Noninvasive Mechanical Ventilation Physiology and Ventilatory Management in Morbidly Obese Patients

Abstract

Obesity is the disease of our age. When the body mass index (BMI) exceeds 40 kg/m2, it is called morbid obesity. Morbid obesity is a disease that can be seen in as high as 2–8% of the population. Expiratory reserve volume (ERV) and total lung capacity (TLC) decrease due to decreased functional residual capacity (FRC) in morbidly obese patients. In addition, lung volumes are lowered due to the upward movement of the diaphragm muscle during supine position. Intrinsic PEEP (auto-PEEP) occurs, and expiratory pressure increases as a result of closure of the airways. This increases work of breathing. In addition, the excess soft tissue in the upper airways contributes to increase in airway resistance resulting in increased work of breathing. For all these reasons, morbidly obese patients are prone to respiratory support. Delivering oxygen is not usually enough for these patients. Noninvasive mechanical ventilation (NIV) should be the first choice. The ventilation modes in NIV treatment may be CPAP, BiPAP, volume- or pressure-targeted pressure support, or pressure support by using appropriate interfaces (nasal cannula, nasal, and oronasal fullface masks or helmet). Monitoring SpO2 or transcutaneous carbon dioxide analyzer may be used during NIV administration. In addition, patient’s consciousness, respiratory frequency, respiratory depth-pattern, and arterial blood gas analysis should also be observed. Oxygen administration may also be added to the treatment to patients with SpO2 90% and below. Tidal volumes should be adjusted according to the ideal weight in morbidly obese patients.