Laryngeal mask airway (LMA™)

The laryngeal mask air is an airway device that is positioned around the glottis to allow ventilation, typically at low airway pressures. It is also utilized as a rescue device in the difficult airway algorithm when you are unable to intubate or bag-mask-ventilate the patient.

The appropriate size for a laryngeal mask airway is based on the patient's weight: < 5 kg (size 1); 5 - 10 kg (size 1.5); 10 - 20 kg (size 2); 20 - 30 kg (size 2.5); 30 - 50 kg (size 3); 50 - 70 kg (size 4); 70 - 100 kg (size 5); and > 100 kg (size 6).*

The laryngeal mask airway protects the glottis from pharyngeal secretions but does not protect against gastric regurgitation; therefore, it should not be used in patients at risk for gastric regurgitation (e.g., patients who have not fasted or have small bowel obstruction, obesity) if tracheal intubation can be achieved.

Table. Contraindications, advantages, and disadvantages of laryngeal mask airways

Contraindications	Advantages	Disadvantages
Pharyngeal pathology Pharyngeal obstruction Paralysis Full stomach and procedures involving significant abdominal manipulation or pressure (e.g., laparoscopic procedures) Significant airway disease causing low pulmonary compliance requiring high inspiratory pressures Small mouth opening ( opening < 1.5cm) Obesity (due to likely increased airway pressures > 20 cmH2O)	Less invasive, better tolerated by patient Less risk of tooth/laryngeal trauma Doesn't require muscle relaxation (pharyngeal reflexes still require blunting) No risk of esophageal/endobronchial intubation	Increased risk of GI aspiration Less safe in prone position Airway is not protected, and does not protect against laryngospasm Limits maximum positive pressure ventilation Can cause gastric distension

The technique for inserting the LMA is described in the reference.*

* Ref. Sullivan P, Birdi T, Jeyaraj LM. Chapter 8. The laryngeal mask airway device (LMAD). In: Sullivan P, editor. Ottawa Anesthesia Primer. Toronto: ECHO Book Publishing, 2012.

Figure. Laryngeal mask airway
Image by Dr. Chris Wheatley - Own work, CCA 3.0, https://en.wikipedia.org/wiki/File:Laryngeal_mask_100.jpg

Endotracheal Tubes

See this video for an overview of intubation technique.

The endotracheal tube (ETT) is the main device for securing and maintaining a patient’s airway for ventilation. The size of the ETT refers to the internal diameter (in mm). Endotracheal tubes are inserted into the trachea, usually under direct or indirect (video) view of the larynx ("laryngoscopy") and vocal cords.

For adults, ETTs with a distal cuff ("cuffed" ETT) are used to prevent tracheal or pulmonary aspiration by inserting the cuff beyond the vocal cords. Adult cuffed ETT sizes range from 6.5 to 9 mm. The usual sizes are 7 to 7.5 mm for women and 8 to 8.5 mm for men.

For children, ETTs may or may not have a distal cuff due to concerns that pressure from an inflated cuff can cause tracheal mucosal pressure necrosis and result in softening of the still-developing tracheal tissue (tracheomalacia) as a complication. Uncuffed ETTs may be less likely to cause tracheomalacia and allow the use of a slightly larger size (due to absence of a cuff) but do not prevent aspiration.

Selecting an appropriately sized endotracheal tube is an important aspect of pediatric anesthesia. The size of tube changes significantly with the size and age of the child.

The table below summarizes appropriate endotracheal tube size selection by age in children:

Age of Patient	Cuffed Tracheal Tube	Uncuffed Tracheal Tube
Newborn - 6 months	3.0 mm	3.5 mm
6 months - 18 months	3.5 mm	4.0 mm
2 years and older	Age/4 + 3.5 mm	Age/4 + 4 mm

During tracheal intubation, a malleable semi-rigid stylet can be inserted into the ETT to provide some rigidity and facilitate entry into the glottis if needed.

ETT

Figure. Cuffed endotracheal tube
This is an 8.0 mm endotracheal tube, which is usually used in adult males. The distal cuff (on the left side of the tube) is inflated with air. (In clinical practice, the amount of air required to achieve a seal is a lot smaller than depicted here.) The broad black line shows the approximate location for the vocal cords. The proximal blue cuff (attached to the syringe) has a one-way valve to prevent leakage of air out of the distal cuff.

Image by Bigomar2 - Own work, CCA-SA 2.5, https://commons.wikimedia.org/wiki/File:Sondeintubation.jpg

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Laryngoscopy

Insertion of the endotracheal tube is usually performed under direct vision using a laryngoscope (direct laryngoscopy) or under indirect vision with a video laryngoscope (indirect laryngoscopy). In some situations (e.g., awake tracheal intubation), visualization of the glottis may be accomplished using a fiberoptic bronchoscope.

Laryngoscopes
A laryngoscope consists of a handle, which houses the power source, and a blade, which contains the light source and is used to manipulate the tongue and pharyngeal tissues so the larynx can be seen. The laryngoscope should be held in the left hand due to the shape of the laryngeal blades. The most commonly used blade is the curved Macintosh ("Mac") blade. The tip of the Macintosh blade is inserted into the vallecula during direct laryngoscopy. Less frequently used is the straight Miller blade. The tip of the Miller blade is inserted under the epiglottis during direct laryngoscopy.

Figure. Laryngoscope with different sizes of Macintosh laryngoscope blades
The blades shown are (from top to bottom) for large adults (size 4), small to normal adults (size 3), large children (size 2), small children (size 1), and neonates (size 0).

Image by Sasata - Own work, CCA 3.0, https://en.wikipedia.org/wiki/File:Macintosh_Blades.jpg

Figure. Laryngoscopes handles with different sizes of Miller laryngoscope blades
The blades shown are for the same populations as the ones in the above Figure. The narrow handle on the left is often used with the pediatric and neonatal blades in pediatric anesthesia. The handle in the middle is the one commonly used with adult blades. The short handle on the right is often used with patients who do not have a lot of space between the mouth and the chest wall (e.g., morbid obesity, pregnancy), which necessitates a shorter handle to enable insertion of the laryngoscope into the mouth. This handle is commonly used in obstetric anesthesia.

Image by DiverDave - Own work, CCA 3.0, https://commons.wikimedia.org/wiki/File:Laryngoscopes-Miller_blades.JPG