Emergency Airway Management in the Morbidly Obese

Introduction

Recent times have witnessed an increase in the global incidence and prevalence rates of obesity, which causes an immense burden on healthcare resources worldwide. Obesity is now considered a multisystemic disease and is prevalent in all age groups. Obesity is considered a gateway for many systemic diseases, including cardiovascular disease, diabetes mellitus, insulin resistance, certain malignancies, sleep disorders like obstructive sleep apnea (OSA) or obesity hypoventilation syndrome (OHS), liver disease, and kidney diseases. Managing such patients requires special attention by the anesthesiologists, and various factors like anatomical airway obstructions, altered respiratory mechanics and pharmacokinetics, and modified drug dosing should be considered.

What Is Obesity?

• The WHO (World Health Organization) defines obesity as the accumulation of excess fat in the body, which leads to improper functioning of body systems. According to WHO, a person having a BMI (body mass index) greater than or equal to 30 is considered obese.

• Obesity is further classified into three subgroups based on severity, which are as follows:

• Class I obesity - BMI 30 to 34.9 kg/m2.

• Class II obesity - BMI 35 to 39.9 kg/m2.

• Class III obesity - BMI ≥40 kg/m2.

• Class III obesity is also called morbid obesity. The patients will have a BMI greater or equal to 40 and will be suffering from at least one obesity-associated systemic disorder.

What Are the Airway Challenges Encountered in a Morbidly Obese Patient?

• American Society of Anesthesiologists (ASA) defines an airway to be difficult when a trained anesthesiologist finds it difficult to provide face mask ventilation of the upper airway, and tracheal intubation becomes challenging, or both.

• Obesity leads to the formation of a lot of redundant tissue (loose or flabby tissues) that causes anatomical changes in the upper airways, head, and neck region.

• Narrowing of the airway occurs due to these redundant tissue formations in the pharynx and hypopharynx.

• Laryngoscopy becomes more challenging to perform with the large tongue, not being able to fit the submental space, and large tonsils, further interfering with the accessibility of the oropharyngeal space, making the laryngoscopy difficult to perform.

• Laryngoscopy is best performed in the “sniffing the morning air” position, and this is difficult to achieve in obese patients due to excess fat deposition in the neck, shoulder, and back region.

• Bag-mask ventilation and adequate mask seal cannot be achieved due to the deposition of excess adipose tissue in the face and neck region in obese patients.

• Due to altered respiratory mechanics, inadequate mask seal, and difficult tracheal intubation in morbidly obese patients, emergency airway management becomes highly challenging.

• Often these patients end up having reduced functional residual capacity (FRC), reduced chest wall compliance, micro atelectasis (complete or partial collapse of a lung or a part of the lung), early airway closure, and increased oxygen demand.

• Even after the anesthesia is induced, these patients are at high risk of rapid desaturation. Hence, anesthesiologists must provide adequate ventilation and oxygenation as soon as possible to secure the airway.

What Are the Measures Taken to Improve Airway Management In Morbidly Obese Patients?

1. Preoperative Management:

• The preoperative evaluation before performing airway management plays a crucial role.

• Successful airway manipulation is a result of careful assessment of patient factors, which can help in assessing the difficulty level and help in modifying the airway management procedures according to the patient factors.

• Dentition factors should also be considered, which may cause difficulties in intubation, and the dentist should be consulted for appropriate modifications.

• The various risk factors for difficult airway management should be considered, which are as follows:

• Presence of excess soft tissue around the face and neck.

• The extent of mouth opening.

• Facial hair.

• Short thyromental distance (total distance from the neck to the chin).

• High Mallampati score (tool for evaluating the ease of intubation).

• Movements of the neck and jaw.

• Large neck circumference.

• High BMI.

• Old age.

• Obese male patients.

• Patients suffering from OSA (obstructive sleep apnea), a condition in which a patient suffers difficulty in breathing when he sleeps during the night.

• X-rays and ultrasound studies are of great help in detecting intubation difficulties.

• In the case of head and neck pathologies, computerized tomography (CT) or magnetic resonance imaging (MRI) scans are very useful in planning airway management.

2. Preoxygenation:

• The principle of preoxygenation lies in increasing the safe apnea time for intubation by replacing nitrogen with oxygen in the FRC (functional residual capacity), which is the remaining volume of air in the lungs after the passive expiration of air.

• Morbidly obese patients require adequate preoxygenation as they tend to have greater oxygen consumption and reduced FRC.

• This enables longer safe apnea time in such patients, slowing the desaturation rate, which is faster in obese patients.

• An adequate preoxygenation protocol involves placing a tight-fit face mask and supplying 100 percent oxygen to inhale.

• Oxygen supplementation via nasal prongs with a tight-fitting face mask has been shown to extend safe apnea time and delay significant desaturation.

• An HFNC (high-flow nasal) cannula is used to blow 60 L of warm, humidified 100 percent oxygen with the help of modified nasal prongs.

• Other adjunctive techniques of preoxygenation include continuous positive airway pressure (CPAP), non-invasive ventilation (NIV), or pressure support to maintain PEEP (positive end-expiratory pressure) and prevent atelectasis.

3. Positioning:

• Anesthetic induction is majorly dependent on the position of the patient and the “sniffing the morning air” position causing neck flexion and head extension, allowing a patent airway passage by aligning laryngeal, oral, and pharyngeal structures in the same plane to ensure better access for laryngoscopy.

• However, this position is difficult to attain in obese patients as the supine position, in turn, decreases normal respiratory mechanics.

• In such cases, a ramped-up position is advised. This is attained by elevating the head and shoulder with the help of additional blankets or pillows. Commercial pillows, such as the troop elevation pillow, can be useful.

• The ramped-up position is widely accepted as it regularizes respiratory mechanics, and improves preoxygenation, and aligns the oro-laryngeal structures in a single plane, enabling better accessibility to perform laryngoscopy.

4. Laryngoscopy and Intubation:

A. Laryngoscopy:

• Laryngoscopy refers to the visualization of the larynx to achieve successful airway management and is usually performed with the help of direct laryngoscopes, video laryngoscopes (VLs), optical styles, and fiberoptic scopes.

• VLs are provided with a video-camera setup, which provides a good view and accessibility of the structures.

B. Intubation:

Awake Technique:

• Tracheal intubation can be carried out safely and successfully by awake fiberoptic intubation technique.

• With this technique, better visualization of the tracheal tube can be achieved with the help of a fiberoptic scope.

• Enables the patients to breathe freely before intubating and protects intrinsic airway tone.

• One should make sure to check the availability of all the necessary armamentariums, like fiberoptic scope, before starting the procedure, and it should be carried out by an experienced and trained person to prevent unnecessary delays.

5. Postoperative Management:

• Extubation in a postoperative management phase should be planned carefully to avoid extubation failure or the need for reintubation.

• Morbidly obese patients are considered high-risk patients in the postoperative ward, and the extubation, which is either carried out in an ICU (intensive care unit) or after an elective procedure, should be performed with great care.

• A difficult airway trolley should always be kept ready in the postoperative ward to intubate in cases of extubation failure.

• Extubation involves complete reversing of the neuromuscular blockade and should make sure that the patient is well-oriented before the removal of airway devices.

• Postoperative pulmonary complications, especially in patients with obesity or OSA (obstructive sleep apnea), can be prevented by providing NIV (non-invasive ventilation) or CPAP (continuous positive airway pressure) for a short period after extubation.

Conclusion

Performing successful airway management in morbidly obese patients is quite challenging, most of the time. Careful evaluation of respiration in the postoperative phase is crucial and should be carried out in an intensive care unit to prevent further complications. Anesthesiologists need to have adequate knowledge of challenges encountered and the measures to be taken in high-risk patients suffering from obesity to successfully carry out effective airway management.