Intubation

Intubation being practiced on a dummy (conventional technique using a laryngoscope).

In medicine, intubation refers to the placement of a tube into an external or internal orifice of the body. Although the term can refer to endoscopic procedures, it is most often used to denote tracheal intubation. Tracheal intubation is the placement of a flexible plastic tube into the trachea to protect the patient's airway and provide a means of mechanical ventilation. The most common tracheal intubation is orotracheal intubation where, with the assistance of a laryngoscope, an endotracheal tube is passed through the mouth, larynx, and vocal cords, into the trachea. A bulb is then inflated near the distal tip of the tube to help secure it in place and protect the airway from blood, vomit, and secretions. Another possibility is nasotracheal intubation where a tube is passed through the nose, larynx, vocal cords, and trachea.

Extubation is the removal of the tube.

Risk vs. benefit

Tracheal intubation is a potentially very dangerous invasive procedure that requires a great deal of clinical experience to master.^[1] When performed improperly (e.g., unrecognized esophageal intubation), the associated complications may rapidly lead to the patient's death.^[2] Subsequently, tracheal intubation's role as the "gold standard" of advanced airway maintenance was downplayed (in favor of more basic techniques like bag-valve-mask ventilation) by the American Heart Association's Guidelines for Cardiopulminary Resuscitation in 2000,^[2] and again in 2005.^[3]

Risk management

No single method for confirming tube placement has been shown to be 100% reliable. Accordingly, the use of multiple methods to confirm correct tube placement is now the standard of care. At least one of the methods utilized should be an instrument. Waveform capnography is emerging as the gold standard instrument for the confirmation of correct tube placement and maintenance of the tube once it is in place.

Predicting ease of intubation

• Look externally (history of craniofacial traumas/previous surgery)
• Evaluate 3,3,2 - three of the patient's fingers should be able to fit into his/her mouth when open, three fingers should comfortably fit between the chin and the throat, and two fingers in the thyromental distance (distance from thyroid cartilage to chin)
• Mallampati score
• Obstructions (stridorous breath sounds, wheezing, etc)
• Neck mobility (can patient tilt head back and then forward to touch chest)
• Cormack-Lehane grading system (according to the percentage of glottic opening on laryngoscopy)

Observational methods to confirm correct tube placement

• Direct visualization of the tube passing through the vocal cords
• Clear and equal bilateral breath sounds on auscultation of the chest
• Absent sounds on auscultation of the epigastrium
• Equal bilateral chest rise with ventilation
• Fogging of the tube
• An absence of stomach contents in the tube
• Boggie suctioned from the endotracheal tube

Instruments to confirm correct tube placement

• Colorimetric end tidal CO₂ detector
• Waveform capnography
• Self inflating esophageal bulb
• Pulse oximetry (patients with a pulse) - delay in fall of saturation, especially if pre-oxygenated

Tube maintenance

The tube is secured in place with tape or an endotracheal tube holder. A cervical collar is sometimes used to prevent motion of the airway. Tube placement should be confirmed after each physical move of the patient and after any unexplained change in the patient's clinical status. Continuous pulse oximetry and continuous waveform capnography are often used to monitor the tube's correct placement.

Indications

Tracheal intubation is performed by practitioners in various medical conditions:

• Comatose or intoxicated patients who are unable to protect their airways. In such patients, the throat muscles may lose their tone so that the upper airways obstruct or collapse and air can not easily enter into the lungs. Furthermore, protective airway reflexes such as coughing and swallowing, which serve to protect the airways against aspiration of secretions and foreign bodies, may be absent. With tracheal intubation, airway patency is restored and the lower airways can be protected from aspiration.
• General anesthesia. In anesthetized patients spontaneous respiration may be decreased or absent due to the effect of anesthetics, opioids, or muscle relaxants. To enable mechanical ventilation, an endotracheal tube is often used, although there are alternative devices such as face masks or laryngeal mask airways.
• Diagnostic manipulations of the airways such as bronchoscopy.
• Endoscopic operative procedures to the airways such as laser therapy or stenting of the bronchi.
• Patients who require respiratory support, including cardiopulmonary resuscitation.

Types of tubes

There are various types of tracheal tubes for oral or nasal intubation. Tubes may be flexible or preformed and relatively stiff. They are usually made of flexible plastic or silicone, though they may be armored with metallic rings to prevent kinking. Adult tubes have an inflatable cuff to seal the lower airways against air leakage and gross aspiration. The cuff must be maintained diligently in order to avoid complications from over-inflation, which can include rupture of the trachea, tracheal malacia, tracheoesophageal fistula. Many of the complications of over-inflated cuffs can be traced to cuff pressure against the tracheal wall causing ischemia of the mucosa underneath. ^[4]

Special double-lumen endotracheal tubes have been developed for ventilating each lung independently -- this is useful during lung and other intra-thoracic surgery. Smaller pediatric tubes generally are uncuffed, as the cricoid cartilage, the narrowest portion of the pediatric airway, often provides an adequate seal for mechanical ventilation. An excessive leak can sometimes be corrected through the placement of a larger (0.5mm larger in internal diameter) endotracheal tube, although in difficult-to-ventilate patients even children may need to use cuffed tubes to allow for high pressure ventilation if the leak is too great to overcome with the ventilator. [1].

Techniques

Nasal intubation

Several techniques exist. Tracheal intubation can be performed by direct laryngoscopy (conventional technique), in which a laryngoscope is used to obtain a view of the glottis. A tube is then inserted under direct vision. This technique can usually only be employed if the patient is comatose (unconscious), under general anesthesia, or has received local or topical anesthesia to the upper airway structures (e.g., using a local anesthetic drug such as lidocaine).

Rapid sequence induction (RSI) is a variation of the standard technique for patients under anesthesia. It is performed when immediate definitive airway management through intubation is required, and especially when there is a risk of aspiration. For RSI, a short acting sedative such as etomidate, propofol, thiopental or midazolam is normally administered, followed shortly thereafter by a paralytic such as succinylcholine or rocuronium. RSI is only correctly performed using an induction agent with a 1 arm-brain circulation time. The only agents classically used are those with 1 arm brain circulation times and are Thiopentone and etomidate. This provides the shortest induction time, and provided the appropriate dose based on body mass is used, protects against awareness during the RSI. Propofol and midazolam (in combination with other induction agents) may be used for induction where there is more time, however, propofol is increasingly being used to good effect for RSI.

Another alternative is intubation of the awake patient under local anesthesia using a flexible endoscope or by other means (e.g., using a video laryngoscope). This technique is preferred if difficulties are anticipated, as it allows the patient to breathe spontaneously throughout the procedure, thus ensuring ventilation and oxygenation even in the event of a failed intubation.

Some alternatives to intubation are

• Tracheotomy - a surgical technique, typically for patients who require long-term respiratory support
• Cricothyrotomy - an emergency technique used when intubation is unsuccessful and tracheotomy is not an option.

Because the life of a patient can depend on the success of an intubation, it is important to assess possible obstacles beforehand. The ease of intubation is difficult to predict. One score to assess anatomical difficulties is the Mallampati score,^[5] which is determined by looking at the anatomy of the oral cavity and based on the visibility of the base of uvula, faucial pillars and the soft palate. It should however be noted that no single score or combination of scores can be trusted to detect all patients who are difficult to intubate. Therefore, persons performing intubation must be familiar with alternative techniques of securing the airways.

History

The first known description on the surgical procedure of intubation was given in the 1020s by Avicenna in The Canon of Medicine in order to facilitate breathing.^[6] The first detailed report on endotracheal intubation and following artificial respiration of animals was in 1543, when Andreas Vesalius pointed out in this report that such a measure could sometimes be life-saving. It remained unnoticed however.

In 1869, the German surgeon Friedrich Trendelenburg accomplished the first successful intubation of humans for anaesthesia. He introduced the tube through a temporary tracheotomy. In 1878, the British surgeon McEwen performed the first oral intubation.

During the First World War, Magill and Macintosh achieved profound improvements in the application of intubation. The most used replaceable spatula of the laryngoscope is named after Macintosh. The Magill curve of an endotracheal tube and the Magill pliers for positioning the tubus during nasal intubation are named after Magill.

Technology

Laryngoscope

Historically, the most common device used for intubation has been the laryngoscope. Although it has proven sufficient throughout history, many serious problems can arise from its misuse (ex. dental trauma). Newer technologies such as flexible laryngoscopy have fared better in reducing problematic incidence, though the most common cause of intubation trauma is a lack of skill on the part of the laryngoscopist.

The laryngoscope consists of a handle, usually containing batteries, and an interchangeable blade. There are two styles of laryngoscope blades commercially available: the straight blade, and the curved blade. The most popular style of straight blade is the Miller blade, with the Macintosh being the most popular style of curved blade. The technique required is slightly different depending on the style of blade being used; in adults, the Macintosh blade is usually preferred by practitioners, whereas with neonates the Miller blade is the more commonly-used style.

There are many other styles of straight and curved blades, with accessories such as prisms (for enlarging the field of view) and ports for the administration of oxygen. These specialty blades are primarily designed for use by the anaesthetist in the operating room.

Fiber optics

Another common technology used for intubation has been fibre optics, most notably the fibre optic bronchoscope. Intubation over a fibre optic bronchoscope is the preferred method for those who have been deemed difficult to intubate using traditional methods (colloquially known as a "difficult airway".) Using fibre optic bronchoscopy or rhinoscopy still has its drawbacks, however; it requires a significant degree of skill to manipulate the bronchoscope, making this method somewhat inaccessible to practitioners who are not proficient in its use. The equipment has a high initial cost of purchase, is extremely fragile, and very expensive to repair. ^[7] While traditional intubation with laryngoscopy is ideally achieved in less than 20 seconds, intubation with a bronchoscope can take considerably longer, making its use in highly emergent situations somewhat limited.

Image sensor

The latest technology used to intubate is a computer system utilizing CMOS image sensors. Visibility failures still occur but to a lesser extent. Also, this technology is still extremely expensive and little used, but progress has been made to reduce visibility failures and costs.

Pediatric Intubation ^[8]

Most of the general principles of anaesthesia can be applied to children, but there are some significant anatomical and physiological differences between children and adults that can cause problem, especially in neonates and children weighing less than 15 kg.

Route for intubation

For infants and young children oral intubation is easier than nasal. Nasal route carries risk of dislodgement of adenoid tissue and epistaxis, but advantages in good fixation of tube. Because of good fixation, Nasal route is preferable then oral route in children undergoing intensive care and requiring prolonged intubation.

Position of tube

The tip of tube should be at midtrachea (between the clavicles on an AP chest X-ray). The position of the tube is checked by auscultation (equal air entry on each side and, in long-term intubation, by chest X-ray).

Type of tubes

Uncuffed tubes (plain tubes) are commonly used in prepubescent children. In cross section the airway in children is circular which makes plain tracheal tube fits better than cuffed tube.

Cuffed tubes less than 6.0 mm and not inflated are accepted for use in paediatry but generally in children less than 10 years old cuffed tubes are avoided to minimize subglottic swelling and ulceration.

Size of tube

Because the airway of a child is narrow, a small amount of oedema can produce severe obstruction. Oedema can easily be caused by forcing in a tracheal tube that is too tight. (If length of the tube is suspected to be large, immediate changing it to the smaller size is suggestible.)

The correct diameter of the tube is that which results in a small leak at a pressure of about 25cm of water (the tip should be at midtrachea, between the clavicles on an AP chest Xray).

For normally nourished children more than about 2 years old, the following formula to calculate the internal diameter of the tube is likely to be of the correct size

Formula

Internal diameter of tube (mm) = (age in years ÷ 4) + 4

Rough idea

Roughly correct tube size can be indicated by: Inner Diameter: can be estimated by the size of the child's little finger. (For neonates, 3 mm internal diameter is accepted while for premature infants 2.5 mm internal diameter may be necessary.) Length: can be estimated by doubling the distance from the corner of the child's mouth to the ear canal.

• Looking from side of the child’s head while holding the upper end of the tube level with the mouth can provide an idea of how far into the chest the tube will go.

References

External links

• Airway devices for intubation

Relevant journal articles

• Fridrich P, Frass M, Krenn CG, Weinstabl C, Benumof JL, Krafft P. The UpsherScope in routine and difficult airway management: a randomized, controlled clinical trial. Anesth Analg. 1997 Dec;85(6):1377-81.
• Mallampati SR, Gatt SP, Gugino LD, Desai SP, Waraksa B, Freiberger D, Liu PL. A clinical sign to predict difficult tracheal intubation: a prospective study. Can Anaesth Soc J. 1985 Jul;32(4):429-34.
• Adnet F, Borron SW, Racine SX, Clemessy JL, Fournier JL, Plaisance P, Lapandry C. The intubation difficulty scale (IDS): proposal and evaluation of a new score characterizing the complexity of endotracheal intubation. Anesthesiology. 1997 Dec;87(6):1290-7.
• Ovassapian A. Conduct of anesthesia. In: Shields TW, ed. General thoracic surgery. 4th ed.Baltimore:Williams & Wilkins, 1994:307–23.
• de Menezes Lyra R. Glottis simulator. Anesth Analg. 1999 Jun;88(6):1422-3.[2]
• Smith, N Ty. Simulation in anesthesia: the merits of large simulators versus small simulators. Current Opinion in Anaesthesiology. 13(6):659-665, December 2000.
• Kabrhel C, Thomsen TW, Setnik GS, Walls RM (2007). "Videos in clinical medicine. Orotracheal intubation". N. Engl. J. Med. 356 (17): e15. doi:10.1056/NEJMvcm063574. PMID 17460222.