Equipment

In addition to endotracheal tubes and laryngoscopes, other essential items include an oxygen source, bag and mask, airways, stylet, lubricant, tape, and reliable suction. Other devices that may be used in special situations are also discussed.

Endotracheal Tubes

The endotracheal tube that is most commonly used in current practice is a polyvinyl chloride tube that has a low-pressure, high-volume cuff. This type of tube is illustrated in Figure 42-14B . Clinical use of the tube is generally dictated by the internal diameter that limits airflow. The external diameter of the tube depends on the internal diameter and on the thickness of the tube's wall, which varies among manufacturers. In adults, external diameter

Figure 42-14 Four types of commonly available endotracheal tubes. The cuffs are inflated with 10 mL of air. A, Microlaryngoscopy (MLT) tube (Mallinckrodt Co., St. Louis, MO) and extra-long, small-caliber (6.0-mm) polyvinyl chloride tube useful for laryngeal surgery. B, Standard intermediate pressure cuff and polyvinyl chloride tube (Mallinckrodt Co.). C, Armored "anode" tube with built-in spiral wire to minimize the opportunity of collapse or kinking. D, Flex-tip tube (Parker Medical, Englewood, CO) to facilitate insertion over a stylet or bougie. The numbers and letters visible on the tubes denote tube diameter, length from the tracheal end, and confirmation that the tubes have been tested for tissue compatibility (IT or Z-79).

The tube material itself is stamped Z-79 (Committee Z-79 on Anesthesia Equipment of the American National Standards Institute) or IT (implantation tested), indicating that the tube is free of toxic or irritant properties as far as testing can indicate. A line of x-ray-opaque material is manufactured into the wall of the tube to aid in placement. Most tubes have a hole cut in the wall opposite to the bevel. This hole is known as the Murphy eye and is designed to allow gas passage if the bevel lumen is occluded. The tube is manufactured to be sterile, and most current tubes are disposable. It is wise to check the free flow of air through the tube as part of the precase checkout. The interface between the plastic tube and 15-mm connector should be tightened snugly.

The cuffs of current plastic tubes are so-called high-volume, low-pressure cuffs. These compliant cuffs are designed to accommodate a relatively large volume of inflation before pressure rises. High pressure in the cuff lumen is transmitted to the tracheal mucosa, where it can

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Uncuffed endotracheal tubes have been used in children younger than 8 years. The narrow subglottic area is believed to limit the size of tubes in these young children. Endotracheal tube leak pressure is a clinically useful way to fit or confirm proper selection of uncuffed tube size in children.^[17] Leak should occur at 15 to 20 cm H₂ O pressure. The use of cuffed tubes in neonates, infants, and children has undergone renewed scrutiny and has the advantages of reducing waste gas exposure, allowing lower fresh gas flows, and avoiding repeat laryngoscopy without an increased incidence of croup.^[18] This is because a smaller-caliber tube, which causes less pressure in the immediately subglottic area, can be used. The cuff seal is achieved lower in the trachea. The same investigators used a new formula (cuffed endotracheal tube internal diameter = age/4 + 3) to successfully predict the required cuffed tube size in 99% of 488 children younger than 8 years.

The tube shown in Figure 42-14C is reinforced with a spiral wire to reduce kinking or collapse. These tubes are known as armored, anode, spiral embedded, or reinforced tubes, among other names. They are useful when an endotracheal tube is placed in a tracheostomy or laryngectomy stoma to provide an airway. They may also be used in head and neck or neurosurgical procedures when kinking of the tube is a strong possibility. However, care must be taken to avoid an excessive degree of neck flexion by overenthusiastic surgeons because increased peak airway pressures during positioning are not available as a monitor for excessive flexion or head turning. The RAE tube is made in oral and nasal versions and is bent to keep the tube out of the respective surgical fields ( Fig. 42-15 ). It may be somewhat difficult to secure the tube tip at an appropriate tracheal level if the patient has an unusually long or short lip-to-midtracheal distance. Further information on the equipment employed in airway management can be found in the monograph by Dorsch and Dorsch.^[19]

Tube Size Compared with Age and Sex

In men, an 8.0-mm ID endotracheal tube is appropriate, whereas in women, a 7.0-mm ID endotracheal tube is usually suitable. Given the variation between individuals, a tube of 1-mm ID size smaller or larger may be best for an individual patient. In general, the larynx is smaller in women, and it is the glottic aperture that limits the size of endotracheal tubes in adults. Uncuffed tubes have traditionally been used in young children. The sizes of uncuffed endotracheal tubes for use in children are given in Table 42-5 . Tubes of 0.5-mm ID smaller and larger sizes must be immediately available. Tube size on children can be estimated from the formula (16 + age)/4, but variation between individuals requires the availability of multiple tube sizes. If there is a suspicion of laryngeal or tracheal disease in any age group, smaller tubes should be available. A small tube (such as 6-mm ID in adults) may facilitate an otherwise difficult intubation.

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Figure 42-15 Preformed RAE endotracheal tubes: nasal (top) and oral (bottom).

Laryngoscopes

The standard rigid laryngoscope consists of a detachable blade with removable bulb that connects to a battery-containing handle. Each of the standard blades has a flange for displacing the tongue to the side and an open side for visualization of the larynx ( Fig. 42-16 ). Sizes range

Figure 42-16 Examples of the most frequently used detachable laryngoscope blades, which can be used interchangeably on the same handle. The upper blade is the straight or Jackson-Wisconsin design. The middle blade incorporates a curved distal tip (Miller). The lower blade is the curved or MacIntosh blade. All three blades are available in lengths appropriate for neonates and adults.

The curved blade introduced by MacIntosh is probably most popular for adult use. The commonly used straight blades are the Miller, which has a curved tip, and the Wisconsin blade (and its modified forms), which has a straight tip. Although straight blades may be advantageous in young children, the choice of blade in older children and adults is really a matter of familiarity and taste. The practitioner should be trained in the use of curved and straight blades, because when laryngoscopy is difficult with one type of blade, use of the other type may permit adequate laryngeal visualization. For example, the straight blade may be advantageous when the mouth opening is vertically limited or the larynx is anterior. It has been reported that less force and head extension is required with the Miller blade.^[20] The curved blade may be advantageous when mouth opening is horizontally limited or when more room is needed to perform the instrumentation desired (e.g., use of Magill forceps, changing tubes, intubation with endobronchial tubes). Many other types of blades have been designed, but their use is too limited to warrant additional discussion.

Other Equipment for Routine Use

A stylet is a rigid implement usually made of a flexible metal. It is inserted into the endotracheal tube to maintain a chosen shape. This facilitates intubation when the glottis is visualized, but the tube tip cannot be directed through the glottis or when glottic visualization is minimal or absent and a semiblind or blind technique is required. The usual shape used is that of a hockey stick, but more

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The Eschmann introducer (Connell Neurosurgical, Exton, PA) is a 60-cm, stylet-like device that has a 5-mm external diameter and a 35-degree bend 2.5 cm from the end that is inserted into the trachea. Its structure is designed to provide a combination of stiffness and flexibility. It is more commonly known as the gum elastic bougie, although it is not gum, elastic, or a bougie. It is an extremely useful instrument when laryngoscopic view is poor or the tube cannot be otherwise guided into the glottis. It is also useful in limiting the degree of necessary neck movement during intubation with potential cervical spine injuries and to lessen the risk of dental damage.^[21] The bent tip is directed blindly or under reduced vision into the glottic inlet and passed about 30 cm into the trachea (the bougie has distance markings). Tracheal entry is marked by the sensation of clicking over the tracheal cartilages and by the holdup by the reduction in luminal size near the carina. While keeping the laryngoscope in place, the endotracheal tube is slid over the bougie into the trachea; a 90-degree counterclockwise turn facilitates glottic passage by presenting the bevel posteriorly. A smaller tube may also be required for passage.

Tube passage over the bougie or any stylet may be enhanced by the soft flexible bevel of the armored tube, but special tubes such as the Parker Flex-Tip tube (Parker Medical, Englewood, CO) are far more effective. The beaklike tip of the tube (see Fig. 42-14D ) allows passage without impingement at the glottic inlet. This latter is common with a standard tube bevel. The bougie can also be used as tube changer, although it is a bit short for this purpose. It is reasonable to practice use of the bougie in a simulated difficult laryngoscopy in which a good glottic view is progressively reduced by lessening the force on the laryngoscope. This device is an indispensable part of clinical practice and allows a significant number of direct laryngoscopic intubations that cannot be otherwise accomplished. It is a relatively expensive piece of equipment, and care must be taken that it is not inadvertently thrown out in the course of a difficult airway situation.

Some clinicians lubricate the tip of the endotracheal tube with local anesthetic ointment. This is not necessary, and the ointment may actually increase the incidence of sore throat. The greasy ointment may also interfere with handling of the endotracheal tube. The ointment is useful for placing nasal instruments (e.g., airways, endotracheal tubes, nasogastric tubes) with oral airways and for lubricating the stylet. Some kind of adhesive tape is necessary for securing the tube after placement. Taping methods that avoid splitting the tape and that include additional reinforcing segments over the tape applied directly to the tube are most effective in preventing dislodgment.^[22] Particular care in securing the tracheal tube is indicated for surgical positions in which later access is difficult (e.g., prone neurosurgical patient in head pins with table turned away from the anesthesiologist), when dislodgment is likely (e.g., cleft palate repair), and when intubation is difficult. Cloth (twill) tape is useful in trauma cases in which blood makes adhesive tape less effective and in patients with heavy beards. It cannot be overemphasized that oxygen, bag and mask, and suction should be available for all but the most emergent intubations. An additional oxygen source connected to a manual ventilation bag should be available in the operating room to back up and supplement the oxygen supply available from the anesthesia machine.