Citrate Storage Affects Thrombelastograph® Analysis

Background: Thrombelastograph(R) analysis (TEG(R)) is used to evaluate blood coagulation. Ideally, whole blood is immediately processed. If impossible, blood may be citrated and assessed after recalcification. No data describe the effect of such treatment and storage on TEG(R) parameters.

Methods: Three studies were performed in 90 surgical patients. In 30 patients, blood was citrated (1:10, 0.129 M) and recalcified (20 [mu]l 2 M CaCl2 to 340 [mu]l citrated blood), and TEG(R) was performed with native blood and after recalcification after 0, 15, and 30 min of citrate storage. In another 30 patients, TEG(R) was performed with citrated blood recalcified immediately and after 1-72 h storage. In a third study, thrombin-antithrombin complex, prothrombin fragment 1+2, and [beta]-thromboglobulin were measured (using enzyme-linked immunoabsorbant assay tests) at corresponding time points. Data were compared using repeated-measures analysis of variance and post hoc paired t tests.

Results: TEG(R) parameters were different in recalcified citrated blood compared with native blood (P < 0.05) and changed significantly during 30-min (P < 0.025) and 72-h (P < 0.001) citrate storage. TEG(R) parameters measured between 1 and 8 h of citrate storage were stable. Thrombin-antithrombin complex and prothrombin fragment 1+2 values were not elevated in native blood. After 30 min of citrate storage a gradual thrombin activation was observed, as evidenced by increasing thrombin-antithrombin complex and prothrombin fragment 1+2 values (P < 0.05). [beta]-Thromboglobulin level was increased after 2 and 8 h of citrate storage (P < 0.01).     

Comparative Efficacy of Acustimulation (ReliefBand®) versus Ondansetron (Zofran®) in Combination with Droperidol for Preventing Nausea and Vomiting

Background: Antiemetic drugs are costly, are associated with variable efficacy, and can produce unwanted side effects when used for prophylaxis against postoperative nausea and vomiting. This clinical study was designed to compare the efficacy of transcutaneous electrical acupoint stimulation using a ReliefBand(R) to ondansetron (Zofran(R)) when utilized alone or in combination for preventing postoperative nausea and vomiting after plastic surgery.

Methods: A single-center, randomized, double-blind, placebo- and sham-controlled study design was conducted to compare three prophylactic antiemetic treatment regimens in 120 outpatients undergoing plastic surgery procedures with routine low-dose droperidol prophylaxis: (1) ondansetron (n = 40), 4 mg intravenous ondansetron and a sham ReliefBand(R); (2) acustimulation (n = 40), 2 ml intravenous saline and an active ReliefBand(R); and (3) combination (n = 40), 4 mg intravenous ondansetron and an active ReliefBand(R). The incidences of postoperative nausea and vomiting, as well as the need for "rescue" antiemetics, were determined at specific time intervals for up to 72 h after surgery. The outcome variables assessed included recovery times, quality of recovery score, time to resumption of normal diet, and patient satisfaction with the prophylactic antiemetic therapy.

Results: Use of the ReliefBand(R) in combination with ondansetron significantly reduced nausea (20 vs. 50%), vomiting (0 vs. 20%), and the need for rescue antiemetics (10 vs. 37%) compared with ondansetron alone at 24 h after surgery. Furthermore, the ability to resume a normal diet (74 vs. 35%) within 24 h after surgery was significantly improved when the ReliefBand(R) was used to supplement ondansetron (vs. ondansetron alone). Finally, the quality of recovery (90 +/- 10 vs. 70 +/- 20) and patient satisfaction (94 +/- 10 vs. 75 +/- 22) scores were significantly higher in the combination group versus the ondansetron group. There were no significant differences between the ReliefBand(R) and ondansetron when administered as adjuvants to droperidol for antiemetic prophylaxis.     

Comparison of Amsorb®, Sodalime, and Baralyme® Degradation of Volatile Anesthetics and Formation of Carbon Monoxide and Compound A in Swine In Vivo

Background: Consequences of volatile anesthetic degradation by carbon dioxide absorbents that contain strong base include formation of compound A from sevoflurane, formation of carbon monoxide (CO) and CO toxicity from desflurane, enflurane and isoflurane, delayed inhalation induction, and increased anesthetic costs. Amsorb(R) (Armstrong Ltd., Coleraine, Northern Ireland) is a new absorbent that does not contain strong base and does not form CO or compound A in vitro. This investigation compared Amsorb(R), Baralyme(R) (Chemetron Medical Division, Allied Healthcare Products, St. Louis, MO), and sodalime effects on CO (from desflurane and isoflurane) and compound A formation, carboxyhemoglobin (COHb) concentrations, and anesthetic degradation in a clinically relevant porcine in vivo model.

Methods: Pigs were anesthetized with desflurane, isoflurane, or sevoflurane, using fresh or partially dehydrated Amsorb(R), Baralyme(R), and new and old formulations of sodalime. Anesthetic concentrations in the fresh (preabsorber), inspired (postabsorber), and end-tidal gas were measured, as were inspired CO and compound A concentrations and blood oxyhemoglobin and COHb concentrations.

Results: For desflurane and isoflurane, the order of inspired CO and COHb formation was dehydrated Baralyme(R) >> soda-lime > Amsorb(R). For desflurane and Baralyme(R), peak CO was 9,700 +/- 5,100 parts per million (ppm), and the increase in COHb was 37 +/- 14%. CO and COHb increases were undetectable with Amsorb(R). Oxyhemoglobin desaturation occurred with desflurane and Baralyme(R) but not Amsorb(R) or sodalime. The gap between inspired and end-tidal desflurane and isoflurane did not differ between the various dehydrated absorbents. Neither fresh nor dehydrated Amsorb(R) caused compound A formation from sevoflurane. In contrast, Baralyme(R) and sodalime caused 20-40 ppm compound A. The gap between inspired and end-tidal sevoflurane did not differ between fresh absorbents, but was Amsorb(R) < sodalime < Baralyme(R) with dehydrated absorbents.     

Utility of Whole Blood Hemostatometry Using the Clot Signature Analyzer® for Assessment of Hemostasis in Cardiac Surgery

Background: A hemostatic monitor capable of rapid, accurate detection of clinical coagulopathy within the operating room could improve management of bleeding after cardiopulmonary bypass (CPB). The Clot Signature Analyzer(R) is a hemostatometer that measures global hemostasis in whole blood. The authors hypothesized that point-of-care hemostatometry could detect a clinical coagulopathic state in cardiac surgical patients.

Methods: Fifty-seven adult patients scheduled for a variety of elective cardiac surgical procedures were studied. Anesthesia, CPB, heparin anticoagulation, protamine reversal, and transfusion for post-CPB bleeding were all managed by standardized protocol. Clinical coagulopathy was defined by the need for platelet or fresh frozen plasma transfusion. The Clot Signature Analyzer(R) collagen-induced thrombus formation (CITF) assay measured platelet-mediated hemostasis in vitro. The activated clotting time, platelet count, prothrombin time, activated partial thromboplastin time, and fibrinogen concentration were also measured.

Results: The postprotamine CITF was greater in patients who required hemostatic transfusion than in those who did not (17.6 +/- 8.0 min vs. 10.5 +/- 5.7 min, respectively;P < 0.01). Postprotamine CITF values were highly correlated with platelet and fresh frozen plasma transfusion (Spearman r = 0.50, P < 0.001 and r = 0.40, P < 0.005, respectively). Receiver operator characteristic curves showed a highly significant relation between the postprotamine CITF and intraoperative platelet and fresh frozen plasma transfusion (area under the curve, 0.78-0.81, P < 0.005) with 60-80% sensitivity, specificity, positive and negative predictive values at cutoffs of 12-14 min. Logistic regression demonstrated that the CITF was independently predictive of post-CPB hemostatic transfusion, but standard hemostatic assays were not.     

Critical Oxygen Delivery in Conscious Humans Is Less Than 7.3 ml O2 · kg-1 · min-1

Background: The "critical" level of oxygen delivery (DO2) is the value below which DO2 fails to satisfy the metabolic need for oxygen. No prospective data in healthy, conscious humans define this value. The authors reduced DO2 in healthy volunteers in an attempt to determine the critical DO2.

Methods: With Institutional Review Board approval and informed consent, the authors studied eight healthy, conscious volunteers, aged 19-25 yr. Hemodynamic measurements were obtained at steady state before and after profound acute isovolemic hemodilution with 5% albumin and autologous plasma, and again at the reduced hemoglobin concentration after additional reduction of DO2 by an infusion of a [beta]-adrenergic antagonist, esmolol.

Results: Reduction of hemoglobin from 12.5 +/- 0.8 g/dl to 4.8 +/- 0.2 g/dl (mean +/- SD) increased heart rate, stroke volume index, and cardiac index, and reduced DO2 (14.0 +/- 2.9 to 9.9 +/- 2.0 ml O2 [middle dot] kg-1 [middle dot] min-1; all P < 0.001). Oxygen consumption (VO2; 3.0 +/- 0.5 to 3.4 +/- 0.6 ml O2 [middle dot] kg-1 [middle dot] min-1;P < 0.05) and plasma lactate concentration (0.50 +/- 0.10 to 0.62 +/- 0.16 mM;P < 0.05; n = 7) increased slightly. Esmolol decreased heart rate, stroke volume index, and cardiac index, and further decreased DO2 (to 7.3 +/- 1.4 ml O2 [middle dot] kg-1 [middle dot] min-1; all P < 0.01 vs. before esmolol). VO2 (3.2 +/- 0.6 ml O2 [middle dot] kg-1 [middle dot] min-1;P > 0.05) and plasma lactate (0.66 +/- 0.14 mM;P > 0.05) did not change further. No value of plasma lactate exceeded the normal range.     

Spinal Nitric Oxide Contributes to the Analgesic Effect of Intrathecal [D-Pen2,D-Pen5]-Enkephalin in Normal and Diabetic Rats

Background: Spinal nitric oxide (NO) is important for the analgesic actions of morphine and cholinergic agents. Its role in the analgesic effect of [delta]-opioid receptor agonists is not known. In the present study, the authors determined the role of spinal endogenous NO in the antinociceptive effect of intrathecal [D-Pen2, D-Pen5]-enkephalin (DPDPE), a [delta]-opioid receptor agonist, in normal rats and a rat model of diabetic neuropathic pain.

Methods: Rats were rendered diabetic with streptozotocin (50 mg/kg, intraperitoneal). Intrathecal catheters were implanted in age-matched normal and diabetic rats. Nociceptive thresholds were determined by application of a noxious pressure stimulus to the hind paw. The dose-dependent effect of intrathecal DPDPE was first determined. The role of spinal NO in the analgesic effect of intrathecal DPDPE was then examined through intrathecal treatments with NO synthase inhibitors (NMMA and TRIM) and a specific NO scavenger (carboxy-PTIO).

Results: The diabetic rats developed a sustained mechanical hyperalgesia within 3 weeks after streptozotocin injection. Intrathecal DPDPE, 2-20 [mu]g, dose-dependently increased the withdrawal threshold in response to the noxious pressure in normal and diabetic rats. However, the ED50 of DPDPE in diabetic rats was about twofold higher than that in normal rats. Intrathecal pretreatment with NMMA, TRIM, or carboxy-PTIO diminished the analgesic effect of DPDPE in both normal and diabetic rats. Furthermore, the inhibitory effect of NMMA on the action of intrathecal DPDPE was reversed by intrathecal l-arginine but not d-arginine.     

Anesthetic Preconditioning Enhances Ca2+ Handling and Mechanical and Metabolic Function Elicited by Na+-Ca2+ Exchange Inhibition in Isolated Hearts

Background: Anesthetic preconditioning (APC) is well known to protect against myocardial ischemia-reperfusion injury. Studies also show the benefit of Na+-Ca2+ exchange inhibition on ischemia-reperfusion injury. The authors tested whether APC plus Na+-Ca2+ exchange inhibitors given just on reperfusion affords additive protection in intact hearts.

Methods: Cytosolic [Ca2+] was measured by fluorescence at the left ventricular wall of guinea pig isolated hearts using indo-1 dye. Sarcoplasmic reticular Ca2+-cycling proteins, i.e., Ca2+ release channel (ryanodine receptor [RyR2]), sarcoplasmic reticular Ca2+-pump adenosine triphosphatase (SERCA2a), and phospholamban were measured by Western blots. Hearts were assigned to seven groups (n = 8 each): (1) time control; (2) ischemia; (3, 4) 10 [mu]m Na+-Ca2+ exchange inhibitor KB-R7943 (KBR) or 1 [mu]m SEA0400 (SEA), given during the first 10 min of reperfusion; (5) APC initiated by sevoflurane (2.2%, 0.41 +/- 0.03 mm) given for 15 min and washed out for 15 min before ischemia-reperfusion; (6, 7) APC plus KBR or SEA.

Results: The authors found that APC reduced the increase in systolic [Ca2+], whereas KBR and SEA both reduced the increase in diastolic [Ca2+] on reperfusion. Each intervention improved recovery of left ventricular function. Moreover, APC plus KBR or SEA afforded better functional recovery than APC, KBR, or SEA alone (P < 0.05). Ischemia-reperfusion-induced degradation of major sarcoplasmic reticular Ca2+-cycling proteins was attenuated by APC, but not by KBR or SEA.     

Halothane and Isoflurane Augment Depolarization-induced Cytosolic CA2+ Transients and Attenuate Carbachol-stimulated CA2+ Transients

Background: Neuronal excitability is in part determined by Ca2+ availability that is controlled by regulatory mechanisms of cytosolic Ca2+ ([Ca2+]cyt). Alteration of any of those mechanisms by volatile anesthetics (VAs) may lead to a change in presynaptic transmission and postsynaptic excitability. Using a human neuroblastoma cell line, the effects of halothane and isoflurane on cytosolic Ca2+ concentration ([Ca2+]cyt) in response to K+ and carbachol stimulation were investigated.

Methods: Volatile anesthetic (0.05-1 mm) action on stimulated [Ca2+]cyt transients were monitored in suspensions of SH-SY5Y cells loaded with fura-2. Potassium chloride (KCl; 100 mm) was used to depolarize and activate Ca2+ entry through voltage-dependent calcium channels; 1 mm carbachol was used to activate muscarinic receptor-mediated inositol triphosphate (IP3)-dependent intracellular Ca2+ release. Sequential stimulations, KCl followed by carbachol and vice versa, were used to investigate interactions between intracellular Ca2+ stores.

Results: Halothane and isoflurane in clinically relevant concentrations enhanced the K+-evoked [Ca2+]cyt transient whether intracellular Ca2+ stores were full or partially depleted. In contrast, halothane and isoflurane reduced the carbachol-evoked [Ca2+]cyt transient when the intracellular Ca2+ stores were full but had no effect when the Ca2+ stores were partially depleted by KCl stimulation.     

A Multicenter Study Comparing the ProSealTM and ClassicTM Laryngeal Mask Airway in Anesthetized, Nonparalyzed Patients

Background: The laryngeal mask airway ProSeal(TM) (PLMA(TM)), a new laryngeal mask device, was compared with the laryngeal mask airway Classic(TM) (LMA(TM)) with respect to: (1) insertion success rates and times; (2) efficacy of seal; (3) fiberoptically determined anatomic position; (4) orogastric tube insertion success rates and times; (5) total intraoperative complications; and (6) postoperative sore throat in nonparalyzed adult patients undergoing general anesthesia, hypothesizing that these would be different.

Methods: Three hundred eighty-four nonparalyzed anesthetized adult patients (American Society of Anesthesiologists physical status I-II) were randomly allocated to the PLMA(TM) or LMA(TM) for airway management. In addition, 50% of patients were randomized for orogastric tube placement. Unblinded observers collected intraoperative data, and blinded observers collected postoperative data.

Results: First-attempt insertion success rates (91 vs. 82%, P = 0.015) were higher for the LMA(TM), but after three attempts success rates were similar (LMA(TM), 100%;PLMA(TM), 98%). Less time was required to achieve an effective airway with the LMA(TM) (31 +/- 30 vs. 41 +/- 49 s;P = 0.02). The PLMA(TM) formed a more effective seal (27 +/- 7 vs. 22 +/- 6 cm H2O;P < 0.0001). Fiberoptically determined anatomic position was better with the LMA(TM) (P < 0.0001). Orogastric tube insertion was more successful after two attempts (88 vs. 55%;P < 0.0001) and quicker (22 +/- 18 vs. 38 +/- 56 s) with the PLMA(TM). During maintenance, the PLMA(TM) failed twice (leak, stridor) and the LMA(TM) failed once (laryngospasm). Total intraoperative complications were similar for both groups. The incidence of postoperative sore throat was similar.     

Droperidol Inhibits Intracellular Ca2+, Myofilament Ca2+ Sensitivity, and Contraction in Rat Ventricular Myocytes

Background: Droperidol has recently been associated with cardiac arrhythmias and sudden cardiac death. Changes in action potential duration seem to be the cause of the arrhythmic behavior, which can lead to alterations in intracellular free Ca2+ concentration ([Ca2+]i). Because [Ca2+]i and myofilament Ca2+ sensitivity are key regulators of myocardial contractility, the authors' objective was to identify whether droperidol alters [Ca2+]i or myofilament Ca2+ sensitivity in rat ventricular myocytes and to identify the cellular mechanisms responsible for these effects.

Methods: Freshly isolated rat ventricular myocytes were obtained from adult rat hearts. Myocyte shortening, [Ca2+]i, nitric oxide production, intracellular pH, and action potentials were monitored in cardiomyocytes exposed to droperidol. Langendorff perfused hearts were used to assess overall cardiac function.

Results: Droperidol (0.03-1 [mu]m) caused concentration-dependent decreases in peak [Ca2+]i and shortening. Droperidol inhibited 35 mm KCl-induced increase in [Ca2+]i, with little direct effect on sarcoplasmic reticulum Ca2+ stores. Droperidol had no effect on action potential duration but caused a rightward shift in the concentration-response curve to extracellular Ca2+ for shortening, with no concomitant effect on peak [Ca2+]i. Droperidol decreased pHi and increased nitric oxide production. Droperidol exerted a negative inotropic effect in Langendorff perfused hearts.     

Propofol Modulates Na+-Ca2+ Exchange Activity via Activation of Protein Kinase C in Diabetic Cardiomyocytes

Background: The authors' objective was to identify the role of the Na+-Ca2+ exchanger (NCX) in mediating the contractile dysfunction observed in diabetic cardiomyocytes before and after exposure to propofol.

Methods: Freshly isolated ventricular myocytes were obtained from normal and diabetic rat hearts. Intracellular concentration of Ca2+ and cell shortening were simultaneously measured in electrically stimulated, ventricular myocytes using fura-2 and video-edge detection, respectively. Postrest potentiation (PRP) and sarcoplasmic reticulum Ca2+ load were used to assess propofol-induced changes in the activity of the NCX.

Results: Propofol (10 [mu]m) increased PRP in diabetic cardiomyocytes but had no effect on PRP in normal cardiomyocytes. Removal of sodium enhanced and KB-R7943 (reverse mode NCX inhibitor) blocked PRP in both normal and diabetic cardiomyocytes. In the absence of sodium, propofol enhanced PRP in diabetic cardiomyocytes but had no additional effect in normal cardiomyocytes. KB-R7943 completely blocked propofol-induced potentiation of peak intracellular concentration of Ca2+ and shortening in both cell types. Propofol increased sarcoplasmic reticulum Ca2+ load and prolonged removal of cytosolic Ca2+ in diabetic cardiomyocytes, but not in normal cardiomyocytes. Removal of sodium enhanced propofol-induced increases in sarcoplasmic reticulum Ca2+ load and further prolonged removal of cytosolic Ca2+, whereas KB-R7943 completely blocked propofol-induced increase in sarcoplasmic reticulum Ca2+ load. Protein kinase C inhibition with bisindolylmaleimide I prevented the propofol-induced increase in PRP and prolongation in Ca2+ removal.     

Inhibitory Effects of Volatile Anesthetics on K+ and Cl- Channel Currents in Porcine Tracheal and Bronchial Smooth Muscle

Background: K+ and Ca2+-activated Cl- (ClCa) channel currents have been shown to contribute to the alteration of membrane electrical activity in airway smooth muscle. This study was conducted to investigate the effects of volatile anesthetics, which are potent bronchodilators, on the activities of these channels in porcine tracheal and bronchial smooth muscles.

Methods: Whole-cell patch clamp recording techniques were used to investigate the effects of superfused isoflurane (0-1.5 minimum alveolar concentration) or sevoflurane (0-1.5 minimum alveolar concentration) on K+ and ClCa channel currents in dispersed smooth muscle cells.

Results: Isoflurane and sevoflurane inhibited whole-cell K+ currents to a greater degree in tracheal versus bronchial smooth muscle cells. More than 60% of the total K+ currents in tracheal smooth muscle appeared to be mediated through delayed rectifier K+ channels compared with less than 40% in bronchial smooth muscle. The inhibitory effects of the anesthetics were greater on the delayed rectifier K+ channels than on the remaining K+ channels. Cl- currents through ClCa channels were significantly inhibited by the anesthetics. The inhibitory potencies of the anesthetics on the ClCa channels were not different in tracheal and bronchial smooth muscle cells.     

Isoflurane Neuroprotection in Rat Hippocampal Slices Decreases with Aging: Changes in Intracellular Ca2+ Regulation and N-methyl-d-aspartate Receptor-mediated Ca2+ Influx

Background: Most in vitro neuroprotection studies with isoflurane have involved cells obtained during the embryonic or early postnatal period. However, in mature rodents, isoflurane neuroprotection does not persist. The authors determined whether neuroprotection of hippocampal slices with isoflurane decreases with aging and is due to decreased intracellular Ca2+ regulation and survival protein phosphorylation.

Methods: Hippocampal slices from 5-day-old, 1-month-old, and 19- to 23-month-old rats were deprived of oxygen and glucose for 5-30 min in media bubbled with 1% isoflurane. Cell death was assessed in the CA1, CA3, and dentate regions, and intracellular Ca2+ concentration was measured in CA1 neurons. N-methyl-d-aspartate receptor (NMDAR)-dependent Ca2+ influx was measured and the phosphorylation of NMDARs, and the survival proteins Akt and mitogen-activated protein kinase p42/44 were quantified.

Results: Twenty minutes of oxygen and glucose deprivation killed approximately 40-60% of neurons in CA3 and dentate in all age groups. Isoflurane, 1%, reduced death of CA1, CA3, and dentate neurons in slices from 5-day-old rats but not those from 23-month-old rats. In 5-day slices, isoflurane attenuated NMDAR-mediated Ca2+ influx, whereas in aging slices, Ca2+ influx was increased protein kinase C. In aging slices, isoflurane did not increase the phosphorylation of Akt and p42/44.     

Mg2+ Dependence of Halothane-induced Ca2+ Release from the Sarcoplasmic Reticulum in Skeletal Muscle from Humans Susceptible to Malignant Hyperthermia

Background: Recent work suggests that impaired Mg2+ regulation of the ryanodine receptor is a common feature of both pig and human malignant hyperthermia. Therefore, the influence of [Mg2+] on halothane-induced Ca2+ release from the sarcoplasmic reticulum was studied in malignant hyperthermia-susceptible (MHS) or -nonsusceptible (MHN) muscle.

Methods: Vastus medialis fibers were mechanically skinned and perfused with solutions containing physiologic (1 mm) or reduced concentrations of free [Mg2+]. Sarcoplasmic reticulum Ca2+ release was detected using fura-2 or fluo-3.

Results: In MHN fibers, 1 mm halothane consistently did not induce sarcoplasmic reticulum Ca2+ release in the presence of 1 mm Mg2+. It was necessary to increase the halothane concentration to 20 mm or greater before Ca2+ release occurred. However, when [Mg2+] was reduced below 1 mm, halothane became an increasingly effective stimulus for Ca2+ release; e.g., at 0.4 mm Mg2+, 58% of MHN fibers responded to halothane. In MHS fibers, 1 mm halothane induced Ca2+ release in 57% of MHS fibers at 1 mm Mg2+. Reducing [Mg2+] increased the proportion of MHS fibers that responded to 1 mm halothane. Further experiments revealed differences in the characteristics of halothane-induced Ca2+ release in MHS and MHN fibers: In MHN fibers, at 1 mm Mg2+, halothane induced a diffuse increase in [Ca2+], which began at the periphery of the fiber and spread slowly inward. In MHS fibers, halothane induced a localized Ca2+ release, which then propagated along the fiber. However, propagated Ca2+ release was observed in MHN fibers when halothane was applied at an Mg2+ concentration of 0.4 mm or less.     

Isoform-selective Effects of Isoflurane on Voltage-gated Na+ Channels

Background: Voltage-gated Na+ channels modulate membrane excitability in excitable tissues. Inhibition of Na+ channels has been implicated in the effects of volatile anesthetics on both nervous and peripheral excitable tissues. The authors investigated isoform-selective effects of isoflurane on the major Na+ channel isoforms expressed in excitable tissues.

Methods: Rat Nav1.2, Nav1.4, or Nav1.5 [alpha] subunits heterologously expressed in Chinese hamster ovary cells were analyzed by whole cell voltage clamp recording. The effects of isoflurane on Na+ current activation, inactivation, and recovery from inactivation were analyzed.

Results: The cardiac isoform Nav1.5 activated at more negative potentials (peak INa at -30 mV) than the neuronal Nav1.2 (0 mV) or skeletal muscle Nav1.4 (-10 mV) isoforms. Isoflurane reversibly inhibited all three isoforms in a concentration- and voltage-dependent manner at clinical concentrations (IC50 = 0.70, 0.61, and 0.45 mm, respectively, for Nav1.2, Nav1.4, and Nav1.5 from a physiologic holding potential of -70 mV). Inhibition was greater from a holding potential of -70 mV than from -100 mV, especially for Nav1.4 and Nav1.5. Isoflurane enhanced inactivation of all three isoforms due to a hyperpolarizing shift in the voltage dependence of steady state fast inactivation. Inhibition of Nav1.4 and Nav1.5 by isoflurane was attributed primarily to enhanced inactivation, whereas inhibition of Nav1.2, which had a more positive V1/2 of inactivation, was due primarily to tonic block.     

Circulating Blood Volume Measured by Pulse Dye-Densitometry: Comparison with131 I-HSA Analysis

Background: Pulse dye-densitometry (PDD) is a newly developed technique for monitoring the arterial concentration of indocyanine green. Using this method, circulating blood volume (CBV) can be calculated without using radioisotopes. In this study, the CBV value obtained by PDD was validated by comparison using the human serum albumin (131) I-HSA) dilution method.

Methods: Eleven healthy volunteers underwent placement of cannulae into the radial artery and antecubital vein for withdrawal of blood samples and injection of indicator. Probes for PDD were attached to the right nostril and the right index finger. Indocyanine green (20 mg), dissolved in 4 ml water, and 25 [micro sign]Ci131 I-HSA in 1 ml distilled water were injected simultaneously into the left antecubital vein. Blood samples were withdrawn 3, 6, 10, 20, 30, and 45 min after injection, then processed for spectrophotometric measurement of indocyanine green and scintillation counting.

Results: The blood dye concentration correlated well with the values obtained by PDD (r = 0.986, imprecision 0.04 +/- 0.11 mg/l, 10.0 +/- 31%. The imprecision of the CBV value obtained by PDD (nose probe) and by the131 I-HSA dilution method was 3.99 +/- 10.54%, 0.259 +/- 0.593 l. The imprecision of the CBV obtained by in vitro spectrophotometry compared with PDD was 2.47 +/- 9.00%, 0.100 +/- 0.446 l.