Chronobiology international
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Pain exhibits temporal variations in intensity due to multiple factors, including endogenous neuroendocrine and various external influences that vary over the 24 h. Also, medications can vary in potency and/or toxicity according to the time when they are administered. However, there is no consensus among studies regarding the 24-h pattern of analgesia during labor. ⋯ However, the duration of intrathecal analgesia showed two peaks, i.e., at approximately 00:00 and approximately 12:00 h. These results demonstrate that labor analgesia achieved by fentanyl combined with bupivacaine shows a diurnal pattern in pain relief and duration of spinal analgesia. However, part of these temporal patterns was explained by the association with duration of labor.