Topical Bupivacaine Effect On The Response To Awake Extubation During Emergence From General Anesthesia

* Emergence from general anesthesia is often complicated by the ETT-induced emergence phenomena (EP), which include coughing, sympathetic stimulation, sore throat, increased bleeding from the surgical site, and increased intracranial and intraocular pressures.
* Techniques that have been used to help diminish coughing during emergence include "deep" extubation (removal of the endotracheal tube \[ETT\] while the patient is still in a deep plane of general anesthesia), administration of intravenous (IV) narcotics, or administration of IV lidocaine prior to emergence since systemic narcotics and lidocaine have antitussive properties. However, each of these techniques has limitations. A reliable technique for improving ETT tolerance while facilitating rapid and full emergence from general anesthesia would be desirable in many situations.
* Topical application of bupivacaine to the pharyngeal, laryngeal, and tracheal mucosa will attenuate or even abolish coughing as well as a hemodynamic response during extubation, thus result in increasing the patient's comfort and avoiding potential complications of extubation process.
* Up to the investigator's knowledge there is no study done to evaluate the effect of topical bupivacaine on the incidence of coughing and hemodynamic response during emergence from general anesthesia in patients undergoing elective thyroidectomy.

The process of manipulation of the airway during laryngoscopy, endotracheal intubation, and extubation is usually associated with exaggerated hemodynamic response including tachycardia, hypertension as well as increase intraocular and intracranial pressure\[1,2\]. The exact mechanism to these hemodynamic responses may be due to the release of catecholamine in the blood by stimulating the sympathetic nervous system during these stressful periods. Acute hemodynamic changes during extubation may lead to life-threatening myocardial ischemia, arrhythmias, pulmonary edema, acute heart failure, or cerebrovascular hemorrhage in high-risk patients and this can increase morbidity and mortality of the patients \[3\].

Respiratory complications after tracheal extubation are three times more common than induction of anesthesia and intubation \[4\], as intratracheal tube induces laryngeal irritation that transmitted through rapidly acting receptors which are located throughout the trachea, involved in the cough reflex and subsequently lead to coughing and bucking that frequently occur during extubation and may lead to negative pressure pulmonary edema as well as, laryngeal edema and sore throat \[5, 6\].

Various techniques have been applied to attenuate the hemodynamic responses and coughing during emergence and extubation. They include deep extubation, administration of intravenous (IV) short-acting narcotics, calcium channel blockers, and dexmedetomidine \[7,8\], as well as lidocaine which is considered one of the commonly used drugs either through IV route, endotracheal tube (ETT) cuff, or laryngotracheal route\[1,9\]. Concern about the use of these drugs includes respiratory depression, delayed emergence from anesthesia, postoperative nausea and vomiting, sedative effects, and short action time \[10\].

Bupivacaine is a kind of sodium channel blocker local anesthetics used as topical anesthesia that suppresses cough by inhibiting the progression of the action potential in the tracheal touch-sensitive Aδ fibers (cough receptors)\[10\]. The plasma protein binding of bupivacaine exceeds 90%, whereas lidocaine protein binding is 65- 75%, \[11\] and it is well known that the duration of local anesthetics is influenced by their protein binding characteristics, as the affinity for plasma proteins corresponds to the affinity for protein binding at the sodium channel receptor site, that results in prolongation of the presence of the anesthetic effect at the site of action \[12, 13\].

the investigators hypothesize that usage of topical bupivacaine may have an impact on decreasing incidence of coughing and alleviating hemodynamic response during awake extubation and emergence from general anesthesia in post-thyroidectomy patients.

Eligibility Criteria:
Inclusion Criteria:

Patient acceptance. BMI \< 35kg/m2. ASA I and ASA II. Scheduled for elective thyroidectomy under general anesthesia

Exclusion Criteria:

Patient refusal. History or anticipated difficult intubation. Chronic respiratory disease such as chronic obstructive pulmonary disease or asthma.

Recent respiratory tract infection in the last month, chronic cough, and current smoking.

History of laryngeal or tracheal surgery or pathology. Patients with symptomatic gastric reflux. Patients with a known history of allergy to study drugs.