Introduction:

The most common method used for maintaining a secured airway during general anaesthesia is endotracheal intubation using direct laryngoscopy¹.  Laryngoscopy, endotracheal intubation are linked with hemodynamic changes and increased sympathetic system activity². Such increased stimulus leads to increase in blood pressure, tachycardia, arrhythmia, increased oxygen consumption, decreased diastolic filling and reduced coronary blood flow³.

The above events start within 5 seconds of laryngoscopy and peaks in 1 to 2 minutes and returns to normal in 5 minutes in normal people⁴. In moribund patients and those with cardio vascular disease, hypertension and myocardial insufficiency it can cause catastrophic effects⁵.

Many drugs, either alone or in combination, are used for attenuating such hemodynamic response by increasing the depth of anesthesia, local anesthetic aerosols, high doses of opioids like fentanyl and recently alpha-2 agonist dexmedetomidine. In all these drugs a basic need is continuously felt among anesthetists to have such desired effects at a dose of drug that effectively surpasses all obnoxious stimuli with maximum safety margin⁶.

So this study is planned with above view to compare the effects of different dose of intravenous dexmedetomidine when used along with usual standard dose of intravenous fentanyl to elicit the safe dose of dexmedetomidine with maximum benefits.

Review of Literature:

A literary search on various articles revealed that Hall JE et al, Gerlach et al have studied the analgesic, sedation, anxiolytic, sympatholytic and blunting of exaggerated hemodynamic responses by administration of dexmedetomidine, mediated by the activation of  alpha-2 receptors located in the post-synaptic terminals in the central nervous system, which causes decreased neuronal activity, augmentation of the vagal activity^7,8.

Abou-Arab MH et al has highlighted that the use of intravenous opioids alone in varying doses for suppression of stress response has significant incidence of side-effects, especially with higher doses of opioids⁹.

Belleville JP et al has compared intravenous dexmedetomidine       1 mcg/kg and 2 mcg/kg used alone but with a significant incidence of bradycardia and hypotension in such higher doses¹⁰.

Based on the above literature we planned to study on comparison of 0.5 and 0.75 mcg/Kg of intravenous dexmedetomidine when used along with intravenous fentanyl to elicit the dose which has both the desired effect and also lesser side effects.

Aims and Objectives:

The study is aimed at:

·       Attenuation of hemodynamic response during laryngoscopy by use of intravenous dexmedetomidine along with intravenous fentanyl.

With the objectives:

·       To compare intravenous dexmedetomidine at 0.5 and        0.75 mcg /kg when used along with intravenous fentanyl at standard 2 mcg/kg.

·       To elicit the safe dose of intravenous dexmedetomidine among the two doses which has least side effect.

Material and Methods:

Study site                      :        Department of Anaesthesia,

Sri Ramakrishna Hospital.

Study population        :        Patients of age group 18 to 60 years posted for elective surgeries under general anesthesia during study period.

o   Inclusion Criteria:     

Ø ASA grade I and II patients.

Ø Patients scheduled for elective surgery under general anesthesia.

Ø Patients who provide consent for the study.

o   Exclusion Criteria:

Ø >ASA grade III patients.

Ø Patients with suspected difficulty in intuabtion resulting in more than one attempt or > 30 sec taken.

Ø Patients who refused to consent for the study.

Ø Patients allergic to study drug.

Ø Patient who are pregnant, patient on any antidepressant, antipsychotics, patients having history of drug abuse.

Study Design               : A prospective randomized double blinded study.

Sample size with justification: The sample size was estimated from previous study done by Telikota et al ¹¹. Taking the mean HR at 5 min, mean difference of 7.91, standard deviation of 9.1,  at 95% confidence limit, 90% power  and with expected 10 percent erroneous sample the sample size was calculated as 30 (27.7+2.7) in each group  using the below formula.

Sample size        = 2SD²(Z _alpha +Z _Beta)²/d²

SD    = standard deviation    = 9.1

 d      = mean differnece        = 7.91

From z table; Z _{alpha / 2} = Z _{0.05 /2} = Z _0.025 = 1.96 ; Z _beta = Z _0.90 = 1.2815

Sample size         = 2 X (9.1 X 9.1)² (1.96 + 1.28)² / ( 7.91 X 7.91 )²

= 27.7

Adding 10 percent erroneous to the above = 27.7 + 2.7

Sample size         = ~30 in each group

Groups       :       

Ø Group D1 [Dexmedetomidine 0.5mcg/kg]

Ø Group D2 [Dexmedetomidine 0.75mcg/kg]

Methodology:  After getting prior consent, patient participating in the study will be received at preop room and baseline vital parameters will be monitored. Randomization will be done using sealed envelope method. Then patients will be preloaded with IV fluids RL at 7ml/kg.

Patients will be then shifted to OT and connected to vitals monitor standard intubation procedure will be followed uniformly for all patients. Patients will be given intravenous ondansetron at 0.15mg/KG and intravenous glycopyrrolate at 0.004mg/kg and preoxygenated for 3 minutes

The study drug prepared by an anaesthetist who is not a part of the study will be administered as:

o   Group D1 will be infused with intravenous dexmedetomidine at 0.5 mcg/kg in 100ml NS over 10 mins

o   Group D2 with intravenous dexmedetomidine 0.75 mcg/kg  in 100ml NS over  10 mins respectively.

o   Both the groups will be infused with intravenous 2mcg/kg fentanyl in 5ml NS over 1 min.

Patients will be induced with propofol at 2mg/kg, after ensuring ventilation can be maintained patients will be given Atracurium at 0.4mg/kg and intubated after 3 minutes. Patients will be maintained with air, oxygen, sevoflurane titrated to effect.

Any episode of severe bradycardia <50 beats per minute in patients will be treated with intravenous atropine, severe hypotension of Mean Arterial Pressure < 60 mmHg will be treated with intravenous fluids, intravenous ephedrine and such patients will be excluded from the study

Parameters noted will be recorded as follows

o   ID number

o   Demographic data:

§  Age, Male/Female, Weight

o   and 6 readings of Heart Rate, Mean Arterial Pressure, SpO2 at

§  T _{preop room}

§  After infusion

§  Post intubation T _0min, T _1min, T _3min, T _5min.

Incision and surgery will proceed after 5 min

References:

1.     Yallapragada S, Vutukuri G, Vemuri N, Shaik M. Dexmedetomidine and sodium bicarbonate as adjuvants to epidural lidocaine: A comparative study. Ain-Shams Journal of Anaesthesiology. 2016;9(2):256.

2.     Black T, Kay B, Healy T. Reducing the haemodynamic responses to laryngoscopy and intubation. 1984;39(9):883–887.

3.    Bansal S, Pawar M. Haemodynamic responses to laryngoscopy and intubation in patients with pregnancy-induced hyperten- sion: effect of intravenous esmolol with or without lidocaine. International Journal of Obstetric Anesthesia. 2002;11(1):4-8.

4.    Rose D, Cohen M. The airway: problems and predictions in 18,500 patients. Canadian Journal of Anaesthesia. 1994;41(5):372-383.

5.    Kovac A. Controlling the hemodynamic response to laryngoscopy and endotracheal intubation. Journal of Clinical Anesthesia. 1996;8(1):63-79.

6.    Bajwa S, Singh A, Singh G, Gupta S, Panda A, Kaur J et al. Attenuation of pressor response and dose sparing of opioids and anaesthetics with pre-operative dexmedetomidine. Indian Journal of Anaesthesia. 2012;56(2):123.

7.    Hall J, Uhrich T, Barney J, Arain S, Ebert T. Sedative, amnestic and analgesic properties of small-dose Dexmedetomidine infusions. Anesthesia Analgesia. 2000;90(3):699–705.

8.    Gerlach A, Dasta J. Dexmedetomidine: An updated review. Annals of Pharmacotherapy. 2007;4(2):245–254.

9.    Abou-Arab M, Heier T, Caldwell JE. Dose of alfentanil needed to obtain optimal intubation conditions during rapid-sequence induction of anaesthesia with thiopentone and rocuronium. BJA: British Journal of Anaesthesia. 2007;98(5):604–610.

10.  Belleville J, Ward D, Bloor B, Maze M. Effects of intravenous dexmedetomidine in humans. Anesthesiology. 1992;77:1125-1133.

11.  Talikoti A, Sebastian B, Krishnamurty D. Attenuation of hemodynamic responses to laryngoscopy and endotracheal intubation with intravenous dexmedetomidine: A comparison between two doses. Indian Journal of Anaesthesia. 2017;61(1):48.

                         Summary

      Endotracheal intubation using direct laryngoscopy establishes a definitive airway during general anaesthesia. It provides maximal protection against the aspiration of gastric contents and allows for positive pressure ventilation with high airway pressures, when compared with facemask and supraglottic airway devices.  Laryngoscopy and endotracheal intubation are linked with hemodynamic changes and increased sympathetic system activity like increase in blood pressure, tachycardia, arrhythmia, increased oxygen consumption, decreased diastolic filling and reduced coronary blood flow. In moribund patients and those with cardio vascular disease, it can cause catastrophic effects. Various techniques, drugs in different doses has been used in past for attenuation of such hemodynamic responses. In this study we compared the attenuation of such hemodynamic responses namely heart rate, mean blood pressure by 0.5 mcg/kg and 0.75 mcg/kg of intravenous dexmedetomidine during laryngoscopy in induction technique where opioid is routinely used and to elicit the safe dose of dexmedetomidine with maximum benefits. Two groups of total 60 patients with 30 in each group were taken and study was carried out after randomization and double blinding. Standard intubation procedure was followed in both groups. The results were analysed and there was no statistically significant difference between both groups in attenuating the hemodynamic parameters namely heart rate, mean blood pressure during laryngoscopy. Hence we recommend 0.5 mcg/kg of dexmedetomidine as a safe dose for attenuating the hemodynamic response during laryngoscopy in induction technique where opioid is used.