Apparatus and Equipment

The Macintosh laryngoscope is the most popular curved laryngoscope blade in use for laryngeal visualization. Robert R. Macintosh designed it in 1943. Contrary to popular belief, the curved shape of the blade was not intended to avoid damage to the subject’s upper teeth and soft tissue. The primary focus of Macintosh was to allow easy and correct visualization of the vocal cords which was challenging to do with the straight blades of that time. The design of the blade pushes the base of the tongue upwards elevating the laryngoscope, while the epiglottis due to its attachment to the tongue (vallecula) is drawn upwards. Through this process, the MacIntosh blade can allow a clear view of the larynx.

Over the years, the MacIntosh blades have seen many modifications. The blades have proven to be easily translatable into plastic. Of all available laryngoscope blades, the MacIntosh blade has been the most successful and widely used blade in laryngoscopy.

Pre-laryngoscopy Preparations

Pre-anesthesia fasting of 8 to 12 hours is required in larger animals to minimize the risk of vomiting during induction or recovery from anesthesia. In smaller animals this step is unnecessary. However, guinea pigs may retain food in their pharynx. If this phenomenon is observed in a significant number of subjects (guinea pigs) then fasting them for 3 to 4 hours prior to anesthesia may be sufficient. Pre-anesthesia tests should also be performed to assess the subject’s health status and age.

Laryngoscopy can be performed in lightly anesthetized subjects; however, it is recommended that this method only be used once proficiency in the technique has been achieved. Before intubating, the subject should be administered oxygen for about 2 minutes as a preemptive measure to slow down the onset of hypoxia that could arise from the inadvertently obstructed larynx. Although laryngoscopy can be performed as an emergency diagnostic tool before surgical correction, it is most effectively performed in stable subjects.

Performing Laryngoscopy Using MacIntosh Blades

• Place the subject on its back.
• Hold the laryngoscope in your dominant hand.
• Extend the subject’s tongue forward and to the left.
• Slowly insert the blade into the right side of the subject’s mouth.
• Advance the blade inward and midline towards the base of the tongue.
• Place the tip of the blade in front of the epiglottis in the vallecula.
• Apply pressure caudally and upward with the handle placed at an angle of 45 degrees.
• Lift the handle until vocal cords are visualized.
• Perform intubation under direct visualization of vocal cords.
• Withdraw the blade while firmly holding the endotracheal tube in place.

Cleaning Procedure

Remove blade from the handle and tighten bulb before rinsing the blade under cool running tap water to remove all visible soil. Scrub the blade thoroughly using a soft bristle blade after soaking the blades in an enzymatic detergent. Wash once again under cool running tap water to remove residual detergent. Dry the blade using a clean lint-free cloth.

Precautions

Skeletal and soft tissue factors of the subjects may affect the visibility of the line of sight of the larynx. Failure to achieve line of sight around the base of the tongue may also make direct laryngoscopy using the MacIntosh blade difficult. The curvature of the MacIntosh laryngoscope can tend to intrude the line of sight during laryngoscopy. Improper usage of the blade can result in trauma to soft tissues and may damage frontal teeth. Always test the laryngoscope blades and handles should after cleaning, disinfection, sterilization and before usage. When selecting blade size, consider the weight of the subject. Since the handles of the blades also serve as counterbalance an appropriate size of the handle should be selected to match the blade size used.

References

Henderson JJ (2000). Questions about the macintosh laryngoscope and technique of laryngoscopy. Eur J Anaesthesiol. 17(1):2-5.

Jephcott A (1984). The Macintosh laryngoscope. A historical note on its clinical and commercial development. Anesthesia. 39(5):474-9.

Robert Reynolds Macintosh (1943). “A new laryngoscope.” The Lancet. 1 (6): 205. doi:10.1016/S0140-6736(02)95524-8.