One of the most important responsibilities for EMS providers at every level of certification is to control a patient’s airway and provide effective ventilation when necessary. Unfortunately, anatomic and physiologic changes related to severe obesity can significantly alter the provider’s ability to meet that responsibility.
Excess abdominal and thoracic adipose reduces the ability of the chest to expand, thereby decreasing chest wall compliance.[1] Obese patients have an increased pulmonary blood volume, which interferes with normal lung inflation, a condition known as decreased lung compliance.[2] Subsequently, both lung volumes and gas exchange becomes impaired.
Despite not being as metabolically active as muscle, excess adipose increases the metabolic burden, resulting in increased oxygen demand and carbon dioxide production, even at rest. The increased carbon dioxide production requires more ventilation to prevent hypercapnea.
Placing patients in a supine position, as may be needed for airway control and assisted ventilation, further reduces total respiratory compliance.[3]
Reduced respiratory compliance forces the bariatric patient to work harder to breathe.[4] Severely obese patients often exhibit some degree of hypoxemia resulting from regional ventilation-perfusion mismatching.[5] Alveolar collapse and airway closure at the bases can exacerbate this hypoxemia.[6]
Tilting the stretcher helps with ventilation
Increased body mass coupled with excess soft-tissue in the upper airway increases airway resistance. During bag-mask ventilation, overcoming this increased resistance requires the medic to squeeze the bag with more force. This can easily result in loss of mask seal and ineffective ventilation.
To facilitate ventilation with a bag-mask, rescuers should use a two-person technique. Oropharyngeal or nasopharyngeal tube insertion may help provide a patent airway and assist rescuers in maintaining an effective mask seal.
Unless contraindicated, raising the patient’s head and torso by titling the head of the stretcher reduces pressure on the diaphragm produced by the abdominal contents and can facilitate effective ventilation.
When compared to the supine position, ventilating patients at a 25-degree head-up tilt increases oxygen tension by about 23 percent and lengthens the desaturation safety period during endotracheal intubation of obese patients.[7]
The correlation between obesity and difficulty with laryngoscopy and endotracheal intubation is well known.[4, 8, 9, 10,11, 12, 13] Obesity alters upper airway anatomy and reduces glottic visualization even with optimal laryngoscopy technique.
Short, thick necks may limit the medic’s ability to optimize patient positioning for endotracheal tube insertion. As many as 13 percent of failed intubations in the field may be the result of factors related to obesity.[14, 12]
If clinical circumstances allows, place obese patients in an upright or semi Fowler’s position, depending on the degree of respiratory distress. This shifts the abdominal contents away from the diaphragm and improves ventilation.
Even in patients who must remain supine, such as those who require cervical spine stabilization or those receiving chest compressions, elevating the head of the backboard may improve ventilation during intubation preparation.
For patient’s undergoing pharmacologically assisted intubation, elevating and maintaining blood oxygen levels prior to medication administration is critically important for preventing blood desaturation during the procedure.
Reduced respiratory compliance and increased metabolic demand required of excessive adipose tissue will shorten desaturation times, which can critically reduce the safe apnea period associated with rapid sequence induction procedures.[15]
Position for nasal cannula oxygen
Preoxygenation by administering the highest concentration of supplemental oxygen in an upright position, rather than supine, for three to five minutes prior to induction will help mitigate this potentially lethal complication. If the patient is unable to effectively self-ventilate, non-invasive positive pressure ventilation can improve oxygen saturation levels.
In patients with a patent airway, providing oxygen via nasal cannula during the apneic phase of rapid sequence induction may improve oxygenation in obese patients. During a simulation of difficult laryngoscopy and following standard oxygenation and induction protocols in an operating room, the administration of supplemental oxygen at 5 liters per minute via nasal cannula maintained pulse oximetry values above 95 percent for almost two minutes longer than when nasal cannula oxygen was not used (5.29 minutes vs. 3.49 minutes, respectively).[16]
This occurs because blood continues to flow through the pulmonary capillary beds despite the fact the patient is no longer breathing. The flowing blood extracts oxygen from the alveolus, thereby reducing oxygen concentration in the lower airways.
Nasal cannula oxygen administration increases oxygen concentration in the upper airway and the oxygen diffuse toward the alveolar membrane even though the patient no longer inhales. This continued oxygenation of the alveolus can only happen if the airway remains patent.[17]
Although paramedics are often taught sniffing position as the optimal position for facilitating endotracheal intubation, many anesthesiologists use a maneuver called “stacking” or “ramping” whereby towels or folded blankets are placed under the shoulders and head to raise the tip of the chin to a level higher than the chest.[18] In this position, the auditory meatus will be at the level of the sternal notch.[19]
Stacking compensates for exaggerated flexing caused by posterior cervical fat and facilitates laryngoscopy and correct endotracheal tube placement. This position appears to be more effective than the traditional sniffing position for obese patients.[20, 21, 22, 23, 19]
Clinicians generally accept that obese patients have a higher risk of aspirating gastric contents into the lower airways because of increased intra-abdominal pressure and the frequency of hiatus hernia.[24] There is a strong correlation between increasing weight and body mass index with esophageal acid exposure.[25, 26]
However, several authors suggest the risk of aspiration in the obese population may not be higher than in the general population.[27, 28, 29]
Supraglottic airway insertion vs. endotracheal intubation
Supraglottic airway insertion may provide an effective alternative to endotracheal intubation for some patients. Several case reports describe the successful use of a tracheal-esophageal combitube in obese patients following failed intubation attempts.[30, 31]
In a PACU, use of a SAD for airway control in the obese patient resulted in a 75 percent reduction in hypoxemic episodes [32] and a 2.5 percent improvement in oxygenation saturation.[33] Unfortunately, supraglottic airway device (SAD) placement fails in about 3 to 5 percent of obese patients requiring the use of a tracheal tube.[24]
A meta-analysis conducted 20 years ago concluded that aspiration of gastric contents during airway control with a SAD is a rare event.[34] However, that meta-analysis only included the use of the first generation Laryngeal Mask Airway (LMA). When using this device, positive-pressure ventilation exceeding 20 cm H2O pressure can cause the mask seal to leak resulting in gastric insufflation, which increases the risk of vomiting.[24] (Nicholson, Cook, Smith, Lewis, & Reed, 2013).
Despite the rarity of aspiration complications, many consider obesity to be contraindication to the use of supraglottic airway devices (SADs) for airway control. However, many second generation SADs have structural improvements designed to resist mask seal leak or to provide direct access to the stomach for gastric decompression. The improvements suggest, but are not conclusive, of a reduced incidence of gastric aspiration.[35]
After gaining control of the patient’s airway, it is important to confirm proper tube placement and to secure the device to prevent tube migration and inadvertent extubation. Physical exam techniques should confirm rise and fall of the patient’s chest.
Ventilation with a bag mask should not produce epigastric sounds. Auscultation of the thorax should confirm the presence of bilateral lung sounds.
Verify proper tube placement
Finally, the American Heart Association recommends the use of continuous waveform capnography for verifying proper tube placement and ongoing tube surveillance.[36] Head flexion and extension during movement can produce a significant amount of distal tube movement.
EMS providers should secure the tube with either tape or a commercial product in such a way as to avoid compressing the sides of the neck and potentially reducing venous return from the brain.
It is important to note that much of the published research concerning airway control in the obese patient was conducted in the operating room or emergency department setting. Bariatric patients in need of airway control in the prehospital environment present unique challenges.
It is reasonable to expect both the incidence of failed intubation and the incidence of aspiration to be higher in the prehospital group compared to the operating room group. There is little prehospital data upon which to provide evidence-based recommendations in the obese patient.
References
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