Intensive care unit management of patients with obesity

INTRODUCTION — The patient with obesity among multiple or refractory comorbid illnesses presents many challenges for providing medical and nursing care, as well as for hemodynamic monitoring, respiratory management, vascular access, proper medication dosing, and nutrition [1]. Optimal care can be provided effectively and efficiently when the institution has invested in accommodating them with appropriate facilities, such as bed size and patient lifts, and training for the allied health care personnel [2]. (See "Hospital accreditation, accommodations, and staffing for care of the bariatric surgical patient".)

The critical care management of patients with obesity will be reviewed here and includes patients who have undergone bariatric surgery. A description of specific bariatric operations and management of bariatric patients are reviewed in separate topics, including:

●(See "Bariatric procedures for the management of severe obesity: Descriptions".)

●(See "Bariatric surgery: Postoperative and long-term management".)

INDICATIONS FOR INTENSIVE CARE UNIT ADMISSION — Patients with severe obesity and/or multiple comorbidities may require admission to an intensive care unit (ICU) for medical or surgical reasons [3-8].

For patients with medical conditions, we use the same indications for ICU admission as for patients who are not obese. On occasion, transfer is indicated for staffing reasons.

Following surgery (eg, bariatric surgery), there is no consensus on the criteria for admission to the ICU [9]. The following are some of the common reasons for ICU admission after surgery [10,11]:

●Severe obstructive sleep apnea

●Requirement of continuous cardiac monitoring for cardiac abnormalities

●Refractory diabetes

●Intraoperative surgical or anesthetic complications, such as bleeding, or a cardiac or respiratory event

Patients with an uncomplicated operation and recovery room admission are transferred directly from the recovery room (postanesthesia care unit) to the inpatient surgical floor. (See "Bariatric surgery: Postoperative and long-term management".)

CARDIAC AND HEMODYNAMIC MONITORING — Hemodynamic monitoring devices that are used in the ICU include central venous catheters and arterial lines. In addition, special equipment, such as large blood pressure cuffs and an ultrasound machine, are useful. Such equipment may need to be adapted for use by patients with obesity and may be more difficult to place than in those without obesity.

●Blood pressure cuff – If too small a cuff is used, the pressure generated by inflating the cuff may not be fully transmitted to the brachial artery; in this setting, the pressure in the cuff may be considerably higher than the intra-arterial pressure, which can lead to overestimation of the systolic pressure by 10 to as much as 50 mmHg. (See "Blood pressure measurement in the diagnosis and management of hypertension in adults".)

●Central line and arterial line – Placement of central venous access catheters and arterial lines in the patient with obesity can be challenging. The usual anatomic landmarks are obscured, the distance from skin to vessel is much further than normal, and the angle of approach may be too steep to allow cannulation even after reaching the vessel. Ultrasound can help identify vascular structures and assist in the placement of venous and arterial catheters [12,13]. (See "Indications for bedside ultrasonography in the critically ill adult patient", section on 'Vascular ultrasonography'.)

●Peripherally inserted central catheter – Peripherally inserted central catheters (PICCs) should be placed early when an extended ICU admission is anticipated for durable venous access. PICC lines can generally be placed without difficulty, can deliver hemodynamic information, and can be changed over a guidewire [14,15]. Hemodynamic measurements made using a standard pressurized transducer system through an open-ended PICC line are reliable when compared with centrally inserted catheters [14]. (See "Central venous access: Device and site selection in adults", section on 'Peripheral versus central vein insertion'.)

●Bedside ultrasound – Bedside ultrasound is being increasingly used for point-of-care use in critically ill patients. Although similar probes and ultrasound equipment are used in patients who are obese, imaging may be challenging since distance from skin to the target is much further than usual and may reduce image quality. Indications for bedside ultrasonography in the critical care setting are discussed separately. (See "Indications for bedside ultrasonography in the critically ill adult patient" and "Bedside pleural ultrasonography: Equipment, technique, and the identification of pleural effusion and pneumothorax" and "Ultrasound-guided thoracentesis".)

●Others – The utility of other cardiac monitoring devices (eg, pulmonary artery catheter, transesophageal echocardiography) and the technical details of insertion are reviewed as separate topics. (See "Intra-arterial catheterization for invasive monitoring: Indications, insertion techniques, and interpretation" and "Pulmonary artery catheterization: Indications, contraindications, and complications in adults" and "Intraoperative transesophageal echocardiography for noncardiac surgery".)

RESPIRATORY MANAGEMENT — Some patients with obesity require intubation, and in some cases prolonged intubation and a tracheostomy may be required.

Mechanical ventilation — Static pulmonary compliance is decreased in patients with severe obesity [16]. This is generally due to a heavy, noncompliant chest wall, rather than pulmonary parenchymal restriction. For patients who require mechanical ventilation, initial tidal volumes should be set to approximately 8 mL/kg of ideal body weight (IBW), unless patients have acute respiratory distress syndrome (ARDS), in which case initial tidal volume is set to 6 mL/kg IBW. Subsequent settings are determined by peak airway pressures and results of arterial blood gas measurements [17,18]. Initial ventilator management and management of patients with ARDS are discussed separately. (See "Overview of initiating invasive mechanical ventilation in adults in the intensive care unit" and "Acute respiratory distress syndrome: Ventilator management strategies for adults".)

In general, plateau airway pressures should be maintained below 35 cm H₂O. If this is not possible, esophageal manometry can help to quantify the relative contribution of the chest wall to decreased respiratory system compliance, and transpulmonary pressure should be kept below 35 cm H₂O [19]. The addition of 10 cm H₂O of positive end expiratory pressure may help improve lung compliance by reversing atelectasis and increasing functional residual capacity [20]. (See "Assessment of respiratory distress in the mechanically ventilated patient".)

Ventilation management of the patient with obesity during surgery is reviewed separately. (See "Anesthesia for the patient with obesity", section on 'Ventilation management'.)

Pulmonary physiotherapy — There are some data that suggest aggressive perioperative pulmonary toilet, as well as having the patient in the sitting position as much as possible, may decrease the incidence of aspiration as well as time to liberation from mechanical ventilation [21]. (See "Strategies to reduce postoperative pulmonary complications in adults" and "Initial weaning strategy in mechanically ventilated adults".)

Extubation — Immediately following surgery, patients with obesity should be extubated only when they are nearly completely awake, they are able to follow straightforward commands (eg, raise your hand), and all neuromuscular blockade has been reversed. (See "Anesthesia for the patient with obesity", section on 'Extubation'.)

If the patient demonstrates either respiratory or hemodynamic instability in the postanesthesia care unit, the patient should remain intubated and be immediately transferred to the ICU. At times, patients will be extubated the following day when they are more likely to meet the criteria for extubation with minimal risk of an emergency reintubation.

For patients who remain intubated in the ICU, we apply the same principles of extubation to patients who are obese as those to patients who are not obese. Patients with obesity are not classically considered high risk for postextubation respiratory failure. However, while not routine, extubation to high-flow oxygen or noninvasive ventilation (NIV) is not unreasonable for short-term support after extubation, particularly if patients have obstructive sleep apnea, obesity hypoventilation syndrome, or other risk factors for postextubation respiratory failure. In support, one randomized trial reported a lower rate of treatment failure in patients who were treated with NIV compared with oxygen following extubation [22]. However, the benefit was largely determined by crossover from the oxygen group into the NIV group and reintubation rates were no different among the groups. Further details are discussed separately. (See "Weaning from mechanical ventilation: Readiness testing" and "Initial weaning strategy in mechanically ventilated adults" and "Extubation management in the adult intensive care unit".)

If a respiratory complication arises following extubation, reintubation can be challenging due to swelling of the oropharyngeal tissues and the large amount of redundant oropharyngeal tissue, small oral opening, and a thick neck with limited flexibility [23-26]. (See "Approach to the difficult airway in adults for emergency medicine and critical care" and "Management of the difficult airway for general anesthesia in adults".)

Noninvasive ventilation — Surgical patients with obesity undergoing elective surgery who use NIV at home are instructed to bring their machine to the hospital on the day of surgery [27-29]. Following extubation in the operating room or the recovery room, we often transition patients directly from the critical care ventilator to their own NIV machine, frequently alleviating a degree of postprocedural anxiety [30]. (See "Noninvasive positive airway pressure therapy for the obesity hypoventilation syndrome".)

For medical patients who require NIV for respiratory failure, we traditionally use estimated settings as outlined separately. (See "Noninvasive ventilation in adults with acute respiratory failure: Practical aspects of initiation" and "Noninvasive ventilation in adults with acute respiratory failure: Benefits and contraindications".)

Role of tracheostomy — Early tracheostomy should be performed if it appears that the patient will require prolonged mechanical ventilation [31]. Tracheostomy can often be technically challenging, and a customized tracheostomy tube may be required [4,32]. Percutaneous tracheostomy has been successfully performed in patients with severe obesity, but only clinicians with significant experience should attempt this approach [33]. (See "Tracheostomy in adults: Techniques and intraoperative complications" and "Tracheostomy: Rationale, indications, and contraindications" and "Tracheostomy: Postoperative care, maintenance, and complications in adults".)

NUTRITION

Caloric requirement — The estimated metabolic energy requirements of adequately nourished ICU patients with a normal body mass index are generally based upon actual body weight using the Harris-Benedict equation [34]. However, this equation may overestimate the metabolic demand of patients with obesity and can lead to overfeeding [35]. Indirect calorimetry can be used to measure energy expenditure [34], but this is not widely available and may be difficult in patients receiving mechanical ventilation [4]. Determining the calorie needs of patients with obesity in the ICU is discussed separately. (See "Nutrition support in intubated critically ill adult patients: Initial evaluation and prescription".)

Glycemic control — We use the same approach to glycemic control in both patients with and without obesity. Glycemic targets for inpatients are evolving and under debate as there is a positive association with stringent glycemic control and increased mortality [36].

Management of glycemic control in the ICU and hospital settings is reviewed separately. (See "Glycemic control in critically ill adult and pediatric patients" and "Management of diabetes mellitus in hospitalized patients".)

Management of glycemic control in patients with refractory or persistent hyperglycemia is reviewed separately. (See "Management of persistent hyperglycemia in type 2 diabetes mellitus".)

Micronutrient deficiency — Some of the patients with obesity in the ICU have undergone reoperative bariatric surgery. For such patients, it is important to diagnose and treat any micronutrient deficiency that may have resulted from previous bariatric procedures or their complications. This is discussed in detail in another topic. (See "Bariatric surgery: Postoperative nutritional management", section on 'Micronutrient management'.)

PROPHYLAXIS FOR PRESSURE ULCERS — The risk of pressure ulcers can be reduced with repositioning patients with obesity, just like all patients with limited self-mobility [37]. Pressure ulcers develop when there is unrelieved pressure on soft tissue or compression between a bony prominence or hard surface (eg, bed rail) and the skin for a prolonged period of time.

The consequences of pressure-induced skin injury range from nonblanchable erythema of intact skin to deep ulcers extending to the bone. (See "Epidemiology, pathogenesis, and risk assessment of pressure-induced skin and soft tissue injury" and "Prevention of pressure-induced skin and soft tissue injury".)

PROPHYLAXIS FOR VENOUS THROMBOEMBOLIC EVENTS — Patients with obesity who are admitted to the ICU are considered high risk for venous thromboembolism (VTE). VTE prophylaxis includes extremity compression devices (mechanical prophylaxis), medications (chemoprophylaxis), and physical activity. (See "Prevention of venous thromboembolic disease in adult nonorthopedic surgical patients" and "Prevention of venous thromboembolic disease in acutely ill hospitalized medical adults".)

The optimal goal and approach for VTE chemoprophylaxis in patients with obesity remain undefined. Currently, both unfractionated heparin (UFH) and low molecular weight (LMW) heparins are used in conjunction with mechanical prophylaxis [38]. The American Society for Metabolic and Bariatric Surgery does not endorse any specific anticoagulant or specific dose for chemoprophylaxis due to lack of high-quality clinical evidence [39]. UFH and LMW heparins used in clinical practice are dosed based on expert opinion and observational studies. Suggested dosing is listed in the table (table 1) [40,41]. (See 'Anticoagulants' below.)

Most studies in patients undergoing bariatric surgery use anti-factor Xa (anti-Xa) activity as a surrogate marker for adequate VTE prophylaxis [42], although it does not always correlate with patient outcomes [43]. In a small study of 60 patients undergoing sleeve gastrectomy, those receiving enoxaparin (40 mg twice daily) were more likely to achieve target range in both anti-Xa (94 versus 5 percent) and thrombin generation assays (50 versus 28 percent) compared with patients receiving unfractionated heparin (5000 to 7500 units every eight hours). However, minor bleeding was more common in the enoxaparin group (88 versus 27 percent), and no patient in either group developed a VTE event within 30 days of hospital discharge [44].

Prevention of a VTE in ICU patients, and in particular, patients undergoing a bariatric procedure, is reviewed elsewhere. (See "Prevention of venous thromboembolic disease in adult nonorthopedic surgical patients" and "Bariatric operations: Early (fewer than 30 days) morbidity and mortality", section on 'Venous thromboembolism' and "Prevention of venous thromboembolic disease in acutely ill hospitalized medical adults".)

DRUG THERAPIES — Given the unique challenges of obesity, individualized dosing of drugs for patients with obesity in the ICU is advised. A consultation with a critical care pharmacist skilled in drug therapeutic monitoring and pharmacokinetic dose adjustment is helpful.

Unique challenges of obesity — Patients with obesity have a larger volume of distribution for lipophilic drugs, increased clearance of hydrophilic drugs, and a decrease in lean body mass and tissue water compared with those without obesity [4,45]. As such, decreased drug metabolism via CYP3A4 pathway, a member of the cytochrome P450 family that deactivates many drugs, or increased clearance by glucuronidation or glomerular filtration predisposes patients with obesity to both subtherapeutic and toxic responses to medication [46].

Some agents are administered using non-weight-based approaches while others use weight-based dosing [47-52]. These calculations include the following:

●Ideal body weight (IBW) – IBW is also referred to as standard (non-weight-based) dosing. It is calculated solely from the patient's height, with different equations for males and females, based on actuarial tables (calculator 1).

●Total body weight (TBW) – TBW is the patient's actual weight.

●Adjusted body weight/dosing weight (DW) – For patients whose body mass index (BMI) is ≥30 kg/m², the DW may be adjusted to account for the absence of metabolic requirements by fat tissues. The most commonly employed method is to add 0.4 times the difference between the IBW and the TBW to the IBW. In other words, DW = IBW + 0.4 (TBW - IBW) (calculator 1).

Antibiotics — Individualized dosing of antibiotics for patients with obesity is advised given the potential consequences of inadequate treatment in this population [53,54]. Dose adjustments should be guided based upon therapeutic concentrations whenever available. Guidance on obesity dosing for common antimicrobials used in critically ill patients can be found using the drug interactions program.

Sedatives, analgesics, and neuromuscular blockers

●Sedatives – Similar to intubated patients who are not obese, intubated patients who are obese should be adequately sedated, starting with intermittent agents, and if that is inadequate, an infusion of a short-acting sedative such as propofol or dexmedetomidine. Specific to obesity, propofol, midazolam, lorazepam, and dexmedetomidine are lipophilic agents that redistribute widely to adipose tissue following initial rapid distribution to the central nervous system when administered intravenously, which may affect efficacy. The amount of sedation necessary should be assessed daily in patients requiring prolonged care [55-57] since excessive adipose stores of sedatives can prolong the sedative effect. The intravenous sedative and analgesic dosing regimens for managing pain, agitation, and delirium in the ICU can be found in the drug interactions program. Sedation management in critically ill patients is discussed separately. (See "Sedative-analgesia in ventilated adults: Management strategies, agent selection, monitoring, and withdrawal".)

●Neuromuscular blockers – Dosing for individual anesthetic drugs, such as neuromuscular blockers, in patients with obesity is available in the drug interactions program and is reviewed separately. (See "Anesthesia for the patient with obesity".)

●Analgesics – Patients with obesity-hypoventilation syndrome (OHS) and patients with obstructive sleep apnea (OSA) are at risk of hypercarbic respiratory failure during hospitalization, and opiate administration may increase this risk. For these reasons, the use of epidural analgesia and nonopiate adjuncts for postoperative pain control should be considered in this patient population. Postoperative management of OSA and management of OHS are reviewed separately. (See "Postoperative management of adults with obstructive sleep apnea", section on 'Pain control' and "Treatment and prognosis of the obesity hypoventilation syndrome".)

An opiate should be provided as needed for analgesia; fentanyl appears to have the fewest hemodynamic side effects. (See "Sedative-analgesia in ventilated adults: Management strategies, agent selection, monitoring, and withdrawal".)

For dosing of intravenously administered opioids, it is reasonable to use a series of small standard doses frequently (eg, every 5 to 15 minutes) until the desired level of pain control is achieved. For agents that need weight-based dosing (eg, fentanyl, morphine, hydromorphone, and remifentanil), dosing guidance can be found in the drug interactions program.

The approaches for control of postoperative pain and pain in the critically ill patient are reviewed separately. (See "Pain control in the critically ill adult patient" and "Approach to the management of acute pain in adults" and "Use of opioids for postoperative pain control".)

Anticoagulants — The volume of distribution of heparin in patients with obesity differs from that in patients who are not obese since adipose tissue has a lower blood volume than lean tissue; as a result, heparin dosing requirements do not increase linearly with body weight [58,59].

The optimal dosing method for heparin and low molecular weight (LMW) heparins in obesity is not well established, as most studies exclude patients with obesity [40]. The dosing information presented here is supported by the literature. However, individual practices may vary according to surgeon or institution preferences and patient conditions.

Unfractionated heparin — The 2012 American College of Chest Physicians guidelines on parenteral anticoagulants suggested that weight-based dosing using TBW (ie, actual body weight) was preferable to fixed dosing in patients with obesity [60,61]. The initial rate should be adjusted according to activated partial thromboplastin time (aPTT) measurements after six hours.

The data available support the use of TBW to calculate the initial bolus dose and infusion rate to achieve a therapeutic partial thromboplastin time (PTT) [62-64]. In one study of unfractionated heparin dosing in critically ill patients, patients weighing ≥130 kg had lower weight-based heparin requirements compared with patients weighing between 95 and 104 kg (13.1 versus 15.8 unit/kg/hour) [65]. Post-hoc analyses indicated that this difference was driven by a subgroup of patients who were ≥165 kg.

Maximum initial bolus and infusion rates have been suggested [66,67]. However, the available data show that patients receiving unfractionated heparin without initial dose maximums have an increased mean initial aPTT but not an increased frequency of bleeding [62,68-70]. The functional heparin assay (the anti-factor Xa [anti-Xa] activity) provides a reference standard for testing the in vivo activity of heparin and, in patients with obesity, may be more useful for heparin monitoring than the aPTT.

Low molecular weight heparins — LMW heparins, such as enoxaparin, should also be adjusted according to TBW [63,64,71]. Enoxaparin 40 mg every 12 hours subcutaneously provides effective prophylaxis against venous thromboembolism (VTE) in patients up to a BMI of 50 kg/m² and 60 mg every 12 hours for a BMI exceeding 50 kg/m² [72,73]. Variable absorption of LMW heparin by subcutaneous injection in severe obesity is a concern, leading to under- or overdosing in up to 15 percent of patients [74]. Thus, anti-Xa monitoring is appropriate for patients with obesity receiving LMW heparin, especially those who weigh more than 150 kg [40,74,75]. (See "Bariatric operations: Early (fewer than 30 days) morbidity and mortality", section on 'Venous thromboembolism'.)

Suggested dosing for LMW heparin in patients with obesity is presented in the table (table 1), and these issues are discussed in more detail elsewhere. (See "Clinical use of coagulation tests" and "Heparin and LMW heparin: Dosing and adverse effects".)

Direct oral anticoagulants — According to International Society on Thrombosis and Haemostasis guidelines [76], the use of any direct oral anticoagulant (DOAC) is appropriate for patients with BMI ≤40 kg/m² or weight ≤120 kg. For heavier patients, standard doses of rivaroxaban or apixaban are among appropriate anticoagulant options regardless of BMI and weight. Due to a lack of data, dabigatran or edoxaban should not be used for VTE treatment and prevention in patients with BMI >40 kg/m² or weight >120 kg.

DOACs should not be used for treatment or prevention of VTE in the acute setting after bariatric surgery because of concerns of decreased absorption. Similarly, DOACs are not typically used in unstable critically ill patients. Instead, such patients should receive parenteral anticoagulation for a short period until absorption issues and stability have been achieved. At that point, if patients are to be switched to a DOAC, a trough level should be checked for drug absorption and bioavailability, as certain bariatric procedures can affect the absorption of DOAC agents (eg, four weeks after bariatric surgery) (table 2)

Cardiac medications — We suggest use of IBW adult doses for initial and maintenance dosing of intravenous beta blockers, digoxin, and calcium channel blockers. If a weight-based dose is used, IBW is appropriate for the initial intravenous digoxin loading dose or intravenous beta blocker while DW is suggested for the initial dose of calcium channel blockers. Supplemental and maintenance doses are based upon clinical effect using usual IBW adjustment methods [49].

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Bariatric surgery".)

SUMMARY AND RECOMMENDATIONS

●Indications for intensive care unit (ICU) admission – For patients with obesity, criteria for admission to an ICU for postsurgical or for medical care are not standardized but often include complicated operative course and/or multiple comorbid illnesses. (See 'Indications for intensive care unit admission' above.)

●Cardiac and hemodynamic monitoring – Standard ICU monitoring equipment, such as a central line, arterial line, and peripherally inserted central line, among others, may need to be adapted for use by patients with obesity and may be more difficult to place than in those without obesity. (See 'Cardiac and hemodynamic monitoring' above.)

●Respiratory management – Some patients with obesity require intubation, and in some cases prolonged intubation and a tracheostomy may be required. (See 'Respiratory management' above.)

•Ventilation – Static pulmonary compliance is decreased in patients with severe obesity due to a heavy, noncompliant chest wall. Initial tidal volumes should be set to approximately 8 mL/kg of ideal body weight (IBW), unless patients have acute respiratory distress syndrome, in which case initial tidal volume is set to 6 mL/kg IBW. Subsequent settings are determined by peak airway pressures and results of arterial blood gas measurements. In general, plateau airway pressures should be maintained below 35 cm H₂O. (See 'Mechanical ventilation' above.)

•Extubation – Immediately following surgery, patients with obesity should be extubated when they are nearly completely awake, when they can follow straightforward commands, and when the entire neuromuscular blockade has been reversed. For patients who remain intubated, we apply the same principles of extubation as those who are not obese; while not necessarily routine, extubation to high-flow oxygen or noninvasive ventilation is not unreasonable. (See 'Extubation' above.)

•Prolonged intubation – For patients that require prolonged intubation, attention should be drawn early to accessing durable venous access, a tracheostomy, and nutritional support. (See 'Role of tracheostomy' above and 'Nutrition' above.)

●Drug therapies – Medication dosing is challenging in patients with obesity due to a large volume of distribution for lipophilic drugs, increased clearance of hydrophilic drugs, and a decrease in lean body mass and tissue water. A consultation with a critical care pharmacist skilled in drug therapeutic monitoring and pharmacokinetic dose adjustment is helpful. (See 'Drug therapies' above.)

Depending on the agent in question, drugs may be dosed by non-weight based approach or a weight-based approach that uses ideal body weight, total body weight, or an adjusted body weight (calculator 1). Examples are given in each drug class below (see 'Unique challenges of obesity' above):

•Antibiotics (see 'Antibiotics' above)

•Sedatives, analgesics, and neuromuscular blockers (see 'Sedatives, analgesics, and neuromuscular blockers' above)

•Anticoagulants, including low-molecular-weight heparin (table 1) and direct oral anticoagulants (table 2) (see 'Anticoagulants' above)

•Cardiac medications (see 'Cardiac medications' above)

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Michael A Gropper, MD, PhD, who contributed to earlier versions of this topic review.