Obese patients undergoing surgery are less frequently developing respiratory insufficiency (RI) and adult respiratory distress syndrome (ARDS), and when they do, they are less likely to have fatal outcomes, according to a new study published in the Journal of Intensive Care Medicine.

The researchers involved with the study say they have several theories of how obesity protects patients from mortality associated with RI/ARDS. In addition, the researchers believe pinpointing the protective mechanism could help them develop interventions to help non-obese patients avoid adverse outcomes.

For the study, the researchers used a large national database sponsored by the Agency for Healthcare Research and Quality to identify patients who underwent common surgical procedures known to have a high risk of leading to RI/ARDS between 1998 and 2007. Procedure types included open abdominal and laparoscopic abdominal surgeries; hip and knee arthroplasty; spine, cardiac, thoracic, major vascular surgeries; and surgeries of the head and neck. Roughly 9 million patients were identified.

The researchers found that 5.48% of patients had a diagnosis of obesity, and the incidence of RI/ARDS was 1.82% among obese patients and 2.01% among non-obese patients. In patients with RI/ARDS, in-hospital mortality was significantly lower in obese patients—5.45% versus 18.72%. Further, the need for mechanical ventilation, which may indicate more severe cases of RI/ARDS, was lower in obese than non-obese patients—50% versus 55%. In-hospital mortality in those requiring intubation was also lower in obese patients—11% versus 25%.

Among the theories as to how obesity could protect against mortality in patients with RI/ARDS, the researchers believe obese people may just have more energy stores or better nutritional status to help them get through an acute illness. Another theory is that fatty tissue may have some advantageous effect in the setting of a high inflammatory state; fatty tissue may act as a sink for the inflammatory proteins or cytokines, thus neutralizing them. A third hypothesis is that doctors are often more vigilant with obese patients, because they worry they will have more health problems, and this extra vigilance could be the cause of the “obesity paradox.”

If obesity protects in the latter way, the researchers believe that perhaps just extending that vigilance and the use of monitoring resources to non-obese patients would lower the rates of RI/ARDS. If the second theory—that fatty tissues can suck up inflammatory portents—is true, understanding this mechanism could lead to the development of interventions to prevent or treat the disease. For example, creating an intervention that mimics the physiological process that seems to offer natural protection to obese patients, such as binding of cytokines and other inflammatory mediators to fat, could have a protective effect, according to the researchers.

Source: Hospital for Special Surgery