The Relationship of Postoperative Pain and Opioid Consumption to Postoperative Delirium After Spine Surgery.

Purpose: To examine the relationship between postoperative pain and opioid use and the development of postoperative delirium (POD), with attention to the preoperative opioid use status of patients. Methods: This was a secondary analysis of data from a prospective observational study of patients (N = 219; ≥70 years old) scheduled to undergo elective spine surgery. Maximal daily pain scores (0-10) and postoperative morphine milligram equivalents per hour (MME/hr) were determined for postoperative days 1-3 (D1-3). POD was assessed by daily in-person interviews using the Confusion Assessment Method and chart review. Results: Patients who reported regular preoperative opioid use (n = 58, 27%) reported significantly greater maximal daily pain scores, despite also requiring greater daily opioids (MME/hr) in the first 3 days after surgery. These patients were also more likely to develop POD. Interestingly, while postoperative pain scores were significantly higher in patients who developed POD, postoperative opioid consumption was not significantly higher in this group. Conclusion: POD was associated with greater postoperative pain, but not with postoperative opioid consumption. While postoperative opioid consumption is often blamed for delirium, these findings suggest that uncontrolled pain may actually be a more important factor, particularly among patients who are opioid tolerant. These findings underscore the importance of employing multimodal perioperative analgesic management, especially among older patients who have a predilection to developing POD and baseline tolerance to opioids.

Neonatal anesthesia impairs synapsin 1 and synaptotagmin 1, two key regulators of synaptic vesicle docking and fusion.

Early exposure to anesthetics may interfere with synaptic development and lead to cognitive deficits. We previously demonstrated a decrease in vesicles docked at and within 100 nm from the presynaptic membrane in hippocampal nerve terminals of neonatal rats after anesthesia. Hence, we designed this study to assess the effects of neonatal anesthesia on synapsin 1 (Syn1) and synaptotagmin 1 (Syt1), two key regulators of vesicle docking and fusion. To test the link between changes in Syn1 and Syt1 and behavioral deficits observed after neonatal anesthesia, we also assessed retention memory and fear conditioning in adolescent rats after neonatal anesthesia. Pups received a combination of clinical anesthetics, then Syn1 and Syt1 mRNA and protein expression were determined at the peak (postnatal day 8, P8), part-way through (P12) and end of synaptogenesis (P24) in the CA1-subiculum by qPCR and western blotting. Anesthesia decreased Syn1 and Syt1 mRNA expression at P8 (P<0.01 and <0.001) and P12 (P=0.001 and 0.017), but not P24 (P=0.538 and 0.671), and impaired Syn1, p-Syn1, and Syt1 protein levels at P8 (P=0.038, 0.041, and 0.004, respectively), P12 (P<0.001, P=0.001, and P<0.0001), and P24 (P=0.025, 0.031, and 0.001). Anesthetic-challenged rats displayed deficient long-term retention memory (P=0.019) and hippocampus-dependent fear conditioning (P<0.001). These results suggest that anesthetics alter Syn1 and Syt1 during synapse assembly and maturation, raising the possibility that anesthetic interference with Syn1 and Syt1 could initiate changes in synaptic function that contribute to the cognitive deficits observed after neonatal anesthesia.

Disruption of Rapid Eye Movement Sleep Homeostasis in Adolescent Rats after Neonatal Anesthesia.

BACKGROUND: Previous studies suggest that rapid eye movement sleep rebound and disruption of rapid eye movement sleep architecture occur during the first 24 h after general anesthesia with volatile anesthetics in adult rats. However, it is unknown whether rapid eye movement sleep alterations persist beyond the anesthetic recovery phase in neonatal rats. This study tested the hypothesis that rapid eye movement sleep disturbances would be present in adolescent rats treated with anesthesia on postnatal day 7. METHODS: Forty-four neonatal rats were randomly allocated to treatment with anesthesia consisting of midazolam, nitrous oxide, and isoflurane or control conditions for 2 h or 6 h. Electroencephalographic and electromyographic electrodes were implanted and recordings obtained between postnatal days 26 and 34. The primary outcome was time spent in rapid eye movement sleep. Data were analyzed using two-tailed unpaired t tests and two-way repeated measures analysis of variance. RESULTS: Rats treated with midazolam, nitrous oxide, and isoflurane exhibited a significant increase in rapid eye movement sleep three weeks later when compared with control rats, regardless of whether they were treated for 2 h (174.0 ± 7.2 min in anesthetized, 108.6 ± 5.3 in controls, P < 0.0001) or 6 h (151.6 ± 9.9 min in anesthetized, 108.8 ± 7.1 in controls, P = 0.002). CONCLUSIONS: Treatment with midazolam, nitrous oxide, and isoflurane on postnatal day 7 increases rapid eye movement sleep three weeks later in rats.