Difficult Intubation in the Obese Patient

by Craig Troop, MD

Reprinted with permission of Texas Medical Liability Trust.

The following scenario is a synopsis of the anesthesiologist’s worst nightmare: can’t intubate/can’t ventilate. This ongoing concern in anesthesiology is being revisited in light of the personal observation that as the prevalence of obesity increases, standard oral intubation is becoming more difficult. The following summary is based on an actual closed claim case.

Case

A 54-year-old man was scheduled for a total knee replacement. The patient was 5’6” and weighed 250 pounds. His BMI was 40 kg/m2. In addition to obesity concerns, his medical history included hypertension, hypercholesterolemia, GERD, type II diabetes (diet controlled), and possible sleep apnea. The patient agreed to the placement of an epidural catheter for postoperative pain control but demanded to “be asleep” for the surgery.

Following the uneventful placement of an epidural catheter, the patient was placed in a fully supine position, monitors were connected, and a rapid sequence induction was performed. Oral laryngoscopy with a MAC 3 blade was attempted which revealed a grade 4 view (no identifiable laryngeal anatomy).1 Mask ventilation with an oral airway/bag and mask was attempted and noted to be difficult requiring high positive inspiratory pressures. Oral laryngoscopy with a MAC 4 and then a Miller 2 blade was attempted. The difficult airway cart, an intubating LMA, and additional anesthesia assistance were summoned. Between each attempt to secure an airway, mask ventilation became increasingly difficult; peak airway pressures were reported to be “sky high.” After several minutes of unsuccessful airway management, a general surgeon arrived. As the surgeon attempted a difficult tracheotomy, the patient arrested and further resuscitation efforts failed.

Discussion

For every dramatic, worst-case scenario as above, how many countless near misses occur? This article is not intended to be a lengthy review of the difficult airway. There are many excellent resources addressing this topic by notable national airway educators. (Please see Caplan, et al.’s “Practice Guidelines for Management of the Difficult Airway.”2,3 The House of Delegates of the American Society of Anesthesiologists spent more than 18 months and more than $150,000 in approving these guidelines.) The intent of this article is to share some suggestions based on personal experience.

As mentioned earlier, I have observed a trend of an increase in the overall number of difficult airway patients. There are several reasons for this, but perhaps an identifiable problem is the ever-increasing incidence of obesity with attendant comorbid disease processes. Five of the top 10 most “overweight cities” in the U.S. are in Texas.

As a broad classification, the morbidly obese patient is “apple-shaped” (tight fat) in appearance or is “pear-shaped” (loose fat) in appearance.4 Based on my experience, the “tight fat” obese patient tends to have a higher incidence of difficult airway issues.
There are several physical signs that can alert one to the possibility or probability of a patient having a difficult airway. The 6-Ds of airway assessment are 1 method used to evaluate for signs of difficulty:

  1. Disproportion (tongue to pharyngeal size/
    Mallampati classification)
  2. Distortion (e.g., neck mass)
  3. Decreased thyromental distance (receding or weak chin)
  4. Decreased interinscisor gap (reduced mouth opening)
  5. Decreased range of motion of the cervical spine, and
  6. Dental overbite.5,6

Although all 6 points are important, in my opinion, “the jaw tells the story.” An over-looked and simple clinical sign to assess the jaw is the upper lip bite test.7 The patient is asked to touch their upper lip with their lower teeth, i.e., protrude the mandible. This simple test addresses D3 and D6. Concerning point D5, ask the patient to look up at the ceiling or tilt their head backward. Any launching forward of the patient’s shoulders confirms that the range of motion of the cervical spine is limited.

Having clinically identified a potentially difficult airway and especially for the “tight- fat”/“apple shaped” obese patient, here are some personal, practical suggestions:

  1. Start from a position of strength. The term HELP (head elevated laryngoscopy position) was coined by Dr. R. Levitan.8 Two articles on pre-positioning the morbidly obese patient have shown that this position improves the laryngoscopy view9 and that there is an increase in the desaturation safety period.10 Rescue ventilation techniques, (oral airway/bag and mask) are facilitated by the HELP position. The head and neck are elevated above the chest and abdomen. The airway is therefore more isolated and easier to work with. Further, the weight of the abdomen is falling away from the diaphragm and less positive airway pressure is required. Stacking with blankets can create the HELP position, but may cause variable and/or unstable results. A pre-cut foam positioner designed to quickly achieve the HELP position is commercially available.
  2. Have airway management plans A, B, and C worked out, and all materials immediately available in the OR before the induction of anesthesia. If plan A is not achieving the desired result, activate plan B, or C early. There is much wisdom in the phrase, “Don’t persist in the same technique and expect a different result.” There are numerous airway devices available for advanced airway management. In my opinion, it is important to master 3 or 4 different techniques, and maintain a comfort level with each through constant practice.

Again, the above suggestions are my opinions based on personal experience. For more information, please review the ASA algorithm for managing difficult airways, available at http://www.asahq.org/publicationsAndServices/Difficult Airway.pdf.

 

References

  1. Cormack RS, Lehane J. Difficult tracheal intubation in obstetrics. Anaesthesia 1984;39:1105-11.
  2. Caplan RA, Benumof JL, Berry FA, et al. Practice guidelines for management of the difficult airway. A report by the American Society of Anesthesiologists Task Force on Management of the Difficult Airway. Anesthesiology 1993;78:597-602.
  3. Caplan RA, Benumof JL, Berry FA, et al. Practice guidelines for management of the difficult airway: an updated report by the American Society of Anesthesiologists Task Force on Management of the Difficult Airway. Anesthesiology 2003;98:1269-1277.
  4. American Society of Bariatric Surgery. Rationale for the surgical treatment of morbid obesity. Available at www.asbs.org/html/patients/rationale.html. Accessed August 22, 2005.
  5. Mallampati S. Clinical Assessment of the Airway. Anesthesiology 1995;13:301-308.
  6. Benumof JL. Airway Management: Principles and Practice. St. Louis: Mosby, 1996:126-42.
  7. Khan ZH, Kashfi A, Ebrahimkhani F. A comparison of the upper lip bite test (a simple new technique) with modified Mallampati classification in predicting difficulty in endotracheal intubation: a prospective blinded study. Anesth Analg 2003;96:595-9.
  8. Levitan RM, Mechem CC, Ochroch EA, et al. Head-elevated laryngoscopy position: improving laryngeal exposure during laryngoscopy by increasing head elevation. Ann Emerg Med 2003;41:322-30.
  9. Collins JS, Lemmons HJ, Brodsky JB, et al. Laryngoscopy and morbid obesity: a comparison of the “sniff” and “ramped” positions. Obes Surg 2004;14:1171-5.
  10. Dixon BJ, Dixon JB, Carden JR, et al. Preoxygenation is more effective in the 25 degrees head-up position than in the supine position in severely obese patients: a randomized controlled study. Anesthesiology 2005;102:1110-5.

DISCLOSURE: Dr. Troop is the inventor of a commercially available pre-formed positioning aid mentioned in this article.