Obesity in ICUHooi Hooi KoayICU registrar

Rockhampton Base Hospital20/11/2015

Body Mass Index (kg/m2)

Adapted from WHO

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)

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

Clinical Challenges

• Monitoring and investigation difficulties• Difficult vascular access• Nursing care difficulties• Airway management, respiratory and cardiovascular

considerations• Nutritional, thromboembolism prophylaxis• Drug dosing

Respiratory Evaluation and Considerations

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

Airway Complications

• Airway obstruction during the use of supraglottic airway devices

• Aspiration of gastric contents during RSI• Difficult intubation• Displaced tracheostomy and tracheal tubes

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

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

• 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

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

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

Cardiovascular Evaluation and Considerations

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

• Chronic hypoxemia that occurs with sleep apnoea may result in polycythemia and pulmonary hypertension

right ventricular dysfunction

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)

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

Nutrition and Obesity

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

Do Not Overfeed

• Volume overload congestive heart failure & pulmonary oedema

• Glucose intolerance• Excess carbon dioxide production increased respiratory

work and respiratory failure

Thromboembolic Prophylaxis

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)

Pharmacologic Concerns

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

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

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

Distribution

• Larger volume of distribution (Vd) for lipophilic drugsdose lipid soluble drugs on actual body weight• No change in Vd of water soluble drugsdose on ideal or lean body weight• Protein binding: Malnourished may have low protein

stores, decrease in drug binding and increase in free drug

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)

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)

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

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

Muscle Relaxants

• Succinylcholine: TBW• Vecuronium and rocuronium: IBW• Cisatracurium, atracurium, mivacurium: TBW

Outcomes After ICU CareMore 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