Free
Case Reports  |   December 1999
The Changes in Bispectral Index during a Hypovolemic Cardiac Arrest 
Author Affiliations & Notes
  • Michael R. England, M.D.
    *
  • *Assistant Professor.
Article Information
Case Reports
Case Reports   |   December 1999
The Changes in Bispectral Index during a Hypovolemic Cardiac Arrest 
Anesthesiology 12 1999, Vol.91, 1947. doi:
Anesthesiology 12 1999, Vol.91, 1947. doi:
ANESTHESIOLOGISTS for many years have sought to monitor brain function during surgery to assist in proper administration of sedative–hypnotic agents and to detect early signs of inadequate cerebral perfusion. A processed electroencephalographic device (Aspect Medical Systems, Natick, MA) newly approved by the Food and Drug Administration produces a unitless scale from 0 to 100 that correlates with a patient's hypnotic state. 1 At the top of the scale (100), a patient is awake and responsive. As hypnotics are administered, the scale (Bispectral Index, BIS) decreases in a dose-related fashion. Generally, free recall is lost at 70 and consciousness is lost at 60. 2 As the Index approaches 0, burst suppression becomes more prominent as electroencephalographic activity is lost.
We describe a patient in whom this monitor was used for titration of anesthetic agents for a tricuspid valve replacement, during which she had transient hypovolemic cardiac arrest. The BIS and hemodynamics were stored real-time into a laptop computer. This case report shows the potential value of BIS monitoring, not only for intraoperative drug titration, but also as a sign of return of cerebral function after an intraoperative threat to neurologic integrity. It was possible to track how the patient was responding to resuscitation.
Case Report 
The patient was a 22-yr-old woman scheduled for tricuspid valve replacement. She had undergone closure of a ventricular septal defect in the distant past, and now presented with pulmonary artery hypertension and progressive right ventricular failure because of tricuspid valve insufficiency.
She received 10 mg morphine sulfate and 5 mg midazolam (in divided doses) for sedation during (peripheral) intravenous (8.5 French), arterial and internal jugular (9 French) line placement. Induction then consisted of 25 μg sufentanil, 125 mg thiopental, and 6 mg pancuronium with 0.25 μg · kg−1· h−1sufentanil and 0.5% isoflurane for maintenance. The BIS decreased to 55 with this induction sequence.
During sternotomy, using an oscillating saw, the right atrium was lacerated. There was sudden loss of blood volume within 2 min. (fig. 1) Despite having seemingly adequate intravenous access, we were unable to maintain cardiac filling, and the patient's systolic blood pressure decreased to 20 mmHg (fig. 1). Extra surgical personnel were called in to assist with immediate femoral cannulation and start cardiopulmonary bypass. Simultaneously, another surgical team repaired the damage to the atrium. During the whole sequence, an automatic record was kept of heart rate, mean arterial pressure, and BIS value on a laptop computer.
Fig. 1. Changes in the Bispectral Index with severe hypotension. 
Fig. 1. Changes in the Bispectral Index with severe hypotension. 
Fig. 1. Changes in the Bispectral Index with severe hypotension. 
×
As can be seen in figure 1, (A) at 9:00 AM, just after incision, vital signs and BIS were stable. However, with sternotomy, large amounts of blood were lost, causing hypotension (approximately 9:01 AM;[B]), which was treated with a rapid infusion of phenylephrine (C), resulting in a rise of the mean arterial blood pressure to 85 mmHg. After the patient started to exsanguinate, blood pressure could not be maintained despite adding as much heated volume as possible (D). Approximately 4 min after the start of the sternotomy, she underwent hypovolemic arrest, with mean arterial pressure decreasing to 20 mmHg. It took approximately 9 min for the patient's blood pressure to be stabilized as cardiopulmonary bypass was initiated. During this time, manual cardiopulmonary resuscitation was performed as best as possible.
Of note are the concurrent tracings of BIS and blood pressure. As the blood pressure decreased with cardiac laceration, the decrease in BIS lagged behind the decrease in blood pressure by approximately 2 min. This may be caused, in part, by the 30- to 60-s delay inherent to the smoothing algorithm used to calculate BIS, and autoregulation and the lag between decreases in blood pressure, cerebral blood flow, and neuronal dysfunction. As blood pressure was corrected by volume replenishment (via  femoral arterial cannulation), an additional 2 min was necessary for neuronal function, as indicated by the BIS, to return to the premorbid level. During the time in which neuronal function, as indicated by the BIS, was low, the burst suppression ratio was high. As cerebral blood flow was reinstituted, the BIS returned and the percentage of burst suppression decreased. During the case, we believed that the return of the BIS was a reassuring sign of successful resuscitation.
The remainder of the case continued without difficulty. The patient was able to be weaned from cardiopulmonary bypass without problem or vasoactive agents. Because of our concern about possible ischemic brain injury because of the episode of hypotension, the patient was awakened promptly after skin closure. She awoke without incident and was able to move herself off the operating room table onto the stretcher. She was extubated within 4 h of intensive care unit arrival.
Discussion 
Using the the BIS in cardiac surgery and in the ambulatory setting has been shown to optimize titration of anesthetic and hypnotic agents 3 to achieve faster recovery times. 4 
While using the BIS in our usual fashion, we suddenly were confronted with a crisis. The sudden loss and return of blood pressure evoked a parallel but delayed pattern in the BIS, with transient electroencephalographic silence (100% burst suppression). The reversible nature of the BIS (electroencephalography) suggested that the patient was not going to experience permanent ischemic brain injury. In fact, that turned out to be the case.
It is clearly acknowledged by the makers of the product that the BIS is not intended as an ischemic monitor nor as a predictive device. Further studies need to be performed to evaluate such applications. However, this case shows how the availability of a simple-to-use monitor of brain function can provide useful new information regarding patient response to unexpected events.
The authors thank Daniel B. Carr, M.D., for helpful editorial comments, and Paul Manberg, Ph.D., Aspect Medical Systems, Natick, Massachusetts, for his technical advice.
References 
References 
Rosow C, Manberg PJ: Bispectral Index Monitoring. Anesthesiology Clinics of North America: Ann Anesth Pharmacol 1998; 2: 89–107
Glass P, Bloom M, Kearse L, Rosow C, Sebel P, Manberg P: Bispectral analysis measures sedation and memory effects of propofol, midazolam, isoflurane, and alfenanil in healthy volunteers. A NESTHESIOLOGY 1997; 86: 836–47
England MR, Murphy MC, Court M: How much is enough: Titrating to the Bispectral Index during cardiac anesthesia. Anesth Analg 1997; 84(suppl 2): S73.
Song D, van Vlymen J, White PF: Is the Bispectral Index useful in predicting fast-track eligibility after ambulatory anesthesia with propofol and desflurane? Anesth Analg 1998; 87: 1245–8. (Aspect Medical Systems, Natick, MA)
Fig. 1. Changes in the Bispectral Index with severe hypotension. 
Fig. 1. Changes in the Bispectral Index with severe hypotension. 
Fig. 1. Changes in the Bispectral Index with severe hypotension. 
×