The handle houses the power source (batteries) and is designed in different sizes.

The blade is fitted to the handle and can be either curved or straight. There is a wide range of designs for both curved and straight blades ( Fig. 7.2 ).

A wide range of laryngoscope blades. (A) Miller blades (large, adult, infant, premature); (B) Macintosh blades (large, adult, child, baby); (C) Macintosh polio blade; (D) Soper blades (adult, child, baby); (E) left-handed Macintosh blade; (F) Wisconsin blades (large, adult, child, baby, neonate); (G) Robertshaw blades (infant, neonatal); (H) Seward blades (child, baby); (I) Oxford infant blade.

Usually the straight blade is used for intubating neonates and infants. The blade is advanced over the posterior border of the relatively large, floppy V-shaped epiglottis which is then lifted directly in order to view the larynx ( Fig. 7.3B ). Larger size straight blades can be used in adults.

Use of the laryngoscope.

The curved blade ( Macintosh blade ) is designed to fit into the oral and oropharyngeal cavity. It is inserted through the right angle of the mouth and advanced gradually, pushing the tongue to the left and away from the view until the tip of the blade reaches the vallecula. The blade has a small bulbous tip to help lift the larynx ( Fig. 7.3A ). The laryngoscope is lifted upwards elevating the larynx and allowing the vocal cords to be seen. The Macintosh blade is made in five sizes: neonate (0), infant (1), child (2), adult (3) and large adult (4).

In the standard designs, (colour-coded black) the light source is a bulb screwed on to the blade and an electrical connection is made when the blade is opened ready for use. In more recent designs, the bulb is placed in the handle and the light is transmitted to the tip of the blade by means of fibreoptics (colour-coded green) ( Fig. 7.4 ). Opening the blade turns the light on by forcing the bulb down to contact the battery terminal. Acrylic fibre is used in the disposable blades. The two systems are not cross-compatible.

Standard disposable laryngoscope blade (top) with the light bulb mounted on the blade; fibreoptic disposable laryngoscope blade (bottom).

(Courtesy Smiths Medical, Ashford, Kent, UK.)

A left-sided Macintosh blade is available. It is used in patients with right-sided facial deformities making the use of the right-sided blade difficult.

The McCoy laryngoscope (Penlon Ltd, Abingdon, UK) is based on the standard Macintosh blade. It has a hinged tip which is operated by the lever mechanism present on the back of the handle. It is suited for both routine use and in cases of difficult intubation ( Figs 7.5 and 7.6 ). A more recent McCoy design has a straight blade with a hinged tip. Both the curved and the straight McCoy laryngoscopes use either a traditional bulb in the blade or a lamp mounted in the handle which fibreoptically transmits the light to the blade.

The McCoy laryngoscope (Penlon Ltd, Abingdon, UK), based on a standard Macintosh blade.

Demonstrating the McCoy laryngoscope’s hinged blade tip.

A modified design called the Flexiblade exists, where the whole distal half of the blade can be manoeuvred rather than just the tip, as in the McCoy. This can be achieved using a lever on the front of the handle.

A more recent design the LpEx Dual Purpose blade (PROACT Medical Ltd, Corby, UK) ( Fig. 7.7 ), allows tracheal intubation as with a traditional blade in addition to an excellent visualization of the hypopharynx. This allows easier insertion of a nasogastric tube into the oesophagus in the presence of a tracheal tube. By positioning the in-situ tracheal tube in the groove of the blade, a clear view of the hypopharynx is achieved.

LpEx Dual Purpose blade. The inset image shows the groove to position an in-situ tracheal tube allowing visualization of the hypopharynx.

The blades are designed to be interchangeable among different manufacturers and laryngoscope handles. Two international standards are used: ISO 7376/2009 (green system) and ISO 7376/1 (black system) with a coloured marking placed on the blade and handle. The two systems have different dimension hinges and with different light source positions. The ‘green system’ is the most commonly used fitting standard.

The risk of trauma and bruising to the different structures (e.g. epiglottis) is higher with the straight blade.

It is of vital importance to check the function of the laryngoscope before anaesthesia has commenced. Reduction in power or total failure due to the corrosion at the electrical contact point is possible.

Patients with large amounts of breast tissue present difficulty during intubation. Insertion of the blade into the mouth is restricted by the breast tissue impinging on the handle. To overcome this problem, specially designed blades are used such as the polio blade. The polio blade is at about 120 degrees to the handle allowing laryngoscopy without restriction. The polio blade was first designed to intubate patients ventilated in the iron lung during the poliomyelitis epidemic in the 1950s. A Macintosh laryngoscope blade attached to a short handle can also be useful in this situation.

To prevent cross-infection among patients, a disposable blade (see Fig. 7.4 ) is used.

Laryngoscope handles must be appropriately decontaminated between patients to prevent cross-infection.