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Alteration in transthoracic impedance following cardiac surgery

Khan NU|Strang T|Bonsheck C|Krishnamurty B|Hooper TL
Resuscitation (2008) 77, 374—378
DESIGN: Haemodynamically significant ventricular tachyarrhythmias are a frequent complication in the immediate post-operative period after cardiac surgery. Successful cardioversion depends on delivery of sufficient current, which in turn is dependent on transthoracic impedance (TTI). However, it is uncertain if there is a change in TTI immediately following cardiac surgery using cardiopulmonary bypass (CPB).
SUBJECTS/METHODS: TTI was measured on 40 patients undergoing .rst time isolated cardiac surgery using CPB. TTI was recorded at 30 kHz using Bodystat® Multiscan 5000 equipment before operation (with and without a positive end-expiratory pressure (PEEP) of 5 cm of H2O) and then at 1, 4 and 24 h after the operation. Data was analyzed to determine the relationship between pre and post-operative variables and TTI values.
RESULTS: Mean pre-operative TTI was 54.5±10.55_ without PEEP and 61.8±15.4_ on a PEEP of 5cm of H2O. TTI dropped significantly (p < 0.001) after the operation to 47.2±10.6_ at 1 h, 42.6±10.2_ at 4 h and 41.8±10.4_ at 24 h. A positive correlation was noted between duration of operation and TTI change at 1 h (r = 0.38; p = 0.016). There was no significant correlation between the duration of bypass and change in TTI.
CONCLUSION: TTI decreases by more than 30% in the immediate post-operative period following cardiac surgery. This state may favour defibrillation at lower energy levels.
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