INTRODUCTION
Patients for microlaryngoscopy (ML Scopy) and direct laryngoscopy (DL Scopy) may be of all ages, including paediatric,1 adult, or geriatric.2 They are posted for the procedure for diagnostic or therapeutic purposes. They may present with hoarseness of voice, change of voice, difficulty in breathing, and inspiratory or expiratory stridor. These patients may have associated congenital and acquired conditions other than airway disease, such as smoking-related pulmonary conditions, hypertension, ischemic heart disease, endocrinopathies like diabetes mellitus and thyroid diseases, and cardiac anomalies especially in pediatric age group. The main anesthetic considerations are as follows:3
Adequate preoperative evaluation and optimization
Maintaining adequate depth of anesthesia intraoperatively to maintain stable hemodynamics in a still patient
To share the airway in such a way to give good visualization to the surgeon so as to diagnose the pathological conditions
To give enough time to the surgeon to diagnose and treat the airway diseases
Protection of lower airway from blood and debris
Postoperative monitoring and early recovery to fast track the patient.
PREOPERATIVE EVALUATION
A thorough medical evaluation is necessary for all patients requiring anesthesia. These patients may present with history of hoarseness of voice, voice change (low pitch, coarse fluttering – subglottic/ high pitch, cracking voice, aphonia – glottis), stridor (inspiratory or expiratory). Patients may present with dysphagia. The best breathing position, breathing pattern during sleep give an indication of the severity of the disease. Patients are likely to have cardiovascular (hypertension, ischemic heart disease, coronary artery disease) or respiratory dysfunction (chronic obstructive pulmonary disease). History of previous endoscopic procedures and their outcome is very important. When the lesions occur in or near the airway, there is possibility of life-threatening airway obstruction during the induction of anesthesia. Also, because of manipulation, the airway lesions can cause bleeding or edema, which results in airway occlusion. The difficulties may occur during intubation of trachea. Hence the oropharynx should be evaluated carefully. The range of motion of neck should be examined carefully to assess difficulties with airway management. The radiological investigations and records, such as computed tomography (CT) scan, magnetic resonance imaging (MRI),4,5 and X-ray will help to assess the potential difficulties in securing the airway and endotracheal intubation.6 Patients may have prolonged endotracheal intubation with previous intensive care unit/neonatal intensive care unit admissions and associated lung pathologies. They should be thoroughly evaluated and optimized preoperatively by giving nebulization with β2 agonist and adequate hydration.
A discussion with the surgeon is necessary for any potential airway difficulties with anesthesia and to know the plan of surgery.
Prior to anesthesia, the following should be identified.
INTRAOPERATIVE MONITORING
INDUCTION OF ANESTHESIA3
Patients who are not at risk of respiratory obstruction can have standard endotracheal following preoxygenation. If obstruction of the airway is anticipated, difficult airway equipments are mandatory. Different size of laryngoscope blades, oral and nasal airway, fibreoptic bronchoscope or video endoscope, rigid bronchoscope, and tracheostomy tray should be available.
Anesthesia is induced with barbiturates like thiopentone sodium 5 mg/kg iv or Inj. Propofol 2 to 3 mg/kg and muscle relaxants, such as intravenous (iv) succinylcholine 2 mg/kg. Patient is ventilated with oxygen/sevoflurane, and endotracheal intubation is performed. Anesthesia is maintained with oxygen, sevoflurane, and intermittent-acting nondepolarizing muscle relaxants like vecuronium bromide.
The surgeon should be present at the time of anesthetic induction. Many times awake intubation of the trachea using topical anesthesia is the technique recommended in these cases. Transtracheal instillation of local anesthetics and superior laryngeal nerve blocks may be useful. In difficult cases fiberoptic laryngoscope should be considered.7 Intravenous anesthetics should be used carefully so that adequate and unobstructed respiration is maintained.
Microlaryngeal tube can be used when endotracheal intubation is planned.
MICROLARYNGEAL TUBES OR MALLINCKRODT CRITICAL CARE TUBE
Small internal and external diameter
Can be used orally or nasally.
4 to 6 mm ID, 30 cm long with standard cuff
Low-pressure high-volume cuff
Lies between arytenoid cartilages, leaving at least anterior 2/3 of glottis unobscured
NONINTUBATION TECHNIQUES OF ANESTHESIA IN DIFFICULT MICROLARYNGOSCOPY PROCEDURES8-10
Spontaneous Ventilation
When there is anticipated difficult intubation and ventilation, spontaneous ventilation technique using inhalational induction with sevoflurane or halothane in oxygen is used. In this technique, laryngoscopy is done and topical local anesthetic is instilled on and above vocal cords and mask ventilation with 100% oxygen is given. As suitable depth of anesthesia is achieved, rigid laryngoscopy or bronchoscopy is performed. It has its own advantages as there is excellent visualization of the surgical field and ability to evaluate vocal cord function. Also, it is good for otherwise stable patients with compromised airway. Spontaneous ventilation has disadvantages as oxygenation and ventilation is more difficult to assess, surgical field is not still, there is risk of aspiration, and depth of anesthesia is not consistent.
INSUFFLATION TECHNIQUE
Insufflation technique incorporates the following routes:
A small catheter in the nasopharynx placed above the laryngeal opening
A tracheal tube cut short and placed through the nasopharynx emerging just beyond the soft palate
A nasopharyngeal airway
Side arm or channel of the laryngoscope
It has some potential disadvantage as there is no control over ventilation. There can be loss of protective airway reflexes and potential for airway soiling. It also causes gastric distention and theatre pollution. It is not suitable for soft floppy lesion.
INTERMITTENT APNEA TECHNIQUE
Standard anesthesia induction with induction agents as thiopentone sodium 4 to 5 mg/kg iv and muscle relaxants, such as vecuronium bromide is given and the patient is intubated. Anesthesia is maintained with intermittent nondepolarizing muscle relaxants and inhalational agents like sevoflurane. Patient is handed over to the surgeon after adequate ventilation and surgeon does diagnostic and therapeutic ML Scopy procedure on the patient's airway. Meanwhile, oxygen saturation and other vital parameters are monitored. As the oxygen saturation goes below 97% the patient is reintubated and ventilated till oxygenation improves. At the end of procedure, patient is reintubated and hyperventilated. Anesthesia is reversed with standard anticholinesterase like neostigmine and anticholinergics like glycopyrrolate.
Intermittent apnea technique has excellent visibility of surgical field and safety in the use of LASER. It has certain disadvantages, such as there is limitation of surgical time, inadequate ventilation, aspiration risk, variable level of anesthesia, ad potential trauma through multiple reintubations.
DIRECT LARYNGOSCOPY11
Definition and Introduction
It is a procedure i.e., used to obtain a view of the vocal folds and the glottis. Laryngoscopy may be performed to facilitate tracheal intubation during general anesthesia or to secure airway in cardiopulmonary resuscitation or for procedures on the larynx or other parts of the upper tracheobronchial tree.
History
Alfred Kirstein (1863–1922), Chevalier Jackson (1865–1958), and Gustav Killian (1898–1912) – are all contributors to the introduction of the handheld laryngoscope.
Manuel Garcia (1805–1868) – indirect laryngoscope.
Instruments/Equipment
Laryngoscopy can be performed by using rigid or flexible instruments.
Rigid laryngoscopy: A rigid laryngoscopy may be done by using an indirect or direct method.
Indirect laryngoscopy: It is performed by using specially designed laryngeal mirrors in combination with a headlight. This enables the larynx and the nasopharynx to be visualized. This is frequently used in adults and children. It is often difficult to carry out this procedure.
Direct laryngoscopy:11 It is performed with handheld curved or straight blade instruments or by using a suspension laryngoscope, which leaves both hands free to manipulate instruments. The curved Macintosh blade and the straight Miller blade laryngoscopes are routinely used.
Equipment for Laryngoscopy12
Oxygen source and self-inflating ventilation bag (e.g., Ambu bag)
Face mask
Oropharyngeal and nasopharyngeal airways
Tracheal tubes
Tracheal tube stylet13
Syringe for tracheal tube cuff inflation
Suction apparatus
Laryngoscope handle (two)
Laryngoscope blades: Common blades include the curved (Macintosh) and straight (Miller)
Stethoscope
Technique
Sniffing position:14-16 The sniffing position is the best starting position for laryngoscopy. In the sniff position, the cervical spine below C5 is relatively straight, there is increasing flexion from C4 to C2, and the head is fully extended (occipito–atlantoaxial complex).4,17 Neck flexion between C2 and C4 is achieved by elevating the head.5,18,19
Suspension Laryngoscope
Frequently carried out by ENT surgeons as this arrangement leaves the surgeon's hands free to use instruments and even to position an operating microscope for precise surgery.
The surgical procedures that can be done with the suspension laryngoscope include:
Aspiration/marsupialization of cysts
Excision of nodules
Laser vaporization of papilloma
Injection of bleomycin in cystic hygroma with laryngeal involvement.
Anesthesia Management
The requirements of anesthesia for laryngoscopy must be compatible with maximum safety and minimum patient discomfort.
Premedication: With anticholinergics (glycopyrrlate), benzodiazepines, and opioids
Induction of anesthesia: Thiopentone sodium (5 mg/kg)/propofol (2 mg/kg).
Only after confirming that the patient can be ventilated by mask (100% oxygen given for 2–3 minutes) a longacting muscle relaxant will be administered.
Four minutes after the injection of NDMR or after the patient is adequately under the inhalational anesthesia, intubation will be attempted by performing direct laryngoscopy.
Laryngoscopy Response
Direct laryngoscopy is a noxious stimuli that can provoke adverse responses in the cardiovascular, respiratory, and other physiologic systems.
The magnitude of the response is greater with increasing force and duration of laryngoscopy.
Elevation in arterial pressure typically starts within 5 seconds of laryngoscopy, peaks in 1 to 2 minutes, and returns to control levels within 5 minutes. Such hemodynamic changes are undesirable in patients with cardiac disease.
Many techniques have been tried in an effort to attenuate adverse hemodynamic responses to intubation, but none is ideal.
Prevention by use of an increased depth of anesthesia
Use of N2O with a volatile agent may be beneficial.
Large doses of narcotics (other than morphine), such as fentanyl 2–3 μg/kg, suppress the hemodynamic response but risk prolonged respiratory depression.
Intubation response suppression using vasodilators, beta blockers/Ca blockers/Xylocard, etc.
Aerosol or other application of topical anesthetics may be beneficial with a low risk of adverse effects.
Awake flexible fiberoptic intubation with effective topical anesthesia almost eliminates the hemodynamic response to tracheal intubation.