Endotracheal Intubation: Principles and Equipment

Overview of Endotracheal Intubation

Endotracheal intubation is the placement of a cuffed or uncuffed tube through the mouth or nose, past the vocal cords, and into the trachea to secure and maintain a patent airway. As a respiratory therapist you will assemble the equipment, assist physicians and advanced practitioners, and in many clinical settings perform or verify intubations directly under protocol. Mastery of every item in the intubation kit — and the reasoning behind each choice — is a patient-safety requirement before you enter the clinical lab.

Physiological Goals of Intubation

The primary goals are to protect the airway from aspiration, deliver controlled ventilation, and allow precise management of oxygenation and carbon dioxide elimination. A secured airway also permits reliable delivery of inhaled medications and facilitates suction of secretions from the lower airway.

When laryngoscopy is performed, the stimulation of the hypopharynx and larynx triggers a stress response through the sympathetic nervous system. Heart rate rises, blood pressure increases, and intracranial pressure can spike — changes that may be dangerous for patients with coronary artery disease, head injury, or stroke. This is why adequate pre-oxygenation (breathing 100% oxygen for at least three minutes, or eight vital-capacity breaths, before the attempt) is standard practice: it loads the functional residual capacity with oxygen and extends the safe apneic period. Suction must also be immediately available before every intubation attempt because vomiting or secretion pooling can occur the moment protective reflexes are bypassed.

Components of the Intubation Kit

Laryngoscope handle and blades. The handle houses batteries and provides the light source through a fiber-optic or LED connection in the blade. Blades come in two main shapes:

• Macintosh (curved) blade: the tip is placed in the vallecula (the space between the base of the tongue and the epiglottis). Lifting forward and upward indirectly lifts the epiglottis, exposing the glottis. Sizes range from 0 (neonate) to 4 (large adult); size 3 is most commonly used for average adults.
• Miller (straight) blade: the tip passes beneath and directly lifts the epiglottis. Preferred in infants and young children because their epiglottis is floppy and omega-shaped; also useful for adults with a large or stiff epiglottis. Same size range as Macintosh.

Always test the light before the patient arrives. A dim or flickering light is an equipment failure and must be corrected.

Endotracheal (ET) tubes. ET tubes are sized by their internal diameter (ID) in millimeters. The cuff — a soft balloon near the distal tip — is inflated after placement to seal the trachea and prevent aspiration and air leak. The pilot balloon on the exterior indicates cuff status. Have at least one size smaller and one size larger than your planned size available at the bedside.

Stylet. A malleable metal wire inserted inside the ET tube to give it a rigid, curved shape (often a "hockey stick" or gentle J-curve) to guide the tube tip through the cords. The stylet tip must be recessed at least 1–2 cm from the Murphy eye (the side hole near the tube tip) so it cannot protrude and lacerate tissue. Remove the stylet immediately after the tube passes the cords.

10 mL syringe. Used to inflate the cuff with air after tube placement. The volume needed varies; inflate just until the air leak stops during a positive-pressure breath (minimal occluding volume technique), then check cuff pressure with a manometer — generally kept between 20 and 30 cmH₂O to perfuse the tracheal mucosa while maintaining a seal.

Magill forceps. Angled forceps used during nasotracheal intubation or to retrieve a foreign body; they allow the practitioner to direct the tube tip under direct laryngoscopy without blocking the view.

Tape or commercial holder. Secures the tube at the confirmed depth after placement. Mark and document the centimeter marking at the lip or nare.

ET Tube Size Selection

Adults: Standard practice uses fixed sizes based on sex and body habitus.

• Men: 8.0–8.5 mm ID is a common starting point.
• Women: 7.0–8.0 mm ID is a common starting point.

Pediatric patients (age 1 and older, uncuffed tubes historically):

Uncuffed tube ID (mm) = (Age in years ÷ 4) + 4

Pediatric patients — cuffed tubes (increasingly preferred to allow lower cuff pressures):

Cuffed tube ID (mm) = (Age in years ÷ 4) + 3.5

For neonates and infants under 1 year, gestational age and weight guide selection; consult institutional charts and the Broselow tape for emergency reference.

Insertion depth (oral route):

Approximate depth at lip (cm) = tube ID × 3 (a widely used clinical rule of thumb; always confirm with chest auscultation and chest X-ray).

Hazards of Laryngoscopy

• Hypoxemia: Apnea during the attempt consumes the pre-oxygenation reserve. Limit each attempt to approximately 30 seconds; re-oxygenate between attempts.
• Right mainstem intubation: The right mainstem bronchus branches at a less acute angle. If the tube is advanced too far, the left lung will not be ventilated. Confirm bilateral breath sounds and equal chest rise after every intubation.
• Esophageal intubation: The most immediately life-threatening error. Confirm with waveform capnography (gold standard), auscultation over the epigastrium (gurgling suggests esophageal placement), and chest rise.
• Dental and soft-tissue trauma: Using the upper teeth as a fulcrum for the laryngoscope handle can chip teeth; keep the wrist straight and lift along the handle's long axis.
• Hemodynamic stress response: As described above, pre-treatment with adequate sedation and analgesia, per physician order, attenuates this response.
• Aspiration: Have suction running and at hand before every attempt.