Obesity is a chronic metabolic condition with important public health implications. It has been linked to increased morbidity and mortality from acute and chronic medical problems including hypertension, cardiovascular diseases, dyslipidemia, diabetes mellitus, arthritis, sleep apnea, and certain forms of cancer.
Although far from being ideal, the most convenient method of quantifying and defining the degree of obesity is with the body mass index (BMI), which is the ratio of a person’s weight (in kilograms) to height (in meters) squared. In 1998, the World Health Organization committee and the National Institutes of Health (NIH) put forward a classification that became the worldwide standard for comparison of obesity rates within and across populations. The consensus defined “morbid obesity” (MO)—also termed clinically severe obesity —as a BMI of 40 kg/m 2 or more or a BMI of more than 35 kg/m 2 and significant comorbidities.
Although the U.S. prevalence of obesity has leveled in the last decade, compared with some European countries, the prevalence of obesity in the United States is three times higher than that in France and 1.5 times higher than that in the United Kingdom. According to the latest National Health and Nutrition Examination Survey (NHANES), the age-adjusted obesity prevalence was 35.7% in the United States in 2010 with no sex differences. Extreme obesity has more than doubled since the 1988-1994 NHANES, shifting from 2.9% to 6.3% in 2010 for grade 3 (severe) obesity and reaching 15.2% for grade 2 obesity. The age-adjusted prevalence of overweight and obesity combined (BMI ≥25 kg/m 2 ) was 68.8% in 2010 with a mean BMI of 28.7 kg/m 2 in the U.S. population. With such a global epidemic, it is not surprising that an increasing number of morbidly obese patients are admitted to the intensive care unit (ICU). Hence, what are the special considerations in the management of morbidly obese patients in the ICU?
Critically ill obese patients present intensive care physicians with unique challenges that only a thorough knowledge of the peculiar pathophysiologic changes that occur in this population will allow for anticipation of complications and effective delivery of care.
Airway Management
MO has been considered one of the risk factors for difficult intubation. However, the reader should be aware that MO, as defined by BMI, does not necessarily indicate increased fat deposits in and around the airway: Many patients have a gynecoid pattern of obesity. In two series of morbidly obese patients undergoing upper abdominal surgery, the incidence of difficult intubation was estimated at 13% and 24%, respectively. More recently, the magnitude of this risk was challenged. A study of more than 90,000 Danish patients undergoing intubation for surgery put the frequency of difficult intubation closer to 6.4% in those with a BMI of 35 kg/m 2 or more compared with 5.2% in the overall population. In the Australian Incident Monitoring Study, limited neck mobility and mouth opening accounted for most cases of difficult intubation in obese subjects. Other studies added to the preceding list a short sternomental distance, a receding mandible, a large neck circumference, and a Mallampati score of 3 or greater as predictors of difficult intubation. Although these multivariate predictive models have yet to be tested in an ICU setting, neither obesity nor BMI predicted problems with tracheal intubation. One of the reasons for the observed differences among these studies is the lack of consensus on the definition of the term difficult intubation. Nonetheless, the increased bulk of soft tissues in the upper airway make the morbidly obese, particularly those with obstructive sleep apnea, prone to partial obstruction. Hiremath et al. found that 8 of 15 individuals with Cormack and Lehane grade 4 laryngoscopic views had apnea-hypopnea indices consistent with previously undiagnosed sleep apnea syndrome whereas only 2 matched controls without a difficult laryngoscopic view had similar scores. Within this context, the American Society of Anesthesiology recommends that awake intubation be considered in the morbidly obese patient if difficult mask ventilation and difficult intubation are anticipated.
Emergency airway management of the critically ill morbidly obese patient is frequently complicated by the patient’s limited physiologic reserve. Morbidly obese patients are more prone to hypoxemia because of reductions in expiratory reserve volume, functional residual capacity (FRC), and maximum voluntary ventilation. Severely obese patients undergoing surgery have significantly lower nadir SpO 2 (oxygen saturation by pulse oximetry) during intubation compared with normal and overweight patients despite similar preoxygenation duration and baseline SpO 2 readings. Moreover, the increased intra-abdominal pressure is thought to place the obese patient at a higher risk of aspiration of gastric content. These levels are traditionally considered to be a risk factor in the adult obese patient for aspiration pneumonitis. Given these physiologic changes, a rapid sequence induction (RSI) has been advocated. However, the use of RSI in fasted patients with no risk factors for aspiration other than obesity is debatable. Obese patients without symptoms of gastroesophageal reflux have a resistance gradient between the stomach and the gastroesophageal junction similar to that in nonobese subjects. In addition, there are drawbacks for RSI that could prove deleterious in these patients. First, although cricoid pressure may or may not decrease the risk of aspiration, there is evidence that it may worsen the quality of laryngeal exposure. Second, the application of cricoid pressure can lead to a complete airway occlusion, occurring between 6% and 11% of the time.
In short, the degree of obesity or neck size that justifies advanced interventions for intubation remains unknown. The experience and ability of the laryngoscopist are probably the most important determinants for establishing an airway in the morbidly obese patient.
In patients who require tracheostomy, morbidly obese patients with increased submental and anterior cervical adipose tissue present a unique surgical challenge. The initial goal of securing a stable airway can be compromised by the size discrepancy and curvature mismatch between a standard-size tracheostomy tube and the increased distance between the skin and trachea. Standard tracheostomy tubes are typically too short and too curved. One study of 427 critically ill morbidly obese patients undergoing surgical tracheostomy reported a complication rate of 25%; most complications were minor. Life-threatening complications occurred in 10% and were related to tube obstruction and extratracheal tube placement. Some surgeons advocate performing a Bjork flap at the time of surgery to prevent tube misplacement in the pretracheal fascia. Others favor a cervical lipectomy in combination with tracheostomy. There are no studies that prove that these interventions are effective.
Percutaneous dilational tracheostomy (PDT) remains controversial for these patients. Obese patients with large and thick necks were traditionally considered poor candidates for PDT. However, PDT has been performed in these patients with low rates of complications. A large retrospective study of more than 3000 cases of PDT in which 16% of patients had a BMI of 35 kg/m 2 or greater appears to confirm the safety of this procedure in this high-risk group. The authors postulated that the introduction of extra-long tracheostomy tubes in obese patients may have contributed to the low complication rate in this high-risk group. There was likely selection bias in this study because high BMI does not necessarily translate into airway disease and the best “obese” candidates were likely selected for PDT. In the absence of large randomized trials, no recommendation could be made regarding PDT in this population. The outcome of PDT depends largely on the skills and the experience of the operator.
Despite substantial investigation, the optimal timing of tracheotomy for critically ill obese patients requiring mechanical ventilation (MV) continues to be debated between those who support early intervention, citing the benefits of early liberation from MV, and those who argue against this approach because of a lack of supportive evidence. To date, no randomized trial of tracheotomy time has been completed in morbidly obese patients. One retrospective study of 102 morbidly obese patients requiring artificial ventilation did suggest a reduced duration of MV and ICU length of stay and a lower incidence of nosocomial pneumonia in those who underwent early tracheostomy (≤9 days) compared with late tracheostomy. However, no difference in hospital mortality was observed. Because of the possibility of selection bias in retrospective designs, a consensus on when a tracheostomy should be performed in these patients awaits a randomized clinical trial.
Respiratory
The most prominent pulmonary function test abnormalities associated with obesity are decreased expiratory reserve volume and FRC, whereas the vital capacity and total lung capacity are essentially unchanged. Relative to nonobese subjects, the total respiratory system compliance is decreased because of the greater degree of chest wall compression and cephalad displacement of the diaphragm. In the supine and Trendelenburg positions, FRC may fall below the closing capacity, leading to small airway collapse, atelectasis, ventilation perfusion mismatch, and hypoxemia. As lung volumes are reduced and airway resistance is increased, a tidal volume based on a patient’s actual body weight is likely to result in high airway pressures, alveolar overdistention, and barotrauma. The current consensus would favor that the initial tidal volume be calculated according to ideal body weight (IBW), on the basis of the patient’s height, and then adjusted according to the desired plateau pressure and systemic arterial blood gases.
The role of positive end-expiratory pressure (PEEP) on respiratory mechanics and blood gases in postoperative mechanically ventilated morbidly obese subjects has been tested by several studies. Pelosi et al. applied a PEEP of 10 cm H 2 O to nine anesthetized-paralyzed morbidly obese subjects after abdominal surgery and found a significant reduction in respiratory system elastance and resistance. This reduction was attributed to alveolar recruitment or to the re-opening of closed airways. The authors also found a small but significant improvement in arterial oxygenation, which was correlated with the amount of recruited volume. In a similar group of subjects, Koutsoukou and colleagues found that the PEEP used (4 to 16 cm) caused a significant reduction in elastance and resistance of the respiratory system. However, PEEP had no significant effect on gas exchange. In both studies, oxygenation remained markedly abnormal even after the application of PEEP, probably reflecting residual atelectasis. Indeed, the extent of atelectasis, which was correlated with the amount of venous admixture, was not reduced by inflation of the lungs with conventional tidal volume, or even with a doubled tidal volume.
In patients with acute respiratory distress syndrome (ARDS), prone positioning is known to improve gas exchange and outcomes (see Chapter 32 ). With the weight of the mediastinal structures, particularly the heart, supported by the sternum, less pulmonary tissue is compressed. The delivered tidal volume and peak pressure are dispersed to more alveoli, decreasing the risk of further alveolar injury from stretch and strain forces. Proning reduces <SPAN role=presentation tabIndex=0 id=MathJax-Element-1-Frame class=MathJax style="POSITION: relative" data-mathml='V˙/Q˙’>V˙/Q˙V˙/Q˙
V ˙ / Q ˙
(ventilation-perfusion) mismatch, reduces right-to-left shunt, and improves oxygenation. One case control study with morbidly obese patients (BMI ≥35 kg/m 2 ) and ARDS (Pa o 2 [partial pressure of oxygen, arterial]/F io 2 [fraction of inspired oxygen] ratio ≤200 mm Hg) documented improvement in oxygenation and decreased 90-day mortality without significant increase in duration of MV, length of stay, or incidence of nosocomial pneumonia. However, abdominally obese patients (with sagittal abdominal diameter ≥26 cm) were at higher risk of renal failure and hypoxic hepatitis. It is speculated that the increased intra-abdominal pressure from prone positioning might have been the culprit. Given the limited data specific to prone positioning in morbidly obese patients, the feasibility and effect of proning in morbidly patients with ARDS will likely be affected by the degree of familiarity of nurses and physicians with proning and the availability of the appropriate resources.
The rate of reintubation after extubation in severely obese patients has been reported at 8% to 14% among patients undergoing MV for more than 48 hours. Earlier investigations suggested that the prophylactic use of noninvasive ventilation (NIV) in morbidly obese patients during the first 24 hours postoperatively reduced pulmonary dysfunction after gastroplasty and accelerated reestablishment of preoperative pulmonary function. Joris and colleagues demonstrated that the application of bilevel positive airway pressure set at 12 and 4 cm H 2 O significantly improved the peak expiratory flow rate, the forced vital capacity, and the oxygen saturation on the first postoperative day. This improvement was attributed to a combined effect of improved lung inflation, prevention of alveolar collapse, and reduced inspiratory threshold load. In a parallel study of 50 morbidly obese patients admitted to a medical ICU with acute respiratory failure, patients who were successfully treated with NIV had a shorter hospital stay and a lower mortality. The reduction in the rate of respiratory failure was more pronounced when NIV was immediately instituted afterextubation. Subgroup analysis of patients with hypercapnia showed reduced hospital mortality in the NIV group compared with controls. In contrast, patients who failed a trial of NIV and those who required invasive MV demonstrated a longer ICU and hospital length of stay and higher mortality (31%).
Deep Venous Thrombosis Prophylaxis
MO is a risk factor for venous thromboembolic disease (VTE) because of increased venous stasis, decreased mobility, and a possibly a hypercoagulable state. Unfortunately, limited data exist on effective prophylactic regimens of anticoagulation in critically ill morbidly obese patients. These patients are typically excluded from trials because of the equivocal results of the diagnostic tests used to confirm or exclude thromboembolic disease.
Studies in which the effectiveness of VTE prophylaxis in obese hospitalized patients is evaluated are listed in Table 23-1 . Despite the absence of well-designed randomized controlled trials in critically ill morbidly obese patients, the use of prophylaxis is indicated. Pharmacokinetic and epidemiologic studies suggest that the standard fixed doses of thromboprophylaxis are suboptimal in this population. A retrospective study demonstrated that high-dose thromboprophylaxis (heparin 7500 U 3 times a day instead of standard dosing of 5000 U 2 to 3 times a day or enoxaparin 40 mg twice a day [instead of 40 mg once a day]) approximately halved the odds of symptomatic VTE in patients with weight greater than 100 kg or BMI greater than 40 kg/m 2 , with no increased risk of bleeding. Although this would appear to be a reasonable starting point, there is no universal consensus on the optimal regimens (mechanical or pharmacologic) and duration of VTE prophylaxis in these patients.
| Author, Year | Study Design | Intervention | Outcome |
|---|---|---|---|
| Samama, 1999 | Randomized, controlled trial | 738 hospitalized medical patients > 40 years old, including 20% of obese patients randomized to enoxaparin 40 mg/day or placebo | RR, 0.37 (97.6% CI, 0.22-0.63) with enoxaparin 40 mg/day. Major hemorrhage in 1.7% vs. 1.1% in the placebo group. |
| Kalfarentzos, 2001 | Randomized, controlled trial | 60 patients undergoing bariatric surgery, randomized to 5700 or 9500 IU of nadroparin | No incidence of DVT in both groups receiving nadroparin. Major hemorrhage reported in 6.7% in the group receiving higher dose of nadroparin. |
| Scholten, 2002 | Prospective noncontrolled study | 481 patients undergoing bariatric surgery receiving prophylaxis with 30 mg SC q12h or 40 mg q12h of enoxaparin | Incidence of symptomatic VTE of 5.4% with enoxaparin 30 mg q12h, and of 0.6% with 40 mg q12h. Major hemorrhage in 1.0% and 0.25% in the two groups of enoxaparin, respectively. |
| Gonzalez, 2004 | Prospective noncontrolled study | 380 patients undergoing bariatric surgery with SCD | Incidence of symptomatic DVT of 0.26%. No PE reported. |
| Alikhan, 2003 | Randomized, controlled trial | 866 hospitalized obese medical patients > 40 years old randomized to enoxaparin 40 mg/day or placebo | RR, 0.49 (95% CI, 0.18-1.36) with enoxaparin 40 mg/day. |
| Shepherd, 2003 | Prospective noncontrolled study | 700 patients undergoing bariatric surgery receiving prophylaxis with continuous intravenous UH during the perioperative period | Incidence of DVT and symptomatic PE of 0% and 0.4%, respectively. Postoperative hemorrhage in 2.3%. |
| Miller, 2004 | Retrospective cohort | 255 patients undergoing bariatric surgery receiving prophylaxis with LDUH 5000 or 7500 IU q8h | Overall incidence of VTE of 1.2%. Prospective hemorrhage in 2.4%. |
| Shepherd, 2004 | Prospective noncontrolled study | 19 patients undergoing bariatric surgery receiving prophylaxis with continuous intravenous UH during the perioperative period | No symptomatic VTE confirmed. Major hemorrhage in 10.5%. |
| Leizorovicz, 2004 | Randomized, controlled trial | 3706 hospitalized medical patients > 40 years, including 30% of obese patients randomized to dalteparin 5000 IU/day or placebo | RR, 0.55 (95% CI, 0.38-0.80) with dalteparin 5000 IU/day. Major hemorrhage in 0.49% vs 0.16% in the placebo group. |
| Kucher, 2005 | Subgroup analysis of randomized, controlled trial | 1118 hospitalized obese medical patients > 40 years randomized to dalteparin 5000 IU/day or placebo | VTE occurred in 2.8% of the dalteparin and 4.3% of the placebo group. RR, 0.64 (95% CI, 0.32-1.28) with dalteparin 5000 IU/day. |
| Hamad, 2005 | Multicentric retrospective cohort | 668 patients undergoing bariatric surgery receiving prophylaxis with enoxaparin 30 mg (daily or q12h) or 40 mg (daily or q12h) or no prophylaxis | Overall incidence of objectively confirmed symptomatic PE of 0.9%, and DVT of 0.1%; highest incidence without prophylaxis. Major hemorrhage in 0.9%. |
| Quebbemann, 2005 | Prospective noncontrolled study | 822 patients undergoing bariatric surgery receiving prophylaxis with continuous intravenous UH at 400 U/hr from the preoperative period until discharge | Overall incidence of objectively confirmed symptomatic VTE of 0.1%. Major hemorrhage in 1.3%. |
| Cossu, 2007 | Retrospective cohort | 151 patients underwent surgery for morbid obesity. In the first 65 cases, prophylaxis consisted in a single intravenous injection of heparin sodium (2500-5000 IU) at the time of induction of anesthesia. Later cases (86 cases) adjusted according to PT, TT, and aPTT. | Two cases of VTE in the first group and one in the second group. Major bleeding occurred in 2.33%. |
| Raftopoulos, 2008 | Retrospective cohort | Group A: Enoxaparin 1 hour before surgery followed by enoxaparin 30 mg SC twice a day until discharge from hospital. Group B: No preoperative heparin, then enoxaparin 30 mg SC twice a day followed by a 10-day course of enoxaparin 40 mg SC once a day at home after hospital discharge. | VTE event occurred in Group A (1.14%) vs. Group B (0%). The incidence of significant bleeding was lower in Group B (Group A [5.3%] vs. Group B [0.56%], P = 0.02). |
| Borkgren-Okonek, 2008 | Prospective open trial | 223 undergoing Roux-en-Y gastric bypass assigned to receive enoxaparin 40 mg (BMI < 50 kg/m 2 ) or 60 mg (BMI > 50 kg/m 2 ) every 12 hours during hospitalization and once daily for 10 days after discharge. | One patient had nonfatal venous thromboembolism (0.45%). Four patients required transfusion (1.79%). |
| Wang, 2014 | Retrospective cohort | 9241 inpatients with weight > 100 kg comparing high-dose thromboprophylaxis (heparin 7500 U three times daily or enoxaparin 40 mg twice daily) to standard doses (heparin 5000 U two or three times daily or enoxaparin 40 mg once daily). | The rate of VTE was 1.48% of those who received standard doses compared with 0.77% in those who received high doses. High-dose thromboprophylaxis did not increase bleeding (OR, 0.84; 95% CI, 0.66-1.07; P = 0.15). |
Related posts:
What Lessons Have Intensivists Learned During the Evidence-Based Medicine Era?
What Is the Role of Invasive Hemodynamic Monitoring in Critical Care?
Should Fever Be Treated?
Should Exacerbations of COPD Be Managed in the Intensive Care Unit?
Are Anti-inflammatory Therapies in ARDS Effective?
Has Outcome in Sepsis Improved? What Has Worked? What Has Not Worked?
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
