Evaluation Of Nebulized Dexmedetomidine As a premedication In Blunting Hemodynamic Response To Intubation

Laryngoscopy and tracheal intubation are noxious stimuliassociated with a transient increase in autonomic response.Thisresponse varies with depth of anaesthesia, duration and difficulties duringlaryngoscopy and intubation, and certain patient factors including history ofdiabetes and cardiovascular disease.The precise mechanism of the intubation response (IR) is elusive but ithas been established that it has both a sympathetic and parasympatheticelement. The effect is transient occurring 30 seconds after intubation andlasting for less than 10 minute. The sympathetic response is a polysynapticpathway with the glossopharyngeal and vagus nerve forming the afferent arc tothe sympathetic nervous system via the brain stem and spinal cord. This ensuresa diffuse autonomic response at the efferent side including increased firing ofthe cardio-accelerator fibres and release of adrenergic mediators includingnorepinephrine, epinephrine and vasopressin.

The net effect of this autonomic surge is an increased blood pressure(BP), heart rate (HR), pulmonary artery wedge pressure and decreased ejectionfraction.

The parasympathetic reflex is monosynaptic and more common in childrenbut can occur in some adults. The reflex is mediated by increased vagal tone atthe Sinoatrial node .

 The haemodynamic response to laryngeal and endo- trachealintubation  is transient and in mostpatients thought to be of little consequence, but in patients with coronaryartery disease (CAD), hypertension, raised intra cranial pressure, it may beassociated with deleterious effects like myocardial ischaemia, infarction,arrhythmias, cardiac failure, pulmonary oedema and cerebral haemorrhage.

 Various drugregimens and techniques have been used from time to time for attenuating thestress response to laryngoscopy and intubation, including opioids, barbiturates,benzodiazepines, beta blockers, calcium channel blockers, vasodilators, various blades and conduits for intubations.

 Alpha-2agonists like clonidine  and dexmedetomidine  have been used recently for attenuationof sympathoadrenal stimulation caused by tracheal intubation and surgery.Clonidine stimulates α2 adrenergic inhibitory neurons in the medullaryvasomotor center. As a result there is a decrease in sympathetic nervous systemoutflow from central nervous system to peripheral tissues

Dexmedetomidine aselective alpha2-adrenoceptor agonist, is short acting  and has a reversal drug for its sedativeeffect, atipamezole which  renderdexmedetomidine suitable for sedation and analgesia during the wholeperioperative period. It can be administered by various routes like IV, IM, asadjuvant to local anesthetics, nasal and orally and as nebulized form.Nebulized dexmedetomidine administration may allow rapid drug absorptionthrough nasal, respiratory, and buccal mucosa, which allow bioavailability of65% through nasal mucosa and 82% through buccal mucosa.Nebulized drug administration may be preferredover intranasal administration, as it avoids transient nasal irritation, cough,vocal cord irritation, or laryngospasm as seen with intranasal administration.In our study we hypothesize that nebulized dexmedetomidine also blunts theintubation response due to its rapid absorption. As dexmeditomidine also causessedation we also contemplated entropy monitoring. ENTROPY  is a new monitor based on the analysis of theEEG signal2. The State Entropy (SE) is computed overthe frequency range from 0.8 Hz to 32 Hz and primarily reflects the corticalstate of the patient. The Response Entropy (RE) is computed over a frequencyrange from 0.8 Hz to 47 Hz, and includes both the EEGâ€dominant and EMGâ€dominantpart of the spectrum. dexmedetomidine nebulization  in blunting the hemodynamic response tolaryngoscopy and tracheal intubation.