ANESTHESIA IN ENT
Skilled anesthesia is required in ENT surgery as both the surgeon and the anesthetist often share the same operative field and airway. ENT surgery has a variety of major and minor surgeries including laser and endoscopic surgeries performed under both local anesthesia with sedation (MAC- Monitored anesthesia care), general anesthesia (with endotracheal intubation or LMA- Laryngeal mask airway) and TIVA (Total intravenous anesthesia).
Local Anesthesia in ENT:
Prior to local anesthesia a sensitivity test needs to be done. Over sedation should be avoided to maintain the pharyngo-laryngeal reflex to prevent any aspiration.
Local Anesthesia is commonly used for:
- Ear surgeries like Tympanoplasty, Stapedotomy, Auroplasty, Ossiculoplasty, Mastoidectomy.
- Nasal surgeries like Submucous resection, Septoplasty, Endoscopic sinus surgery (FESS).
- Oral surgeries like tonsillectomy in adults, oral biopsies etc.
i. local infiltration anesthesia- Drugs used includes 2% Lignocaine with adrenaline, 1% Lignocaine, 0.25 and 0.75% Ropivacaine.
ii. Topical anesthesia- 4% Lignocaine, 10% Lignocaine spray, oral gargles.
iii. Sedation- Fentanyl 1-2 ug/kg, Dexmedetomedine 1ug/kg, Midazolam 0.5 – 1 mg/kg, Propofol 1-2 mg/kg.
II. General Anesthesia in ENT:
Major ENT surgeries are done under general anesthesia using a cuffed endotracheal tube with a throat pack. LMA (supraglottic airway devices) can be used except in oral and throat surgery.
Common surgeries performed under general anesthesia:
b) Facial nerve decompression.
c) Endolymphatic sac decompression.
d) Tympanoplasty in uncooperative patients.
f) Lateral skull base surgery.
- Nasal polypectomy.
- Excision of nasopharyngeal angiofibroma.
- FESS (Functional Endoscopic Sinus Surgery) and its extended approaches.
- Anterior skull base surgery.
- Palatal surgeries.
- Radical neck dissection.
- Direct laryngoscopy.
- Functional Endoscopic Sinus Surgery (FESS).
- Inj Midazolam 0.25 mg/kg body weight is given as sedation.
- Inj Fentanyl 1-2 ug/kg body weight as analgesia.
- Inj Atropine 0.02 mg/kg or injection Glycopyrrolate 0.004 mg/kg is given as antisialagogue and vagolytic.
- Induction of anesthesia is done by injection Thiopentone 5mg/kg or Propofol (1-2 md/kg).
- Endotracheal intubation done with depolarizing muscle relaxant (Scoline 1-2 mg/kg) or non-depolarizing muscle relaxant (Atracurium 0.5 mg/kg)
- Intra-operative patient is maintained on nitrous oxide, oxygen and inhalational anesthetics like Sevoflurane and Isoflurane and non-depolarising muscle relaxant like Atracurium or Vecuronium with constant monitoring.
- Reversal of patient from anesthesia is done by injection Myopyrolate (Neostigmine 0.05 mg/kg + Glycopyrrolate 0.004mg/kg).
- Extubation done only after complete recovery of all oropharyngeal, laryngeal reflexes and patient is responding to verbal commands.
- To reduce bleeding and provide a clear operating field as in ear surgeries (under microscope), Septorhinoplasty and FESS; hypotensive anesthesia with a controlled pulse rate is required. Drugs used are
a) Antihypertensive drugs like Nitroglycerine, Beta blockers like Metoprolol, Labetalol, Esmolol and alpha agonist like Clonidine.
b) Dexmeditomedine and Propofol as continuous infusion.
c) Inhalational anesthetics like Isoflurane and Sevoflurane.
III. Anesthesia in specific cases:
- Ear surgery: Since ear surgeries are under microscopic vision, minimal bleeding may hamper the operative field. Hypotensive anesthesia with controlled pulse rate and blood pressure is done as mentioned above.
- Endoscopic nasal surgery:
- The majority of bleeding encountered during endoscopic sinus surgery is from the well vascularized capillary beds of the sinonasal mucosa.
- Bleeding from nasal mucosa is due to the mean arterial pressure (MAP) and central venous pressure. MAP is dependent on both the systemic vascular resistance (SVR) and cardiac output (CO) (MAP¼ SVR CO). Deliberate hypotension can therefore be achieved either via decreasing the systemic vascular resistance using vasodilatory agents (sodium nitroprusside, calcium channel blockers, sevoflurane, isoflurane) or by decreasing the cardiac output by choosing anesthetic agents that decrease preload and contractility (b-blockers, remifentanil). Vasodilatation results in a compensatory reflex tachycardia to maintain cardiac output.
- Mean arterial pressures between 50 and 70mm Hg are generally considered the goal for deliberate hypotension.
- Deliberate hypotension achieved through decreasing cardiac output is believed to be superior to decreasing systemic vascular resistance with respect to the surgical field quality.
- CO is decreased with use of alpha-2 adrenergic agonists (such as clonidine or dexmedetomidine) or via beta-blockade that decrease heart rate and contractility.
- Total intravenous anesthesia (TIVA)- It is achieved with a continuous infusion of propofol and opiods to improve surgical fields. Propofol infusion causes a decrease in cerebral perfusion thereby decreasing perfusion pressure to the nasal cavity via the anterior and posterior ethmoid arteries. This is in contrast to inhalational anesthetics that cause vasodilatation and increased blood flow to the ethmoid arteries.
- Regional anesthesia technique- Infraorbital nerve blocks and pterygopalatine fossa injections with lidocaine and epinephrine are two methods used to assist with analgesia and improve surgical field conditions. One potential issue with this block is distortion of the skin contour that may interfere with intraoperative image guidance registration.
- Patient positioning- The reverse Trendelenburg position (RTP) reduces Cardiac output by causing a pooling of blood in the lower extremities that decreases cardiac preload. Both 10-degree and 15-degree RTP improves the surgical field of view and total blood loss during the procedure.
- Cerebral oximetry and blood flow monitoring- The concern for cerebral hypoperfusion and ischemia because of the RTP and deliberate hypotension has led to the monitoring of cerebral oximetry and middle cerebral artery blood flow rate. Cerebral oximetry monitoring is feasible during FESS by the collection of continuous cerebral oxygen saturations.
- Ventilatory strategies- There is benefit to hypocapnia and hyperventilation during sinus surgery because of the vasodilatory effect of carbon dioxide on mucosal smooth muscle tone.
- Bronchoscopy: In rigid bronchoscopy the surgeon and the anesthetist share the same field. Hence, it is important to avoid hypercarbia and hypoxemia. Ventilation is done by Saunders jet injector based on venturi effect for the airway management. Nowadays, flexible fibreoptic bronchoscopy is done.
- Laser surgery: Lasers used for the surgeries in larynx and oral cavity can damage the endotracheal tube by excessive heat generation and start a fire. Apart from the routine anesthesia, the anesthetic precautions are:
a) Limited duration of the laser intensity.
b) Inspired O2 concentration should be low by 21-30%. Nitrous oxide supports combustion and should be avoided.
c) The endotracheal tube is wrapped by a thin aluminum foil to prevent damage by the laser beam.
d) Saline soaked pledgets should be placed in the airway to reduce the thermal damage to surrounding structures.
- Head and neck surgeries: Surgeries for malignancies like pharyngectomy, glossectomy, laryngectomy, parotidectomy have to be carried out with great care, with the aim of establishing and securing an airway. Elective tracheostomy can be done for high risk cases. Close monitoring for complications like bleeding, air embolism, arrhythmias should be done.