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Differential contribution of skin impedance and thoracic volume to transthoracic impedance during external defibrillation

Differential contribution of skin impedance and thoracic volume to transthoracic impedance during external defibrillation
Differential contribution of skin impedance and thoracic volume to transthoracic impedance during external defibrillation
Background: Two mechanisms by which firm external paddle force decreases transthoracic impedance (TTI) have been proposed. Decreased impedance at the paddle-skin interface has been assumed to be the primary mechanism, but expulsion of air from the lungs, reducing lung volume is also likely to contribute. The relative contribution of each mechanism is unknown. Methods and results: Thirty five intubated patients undergoing general anaesthesia for cardiac surgery were studied. TTI across external defibrillation paddles was measured as paddle force was increased to 12 kgf. Measurements were performed twice; once allowing the volume of the lungs to change and once with lung volume held at functional residual capacity. TTI with constant lung volume was significantly higher at all paddle forces (P<0.001), confirming that a reduction in lung volume contributes to the decrease in TTI. At an optimal paddle force of 8 kg, the reduction in lung volume contributed to 16.2% of the overall decrease in TTI. Conclusion: The decrease in TTI seen with increasing external paddle force is due primarily to improved electrical contact at the paddle-skin interface, with a decrease in thoracic volume accounting for no more than 16% of the overall decrease at forces used clinically.
0300-9572
171-174
Deakin, Charles D.
560d993b-bbc9-4548-9990-272ed18a011d
Sado, Daniel M.
d2762586-ebb0-4e7e-8763-5413e45ea0ad
Petley, Graham W.
4f2da40b-3c7b-4adc-b75c-e24e62bb1cf0
Clewlow, Frank
94c8568b-d5ea-4446-a712-4fa1560895c2
Deakin, Charles D.
560d993b-bbc9-4548-9990-272ed18a011d
Sado, Daniel M.
d2762586-ebb0-4e7e-8763-5413e45ea0ad
Petley, Graham W.
4f2da40b-3c7b-4adc-b75c-e24e62bb1cf0
Clewlow, Frank
94c8568b-d5ea-4446-a712-4fa1560895c2

Deakin, Charles D., Sado, Daniel M., Petley, Graham W. and Clewlow, Frank (2004) Differential contribution of skin impedance and thoracic volume to transthoracic impedance during external defibrillation. Resuscitation, 60 (2), 171-174. (doi:10.1016/j.resuscitation.2003.10.001). (PMID:15036735)

Record type: Article

Abstract

Background: Two mechanisms by which firm external paddle force decreases transthoracic impedance (TTI) have been proposed. Decreased impedance at the paddle-skin interface has been assumed to be the primary mechanism, but expulsion of air from the lungs, reducing lung volume is also likely to contribute. The relative contribution of each mechanism is unknown. Methods and results: Thirty five intubated patients undergoing general anaesthesia for cardiac surgery were studied. TTI across external defibrillation paddles was measured as paddle force was increased to 12 kgf. Measurements were performed twice; once allowing the volume of the lungs to change and once with lung volume held at functional residual capacity. TTI with constant lung volume was significantly higher at all paddle forces (P<0.001), confirming that a reduction in lung volume contributes to the decrease in TTI. At an optimal paddle force of 8 kg, the reduction in lung volume contributed to 16.2% of the overall decrease in TTI. Conclusion: The decrease in TTI seen with increasing external paddle force is due primarily to improved electrical contact at the paddle-skin interface, with a decrease in thoracic volume accounting for no more than 16% of the overall decrease at forces used clinically.

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Published date: February 2004
Organisations: Clinical & Experimental Sciences

Identifiers

Local EPrints ID: 383371
URI: https://eprints.soton.ac.uk/id/eprint/383371
ISSN: 0300-9572
PURE UUID: 5acdc8df-6c2d-4285-b185-72eba4735c36
ORCID for Graham W. Petley: ORCID iD orcid.org/0000-0002-3295-0444

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Date deposited: 25 Jan 2016 15:10
Last modified: 06 Jun 2018 13:01

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