Aldosterone and potassium secretion by the cortical collecting duct

BACKGROUND.: Aldosterone has been implicated in the regulation of both Na and K concentrations in the plasma. Release of the hormone is known to be stimulated by high plasma K, and infusion of aldosterone lowers plasma K. However, the correlation between changes in mineralocorticoid levels and rates of K secretion is not perfect, suggesting that other factors may be involved. METHODS.: Patch-clamp recordings were made of K-channel activity in the split-open cortical collecting tubule of the rat. Estimates of channel density were made in cell-attached patches on the luminal membrane of principal cells of this segment. RESULTS.: Most of the K conductance of the apical membrane is mediated through low-conductance "SK" channels. The number of conducting SK channels is increased when animals are placed on a high-K diet. However, increasing plasma aldosterone levels by infusion of the hormone or by sodium restriction failed to change the number of active channels. CONCLUSIONS.: At least two circulating factors are required for the regulation of renal K secretion by the cortical collecting tubule. Aldosterone mainly stimulates secretion by increasing the driving force for K movement through apical channels. A second, as yet unidentified, factor increases the number of conducting K channels.     

产后出血量测评方法的研究进展

介绍目测法、客观量化法以及依据生化指标和症状体征参数等方法在评估产后出血量过程中的应用,并分析上述方法在临床应用中的优点和局限性,以期为优化产后出血量测评方法的应用提供更多思路。     

去氨加压素减少全髋关节置换术患者围手术期出血量的临床研究

目的 评价去氨加压素减少全髋关节置换术(THA)患者围手术期出血量的效果.方法 2007年9月至2009年6月,选取62例拟行单侧THA的患者,男28例,女34例.采用随机数字表法分为治疗组和对照组,每组31例:治疗组用去氨加压素按照0.3 μg/kg体质量溶于100 mL生理盐水配制,静脉滴注,术前30 min应用1次,术后1次/d,连续用2 d;对照组仅给予等剂量生理盐水静脉滴注.比较两组患者失血总量、术中失血量、术后可见失血量、输血量、术前及术后血红蛋白(Hb)、红细胞比容(Hct)、血小板(Plt)、纤维蛋白原(Fib)、凝血酶原时间(PT)及活化部分凝血活酶时间(APTT)等指标,并以彩色多普勒超声观察患者术后下肢深静脉血栓形成的发生情况.结果 两组患者的总输血比例、实际失血总量、输血量比较差异均有统计学意义(P＜0.05);而术后输血比例、手术时间、术中失血量、术后24 h可见失血量、全部可见失血量差异无统计学意义(P＞0.05).两组患者术后Hb、Hct、Plt及APTT比较差异均有统计学意义(P＜0.05),而Fib、PT比较差异无统计学意义(P＞0.05).术后14 d两组均未发现下肢深静脉血栓形成.45例患者获1～3个月随访,仅2例表现为下肢静脉功能不全.结论 在THA术中及术后短期使用去氨加压素能有效减少患者的失血量和输血量.

Abstract：

Objective To evaluate the clinical value of desmopressin in reducing blood loss following total hip arthroplasty (THA) .Methods From September 2007 to June 2009, 62 patients (28 males and 34 females) underwent THA.They were randomly divided into 2 even groups.Group A (desmopressin group) received intravenous administration of desmopressin(0.3 μg/kg diluted in 100 mL normal saline) at 30 minutes preoperatively and in 2 consecutive days postoperatively.Instead Group B (control group) received intravenous administration of normal saline of the same volume and in the same manner.The amounts of calculated total blood loss, intraoperative blood loss, postoperative wound blood loss and blood transfusion were recorded.The hemoglobin concentration (Hb) , hematocrit (Hot), platelet (Plt),fibrinogen (Fib), prothrombin time (PT), activated partial thromboplastin time (APTT) were also examined one day before and one day after operation for comparison.The patients were examined for occurrence of deep vein thrombosis(DVT) by Color Doppler Flow Imaging.Results The intraoperative blood loss was 375 ±43 mL in Group A and 392 ± 55 mL in Group B, without significant difference between the 2 groups ( P ＞0.05 ).The postoperative drainage volume was 276 ± 49 mL in Group A and 294 ± 52 mL in Group B with no significant difference either ( P ＞ 0.05).The total blood loss was 920 ±80 mL in Group A and 1150 ±99 mL in Group B, with a significant difference between the 2 groups ( P ＜ 0.05) .There were also significant differences between the 2 groups in average amount of blood transfusion, patients needing blood transfusion and postoperative Hb, Hct, Plt levels and APTT( P ＜ 0.05).No DVP event was found 14 days postoperation in either group.Conclusion During and following THA, a short-term use of desmopressin can significantly decrease blood loss and transfusion required.     

Propofol anaesthesia in mice is potentiated by muscimol and reversed by bicuculline

We have examined the role of gamma-aminobutyric acid (GABA) neurones in propofol anaesthesia in mice using the righting reflex. Propofol i.p. increased the percentage of loss of the righting reflex in a dose- dependent manner with an ED50 value of 140 (95% confidence limits 123- 160) mg kg-1 (n = 40; eight animals per dose, five doses per dose- response curve). The ED50 for propofol decreased significantly to 66 (58-75) mg kg-1 in the presence of the GABAA receptor agonist muscimol 1 mg kg-1 i.p. (n = 40) (P < 0.05). In contrast, the ED50 increased significantly to 240 (211-274) mg kg-1 in the presence of the antagonist bicuculline 5 mg kg-1 i.p. (n = 40) (P < 0.05). Our results suggest that propofol anaesthesia may be mediated, at least in part by GABA neurons.      

Hidden blood loss following hip and knee arthroplasty. Correct management of blood loss should take hidden loss into account

Following total hip arthroplasty (THA) and total knee arthroplasty (TKR) only the 'visible' measured blood loss is usually known. This underestimates the 'true' total loss, as some loss is 'hidden'. Correct management of blood loss should take hidden loss into account. We studied 101 THAs and 101 TKAs (with re-infusion of drained blood). Following THA, the mean total loss was 1510 ml and the hidden loss 471 ml (26%). Following TKA, the mean total loss was 1498 ml. The hidden loss was 765 ml (49%). Obesity made no difference with either operation. THA involves a small hidden loss, the total loss being 1.3 times that measured. However, following TKA, there may be substantial hidden blood loss due to bleeding into the tissues and residual blood in the joint. The true total loss can be determined by doubling the measured loss.     

Characteristics of hidden blood loss following hybrid total knee arthroplasty

BackgroundHidden blood loss (HBL) unrecognized by the usual practice of assessing intraoperative loss and postoperative drainage comprises a considerable proportion of total blood loss (TBL) during primary total knee arthroplasty (TKA). However, HBL has not been adequately investigated in hybrid TKA (uncemented femur, cemented tibia). The purpose of this study was to clarify the amount and influential factors of HBL in hybrid TKA.MethodsA consecutive series of 151 knees in 137 patients with knee osteoarthritis who underwent hybrid TKA were retrospectively evaluated. We examined the correlations between HBL and various factors of concern for their effects on TBL, including age, sex, body weight (BW), body height, body mass index, operation time, tourniquet time, and visible blood loss (VBL) in three periods (intraoperative: VBL₁; until 3 h postoperatively: VBL₂; from 3 h to 1 day postoperatively: VBL₃).ResultsMedian (interquartile range) HBL and TBL were 528 (388, 711) mL and 725 (582, 926) mL, respectively. HBL relative to TBL (H/T) was 73%. There were weak correlations between HBL and BW (r = 0.249, p = 0.002) and between HBL and VBL₃ (r = −0.261, p = 0.001). Multivariate analyses confirmed a positive correlation between HBL and BW (β = 0.296, p < 0.001) and a negative correlation between HBL and VBL₃ (β = −0.270, p < 0.001).ConclusionsHybrid TKA showed comparable values of HBL and H/T to those reported for cemented TKA. Therefore, management strategies for HBL in hybrid TKA can follow the same protocols used for cemented TKA. High BW and low VBL₃ may be predictors of postoperative HBL in hybrid TKA.     

Phenylephrine increases regional cerebral blood flow following hemorrhage during isoflurane-oxygen anesthesia

Using the radioactive microsphere technique regional cerebral blood flow (rCBF) and total CBF (tCBF) were examined in rats at three time periods: baseline (CBF1) during 1.5 MAC inspired isoflurane-oxygen anesthesia, CBF2; during 1.5 MAC inspired isoflurane anesthesia combined with hypotension induced by hemorrhage and CBF3; during isoflurane and hemorrhage plus phenylephrine infused to restore mean arterial pressure (MAP) to baseline. For CBF1 MAP was 89 +/- 3 mmHg (mean +/- SEM, n = 9) with PaCO2 44 +/- 1 mmHg. For CBF2 following graded hemorrhage MAP was 48 +/- 2 mmHg and PaCO2 43 +/- 1 mmHg. For CBF3 MAP was 93 +/- 2 and PaCO2 45 +/- 1 mmHg, following infusion of phenylephrine (PE) at 13.9 +/- 4.0 micrograms.kg-1.min-1. Total CBF1 was 1.84 +/- 0.18 ml.g-1.min-1, tCBF2 1.32 +/- 0.09 ml.g-1.min-1 (P less than 0.05 vs. tCBF1) and tCBF3 2.60 +/- 0.18 (P less than 0.05 vs. tCBF1 and 2). For tCBF3 hemoglobin concentration had decreased 23% from 14.2 +/- 0.2 g.100 ml-1 to 11.0 +/- 0.5 g.100 ml-1 (P less than 0.05). Regional CBF decreased significantly in seven of 12 regions examined from CBF1 to CBF2 and was significantly higher in all regions for CBF3. For CBF1-3 infratentorial blood flows (cerebellar and brain stem) were significantly higher than flows to the supratentorial structures (cerebral cortical and basal ganglia). During isoflurane anesthesia, phenylephrine infused to support MAP following hemorrhagic hypotension effectively maintains rCBF and tCBF. There is no indication that phenylephrine infused to increase MAP following hemorrhage results in cerebral vasoconstriction in rats anesthetized with isoflurane.     

Accurate monitoring of blood loss: thoracic electrical impedance during hemorrhage in the pig

BACKGROUND: Cardiovascular variables are closely regulated in that they remain relatively stable during minor hemorrhage. We considered that such stability would make these variables less accurate for monitoring a blood loss. In contrast, thoracic electrical impedance would be unlikely to be a regulated variable and could serve as a non-invasive monitor of a volume deficit. METHODS: In 10 pigs bled (0-24 ml kg(-1)) and retransfused (to 28 ml kg(-1)) during halothane anesthesia, the magnitude of the electrical impedance, cardiovascular, blood gas and temperature variables, atrial natriuretic peptide and near infrared spectroscopy of the leg muscles were recorded. RESULTS: During hemorrhage and retransfusion, the median correlations between changes in the magnitude of the thoracic impedance and the external blood loss ranged from 0.97 to 0.98 with an individual range from 0.80 to 1.0. These correlation coefficients were higher and their ranges were lower than correlations established for any other measured parameter. CONCLUSION: During hemorrhage and retransfusion in the halothane anesthetized pig, a change in the magnitude of thoracic electrical impedance appears to be an accurate and also non-invasive monitor of a blood volume deficit.