High thoracic epidural and remifentanil for anaesthesia for cardiac surgery in morbidly obese patients with obese hypoventilation syndrome
© Current Science Ltd 2000
Published: 12 June 2000
Patients with morbid obesity and obese hypoventilation syndrome are at a high risk for respiratory complications after surgery. This risk is increased substantially if sedative opioid analgesia is necessary. This group of patients present particular challenges when undergoing cardiac surgery, in which opioid anaesthesia is a mainstay of perioperative management. We present a series of such patients anaesthetized using a combination of high thoracic epidural and remifentanil infusion.
Methods and results
Over the past 2 years, nine patients presented for anaesthesia to one of the authors (JCB) for cardiac surgery, with both morbid obesity (body mass index ranged from 40.3 to 45.7) and obese hypoventilation syndrome requiring either nocturnal continuous positive airways pressure or, in two cases, nocturnal biphasic positive airways pressure. There were eight men and one woman (age range 43-69 years); seven required coronary revascularization and two required aortic valve replacement.
No sedative premedication was administered. All patients consented to a high thoracic epidural, which was placed by one of the authors (JCB) immediately before induction of anaesthesia after arterial and venous cannulae were in place. The epidural was sited using loss of resistance to saline through a 16 g Tuohy needle with the patient in the sitting position in either the C7/T1 (seven cases) or the T1/T2 (two cases) intervertebral space. Anaesthesia was induced with propofol 0.5 mg/kg and remifentanil 1 μg/kg ideal body weight, muscle relaxation with atracurium 0.5 mg/kg, and the patient was intubated.
In the patients who required coronary revascularization 15 ml 0.5% bupivacaine was given as a bolus before sternotomy, and the remifentanil was titrated back to 0.1-0.15 μg/kg per min. In the patients who required aortic valve replacement the bupivacaine was given after the institution of cardiopulmonary bypass, and the remifentanil was maintained at 0.5-1 μg/kg per min until that point. Propofol 3 mg/kg per h was administered throughout.
Propofol and remifentanil were continued after surgery in the intensive care unit, where an epidural infusion of 0.15% bupivacaine was commenced at 8 ml/h. All patients were weaned from mechanical ventilation when usual criteria had been met. The time to extubation ranged from 2 to 18 h (median 7.5) after the end of surgery. No patient required reintubation. One patient spent 3 days in intensive care because of a post-drain removal pneumothorax; no other patient spent more than the first postoperative night in intensive care. Only one patient remained an inpatient longer than 7 days, and he went home 10 days after surgery. The epidural infusions were continued for between 48 and 72 h after surgery and supplemental analgesia was with diclofenac 50-75 mg three time a day or tramadol 50-100 mg three times a day. The epidural infusion required to produce satisfactory analgesia ranged from 6 to 18 ml/h (median 8 ml/h).
The use of opioids in patients with obese hypoventilation syndrome is known to carry a significant risk of respiratory depression and cardiorespiratory arrest. Providing postoperative analgesia with epidural local anaesthesia avoids the use of opioids postoperatively. Remifentanil administered during anaesthesia allows the benefits of opioid analgesia in such patients during surgery without any residual effects after surgery due to its rapid metabolism by tissue esterases. By using this combination of ultrashort-acting opioid and high thoracic epidural, it has been possible to anaesthetize this high-risk group of patients safely with no increase in duration of intensive care or hospital stay.