EM Care of the Obese Patient: Pearls & Pitfalls

Author: Haney A. Mallemat, MD (EM/Critical Care Attending Physician, University of Maryland – @CriticalCareNow) // Editors: Alex Koyfman, MD (@EMHighAK) and Manpreet Singh, MD (@MPrizzleER)

Featured on the LITFL Review #175 – Thanks to Dr. Anand “Swami” Swaminathan (@EMSwami) and the LITFL Review group for the shout out!

Defining Obesity

• Body Mass Index (BMI) = Mass (Kilograms) / Height (meters)²
• National Institute of Health / World Health Organization categorize BMI:
  • Underweight: <18.5 kg/m²
  • Normal weight: ≥18.5 – 24.9 kg/m²
  • Overweight: ≥25.0 – 29.9 kg/m²
  • Obese: ≥30 kg/m²
    • Class I Obesity: 0 – 34.9 kg/m²
    • Class II Obesity: 0 – 39.9 kg/m²
    • Class III Obesity: ≥40 kg/m²
      • Class III sometimes referred to as severe, extreme, or morbid obesity
    • Super-obese: >50 kg/m²
  • This is a general definition as data is derived from Caucasian patients
    • Actual definitions may vary among different ethnicities
      • For example, Asians with BMI >23 – 24.9 kg/m² are considered to be overweight and >25 kg/m² obese

Epidemiology

• Obesity is a major problem in the United States and worldwide
  • Increasing incidence in children, adolescences, and adults
• 1962 -> 47% Americans were either overweight or obese
• 2004 -> 66% Americans were either overweight or obese
• 2011 -> 70% Americans were either overweight or obese (30% obese)
  • Overall rates of obesity have plateaued in recent years, but the Class III subgroup of obesity has continued to rise
• Obesity is associated with co-morbid diseases (e.g. diabetes, hypertension, cancer, etc.) and with increased mortality.
• Do morbidly critically ill obese patients have a higher mortality than non-obese patients? Data is uncertain:
  • It would seem logical to assume that mortality is higher in obese patients, because morbidly obese patients have serious comorbid conditions (e.g. cardiac disease, vascular disease, etc.) and are often difficult to medically manage because of their changes in baseline physiology
  • The “Obesity” Paradox
    • There is evidence that obese patients have equal or even a reduced mortality compared to non-obese cohorts
    • Theories to explain the obesity paradox
      • Increased nutritional reserves (e.g. adipose tissue) that may deal with inflammation and metabolic stress
      • Patients may receive more aggressive care than their normal weight cohorts
      • The severely obese may be a younger cohort of patients and may skew the data
      • Sample size of critically ill obese patients still too small to conclude from studies
    • Obese patients may have increased:
      • duration of intubation and mechanical ventilation
      • longer length of ICU stay

What are the differences between caring for the critically ill obese and non-obese patients?

• Attention to maintaining patient respect and dignity
• Proper equipment (e.g. stretchers, gowns, lifts, etc.)
• Inaccuracies in assessing blood pressure secondary to improper cuff size
  • A small bladder cuff may overestimate blood pressure by up to 50 mmHg
  • Appropriate bladder length should be at least 75% of upper arm circumference and a width greater than 50% the length of the upper arm
• Difficulty in obtaining peripheral intravenous access even with ultrasound assistance
• Difficulty in obtaining or interpreting diagnostic imaging
  • Limitations of ultrasound
  • Underpenetrated X-rays
  • Weight limits of CT/MRI machines
• Appropriate and therapeutic dosing of medications is challenging
  • Larger volume of distribution for lipophilic drugs
  • Increased clearance of hydrophilic drugs
  • Reduction in lean body mass and tissue water
  • An overall understanding that drugs differ by the way they should be dosed
    • Ideal body weight?
    • Total body weight?
    • Dosing weight?
  • Consider using clinical pharmacologists when you have them either available in person or by phone
• Procedures can be difficult and increased risks of complications. Examples:
  • Endotracheal intubation
  • Central line placement
  • Thoracostomy

Physiologic and anatomic changes with obesity

• Differences in airway anatomy in the critically ill obese patient
  • Attempts at intubation are more challenging and have an increased risk of failure
    • Increased oropharyngeal tissue / Mallampati (III-IV)
    • Small oral opening
    • Limited neck flexibility
    • Increased neck circumference
  • Pulmonary changes in the critically ill obese patient
    • Restrictive physiologic pattern secondary to a reduction in chest wall compliance
      • Increased adipose tissue surrounding chest wall, diaphragm, and abdomen
      • Increased pressure on anterior chest from adipose tissue
    • Increased airway resistance
      • Para-pharyngeal fat deposition
      • Fibrosis from chronic airways changes
      • Repetitive opening and closing of small airways
    • Respiratory muscles endure an increased workload and oxygen consumption
    • Reduction in lung volumes
      • Total Lung Capacity
      • Functional residual capacity
      • Vital Capacity
      • Expiratory reserve volume
    • Intrapulmonary shunting
    • V/Q mismatch
    • All of the above changes may lead to severe hypoxemia, hypercarbia, and rapid desaturation during intubation

Circulatory changes in the critically ill obese patient

• Hyperdynamic circulation and increased intravascular volume
• Increased pulmonary hypertension
• Increased systemic pressure
• Hypertrophy of the LV
• LV diastolic dysfunction
• RV dysfunction

Hematologic changes in the critically ill obese patient

• Atherosclerotic changes
• Prothrombotic state (increased blood viscosity)
• Increased fibrinogen
• Increased anti-thrombin III levels
• Increased plasmin activator inhibitor levels
• Decreased fibrinolysis

Gastrointestinal changes in the critically ill obese patient

• Increased risk of aspiration
  • Increased gastric capacity at baseline
  • Increased intra-abdominal pressure
  • Increased incidence of gastro-esophageal reflux disease
  • Lower esophageal sphincter relaxation
• Intra-abdominal hypertension
  • Association between increased BMI and intra-abdominal hypertension (IAP 12 – 20 mm Hg).
  • Increased risk of developing abdominal compartment syndrome (IAP > 20 mm Hg with evidence of end-organ dysfunction)

General approach to the critically-ill obese patient

• Early assessment of airway and breathing
  • Early application of oxygenation because obese patients may desaturate quickly secondary to little pulmonary reserve
  • Consider early non-invasive positive pressure ventilation
  • Pulmonary changes with obesity may be worsened with supine positioning and increased risk of aspiration
    • Consider reverse Trendelenburg (30-45 degrees)
      • Reduces risk of aspiration
      • Improve lung perfusion and diaphragm function
    • Considerations for endotracheal intubation
      • Consider head of bed elevation during or just prior to intubation
      • Most experienced person should be available
      • Utilize apneic oxygenation
      • Video laryngoscopy should be considered for the first attempt or should be ready and available if direct laryngoscopy is performed first
      • Backup devices
        • LMA; intubating-type is preferable
        • Bougie
        • Cricothyroidotomy kits
      • Settings for the mechanical ventilator
        • 6-8 cc/kg ideal body weight
          • Based on height and gender; not actual weight
        • Positive end-expiratory pressure (PEEP)
          • Difficult to know the “real” PEEP the patient encounters
          • Consider a minimum PEEP of 10 cm H₂O
          • A starting PEEP of 15 cm H₂O may be better in ALI /ARDS
        • Maintain plateau pressures < 30mmHg

Access and monitoring of circulation

• Venous access
  • Central line
    • Despite ultrasound, access can still be challenging
      • Increased risk of complications with femoral or subclavian access
    • Consider early intraosseous (IO) placement
  • Consider early intra-arterial catheter for accurate blood pressure assessment and control
  • Screen and monitor for abdominal compartment syndrome

Tips and Tricks for the management of critically ill obese patients

• Using ultrasound during intubation
  • Monitoring for esophageal intubations
    • UMEM pearl , ALiEM post, and Maryland CC post
  • Assessing neck for potential cricothyroidotomy
  • Assessing tube position post-intubation
• Ultrasound for subclavian vein cannulation
  • Ultrasound Podcast
  • emCurious
• Ultrasound to assist during lumbar puncture
  • Ultrasound Podcast
  • SGEM #41: Ultra Spinal Tap (Ultrasound Guided Spinal Tap)
  • ACEP Focus On: Ultasound-Guided Lumbar Puncture

References / Further Reading

1. Vasan R., et al Estimated risks for developing obesity in the Framingham Heart Study. Ann Intern Med. 2005;143(7):473.
2. Amundson, D. et al. Theobesity paradox. Crit Care Clinic 2010 Oct;26(4):583-96.
3. Akinnusi, M. et al. Effect of obesityon intensive care morbidity and mortality: a meta-analysis. Critical care medicine 2008 Jan;36(1):151-8.
4. Martino, J. et al. Extreme obesity and outcomes in critically ill patients. Chest 2011 Nov;140(5):1198-206.
5. El-Solh A, et al. Morbid obesity in the medical ICU. Chest. 2001;120(6):1989.
6. Williamson J, et al. The Australian Incident Monitoring Study. Difficult intubation: an analysis of 2000 incident reports. Anaesth Intensive Care. 1993;21(5):602.
7. Brodsky J, et al. Morbid obesity and tracheal intubation. Anesthesia Analgesia 2002;94(3):732.
8. Juvin P, et al. Difficult tracheal intubation is more common in obese than in lean patients. Anesthesia Analgesia. 2003; 97(2):595.
9. Boyce, J. et al. A preliminary study of the optimal anesthesia positioning for the morbidly obese patient. Obese Surgery 2003 Feb;13(1):4-9.
10. Burns, S. et al. Effect of body position on spontaneous respiratory rate and tidal volume in patients with obesity, abdominal distention and ascites.Am J Crit Care 1994 Mar;3(2):102-6.