ARDS and the Obese Patient

In addition to an increased risk for Type II diabetes, cardiovascular disease, and other illnesses, obese patients often experience acute respiratory distress syndrome. But treating obese patients with ARDS presents its own challenges, specifically with intubation and ventilation. 

By Phyllis Hanlon

Obesity has taken the international spotlight as a serious chronic illness with both medical and financial implications. The World Health Organization (WHO) reported that in 2014 there were more than 1.9 billion adults across the globe who were overweight; at least 600 million were clinically obese. The National Institutes of Health (NIH) estimates the indirect and direct costs associated with obesity at approximately 5% to 10% of US healthcare spending.

According to Hibbert, obese patients commonly “experience alterations in baseline pulmonary mechanics, including airflow obstruction, decreased lung volumes, and impaired gas exchange, and these changes have implications in many diseases, including ARDS.”¹ Many hospitals use the ARDSNet protocol as a baseline for treatment, aiming for an oxygenation goal of Pao₂ of 55-88 mm Hg or SpO₂ of 88-95%, a minimum positive end expiratory pressure (PEEP) of 5 cm H₂O, and a plateau pressure goal of less than or equal to 30 cm H₂O. But one size does not fit all when treating the obese patient.

High Frequency Ventilation 

Legacy Emanuel & Randall Children’s Hospital finds the use of high frequency percussive ventilation (HFPV) to be effective for this demographic. “The bariatric population presents some unique challenges as they are typically more difficult to ventilate and have more comorbidities. We widely use the P/F (PaO₂/FiO₂) ratio to establish the level of refractory hypoxemic respiratory failure,” said Bob Apsey, RRT, clinical specialist, Adult Critical Care. “If the P/F ratio approaches <200 and failure is imminent, we allow very little time between conventional lung protective management and a change to the Percussionaire VDR-4 HFPV. This change occurs as soon as increased PEEP and MAP requirements become imminent.”

Jimbo Varnum, senior product manager for the 3100 high frequency oscillatory ventilator (HFOV) at CareFusion, also emphasized the importance of taking action quickly when a patient with ARDS is admitted. He explained that acute kidney or lung injury, or renal or multiple system organ failure, could occur with delays in treatment. “The cascade starts with the lungs. Getting the lungs open will hopefully keep all the systems working,” he said.

For proper and safe ventilation, he recommended monitoring transpulmonary pressure (TPP).

By exchanging the patient’s nasogastric (NG) tube for one that works with a HFOV, which uses very small tidal volume (eg, 1-3 mL/kg), oxygenation, as well as chances for survival, may be improved. “Putting in the NG tube to measure TPP will allow the rest of the organs to keep working. The biggest thing is getting the patient oxygenated and keeping him oxygenated,” said Varnum, noting that while the ARDS protocol calls for less than 30 cm of plateau pressure, TPP requires a tighter measurement of less than 20 cm.

The 3100B HFOV delivers 18-20 cm of pressure, helps protect lungs from stretching, and recruits and normalizes lung architecture while ventilating with near-dead space tidal volumes. Research has shown a relationship between dead space and morbidity in ARDS patients, but once the lungs are open, volumetric capnography can help reduce dead space, according to Varnum. A study² showed that the 3100B HFOV used in adults with ARDS demonstrated a 29% relative reduction in mortality compared to conventional ventilation.

Along with a lower TPP measurement, Varnum believes that higher PEEP can help with the work of breathing. “The patient might need two times the PEEP [he is receiving]. Patients haven’t gotten a lot of pneumothorax with higher PEEP,” he said, noting that at times he has gone up to 40 PEEP. Varnum asserted using PEEP earlier and more appropriately might also result in cost savings for the hospital.

Careful monitoring of obese patients with ARDS is critical in detecting any changes that might warrant altering an intervention. AVEA ventilators monitor real-time pressure waveforms continuously, which give the clinician added insight, according to Varnum. For instance, when a patient is placed in a different position or when the patient is diuresing, he might need a lot of PEEP. The AVEA measures and displays the actual work imposed by the trach tube, and monitors the trach pressure, esophageal pressure, and transpulmonary pressure. The latter measure allows the clinician to optimize PEEP titration.

Natasha Barany, product manager for AVEA ventilators, pointed out that the automatic inflation of esophageal balloons is unique to CareFusion’s Avea ventilator. When the ventilator can monitor esophageal pressure and the work of breathing, PEEP can better be titrated and overall the technology has been shown to reduce time on the vent, she noted.

Esophageal Pressure Monitoring  

The Geisinger Health System makes stringent efforts to minimize unwarranted variations to a patient’s respiratory condition, according to A. Joseph Layon, MD, FACP, system director, Critical Care Medicine at Geisinger and clinical professor of medicine at Temple University. “We try to protocolize what can be automated and delegate what can be delegated,” he said. Although Geisinger has developed protocols for sedation and ARDS, no specific procedures for obese patients with decreased chest wall compliance or increased pressure have been created. “We’ve used ARDSNet data and protective lung strategies of 6-8 cc/kg ideal body weight and reduce it to 4 when possible, but 10% of patients don’t respond,” he noted.

When he was a fellow at the University of Florida, Layon examined esophageal monitoring as a way to measure airway inclusive pressure. He explained that studies have looked at reducing plateau pressure to decrease pulmonary complications and asserted that the plateau pressure recommendation of 30 or less is appropriate, “but not great.” He said, “The lowest is what’s good and what you want. But how do you know it’s appropriate?”

Layon asserted that with a noncompliant chest wall, it is important during the inspiratory and expiratory portions of the respiratory cycle to work to prevent ventilator-induced lung injury, such as barotrauma, volutrauma, or what he calls sheer trauma. He cited esophageal manometry as a viable solution. “The ability to use esophageal pressure measurements during the inspiratory and expiratory cycles is a remarkable tool,” he said. “As long as the end expiratory pressure is between 0 and 5, the alveoli will stay open.” Layon has found Puritan Bennett devices to be quite effective, but noted that the Hamilton-Medical G5 has “salvaged a lot of patients.”

He explained that Pennsylvania has a morbidly obese rate of 30% and patients are very sick upon admission, particularly in the winter months. “We can’t vent them and thought we’d have to use ECMO, which is very difficult in obese patients,” he said pointing out that the use of esophageal balloons helped monitor pulmonary pressure and facilitated patient care.

“By keeping inspiratory pressure in the 20 to 25 cm/H₂O range and the expiratory pressure between 0 and 5 cm, we can oxygenate and ventilate obese patients. This obviates the need for ECMO,” Layon said. “It’s a unique tool for use in very difficult cases.” Geisinger is now in the process of modifying its ventilator protocol for patients who are morbidly obese; the system will utilize esophageal monitoring.

ECMO

While extracorporeal membrane oxygenation (ECMO) is considered a last resort treatment option, Legacy Emanuel & Randall Children’s Hospital has had much success with the therapy. “Typically, patients referred to our Respiratory Failure and ECMO center have failed conventional ventilation modes and strategies. These include ARDSNet, APRV, and HFOV at referring facilities. These patients frequently have severe ARDS (P/F <100) and septic shock in the setting of morbid obesity and present significant and unique challenges in ventilator and overall critical care management,” said Apsey.

He continued, “All eligible patients are considered for ECMO. Patients over 340 pounds present unique challenges that must be taken into consideration. Limitations are cannula size; specifically obtaining a cannula long enough to support the flow required as well as sufficient drainage. We also incorporate use of the Avalon ECMO catheter into the internal jugular vein. That catheter increases the efficiency of blood gas exchange by draining blood from both the upper and lower body and allows greater mobility during positional therapy.”

Other Concerns

Mike Hess, RRT, at the Department of Veterans Affairs in Kalamazoo, Mich, pointed out that ventilating the patient with extra mass and extra pressure is itself the biggest challenge the clinician faces. “Commonly, a lot of clinicians seem to forget to use ideal body weight measure to figure out the tidal volume. They use actual patient weight so the patient is getting too much tidal volume. The lungs don’t grow as the person gains weight. You have to keep the tidal volume at the correct level to prevent barotrauma and ventilator-associated events,” he said.

Additionally, although monitoring TPP is important, other issues, such as fluid management and positioning, bear consideration. Studies on fluid management in an obese population are scarce. Recent trends tend to be relatively conservative with fluid, said Hess. He cited the Fluid and Catheter Treatment Trial³ (FACTT), which compared conservative, liberal, and simplified conservative fluid protocols in treating patients with ARDS, although not specifically obese patients. The results found that FACTT Lite and FACTT Conservative had the same clinical and safety outcomes, but the former had greater cumulative fluid balance and could be an alternative to the latter.

Studies on prone positioning report conflicting findings, according to Hess. A 2013⁴ study published in Chest cited prone positioning as a safe practice for those who are obese, while a trial 1 year later arrived at vastly different conclusions. “A 2014 study⁵ indicated that patients who carry weight in the abdomen versus lower in the hips have an increased risk for renal failure and hypoxia,” Hess said, adding that the time an obese patient remains in a prone position can also impact outcomes. “We have found the reverse Trendelenburg takes the stress off the diaphragm and lets the lungs expand.”

Legacy Emanuel & Randall Children’s Hospital has developed positioning protocols with specific roles for its team members. “The RT leads this team by securing the ECMO and ventilator circuits. The RT then leads the team through a series of safety checks before ‘counting down’ to the initial maneuver,” said Apsey. A step-by-step guideline has been developed and is part of the mandatory education that staff receives. The entire process has been video recorded for staff to view. Competence must be verified before participating in the proning team.”

Ann Whitson, RRT, staff respiratory therapist at Legacy, added, “One of our biggest challenges is the skin breakdown of these patients during proning. We have worked with all team disciplines (ECMO surgeon, nursing, and wound care) to develop very specific procedures when securing the endotracheal tube to provide the best protection against skin breakdown and pressure ulcers.”

The presence of excess fat in the neck raises concerns about line placement in the obese patient, said Atul Malhotra, MD, professor of medicine, division chief, Pulmonary and Critical Care Medicine, University of California San Diego School of Medicine. “The risk of pneumothorax increases with morbidly obese patients,” he said. “It’s hard to find a vein or visualize without ultrasound.”

But obtaining an ultrasound or CT scan can pose logistical challenges since the patient must be transported to the imaging suite, an often-daunting task. The process of loading a large patient onto the stretcher and then transferring the patient onto the scanner without dislodging a tube may require several people, noted Malhotra. Once the patient is in position, the scanner may not be able to capture the entire body on film and/or adequately penetrate the chest wall. “There is a technical issue of getting adequate resolution of chest parenchyma,” he said.

Inhaled nitric oxide (iNO) was at one point in time considered as an appropriate treatment for ARDS in obese patients. However, the therapy is extremely expensive and clinical data does not support its use.

Malhotra reported that multicenter trials have shown no benefit to using iNO. “In newborns, it can be helpful, but in adults there have primarily been negative results,” he said, pointing out that the aforementioned study was based on gas exchange and used inhaled NO to drive down PEEP.

Moreover, the cost of inhaled NO can be burdensome. “It used to cost $3,000 a day, but now the charge is per hour,” Malhotra said. However, he noted that iNO could be useful as a test to elicit response. “Then you could look to other therapies. It’s convenient as a provocative maneuver,” he added.

Individualized treatment is the best option for optimal outcomes; at the same time a multimodal monitoring strategy that includes esophageal manometry could help provide the most effective treatment option for obese patients with ARDS. RT 

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Phyllis Hanlon is a contributing writer to RT. For further information, contact [email protected].

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References

1. Hibbert K, Rice M, Malhotra A. Obesity and ARDS. Chest. 2012 Sep;142(3):785-90.

2. Derdak S, Mehta S, Stewart T, Smith T, Rogers M, Buchman T, Carlin B, Lowson S. and the Multicenter Oscillatory Ventilation for Acute Respiratory Distress Syndrome Trial (MOAT) study investigators. “High Frequency Oscillatory Ventilation for Acute Respiratory Distress Syndrome in Adults: A Randomized, Controlled Trial.” Am J Respir Crit Care Med 2002; 166:801-808.

3. Grissom CK, Hirshberg EL, Dickerson JB et al. “Fluid management with a simplified conservative protocol for the acute respiratory distress syndrome.” Crit Care Med. 2015 Feb;43(2):288-295.

4. DeJong A, Molinari N, Sebbane M et al. “Feasibility and effectiveness of prone position in morbidly obese patients with ARDS: a case-control clinical study.” 2013 Jun;143(6):1554-61. doi: 10.1378/chest.12-2115.

5. Weig T, Janitza S, Zoller M et al. “Influence of abdominal obesity on multiorgan dysfunction and mortality in acute respiratory distress syndrome patients treated with prone positioning.” J Crit Care. 2014 Aug;29(4):557-61. doi: 10.1016/j.jcrc.2014.02.010. Epub 2014 Feb 25.