Get access

Real time estimation of brain water content in comatose patients

Authors

  • Sang-Bae Ko MD, PhD,

    1. Department of Neurology, Seoul National University Hospital, Seoul, South Korea
    Search for more papers by this author
  • H. Alex Choi MD,

    1. Departments of Neurology, Columbia University College of Physicians and Surgeons, New York, NY
    Search for more papers by this author
  • Gunjan Parikh MD,

    1. Departments of Neurology, Columbia University College of Physicians and Surgeons, New York, NY
    Search for more papers by this author
  • J. Michael Schmidt PhD,

    1. Departments of Neurology, Columbia University College of Physicians and Surgeons, New York, NY
    Search for more papers by this author
  • Kiwon Lee MD,

    1. Departments of Neurology, Columbia University College of Physicians and Surgeons, New York, NY
    2. Neurosurgery, Columbia University College of Physicians and Surgeons, New York, NY
    Search for more papers by this author
  • Neeraj Badjatia MD, MS,

    1. Departments of Neurology, Columbia University College of Physicians and Surgeons, New York, NY
    2. Neurosurgery, Columbia University College of Physicians and Surgeons, New York, NY
    Search for more papers by this author
  • Jan Claassen MD, PhD,

    1. Departments of Neurology, Columbia University College of Physicians and Surgeons, New York, NY
    2. Neurosurgery, Columbia University College of Physicians and Surgeons, New York, NY
    Search for more papers by this author
  • E. Sander Connolly MD,

    1. Neurosurgery, Columbia University College of Physicians and Surgeons, New York, NY
    Search for more papers by this author
  • Stephan A. Mayer MD

    Corresponding author
    1. Departments of Neurology, Columbia University College of Physicians and Surgeons, New York, NY
    2. Neurosurgery, Columbia University College of Physicians and Surgeons, New York, NY
    • Division of Neurocritical Care, Department of Neurology, Columbia University College of Physicians and Surgeons, Milstein Hospital Building 8 Center, 177 Fort Washington Ave, New York, NY 10032
    Search for more papers by this author

Abstract

Objective:

Although brain swelling is an important cause of neurological deterioration, real time measurement of brain edema does not currently exist. Because thermal conductivity is proportional to percentage water content, we used the thermal conductivity constant to estimate brain water content (BWC).

Methods:

Between June 2008 and November 2010, 36 comatose brain-injured patients underwent cerebral blood flow monitoring using a thermal diffusion probe in our neurocritical care unit. BWC was estimated hourly utilizing the measured thermal conductivity and the known temperature-adjusted thermal conductivity of water. In vitro experiments were performed to validate this formula using agar, glycerol, and water mixtures with different water content.

Results:

Thermal conductivity was highly correlated (R2 = 0.99) and estimated water content was well correlated with actual water content (mean difference, 0.58%) in the in vitro preparations. The majority of the 36 patients (median age, 57 years; 44% female) had subarachnoid hemorrhage (n = 14) or cardiac arrest (n = 9). Initial BWC at the time of monitoring ranged from 67.3 to 85.5%. Brain regions appearing edematous on computed tomography showed higher estimated BWC than normal-appearing brain regions (79.1 vs 70.2%; p < 0.01). Bolus osmotherapy (20% mannitol or 23.4% hypertonic saline) decreased BWC from 77.2 ± 0.7% (mean ± standard error) at baseline to 76.1 ± 0.5% at 1 hour, 76.5 ± 0.3% at 2 hours, and 76.7± 0.2% at 3 hours (all p ≤ 0.03).

Interpretation:

Real time monitoring of BWC is feasible using thermal conductivity. Further studies are needed to confirm the clinical utility of this technique. ANN NEUROL 2012;72:344–350

Ancillary