There are several factors to consider in the management of morbidly obese patients undergoing robot-assisted gynecological surgeries. Preoperative assessment of the patient’s chronic medical conditions, such as hypertension, cardiovascular disease, central or obstructive sleep apnea, and impaired glucose tolerance, is indispensable. Preoperatively, evaluation and preparation for the management of a difficult airway should be performed. During robotic surgery of obese patients with pneumoperitoneum using CO2 insufflation and a steep Trendelenburg position, the decrease in chest wall compliance is augmented by the large amount of fatty tissue in the thoracoabdominal region, which increases the risk of atelectasis and hypercapnic acidosis. Protective lung strategies using low tidal volumes or limiting plateau airway pressure and PEEP can be challenging in these circumstances. Furthermore, increases in intrathoracic pressure might subsequently increase intraocular and intracranial pressures [1,2,3,4], and induce upper airway edema [5]. Not only are these intraoperative problems increased in morbidly obese patients, but pharmacological considerations are also more complicated.
For the present patient, preoperative evaluation and management were crucial for successful perioperative management. As we received a preoperative consultation from the surgeon in charge 1 month prior to the surgery, we were able to instruct the patient to lose weight before the surgery, and she successfully lost 10 kg. In addition, we simulated the surgery in the operating room with the patient before the surgery, to confirm that there were no inconveniences or flaws regarding the procedure for establishment of the airway and when the patient was in the Trendelenburg position. The patient’s SpO2 did not decrease below 90% during the actual operation in this position.
In obese patients, desflurane, which has a low blood gas partition coefficient, confers greater intraoperative control of the depth of anesthesia, as well as rapid and consistent postoperative emergence and recovery [6]. However, in the present case, the patient had experienced an asthma attack 2 months before the surgery. Thus, sevoflurane, which causes less airway irritability and a relatively strong bronchodilation effect, was considered to be more preferable.
The dosing of rocuronium in obese patients is still controversial [7, 8]. Rocuronium is a slightly lipophilic drug, and it has been suggested that the duration of action of such a drug is prolonged when administered based on actual body weight rather than ideal body weight. However, there are reports suggesting that at a rocuronium dose of 0.6 mg/kg, there is no difference in the recovery rate even when it is administered according to the patients’ actual weight [9]. We acknowledge that administering a drug based on the patient’s ideal body weight is safer for morbidly obese patients, considering their postsurgical recovery. In the present patient, a dose of 0.6 mg/kg of her actual weight was administered to facilitate tracheal intubation, followed by continuous infusion under neuromuscular monitoring to maintain the train-of-four ratio at 0 and post-tetanic count between 0 and 5 [10,11,12]. After surgery, 4 mg/kg of sugammadex was sufficient to achieve full recovery of neuromuscular activity, as confirmed by a train-of-four ratio of 1.0. Extubation was performed without any sequelae, and no pulmonary complications were observed postoperatively.
For postoperative analgesia, we simulated fentanyl blood concentrations by pharmacokinetic simulations using the Shafer model [13]. But it may be inappropriate in an extremely obese patient. We should have used Shibutani’s “pharmacokinetic mass” for our simulation. Using “pharmacokinetic mass” and the time course of fentanyl administration, we will be able to estimate fentanyl effect-site concentrations more accurately [14, 15].
Placing a patient with pneumoperitoneum in the Trendelenburg position promotes atelectasis, particularly in morbidly obese patients [16]. Although PEEP and recruitment maneuvers are effective for the prevention of atelectasis, a reasonable approach to determining the appropriate level of PEEP has not yet been established. The PEEP level of 10 cmH2O that was used in the present patient appeared to be insufficient, because during the surgery, the SpO2 fluctuated between 96 and 98% with an ORi of 0.00, and SpO2 increased to 100% following the recruitment maneuver whereas ORi spontaneously increased to 0.30. Atelectasis thus appeared to develop at a PEEP of 10 cmH2O. Mazzinari et al. measured esophageal pressure in patients who underwent laparoscopic cholecystectomy, and showed that by setting the PEEP to a value 2 cmH2O higher than the intraperitoneal pressure, the driving pressure based on transpulmonary pressure can be reduced compared with that using the standard PEEP value (5 cmH2O) [17]. In the present case, as the patient’s intraperitoneal pressure was 10 mmHg (≒ 13 cmH2O) and she was placed in the Trendelenburg position, it might have been more appropriate if the PEEP level had been set to more than 15 cmH2O. Furthermore, as pressure-controlled ventilation was set to achieve a tidal volume of 7 mL/kg based on the patient’s ideal weight, the plateau pressure was approximately 29 cmH2O and the driving pressure was 19 cmH2O. Therefore, in the present patient, the PEEP level should have been set to a higher value while lowering the plateau pressure. ORi was monitored throughout the anesthetic period to keep track of oxygenation. ORi is an index reflecting moderate hyperoxia (PaO2 of 100–200 mmHg) and is expressed on a non-unit scale of 0.00 to 1.00. During the induction of anesthesia, ORi increased to 0.52 owing to preoxygenation, and from after intubation to after the patient was positioned in the Trendelenburg position, ORi fluctuated between 0.20 and 0.30, with an FiO2 of 0.45. We believe that ORi is a useful reference for the estimation of oxygenation, and that the measurement of ORi enabled us to perform early interventions, such as the setting of PEEP levels and performing recruitment maneuvers [18,19,20].
Obesity exacerbates the complications associated with robot-assisted pelvic surgery. Specifically, proper airway and respiratory management is difficult when obese patients are placed in the Trendelenburg position. Therefore, rehearsal of the surgery in the Trendelenburg position prior to the actual surgery should be performed, and in addition, appropriate respiratory management and evaluation of oxygenation using ORi are also very helpful. Anesthetics, such as remifentanil, rocuronium, and sugammadex, which facilitate the awakening and recovery of obese patients and reduce postoperative lung complications, should be used. It is well known that robot-assisted laparoscopic surgery reduces surgical site infections and shortens the duration of hospitalization; hence, in the future, this type of surgery is expected to become more common, even in obese patients.