Home Educatione-Learning Caring for the Critically Ill Obese Patient
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Caring for the Critically Ill Obese Patient

PCCSU Volume 25, Lesson 16

PCCSU

The American College of Chest Physicians offers this lesson as a review of a previously offered self-study program. The program provides information on pulmonary, critical care, and sleep medicine issues. CME is no longer available for the PCCSU program.

Objectives

  • Update your knowledge and understanding of pulmonary medicine topics.
  • Update your knowledge and understanding of critical care medicine topics.
  • Update your knowledge and understanding of sleep medicine topics.
  • Learn clinically useful practice procedures.

CME Availability

Effective July 1, 2013, PCCSU Volume 25 is available for review purposes only.

Effective December 31, 2012, PCCSU Volume 24 is available for review purposes only.

Effective December 31, 2011, PCCU Volume 23 is available for review purposes only. CME credit for this volume is no longer being offered

Effective December 31, 2010, PCCU Volume 22 is available for review purposes only. CME credit for this volume is no longer being offered.

Accreditation Statement

The American College of Chest Physicians is accredited by the Accreditation Council for Continuing Medical Education (ACCME) to provide continuing medical education for physicians.

CME Statement

Credit no longer available as of July 1, 2013.

Disclosure Statement

The American College of Chest Physicians (CHEST) remains strongly committed to providing the best available evidence-based clinical information to participants of this educational activity and requires an open disclosure of any potential conflict of interest identified by our faculty members. It is not the intent of CHEST to eliminate all situations of potential conflict of interest, but rather to enable those who are working with CHEST to recognize situations that may be subject to question by others. All disclosed conflicts of interest are reviewed by the educational activity course director/chair, the Education Committee, or the Conflict of Interest Review Committee to ensure that such situations are properly evaluated and, if necessary, resolved. The CHEST educational standards pertaining to conflict of interest are intended to maintain the professional autonomy of the clinical experts inherent in promoting a balanced presentation of science. Through our review process, all CHEST CME activities are ensured of independent, objective, scientifically balanced presentations of information. Disclosure of any or no relationships will be made available for all educational activities.

CME Availability

Volume 25 Through June 30, 2013
Volume 24 Through December 31, 2012
Volume 23 Through December 31, 2011
Volume 22 Through December 31, 2010

Hardware/software requirements: Web browsing device with working Web browser.

PCCSU Volume 25 Editorial Board

Editor-in-Chief
Steven A. Sahn, MD, FCCP

Director, Division of Pulmonary and Critical Care Medicine, Allergy, and Clinical Immunology
Medical University of South Carolina
Charleston, SC

Dr. Sahn has disclosed no significant relationships with the companies/organizations whose products or services may be discussed within Volume 25.

Deputy Editor
Richard A. Matthay, MD, FCCP

Professor of Medicine
Section of Pulmonary and Critical Care Medicine
Yale University School of Medicine
New Haven, CT

Dr. Matthay has disclosed no significant relationships with the companies/organizations whose products or services may be discussed within Volume 25.

Alejandro C. Arroliga, MD, FCCP
Professor of Medicine
Texas A&M Health Science Center
College of Medicine
Temple, TX

Dr. Arroliga has disclosed no significant relationships with the companies/organizations whose products or services may be discussed within Volume 25.

Paul D. Blanc, MD, FCCP
Professor of Medicine
University of California, San Francisco
San Francisco, CA

Dr. Blanc has disclosed significant relationships with the following companies/organizations whose products or services may be discussed within Volume 25:

National Institutes of Health, Flight Attendants Medical Research Institute – university grant monies
University of California San Francisco, US Environmental Protection Agency, California Environmental Protection Agency Air Resources Board – consultant fee
Habonim-Dror Foundation Board of Trustees – fiduciary position

Guillermo A. do Pico, MD, FCCP
Professor of Medicine
University of Wisconsin Medical School
Madison, WI

Dr. do Pico has disclosed no significant relationships with the companies/organizations whose products or services may be discussed within Volume 25.

Ware G. Kuschner, MD, FCCP
Associate Professor of Medicine
Stanford University School of Medicine
Palo Alto, CA

Dr. Kuschner has disclosed no significant relationships with the companies/organizations whose products or services may be discussed within Volume 25.

Teofilo Lee-Chiong, MD, FCCP
Associate Professor of Medicine
National Jewish Medical Center
Denver, CO

Dr. Lee-Chiong has disclosed significant relationships with the following companies/organizations whose products or services may be discussed within Volume 25:

National Institutes of Health – grant monies (from sources other than industry)
Covidien, Respironics, Inc. – grant monies (from industry-related sources)
Elsevier – consultant fee

Margaret Pisani, MD, MPH, FCCP
Assistant Professor of Medicine
Yale University School of Medicine
New Haven, CT

Dr. Pisani has disclosed no significant relationships with the companies/organizations whose products or services may be discussed within Volume 25.

Stephen I. Rennard, MD, FCCP
Professor of Medicine
University of Nebraska Medical Center
Omaha, NE

Dr. Rennard has disclosed significant relationships with the following companies/organizations whose products or services may be discussed within Volume 25:

AstraZeneca, Biomark, Centocor, Novartis – grant monies (from industry-related sources)

Almirall, Aradigm, AstraZeneca, Boehringer Ingelheim, Defined Health, Dey Pharma, Eaton Associates, GlaxoSmithKline, Medacrop, Mpex, Novartis, Nycomed, Otsuka, Pfizer, Pulmatrix, Theravance, United Biosource, Uptake Medical, VantagePoint – consultant fee/advisory committee

AstraZeneca, Network for Continuing Medical Education, Novartis, Pfizer, SOMA – speaker bureau

Ex Officio
Gary R. Epler, MD, FCCP

Clinical Associate Professor of Medicine
Harvard Medical School
Brigham & Women's Hospital
Boston, MA

Dr. Epler has disclosed no significant relationships with the companies/organizations whose products or services may be discussed within Volume 25.

Lilly Rodriguez
ACCP Staff Liaison

By Shyoko Honiden, MD, MSc

Dr. Honiden is Assistant Professor of Medicine, Section of Pulmonary and Critical Care Medicine, Yale University School of Medicine, New Haven, Connecticut.

Dr. Honiden has disclosed no significant relationships with the companies/organizations whose products or services may be discussed within this chapter.

Objectives

  1. Describe the key physiologic changes that occur in obese patients.
  2. Identify the definitions for obesity as set forth by the World Health Organization.
  3. Review the strategies that can be used to minimize complications during intubation.
  4. Understand the technical difficulties that accompany central venous catheter insertion.
  5. Describe the concept of hypocaloric, high protein nutrition that can be used to feed the critically ill obese patient.

Key words: critical illness, ICU, obesity

Abbreviations: CVVH = continuous venovenous hemofiltration; FRC = functional residual capacity; IAP = intraabdominal pressure; IBW = ideal body weight

Introduction

The obesity pandemic consumes a large portion of United States health-care dollars. Obesity-associated medical conditions accounted for $147 billion in medical costs in 2006. Prevalence estimates among critically ill patients varies depending on the cohort examined but may be as high as one in four patients. ICU physicians need to be aware of physiologic changes occuring with obesity that become relevant during critical illness. This article will explore special challenges that are encountered when caring for the obese patient in the ICU. These include airway management, bedside procedures and testing, nutritional support, drug dosing, as well as nursing care. Some conditions associated with obesity, including thromboembolic disease, aspiration pneumonia, respiratory failure, and abdominal compartment syndrome are not reviewed in this article in detail; interested readers are referred to a recent review on these topics.1 Obesity-hypoventilation syndrome was previously reviewed in Pulmonary, Critical Care, Sleep Update (PCCSU), formerly PCCU, volume 21.

Obesity Defined

The BMI is a metric that estimates human body fat burden in an individual. BMI correlates well with direct measures of body fat, such as underwater weighing and dual-energy x-ray absorptiometry, and is widely used as an alternative for direct measures of body fat. BMI expresses weight in relation to height. It is calculated as weight in kilograms divided by height in meters squared. A BMI of 18.5 kg/m2 to 25 kg/m2 is normal; 25 kg/m2 to 30 kg/m2 is overweight; and 30 kg/m2 or greater is obese. In 2000, the World Health Organization published updated definitions for obesity. Additional terms, such as morbid obesity and super obesity are often used in the literature (Table 1).

 


Table 1Definitions of Obesity

BMI, kg/m2 WHO Classification Additional Breakdown Sometimes Used to Further Define the Severely Obese
<18.5 Underweight  
18.5-24.9 Normal weight  
25.0-29.9 Overweight  
30.0-34.9 Class I obesity  
35.0-39.9 Class II obesity  
>40.0 Class III obesity
Commonly called severe or morbid obesity
BMI: 40-49.9 kg/m2  morbidly obese
BMI: >50 kg/m2  super obese

 


 

Physiologic Consequences of Obesity

Cardiovascular System
Obesity causes significant changes in cardiac performance and structure. As body weight increases, patients experience a linear increase in blood volume. This, in turn, leads to increases in stroke volume, via its effect on preload. Augmentation of cardiac output follows and may develop as a compensatory response to meet the increased metabolic requirements of obesity. Because of heightened wall tension from higher preload, the left ventricle may develop eccentric hypertrophy.2 The increase in left ventricular mass is correlated with BMI and waist to hip ratio. When the magnitude of left ventricular hypertrophy is discordant with the degree of chamber size dilation, systolic and diastolic compromise, or obesity cardiomyopathy, develops. This can occur independent of concurrent comorbidities such as coronary artery disease, diabetes, and systemic hypertension. Patients with a BMI >40 kg/m2 and those with a long duration of significant obesity are especially vulnerable. Cardiomyopathy may affect up to 10% of this subset of obese patients.3 Subsequently, left-sided heart disease may lead to right ventricular dysfunction, which may be exacerbated by other obesity related disorders, such as obstructive sleep apnea/obesity hypoventilation syndrome. Figure 1 outlines the pathophysiology of obesity cardiomyopathy. New evidence suggests that alterations in neuroendocrine pathways and elaboration of cardiodepressant factors from adipocytes may have direct adverse cardiovascular consequences.4


L16Fig1

Figure 1. Pathophysiology of obesity cardiomyopathy. (Reprinted with permission from Alpert.3)

 


In the context of these changes, it is no surprise that critically ill obese patients may not tolerate large volume shifts and aggressive fluid resuscitation. Patient management is further complicated by challenges in assessing volume status on physical examination due to the obese body habitus. Assessment using echocardiography is also hampered by technical limitations in the obese patient.

Respiratory System
Physiologic changes that affect the respiratory system should be anticipated in the obese patient. Alterations in compliance, resistance, ventilation and perfusion matching, upper airway caliber and tone, ventilatory drive, as well as workload imposed upon the respiratory muscles have been described.5 Typically, functional residual capacity (FRC) and expiratory reserve volume are reduced on pulmonary function testing. When FRC is sufficiently reduced, it can approach the closing capacity and lead to small airway closure. Along with the increases in blood volume seen in the pulmonary circulation, this contributes to decreased lung compliance. Areas of atelectatic lung, especially common in the dependent lung zones, worsen ventilation/perfusion matching and can manifest as hypoxemia. Soft tissue around the thorax and abdomen reduce chest wall compliance and augment resistance, which in turn, heightens the load on the respiratory pump. When supine, mechanical loading of the diaphragm may be even more pronounced. Taken together, total respiratory compliance may decrease nearly 50% in morbid obesity (BMI >40 kg/m2).6

Anatomic changes also occur in the airways. Upper airway caliber decreases due to parapharyngeal fat deposition. Airways tend to be more collapsible for a variety of reasons, but important factors include impaired pharyngeal dilator activity because of altered pharyngeal shape. Airway caliber may also be affected by remodeling that occurs in response to inflammatory adipocytokines or from repeated opening and closing of the airways during tidal breathing that leads to atelectrauma.7 Ultimately, higher airway resistance increases the work of breathing.

Because of the constant increased load on the respiratory muscles, the oxygen cost of breathing is substantially higher for obese patients.8 As oxygen consumption by the respiratory muscles increase, endurance decreases, as measured by maximum voluntary ventilation maneuvers (20% reduction in patients with simple obesity and 45% reduction in patients with morbid obesity).9 In sum, obese individuals, and in particular, the morbidly obese, have significantly reduced respiratory reserve to compensate for critical illness.

Gastrointestinal System
Obesity is a significant risk factor for gastroesophageal reflux.10 The higher incidence of hiatal hernia, increased intraabdominal pressure (IAP), abnormal lower esophageal sphincter tone, as well as derangements in gastric emptying and esophageal motility contribute to reflux and place the patient at risk for aspiration. This may be particularly true in the ICU, when there is concurrent administration of opioids further affecting gastric motility or when patients undergo procedures necessitating placement in the supine position for prolonged periods. Using standard practices, such as head elevation and minimizing administration of opioids, are important preventive strategies.

Several studies have documented an abnormally elevated baseline IAP among obese patients. In one study, patients at normal weight undergoing abdominal surgery had a mean IAP of 0 mm Hg, and morbidly obese patients undergoing gastric bypass surgery had a mean pressure of 12 mm Hg.11 This baseline elevation in IAP may predispose obese patients to develop abdominal compartment syndrome during critical illness, but the true incidence of clinically relevant events is not known. The ICU physician must therefore have a high index of suspicion for abdominal compartment syndrome in the right clinical context.

Fatty liver disease is an often-underdiagnosed problem in this population. Seventy five percent of obese people may have manifestations of nonalcoholic fatty liver disease.12 A subset of obese people develop nonalcoholic steatohepatitis, which can progress to frank cirrhosis in up to 20% of patients. Such severe hepatic dysfunction has important implications in the ICU, in terms of infection risk and drug metabolism.

Renal System
The incidence of acute kidney injury during critical illness among obese patients is unknown. Glomerular filtration rate estimation is particularly challenging in the critically ill obese patient. Commonly used estimating formulas have shortcomings when used during critical illness due to dynamic fluid, metabolic, hemodynamic, and hormonal changes. Adding to this complexity, obese patients often have multiple comorbid illnesses that predispose them to chronic kidney disease. Furthermore, obese individuals may have glomerular hyperfiltration13 and higher creatinine generation due to increases in both fat and lean body mass as total body weight rises. Weight-based creatinine clearance estimating formulas have been developed to accommodate obese patients, but none has been rigorously validated. Timed or 24-h collections of urine can provide more accurate estimations of renal function in the critical care setting but are not always practical.

Kidney dysfunction can develop for a variety of reasons; a few conditions merit special emphasis. Iatrogenic prerenal azotemia may ensue with overly aggressive diuresis, particularly when a difficult physical examination is coupled with a history of cardiac disease, complaints of dyspnea, and findings of peripheral edema. Additionally, fat malabsorption due to bariatric surgery or weight loss medications, such as orlistat, can make obese patients prone to development of acute oxalate nephropathy.14

When overt kidney failure necessitates renal replacement therapy, delivery of such supportive care can be stymied by a few practical obstacles. First, vascular access for initiation of dialysis may be difficult to obtain. Second, when continuous therapies are chosen (such as continuous venovenous hemofiltration [CVVH]), the best method to appropriately calculate the dose of dialysis is not well established. Ronco and colleagues15 showed that weight-based CVVH dosing of at least 35 mL/kg/min improved survival when compared with a lower dose of 20 mL/kg/min in a general ICU population; however, the average weight of patients in this cohort was around 70 kg with a standard deviation of approximately 10 kg. Among morbidly obese patients, dosing based on actual weight leads to an impractical, large, and possibly unsafe volume of replacement fluid. Although there is a dearth of evidence, estimated lean body weight adjustments should probably be used for dose calculations.

Immune System
Although adipocytes were previously thought to represent passive energy stores, they are increasingly recognized as playing an integral role in complex inflammatory and immunomodulatory cascades. Macrophages, leukocytes, preadipocytes, and adipocytes are found in adipose tissue. The composition of cell types become altered in obesity such that macrophages may represent up to 50% of cellularity of adipose tissue (up from 10% among lean individuals).16 Macrophages elaborate a wide array of proinflammatory cytokines and chemokines. Preadipocytes promote further macrophage activation and differentiation. Innate immunity is also affected, as adipose cells express toll-like receptors.17

Furthermore, adipocytes express signaling molecules known as adipokines. Two key examples are leptin and adiponectin. Leptin plays an important role in energy homeostasis and immune modulation.18 Leptin is involved in apoptosis, macrophage phagocytic activity, and T-cell proliferation and activation. Leptin further exerts endothelial effects via plasminogen activator inhibitor-1 and facilitates development of a prothrombotic state. On the other hand, adiponectin has antiinflammatory and antidiabetic properties and is generally decreased among obese people. Obesity, therefore, represents a chronic prothrombotic, proinflammatory state and how this interplays with the complex acute changes seen during critical illness, such as sepsis, is an area of ongoing research.

Obesity and ICU Outcome

Given the multisystem physiologic derangements that accompany obesity, it might be expected that obese patients suffer from higher morbidity and mortality in the ICU. Indeed, some have demonstrated longer ventilator and ICU days, and higher mortality after trauma.19 Overall, however, the existing literature yields mixed results; some reports suggest obesity may play a protective role during critical illness20,21 while others have shown a neutral effect.22,23 A metaanalysis published in 2009, which included 23 studies and more than 88,000 patients, showed that there was no significant difference in ICU mortality when comparing underweight, overweight, obese, and morbidly obese subjects with normal-weight subjects.24 With regard to hospital mortality, obese patients had lower mortality compared with normal weight patients (relative risk, 0.76; 95% CI, 0.59-0.92). Although not statistically significant, similar trends toward improved hospital mortality were observed for overweight as well as morbidly obese patients. There was no difference in ventilator days, but there was a trend toward longer ICU and hospital days among morbidly obese subjects compared to normal-weight control subjects.

Unique Challenges in the Care of the Critically Ill Obese Patient

Procedural
Central Venous Access: When caring for an obese patient, placement of central venous catheters can be challenging for a variety of reasons. Maneuvering around an oversized bed in a small room can add a layer of complexity and ensuring maintenance of sterile conditions becomes difficult. In that regard, availability of special bariatric ICU rooms can be very helpful. Furthermore, in a nonintubated patient, the Trendelenberg position is often not well tolerated for prolonged periods due to the effect of abdominal soft tissue on diaphragmatic excursion. Loss of anatomic landmarks can make catheter insertion nearly impossible, but ready availability of real-time sonographic guidance has enhanced safety and success rates in recent years, and its use has become the standard of care.25 A lower-frequency probe may be needed to image deeper vessels in some cases (5 mHz as opposed to 7.5 mHz or 15 mHz). The standard needle used for catheter placement may be inadequate, and longer needles, such as a spinal needle, may be required to clear the excessive soft tissue. Distortions due to excess adipose tissue may alter the insertion angle of the dilator such that it varies significantly from the initial angle of needle insertion. This may result in an irregular track, cause bending or distortion of the wire, and lead to difficulty in threading the catheter smoothly. Once a catheter is placed, vigilance to prevent infection is paramount because skin infections frequently develop at intertriginous folds. Studies suggest that central venous catheters are kept in place longer in obese patients compared with normal weight patients, likely due to technical difficulties and lack of alternative sites.26 Therefore, daily reassessment of catheter need, diligent site maintenance, and early planning for more permanent access, if necessary, is crucial to reduce catheter-related infections and catheter-related phlebitis and thrombosis.

Blood Pressure/Cardiovascular Monitoring: Noninvasive blood pressure monitoring by cuff sphygmomanometer is often inaccurate because of difficulties with cuff size selection and placement. In fact, some have suggested that inaccuracies may persist, even when an appropriately sized cuff is available.27 Invasive monitoring via arterial line also has limitations; the presence of increased atherosclerosis, changes in arterial wall thickness, and excessive overlying tissue may “dampen” the waveform and affect arterial line readings.

When central venous pressure is obtained, it is important to recognize that elevated measurements may be due to increases in intrathoracic pressure associated with higher IAP. As clinical assessment of volume status can be difficult, some have successfully employed stroke volume variation as a useful guide to assess fluid responsiveness in the obese population.28 There is lack of consensus with regard to accommodations that should be made when indexing measured hemodynamic parameters to body surface area.

Mechanical Ventilation: No single mechanical ventilation mode has been shown to be superior for use among obese patients. The development of atelectasis in the dependent lung zones can be managed with the addition of positive end-expiratory pressure during mechanical ventilation. For patients who have acute lung injury, a low tidal volume strategy with close attention to airway pressures to minimize ventilator induced lung injury has been advocated in the past decade, and the ARDSNet protocol has become the standard of care.29 In obese patients, it is important to remember to use ideal body weight rather than the actual weight when setting the tidal volume. Although esophageal pressures have been measured in research settings to better characterize the transpulmonary distending pressure in ARDS,30 in clinical practice, it is often difficult to know the implications of higher airway pressures when caring for an obese patient. Some of the change in pressure may be accounted for by reductions in chest wall compliance from increased adiposity. Liberally accepting somewhat higher pressures, however, may be detrimental as noted by the exploratory analysis by Gong and colleagues.31 In their study, BMI was associated with an increased risk of developing ARDS later in the ICU course, and obese patients received higher tidal volumes, positive end-expiratory pressure, and peak pressures compared with lean patients during the first day of mechanical ventilation. Airway pressures, therefore, must be carefully monitored.

Imaging: Portable chest radiographs obtained on an obese ICU patient are limited by poor image quality due to inadequate soft tissue penetration. CT scan and MRI are limited by load limits of the scanning table and the diameter of the aperture. In recent years, some manufacturers have increased the aperture to 70 cm (~27.5 in), and newer tables support weights of up to 272 kg (~600 lb). Artificially constricting the girth of the patient by using linen or elastic binders can be helpful but may further compromise comfort as well as the respiratory status, particularly if the patient is already dyspneic when lying supine and not on ventilator support. Newer software can help minimize artifact and can help with image reconstruction. Even when image capture is possible, interventional procedures, such as CT-guided drainage of an abscess, may not be feasible if there is inadequate residual clearance around the patient to allow for needle entry. In rare circumstances, some veterinary hospitals with special equipment to accommodate large animals may be willing to perform scans in patients unable to fit in conventional scanners. Otherwise, ultrasound imaging could be attempted, if applicable. However, even with high energy, low-frequency probes sonographic images are often poor. Operators can increase manual pressure in an attempt to compress soft tissue, but this can lead to rapid fatigue. Sonographic guidance is a powerful tool, however, for procedures. Use of ultrasound during central venous catheter placement is now well established, and there is additional literature supporting its use in other bedside procedures, such as a lumbar puncture.32

Therapeutic Hypothermia: Therapeutic hypothermia (32°C-34°C) has become standard practice after cardiac arrest.33 Surface cooling devices may be less effective in obesity due to the larger body surface area. In one study34 where hypothermia (with target temperature of 33°C) was employed during neurosurgery, the rate of cooling among 22 obese people (BMI >30 kg/m2) was significantly slower when using a surface convective air blanket in comparison with nonobese subjects cooled using a similar device or obese subjects cooled with an endovascular device.

Airway Management: Depending on the cohort examined, there is significant variation in the estimation of additional risk posed by obesity during emergency intubation. Excess soft tissue around the neck and upper airway can make mask ventilation and intubation difficult. Changes in the gastrointestinal system place obese patients at risk of regurgitation and aspiration. The short and thick neck, as well as limited neck extension and mouth opening, further compromise attempts at intubation via direct laryngoscopy due to incomplete alignment of the pharyngeal, laryngeal, and tracheal axes. Because of reductions in FRC, particularly when a patient is in the supine position, as well as other alterations in respiratory physiology, operators need to be prepared for rapid desaturation. In the ICU, concurrent hemodynamic instability and inability to adequately preoxygenate can add to the complexity of emergency intubation. If the situation is nonemergent, it is best to plan, call for additional help from experienced operators, and gather equipment that may be needed in a difficult to ventilate/difficult to intubate scenario (eg, flexible bronchoscopes, supraglottic devices such as the laryngeal mask airway, video laryngoscopes). Ideally, two experienced intubators should be available. Bilevel positive airway pressure can be used to preoxygenate patients before intubation, when mask ventilation has failed.35 Ultimately, if an airway cannot be secured, a surgical airway may become necessary.

Surgical Airway: The increased soft tissue makes the surgical procedure more difficult; occasionally, the submental and anterior cervical adipose tissue need to be excised to prevent draping over the tracheostomy site. Standard tracheostomy tubes may be too short and too curved. Modified longer tubes are often used, but postoperative care could be complicated because such tubes carry the risk of becoming occluded or dislodged and may have a higher chance of bleeding, scarring, and infection. Some centers preferentially use adjustable-length tubes, but these tubes have a tendency to straighten after placement and may cause tracheal ulceration.36 Despite technical difficulties, percutaneous tracheostomies can be performed, and limited reports do exist with regard to its safety.37 Although higher procedural complication rates have been reported, the true degree of excess risk in experienced hands is not clear.

Nutritional Support: Providing appropriate nutritional support is essential because obesity and malnutrition can coexist, particularly during critical illness. Overfeeding, however, may result in excess CO2 production and prolong ventilator days in an already vulnerable cohort with altered pulmonary physiology. Additionally, overfeeding may contribute to hyperglycemia, azotemia, and hepatic fat accumulation.

Some have promoted the notion of hypocaloric, high-protein feeding as a way to minimize the problems associated with overfeeding while allowing for a net positive nitrogen balance and facilitating fat weight loss. In 2009, the Society for Critical Care Medicine and American Society for Parenteral and Enteral Nutrition released a joint consensus statement in which they endorsed the use of hypocaloric enteral feeding for obese ICU patients.38 In this statement, they suggest providing no more than 60% to 70% of target caloric requirements, or 11 to 14 kcal/kg actual body weight per day. They recommend delivering at least 2.0 g/kg ideal body weight (IBW) per day as protein in class I and II obesity and at least 2.5 g/kg IBW per day for class III obesity. There are relatively few absolute contraindications to this approach, but those with progressive renal and hepatic failure where a high protein load is detrimental, as well as those who require a full caloric load, such as those with recurrent hypoglycemia or severe immunocompromised state, should not be included.

Estimation of target caloric requirements itself is complicated by lack of validated formulas for the critically ill obese patient. Direct calculation using indirect calorimetry may provide useful information but is not practical. When employing the Harris-Benedict equation, for example, there are shortcomings when using IBW as well as actual body weight. Some researchers have advocated the use of an obesity-adjusted weight with a 25% correction of excess weight above the IBW as follows39:

Adjusted body weight = (actual weight - IBW) 0.25 + IBW

Nursing
Nursing staff faces enormous challenges when caring for the obese patient in the ICU. Simple tasks such as turning the patient can cause injury to staff members and the patient, if not performed with adequate staffing, equipment, and training. The physical demands and technical difficulties often lead to suboptimal assessment of skin folds and dependent areas. Obese patients are at risk for development of pressure ulcers due to limited mobility, and early ulcers may go unnoticed, particularly those in the skin folds. Moisture buildup in intertriginous folds may lead to superimposed skin infections.

Recently, there has been renewed interest in promoting early ambulation and mobilization of patients in the ICU. For example, in a randomized control study, critically ill patients supported by mechanical ventilation had fewer delirium days, shorter ventilator days, and better functional status at hospital discharge when rehabilitation began early.40 Mobilization of obese patients requires several physical therapy staff who are experienced in caring for these patients to ensure transfers and weight-bearing exercises can occur safely.41

Finally, the entire ICU team caring for an obese patient should be cognizant of prejudices towards obese people that may be subtle and subconscious. Surveys of patients undergoing weight loss surgery have reported frequent perceptions of discrimination from medical personnel.42

Drug Dosing
Many of the physiologic changes that occur in obesity affect distribution, binding, and elimination of medications. Volume of distribution is largely affected by the lipophilicity of the drug. Careful attention is paramount, and appropriate weight adjustments should be made for lipophilic drugs. One suggested strategy uses the following equation: Adjusted body weight = (Actual body weight – IBW)0.4 + IBW. There is potential for both overdosing and underdosing of medications as a result of complex and simultaneous obesity-related changes such as increases in total blood volume and cardiac output, alterations in renal and hepatic function, and plasma protein binding. Accurate assessment of the net effect is nearly impossible. Evidence and clear guidelines are largely lacking because most clinical trials typically exclude the morbidly obese (BMI >40 kg/m2), and there is a paucity of pharmacokinetic data in this setting. Input from experienced pharmacists and utilization of serum levels, when available, can be helpful. A summary of recommendations for commonly used ICU medications can be found in Table 2. For more details, interested readers can find additional information in a recent article.1

 


Table 2Recommended Drug Dosing for Critically Ill, Obese Patients

Drugs for Dosing using IBW or “Usual Dosing” Drugs for Dosing Using Actual BW Drugs for Dosing Using Adjusted BW Too Little Data to Recommend
Opioids (with titration as needed according to pain scale) LMWHa (with probable ceiling dose that may differ for different drugs) Propofol β-Lactams
Benzodiazepine (with titration as needed according to sedation scale) Thrombolytics (with maximal allowable ceiling dose) Unfractionated heparin (probably with partial thromboplastin time monitoring) Amiodarone
Propofol (propofol is also listed in column 3) Vancomycin (higher end of accepted range or actual BW with therapeutic drug monitoring) Aminoglycosides (with therapeutic drug monitoring for prolonged dosing) Vasopressors
Fluoroquinolones (Very obese patients with severe infections may benefit from the higher end of the usual dosing range.) Activated protein C (drotrecogin alfa; limited data) Corticosteroids (for short courses of high dose therapy for emergent situations; eg, acute spinal cord injury) Inotropes
Digoxin   Lidocaine, verapamil (may need adjusted BW dosing for LOADING doses only)  
Procainamide      
β-Blockers      
Lidocaine, verapamil (usual dosing for maintenance doses)      
H2-blockers      
Corticosteroids      
Neuromuscular blockers      

BW = body weight; LMWH = low-molecular-weight heparin. (Reproduced with permission from Honiden and McArdle.1)

aPer ACCP guidelines, for therapeutic dosing for LMWH. Limited data available for weight up to 144 kg for enoxaparin, 190 kg for dalteparin, and 165 kg for tinzaparin. Concerns remain regarding subcutaneous absorption in obese patients.


 

Summary and Conclusions

The proportion of obese patients is rising in the ICU. Management of the obese patient presents unique challenges to the ICU team. Special attention is required during routine nursing care, ICU procedures (eg, central venous access, intubation, surgical airways), and when making decisions about drug dosing, imaging tests, nutritional support, and ventilator management. Research focused on the obese critically ill patient population is necessary to help elucidate best ICU practices for these complicated patients.


References

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