Anesthesia and analgesia
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Anesthesia and analgesia · Dec 2003
ReviewNew light on intravascular volume replacement regimens: what did we learn from the past three years?
Definition of the "ideal" intravascular fluid volume replacement strategy still remains a critical problem. This article analyzes studies on volume replacement by using a MEDLINE search of the past 3 years (from January 1, 2000, to December 12, 2002). Forty original studies in humans with a total of 2454 subjects were identified. Five studies were performed in volunteers (n = 113); the other 35 studies (n = 2341) were performed in a variety of patients (e.g., cardiac surgery, trauma patients, children, and intensive care unit patients). The influence of different volume replacement regimens on coagulation was one of the major topics of interest (16 studies with 1183 subjects), and other studies focused on metabolic state, alterations in macro- and microcirculation, volume distribution, and organ function (e.g., kidney function and splanchnic perfusion). Among all synthetic colloids, hydroxyethyl starch (HES) was the solution most often studied. Two new HES preparations have been approved (Hextend), a balanced hetastarch solution, and a new third-generation HES [130/0.4]). Only two studies used albumin, and no superiority of albumin was found over less expensive synthetic colloids. In almost all studies, the outcome either was no end-point or was not reported. Volume replacement has often been hitherto based on dogma and personal beliefs. Future well performed studies in this area will hopefully help to shed new light on the ideal volume replacement strategy. ⋯ By using a MEDLINE search covering the last 3 yr, the present knowledge on volume replacement regimens was analyzed. Forty studies in humans were identified. New hydroxyethyl starch preparations have shed light on this topic, whereas no additional data supporting the use of albumin have been presented.
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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
Validation of an original mathematical model of CO(2) elimination and dead space ventilation.
We present an original, mathematical model of ventilation and gas-exchange. Our aim was to validate it using data from previous clinical investigations, allowing our use of it in future investigations. The first previous investigation used a low-dead space, double-lumen, tracheal tube (DLT). We matched the model's PaCO(2) and airway pressures (P(AW)) to the patient mean during use of the DLT and a single-lumen tube (SLT). The model's resulting PaCO(2), PECO(2) and P(AW) were compared with the patients' as tidal volume (VT) changed with constant minute volume. The second investigation examined dead space during anesthesia. The model's VT, respiratory rate, CO(2) production, temperature, and alveolar and anatomical dead spaces were matched to each mechanically ventilated subject. Bias and precision in predictions of PaCO(2) and PECO(2) were calculated. The model's bias in prediction of dead space reduction by the DLT was 6.9%. Bias in prediction of P(AW) was 0.1% (peak) and -5.13% (mean), of PaCO(2) was 1.2% (DLT) and 1.5% (SLT) and of PECO(2) was 1.7% (DLT) and 1.3% (SLT). Prediction of PaCO(2) and PECO(2) in the second investigation (as 95% confidence interval of bias): PaCO(2) -2.6% to 0.8% and PECO(2) -4.9% to 1.2%. This validation allows future application of our model in appropriate theoretical investigations. ⋯ We present an original, mathematical model of ventilation and gas exchange. We validate it against previously published clinical data to allow its use in future theoretical investigations where data may be unavailable from patients.
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Anesthesia and analgesia · Dec 2003
Risk factors for acute lung injury after thoracic surgery for lung cancer.
Acute lung injury (ALI) may complicate thoracic surgery and is a major contributor to postoperative mortality. We analyzed risk factors for ALI in a cohort of 879 consecutive patients who underwent pulmonary resections for non-small cell lung carcinoma. Clinical, anesthetic, surgical, radiological, biochemical, and histopathologic data were prospectively collected. The total incidence of ALI was 4.2% (n = 37). In 10 cases, intercurrent complications (bronchopneumonia, n = 5; bronchopulmonary fistula, n = 2; gastric aspiration, n = 2; thromboembolism, n = 1) triggered the onset of ALI 3 to 12 days after surgery, and this was associated with a 60% mortality rate (secondary ALI). In the remaining 27 patients, no clinical adverse event preceded the development of ALI-0 to 3 days after surgery-that was associated with a 26% mortality rate (primary ALI). Four independent risk factors for primary ALI were identified: high intraoperative ventilatory pressure index (odds ratio, 3.5; 95% confidence interval, 1.7-8.4), excessive fluid infusion (odds ratio, 2.9; 95% confidence interval, 1.9-7.4), pneumonectomy (odds ratio, 2.8; 95% confidence interval, 1.4-6.3), and preoperative alcohol abuse (odds ratio, 1.9; 95% confidence interval, 1.1-4.6). In conclusion, we describe two clinical forms of post-thoracotomy ALI: 1). delayed-onset ALI triggered by intercurrent complications and 2). an early form of ALI amenable to risk-reducing strategies, including preoperative alcohol abstinence, lung-protective ventilatory modes, and limited fluid intake. ⋯ In an observational study including all patients undergoing lung surgery, we describe two clinical forms of acute lung injury (ALI): a delayed-onset form triggered by intercurrent complications and an early form associated with preoperative alcohol consumption, pneumonectomy, high intraoperative pressure index, and excessive fluid intake over the first 24 h.