Effect of Pretreatment of Lignocaine Versus Midazolam in Prevention of Etomidate Induced Myoclonus.

INTRODUCTION:

General anaesthesia is loss of consciousness induced after administration of one or more general anaesthetic agent with overall aim of inducing sleep, amnesia, analgesia and skeletal muscles relaxation. Choosing an induction agent is a very vital step in commencing general anaesthesia1. Use of sedatives can prevent or minimize potentially harmful physiologic affects of airway manipulation that include increase in heart rate, BP, and raised intracranial pressure.

Etomidate, imidazole-derived, sedative-hypnotic agent, blocks neuroexcitation by its direct action on the gamma amino butyric acid (GABA) receptor complex1.Because of its many desirable properties like rapid onset of action, profound hypnosis, minimal histamine release, hemodynamic stability, minimal respiratory depression, and favorable cerebral effects, etomidate is considered as an ideal induction agent2. Concerns with etomidate include adrenal suppression and myoclonus3, 4.

30 to 60% of unpremedicated patients develop myoclonic movements after an induction dose (0.3 mg/kg) of etomidate1. Myoclonus is described as the involuntary contraction of some muscle fibers, leading to short observable movements of the body, more pronounced with the limbs5. In emergency scenarios, myoclonus can lead to increment in the chances of regurgitation and aspiration.

Various drugs like Lignocaine, Midazolam, Magnesium, Dezocine and dexmedetomidine have been used as pretreatment for reducing myoclonus after etomidate injection but the best drug for the purpose is yet to be discovered6, 7, 8, 9. Ideally a pretreatment drug should be short-acting, should affect respiration and hemodynamic minimally, and should not prolong the recovery period.

Lignocaine belongs to amide group of local anaesthetics.Lignocaine alters signal conduction in neuronal cell membrane8. Various studies have been conducted on lignocaine being used as a pretreatment drug; before propofol induction to reduce pain or etomidate to prevent myoclonus associated with etomidateinduction6.

Midazolam, a benzodiazepine, produce a calming effect on the brain and nerves 1, 10. Its various favorable effects include antiepileptic properties, anxiolysis, sedation, reduced attention and amnesia7. In a comparative study conducted by Singh KA (initials for first and second name of the author) et al, effect of pretreatment with lignocaine, midazolam and placebo were compared in prevention of etomidate induced myoclonus and the incidence was found to be 44%, 28% and 76% respectively5 (P<0.05). However, none of these studies have been conducted in Pakistan. The basic aim of my study is to compare the effectiveness of pretreatment with Lignocaine versus Midazolam on the frequency of myoclonus associated with etomidate induction, generate data regarding the effects, so that the more effective drug can be used routinely for the prevention of myoclonus associated with etomidate induction in routine.

METHODOLOGY:

After obtaining approval from the hospital ethics committee and written informed consent, 112 patient were recruited according to selection criteria in each group. All patients were assessed a day before surgery for anaesthesia fitness. Patient were prepared by fasting (8 h for solid foods, 4 hours for clear fluids).Patient were randomly divided into two equal groups by computer-generated numbers.

Group A received 1 ml of 2% lignocaine 2 min before induction with etomidate and Group B received 1 ml (1mg) of midazolam 2 min before induction with etomidate. On reaching the operating theater, standard monitoring were placed on all the participants, which included pulse oximeter, ECG and non-invasive blood pressure. A 20 G cannula with an intravenous line was maintained with 0.9% saline. Vitals such as pulse rate, blood pressure, respiratory rate, and oxygen saturation were recorded and taken as baseline readings. All patients were then preoxygenated with 100% oxygen for 3 min. Patients were divided randomly into two groups of 112 using computer generated random numbers. Group I received 1 ml of 2% lignocaine, and group II received 1 ml of midazolam (1 mg). The test solutions were prepared in coded syringes and were administered 2 min before etomidate induction (0.3 mg/kg) by an observer who was blinded to the allocation of the groups as well as the drug given to him. The time to the loss of eyelash reflex was recorded as the onset of induction, and an additional dose of etomidate was administered if necessary. The patients were observed continuously for myoclonic movements. The time of onset and the duration of myoclonus was observed. One minute post IV injection of etomidate and the observation of myoclonus, 0.5 mg/kg succinylcholine was administered to allow endotracheal tube placement. The vitals were observed after administration of test solution, after induction, and after endotracheal intubation every minute for five minutes, then every five minutes for fifteen minutes, and then every fifteen minutes till the surgery ends. Anesthesia was maintained with isoflurane (0.5-1%) and atracurium.

Data was collected on a standardized Proforma and analyze using SPSS-17 version (Statistical package for the social sciences). Mean ± SD (standard deviation) was calculated for quantitative variables lik age, weight and BMI. Qualitative variables like gender, myoclonus wer expressed as frequencies and percentages. Chi-square was used to compare th frequency of myoclonus in two groups. A P value less than 0.05 was consider statistically significant. Effect modifiers like age and gender were controlled b stratification. Post-stratification Chi-square test was applied.