Email: rknnese@gmail.com, ravinese@yahoo.com  

DISCUSSION

The sequence of induction anaesthesia, laryngoscopy and tracheal intubation are associated with marked haemodynamic changes and autonomic reflex activity which may be a cause of concern in many high risk patients.¹⁴ Laryngoscopy and intubation is associated with rise in heart rate, blood pressure and incidence of cardiac arrhythmias There is a potential for life threatening complications due to these changes in patients with coronary artery disease, systemic arterial hypertension, leading to myocardial ischaemia, heart failure and cerebrovascular catastrophies.^3,15,16,17 It is known that the effect on heart rate after esmolol bolus dose comes on after 1 minute, where as the effect of blood pressure comes after 2 minutes. ¹⁸ Ebert et al 1989 observed that maximum cardiovascular response occurred 2 minutes after intubation. They also noted that the responses (hypertension, tachycardia) are proportional to the duration of laryngoscopy. These responses start showing up at 15 seconds and peak up at 45 seconds. Hence, they recommend that the duration of laryngoscopy and tracheal intubation should be limited to 30 seconds. These potentially dangerous changes disappear within 5 minutes of onset of laryngoscopy. Although these responses of blood pressure and heart rate are transient and short lived, they may prove to be detrimental in high risk patients especially in those with cardiovascular disease, increased intracranial pressure or anomalies of the cerebral blood vessels. In our study, we have excluded cases with anticipated difficult intubation. Laryngoscopy and intubation was done at 2 min after injection of study drug. An increase in mean arterial pressure of 26.5 mm Hg and 20 to 40 torr when compared with awake control levels and 35 to 60 torr when compared with preintubation values have been reported after placement of an endotracheal tube.A rise in mean heart rate of 29.9 beats/min has also been noted¹⁹. Many factors influence the cardiovascular changes associated with laryngoscopy and intubation. Age, drugs, type and duration of procedures, depth of anaesthesia, hypoxia, hypercarbia influence the pressor response^20,21,22. Marked fluctuations in haemodynamic responses are often seen in geriatric patients²². In our study we selected the patients above 18 years. Patients on antihypertensive drugs may exhibit a decrease in pressor response. We excluded the patients on beta –blockers from our study. A variable combination of drugs used for premedication, induction, relaxation and maintenance of anaesthesia can influence the sympathetic response to laryngoscopy and intubation. Propofol was selected for induction since it still continues to be the most popular agent for induction. In normovolemic patients propofol 2 mg kg^-1 IV can transiently decrease 10-20mm Hg of blood pressure and decrease the heart rate by 15- 20 beats min^-1.  Succinylcholine has negative inotropic and chronotrpic effect. It acts on the muscarinic receptors of SA node. A marked noradrenergic response was noted when intubation was performed under succinylcholine.²⁴ Nitrous oxide may increase the tone of sympathetic nervous system. The direct action of nitrous oxide is negative inotropism which is offset by increased sympathetic tone.²⁵ Halothane has a potency to decrease the heart rate but at concentration used for maintenance it does not appreciably change the heart rate.²⁶ Nasotracheal intubation comprises of three distinct phases a) nasopharyngeal intubation b) direct laryngoscopy to identify the vocal cords and c) Passage of tracheal tube into the trachea. Nasopharyngeal intubation causes significant pressor response. This response in heightened by the passage of tracheal tube in the larynx and trachea. In a study conducted, direct laryngoscopy did not increase the response significantly.²⁷ In our study, we included only direct laryngoscopy and orotracheal intubation. Laryngoscopy alone may produce most of the cardiovascular responses reported after laryngoscopy and tracheal intubation during anaesthesia. The most significant laryngoscopic factor influencing cardiovascular responses is found to be the duration of laryngoscopy. A linear increase in heart rate and mean arterial pressure during the first 45 seconds has been observed. Further prolongation has little effect. The force applied during laryngoscopy has only minor effect.¹⁶ In our study the duration of laryngoscopy and intubation was limited to 20 seconds. Adequate care was taken to achieve the required depth of anaesthesia avoiding hypoxia and hypercarbia which can influence the hemodynamic variations. Other contributory causes of hypertension and tachycardia could be continued manifestation of anxiety concerning anaesthesia and surgery, glycopyrrolate premedication and possible effect of suxamethonium. But they seem to be less important than laryngotracheal stimulation during laryngoscopy and intubation. Attenuation of sympathetic responses during laryngoscopy and intubation is of prime concern to the anaesthetist more so in high risk subjects as mentioned earlier. Many strategies have been recommended which include minimising the duration of laryngoscopy to less than 20 seconds¹⁶, iv β-blockers,^8,9,10,11 calcium channel blockers²⁸, nifedepine²⁹, clonidine.³⁰ sodium nitroprusside¹², lignocaine^2,8,9,10,31. No single drug or technique is satisfactory. Each technique has its own advantages and disadvantages. Optimal time for administration is 2 minutes before laryngoscopy and intubation.^2,8 Esmolol is a betablocking agent with several desirable properties. It is relatively cardioselective, ultrashort acting, with rapid onset of action. It has no significant drug interaction. Metabolism independent of vital organs and it is metabolized by RBC esterase. Frequent side effect is hypotension which doesn’t require any other treatment other than discontinuation of theraphy.^4,5,6 Previous studies have shown that the unique pharmacokinetic behavior of esmolol makes it well suited for controlling the cardiovascular responses to tracheal intubation when used as a continuous infusion technique.^18,32,33,34 However the dosing schedule and the time required for preparation of infusion may add a degree of  complexity. An alternative approach is to use a bolus dose of esmolol and many studies have investigated this and concluded it to be efficacious. Various bolus doses ranging from 100, 150 and 200mg have been investigated. In our study we have used 50mg, 100mg, 150mg of esmolol.

TIMING OF DRUG ADMINISTRATION

In our study we administer the drug 2 minute before laryngoscopy and intubation. It correlates with study conducted by Helfman SM et al⁸ who concluded that, esmolol controls the mean rise in systolic blood pressure when it is given 2 minutes before intubation.

COMPARISION OF HEART RATE

In our study the maximum heart rate in group A was 45% after 3 minutes. It correlated with study conducted by Schroff PP et al³⁶ which showed 31.2% increase, Rathore A et al³⁷ which showed 33.4% increase, Sharma J et al ³⁸ which showed 48.1% increase, Korpinen R et al³⁹ which showed 41% increase, Helfman MS et al⁸ which showed 44% and Oxorn D et al⁴⁰ which showed 44.1% increase in maximal heart rate. In our study the maximum heart rate in group B was 35.6% after 3 minutes. It correlated with conducted by Atlee JL et al⁴¹ which showed 21.8% increase and Rathore A et al³⁷ which showed 19.8% increase in heart rate In our study the maximum heart rate in group C was 13.8% after 3 minutes. It correlated with study conducted by Rathore A et al³⁷ which had 15.2% increase, Sheppard S et al⁴³ which had 18.1 increase, Chung KS et al¹¹ which had 18.2% increase, Korpinen R et al ³⁹which had 18.2% increase and Oxorn D et al⁴⁰ which had 19.7% increase in heart rate. Our study did not correlate with study of Sharma S et al⁴⁴ who had 3.4 % decrease in heart rate, Sharma J et al ⁵⁰who had 6.4% decrease in heart rate. It correlated with study conducted by Schroff PP et al ³⁶which had 10% increase, Rathore A et al³⁷ which had 10% increase, and Sheppard S et al ⁴³which had 8.8% increase in heart rate.

SYSTOLIC BLOOD PRESSURE

In our study, the maximum increase in mean systolic blood pressure in group A was 23.6% after 3 minutes. It correlated with study conducted by Schroff PP et al³⁶ which had 16.7% increase, Rathore A et al³⁷ which had 31.6% increase, Kumar S et al⁴⁵ which had 23.8% increase , Atlee JL et al⁴¹ which had 21.8% increase, Sheppard S et al ⁴³which had 27.8 % increase in maximum mean systolic blood pressure. In our study the maximum increase in mean systolic blood pressure in group B was 19.9% after 3 minutes. It correlated with the study conducted by Rathore A et al³⁷ which had 25.8% and Atlee JL et al⁴¹ which had 13.1% increase in maximum mean systolic blood pressure. In our study, the maximum increase in mean systolic blood pressure in group C was 6.2% after 2 minutes. After administration of drug the mean systolic blood pressure decreased below the baseline mean systolic blood pressure. It correlated with the study conducted by Kumar S et al⁴⁵ which had 7.4% increase, Sheppard S et al⁴³ which had 13.6% increase, Korpinen R et al³⁹ which had 13.6% increase and Venkatesha SL et al⁴⁶ which had 8% increase in maximum mean systolic blood pressure.

DIASTOLIC BLOOD PRESSURE

In group A, there was a decrease in mean diastolic blood pressure values after induction and after administration of drug. In our study, the maximum increase in mean diastolic blood pressure was 19.1% after 3 minutes. It correlated with the study conducted by Sharma S et al⁴⁴ which had 20.4% increase, Atlee JL et al⁵² which had 16.6% increase , Venkatesha SL et al⁴⁶ which had 23.4% increase in maximum mean diastolic blood pressure values. In our study, the maximum increase in mean diastolic blood pressure in group B was 18.2% after 3 minutes. It correlated with the study conducted by Atlee JL et al⁴¹ which had 29.3% increase in mean diastolic blood pressure values. In our study, the maximum increase in mean diastolic blood pressure in group C was 3.8 % after 3 minutes. There was decrease in mean diastolic blood pressure values after induction and after administration of drug. It correlated with the study conducted by Sharma J et al³⁸ which had 2.2% increase, Korpinen R et al ³⁹which had 11.7% increase and Venkatesha SL et al ⁴⁶which had 18.3 % increase in maximum mean diastolic blood pressure values. In our study, the maximum increase in mean arterial blood pressure in group A was 21.3% after 3 minutes. There was decrease in mean arterial blood pressure values after induction and after administration of drug. It correlated with the study conducted by Sharma S et al ⁴⁴which had 18.4% increase , Sharma J et al³⁸ which had 11.3 % increase and Atlee JL et al⁴¹ which had 22.5 % increase in mean arterial blood pressure values. In our study, the maximum increase in mean arterial blood pressure in group B was 19.1% after 3 minutes .There was decrease in mean arterial blood pressure values after induction and after administration of drug. It correlated with the study conducted by Atlee JL et al⁴¹ which had 20.5 % increase and Menigaux C et al⁴² which had 23.8% increase in mean arterial blood pressure values. In our study the maximum increase in mean arterial blood pressure in group C there was 4.6 % after 3 minutes. There was decrease in mean arterial blood pressure values after induction and after administration of drug. It correlated with the study conducted by Sharma J et al ³⁸which had 0.1% increase, and Kumar S et al ⁴⁵ which had 14.4 % increase in mean arterial blood pressure values.

CONCLUSION

In this study, all the groups in which esmolol was used showed a decrease in mean value of systolic blood pressure, diastolic blood pressure and mean arterial pressure after administration of drug. The reduction is less in esmolol 50 mg group. Esmolol 50 mg group adequately attenuated the heart rate, but the systolic blood pressure, diastolic blood pressure and mean arterial pressure were not satisfactorily attenuated compared to esmolol 100mg group. In esmolol 100 mg group, heart rate, systolic blood pressure, diastolic blood pressure and mean arterial pressure were adequately attenuated during laryngoscopy and tracheal intubation. From this study, it is concluded that esmolol 100 mg is near an ideal drug for attenuation of pressor response to laryngoscopy and endotracheal intubation.

REFERENCES