Determination of plasma concentrations of propofol associated with 50% reduction in postoperative nausea.

BACKGROUND: Subhypnotic doses of propofol possess direct antiemetic properties. The authors sought to determine the plasma concentration of propofol needed to effectively manage postoperative nausea and vomiting. METHODS: Patients aged 18-70 yr who were classified as American Society of Anesthesiologists physical status 1 or 2 and had surgery during general anesthesia were approached for the study. Only patients who had nausea (verbal rating score > 5 on a 0- to 10-point scale), retching, or vomiting in the postanesthetic care unit participated. Propofol was administered to these patients to achieve target plasma concentrations of 100, 200, 400, and 800 ng/ml using a computer-assisted continuous infusion device. Target concentrations were increased every 15 min until patients described at least a 50% reduction in symptoms on the verbal rating score. An arterial blood sample was obtained at each step. The measured plasma propofol concentrations were used to analyze data. Blood pressure, heart and respiratory rates, arterial blood saturation, sedation score, and overall satisfaction with treatment were recorded. RESULTS: Of the 89 patients who consented to the study, 15 patients met entry criteria and were enrolled. Five of these patients also had retching or vomiting when they entered the study. Fourteen patients responded successfully to treatment. One patient did not achieve the required response at plasma concentrations of 830 ng/ml. Hence the success rate for the treatment of postoperative nausea and vomiting was 93%. Among patients who responded, the median plasma concentration associated with an antiemetic response was 343 ng/ml. There was no difference in sedation scores from baseline and no episodes of desaturation. Hemodynamic parameters were stable during the study. CONCLUSIONS: Propofol is generally efficacious in treating postoperative nausea and vomiting at plasma concentrations that do not produce increased sedation. Simulations indicate that to achieve antiemetic plasma propofol concentrations of 343 ng/ml, a bolus dose of 10 mg followed by an infusion of approximately 10 microg x kg(-1) x min(-1) are necessary.

epsilon-Aminocaproic acid plasma levels during cardiopulmonary bypass.

epsilon-Aminocaproic acid (EACA) concentrations achieved during cardiopulmonary bypass (CPB) have not been previously reported. It is unknown whether plasma concentrations reported to inhibit fibrinolysis in vitro (130 microg/mL) are achieved or whether differences in these levels relate to variability in postoperative bleeding. EACA (total intraoperative dose 270 mg/kg) was administered to 27 patients undergoing cardiac reoperation. The plasma EACA concentration was measured by using high-pressure liquid chromatography: 1) 30 min after initiation of drug administration (baseline); 2) 30 min (CPB + 30) after initiation of CPB; 3) 90 min after initiation of CPB. (CPB + 90); and 4) at cardiopulmonary bypass termination (end CPB). Plasma EACA concentrations (microg/mL, min - max, mean +/- SD) were 276-998, 593 +/- 154 at baseline; 147-527, 302 +/- 95 at CPB + 30; 112-500, 314 +/- 100 at CPB + 90; and 84-537, 317 +/- 100 at end CPB. Twenty-four-hour postoperative thoracic drainage and allogeneic red blood cell transfusions were not associated with plasma levels at any time. Although plasma EACA concentrations greater than 130 microg/mL were consistently achieved, we observed a marked variability (more than sixfold) in plasma concentrations and bleeding outcomes despite the use of a weight-based dosing regimen. This variability in drug levels appears to have little relevance to bleeding outcomes, possibly since mean plasma levels exceeded 130 microg/mL during CPB, and nearly all patients (26 of 27) achieved that target level.

Airway hyperreactivity produced by short-term exposure to hyperoxia in neonatal guinea pigs.

Airway hyperreactivity is recognized as one of the long-term sequelae of bronchopulmonary dysplasia (BPD). Due to the improved care and prognosis of very low-birth weight infants, the incidence of BPD is increasing. There are data that suggest the increased survival of premature infants may be associated with the observed increased incidence of childhood asthma. The hyperoxia received as part of the treatment of respiratory distress syndrome is believed to be partly if not completely responsible for BPD. To gain insight into the potential role that hyperoxia might play in producing airway hyperreactivity, 4-day-old guinea pig pups were exposed to 70% oxygen or air for 96 h, and airway responsiveness to acetylcholine (ACh) was assessed both 2 and 9 days after the completion of the hyperoxia exposures. Unlike ozone, the mechanism for the persistently increased airway reactivity is not related either to the inhibition of neuronal acetylcholinesterase or inhibition of the neuronal M2 muscarinic receptor. A difference in antioxidant protection did not account for the increased response of the neonatal guinea pigs compared with hyperoxia-exposed rat pups. These data support the usefulness of the neonatal guinea pig as a model to study the mechanism responsible for hyperoxia-induced airway hyperreactivity.

Oxygen toxicity to the developing lung of the mouse: role of reactive oxygen species.

Since the description of bronchopulmonary dysplasia (BPD) in premature infants, the supplemental oxygen administered has been suspect in the etiology of BPD. This has prompted studies on the effect of hyperoxia on lung growth in neonatal animals. So far, these have not led to a treatment which either prevents or mitigates BPD. Another approach to investigate the effect of hyperoxia on the immature lung is to use lung explants from 12-d gestation mouse fetuses. Exposing explants to different concentrations of oxygen for 48 h, we found that exposures to oxygen both below (10%) and above (35% or greater) normoxia adversely affected branching morphogenesis and growth. The effect was irreversible at exposures of 50% oxygen and greater. To determine the role of reactive oxygen species (ROS) in the effect of hyperoxia, antioxidants and inhibitors of ROS formation were added to the incubating explants, and their influence on reducing the adverse effect of 50% oxygen was assessed. The combination of CuZn superoxide dismutase (SOD) and catalase, manganese SOD, manganese-3-tetrakis(1-methyl-4-pyridyl)porphorin, a low molecular weight SOD mimetic, and to a lesser extent, deferoximine, an antioxidant and inhibitor of hydroxyl radical formation, were successful in reducing the effect of 50% oxygen on morphogenesis. Not successful were N-nitro-L-arginine methyl ester (an inhibitor of nitric oxide synthase); allopurinol (an inhibitor of xanthine oxidase); N-acetylcysteine and ebselen (a glutathione peroxidase mimetic); Trolox (a synthetic tocopherol); catalase, and CuZnSOD used alone. These results provide evidence that superoxide anion and possibly hydroxyl radical are the ROS most likely responsible for the growth effects of hyperoxia on mouse fetal lung morphogenesis.

Glutathione and glutathione S-transferase in benign and malignant prostate cell lines and prostate tissues.

Metastatic prostate adenocarcinoma is unresponsive to alkylator chemotherapy with virtually no prolonged remissions. Glutathione (GSH) and glutathione S-transferase (GST) have been reported to play a role in tumor resistance to alkylator therapy; however, there are no baseline studies that have investigated and compared GSH and GST in human prostate cell lines and tissues. Thus, we determined the GSH content and GST activity in benign prostate, in primary and metastatic prostate adenocarcinoma tissues, in immortal adenocarcinoma cell lines, and in primary cell cultures derived from both benign prostate and primary prostatic carcinoma tissue. The GSH content was higher in the immortal cell lines than in the fresh tissues and primary cultures. Conversely, the GST activity was significantly higher in the tissues and primary cultures than in the cell lines. The GSH content and GST activity of the primary cultured prostatic cells were similar to those of the prostate tissues. The differences between the immortal prostate cancer cell lines and prostate tissue are of sufficient magnitude to suggest that in vitro results with cell lines may not extrapolate to prostate cancer in vivo. The GSH content and GST activity in a prostate specific antigen-secreting human prostate tumor xenograft, LuCaP23, maintained in nude mice were similar to those of human prostate tissue and primary cultures. Both the xenograft and primary cultures from patients with prostate cancer may be more appropriate models than established cell lines for investigating techniques to increase the effectiveness of alkylators in prostate cancer.

An age-related difference in hyperoxia lethality: role of lung antioxidant defense mechanisms.

The role of animal age in the lethal response to > 98% oxygen has been extensively studied, with the observation that neonatal rats were resistant while mature animals were sensitive. Antioxidant enzymes increased during the oxygen exposure in neonatal but not in mature rats, suggesting they were important in the age-related toxicity difference. Because no studies had compared the response of mature and old rats to hyperoxia, we exposed Fischer 344 rats, aged 2 and 27 mo, to > 98% oxygen. Unexpectedly, the old rats lived significantly longer than young, 114 and 65 h, respectively. No histopathological differences were found to explain the results. Of the antioxidants, only glutathione peroxidase (GPx) activity was higher in the lungs of nonexposed old rats. Superoxide dismutase (SOD) was higher in the young, results opposite those expected if SOD was important in the lethality difference. No antioxidant induction occurred in the old oxygen-exposed rats. These results suggest that although there may be a role for GPx, mechanisms in addition to antioxidant protection and inflammation are likely responsible for the age-related difference in hyperoxia lethality.

Modulation of human colonic T84 cell secretion by hydrogen peroxide.

Hydrogen peroxide (H2O2) is a reactive oxygen species that can be produced in the digestive tract by inflammatory cells or during reperfusion following ischemia. To evaluate a possible direct effect of H2O2 on epithelial secretory cells, well-differentiated colonic T84 cells were grown to confluence on permeable membranes and studied in Ussing chambers. In this model, where the measured short-circuit current (Isc) reflects electrogenic secretion, we observed that H2O2 stimulated a concentration-dependent and transient secretory response: 5.5 mM H2O2 produced a peak Isc of 12.4 microA/cm2 after 4 min, 2.2 mM H2O2 a peak Isc of 7.9 microA/cm2 after 4 min, and 1.1 mM H2O2 a peak Isc of 5.5 microA/cm2 after 16 min (N = 5). When 97 experiments using 5.5 mM H2O2 were reviewed, the mean peak Isc response was 8.9 +/- 0.5 microA/cm2. A similar secretory response was elicited whether H2O2 was added to the serosal, to the mucosal, or simultaneously to both sides of the T84 cell monolayer. This secretory response reflected transcellular chloride secretion because it was inhibited by the depletion of chloride in the medium and by the suppression of the Na+,K+,2Cl- co-transporter activity necessary for the chloride gradient driving chloride secretion. When T84 cell monolayer resistance was studied, 5.5 mM H2O2 produced a transient decrease in resistance, reflecting transcellular chloride secretion, and a gradual decline in resistance (75% of the initial value after 55 min). The secretory response to H2O2 was increased 2-fold in T84 cells maximally stimulated with 10 nM vasoactive intestinal peptide (VIP), a neuropeptide which acts via cAMP, demonstrating synergism between the two agents. In contrast, the secretory responses produced by H2O2 and carbachol, which acts through the Ca2+ pathway, were additive. A late inhibitory effect of H2O2 was also observed: in cells previously treated with 5.5 mM H2O2, the subsequent secretory responses to either VIP or carbachol were partially inhibited. These secretory effects were specific for the oxidant properties of H2O2 because they were inhibited by 450 U/mL catalase and by 5 mM dithiothreitol, but were unaffected by 50 microM deferoxamine B or Fe3+. H2O2 may be a potential modulator of intestinal or colonic secretion in certain pathologic conditions such as inflammation or ischemia-reperfusion.

Adenine nucleotides of ischemic intestine do not reflect injury.

Warm ischemia of the intestine is a medical emergency which results from mesenteric vascular occlusion. In addition, intestinal transplantation techniques will also inevitably result in intestinal ischemia. The recovery of organ function following ischemia depends on the extent of irreversible damage produced by the ischemia and the extent of reflow upon reperfusion. In some organs energy homeostasis has been found to correlate with organ recovery and graft survival following ischemia-reperfusion. Investigating the usefulness of the determination of adenine and pyridine nucleotides as indicators of the extent of ischemic injury in intestinal segments, we found that after an initial 40% decrease in ATP following 30 min of ischemia there was no further decrease despite increasing the ischemia period to 120 min. Similarly, the decrease in NAD+ and NADP which occurred after 30 min of ischemia did not decrease further after 60, 90, or 120 min of ischemia. Xanthine was the only biochemical where an increase appeared to correlate with ischemia duration while energy charge was of no value in indicating injury extent. Additionally, after reperfusion there was at best a poor correlation between recovery of ATP content and the duration of ischemia. Microcirculation reflow after reperfusion indicated ischemia time-related endothelial cell injury. Thus, the measurement of high-energy phosphates in intestinal segments is not of value as an indicator of the extent of intestinal ischemic injury.

Citrus flavonoids stimulate secretion by human colonic T84 cells.

Flavonoids, compounds containing a 2-phenylbenzo(gamma)pyrane nucleus, are universally distributed among vascular plants. Even though flavonoids are ingested in a normal diet in average quantities of 1 g daily, their effects on the digestive system have only been recently investigated. This study used an in vitro model of colonic secretion, monolayers of T84 colonic adenocarcinoma cells mounted in Ussing chambers, to demonstrate that 100 mumol/L of either tangeritin or nobiletin, polymethoxylated flavonoids contained in citrus fruits, stimulated sustained electrogenic chloride secretion with a maximal short-circuit current of 3.3 microA/cm2. In contrast, naringin and hesperidin, glycosylated citrus flavonoids, stimulated minimal secretion, suggesting that carbohydrate substitutions inhibited their secretory potential. The secretion stimulated by tangeritin and nobiletin was synergistic with carbachol but not with vasoactive intestinal peptide and was inhibited by barium chloride, bumetanide, H-89, and Cl- depletion. These properties suggest that tangeritin and nobiletin stimulated Cl- secretion via the cAMP pathway; however, these flavonoids did not stimulate cAMP production to the extent seen with vasoactive intestinal peptide. These flavonoids did not autooxidize, suggesting that reactive oxygen species did not mediate this secretion. These observations suggest that dietary citrus flavonoids may modulate colonic secretion, possibly through direct interaction with intracellular secretory pathways.

Hydrogen peroxide production by monoamine oxidase during ischemia-reperfusion in the rat brain.

Monoamine oxidase (MAO) as a source of hydrogen peroxide (H2O2) was evaluated during ischemia-reperfusion in vivo in the rat brain. H2O2 production was assessed with and without inhibition of MAO during and after 15 min of ischemia. Metabolism of H2O2 by catalase during ischemia and reperfusion was measured in forebrain homogenates using aminotriazole (ATZ), an irreversible H2O2-dependent inhibitor of catalase. Catecholamine and glutathione concentrations in forebrain were measured with and without MAO inhibitors. During ischemia, forebrain blood flow was reduced to 8% of baseline and H2O2 production decreased as measured at the microperoxisome. During reperfusion, a rapid increase in H2O2 generation occurred within 5 min as measured by a threefold increase in oxidized glutathione (GSSG). The H2O2-dependent rates of ATZ inactivation of catalase between control and ischemia-reperfusion were similar, indicating that H2O2 was more available to glutathione peroxidase than to catalase in this model. MAO inhibitors eliminated the biochemical indications of increased H2O2 production and increased the catecholamine concentrations. Mortality was 67% at 48 h after ischemia-reperfusion, and there was no improvement in survival after inhibition of MAO. We conclude that MAO is an important source of H2O2 generation early in brain reperfusion, but inhibition of the enzyme does not improve survival in this model despite ablating H2O2 production.

Biochemical appraisal of models for hepatic ischemia-reperfusion injury.

Since total hepatic ischemia occurs with transplantation, there has been interest in developing a model which could be used to evaluate interventions to mitigate hepatic ischemic injury. The initial model employed global ischemia of the entire liver which necessitated the placement of a portal-femoral shunt (model A). In 1982, a model of hepatic ischemia was proposed in which ischemia was produced only in the left and median lobes which obviated the need for the shunt (model B). Recently, it has been found that with this model, increased flow to the nonischemic right lobe persists after left reperfusion thus effectively "stealing" blood from the reperfusing left lobe. Occlusion (model C) or removal (model D) of the right lobe on reperfusion have been proposed as techniques to reduce the "steal". We found, that after 30 min of ischemia, the ATP recovery for model B was significantly slower than for either model C or D. Similarly, the AMP content of model B lobes was significantly higher after 15 min of reperfusion, while 30 min after reperfusion, the total adenine nucleotide content was significantly lower in model B compared with models C and D. The energy charge returned to normal within 15 min of reperfusion in model C lobes while it was delayed until 60 min of reperfusion for models B and D. This study provides support for the advantages of right lobe occlusion (model C) over model B for acute studies evaluating the effect of interventions on ischemic injury to the liver and of removal (model D) for survival studies.

The evaluation of Escherichia coli as a model for oxidant stress in mammalian hepatocytes: role of glutathione.

Among bacteria, Escherichia coli are unique because they contain an amount of glutathione (GSH) comparable to that of mammalian cells. Thus, this bacterium has been suggested as a model for oxidant stress in mammalian systems. Two common strains of E. coli, ATCC 29682, a B strain, and AB 1157, a K-12 strain, were exposed to paraquat (PQ) or t-butyl hydroperoxide (TBH) and the effect on GSH, growth, and lethality was assessed. Exposure of both strains to 5 mM PQ resulted in an 80% decrease in GSH. Exposure to 5 mM TBH resulted in a 31% decrease in GSH in the K-12 strain and an 80% decrease in the B strain. No correlation was found between the GSH decrease in either strain and the PQ or TBH growth inhibitory effects. TBH exposures increased oxidized GSH (GSSG) export. However, no increase in intracellular GSSG or protein-mixed disulfides was found after exposure to either oxidant nor was GSSG secreted following PQ. After failing to inhibit GSH synthesis with buthionine sulfoximine, a B strain GSH-deficient mutant [RCI-1] was constructed. There was no difference in the growth and lethality responses to the oxidants between GSH-deficient and -sufficient strains. GSH supplementation with N-acetylcysteine or L-2-oxothiazolidine decreased the sensitivity of the E. coli B strain to the growth inhibitory but not the lethality effects of TBH. The lack of a correlation of changes in GSH with either oxidant-induced growth inhibitory or lethality effects, the presence of catalase in the cytoplasm not peroxisomes, and the absence of glutathione peroxidase are limitations to the value of this bacterium as a model for mammalian oxidant stress.

Evaluation of solutions for small intestinal preservation. Biochemical changes as a function of storage time.

A number of organ preservation solutions have been formulated to slow the inevitable progression of ischemic injury, thus prolonging the storage time between removal and implantation. As adenine nucleotide content has been shown to correlate with the functional recovery of transplanted livers and hearts, this study investigated the effects of 24 hr of storage in three preservation solutions, saline (SA), Euro-Collins (CO), and University of Wisconsin (UW) on adenine and nicotinamide adenine nucleotides and inosine content of the rat small intestine. Significant biochemical differences were found between segments as early as after the initial perfusion when the inosine content was higher in UW-perfused than CO- or SA-perfused segments. After 2 hr of storage in CO solution and after 6 and 24 hr in both CO and UW solutions, the ATP content was higher than in SA-stored segments. In addition to inosine, which was significantly higher at all time points for UW-stored segments, the AMP and total adenine nucleotide content of UW-stored segments at 24 hr was significantly higher than SA- or CO-stored segments. After 24 hr of storage, those segments stored in UW were able to utilize significantly more oxygen than SA-stored. These data provide biochemical evidence supporting the advantages of CO and UW storage solutions over SA for preservation of small intestine segments.

Stimulation of secretion by the T84 colonic epithelial cell line with dietary flavonols.

Flavonols are dietary compounds widely distributed in plants and characterized by a 2-phenyl-benzo(alpha)pyrane nucleus possessing hydroxyl and ketone groups at positions 3 and 4, respectively. Kaempferol, quercetin, and myricetin are flavonols that are further mono-, di-, or trihydroxylated on the phenyl ring, respectively. To test whether these ingested flavonols might exert a direct secretory effect on intestinal epithelial cells, monolayers of the T84 colonocyte cell line were mounted in Ussing chambers and examined for ion transport response. Twenty minutes after addition of 100 microM quercetin to either the serosal or mucosal side, the short-circuit current change was maximal at 16.6 microA/cm2. Kaempferol was less potent than quercetin, while myricetin and glycosylated quercetin (rutin) did not induce secretion. The secretion induced by quercetin did not seem to be mediated by the reactive oxygen species generated by quercetin through auto-oxidation and/or redox cycling (superoxide, hydrogen peroxide, and the hydroxyl radical) because it was neither enhanced by iron, nor inhibited by desferroxamine B or catalase (alone or in combination with superoxide dismutase). Like vasoactive intestinal peptide, quercetin induced a secretory response that was inhibited by barium chloride and bumetanide, and which exhibited synergism with carbachol. Quercetin also stimulated a modest increase in intracellular cAMP levels and the phosphorylation of endogenous protein substrates for cAMP-dependent protein kinase. Thus, quercetin is a potent stimulus of colonocyte secretion that resembles secretagogues which act via a cAMP-mediated signaling pathway.

Two reasons for unusual therapeutic drug monitoring results in hospitalized patients.

In programs where therapeutic drug monitoring is accompanied by interpretation of the data, unusual and unanticipated values may mean more than just a laboratory error. Many times such spurious results will be due to unusual circumstances that result in the drug never reaching the bloodstream. In 3 case reports, we show that purposeful inhospital noncompliance and failure to recognize simple drug absorption interactions can be added to the evergrowing list of factors influencing serum concentrations of therapeutic agents.

Interference of allopurinol and alloxanthine in ultraviolet theophylline assay.

A modification of several spectrophotometric methods for assaying theophylline in biological fluids is presented; the maximum absorbances of theophylline, allopurinol and alloxanthine solutions were measured. Plots of absorbance vs wavelength from 320 to 190 nm wer made for four samples in 0.1 N sodium hydroxide. The maximum absorbances for the theophylline sample (20 microgram/ml) were at 274-275 and 217 nm; for allopurinol (1 microgram/ml), at 274, 275 and 216 nm; for alloxanthine (10 microgram/ml), a plot similar to that for allopurinol; and for an equal mixture of the three solutions, at 274 and 218 nm. Especially with allopurinol and alloxanthine, and possibly in the presence of drugs with similar basic structures, one might wich to use a method other than spectrophotometry for the assay of theophylline or discontinue administration of the interfering medication.