4.1 Face Masks, Oral/Nasal Airways & Supraglottic Devices

4.1 Face Masks, Oral/Nasal Airways & Supraglottic Devices

Airway management represents the cornerstone of perioperative anesthesia practice. For the Certified Anesthesia Technologist (Cer.A.T.T.), mastering the design specifications, physiological principles, anatomical landmarks, and clinical troubleshooting protocols for non-invasive airway adjuncts is vital for patient safety. This section covers face masks, pharyngeal airways, and supraglottic airway devices (SADs) encountered in clinical practice.

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Anesthesia Face Masks: Design & Ventilation Mechanics

Anesthesia face masks provide an airtight seal between the patient's respiratory tract and the breathing circuit, enabling pre-oxygenation, spontaneous ventilation, and positive-pressure ventilation.

Mask Architecture & Component Engineering

Modern anesthesia face masks are constructed from medical-grade polymers engineered for optical clarity, patient comfort, and airtight sealing:

• Transparent Shell: The rigid body is fabricated from clear polycarbonate or polysulfone. Optical transparency is a critical safety feature that allows immediate visual detection of regurgitated gastric contents, active bleeding, secretions, or patient lip cyanosis. It also provides immediate visual confirmation of moisture condensation (fogging) during exhalation, indicating tidal airflow.
• Inflatable Cushion: A soft, pliable elastomeric or silicone peripheral cushion conforms to facial contours. The cushion contains a small pneumatic valve that allows adjustment of inflation volume using a standard Luer-slip syringe. Over-inflating the cushion creates a rigid surface that rolls off facial contours, producing massive gas leaks; under-inflating causes the rigid plastic shell to press directly against bony facial structures, causing bruising or skin necrosis.
• Connector Port: The mask features a standardized 22 mm female connector conforming to International Organization for Standardization (ISO 5356-1) specifications, ensuring universal coupling to circle system Y-pieces, heat and moisture exchangers (HMEs), or manual resuscitator bags.
• Retention Hook Ring: A removable four-prong plastic ring encircles the connector collar, serving as an attachment anchor for elastic head straps during prolonged mask ventilation.

Sizing Standards

Mask sizes range from 00 (neonatal) to 5 (large adult). Proper sizing requires fitting three distinct anatomical landmarks:

1. The superior apex must rest securely over the bridge of the nose, avoiding pressure on the nasion and eyes.
2. The lateral borders must seal across the nasolabial folds.
3. The inferior base must rest in the mental groove between the lower lip and the mental protuberance of the chin.

[!CAUTION] Applying mask cushions directly over the orbits can cause severe corneal abrasions or trigger the oculocardiac reflex via the trigeminal-vagal afferent-efferent pathway, resulting in profound sinus bradycardia, nodal rhythms, or asystole.

Single-Hand C-E Technique vs. Two-Hand Jaw-Thrust

Effective mask ventilation requires coordinated airway opening maneuvers that separate the soft palate, tongue, and epiglottis from the posterior pharyngeal wall.

Single-Hand C-E Clamp Technique:
   Thumb & Index Finger  ──>  Form "C" pressing mask downward onto face
   Middle, Ring, Little  ──>  Form "E" lifting bony mandible upward into cushion
   CRITICAL ACTION       ──>  Lift the face into the mask (never smash mask into face!)

• Single-Hand C-E Clamp: The non-dominant hand (typically left) grasps the mask. The thumb and index finger form a 'C' around the mask collar, exerting downward pressure to seat the cushion. The third, fourth, and fifth fingers form an 'E' positioned along the bony horizontal ramus and angle of the mandible. These fingers lift the mandible anteriorly and upward into the mask cushion while performing head tilt and atlanto-occipital extension. A common mechanical error is compressing the submental triangle soft tissues (the submandibular soft space) with the fingertips, which displaces the tongue backward against the posterior pharyngeal wall, causing iatrogenic upper airway obstruction.
• Two-Hand Jaw-Thrust Technique with Assistant: When difficult mask ventilation occurs, a two-handed technique is required. The primary provider uses both hands to place the thenar eminences or thumbs on the lateral mask body while hooking all remaining fingers beneath the bilateral mandibular angles to generate vigorous forward subluxation of the temporomandibular joints. An assistant—frequently the Certified Anesthesia Technologist—squeezes the reservoir bag or controls the manual ventilator mode.
• Difficult Mask Ventilation Risk Factors: Memorized using the BONES mnemonic: Beard (interferes with seal), Obesity (BMI > 26 kg/m² in the original study, redundant pharyngeal tissue), No teeth (edentulous, cheek collapse; managed by leaving dentures in during preoxygenation or using OPAs), Elderly (age > 55, loss of muscular elasticity), and Snoring/Sleep Apnea.

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Oropharyngeal Airways (OPAs): Engineering & Placement

An oropharyngeal airway (OPA) is a semi-rigid device inserted into the mouth to prevent the tongue and relaxed epiglottic structures from occluding the hypopharynx in an unconscious patient.

Guedel vs. Berman Designs

• Guedel Airway: Designed with a hollow, enclosed tubular central lumen. This tubular design accommodates suction catheters directly down the center while shielding the catheter from dental occlusion.
• Berman Airway: Features a solid central I-beam core with dual open lateral slotted channels. The lateral grooves allow suction catheters to pass along either side and make the device useful as a conduit during fiberoptic-assisted oral intubation, as the airway can be split or peeled away from the bronchoscope.

Both designs incorporate four common anatomical zones: the flanged oral end (prevents the device from slipping deep into the pharynx), the reinforced straight bite block (prevents teeth from compressing the lumen or clamping on an endotracheal tube), the curved pharyngeal body (mirrors the palatal curvature), and the distal blunted tip (rests in the hypopharynx above the vocal cords).

   [FLANGE] ─── [BITE BLOCK] ─── [CURVED BODY] ─── [BLUNTED TIP]
    (Lips)        (Teeth)          (Tongue)         (Vallecula)

Sizing & Insertion Protocols

Selecting the correct size is critical:

• Measurement: Place the flange at the corner of the patient's mouth (labial commissure) and measure to the angle of the mandible (gonion). Alternatively, measure from the center of the upper maxillary incisors to the mandibular angle.
• Size Pitfalls: An undersized OPA will push the base of the tongue downward into the pharynx, worsening obstruction. An oversized OPA will force the epiglottis downward directly over the laryngeal inlet, causing complete mechanical airway obstruction, or pass into the upper esophagus, causing gastric distension.

Color codes vary by manufacturer, so confirm OPA size by measurement rather than by color.

Insertion Techniques

1. 180-Degree Rotation Technique (Adults): Open the patient's mouth using a scissors-finger technique. Invert the OPA so the tip points toward the hard palate. Advance the device halfway along the palate until the junction of the hard and soft palate is reached, then smoothly rotate the device 180 degrees into its anatomical position while advancing it fully over the tongue base. This maneuver scoops the tongue forward away from the pharyngeal wall.
2. Tongue Depressor Technique (Pediatric & Frail Dentition): Preferred in infants, small children, and patients with fragile teeth. A wooden or plastic tongue depressor directly depresses the tongue body while the OPA is inserted right-side-up in its final anatomical orientation. Inverting and rotating an OPA in pediatric patients can lacerate the delicate soft palate or avulse immature tooth buds.

[!WARNING] Inserting an OPA in a lightly anesthetized or semi-conscious patient with intact protective airway reflexes triggers severe laryngospasm, coughing, retching, and active regurgitation with pulmonary aspiration. OPAs should only be introduced when the patient is deeply unconscious or under general anesthesia.

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Nasopharyngeal Airways (NPAs): Indications & Contraindications

A nasopharyngeal airway (NPA), or nasal trumpet, is a flexible, uncuffed tube constructed from soft latex, silicone, or neoprene. It provides a patent airflow channel between the anterior external nares and the posterior hypopharynx, terminating just superior to the epiglottis.

Sizing & Insertion Protocol

• Sizing Measurement: Measure the distance from the tip of the patient's nose (ala nasi) to the tragus of the ear (or the angle of the mandible). Diameter is specified in French units (28–32 Fr for average adults) or internal diameter (6.5–8.0 mm ID).
• Topical Preparation: Pre-treating the nasal mucosa with a topical vasoconstrictor (such as oxymetazoline 0.05% or phenylephrine 0.25–0.5% spray) shrinks the highly vascular Kiesselbach's plexus and turbinate mucosa, preventing severe epistaxis. Apply sterile water-soluble lubricant or 2% lidocaine jelly along the entire shaft.
• Insertion Vector: Direct the NPA perpendicular to the facial plane along the floor of the nose, following the contour of the hard palate. Do not direct the tube upward toward the cranial vault. The bevel must face the nasal septum to avoid shearing the vascular inferior turbinate. If resistance is felt, gently rotate the trumpet or switch to the contralateral naris; never force the device.

Clinical Comparison: OPA vs. NPA

Strict Contraindications for NPAs

1. Suspected Basilar Skull Fracture: Evidenced by periorbital ecchymosis (raccoon eyes), mastoid ecchymosis (Battle's sign), hemotympanum, or clear cerebrospinal fluid (CSF) rhinorrhea/otorrhea. The disrupted cribriform plate of the ethmoid bone allows an NPA to enter the cranial vault, leading to direct brain parenchymal trauma and fatal meningitis.
2. Severe Coagulopathy or Therapeutic Anticoagulation: Severe epistaxis can rapidly obstruct the airway and lead to pulmonary aspiration.
3. Nasal Deformity / Severe Septal Deviation: Increases mechanical resistance, mucosal avulsion, and false tracking.

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Supraglottic Airway Devices (SADs)

Supraglottic airway devices seal around the perilaryngeal perimeter to deliver positive-pressure ventilation and volatile anesthetics without entering the trachea.

First-Generation SADs: LMA Classic & Flexible

First-generation devices are simple airway conduits without dedicated gastric drainage channels:

• LMA Classic: The original reusable silicone laryngeal mask airway designed by Dr. Archie Brain. It features an airway tube terminating in an elliptical inflatable silicone cuff that seats into the hypopharynx, sealing over the laryngeal inlet. It provides an oropharyngeal leak pressure of 15 to 20 cmH2O. It offers no protection against gastric regurgitation or aspiration.
• LMA Unique: The single-use polyvinyl chloride (PVC) equivalent of the LMA Classic.
• LMA Flexible (Wire-Reinforced): Incorporates an armored, stainless-steel wire spiral embedded within the airway tube wall. This prevents kinking and allows the tube to be bent sharply away from the surgical field. It is widely used in ophthalmic, dental, maxillofacial, and head and neck procedures. However, the narrower internal lumen increases airway resistance, making it less suitable for unassisted spontaneous ventilation.

Second-Generation SADs: Advanced Gastric Protection

Second-generation devices incorporate mechanical features to isolate the gastrointestinal tract and improve sealing pressures:

• LMA ProSeal: Fabricated from medical-grade silicone. It features a dorsal cuff that inflates behind the standard bowl to enhance the anterior seal, generating oropharyngeal leak pressures of up to about 30 cmH2O. Its defining feature is a dedicated gastric drainage tube running parallel to the airway channel. The gastric lumen terminates at the distal tip of the cuff, seating directly into the upper esophageal sphincter. This channel allows the insertion of an orogastric (OG) tube (14–16 Fr) to evacuate stomach contents and vents passive regurgitation away from the laryngeal inlet, protecting against pulmonary aspiration. It also includes an integral silicone bite block.
• LMA Supreme: A single-use, preformed PVC device that combines the features of the ProSeal with an anatomically curved elliptical shaft for rapid insertion without requiring digital manipulation inside the oral cavity.
• i-gel Airway: A single-use supraglottic device featuring a non-inflatable cuff made of medical-grade thermoplastic elastomer (styrene ethylene butadiene styrene [SEBS]). The gel-like elastomer softens at body temperature and molds to the perilaryngeal anatomy, eliminating cuff hyperinflation and mucosal compression ischemia. It features an integrated gastric suction channel, a built-in bite block, and a wide buccal stabilizer.

   SECOND-GENERATION SAD FEATURES:
   ┌─────────────────────────────────────────────────────────────┐
   │  1. Higher Seal Pressure (25-30+ cmH2O)                     │
   │  2. Dedicated Gastric Drainage Channel (Vents Emesis/OG)    │
   │  3. Integral Bite Block (Prevents Airway Lumen Occlusion)   │
   │  4. Epiglottic Restraint / Elevation Mechanism             │
   └─────────────────────────────────────────────────────────────┘

Intubating LMA (Fastrach / FT-LMA)

The Intubating LMA (Fastrach) was engineered specifically as an intubation conduit for difficult and failed airways:

• Rigid Metal Handle & Anatomical Curve: Consists of a heavy, anatomically curved stainless steel airway tube attached to a rigid metal handle. This allows one-handed insertion, rotation, and positioning of the device without placing fingers in the patient's mouth.
• Epiglottic Elevating Bar: Located at the mask aperture, this single flexible bar replaces the multi-aperture mask bars found on the LMA Classic. As an endotracheal tube is advanced through the Fastrach, the tube pushes the elevating bar upward, lifting the epiglottis anteriorly to prevent it from folding over the vocal cords.
• Dedicated Endotracheal Tube: Accommodates a dedicated straight, cuffed silicone Fastrach ETT (up to 8.0 mm ID) with a soft, rounded blunt bevel (bullet tip) designed to glide atraumatically past the vocal cords. It can also serve as a conduit for flexible fiberoptic-guided intubation.
• Stabilizer Rod: Once the endotracheal tube is positioned in the trachea, a specialized plastic stabilizer rod holds the ETT at the incisors while the Fastrach mask is withdrawn over the tube, preventing accidental extubation.

LMA Classic Sizing and Maximum Cuff Volumes

Maximum volumes are ceilings, not targets. Inflate to the lowest volume that seals and confirm that cuff pressure stays at or below 60 cmH2O. Other devices (LMA ProSeal, LMA Supreme, i-gel) list their own sizing and maximum gastric tube sizes on the device or package.

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Cuff Pressure Monitoring & Cranial Nerve Preservation

Cuff pressure management is a primary responsibility for the anesthesia technologist during SAD use.

The 60 cmH2O Limit & Mucosal Ischemia

The normal capillary perfusion pressure of the human pharyngeal mucosa is approximately 30 mmHg (equivalent to ~40 cmH2O). When supraglottic airway cuffs are inflated beyond 60 cmH2O (44 mmHg), mucosal capillary blood flow is compromised. Sustained hyperinflation causes mucosal ischemia, submucosal edema, tissue ulceration, and postoperative pharyngitis.

Nitrous Oxide Diffusion Dynamics

When nitrous oxide (N2O) is used during general anesthesia, it diffuses into the silicone or PVC cuff down its partial pressure gradient faster than nitrogen can diffuse outward. This gas transfer causes progressive, uncontrolled cuff hyperinflation, and intracuff pressures can exceed 100 cmH2O during longer cases. Cuff pressure must be continuously or serially checked using a calibrated aneroid manometer, venting excess volume to keep pressure at or below 60 cmH2O.

   N2O Diffusion Hazard:
   [Alveolar N2O] ──(Rapid Inward Diffusion)──> [LMA Cuff Cavity]
   [Cuff N2]      ──(Slow Outward Diffusion)──> [Venous Return]
   RESULT: Intracuff Volume Increases ──> Pressure Spikes >100 cmH2O ──> Mucosal Ischemia

Peripheral Cranial Nerve Neuropraxias

Excessive cuff pressure compresses superficial cranial nerves against surrounding bony structures:

1. Lingual Nerve Palsy: Compression of the lingual nerve as it crosses the medial aspect of the mandible near the third molar causes loss of taste and sensation over the anterior two-thirds of the tongue.
2. Hypoglossal Nerve Palsy (CN XII): Compression of the hypoglossal nerve against the hyoid bone horn results in unilateral motor weakness, dysarthria, and tongue deviation toward the side of the lesion.
3. Recurrent Laryngeal Nerve Neuropraxia: Compression of the anterior branch of the recurrent laryngeal nerve between the hyperinflated cuff and the thyroid lamina or cricoid cartilage causes unilateral vocal cord paresis, resulting in postoperative hoarseness, stridor, and aspiration risk.