Respiratory Care of the Morbidly Obese Patient

US Respiratory & Pulmonary Diseases, 2016;1(1):25–6 DOI: http://doi.org/10.17925/USRPD.2016.01.01.25

Abstract:

The prevalence of obesity has been on the rise for the past couple of decades. Although the prevalence has stabilized, it remains quite high. Morbidly obese patients pose many challenges for the clinician. These patients have altered respiratory mechanics and lung volumes that combined with excessive adipose tissue surrounding the thorax and in the airway, affect how clinicians need to approach the situation in terms of both mechanical ventilation and airway management. In particular, with the advent of “lung-protective” ventilation, clinicians need to be aware of what the ventilating pressures are doing (or not doing) in these altered clinical scenarios.
Keywords: Morbidly obese, hypoventilation, plateau pressure, chest wall compliance, airway management, transpulmonary pressure, extubation, mechanical ventilation
Disclosure: John D Davies, MA, RRT, FAARC, is on the ResMed Advisory Board. No funding was received for the publication of this article. This article is a short opinion piece and has not been submitted to external peer reviewers.
Received: August 10, 2015 Accepted December 01, 2015
Correspondence: John D Davies, MA, RRT, FAARC, Duke University Medical Center, Durham, NC 27710, US. E: john.davies@duke.edu
Open Access: This article is published under the Creative Commons Attribution Noncommercial License, which permits any noncommercial use, distribution, adaptation, and reproduction provided the original author(s) and source are given appropriate credit.

Obesity is a medical condition in which excess body fat accumulates to the extent that a patient’s health may be adversely affected. Although the prevalence of morbid obesity has remained stable over the past decade, it is still quite high with significant effects on individuals and healthcare costs.1 The health consequences of obesity range from serious chronic conditions that reduce the general quality of life to significantly increased risk for premature death.2,3 Morbid obesity is associated with a greater incidence of medical and surgical pathologies. The obesity epidemic is taking a toll on the US economy by adding an additional estimated US$147 billion in healthcare costs.4

Obesity directly impairs the respiratory system in a number of ways. Carbon dioxide production is a function of body weight and, therefore, is increased in obese individuals. Ventilation/perfusion mismatch is more pronounced in obese patients due to small-airway collapse from decreased chest wall compliance. The lung bases have sufficient perfusion but are hypoventilated due to airway closure and alveolar collapse from the added weight of the chest wall. The result is a decreased functional residual capacity that can lead to hypoventilation (obesity hypoventilation syndrome) and hypoxemia, especially in the supine position. Respiratory muscle strength in the obese is likely to be compromised as the load of the extra adipose tissue is too much to handle. These patients are severely limited in terms of exercise capacity as well as ventilator reserve, which is key when these patients require mechanical ventilation.

The care of obese patients in the intensive care unit (ICU) poses special challenges in terms of both clinical care and safety. Specifically designed beds are required to accommodate the size and weight, and significant challenges exist in mobilizing or transporting such patients. Obese patients in the ICU are at higher risk for pulmonary emboli, cardiovascular compromise, esophageal reflux, and aspiration. Obesity also affects the pharmacokinetics and pharmacodynamics of many drugs due to changes in tissue distribution, hemodynamics, and blood flow to adipose, splanchnic, and other tissues. Plasma composition and liver and kidney function are also altered.

Airway management is complicated in obese individuals by excessive tissue hindering bag-mask ventilation and direct laryngoscopic view as well as interfering with the actual placement of the tube. A large neck with limited mobility, decreased mouth opening, large tongue, and short sternomental distance can pose serious challenges during endotracheal intubation attempts. Intubation is usually done in the supine position but, as mentioned above, putting obese patients supine can result in hypoventilation and rapid hypoxemia, so there may be less time to place the airway before hemodynamic collapse occurs. Equipment selection must be carefully considered prior to airway management procedures in obese patients. Other than routine laryngoscope blades and endotracheal tubes, equipment should include laryngeal mask airways, flexible bronchoscopes, and an emergency cricothyrotomy kit. If the obese patient requires a tracheostomy, special longer tubes may be required to traverse the excessive neck tissue to reach the trachea.

Ventilating the morbidly obese individual is extremely difficult. Many obese patients benefit from noninvasive ventilation (NIV). However, maintaining an adequate mask seal is complicated by excessive tissue.

References:
1. Ogden CL, Carroll MD, Kit BK, Flegal KM, Prevalence of childhood and adult obesity in the United States, 2011–2012, JAMA, 2014;311:804–14.
2. Fontaine KR, Redden DT, Wang C, et al., Years of life lost due to obesity, JAMA, 2003;289:187–93.
3. Centers for Disease Prevention and Control. Available at, http://www.cdc.gov/obesity/data/prevalence-maps.html (accessed August 26, 2015.)
4. Finkelstein EA, Trogdon JG, Cohen JW, Dietz W, Annual medical spending attributable to obesity: payer and service-specific estimates Health Affairs, 2009;28:w822–31.
Keywords: Morbidly obese, hypoventilation, plateau pressure, chest wall compliance, airway management, transpulmonary pressure, extubation, mechanical ventilation