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Copy of Obesity and Anesthesia

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Veronica Namerow

on 28 February 2014

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Transcript of Copy of Obesity and Anesthesia

Obesity and Anesthesia
Obesity is the second leading cause of preventable death in the United States
65% of US adults are classified as overweight or obese.
The World Health Organization has predicted that the number of severely overweight adults is expected to double by 2025.
BMI

This is the acceptable measure of body habitus that normalizes adiposity for height. BMI can be calculated:
BMI= Weight (kg)/Height (meters squared)
Overweight= BMI of 25-29
Obesity class 1-2= BMI of 30-39.9
Extremely obese (Morbid Obesity)= BMI >40
Super obese= BMI >50
Super-super obese= >60
Ideal Body weight
The measurement of height and body mass that exhibits the lowest morbidity and mortality for a given population.
IBW(men) = Height (cm)-100
IBW (women)= Height (cm)-105
Pathophysiology of Obesity
Pathophysiologic changes occur as a result of obesity.
These changes include all of the major body organs, leading to increased morbidity and premature death.
The risk for many of the medical conditions associated with obesity increases linearly with BMI.
Cardiovascular Considerations
Ischemic heart disease
Hypertension
Cardiomegaly
Cardiac Failure (Biventricular)
Increased cardiac output
Increased stroke volume
Increased oxygen consumption
Increased CO2 production
Ventricular Hypertrophy
Dyslipidemia
DVT's
Respiratory Considerations
Chest wall, lung, parenchyma and pulmonary compliance is reduced to 35% of predicted values.
Increases in CO2 production and retention.
Decreased ventilation.
Reduced respiratory muscle efficacy.
Decreases in FRC to less than closing capacity.
Premature airway closure increases dead space and causes CO2 retention, ventilation perfusion mismatch, shunting and hypoxemia.
Decreased Expiratory Reserve Volume
Decreased total lung capacity.
The decrease in VC, TLC, ERV, IC are evident in rapid shallow breathing.
Restrictive lung disease- characteristic of these breathing patterns
Eventual hypoventilation, hypercarbia and acidosis result from central nervous system responsiveness to chronic hypoxia.
Recurrent hypoxemia leads to secondary polycythemia and is associated with an increased risk of coronary artery disease, and cerebrovascular disease.
Obese Hypoventilation (Pickwickian) Syndrome
OSA
Hypercapnia
Daytime hypersomnolence
Arterial hypoxemia
Cyanosis-induced polycythemia
Respiratory acidosis
Pulmonary hypertension
Right sided heart failure
Evidence of nocturnal episodes of central apnea (apnea without respiratory effort).
Gastrointestinal Disease
Increased incidence of reflux disease, gallstones, and pancreatitis.
Nonalcoholic fatty liver disease- includes steatosis, steatohepatitis, fibrosis, cirrhosis, hepatomegaly, abnormal liver biochemistry
In obese patients the mortality rate from liver cirrhosis is 1.5 to 2.5 times higher than in non-obese persons.
Endocrine and Metabolic Disease
Within groups of people with type 2 diabetes 80% are obese.
The risk of type 2 diabetes increases linearly with BMI.
Hyperinsulinemia and impaired insulin-receptor sensitivity lead to hyperglycemia.
Syndrome X- has been found in patients with abdominal obesity. Characterized by insulin resistance, impaired glucose tolerance, type 2 diabetes, dyslipidemia and hypertension.
Orthopedic and Joint Disease
Osteoarthritis
Bone resorption secondary to limited physical activity may also reduce bone density and contribute to stress fractures.
Degenerative disk disease

Pharmacologic Considerations
Highly lipophilic drugs have an increased volume of distribution in obese people. :
Requires higher doses of lipophilic drugs to provide the desired pharmacologic effect, and prolongs the elimination of certain drugs.
Maintenance doses of narcotics and benzodiazepines should be administered
less frequently
because clearance would be expected to be slower.
Complications during the immediate post operative period have been correlated with the amount of intraoperative opioids administered.
Water soluble drugs such as neuromuscular blockers have a much more limited volume of distribution and maintenance doses should be based on IBW to avoid overdosing.
Decrease dose of spinal and epidural medications.

Guidelines:











Midazolam
- Increased central VD:
increase initial dose for therapeutic effect; prolonged sedation.
Propofol:
Increased VD: increase initial dose; high affinity to fat; high hepatic extraction.
Fentanyl:
Increased VD: increase elimination half time.
Remifentanyl:
Consider age and lean body mass (so short acting, no difference was found between IBW and TBW.
Vecuronium:
Dose on IBW to avoid overdosing
Rocuronium:
Dose on IBW to avoid overdosing
Succinylcholine:
Increase plasma pseudocholinesterase activity. Increase dose.
Other drugs to dose on IBW: Digoxin and Procanamide and Remifentanyl:
No systemic relationship exists between the solubility and the distribution of these highly lipophilic drugs in obese patients.
Airway Problems
The value of Mallampati classification alone is low. Evaluation of the
length of upper incisors,
visibility of the uvula,
shape of the palate,
compliance of the mandibular space
length and thickness of the neck should be included in the airway assessment.
Fat rolls around the neck and in the airway together increase the difficulty of intubation.
Anatomic problems induced by severe obesity include reduced temporomandibular and atlantoocipital joint movement, unsatisfactory mouth opening and inability to place the patient in sniffing position.
Abnormal Lab Findings
CBC's with hematocrits as high as 65% can result from contracted blood volume or polycythemia associated with cardiopulmonary disease.
Leukocytosis greater than 11,000 is a strong predictor of risk for acute myocardial infarction independent of tobacco smoking.
Abnormal glucose and potassium levels which are indicators of insulin resistance and potentiation of myocardial irritability.
BUN and creatinine levels may be elevated in response to dehydration or renal dysfunction.
LFT's are typically elevated in obese patients because of infiltration of hepatocytes with triglycerides.
Bariatric Surgery
The Roux-en-Y gastric bypass is the most commonly performed bariatric procedure in the United States.
Involves the anastamosis of the proximal gastric pouch to a segment of the proximal jejunum, bypassing most of the stomach and the entire duodenum.
The most effective bariatric procedure for weight loss.
Patients are generally less than 65 years of age and weigh 100lbs or more above IBW.
Previous attempts to lose weight must be documented.
Through examination to rule out physiologic and or psychologic disorders.
Failure to assess appropriate candidates for surgical intervention and long term follow up care can lead to recidivism.
The survival rate for morbidly obese patients under 40 years who have bariatric surgery is 13.8% as compared to 3% for those who did not receive surgical management.
Accumulating evidence suggests that adolescents who are currently choosing bariatric surgery should expect significant improvements in obesity status and related comorbidities. It is also possible that improvements in health and psychosocial well being may exceed that which would be expected if operation were delayed until later in the life course of extreme obesity after comorbidities progress and worsen.
Given numerous reports of positive outcomes of bariatric surgery in adolescence in the medical literature and general acceptance in the worldwide media, it is likely that greater numbers of youth will seek surgical interventions for obesity in the future.
Further, without an empirically valid method of assessing an adolescent's capacity to make an informed decision about weight loss surgery, the clinical team must consider the adolescent's cognitive, social and emotional development when considering their candidacy. Adolescents must also be active participants in the decision-making process (e.g., assent/consent, knowledge of risks/benefits) to assure that the decision to have surgery is voluntary, well informed and rational.

References:
Inge1, Xanthakos, Zeller,.
Bariatric surgery for pediatric extreme obesity: now or later?
International Journal of Obesity (2007) 31, 1–14. doi:10.1038/sj.ijo.0803525
Nagelhout, J., Plaus, K., Nurse Anesthesia Fourth Edition 2010. pp 1025-1039
Anesthetic Considerations for Bariatric Surgery
Ramp your patient! HOB up for preoxygenation.
After induction but before intubation CPAP can be used to optimize oxygen transfer at the level of the alveoli and help to decrease atelectasis.
Consider RSI based on pt's history of reflux and morbid obesity.
Calculate initial tidal volume based on ideal body weight.
Consider using an inhalation agent with a low blood gas solubility because it will redistribute to fat tissue to a lesser degree and have a more rapid pulmonary elimination. Ideal agent for obese patients is Desflurane.

Bowel prep and NPO status plus antihypertenisve drugs can exacerbate hypotension post induction. Give fluid bolus preinduction to decrease the degree and duration of hypotensive episodes.
Monitor for effects of pneumoperitoneum
Monitor for right mainstem ventilation in the trendelenburge position- you will see a rapidly occurring desaturation.
Maintain neuromuscular relaxation
Extubate in the sitting position, transfer to PACU with HOB up and supplemental oxygen on.
Journal Article: Bariatric surgery for pediatric extreme obesity: now or later?
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