Obese Animals: Complications of Anesthesia
Obesity is described as an accumulation of excess adipose tissue as a result of a sustained positive energy balance. The high prevalence of overweight and obese companion animals may skew the perception of what is considered ideal body composition. Body Condition Score (BCS) is used most commonly in companion animals to assess body composition.
In obese animals, clinical examination may be hindered, the chest may be more difficult to auscultate and the abdomen more difficult to palpate. Veins and arteries may be more difficult to identify when large amounts of subcutaneous fat are present. Pulses may be more difficult to palpate. Subcutaneous fat may make venous and arterial access challenging and correctly securing appropriately sized cuffs for noninvasive blood pressure measurement can be difficult. Increased subcutaneous fat may obscure identification of landmarks for regional anesthesia.
Increased subcutaneous fat may result in poor drug delivery after intended intramuscular administration. The low perfusion of adipose tissue may delay absorption of subcutaneously administered drugs.
Organ dysfunction as a result of obesity may dictate modification in perioperative care. Change in respiratory and cardiovascular function have been identified in dogs.
Obesity increase anesthetic and operative times in both soft tissue and orthopedic procedure. Surgical access is often more difficult, thus prolonging anesthetic time, which increase risk and potentially lengthens recovery times. General anesthetic agents are lipid-soluble (they need to enter the brain to exert their effect). Problems may occur following large or multiple doses of the slowly metabolised when its cumulation in adipose tissues can delay recovery.
In perioperative setting, oxygenation is further diminished by reduction in muscular tonus of chest wall and diaphragm following general anesthesia induction and and skeletal muscle relaxation. The net effect of this on obesity is the decrease of FRC and ERV and consequent decrease in the number of alveoli making efficient gas exchange, compared to preinduction phase. In addition, reduction in FCR and ERV increases predisposition to post-operation atelectasis and may inhibit effective clearance of secretions. Obese patients in relaxed condition under anesthesia have increased likelihood of hypoxemic complication due to reduction in apneic oxygenation reserve and difficulty of performing positive pressured mask ventilation.
Obesity is associated with some problems also during postoperative period. Postoperative care should aim to prevent from respiratory dysfunction, hypothermia, hemodynamic instability, thromboembolism, nausea, vomiting, and pain. Monitoring should be continued in the recovery unit.
References
Love, L., and Cline, A.G., 2015. Perioperative physiology and pharmacology in the obese small animal patient. Veterinary Anaesthesia ans Analgesia, 42: 119-132.
Michel, K.E., 2012. Nutritional management of body weight. In: Applied Veterinary Clinica Nutrition. Fascetti, A., Delany, S.J., Wiley-Blackwell, Ames, USA.
Demirel, I., Bolat, E., Altun, A.Y., 2016. Obesity and anesthesia management. DOI: 10.5772/65920
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