Bispectral Index Monitor Prevented Intraoperative Awareness During Partial Cardiopulmonary Bypass

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LETTERS TO THE EDITOR

E-DA Hospital I-SHOU University Kaohsiung, Taiwan REFERENCES 1. Toda R, Moriyama Y, Yamashita M, et al: Operation for adult patent ductus arteriosus using cardiopulmonary bypass. Ann Thorac Surg 70:1935-1937, 2000 2. Gurcun U, Boga M, Badak MI, et al: Transpulmonary surgical closure of patent ductus arteriosus with hypothermic circulatory arrest in an adult patient. Tex Heart Inst J 32:88-90, 2005 3. Black LL, Goldman BS: Surgical treatment of the patent ductus arteriosus in the adult. Ann Surg 175:290-293, 1972 4. Aun C, Major E: The cardiorespiratory effects of ICI 35 868 in patients with valvular heart disease. Anaesthesia 39:1096-1100, 1984 5. Stephan H, Sonntag H, Schenk HD, et al: Effect of Disoprivan (propofol) on the circulation and oxygen consumption of the brain and CO2 reactivity of brain vessels in the human. Anaesthesist 36:60-65, 1987 6. Adembri C, Venturi L, Pellegrini-Giampietro DE: Neuroprotective effects of propofol in acute cerebral injury. CNS Drug Rev 13:333-351, 2007 7. Ergun R, Akdemir G, Sen S, et al: Neuroprotective effects of propofol following global cerebral ischemia in rats. Neurosurg Rev 25:9598, 2002 doi:10.1053/j.jvca.2009.07.003

Bispectral Index Monitor Prevented Intraoperative Awareness During Partial Cardiopulmonary Bypass To the Editor: It is well known that a split circuit causes the bispectal index (BIS) value (BIS monitor Aspect A-2000; Aspect Medical Systems, Newton, MA) to decrease to “0” in partial CPB.1 Propofol administered via an upper limb causes an increase in the plasma concentration (Cp) in the area proximal to crossclamping (CC) of the descending thoracic aorta (DTA), resulting in a reduction of the BIS value.2 We experienced a reverse case in which the BIS value increased after CC of the DTA in a patient in whom propofol was administered via a lower limb. The patient was a 60-year-old man (height, 156 cm; weight, 51 kg) who was scheduled to undergo thoracic aortic aneurysm repair. A catheter inserted in the peripheral vein of a lower limb was used to administer propofol because the upper limbs were not suitable due to an internal shunt in the right forearm. The radial and dorsalis pedis arteries were cannulated to monitor invasive blood pressure. Anesthesia was induced and maintained with a continuous infusion of propofol, remifentanil, and dexmedetomidine using a target-controlled infusion (TCI) system (propofol [Diprifusor; AstraZeneca Pharmaceuticals, Cheshire, UK]; remifentanil and dexmedetomidine, STANPUMP software [available at: http://anesthesia.stanford.edu/ pkpd]). The target effect site concentration (ESC) of remifentanil and the target Cp of dexmedetomidine were steady at 12 and 0.5 ng/mL throughout the surgery. Target Cp of propofol was changed to maintain the BIS value close to 40 to 60. The

target Cp of propofol was adjusted in the range of 3.6 to 4.0 ␮g/mL until CC of the DTA. The target Cp of propofol and BIS value were 4.0 ␮g/mL and 40, respectively, at the time of CC of the DTA. Because the BIS value had increased to 58 at 5 minutes after CC, the target Cp of propofol was raised to 4.2 ␮g/mL. The BIS value continued to increase and temporally showed “83,” resulting in the target Cp being raised to 5 ␮g/mL at 30 minutes after CC. Two arterial blood samplings were performed to measure 2 concentrations of propofol at the same time, 1 sample being drawn from the radial artery in the area proximal to CC and the other being drawn from the dorsalis pedis artery in the area distal to the CC, 40 minutes after CC, when target Cp of propofol and BIS value were 5 and 67 ␮g/mL, respectively. The BIS value rapidly decreased from 54 to 26 because of declamping of the DTA when the target Cp of propofol was 5.5 ␮g/mL. The target Cp of propofol was able to be reduced and was adjusted in the range of 1.1 to 3.5 ␮g/mL after declamping. Emergence from anesthesia was smooth, and the patient’s postoperative condition was good with no complications. He did not have any memory intraoperatively. Cps measured at a later date in the upper and lower limbs were 1.224 and 4.972 ␮g/mL. The concentrations of remifentanil and dexmedetomidine were not measured because we had no means for performing the measurements. It had been predicted that the ESC of propofol was reduced and that the BIS value was elevated in cases in which propofol was administered via a lower limb based on the reports by Kakinohana et al.1,2 However, the degree of rise in the BIS value and the difference between the measured Cp in the upper limb and that in the lower limb were larger than expected. Although a TCI system is used to maintain ESCs of anesthetic agents at constant concentrations, the use of a TCI system prevents ESCs of anesthetics from being maintained at constant concentrations during CC of the DTA in cases in which partial cardiopulmonary bypass is performed. A BIS monitor might be useful for preventing intraoperative awareness in cases in which propofol is administered via a lower limb during CC as well as for deep anesthesia in cases in which propofol is administered via an upper limb during CC. Takayuki Kunisawa, MD, PhD Megumi Ueno, MD Akihiro Suzuki, MD, PhD Osamu Takahata, MD, PhD Hiroshi Iwasaki, MD, PhD Department of Anesthesiology and Critical Care Medicine Asahikawa Medical College Hokkaido, Japan REFERENCES 1. Kakinohana M, Miyata Y, Kawabata T, et al: Bispectral index decreased to “0” in propofol anesthesia after a cross-clamping of descending thoracic aorta. Anesthesiology 99:1223-1225, 2003 2. Kakinohana M, Nakamura S, Fuchigami T, et al: Influence of the descending thoracic aortic cross-clamping on bispectral index value and plasma propofol concentration in humans. Anesthesiology 104: 939-943, 2006 doi:10.1053/j.jvca.2009.07.011