Chp 38 Obesity Flashcards
How is obesity defined?
Excessive accumulation of body fat to point of being >20% over ideal body weight
–Morbidly obese = body weight 2x ideal BW
Alt def: excessive accumulation of body fat sufficient to impair body functions, be detrimental to good health and well-being
Ideal BW varies w species, age, sex
Where did term pickwickian syndrome come from?
Morbidly obese character in 1836 novel Pickwick Papers by Charles Dickens
What are the signs of pickwickian syndrome in animals?
- -Preoperative hypoxemia caused by obesity
- -Lethargy, somnolent
- -Intermittent respirations with brief periods of apnea
- -Condition usually markedly worsened by anesthetic drug administration in the absence of ventilatory support
How does obesity affect respiration?
- -Decreases ventilatory capacity of patient through decreased thoracic compliance –> impaired diaphragmatic motion DT increased weight of abdominal contents
- -Resp pattern is shallow –> decreased Tv, increased work of breathing, increased RR
- -Increased mass of pharyngeal tissues, tongue may lead to upper airway obstruction following premedication with sedatives and tranquilizers and during induction of anesthesia before a secure airway has been established
What should I do differently during anesthesia of an obese patient?
- -Observe obese patient for signs of airway obstruction following premedication
- -Ventilatory support may be required during anesthesia
- -Endotracheal intubation required, tidal volume monitored
- -Capnography, pulse ox, blood gas analysis will help warn of need for ventilatory assistance
How does obesity affect the circulatory system?
Circulating blood volume, plasma volume, CO increase proportionally with increasing body weight
- HR usually remains within normal limits
- Excess cardiac output generated from increased stroke work
- Worse case: increase in cardiac work will result in ventricular failure
What other conditions commonly occur with obesity?
Pancreatitis DM Hepatic lipidosis Hypothyroidism Cardiac, orthopedic, intervertebral disk disease
How should induction drug dosages be altered in obese animals?
- -Depending on the drug, route of administration - dose may need to be increased, be decreased or remain unchanged
- -Highly lipophilic drug that has a large apparent volume of distribution (Vdss) may require a larger initial dose than in a normal weight animal for an equivalent plasma concentration at steady state
Lipid soluble drugs, injectable anesthetics, larger apparent volume of distribution
- -Drugs not usually administered with the goal of attaining steady-state plasma levels
- -Effective concentrations necessary for anesthesia achieved soon after drug administration, before distribution into adipose tissue can occur
- -Increase doses not usually indicated
What is the safest approach to administer drugs in an obese patient?
Slowly to effect
What does dosing to effect mean?
- Administering drugs slowly until the desired effected is achieved
- For anesthetic induction agents, usually until endotracheal intubation can be performed without causing the patient to gag
- Safest method when individual variation makes calculation of a drug dose difficult
- Works best for rapidly acting IV administered drugs but can also be applied to inhalant agents, inotropic agents, analgesia agents, many other classes of drugs
Are obese animals at greater risk of complications during anesthesia?
- Expected that incidence of respiratory depression, airway obstruction, hypoxemia would be greater
- Cases can be managed by proper drug selection, airway management, preoperative monitoring to reduce risk of morbidity or mortality
Is regional anesthesia safer than GA for obese patients?
- May be preferable –> secure airway obtained, high inspired concentrations of oxygen can be delivered
- Respiratory depression from cranial migration of epidural LA or systemic uptake of opioids may lead to decreased minute ventilation, respiratory embarrassment if assisted or controlled ventilation cannot be instituted
What is the rate of perfusion of adipose tissue?
2-3mL/100g of tissue/min
Meyer-Overton rule
Anesthetic potency appears to parallel lipid solubility
