Specific Challenges in Treating the Adult Obese Patient

Linda Harrington, PhD, RN, CNS, CPHQ*
Vice President for Advancing Nursing Practice
Baylor Health Care System
Dallas, Texas, USA

Obesity creates several pathophysiological changes in individuals. These alterations pose unique challenges for critical care clinicians, especially in the areas of assessment and treatment. This article provides an overview of important implications for practice applicable to most critically ill obese patients, highlighting the need for more research in this growing population.

Assessment Challenges
Cardiovascular Considerations. For clinicians, the body habitus of obese patients makes cardiovascular assessment awkward. Both auscultatory and oscillometric measurements can be difficult.(1) Automated noninvasive blood pressure measurements, as well as auscultated measurements, have been empirically demonstrated to underestimate intra-arterial blood pressure.(2,3)

A wide variety of electrocardiographic (ECG) abnormalities is seen in obese patients, most representing changes in cardiac morphology.(4) Clinicians can expect to see the following ECG changes occurring with disproportionately high frequency.(4)

• Leftward shifts of the P-wave, QRS, and T-wave axes
• Changes in P-wave morphology
• Lower QRS voltage
• Various markers of left ventricular hypertrophy
• T-wave flattening in the inferior and lateral leads
• Lengthening of the corrected QT interval
• Prolongation of the QT interval duration

Many of these abnormalities are reversible with substantial weight loss.(4) Clinicians should consider this when ECG changes are observed in obese patients during long lengths of stay in the intensive care unit where dramatic weight loss is possible.

Pulmonary Considerations. Critically ill obese patients are predisposed to respiratory failure due to changes in respiratory mechanics, producing a reduction in functional residual capacity.1 Hypoxemia is the resulting primary gas exchange abnormality.(1) Thus, obese patients experience longer mechanical ventilation times and higher extubation failure rates.(1,5)

The assessment of pulmonary function can be challenging in obese patients. Lung sounds may be underappreciated, and more invasive pulmonary artery catheterization may be required for better evaluation and treatment.(1) Diagnostic radiologic imaging is also affected by obesity. In the morbidly obese patient, the quality of chest radiographs obtained via portable radiography can prevent the distinction between pneumonic infiltrates and pulmonary edema. Excessive ediastinal adipose tissue can mimic a thoracic aortic aneurysm by projecting an abnormal mediastinum on plain chest radiograph.(5) A computed tomography scan should be considered to improve visualization of the pulmonary parenchyma and the surrounding vasculature, assuming a scanner table is available to accommodate the patient’s increased size and weight.(5)

Integumentary Considerations. Adipose tissue is less vascularized, predisposing obese patients to the development of pressure ulcers. The risk is increased due to the difficulty obese patients have in repositioning themselves, as well as the challenges to staff in turning them effectively.(5) These patients may require special beds, such as a bariatric bed with low air-loss surfaces or air-fluidized bed with pressure relief features.(6)

The multiple skinfolds in obese patients create a moist environment that promotes the growth of microorganisms.(5) Soft  folded cloths should be placed in skinfolds to absorb moisture and should be changed routinely. Nonmedicated powders tend to clump in skin voids and generally should be avoided.(5)

Treatment Challenges
Mechanical Ventilation. Ventilator management entails tidal volume calculation based on ideal body weight and not actual body weight.(4) High airway pressures should be avoided to prevent barotrauma.(5) Prophylactic positive end-expiratory pressure up to 10 cm H2O is recommended to promote oxygenation.(7) Consider a reverse Trendelenburg position to reduce intra-abdominal pressure, lessen the impact on the diaphragm and ease breathing.

Pharmacologic Interventions. Published reports on the dosing of medications in critically ill obese adults consistently report a dearth of information and the need for more research.(8-10) Several factors affect the dosing of medications in obese patients, serving to further complicate treatment decisions. What is known is that reliance on scientific principles, such as the lipophilicity and hydrophilicity of medications, is unreliable.(9)

With little research to reference, the best approach to administering medications in critically ill adult patients is to:

• Use ideal body weight for:
   - Weight-based drugs with narrow therapeutic index
   - Loading and maintenance dosing in weight-based medications when type of weight for dosing is unknown

• Titrate weight-based drugs for desired effects.
   - Use them conservatively in non-emergent situations

• Monitor:
   - Clinical end points
   - Therapeutic serum levels, as indicated
   - Signs and symptoms of drug toxicity
   - Serum drug levels when indicated

Cutaneous, subcutaneous and intramuscular routes should be avoided in critically ill obese patients. Adipose tissue has poor blood supply. As a result, drugs that are administered by cutaneous patches or subcutaneously may have delayed onset of action and unpredictable duration.(11)

Correct technique with intramuscular injections is difficult to achieve in obese patients. The depth of adipose tissue makes it difficult to evaluate landmarks. Thus, intramuscular injections may be administered unintentionally in the subcutaneous tissue.(11)

Vascular access can be a technical challenge due to the large body habitus. Excess adipose tissue can obscure anatomic landmarks, interfere with the angle of insertion, and increase the depth of venipuncture required to access veins or arteries.(5) The insertion of both peripheral and central venous catheters may be aided by the use of continuous ultrasound.(1)

The duration of intra-arterial and venous catheterization has been shown to be significantly longer in morbidly obese patients than in the non-obese critically ill.(5)

Complications from prolonged vascular catheter placement have not been demonstrated in well-controlled studies.(5) Peripherally inserted central catheters should be considered when peripheral intravenous catheters are difficult to insert and maintain.

Nutrition Therapy Challenges
Determining the nutritional needs of critically ill obese patients can be difficult. One of the first challenges is determining the energy requirements for these patients. Such an assessment may involve indirect calorimetry (IC), measuring resting energy expenditure (REE) or using predictive equation models.(12) IC may not be available and REE is not considered ideal, leaving predictive equations to be considered.(12)

The challenge is determining which weight to use in the prediction of nutritional needs. Actual body weight may result in an
overestimation of nutritional needs, whereas ideal body weight may result in underestimation. Adjusted body weight has not been validated in determining the nutritional needs of critically ill obese patients.(12)

The Society for Critical Care Medicine (SCCM) and the American Society for Parenteral and Enteral Nutrition (A.S.P.E.N.) recently published guidelines for nutritional assessment and support in critically ill adults.(13) The new guidelines recommend underfeeding or hypocaloric feeding with enteral nutrition in critically ill obese patients.(13) Goals of enteral nutrition in this patient population include:

• Providing 60% to 70% of target energy requirements or 11-15 kcal/kg actual body weight per day (or 22-25 kcal/kg ideal body weight per day) for critically ill patients with a body mass index (BMI) >30

• Providing protein >2.0 g/kg ideal body weight per day in critically ill patients with BMI 30-40 or >2.5 g/kg for BMI > 4013

The SCCM and A.S.P.E.N. guidelines can be combined with evidence-based nutrition practice guidelines published by the American Dietetic Association in 2006.(14) Critical care clinicians should consider the following:

Nutritional Assessment
• If available, use indirect calorimetry for determining resting metabolic rate.(13,14)
• If indirect calorimetry is unavailable, use Ireton-Jones (1992) or Penn State (1998) predictive equations for critically ill, mechanically ventilated, obese patients.(14)

Nutritional Support
• If the critically ill patient is hemodynamically stable and has a functional gastrointestinal tract, choose enteral nutrition over parenteral nutrition.(13,14)
• Bowel sounds, flatus and passage of stool are not prerequisites for initiation of enteral feeding.(13)
• If the patient is in the supine position, under heavy sedation, or shows intolerance to gastric feeding, consider placing small bowel feeding tube.(13,14)
• Start enteral nutrition within 24 to 48 hours following admission to the intensive care unit if the patient has received adequate fluid resuscitation.(13,14)
• Monitor for tolerance of enteral nutrition and do not hold for gastric residuals <500 mL unless the patient shows signs of intolerance.(13)
• Consider immune-modulating enteral formulations for patients with major elective surgery, trauma, burns, head and neck cancer, and those on mechanical ventilation.(13,14)
• Administer promotility agents, unless contraindicated, in patients with history of gastroparesis or repeated high gastric residual volumes.(13,14)
• Maintain strict glycemic control of 110-150 mg/dL.(13)
• Consider parenteral nutrition if the patient cannot tolerate enteral feedings (see guidelines for further details).(13)

Despite the published guidelines, more research is needed on nutritional assessment and therapy, especially in the critically ill obese patient population.

Visit www.learnicu.org access the new nutrition guideline.


Conclusion
The challenges resulting from obesity in critically ill patients are many. The growing number of obese and morbidly obese patients makes this topic all the more pertinent. The difficulties in assessment and treatment, combined with the increased risk for complication and insufficient information, make this an important area for further research.


References:

1. Joffe A, et al. Obesity in critical care. Curr Opin Anaesthesiol. 2007;20:113-118.

2. Araghi A, et al. Arterial blood pressure monitoring in overweight critically ill patients: invasive or noninvasive? Crit Care. 2006;10:R64.

3. Bur A, et al. Factors influencing the accuracy of oscillometric blood pressure measurement in critically ill patients. Crit Care Med. 2003;31:793–799.

4. Fraley MA, et al. Obesity and the electrocardiogram. Obes Rev. 2005;6:275-281.

5. El-Sohl AA. Clinical approach to the critically ill, morbidly obese patient. Am J Respir Crit Care Med. 2004;169:557-561.

6. Cullum N, et al. Systematic reviews of wound care management: (5) beds; (6) compression; (7) laser therapy, therapeutic ultrasound, electrotherapy and electromagnetic therapy. Health Technol Assess. 2001;5:1–221.

7. Pelosi P, 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.

8. Erstad BL. Dosing of medications in morbidly obese patient in the intensive care unit setting.  Intensive Care Med. 2004;30:18–32.

9. Harrington L, et al. Dosing of emergency cardiovascular medications in obese patients. Bariatric Nursing and Surgical Patient Care. 2007; 2:131-139.

10. Lee JB, et al. Pharmacokinetic alterations in obesity. Orthopedics. 2006; 29: 984-988.

11. Barth MM, et al. Postoperative nursing care of gastric bypass patients. Am J Crit Care. 2006;15:378-397.

12. Brown B. Nutrition support for critically ill obese patient. Support Line. 2007; 29:18-26.

13. McClave SA, et al. Guidelines for the provision and assessment of nutrition support therapy in the adult critically ill patient: Society of Critical Care Medicine and American Society for Parenteral and Enteral Nutrition (A.S.P.E.N.). JPEN J Parenter Enteral Nutr. 2009; 33:277-316.

14. American Dietetic Association. Critical illness evidence-based nutrition practice guideline. http://www.adaevidencelibrary.com/topic.cfm?cat=3016. Published September 2006. Accessed on July 22, 2009.

Disclosures:

*Author has no disclosures to report.