Anesthetic Pharmacology and the Morbidly Obese Patient

Abstract

Anesthesiologists are increasingly being faced with treating obese patients. Physiologic and anthropometric associated with obesity—most notably increases in cardiac output, changes in tissue perfusion and increases in total body weight (TBW), lean body weight (LBW), and fat mass affect the pharmacokinetics (PK) of anesthetic agents. In addition, redundancy of airway tissue, obstructive and central sleep apnea and CO2 retention affect the pharmacodynamics (PD) of anesthetics and narrow the therapeutic window of numerous anesthetic drugs. Safe and effective pharmacologic management of the obese patient requires a thorough understanding of how obesity affects the PK and PD of anesthetics.

Pharmacokinetics of anaesthetic drugs at extremes of body weight

“…Increased peripheral compartment volumes can exacerbate drug sequestration within poorly perfused tissues in the obese; an example is the delayed offset of fentanyl after prolonged infusion because of saturation of poorly perfused peripheral compartments. 14 In the malnourished, the increased total body water, reduced fat and lean masses, and reduction in protein synthesis result in an increased free fraction and V D of many drugs.…”

Dosage of Sugammadex in morbidly obese patients

“…rocuronium) should be administered based on ideal body weight [3]. It is known that sugammadex has a weak lipophilic profile like rocuronium [4]. However, dose adjustment of sugammadex according to ideal body weight (IBW) or actual body weight (ABW) is still controversial.…”

Fast wake-up time in obese patients: Which anesthetic is best?

“…1 Anesthetizing obese patients can often be challenging as they have a higher incidence of comorbidities 2 and an increased risk of a difficult airway. 3 Furthermore, obese patients are prone to intraoperative pulmonary complications 4 and acute upper airway obstruction and aspiration following tracheal extubation at the end of surgery.…”

“…A variety of pharmacokinetic models have proposed TBW or LBW-based calculations or plasma concentration and bispectral index parameters as a target. 1 Different ways of calculating the doses of intravenous anesthetics can influence time to wake up in the immediate postoperative period and in the PACU. Until pharmacokinetic models for obese patients are standardized worldwide, it would be difficult to compare recovery parameters between TIVA and inhalation-based anesthesia in obese and non-obese patients.…”

“…Divers modèles pharmacocinétiques ont proposé des calculs fondés sur le PCR ou sur la MM ou des paramètres de concentration plasmatique ou d'indice bispectral comme cible. 1 Différentes façons de calculer les doses d'anesthésiques intraveineux peuvent influencer le temps jusqu'au réveil en période postopératoire immédiate et en salle de réveil. Tant que les modèles pharmacocinétiques destinés aux patients obèses ne sont pas standardisés au niveau mondial, il reste difficile de comparer les paramètres de récupération entre une TIVA et une anesthésie par inhalation -que le patient soit obèse ou non.…”