Airway management for obese patients

Obesity

Obesity has been a health issue of increasing importance all over the globe, its existence is growing in both developed and developing countries. As per WHO data, 39% of the world population above the age of 18 years are overweight 13% of these are obese. A number of different studies have shown a connection between obesity and cardiovascular diseases (stable coronary disease, acute myocardial infarction, heart failure, cardiac arrhythmias, and sudden cardiac death). The relationship between obesity and hypertension, diabetes mellitus, dyslipidaemias, and sleep apnea syndrome has also been found to increase the chances of cardiovascular disorders.

Obesity is measured in the range of body mass index (BMI); however, it provides no details on fat distribution, which is of high importance in cardiovascular risk. Consequently, novel clinical measurements (e.g., abdominal circumference and the calculation of waist/hip ratio) have been launched with the aim of identifying central or abdominal obesity. In the case of men, abdominal circumference above 102 cm and in women above 88 cm is considered as central obesity and includes more cardiovascular risk. A waist/hip ratio above 0.9 in the case of men and above 0.85 in the case of women is an indication of central obesity. ¹

Respiratory Physiology of an Obese Patient

The obese patient’s respiratory system endures different anatomic and physiologic changes that decide emergent airway management and starting of mechanical ventilation. Anatomically, obese patients have an enlarged neck circumference due to additional cervical adipose tissue. Increased neck circumference is strongly connected with the upper airway failure noticed in obstructive sleep apnea. Moreover, increased soft tissue deposition in a comparatively closed area of the oropharyngeal cavity pharyngeal airway narrowing. Increased neck circumference, as well as dorsocervical fat deposition, can reduce neck extension. Overall, the paramedic should be alert to the probability of a difficult airway due to obesity and its related anatomic alterations and prepare suitable planning and back-up.

Physiologically, obese patients have noticeably reduced lung volumes. Indeed, for every unit increase in BMI, functional residual capacity (FRC), vital capacity, total lung capacity, expiratory reserve volume, and residual capacity reduce 0.5% to 5%. Of these alterations in lung volumes, the depletion in FRC is probably the most critical, as further reductions lead to the termination of small airways and growth in airway resistance. The outcome of extended airway resistance is under-ventilated areas of the lung, atelectasis, and intrapulmonary shunting. Finally, chest wall compliance is decreased due to the growth in adipose tissue in the thoracic cage. All of these changes in respiratory physiology can be intensified when the obese patient is placed in the supine position. ²

Intubation

In critically ill obese patients, intubation is a high-risk strategy that can be fraught with dangers. Obese patients have a very small cardiopulmonary reserve and can desaturate quickly to critical oxygen levels during intubation. Many studies have emphasized obesity as a risk factor in difficult intubation. A short neck, a thick neck, diabetes mellitus, and abnormal upper teeth in obese patients have appeared to be other factors that can forecast difficult intubation. Expecting the difficulties of airway management in obese patients, it is necessary for paramedics to optimize intubation conditions to decrease the chance of poor results. ²

Preoxygenation

The main task of preoxygenation is to produce an oxygen reservoir by replacing nitrogen within the FRC with oxygen. The usual mode of preoxygenation comprises the use of a face-mask (FM) with 100% fractional inspired oxygen concentration (FiO2), bag-mask ventilation (BMV), noninvasive positive pressure ventilation (NIV), and high-flow nasal cannula (HFNC) devices. Oftentimes, the conventional mode of preoxygenation using an FM or BMV is not up to the mark in the seriously ill obese patient. But NIV can be helpful and many choose this method of preoxygenation. HFNC devices can be reckoned for obese patients; however, HFNC devices deliver minimum positive pressure that can be believed to have little impact on FRC, evidence assisting their benefit in preoxygenation before RSI is limited. ²

Patient Positioning

Correct positioning is vital for success in both preoxygenation and intubation of the obese patient. Given the changes in respiratory physiology, obese patients must be positioned in either a semirecumbent (head of the bed elevated to 25 degrees) or a sitting position in the course of preoxygenation. The upright or semirecumbent position may reduce air trapping, reduce atelectasis, and increase oxygen saturation prior to intubation. Like the optimal position for preoxygenation, obese patients should be positioned in a head-up or ramped position to optimize the laryngoscopic view for intubation. To confirm the correct position, the paramedic should align the patient’s sternal notch with his or her external auditory meatus.²

Mechanical ventilation

It is difficult to start mechanical ventilation in the intubated obese ED patient. Inaccurate ventilator setting can lead quickly to respiratory or hemodynamic deterioration and a rise in morbidity and mortality. Like the mechanical ventilation setting of non-obese patients, the key ventilator setting for the obese patient involves ventilator mode, respiratory rate, positive end-expiratory pressure (PEEP), and, in volume-controlled modes, tidal volume. Volume-controlled ventilation (VCV) and pressure-controlled ventilation (PCV) are the most used methods of mechanical ventilation for obese patients. So far, the advantages of one mode over the other have not been demonstrated in the literature. Nevertheless, some clinicians choose PCV, as the decelerating waveform may increase the distribution of airflow to the alveoli.

Finally, the ventilated obese patient must be positioned in a reverse Trendelenburg or sitting position. Like the optimal patient positioning for preoxygenation and RSI, the sitting position or reverse Trendelenburg decreases intrathoracic pressure, decreases atelectasis, reduces the incidence of hypoxemia, improves V/Q mismatch, and may increase the laryngoscopic view. ²

Conclusion

Different obstacles arise during resuscitation of the crashing obese ED patient for the EP. Even before the initiation of serious illness, obese patients have changes in respiratory physiology, circulatory physiology, and pharmacokinetics that considerably impact their ED evaluation and resuscitation. These changes enormously hit EP’s approach to swift order intubation; initiation and management of mechanical ventilation; circulatory assessment; vascular access; CPR; and the dosing of critical, high-risk medications. We hope that, through the implementation of the pearls and pitfalls discussed in this article, paramedics can reduce morbidity and mortality in this very sick patient population. ²