Abstract
Purpose
To examine the effects of temperature on auditory brainstem responses (ABRs) in infants during hypothermic cardiopulmonary bypass for total circulatory arrest (TCA). The relationship between ABRs (as a surrogate measure of corebrain temperature) and body temperature as measured at several temperature monitoring sites was determined.
Methods
In a prospective, observational study, ABRs were recorded non-invasively at normothermia and at every 1 or 2°C change in ear-canal temperature during cooling and rewarming in 15 infants (ages: 2 days to 14 months) that required TCA. The ABR latencies and amplitudes and the lowest temperatures at which an ABR was identified (the threshold) were measured during both cooling and rewarming. Temperatures from four standard temperature monitoring sites were, simultaneously recorded.
Results
The latencies of ABRs increased and amplitudes decreased with cooling (P < 0.01), but rewarming reversed these effects. The ABR threshold temperature as related to each monitoring site (ear-canal, nasopharynx, esophagus and bladder) was respectively determined as 23 ± 2.2°C, 20.8 ± 1.7°C, 14.6 ± 3.4°C, and 21.5 ± 3.8°C during cooling and 21.8 ± 1.6°C, 22.4 ± 2.0°C, 27.6 ± 3.6°C, and 23.0 ± 2.4°C during rewarming. The rewarming latencies were shorter and Q10 latencies smaller than the corresponding cooling values (P < 0.01). Esophageal and bladder sites were more susceptible to temperature variations as compared with the ear-canal and nasopharynx.
Conclusion
No temperature site reliably predicted an electrophysiological threshold. A faster latency recovery during rewarming suggests that body temperature monitoring underestimates the effects of rewarming in the core-brain. ABRs may be helpful to monitor the effects of cooling and rewarming on the core-brain during pediatric cardiopulmonary bypass.
Résumé
Objectif
Examiner les effets de la température sur les réponses du tronc cérébral à des stimuli auditifs chez des enfants pendant la circulation extracorporelle hypothermique dans le cas d’un arrêt circulatoire total (ACT). La relation entre les réponses du tronc cérébral (en tant que mesure substitutive de la température cérébrale centrale) et la température du corps (mesurée à différents points d’enregistrement) a été déterminée.
Méthode
Lors d’une étude prospective d’observation, on a enregistré les réponses du tronc cérébral à des stimuli auditifs, de manière non effractive, à la température normale et à chaque changement de température de 1 ou 2 °C du canal auditif pendant le refroidissement et le réchauffement de 15 enfants (âgés de 2 jours à 14 mois) qui ont eu besoin d’ACT Les temps de latence et les amplitudes des réponses aux températures les plus basses auxquelles une réponse a été perçue (le seuil) ont été mesurés pendant le refroidissement et le réchauffement. Les températures de quatre points d’enregistrement standards ont été notées simultanément.
Résultats
Les temps de latence des réponses ont augmenté et les amplitudes ont diminué pendant le refroidissement (P < 0,01), mais le réchauffement a renversé ces effets. La température du seuil de réponse au canal auditif, au nasopharynx, à l’oesophage et à la vessie a été respectivement déterminée: 23 ± 2,2 °C, 20,8 ± 1,7 °C, 14,6 ± 3,4 °C, et 21,5 ± 3,8 °C pendant le refroidissement et 21,8 ± 1,6 °C, 22,4 ± 2,0 °C, 27,6 ± 3,6 °C, et 23,0 ± 2,4 °C pendant le réchauffement. Les temps de latence du réchauffement ont été plus courts et les temps de latence de Q10 plus faibles que les valeurs correspondantes du refroidissement (P < 0,01). L’oesophage et la vessie sont des points plus susceptibles aux changements de température en comparaison avec le canal auditif et la nasopharynx.
Conclusion
En aucun point d’enregistrement de la température on n’a pu prédire fidèlement un seuil électrophysiologique. Une récupération plus rapide du temps de latence pendant le réchauffement laisse croire que l’enregistrement de la température corporelle sous-évalue les effets du réchauffement central du cerveau. Les réponses du tronc cérébral aux stimuli auditifs peuvent servir à enregistrer les effets du refroidissement et du réchauffement central du cerveau pendant la circulation extracorporelle chez des enfants.
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RAR was a Cadwell Laboratories Clinical Fellow and partially supported by the Alliant Community Trust. Monitors and accesories were provided by Cadwell Laboratories (USA)
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Rodriguez, R.A., Edmonds, H.L., Auden, S.M. et al. Auditory brainstem evoked responses and temperature monitoring during pediatric cardiopulmonary bypass. Can J Anesth 46, 832–839 (1999). https://doi.org/10.1007/BF03012971
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DOI: https://doi.org/10.1007/BF03012971