Reseasrch Of The Relativity Between LBW (Lean Body Weight) And The Inductive Dose Of Intravenous Anesthesia

Objective:The population of obeses is increasing worldwide every year recently. Obesity can cause the body a series of pathophysiological changes, which raise a tough problem to anesthesiologists. Especially in the induction of anesthesia, anesthetic drugs will cause some inhibition of the cardiovascular system by over-deep or shallow deep anesthesia. For some short surgeries, inducing agent can be a direct cause of delayed recovery. This research intends to observe the impact of the stability of cardiovascular system and postoperative recovery time when induced by LBW, inorder to explore the relationship between LBW and the inductive dose of intravenous anesthesia.Methods:150 ASAⅡ～Ⅲcases aging from 20 to 65 years old were selected for the research,75males and 75 females, including 50 cases of abdominal surgery,50 cases of orthopedic surgery and 50 cases of breast and thyroid surgery. Control the operation time within 2 hours.150 patients were divided into five groups according to BMI naming:the standard weight group (groupⅠ) (BMI 18.5～23.9), overweight group (groupⅡ) (BMI24.0～26.9), obese group (groupⅢ) (BMI27.0～29.9), severe obesity group (groupⅣ) (BMI30.0～35.0) and morbidly morbidly obese (GroupⅤ) (BMI≥35.0) Each group had 30 cases. GroupⅠ～Ⅴwas randomly divided into three groups:group A, group B and group C and they were induced by LBW, TBW and IBW respectively. All patients were treated with inhalation general anesthesia, monitored by non-invasive blood pressure, electrocardiogram and oxygen saturation (SPO2) routinely. Recorded blood pressure and heart rate respectively. Opened venous access and gave penehyclidine 1mg 15min before surgery. Induction of anesthesia:injected the anesthetics by intravenous followed by midazolam 0.04mg/kg, vecuronium 0.1mg/kg, propofol 2mg/kg, sufentanil 0.5ug/kg. Pressurized oxygen via face mask for 3mins for tracheal intubation, and then connected anesthesia machine for mechanical ventilation. Recorded the heart rate, systolic and diastolic blood pressure respectively at the moment just before intubation (T2) and the moment intubating (T3). Set tidal volume 10ml/kg, frequency 12 times/min, inspiratory to expiratory ratio of 1:1.5. Monitored end-tidal CO2 concentration (Pet CO2), sevoflurane minimum alveolar concentration (MAC), end-tidal sevoflurane concentration, end-tidal nitrous oxide (N2O) concentration and peak airway pressure (Ppeak) during operation. Maintenance of anesthesia:Inhaled 50% oxygen,50% nitrous oxide and (2～3%) sevoflurane during the surgery. Adjusted the concentration of sevoflurane according to surgical stimulating intensity and no additional sedation, analgesia or muscle relaxants would be used. Stopped inhalation of sevoflurane when the surgery was complete and gave neostigmine 0.02 mg/kg and atropine 0.01 mg/kg intravenously to antagonize residual muscle relaxant. No analgesic or sedative drugs would be used after surgery. Extubation criteria:recovery of spontaneous breathing with regular rhythm, tidal volume>5ml/kg, respiratory frequency<20 times/min, Pet CO2 <45mmHg, recovery of swallowing reflex and eyes open. Extubated when the conditions all met and gave oxygen by masks. Recorded extubation time (time from the end of surgery to extubation).Results:In groupⅠand groupⅡ,there were no statistically differences between groupA, groupB and Group C both in anesthetic depth after induction or in recovery time after anesthesia. But in groupⅢ,Ⅳ,Ⅴ, the comparison of anesthetic depth after induction was group B> group A> group C and the differences between group A,B,C were significant to each other(in groupⅢ, p<0.05; in groupⅣand groupⅤ, p<0.01). In groupⅢ,Ⅳ,Ⅴ, the comparison of postoperative recovery time was group B> group A> group C. The difference to goup B was significant(in groupⅢ, p<0.05; in groupIV and group V, p<0.01), but there was no statistic difference between group A and group C. No matter the anesthetic depth after induction or the recovery time after anesthesia, the differences between group A,B and C was more and more significant according to the increasing of BMI.Conclusion:For obese patients without underlying systemic diseases, LBM may be considered as a standard to calculate the inductive doses due to the appropriate anesthesic depth after induction and the little impact on recovery time after anesthesia. There is a kind of relationship between LBM and the inductive doses. It seems that the greater the BMI is, the more reasonable to use LBM as standard.