SAN DIEGO—As the epidemic of obesity continues unabated in the United States, an increasing number of morbidly obese patients are being admitted to intensive care units (ICUs). Management of these patients is always challenging—and sometimes a nightmare, admits Paul E. Marik, MD.

Morbidly obese patients (those with a body mass index above 40) appear to be at higher risk for pulmonary complications and death, said Dr. Marik, of the Department of Critical Care, University of Pittsburgh. Morbid obesity may also lengthen the ICU stay, increase the need for and duration of mechanical ventilation, and prolong weaning.

Dr. Marik and four other experts discussed the challenges presented by morbidly obese patients at a multidisciplinary lecture held during the Society of Critical Care Medicine’s annual meeting in San Diego.[1] Among the questions addressed were: Can pulmonary complications be prevented? What strategies work best for respiratory insufficiency? How do you calculate drug dosages?

PULMONARY COMPLICATIONS

Dr. Marik noted that pulmonary complications are especially common in morbidly obese patients who have suffered blunt trauma or who have undergone thoracic or abdominal surgery. However, early postoperative mobilization, incentive spirometry, and physical therapy help prevent these complications. Raising the head of the bed to at least 30º and administering promotility agents may diminish the risk of aspiration pneumonia.

Because of their weight, morbidly obese patients may become hypoxic in the supine position, particularly if they are also under anesthesia. However, positive end-expiratory pressure (PEEP) may help minimize the problem. In a study of nine obese patients who were anesthetized and supine after abdominal surgery, 10 cm H2O of PEEP was shown to markedly improve lung volumes and pulmonary compliance.[2] Those improvements were minimal in a comparison group of normal-weight patients.

Complications may also arise because vascular access is difficult in morbidly obese patients. A finder needle should be used to establish such access, said Dr. Marik. “It obviously can take multiple attempts to locate the vein, and you will probably cause less damage using a finder needle,” he noted. Ultrasonography may help in locating a vein, but a Doppler probe with a depth greater than 2 cm is needed.

RESPIRATORY INSUFFICIENCY

Due to their high oxygen consumption and poor tolerance for respiratory loads, morbidly obese patients may develop respiratory failure from even trivial insults. “You must be prepared to begin mechanical support early and electively,” stated Jesse B. Hall, MD, a Professor of Medicine, Anesthesia, and Critical Care at the University of Chicago. Noninvasive positive-pressure ventilation can be tried before mechanical ventilation is started, he said. Dr. Hall acknowledged, though, that there are no high-quality studies, only clinical judgment, to support that recommendation.

For morbidly obese patients with acute respiratory failure, he suggested that mechanical ventilation be initiated with a tidal volume in the range of 5 to 7 mL/kg—but it should be based on ideal, not actual, body weight. Tidal volume can then be titrated to the patient’s ventilator mechanics, he instructed.

THROMBOEMBOLIC DISEASE

Both Dr. Hall and Dr. Marik stressed the importance of aggressive anticoagulation. Empiric heparin therapy is probably necessary when suspicion of pulmonary embolism (PE) is strong, said Dr. Hall, because morbidly obese patients are typically too large for the imaging equipment used to test for PE. Prophylaxis with unfractionated heparin or low-molecular-weight heparin (LMWH) is prudent even if PE is not suspected.

In this setting, standard heparin may be preferable to LMWH, said Brian L. Erstad, PharmD, Associate Professor of Pharmacy at the University of Arizona in Tucson. Heparin use requires regular testing of clotting factors, which makes it easier to gauge the adequacy of anticoagulation in morbidly obese patients. Because these tests have a rapid turnaround time, prophylaxis can be started with an unadjusted, weight-based standard heparin dose, which can be quickly altered according to test results.

ADVERSE DRUG EVENTS

Dr. Erstad acknowledged, however, that excessive weight-based dosages may be responsible for medication-related adverse events in morbidly obese patients. He noted that few good pharmacologic studies are available to guide drug dosing in these patients—critically ill or not—but it is possible nonetheless to make a few recommendations aimed at minimizing adverse events.

With opioids, “we use an approach that is similar to [one used in] a recovery room,” he explained. This consists of administering frequent small doses of an opioid until the desired level of pain control is achieved.

When infection is suspected, a conventional aminoglycoside regimen (eg, 7 mg/kg as a single daily dose) should not be considered. “The concern here is the gigantic dose,” said Dr. Erstad. He suggested capping the dose or using a twice-daily, adjusted weight-based regimen when an aminoglycoside is the only therapeutic option.

NUTRITIONAL CONCERNS

Weight loss during critical illness is generally not recommended, but it may sometimes be beneficial when the patient is obese. For example, even a 10% weight reduction may decrease the risk of pulmonary hypertension or improve the ventilatory status of an obese patient who cannot be weaned from the ventilator, said Gary P. Zaloga, MD, Medical Director of the Methodist Research Institute in Indianapolis.

In obese patients who are not critically ill, there is some evidence that weight can be reduced (mostly through fat loss) if a strategy of permissive underfeeding that cuts calories but maintains protein intake is used. This strategy calls for daily consumption of 1.2 to 1.5 g of protein per kilogram of ideal body weight but a total caloric intake of only 10 to 15 kcal/kg. Short periods of permissive underfeeding have been associated with lower infection rates and insulin needs in humans and with decreased mortality in animal models of critical illness. A dietitian’s help is required to properly prepare the nutritional formula for permissive underfeeding, noted Dr. Zaloga.

Enteral feeding is the preferred form of nutritional support for critically ill, morbidly obese patients, he stressed, and it should be started early. In general, critically ill patients have significantly fewer infections and shorter lengths of hospital stay when enteral feeding is started within 24 hours of admission rather than three days later.[3]

PATIENT POSITIONING

Proper positioning can be crucial in critically ill, morbidly obese patients, both to maximize lung function and to increase the likelihood of successful weaning. A 90º upright, sitting position has been recommended for these patients, but it may be better to have them sit up at a 45º angle or in a reverse Trendelenburg position (feet down at 45º), said Suzanne M. Burns, RN, MSN, an Associate Professor of Nursing at the University of Virginia Health Sciences Center in Charlottesville.

In a study of 19 obese patients being weaned from mechanical ventilation, she and her colleagues found that the 45º upright and reverse Trendelenburg positions were associated with better respiratory mechanics than were the 90º upright and supine positions.[4] Furthermore, patients typically preferred them. “[Supine] is probably the worst position for these large patients,” commented Professor Burns, who explained that in these patients, the supine position reduces pulmonary compliance and increases airway resistance.

Proning morbidly obese patients is not impossible, just difficult, she added. Evidence suggests that proning can improve functional residual capacity, pulmonary compliance, and oxygenation.

Hydraulic lifts, oversized wheelchairs, and other special equipment facilitate positioning of these patients, Professor Burns said. A positive attitude and determination on the part of caregivers to position these patients properly despite their size are also essential, she emphasized.

—Timothy Begany

References
1. Marik PE, Zaloga GP, Hall JB, et al. Multidisciplinary management of the morbidly obese patient. Presented at: Annual Meeting of the Society of Critical Care Medicine; January 29, 2002; San Diego, Calif.
2. Pelosi P, Ravagnan I, Giurati G, et al. Positive end-
expiratory pressure improves respiratory function in obese but not in normal subjects during anesthesia and paralysis. Anesthesiology. 1999;91:1221-1231.
3. Marik PE, Zaloga GP. Early enteral nutrition in acutely ill patients: a systematic review. Crit Care Med. 2001;29:2264-2270.
4. Burns SM, Egloff MB, Ryan B, et al. Effect of body position on spontaneous respiratory rate and tidal volume in patients with obesity, abdominal distension and ascites. Am J Crit Care. 1994;3:102-106.