1) Obesity poses several clinical challenges in the ICU such as difficulties with monitoring, vascular access, nursing care, airway management, and drug dosing. 2) Obese patients are at higher risk for respiratory complications due to reduced lung volumes and compliance. They require specialized ventilator settings including higher PEEP and targeting tidal volumes based on ideal body weight. 3) Nutrition is also complex in obese ICU patients. Overfeeding can cause complications while underfeeding risks protein-energy malnutrition. Initial calorie targets are based on obesity-adjusted body weight.

1. Obesity in ICU
Hooi Hooi Koay
ICU registrar
Rockhampton Base Hospital
20/11/2015

3. Body Mass Index (kg/m2)
Adapted from WHO

4. Increasing Prevalence of Obesity
• 1997 WHO recognized obesity as a global epidemic
• In Australia, almost 2 in 3 adults are overweight
• 1 in 4 children are overweight
• 15% more people living in outer regional and remote areas are overweight or obese
than people living in major cities
• 2nd contributor to burden of disease, after dietary risk, smoking is the third highest
(Australian Institute of Health and Welfare: Based on measured height and weight from the 2011–12 Australian Bureau of Statistics Australian Health
Survey)

5. Obesity as a Risk Factor
• Hypertension
• Diabetes mellitus
• Coronary artery disease
• Dyslipidemia
• Gall bladder disease
• Osteoarthritis
• Respiratory problems
• Cancer (endometrial, breast and colon)

6. Clinical Challenges
• Monitoring and investigation difficulties
• Difficult vascular access
• Nursing care difficulties
• Airway management, respiratory and cardiovascular considerations
• Nutritional, thromboembolism prophylaxis
• Drug dosing

7. Respiratory Evaluation and Considerations

8. Airway Management
• Limited neck mobility and mouth opening, large breasts, short neck, large
tongue, excessive palatal and pharyngeal soft tissue, high anterior larynx,
short sternomental distance, receding mandible, prominent teeth, Mallampati
score 3 or more, large neck circumference
difficult intubation
• Excess abdominal fat  diaphragmatic splinting  decreased expiratory
reserve volume and functional residual capacity  decreased oxygen reserve
(and increased consumption)  rapid deterioration

10. Airway Complications
• Airway obstruction during the use of supraglottic airway devices
• Aspiration of gastric contents during RSI
• Difficult intubation
• Displaced tracheostomy and tracheal tubes

11. Gas Exchange
• Decreased functional residual capacity with a high closing volume
 closure of peripheral lung units, ventilation to perfusion ratio abnormalities and
hypoxemia, especially in the supine position
• Ventilatory failure is uncommon because retention of carbon dioxide is easily offset
by an increase in minute ventilation
• However, when an obstructive component or accompanying pulmonary or systemic
pathological change occurs, making it impossible to maintain the work of breathing
ventilatory failure

12. Pulmonary Compliance and Work of Breathing
• Chest wall compliance is decreased by the deposition of fat  inspiratory
muscles work harder to overcome the lung’s elastic properties
• Lung compliance is decreased because the alveoli collapse
• Reduced lung volume  increase airway resistance
The combined effect  increased work of breathing
• Twice as much work as non-obese

13. • In healthy obese persons, pulmonary reserve is limited
• A pathological changes can be a substantial risk for respiratory failure
• Early mechanical ventilatory support should be considered

14. Controlled Mechanical Ventilation
• Initially parameters based on ideal body weight
• Subsequently adjust according to regular ABG measurements
• A tidal volume calculated according to total body weight is likely to result in
excessively high airway pressure, alveolar over distention, baro/ atelectrauma
• Positioning patient in a semi-erect posture at 45 degree will increase
ventilation volumes

15. Suggested Initial Ventilator Settings
• High FiO2 (0.6)
• Tidal volume 5-7 ml/kg based on IBW
• PEEP of 7-10 cmH2O
• Peak inspiratory pressure < 35cmH2O

16. Cardiovascular Evaluation and Considerations

17. Altered Cardiovascular Physiology & Structure
• A variety of adaptations/alterations in cardiac structure and function occur
• Eccentric left ventricular hypertrophy is common in BMI >40, often associated with
left ventricular diastolic dysfunction
• In patients who have hypertension, a combination of concentric and eccentric
hypertrophy occurs
• Blood volume increases in response to accumulation of adipose tissue  increase in
stroke volume & cardiac output
• Obesity cardiomyopathy (adipositas cordis) : metaplasia process = adaptive
substitution of cells to better withstand the stress

18. • Chronic hypoxemia that occurs with sleep apnoea may result in polycythemia
and pulmonary hypertension
 right ventricular dysfunction

19. Whether Obesity Affects CPR Quality?
• Childhood obesity is associated with a lower rate of survival to hospital
discharge after in-hospital, pediatric CPR
(Childhood Obesity and Survival After In-Hospital Pediatric Cardiopulmonary Resuscitation. Childhood Obesity and Survival After In-Hospital Pediatric
Cardiopulmonary Resuscitation. Vijay Srinivasan et al)

20. Cardiovascular Considerations During Weaning
• Monitored for indications of ischaemia, infarction and pulmonary oedema
• As positive pressure (PEEP or CPAP) is removed
 venous return increases
 this increase in volume may exceed the heart’s ability to compensate
 resulting in ischaemia +/- pulmonary oedema

21. Nutrition and Obesity

22. Nutrition
• Metabolic stress + elevated basal insulin suppresses lipolysis, causing breakdown of protein as a primary
energy source
 decrease in lean body mass (and increased in production of urea) protein energy malnutrition
• Start feeding within 24hrs of admission
• 20 -30 kcal/kg/day based on obesity-adjusted body weight IBW + (TBW-IBW)0.25
(Consensus from Dietitian/ Nutritionists from the Nutrition Education Materials Online, "NEMO", team)
• Indirect calorimetry to estimate energy expenditure
• Protein requirement: 1.5 -2g/kg/day of IBW
• Calories to be given as carbohydrates and fat to prevent fatty acid deficiency
• Hypocaloric feeding maybe beneficial

23. Do Not Overfeed
• Volume overload  congestive heart failure & pulmonary oedema
• Glucose intolerance
• Excess carbon dioxide production  increased respiratory work and
respiratory failure

24. Thromboembolic Prophylaxis

25. Thromboembolic Prophylaxis
• Decreased mobility, pulmonary hypertension, venous stasis and potential
hypercoagulable state  predispose obese patients to VTE and PE
• Primary prevention is the key = mobility
• Weight-based enoxaparin dosed at 0.5mg/kg OD is feasible and results in
anti-Xa levels within recommended range for thromboprophylaxis, without
excessive anti-Xa activity
(Weight-based dosing of enoxaparin for VTE prophylaxis in morbidly obese, medically-Ill patients. Rondina et al)

26. Pharmacologic Concerns

27. Pharmacology Considerations in Obesity
• Obesity impacts on PK/ PD properties of drug
• Obese individuals are often excluded from clinical trials during the drug
development process
• Dosing based on TBW can result in overdose, based on IBW may result in a
sub-therapeutic dose

28. Formula
• Total Body Weight (TBW) : patient’s actual weight.
• Ideal Body Weight (IBW):
Males = height – 100
Females = height – 110
• Lean Body Weight (LBW):
Males = 50 + 0.9kg for every cm over 150cm
Females = 45 + 0.9kg for every cm over 150cm
• Adjusted Body Weight (ABW): 0.4 (TBW-IBW) + IBW

29. Pharmacokinetics - Absorption
• Altered absorption of oral medications (diabetic gastroparesis)
• Difficult IV access in the obese
• Decreased SC absorption due to poor subcutaneous blood supply
• IM administration may fail if needles are too short

30. Distribution
• Larger volume of distribution (Vd) for lipophilic drugs
dose lipid soluble drugs on actual body weight
• No change in Vd of water soluble drugs
dose on ideal or lean body weight
• Protein binding: Malnourished may have low protein stores, decrease in drug
binding and increase in free drug

31. Metabolism/Clearance
• Clearance of cytochrome P450 (CYP) 3A4 substrates is lower
• Clearance of drugs primarily metabolized by uridine diphosphate
glucuronosyltransferase (UGT), glomerular filtration and/or tubular-
mediated mechanisms, xanthine oxidase, N-acetyltransferase, CYP2E1,
CYP1A2, CYP2C9, CYP2C19 and CYP2D6 appears higher
(Impact of obesity on drug metabolism and elimination in adults and children. Brill et al)

32. Elimination
• Increased eGFR  increased clearance for hydrophilic drugs
• T1/2 increased of lipid soluble drugs due to accumulation
• Co-existing disease (e.g. nephropathy associated with diabetes and
hypertension)

33. Some Specific Examples:
Antimicrobials
• Penicillins, cephalosporins: IBW, preferably dose at the upper end of recommended ranges
• Beta lactams exert time-dependent bactericidal effects, suggest to decrease dosing intervals or
continuous infusion
• Vancomycin: TBW
• Large increase in Vd, but an even larger increase in Cl  Leading to shortened drug half life
• Decrease dosing interval to Q6-8Hrly or continuous infusion
• Aminoglycosides: ABW
• Frequency of administration is determined by renal function and adjusted based on serum drug
concentrations

34. Sedatives and Analgesics
• Benzodiazepines, propofol: IBW, subsequent titration based on clinical response
• As they are lipophilic, the drugs accumulate in tissue and fat during prolonged infusion
• When the infusion discontinued, the drug is reabsorbed into the plasma, resulting in
potential for delayed awakening
• Opioids: give in a series of smaller dose until the desired level of pain control in achieved
• Remifentanil is preferred to fentanyl or alfentanyl because of lack of accumulation and
quick offset of action
• Based on IBW and titrate to effect

35. Muscle Relaxants
• Succinylcholine: TBW
• Vecuronium and rocuronium: IBW
• Cisatracurium, atracurium, mivacurium: TBW

36. Outcomes After ICU Care
More Complications = Worse Outcomes ?
• A number of studies have looked into ICU and hospital mortality with
conflicting results
• Two recent meta-analyses demonstrated no difference in mortality between
critically ill obese patients and those with normal BMI
• The impact of obesity on outcomes after critical illness: a meta-analysis. Hogue CW Jr., Stearns JD, Colantuon E, et alThere may
even be an improved survival
• Influence of body mass index on outcome of mechanically ventilated patients. Anzueto A et al
• Obesity survival paradox