Comprehensive Review of ENT, Maxillofacial, and Special Surgical Anesthesia

Nasal Intubation and Maxillofacial Airway Management

Nasal intubations are frequently utilized in specialized ear, nose, and throat (ENT) and maxillofacial surgeries. The most common complication associated with this route is epistaxis. Absolute contraindications for nasal intubation include nasal fractures, specifically Lefort II and Lefort III fractures, marked septal deviation, coagulopathy, basilar skull fractures, cerebrospinal fluid (CSF) leaks, pregnancy, and transsphenoidal surgical procedures. Recent research suggests that nasal or oral RAE tubes may be acceptable for Lefort I fractures specifically. However, clinicians must be mindful that any facial fracture carries a high risk of a nasal tube inadvertently entering the brain. Consequently, the placement of endotracheal tubes (ETT) or nasogastric (NG) tubes should be avoided in unconscious patients with facial trauma to prevent potential brain penetration.

Mandibular and maxillofacial trauma management requires careful airway planning. If there is any doubt regarding airway security, a tracheostomy under local anesthesia or an awake fiberoptic oral intubation using topical anesthesia must be considered. These cases should be treated as full-stomach patients requiring rapid sequence induction (RSI) with cricoid pressure. For mandibular or maxillary fractures that are not Lefort II or III, nasal intubation is often the preferred method because the patient's teeth are typically wired or secured with rubber bands at the end of the surgery. Masking at emergence during these cases requires the patient to be fully awake with intact reflexes. Wire cutters or scissors must be available at all times at the bedside to address airway emergencies in patients whose jaws are wired shut.

Nasal and Oral Endotracheal Tube Specialties

Preformed Ring-Adair-Elwyn (RAE) tubes are essential in head and neck surgery. Oral RAE tubes are excellent choices for tonsillectomies, dental cases, laryngeal procedures, and surgeries involving the eye or upper face. Nasal RAE tubes are ideal for maxillofacial surgeries where the oral airway must remain unobstructed. When using a small-diameter tube in a large airway, ventilation efficiency decreases due to increased resistance and decreased cuff contact with the tracheal wall.

Armored or laser tubes feature an embedded metal or nylon wire wound in a spiral throughout the shaft. This design provides significant resistance to kinking and compression, which is necessary when the surgical field is near the airway. A critical caveat is that once an armored tube is kinked, it does not revert to its original shape, potentially causing partial or complete airway obstruction. For laser procedures, double-cuffed tubes are used, where the cuffs are inflated with saline. In the event of an airway fire, the saline drains into the wound or airway to help extinguish the flame.

Pharmacology in ENT and Airway Procedures

Cocaine is frequently used as a local anesthetic in ENT for its potent vasoconstriction properties. It blocks catecholamine reuptake into adrenergic nerve endings, which results in shrunken mucosa and reduced bleeding. The maximum recommended dose of cocaine is $3\,mg/kg$. It is typically applied in a $4\%$ concentration. Epinephrine is often injected shortly after cocaine application, but this combination requires caution. Cocaine absorbed into the plasma can block the systemic uptake of epinephrine, leading to potentially toxic systemic effects of epinephrine.

Glucocorticoids, such as dexamethasone in doses of $8-10\,mg$ IV, are utilized pre-operatively and intra-operatively to reduce laryngeal edema and postoperative nausea and vomiting (PONV). Dexamethasone may also prolong the effects of local anesthetics. If a patient has been taking glucocorticoids chronically before surgery, a steroid stress dose is required, with the gold standard being $100\,mg$ of hydrocortisone IV.

For awake fiberoptic intubations, dexmedetomidine can be administered as a bolus of $1\,\mu g/kg$ over $10\,minutes$, followed by an infusion of $0.2-0.7\,\mu g/kg/hr$. This provides dose-dependent sedation and analgesia while maintaining spontaneous ventilation and aiding a smooth emergence, though it may cause bradycardia and hypotension during the bolus. Glycopyrrolate is often preferred over atropine for reducing secretions because it produces less tachycardia and does not cross the blood-brain barrier, thereby lacking sedative effects. However, glycopyrrolate is contraindicated in patients with glaucoma.

Ludwig’s Angina and Thyroid Surgical Considerations

Ludwig’s Angina is a rapidly progressing, dangerous cellulitis of the submandibular space that can descend into the mediastinum. Rapid sequence induction (RSI) is strictly contraindicated in these patients due to the high risk of total airway loss and the potential inability to provide rescue ventilation. Instead, an awake fiberoptic intubation under topical anesthesia and minimal sedation is recommended to preserve airway reflexes and spontaneous ventilation. The surgical team must be prepared for an emergent surgical airway at all times.

In thyroid surgery, tumors or large goiters may impinge on the tracheal cartilages or esophageal tissues, leading to tracheomalacia. This weakens the tracheal wall, making airway collapse highly likely during the first breath after extubation. Furthermore, in Functional Endoscopic Sinus Surgery (FESS), deliberate controlled hypotension is often used to limit blood loss. During this technique, the Mean Arterial Pressure (MAP) must not fall below $50-60\,mmHg$, and the decrease should not exceed $20\%$ of the patient's baseline MAP.

Tonsillectomy and Airway Fire Prevention

For tonsillectomies, a cuffed ETT is recommended. After the surgeon inserts a mouth gag for retraction, the anesthesia provider must reevaluate the ETT position, as the gag can displace the tube or obstruct its original placement. Overnight admission is mandatory for tonsillectomy patients who have obstructive sleep apnea (OSA) with more than $10$ events per hour, patients younger than $3$ years of age, those with significant comorbidities, or those with poor recovery in the post-anesthesia care unit (PACU) involving severe pain or PONV.

Post-tonsillectomy hemorrhage occurs in $0.5\%$ to $7.5\%$ of cases. While slow oozing is more common, profuse bleeding can lead to hypovolemia, indicated by tachycardia, hypotension, and agitation. These patients must be treated as having a full stomach, and RSI is indicated. Intra-operatively, the patient should be in a slight head-down position to protect the trachea from aspiration, and gastric decompression is necessary to assess blood loss and prevent pulmonary aspirates.

Surgical fire prevention during laser or electrocautery procedures requires maintaining an inspired oxygen concentration of less than $30\%$ before using the cautery. Supplemental oxygen via nasal cannula must be stopped at least $1\,minute$ before and during laser/electrocautery use. Protective eyewear is mandatory for all personnel: green-lensed for Nd:YAG lasers, clear for CO2 lasers, orange-red for KTP lasers, and orange for argon lasers. Water-soluble surgical lubricant should be applied to facial and head hair to reduce flammability.

Ophthalmic Surgery and Intraocular Pressure

The oculocardiac reflex is a trigeminal-vagal reflex triggered by pressure on the globe or orbital structures. It commonly manifests as sinus bradycardia, though it can cause AV block, ventricular ectopy, or asystole. Treatment begins with stopping the stimulus; if the bradycardia persists, atropine is the first-line pharmacologic treatment for complete vagal blockade, while glycopyrrolate is used for less severe episodes. Intraocular pressure (IOP) is significantly increased by coughing, succinylcholine, laryngoscopy, and intubation. Succinylcholine increases IOP within $1\,minute$, peaking at an increase of $9\,mmHg$ within $6\,minutes$.

Glaucoma is managed with various medications that have anesthetic implications. Alpha-2 agonists like Alphagan reduce aqueous humor production but are contraindicated with MAO inhibitors. Ecothiophate iodine, an irreversible cholinesterase inhibitor, can significantly prolong the effects of succinylcholine. Beta-blockers like Timolol also reduce aqueous humor production but require caution in patients with asthma, COPD, heart block, or heart failure. In retinal detachment surgery involving sulfur hexafluoride ($SF_6$) or perfluoropropane ($C_3F_8$) gas bubbles, nitrous oxide should be avoided for up to $3\,months$ to prevent bubble expansion. To minimize systemic absorption of eye drops, patients should close their eyes for $60\,seconds$ and avoid blinking, or the medial canthus can be manually blocked to stop tear outflow into the nasal mucosa.

Regional Anesthesia in Ophthalmology: Gills-Lloyd Technique

The Gills-Lloyd modified retrobulbar technique targets cranial nerves III, IV, V, VI, and VII. The injection is placed in the retrobulbar space (the cone) behind the eyeball. Monitoring for this procedure must include oxygen, bag-valve mask, suction, ECG, and blood pressure monitoring. During needle insertion, the clinician identifies the lateral limbic margin and directs the needle bevel toward the globe, parallel to the lateral limbic margin, inserting to a depth of $25\,mm$. After negative aspiration, a total of $2-5\,mL$ of preservative-free lidocaine ($1\%$ to $2\%$) is injected. Risks include grand mal seizures from systemic absorption, globe puncture (indicated by rapid pupil dilation and paralysis), and catastrophic increases in intraocular pressure over $22\,mmHg$.

Obesity and Bariatric Anesthesia

Medication dosing in obese patients follows distinct principles: water-soluble drugs (non-depolarizing relaxants, remifentanil, sufentanil) are dosed by ideal body weight (IBW). Lipid-soluble drugs (propofol induction, narcotics, sugammadex) and succinylcholine are dosed by total body weight (TBW). Propofol maintenance is based on TBW. Pickwickian Syndrome differs from OSA in that it includes chronic daytime hypercapnia. Bariatric surgery should be canceled and further workup ordered if two or more indicators are present: uncontrolled daytime sleepiness, witnessed apneas/snoring, or a neck circumference greater than or equal to $46\,cm$.

Physiological changes in obesity include a reduced functional residual capacity (FRC) caused by abdominal weight and chest fat. General anesthesia causes a further $50\%$ reduction in FRC. This leads to rapid desaturation during apnea. In such patients, the HELP (Head Elevated Laryngoscopy Position) or sniffing position is vital for induction to align the external auditory meatus with the sternal notch. Preoxygenation should last at least $3-5\,minutes$ with $100\%$ mask oxygen, utilizing CPAP if possible. Pressure control ventilation is the preferred intra-operative mode. For pain, NSAIDs like Toradol are strictly contraindicated in bariatric stomach-stapling procedures.

Geriatric Anesthesia and Physiological Changes

In geriatric patients, the Minimum Alveolar Concentration (MAC) of volatile anesthetics decreases by approximately $6\%$ per decade over the age of $40$. Hepatic mass and blood flow decrease by $20-40\%$, prolonging drug half-lives. Renal function also declines with age; creatinine clearance is the most reliable indicator of drug clearance. Serum albumin decreases, leading to higher free concentrations of acidic drugs. Cardiovascular changes include decreased compliance and ventricular hypertrophy. Atrial contraction (the "atrial kick") becomes critical, as its loss results in a $25\%$ reduction in ventricular filling. Elderly patients often exhibit reduced $\beta$-receptor responsiveness and a prolonged circulation time.

Thermoregulation is severely impaired in the elderly due to decreased basal metabolic rate and loss of subcutaneous fat. Protective reflexes, such as baroreceptor sensitivity and laryngeal cough/swallow reflexes, are significantly decreased. Postoperative delirium (POD) appears acute-on-chronic, while Postoperative Cognitive Dysfunction (POCD) involves subtle deficits that can last months. Standard induction doses for propofol and etomidate should be reduced by $50\%$, and benzodiazepines like Versed should be avoided or reduced by $75\%$ to prevent prolonged sedation.

Orthopedic and Spine Surgical Considerations

For posterior lumbar fusion, Total Intravenous Anesthesia (TIVA) using propofol, remifentanil, and ketamine is preferred to allow for neuromonitoring (EMG/SSEP), as inhaled anesthetics and muscle relaxants interfere with these readings. Prone positioning carries the risk of Postoperative Visual Loss (POVL) due to increased IOP and reduced ocular perfusion. Constant eye checks every $15-20\,minutes$ are required. The Jackson spine table is safer than the Wilson frame; the latter can compress the vena cava and vital organs, reducing venous return and cardiac index.

Tourniquet pressures should be set to $70-90\,mmHg$ above SBP for upper extremities and $2 \times$ SBP for lower extremities. Tourniquets should not exceed $120\,minutes$ of inflation. Release of the tourniquet causes transient metabolic acidosis, hypotension, and increased end-tidal CO2 ($ETCO_2$). During shoulder arthroscopy in the beach chair position, there is approximately a $25\,mmHg$ difference in MAP between the arm and the brain. Bone Cement Implantation Syndrome (BCIS) is characterized by hypoxia and right heart failure; the first sign is often an abrupt decrease in $ETCO_2$. Treat BCIS with $100\%$ oxygen, aggressive fluids, and $\alpha$-agonists like phenylephrine, while avoiding nitrous oxide.

Fat Embolism and Antifibrinolytics

Fat embolism syndrome (FES) is associated with long bone and pelvic fractures. It presents first with pulmonary symptoms (shortness of breath, hypoxemia) and may progress to neurological confusion. Lab findings include $PaO_2 < 60\,mmHg$. Management is primarily supportive. Tranexamic Acid (TXA) is an antifibrinolytic used to decrease blood loss in hip and knee arthroplasty, typically given in a dose of $1-2\,g$. It must be avoided in patients with a history of venous thromboembolism (VTE), cerebrovascular accident (CVA), or myocardial infarction (MI).

Neuromuscular Pharmacology and Reversal

Succinylcholine is a depolarizing blocker that mimics acetylcholine (ACh) and binds both alpha subunits of the nicotinic receptor. It has an onset of $30-60\,seconds$ and lasts $3-5\,minutes$. It can cause a Phase I block (normal) or a Phase II block (desensitization from high doses). It is contraindicated in burn patients ($24\,hours$ to $2\,years$ post-injury) and Myasthenia Gravis. Atypical plasma cholinesterase can prolong its effect; a Dibucaine number of $70-85\%$ is normal, $40-60\%$ (heterozygote) indicates slight prolongation, and $20\%$ or less (homozygote) indicates a block lasting $6-8\,hours$. Side effects include hyperkalemia ($K^+$ increases by $0.5-1\,mEq/L$), myalgias, and masseter spasm.

Non-depolarizing muscle relaxants (NDMRs) are divided into aminosteroids (rocuronium, vecuronium) and benzylisoquinoloniums (cisatracurium, atracurium). They bind only one alpha subunit and competitively block ACh. Acute Dilantin administration makes patients resistant to NDMRs. Sugammadex reverses NDMRs at a $1:1$ ratio and is $100\%$ renally cleared. Dosing is $2\,mg/kg$ for moderate block ($2$ TOF twitches), $4\,mg/kg$ for deep block, and $16\,mg/kg$ for immediate reversal after an intubating dose of rocuronium. Acetylcholinesterase inhibitors like Neostigmine (max dose $5\,mg$ or $0.07\,mg/kg$) have a ceiling effect and must be administered with an anticholinergic to prevent muscarinic side effects. Lambert-Eaton Myasthenic Syndrome is associated with small-cell lung cancer and results in extreme sensitivity to both depolarizing and non-depolarizing blockers.