circulatory response to laryngoscopy and intubation was first documented by
Reid and Brace in 1940 and later by King et al1 in 1951.
Laryngoscopy and tracheal intubation in adults are commonly accompanied by
increase in arterial blood pressure and heart rate1. The principle
mechanism in hypertension and tachycardia is the sympathetic response2,3 which
results in increase in catecholamine activity4.
Intravenous anaesthetic induction
agents do not adequately suppress the circulatory responses evolved by
endotracheal intubation5. Various studies have been conducted using
additional pharmacological measures prior to laryngoscopy. Ideally the drug selected
should prevent impairment of cerebral blood flow, it should neither be time
consuming nor affect the duration or modality of the ensuing anaesthesia.
Dexmedetomidine6 a selective ?2
adrenoceptor agonist with ?2: ?1 binding selectivity
ratio of 1620:1 compared to 220:1 for clonidine7 appear to fulfil all
the above criteria.
The present study
is aimed at the comparison of dexmedetomidine 1µg /kg versus placebo for
attenuation of pressor response during laryngoscopy and intubation, given 10
min prior to intubation and also to study the effect on the level of sedation
of the patient before induction of anaesthesia.
MATERIALS AND METHODS
This prospective randomized double blind
controlled clinical study was conducted at a Government Medical College
Hospital. The study was conducted for the duration of 2 years. The study was
undertaken after obtaining ethical committee clearance as well as informed
consent from all the patients. The study included a total of hundred patients
divided in to two groups.
American Society of Anaesthesiologists
(ASA) class I and II.
Normotensive with age varying
from 18 to 55 years.
Patients with cardiovascular,
renal, hepatic, central nervous system and peripheral vascular diseases.
Bradycardia and hypotension
Patients with anticipated difficult airway.
patients were divided into two groups, group C and group D with 50 patients in
each group. The patients were enrolled in to following groups based on chit
system randomization. Group C received 100 ml of normal
saline intravenously over 10min, and group D received injection dexmedetomidine
1µg/kg body weight diluted in 100 ml normal saline intravenously over 10min.
arrival of the patients in the operating room, iv access was secured with an
18-gauge intravenous cannula and an infusion of ringers lactate was started. Patients
were connected to multipara monitor. All the baseline parameters were recorded.
Patients were premedicated with iv ondansetron 0.1mg/kg body weight and iv
glycopyrrolate 0.01mg/kg body weight. Patients in group C received 100ml of
normal saline and patients in group D received dexmedetomidine 1µg/kg body
weight diluted in 100 ml normal saline intravenously over 10 min, started 10
minutes before induction.
The study drug was prepared by the senior anaesthesiologist
who was not involved in the study. The observer as well as the patient was
blinded for the study.
Patients were then preoxygenated.
Anaesthesia was induced with thiopentone sodium 5 mg/kg body weight. Muscle
relaxation was achieved with vecuronium 0.1mg/kg. Laryngoscopy and intubation
was achieved after 3 minutes of injection vecuronium using Macintosh blade. Measures
were taken to keep the laryngoscopy and intubation within 15 seconds, if time
exceeded 15 seconds, such patients were excluded from the study. After
confirmation of bilateral equal air entry, the endotracheal tube was fixed.
Anaesthesia was maintained using 66% nitrous oxide and 33% of oxygen. No
surgical or any other stimulus was applied during next 10 minutes of study period.
After study period a volatile anaesthetic agent sevoflurane was added and
fentanyl in dose 2µg/kg was injected.
The cardiovascular parameters HR, SBP, DBP,
MAP, the patient’s level of sedation and his response were recorded at 0, 2, 5 ,
8 min after drug administration, a reading after induction of anaesthesia, a
reading after laryngoscopy and intubation, readings at 0 , 2 , 5 , 8 min in all
patients. Sedation scoring was noted as per Ramsay sedation scale8.
The data were analyzed statistically by using
software SPSS (version 14.0). Data was summarized as number, percentage, mean ±
standard deviation (SD) as appropriate. With
reference to the previous study in literature it was found that a sample size of
minimium 50 patients per group was required to achieve 15% change in HR, SBP,
DBP, and MAP between baseline and postintubation, with a power of 90% at the 5%
statistically significant difference of average clinical parameters (such as
HR, SBP, DBP, and MAP) between two study groups has been tested using
independent sample t-test. Repeated measure ANOVA was used to compare variables
like HR, SBP, DBP, MAP and sedation score between the groups for p value. The
level of significance was set at P