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Correspondence |
Chandigarh, India
To the Editor:
Closed mitral commissurotomy (CMC) is still a widely practiced method of treatment in young patients with critical mitral stenosis, especially those without a significant mitral regurgitation or a history of embolism.1 Commissurotomy is a critical part of the procedure since it involves a transient but significant reduction in systemic perfusion. We present a case where an unusually long drop in blood pressure during commissurotomy, resulted in cerebral hypoperfusion, severe enough to depress cortical electroencephalogram (EEG) as measured by bispectral index (BIS).
A 20-yr-old New York Heart Association Class III female with critical mitral stenosis (MVA-0.6 cm2) was scheduled for CMC. Monitoring included invasive arterial blood pressure, electrocardiography, pulse oximetry, end-tidal carbon dioxide and BIS. Following iv induction with propofol and vecuronium, anesthesia was maintained with O2, N2O and propofol infusion titrated to a BIS value of 50. During a longer than usual commissurotomy (55 sec), there was a drop in mean arterial blood pressure (MAP; 20 mmHg) with a coincident decrease in BIS value to 20 (Figure
). The hemodynamic variables and the BIS value improved when the surgeon was asked to stop the manipulation. The patient was extubated after assessing a normal neurological status and had a smooth recovery.
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BIS is routinely used in sophisticated operating rooms to monitor anesthetic depth. There are reports to suggest that acute decreases of the index may be related to cerebral ischemia,3–5 even though this has not been validated. Additionally BIS has the advantage of ease of interpretation as compared to the raw EEG which requires a dedicated neurophysiologist. Transcranial Doppler and jugular bulb venous O2 saturation have been considered to be indicative of cerebral injury, however these monitors are more popular in intensive care units.
In our patient BIS dropped as the duration of CMC increased and may well indicate cerebral hypoperfusion. Further, monitoring blood pressure alone may not be appropriate in clinical situations where there is a discrepancy between cardiac output and cerebral blood flow.
Another interesting observation is a near 50 sec lag between the drop in MAP and BIS. We cannot comment on whether this was due to cerebral autoregulation or BIS computing time.
Nonetheless, BIS can serve as a valuable adjunct to indicate the adequacy of cerebral perfusion and, as in this case, to limit the duration of CMC.
References
1 Avenilo PA. Closed mitral commissurotomy. In: Jamieson SW, Shumway NE (Eds.). Operative Surgery - Cardiac Surgery, 4th ed. London: Butterworths; 1986: 399–404.
2 Billiard V. Brain injury under general anesthesia: is monitoring of the EEG helpful (Editorial). Can J Anesth 2001; 48: 1055–60.
3 Merat S, Levecque JP, Le Gulluche Y, Diraison Y, Brinquin L, Hoffmann JJ. BIS monitoring may allow the detection of severe cerebral ischemia (French). Can J Anesth 2001; 48: 1066–9.
4 Hayashida M, Chizei M, Yamamoto H, Hanaoka K. Detection of compromised cerebral circulation with bispectral index during pediatric cardiac surgery. Anaesthesiology 1999; A1234 (abstract).
5 England MR. The changes in bispectral index during a hypovolemic cardiac arrest. Anesthesiology 1999; 91: 1947–9.[Medline]
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