Page 1840 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

CHAPTER 130: The Obesity Epidemic and Critical Care 1309

the early use of NIV in extremely obese patients who have developed for postextubation respiratory failure are not encouraging. If possible,
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respiratory failure. Extubation to NIV may also be considered for extremely obese patients should be ventilated and undergo spontane-
extremely obese patients at high risk for respiratory failure after thoracic ous breathing trials in the reverse Trendelenburg position, a maneuver
or abdominal surgery. Noninvasive ventilation is discussed in greater that improves respiratory system compliance by shifting the abdominal
detail in Chap. 44. contents off the chest wall.
Intubation of the extremely obese patient can be problematic. The Lung protective ventilatory strategies are challenging to apply in the
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view afforded the operator may be suboptimal because of extensive extremely obese patient with acute lung injury because of the difficulty
soft tissue in the hypopharynx. Reduced functional residual capacity in diagnosing alveolar overdistension in this population. The plateau
from extreme obesity and from sedation diminishes the oxygen stores pressure represents the pressure required to inflate the lung against its
available for the patient during apnea. The risk of aspiration of gastric elastic recoil, as well as that of the chest wall. Because the compliance
contents may be increased in this population, and obese patients should of the chest wall is diminished in extreme obesity, a high plateau pres-
be considered to have “full stomachs” during airway manipulation. For sure does not necessarily indicate alveolar overdistension. Thus, when
these reasons, we recommend that intubation be performed in the using low tidal volume ventilation in the management of acute lung
presence of an experienced operator, if possible. Once the decision has injury or the acute respiratory distress syndrome, the delivery of a tidal
been made to intubate, appropriate planning should commence with- volume of 6 mL/kg ideal body weight may result in a plateau pressure
out delay. Patient positioning is crucial to the success of the procedure. easily exceeding 30 cm H O without necessarily overdistending alveoli.
2
The “ramp” position is preferred in severely obese patients because While esophageal manometry may be considered in such cases we do
it allows increased visualization of the larynx when compared to the not advocate its routine use given the lack of data in this setting. We
“sniff” position. The ramp position is achieved by placing pillows instead recommend measurement of the plateau pressure in the upright
and blankets under the upper body, head, and neck until the exter- or semi-upright position to minimize the contribution of increased
nal auditory meatus and the sternal notch are horizontally aligned intraabdominal pressure from obesity and at times accepting an arbi-
(Fig. 130-2). Critical desaturation during intubation may occur due trarily higher plateau pressure, for example, up to 35 to 40 cm H O in
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2
to reduced FRC and oxygenation stores. Preoxygenation may be useful the extremely obese patient, if necessary.
at preventing this complication. Early planning allows for the con-
sultation of an experienced operator and an opportunity to consider Perioperative Considerations: The reduced functional residual capacity
the approach to airway management, including the use of fiberoptic associated with severe obesity encroaches on the closing capacity, the
assistance (see Chap. 45). lung volume at which small airways in the lung bases begin to close.
Several factors promote the development of atelectasis in the extremely This places severely obese patients at significant risk for atelectasis
obese patient who is intubated for respiratory failure. These include the in the perioperative period, particularly during and following upper
supine position, administration of sedatives and narcotics, and trans- abdominal and thoracic procedures. Hypoxemia may result and may
laryngeal intubation. As a result, extremely obese patients frequently be marked in the setting of a relatively unremarkable chest radiograph.
require increased levels of positive end-expiratory pressure to prevent While pulmonary embolism should always be considered in such
atelectasis and maintain adequate oxygenation, even in the absence of cases, aggressive measures directed at reversing atelectasis are typically
acute lung injury. In our experience, a positive end-expiratory pressure effective. Treatment involves adequate analgesia, avoidance of overse-
of 8 to 15 cm H O is frequently necessary. Because of atelectasis, sig- dation, early mobilization, and vigorous pulmonary toilet. Sleep-
2
nificant hypoxemia may be present at the time that the patient appears disordered breathing may worsen in the postoperative period, thereby
otherwise ready to sustain spontaneous breathing. In such cases it increasing the risk of respiratory failure. Preoperative screening of
may be necessary to “break the rules” that typically guide the deci- obese patients for obstructive sleep apnea is recommended: the STOP-
sion to extubate, while being prepared for possible failure. Extubation BANG (Snoring, Tiredness during daytime, Observed apnea, high blood
to NIV may facilitate this transition and may maintain upper air- Pressure, Body mass index, Age, Neck circumference, Gender) question-
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way patency when residual sedation promotes obstructive respiratory naire represents one such tool for this purpose. The early application
events, recognizing that some data supporting the routine use of NIV of noninvasive ventilation to improve pulmonary function, reduce
atelectasis, and treat latent sleep disordered breathing may decrease the
incidence of postoperative pulmonary complications.
■ TRACHEOSTOMY

Consideration should be given to early tracheostomy in the following
settings: (1) when severe obstructive sleep apnea that is refractory to
medical therapy is present, (2) when long-term nocturnal ventilation
for the treatment of obesity hypoventilation syndrome is planned, and
(3) when the course of recovery is expected to be prolonged. While the
rate of life-threatening complications from tracheostomy is low overall
in extremely obese patients, the risk is not zero, and there are a variety
of challenges to the safe performance and routine maintenance of a tra-
cheostomy in this patient population. Increased submental and anterior
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cervical fat may increase the difficulty of the procedure and also obstruct
the tracheostomy lumen once placed. Increased skin to airway distance
makes routinely available tracheostomy tubes unsuitable for use in many
extremely obese patients. Inadvertant dislodgment of the tracheostomy
tube may be associated with rapid desaturation in the extremely obese
patient lying flat, while the replacement of the tube may be technically
challenging. In such cases, it is preferable to reintubate the patient orally.
FIGURE 130-2. A morbidly obese patient placed in the “ramped” position. The external For all these reasons, the performance of a tracheostomy should ideally
auditory meatus and the sternal notch are horizontally aligned. (Reproduced with permission be conducted by an operator with experience in caring for extremely
from Kristensen MS. Airway management and morbid obesity. Eur J Anaesthesiol. November obese patients, and the patient should be observed in the ICU setting for
2010;27(11):923-927.) a period of time following the procedure.

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