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Influence of closed head injury on isoflurane MAC in the rat
Y Shapira1, B Gurevich, A A Artru
1Division of Anesthesiology, Soroka Medical Center, Ben-Gurion University of the Negev, Beer-Sheva Israel.
Abstract:
We designed the present study to determine whether the minimum alveolar concentration (MAC) for isoflurane is decreased after closed head trauma (CHT) in rats and, if so, whether the decrease of MAC is related to the severity of neurological impairment following CHT. Isoflurane MAC was determined in 36 Sprague-Dawley rats. Then, at time = 0 h, animals were grouped. Group 1 (n = 8) received no CHT, group 2 (n = 14) received moderate CHT, and group 3 (n = 14) received severe CHT. Neurological severity score (NSS, 0 = no deficit and 25 = maximal impairment) and MAC were determined at 1, 4, 24, and 48 h. In groups 1 and 2, isoflurane MAC at 1, 2, 24, and 48 h (1.0-1.1 +/- 0.8-1.2%, median +/- range) was not significantly different from baseline (1.0-1.1 +/- 1.0-1.1%). In group 3, isoflurane MAC at 1, 2, 24, and 48 h (0.4 +/- 0.2-0.5%) was decreased as compared to baseline (1.1 +/- 1.0-1.1%). In group 2, NSS at 1 h was 18 +/- 11-21 and improved by 48 h to 9 +/- 4-15. In group 3, NSS at 1 h was 24 +/- 22-25 and was not significantly different from NSS at 48 h (24 +/- 24-25). Thus, moderate CHT does not significantly alter isoflurane MAC, whereas severe CHT equivalent to a Glasgow Coma Scale score of 3 to 6 significantly decreases isoflurane MAC.
Insights
Severe closed head trauma (CHT) in rats significantly reduces the minimum alveolar concentration (MAC) of isoflurane, indicating altered anesthetic requirements. Moderate CHT did not significantly affect isoflurane MAC, suggesting a dose-dependent relationship with injury severity.
Area of Science:
- Anesthesiology
- Neuroscience
- Trauma Research
Background:
- Anesthetic requirements can be influenced by central nervous system insults.
- The impact of closed head trauma (CHT) on the minimum alveolar concentration (MAC) of isoflurane requires further investigation.
Purpose of the Study:
- To determine if CHT decreases isoflurane MAC in rats.
- To investigate the relationship between the severity of neurological impairment and the change in isoflurane MAC following CHT.
Main Methods:
- 36 Sprague-Dawley rats were subjected to no CHT, moderate CHT, or severe CHT.
- Isoflurane MAC and Neurological Severity Score (NSS) were measured at baseline and at 1, 4, 24, and 48 hours post-trauma.
Main Results:
- Severe CHT significantly decreased isoflurane MAC compared to baseline.
- Moderate CHT did not significantly alter isoflurane MAC.
- Neurological impairment in severe CHT was profound and persistent, correlating with decreased MAC.
Conclusions:
- Severe CHT, equivalent to a Glasgow Coma Scale score of 3-6, significantly reduces isoflurane MAC.
- Moderate CHT does not significantly alter isoflurane MAC, suggesting severity-dependent effects on anesthetic requirements.