Anesthesia and analgesia
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Anesthesia and analgesia · Dec 2003
Case ReportsPreoperative fentanyl infusion with pharmacokinetic simulation for anesthetic and perioperative management of an opioid-tolerant patient.
For opioid-tolerant patients, conventional patient-controlled analgesia dosing may be ineffective. We present a cardiac surgery patient with a history of significant opioid tolerance and prior episodes of severe postoperative pain. Using the patient's response to a large-dose fentanyl infusion in conjunction with a pharmacokinetic simulation, effective intraoperative and postoperative fentanyl plasma concentrations were achieved. ⋯ A preinduction fentanyl infusion used in conjunction with pharmacokinetic simulation can be a useful tool for assessing individual limits of opioid tolerance, as well as determining an appropriate dose for acute pain management in opioid-tolerant patients.
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Anesthesia and analgesia · Dec 2003
Estimating alveolar dead space from the arterial to end-tidal CO(2) gradient: a modeling analysis.
Using an original, validated, high-fidelity model of pulmonary physiology, we compared the arterial to end-tidal CO(2) gradient divided by the arterial CO(2) tension (Pa-E'CO(2)/PaCO(2)) with alveolar dead space expressed as a fraction of alveolar tidal volume, calculated in the conventional manner using Fowler's technique and the Bohr equation: (VDalv/VTalv)(Bohr-Fowler). We examined the variability of Pa-E'CO(2)/PaCO(2) and of (VDalv/VTalv)(Bohr-Fowler) in the presence of three ventilation-perfusion defects while varying CO(2) production (Vdot;CO(2)), venous admixture, and anatomical dead space fraction (VDanat). Pa-E'CO(2)/PaCO(2) was approximately 59.5% of (VDalv/VTalv)(Bohr-Fowler). During constant alveolar configuration, the factors examined (Vdot;CO(2), pulmonary shunt fraction, and VDanat) each caused variation in (VDalv/VTalv)(Bohr-Fowler) and in Pa-E'CO(2)/PaCO(2). Induced variation was slightly larger for Pa-E'CO(2)/PaCO(2) during changes in VDanat, but was similar during variation of venous admixture and Vdot;CO(2). Pa-E'CO(2)/PaCO(2) may be a useful serial measurement in the critically ill patient because all the necessary data are easily obtained and calculation is significantly simpler than for (VDalv/VTalv)(Bohr-Fowler). ⋯ Using an original, validated, high-fidelity model of pulmonary physiology, we have demonstrated that the arterial to end-tidal carbon dioxide pressure gradient may be used to robustly and accurately quantify alveolar dead space. After clinical validation, its use could replace that of conventionally calculated alveolar dead space fraction, particularly in the critically ill.
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Anesthesia and analgesia · Dec 2003
Randomized Controlled Trial Clinical TrialOptimizing the dose of intrathecal morphine in older patients undergoing hip arthroplasty.
Intrathecal (IT) morphine provides excellent postoperative analgesia but may result in many side effects, including postoperative nausea and vomiting, pruritus, and respiratory depression, particularly at larger doses. Older patients may be at particular risk. The optimal dose of spinal morphine in older patients undergoing hip arthroplasty is not known. We designed this prospective, randomized, controlled, double-blinded study to evaluate the analgesic efficacy and side effect profile of 50-200 microg of IT morphine in older patients undergoing elective hip arthroplasty. Sixty patients older than 65 years undergoing elective hip arthroplasty were enrolled. Patients were randomized to receive spinal anesthesia with 15 mg of bupivacaine and IT morphine in four groups: 1). 0 microg, 2). 50 microg, 3). 100 microg, and 4). 200 microg. IT morphine 100 and 200 microg produced effective pain relief and decreased the postoperative requirement for morphine compared with control. IT morphine 50 microg did not provide effective pain relief. Both 100 and 200 microg of IT morphine provided comparable levels of postoperative analgesia. There were no between-group differences in postoperative nausea and vomiting, sedation, respiratory depression, or urinary retention. Pruritus was significantly more frequent with 200 microg of IT morphine. In conclusion, 100 microg of IT morphine provided the best balance between analgesic efficacy and side effect profile in older patients undergoing hip arthroplasty. ⋯ The dosage of intrathecal morphine that provides the best balance between analgesic efficacy and side effect profile in the older patient undergoing hip arthroplasty is not known. This prospective, randomized, controlled, double-blinded clinical trial demonstrates that a dose of 100 microg of intrathecal morphine provides the best balance between efficacy and side effects, compared with doses of 0, 50, and 200 microg of morphine, in this patient population.
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Anesthesia and analgesia · Dec 2003
ReviewKetamine in chronic pain management: an evidence-based review.
Ketamine has diverse effects that may be of relevance to chronic pain including: N-methyl-D-aspartic acid, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, kainate, gamma-aminobutyric acid(A) receptors; inhibition of voltage gated Na(+) and K(+) channels and serotonin, dopamine re-uptake. Ketamine has been in clinical practice for over 30 yr; however, there has been little formal research on the effectiveness of ketamine for chronic pain management. In this review we evaluate the available clinical data as a basis for defining the potential use of ketamine for chronic pain. ⋯ In conclusion, the evidence for efficacy of ketamine for treatment of chronic pain is moderate to weak. However, in situations where standard analgesic options have failed ketamine is a reasonable "third line" option. Further controlled studies are needed.
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Anesthesia and analgesia · Dec 2003
Randomized Controlled Trial Clinical TrialRopivacaine and fentanyl concentrations in patient-controlled epidural analgesia during labor: a volume-range study.
We enrolled nulliparous women in induced labor in a randomized study to determine whether increasing the concentration of the solution used in a patient-controlled epidural analgesia (PCEA) device was required as labor progressed. Patients were assigned to 6 groups (n = 25 in each group), receiving ropivacaine/fentanyl in concentrations of either 0.1%/0.5 microg/mL or 0.2%/1 microg/mL via a PCEA pump. Three groups received boluses of 12, 16, or 20 mL dilute solution in early labor (uterine contractions every 3 min and 4-cm cervical dilation) then 6, 8, and 10 mL concentrated solution in late labor. Three other groups received boluses of 12, 16, or 20 mL dilute solution during both periods. The lockout interval was 25 min. The primary outcome was time until the first request for staff-administered analgesia supplement. Hourly assessments included pain scores on a visual analog scale (VAS) graded from 0 to 10, satisfaction scores, arterial blood pressure, motor block intensity, and the upper sensory level of epidural anesthesia. Patients, midwives, and the observer were unaware of study solutions and PCEA settings. The maximum pain score was defined as the highest score experienced by each patient during each period. Duration of analgesia was defined as the time from the start of each period to the first injection of rescue analgesia and was compared using a survival analysis. There were no differences among the groups with regard to demographic and obstetric variables, arterial blood pressure, motor block intensity, upper sensory level, or satisfaction scores. At least 75% of the women rated their satisfaction as either good or excellent during each period. During late labor, the maximum pain score was lower in the group receiving 20 mL dilute solution compared with the group receiving 6 mL concentrated solution. Maximum pain score was not significantly different between 20 mL dilute solution and 10 mL concentrated solution (difference between VAS values = -0.4; 95% confidence limits, -1.599 and 0.799; P = 0.5055). During late labor, the duration of analgesia was longer in groups receiving 20 mL dilute solution (99 +/- 4 min) (mean +/- SD) than in those receiving 12 mL (77 +/- 30 min) and 16 mL (80 +/- 23 min). Duration of analgesia did not differ between groups receiving 20 mL and 10 mL (92 +/- 23 min) or between groups receiving 12 mL and 6 mL (78 +/- 30 min) of each respective solution. Duration of analgesia was longer in the groups receiving 8 mL concentrated solution (94 +/- 16 min) than in those receiving 16 mL dilute solution. We concluded that 0.1%/0.5 microg/mL ropivacaine/fentanyl was effective throughout labor when 20 mL was injected with each PCEA demand. With 16 mg ropivacaine and 8 microg fentanyl, the duration of analgesia was prolonged by doubling the concentration when labor became active. When 12 mg ropivacaine and 6 microg fentanyl were injected at each demand, analgesia was less satisfactory and doubling the concentration was not clinically effective. These results suggest that the effectiveness of PCEA is dependent on drug mass rather than the volume or concentration administered with each successful pump demand. ⋯ There is no clinical reason for increasing the concentration of the patient-controlled epidural analgesia (PCEA) solution when labor becomes active provided that an effective dose is already being administered with each demand. The quality of PCEA depends on the drug mass given with each demand rather than the concentration of the pump solution.