Obesity has become a public health crisis in the United States. The prevalence of obesity doubled between 1976–1980 and 1999-2000, increasing from 15.1 percent to 30.9 percent [1
]. Results from the 2007-2008 National Health and Nutrition Examination Survey (NHANES) indicate that an estimated 34.2% of US adults aged 20 years and over are overweight, 33.8% are obese, and 5.7% are extremely obese [2
]. With the prevalence of obesity and morbid obesity on the rise, all healthcare specialties will see more and more of these patients. There will be increasing numbers of obese patients presenting for surgical procedures, including ones that require endotracheal tube exchanges.
Obese patients may present a challenge during airway management. However, a debate continues to whether morbidly obese patients are more difficult to intubate than the general population. Juvin et al. reported the incidence of difficult intubation to be 15.5% in morbidly obese patients, compared with 2.2% in controls [3
]. Gonzalez et al. found the difficult intubation rate of 14.3% in obese patients versus 3% in nonobese patients [4
]. In contrast, Ezri et al. and Lundstrøm et al. reported that BMI was weakly associated with difficult intubation in morbidly obese patients, when compared to nonobese patients [5
]. Among morbidly obese patients, Brodsky et al. and Neligan et al. demonstrated that increased BMI was not an independent risk factor of difficult intubation [7
Morbidly obese patients have decreased functional capacity (FRC), increased alveolar-to-arterial (A-a) oxygen gradient [9
], and increased oxygen consumption [11
]. Therefore, even if airway management—including airway tube exchange—is not difficult, they will desaturate faster than their leaner counterpart after cessation of ventilation. Patients whose airway management is difficult will be even more at risk of desaturation.
Due to concerns of possible difficult airway and/or rapid desaturation after cessation of spontaneous ventilation, some anesthesiologists opt to perform awake fiberoptic intubation (AFI) in morbidly obese patients, especially in those with very large BMIs or with other associated characteristics that predict difficult intubation [12
]. When the primary intubation is done with AFI, one misses the opportunity to test the difficulty of mask ventilation, as well as of laryngoscopy and intubation. If one chooses to perform an AFI for primary intubation in the first place because there are concerns that conventional laryngoscopy could be difficult, it will then be illogical to assume that airway exchange with conventional laryngoscopy will be easy.
As for airway management using direct laryngoscopy, it has been demonstrated that, when using direct laryngoscopy for intubation, a “ramped” position or HELP (head-elevated laryngoscopy position: head, shoulders, and upper body elevated so that the suprasternal notch and the external auditory meatus are in the same horizontal imaginary line) provides significantly improved laryngoscopic views in this patient population, when compared to standard sniffing position [13
]. Ramping the patient for primary laryngoscopy is generally done by placing blankets, or premanufactured elevation pillow [15
], on the surgical table before moving the patient onto it. This ramp will have to be removed for most surgical procedures. When the airway device needs to be exchanged, reinserting the ramp underneath an anesthetized, intubated morbidly obese patient may be very difficult and can lead a loss of airway, as well as injuries to anesthesiologists and OR personnel. When reinsertion of the ramp is not possible, a nondifficult primary intubation in the “ramped” position could turn into a difficult one when the patient is in sniffing position.
From the above examples, when the primary intubation has been successful with other methods other than conventional laryngoscopy in standard sniffing position, one should bear in mind that the tube exchange could be more difficult than the primary intubation.
This paper describes airway tube exchanging techniques, besides conventional direct laryngoscopy, in morbidly obese patients, in order to secure the airway and successfully change between a single-lumen tube (SLT) and a double-lumen tube (DLT) when necessary.
The circumstances in some of the references are either airway exchanging techniques in nonobese patients with other causes of difficult airway or primary intubation techniques in morbidly obese patients. There has not been literature specifically dedicated to airway tube exchanging techniques in morbidly obese patients; therefore some extrapolation is required from the existing evidence.
The examples of situations when airway tubes need to be exchanged include, but are not limited to the following: (1) an LMA needs to be upgraded to an endotracheal tube; (2) an SLT needs to be changed to a DLT for lung isolation (e.g., due to anesthesiologist's preference for lung isolation or failure of bronchial blocker to provide adequate isolation); (3) a DLT needs to be exchanged for a SLT (e.g., postoperative mechanical ventilation is required after intraoperative lung isolation with a DLT).
It should be noted that when lung isolation is required, an SLT does not have to always be exchanged for a DLT. Using a bronchial blocker with the indwelling SLT is another alternative, and the endotracheal tube will not need to be exchanged at all.