Anesthesia and analgesia
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Anesthesia and analgesia · May 2004
The relationship between bispectral index and electroencephalographic parameters during isoflurane anesthesia.
Bispectral index (BIS) integrates various electroencephalographic (EEG) parameters into a single variable. However, the exact algorithm used to synthesize the parameters to BIS values is not known. The relationship between BIS and EEG parameters was evaluated during nitrous oxide/isoflurane anesthesia. Twenty patients scheduled for elective ophthalmic surgery were enrolled in the study. After EEG recording with a BIS monitor (A-1050) was begun, general anesthesia was induced and maintained with 0.5%-2% isoflurane and 66% nitrous oxide. Using software we developed, we continuously recorded BIS, spectral edge frequency 95% (SEF95), and EEG parameters such as relative beta ratio (BetaRatio), relative synchrony of fast and slow wave (SynchFastSlow), and burst suppression ratio. BetaRatio was linearly correlated with BIS (r = 0.90; P < 0.01; n = 253) at BIS more than 60. At a BIS range of 30 to 80, SynchFastSlow (r = 0.60; P < 0.01; n = 3314) and SEF95 (r = 0.75; P < 0.01; n = 3339) were linearly correlated with BIS. The correlation between BIS and SEF95 was significantly better than the correlation between BIS and SynchFastSlow (P < 0.01). At BIS less than 30, the burst suppression ratio was inversely linearly correlated with BIS (r = 0.76; P < 0.01; n = 65). At BIS less than 80, burst-compensated SEF95 was linearly correlated with BIS (r = 0.78; P < 0.01; n = 3404). In the range of BIS from 60 to 100, BIS can be calculated from BetaRatio. At surgical levels of anesthesia, BIS and SynchFastSlow (a parameter derived from bispectral analysis) or burst-compensated SEF95 (derived from power spectral analysis) are well correlated. However, our results show that SynchFastSlow has no advantage over SEF95 in calculation of BIS. ⋯ The relationship between bispectral index (BIS) and electroencephalographic parameters was evaluated during nitrous oxide/isoflurane anesthesia. At surgical levels of anesthesia, BIS and the relative synchrony of fast and slow wave (a parameter derived from bispectral analysis) or burst-compensated spectral edge frequency 95% (a parameter derived from power spectral analysis) are well correlated.
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Anesthesia and analgesia · May 2004
The effect of repeated isoflurane anesthesia on spatial and psychomotor performance in young and aged mice.
Exposure to general anesthesia may contribute to postoperative cognitive impairment in elderly patients, but the relationship remains poorly understood. We investigated whether aged mice, 18-19 mo, are more susceptible to postanesthetic cognitive impairment than young mice, 3-4 mo, using spatial memory (Barnes maze) and psychomotor (rotarod) tasks. Initially we studied the effect of a single anesthetic episode on asymptotic maze performance. We then tested whether repeated anesthesia would impair spatial memory and psychomotor performance to a greater extent in aged mice. Mice were anesthetized with isoflurane (1.4% atm) for 30 min; controls received 90% oxygen. Anesthesia, administered during the asymptotic period of maze learning, did not impair performance tested the following day (P > 0.05). Repeated anesthesia, 2-3 h after each session, did not impair overall maze or rotarod performance in young or aged mice (P > 0.05). Spatial learning appeared to be facilitated by anesthesia, F(1,204) = 7.97, P < 0.01 for pooled results. Asymptotic performance-when learning had stabilized-remained unimpaired in both the maze and rotarod tasks. These results suggest that an age-related risk of anesthetic-induced impairment appears to be limited to acquisition of a novel motor skill and that anesthesia alone does not lead to prolonged cognitive impairments in aged mice. ⋯ This study demonstrates that repeated isoflurane general anesthesia impaired psychomotor performance in aged mice during the initial learning period; however, spatial learning improved and, overall, spatial memory and psychomotor performance were unimpaired. Thus, general anesthesia alone does not appear to result in prolonged cognitive deficits in aged mice.
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Anesthesia and analgesia · May 2004
Intraarterial pulmonary pentoxifylline improves cardiac performance and oxygen utilization after hemorrhagic shock: a novel resuscitation strategy.
The role of pentoxifylline (PTX) as a resuscitation adjunct in hemorrhagic shock is unclear. PTX infusion into the pulmonary artery and its effects on cardiac performance and oxygen utilization have not been defined. We hypothesized that pulmonary PTX is superior to systemic PTX or lactated Ringer's (LR) solution alone. The effects of LR solution, systemic PTX, and pulmonary PTX on cardiac performance and oxygen utilization in a hemorrhagic shock model in dogs were compared. Animals were bled to a mean arterial blood pressure (MAP) of 40 mm Hg maintained for 30 min and randomized into 3 resuscitation groups: LR solution (2x shed blood), systemic PTX (10 mg/kg bolus i.v.) in addition to LR solution (2x shed blood) + PTX (5 mg/kg for 45 min i.v.), and pulmonary PTX (10 mg/kg bolus + 5 mg/kg for 45 min via a pulmonary artery catheter) plus LR solution (2x shed blood, i.v.). Arterial blood gases, hemoglobin levels, MAP, cardiac index, systemic vascular resistance index, pulmonary vascular resistance index, oxygen delivery, oxygen consumption, and oxygen extraction ratio (O(2)ER) were measured serially. No differences in blood loss, hemoglobin, and MAP were observed. Pulmonary PTX increased cardiac index to levels more than baseline (P = 0.012) and decreased systemic vascular resistance index and pulmonary vascular resistance index to levels less than baseline (P < 0.0001). Pulmonary PTX increased oxygen delivery and oxygen consumption to baseline levels. Postresuscitation O(2)ER levels in LR-treated animals remained more than baseline (P < 0.0001). Systemic and pulmonary PTX significantly decreased O(2)ER compared with shock levels. PTX resuscitation is superior compared with LR solution alone. Intraarterial pulmonary PTX administration is safe, and improves cardiac performance as well as O(2) utilization. ⋯ This study shows that a novel route (via the pulmonary circulation) used to administer pentoxifylline after hemorrhagic shock leads to superior cardiac performance in comparison with administration via lactated Ringer's solution or i.v. systemic pentoxifylline.
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Anesthesia and analgesia · May 2004
The monoamine reuptake inhibitor milnacipran does not affect nociception to acute visceral distension in rats.
The role of antidepressants in the treatment of visceral pain has not been extensively examined. Milnacipran, an antidepressant that inhibits monoamine reuptake, is widely used in the treatment of depression and fibromyalgia. In this study, we sought to determine the activity of milnacipran against acute visceral nociception. Female virgin rats were studied 7 days after bilateral ovariectomy. For uterine cervical distension (UCD), two metal rods were inserted into the cervical osses under general anesthesia for manual distension. Colorectal distension (CRD) was performed by insertion of a balloon catheter into the descending colon and rectum, followed by manual inflation. Two electrodes were inserted into the rectus abdominus muscle for recording UCD- or CRD-induced reflex contraction, which was quantified by electromyography (EMG). A dose response for milnacipran, administered intrathecally or i.v., was obtained for UCD and CRD stimulation. Milnacipran failed to inhibit the UCD-induced EMG response, whether administered i.v. or intrathecally. Similarly, i.v. milnacipran, administered either acutely or chronically, failed to inhibit the CRD-induced EMG response. CRD and UCD are well established animal models for the study of acute visceral pain. Milnacipran, although it provides some unique advantages compared with other antidepressants, is unlikely to produce analgesia after acute administration in the setting of acute visceral pain. ⋯ Neither intrathecal nor i.v. milnacipran, a monoamine reuptake inhibitor, inhibits an acute visceral pain response induced by colorectal or uterine cervical distension.