Anesthetic Aspects of Bariatric Surgery: Addressing Challenges

| June 12, 2012

This ongoing column is authored by members of the International Society for the Perioperative Care of the Obese Patient (ISPCOP), an organization dedicated to the bariatric patient.

Column Editor: Stephanie B. Jones, MD
Dr. Jones is Vice Chair for Education, Department of Anesthesia, Critical Care and Pain Medicine, Beth Israel Deaconess Medical Center, Boston, Massachusetts

This month: Addressing challenges
by Ashish C. Sinha, MBBS, MD, PhD, DABA
Dr. Sinha is Professor and Vice Chairman for Research;Director of Clinical Research Anesthesiology, and Perioperative Medicine at Drexel University College of Medicine, Hahnemann University Hospital in Philadelphia, Pennsylvania.

Bariatric Times. 2012;9(6):18–19

Funding: No funding was provided.

Disclosures: The author reports no conflicts of interest relevant to the content of this article.

ABSTRACT
Airway management in patients with morbid obesity continues to worry and scare anesthesia providers. Most patients in this population can be approached in a systemic manner with a high degree of success. Appropriate positioning and pre-oxygenation are other keys to successful intubations.

It is inherently difficult to manage the airway and ventilation of a patient with morbid obesity in the anesthetic setting. While there are anesthetic concerns in this patient population, there are certain predictable characteristics that may allow us to design a strategy with a high probability of success.

One of the challenges of caring for this patient population is the airway anatomy with which many patients present. For example, a patient weighing 400 pounds or more might present with a Mallampati class III or IV airway.[1] In one experience at my clinic, Patient A, with a body mass index (BMI) of 110.7kg/m2 presented emergently with with cellulitis of the left thigh, suspicious for necrotizing fasciitis. Airway examination revealed Mallampati class IV airway, small oral opening, and a relatively large tongue, along with large neck circumference (Figure 1A and Figure 1B).

Functional reserve capacity (FRC) is decreased in patients with obesity and morbid obesity. The consequent reduced oxygen reserve is compounded by a larger metabolic demand and the supine tidal volume is even less than closing volume. A careful, thorough, and maximal preoxygenation is necessary prior to inducing and attempting to intubate the airway in this patient population.

One option of preoxygenation is employing the conventional three minutes of normal breathing with 100 percent oxygen, or five vital capacity breaths with 100 percent oxygen. If this is accomplished with a 25-degree head-up position, PaO2 is increased by 82mm Hg and apnea time to reach 92 percent oxygen saturation is increased by one minute.[2] Alternately, oxygen via continuous positive airway pressure (CPAP) of 10 cmH2O plus positive end-expiratory pressure (PEEP) of 10 cmH2O provides an additional one minute of safe apnea time.[3]

Data regarding mask ventilation are mixed. The general rule of thumb is that in 10 percent of patients with morbid obesity it is difficult to mask ventilate and in one percent it is difficult to intubate the airway. The risk factors that have been associated with difficult mask ventilation include the following: 1) Patients 55 years or older, 2) Patients with BMI greater than 25kg/m2, 3) Patients without teeth (edentulous), and 4) Patients with beards who also snore.[4]

Another study[5] found that the only correlates of difficult intubation of the airway in patients with obesity and morbid obesity are Mallampati airway greater than class III and a neck circumference more than 40cms. Collins et al[6] have shown that the difficulty of intubation increases with neck size; with each 1cm increase in neck circumference, the odds of problematic intubation increase by 1.13 percent (i.e., in a patient with a neck size of 40cms, the odds of problematic intubation are 5% and at 60cm neck circumference, the odds increase to 35%).

Positioning of patients with morbid obesity prior to induction and intubation is critical to optimize gas exchange and increase the probability of a successful intubation. The head elevated laryngoscopy position seems to be the most effective. A ramp that is a combination of two inflatable pillows makes achieving the position easier (Figure 2). A ramp can also be created by positioning blankets (about six depending on thickness) under the patient’s upper torso and head.

There are multiple options for intubating the airway. After good preoxygenation, adequate induction drugs, and complete paralysis, one can do a direct laryngoscopy using a Macintosh 3 blade. Alternately, the video laryngoscopes have a high rate of first pass intubation success, and have been shown to improve the Cormack-Lehane view by one or two units.7 In patients with super morbid obesity (BMI >70kg/m2), it behooves the most experienced provider available, to have a low threshold for taking over the airway management. Fiber optic bronchoscopy, either in an awake (when the airway appears truly challenging) or sleeping patient, continues to be an easy choice and a logical option for many experienced anesthesiologists.

Using the laryngeal mask airway (LMA) as a temporizing device in the event of difficulty in securing the airway with direct laryngoscopy or as a planned first step works well. After the intubating LMA is well placed an endotracheal tube can be passed through it directly or assisted by utilizing a fiber optic bronchoscope.

In Patient A described previously, the airway was initially secured by using an LMA and then an endotracheal tube was placed using a fiberoptic bronchoscope as a guide, in a Seldinger-like technique.

The use of short acting, rapid onset drugs at induction, especially in terms of neuromuscular blockade, seems intuitive. Unless contraindicated, succinylcholine is ideal in this situation. In patients with normal cardiac function, propofol and succinylcholine are appropriate. Once the airway is secured and recovery from succinylcholine established, an intermediate- or long-acting neuromuscular blocking agent can be added. The choice of volatile agent tends toward sevoflurance or desflurance because the limited fat solubility of both drugs speeds elimination at the end of the case. Propofol infusions can be utilized as long as the concept of context sensitive half-life is not ignored, especially if relatively rapid wake up is desired after the surgery is concluded.

Pain control is best addressed in a multimodal manner utilizing local anesthetics, nonsteroidal anti-inflammatory drugs (NSAIDs) and a limited amount of narcotics, to decrease the probability of postoperative sedation in a patient at high risk for serious outcomes in cases of sleep apnea. For the same reason, same day surgery in these patients should be evaluated in light of narcotics used, care at home, and use of CPAP.

Patients with morbid obesity in the anesthetic setting present with challenges. Airways in this patient population can be secured, and patient risk reduced, with careful planning and thoughtful execution of induction and emergence.

References
1.    Mallampati SR, Gatt SP, Gugino LD, et al. A clinical sign to predict difficult tracheal intubation; a prospective study. Can Anaesth Soc J. 1985;32(4):429–434.
2.    Dixon B, Dixon J, Garden J, 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(6):1110–1115; discussion 5A.
3.    Gander S, Frascarolo P, Suter M, et al. Positive end-expiratory pressure during induction of general anesthesia increases duration of nonhypoxic apnea in morbidly obese patients. Anesth Analg. 2005;100(2):580–584.
4.    Langeron O, Masso E, Huraux C, et al. Prediction of difficult mask ventilation. Anesthesiology. 2000;92(5):1229–1236.
5.    Gonzalez H, Minville V, Delanoue K, et al. The importance of increased neck circumference to intubation difficulties in obese patients. Anesth Analg. 2008;106(4):1132–1136.
6.    Collins JS, Lemmens HJ, Brodsky JB. Obesity and difficult intubation: where is the evidence. Anesthesiology. 2006;104(3):617; author reply 618–619.
7.    Goel S, Ochroch EA, Sinha A. Improvement of Cormack Lehane scores via direct laryngoscopy versus video laryngoscopy in morbidly obese patients undergoing elective weight loss surgery. The ASEAN Journal of Anaesthesiology. 2011;12(12): 49–55.

Address for Correspondence:
Ashish C. Sinha, MBBS, MD, PhD, DABA, Professor and Vice Chairman for Research; Director of Clinical Research, Anesthesiology and Perioperative Medicine, Drexel University College of Medicine, Hahnemann University Hospital, 245 N. 15th Street; MS 310, Philadelphia, PA 19102; E-mail: Ashish.Sinha@DrexelMed.edu

Category: Anesthetic Aspects of Bariatric Surgery

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