M. Zinc released from injured cells is acting via the Zn2+-sensing receptor, ZnR, to trigger signaling leading to epithelial repair. J Biol Chem. 2010 Aug 20;285(34):26097-106.

6) Farhang B, Grondin L. The Effect of Zinc Lozenge on Postoperative Sore Throat: A Prospective Randomized, Double-Blinded, Placebo-Controlled Study. Anesth Analg 2018; 126(1):78–83.