Effect of Dexmedetomidine infusion on Minimum Alveolar Concentration of Isoflurane And Quality of Surgical field in patients undergoing Middle ear surgery guided by Bispectral Index Analysis

After approval from institutional ethics committee patients fulfilling the inclusion criteria undergoing middle ear surgeries under general anaesthesia with or without dexmedetomidine will be observed.

After thorough preoperative evaluation, written informed consent will be obtained from the patients. Monitoring will include electrocardiography, pulse oximetry (SPo2), Etco2, NIBP, end tidal concentration of isoflurane, MAC of isoflurane and BIS. Baseline readings will be noted before premedication.

Routine induction protocol will be followed which will consists of premedication with Inj.Glycopyrrolate 0.04mg/kg, Inj.Midazolam0.02mg/kg, Inj.Fentanyl 2mcg/kg. This is then followed by induction with inj.Propofol 2-2.5mg/kg and Inj.Vecuronium 0.08-0.1mg/kg to facilitate tracheal intubation. Anesthesia is then maintained on isoflurane in O2 and Air (50:50) at flow rate of 4lit/minute with or without dexmedetomidine infusion in a loading dose of 1mcg/kg for 10minutes followed by a maintenance dose of 0.5mcg/kg. MAC of isoflurane at BIS value of 45-50 will be noted. At this time the dial concentration of isoflurane, end tidal concentration of isoflurane, inspired concentration of isoflurane will also be noted. Flow rates of gases are then decreased to 2lit/min. MAC of isoflurane at BIS value of 45-50, inspired concentration of isoflurane, end tidal concentration of isoflurane will be noted down every 10 minutes.

Muscle relaxation during surgery is maintained on intermittent doses of Inj.Vecuronium.

Any increase in heart rate and MAP of more 20% from the baseline despite keeping the BIS of 45-50 will be noted and treatment given will be noted. Any decrease in heart rate and MAP of more than 20%will be noted and treatment given for it will be noted.

Intraoperative quality of surgical field will be evaluated using a Fromme’s bleeding score which is as follows. (12)

Table showing the bleeding score.

Grade

Parameter/Observation

  |Grade 0

No bleeding

  |Grade 1

Slight     bleeding-             No                 suction required

  |Grade 2

Slight bleeding- Occasional suctioning required

  |Grade 3

Slight     bleeding-Frequent suctioning required

  |Grade 4

Moderate bleeding-Frequent suctioning required.Bleeding threatens the surgical field immediately after suction is removed.

  |Grade 5

Severe bleeding-Constant suctioning required. Bleeding appears faster than that can be removed by suction. Surgery is impossible.

A category scale values of 2 and 3 in the score is considered ideal.

 Dexmedetomidine infusion is stopped 30 minutes before completion of surgery. Isoflurane is stopped 20 minutes before completion of surgery. At the end of surgery routine extubation protocol will be followed.MAC of isoflurane when the patient becomes responsive to command will be noted. Time from discontinuation of dexmedetomidine infusion to responsiveness to oral commands will be noted. Time required to achieve BIS of 90 will also be noted. Total dose of fentanyl required will be noted.

 Total consumption of isoflurane will be noted using Dion’s formula.

 Parameters to be studied.

 1)  Minimum alveolar concentration of isoflurane at BIS value of 45-50

2)  Fraction of inspired concentration of isoflurane

3)  End tidal concentration of isoflurane

4)  Quality of surgical field

5)  Total dose of intraoperative fentanyl

6)  Total consumption of isoflurane

Total consumption of isoflurane will be calculated using Dion’s formula (13)

Fresh gas flow(lit permin )×dial concentration(%)×1000 isoflurane fluid volume(ml)= ×Period of each instance.

Conversion factor

 A conversion factor is the amount of volatile agent vapour derived from 1 ml of fluid agent.