Randomized clinical trial of fluid and salt restriction compared with a controlled liberal regimen in elective gastrointestinal surgery.

BACKGROUND: Excessive intravenous fluid prescription may play a causal role in postoperative complications following major gastrointestinal resectional surgery. The aim of this study was to investigate whether fluid and salt restriction would decrease postoperative complications compared with a more modern controlled liberal regimen. METHODS: In this observer-blinded single-site randomized clinical trial consecutive patients undergoing major gastrointestinal resectional surgery were randomized to receive either a liberal control fluid regimen or a restricted fluid and salt regimen. The primary outcome was postoperative complications of grade II and above (moderate to severe). RESULTS: Some 240 patients (194 colorectal resections and 46 oesophagogastric resections) were enrolled in the study; 121 patients were randomized to the restricted regimen and 119 to the control (liberal) regimen. During surgery the control group received a median (interquartile range) fluid volume of 2033 (1576-2500) ml and sodium input of 282 (213-339) mmol, compared with 1000 (690-1500) ml and 142 (93-218) mmol respectively in the restricted group. There was no significant difference in major complication rate between groups (38·0 and 39·0 per cent respectively). Median (range) hospital stay was 8 (3-101) days in the controls and 8 (range 3-76) days among those who received restricted fluids. There were four in-hospital deaths in the control group and two in the restricted group. Substantial differences in weight change, serum sodium, osmolality and urine : serum osmolality ratio were observed between the groups. CONCLUSION: There were no significant differences in major complication rates, length of stay and in-hospital deaths when fluid restriction was used compared with a more liberal regimen. REGISTRATION NUMBER: ISRCTN39295230 (http://www.controlled-trials.com).

Anaesthetic specialisation leads to improved early- and medium-term survival following major vascular surgery.

OBJECTIVE: Vascular surgical specialisation is associated with improved outcomes. We aimed to assess the effect of anaesthetic specialisation on outcome following major vascular surgery. DESIGN: Retrospective cohort study. METHODS: Patients undergoing major vascular surgery (lower limb revascularisation, elective and ruptured abdominal aortic aneurysm repair, endovascular aneurysm repair and carotid endarterectomy) over a five-year period were identified from a prospective database. The primary outcomes were death within 30 days and death within two years of surgery. Potential risk factors for mortality were assessed using multivariate logistic regression modelling. RESULTS: The analysis cohort comprised 1155 patients followed up for a median of 583 days. Mortality within two years of surgery was 16%. For the overall cohort, care from vascular anaesthetists was independently associated with reduced 30-day (odds ratio 0.22; 95% CI 0.12-0.62) and medium-term mortality (0.31; 95% CI 0.18-0.55). For elective patients (n=851), vascular anaesthesia reduced two-year mortality (odds ratio 0.29; 95% CI 0.15-0.58; P=0.0004) though not 30-day mortality (odds ratio 0.55; 95% CI 0.15-1.95; P=0.35). For emergency patients, care by a vascular anaesthetist influenced neither 30-day mortality (odds ratio 0.33; 95% CI 0.08-1.41; P=0.13) nor medium-term mortality (odds ratio 0.45; 95% CI 0.17-1.21; P=0.11). CONCLUSIONS: Anaesthetic specialisation reduced early- and medium-term mortality rates following major vascular surgery. If replicated by prospective studies, these results suggest that vascular surgery services would benefit from specialised anaesthetic support.

Luminal Ca2+ increases the sensitivity of Ca2+ stores to inositol 1,4,5-trisphosphate.

Ca2+ within intracellular stores has been proposed to act with cytosolic inositol 1,4,5-trisphosphate (InsP3) to cause opening of the integral Ca2+ channel of the InsP3 receptor, leading to mobilization of intracellular Ca2+ stores [FEBS Lett. 263:5-9 (1990)]. We have tested that suggestion in saponin-permeabilized rat hepatocytes by manipulating the Ca2+ content of the stores and then determining their sensitivity to InsP3, while keeping the cytosolic Ca2+ concentration constant. Stores depleted of Ca2+ by incubation with ionomycin were significantly less sensitive to InsP3, an effect thought likely to result from the decrease in luminal free Ca2+ concentration rather than from direct effects of ionomycin on InsP3 binding or Ca2+ permeability. The luminal free Ca2+ concentration of stores loaded in the presence of pyrophosphate appeared to be substantially reduced, and again there was a significant inverse correlation between the estimated free Ca2+ concentration of the stores and their sensitivity to InsP3. By following the kinetics of 45Ca2+ uptake into empty stores in the presence of inositol trisphosphorothioate, a stable InsP3 analogue, we demonstrated that stores respond to inositol trisphosphorothioate only after their luminal free Ca2+ concentration exceeds a critical level. We conclude that InsP3 and luminal Ca2+ together regulate Ca2+ mobilization from intracellular stores, and we discuss some of the implications of this interaction for the complex Ca2+ signals evoked by extracellular stimuli.

Quantal Ca2+ mobilization stimulated by inositol 1,4,5-trisphosphate in permeabilized hepatocytes.

In several cell types, including hepatocytes, submaximal concentrations of Ins(1,4,5)P3 stimulate an initial rapid mobilization of intracellular Ca2+ stores that is followed by either no further Ca2+ release or very much slower release. Further additions of Ins(1,4,5)P3 then evoke further Ca2+ mobilization. Such 'incremental' responses [Meyer & Stryer (1990) Proc. Natl. Acad. Sci. U.S.A. 87, 3841-3845] could result from all-or-nothing emptying of stores that differ in their sensitivities to Ins(1,4,5)P3 or from partial emptying of stores that are more uniformly sensitive, but unable to release all of their Ca2+ because the response to Ins(1,4,5)P3 rapidly attenuates. By measuring unidirectional 45Ca2+ efflux from intracellular stores stimulated with Ins(1,4,5)P3 under conditions where they continue to sequester 40Ca2+, we provide evidence suggesting that Ins(1,4,5)P3 stimulates all-or-nothing emptying of stores that differ in their sensitivities to Ins(1,4,5)P3, a quantal response pattern.

Liver inositol, 1,4,5-trisphosphate-binding sites are the Ca2(+)-mobilizing receptors.

Ins(1,4,5)P3 is the intracellular messenger that in many cells mediates the effects of Ca2(+)-mobilizing receptors on intracellular Ca2+ stores. An Ins(1,4,5)P3 receptor from cerebellum has been purified and functionally reconstituted, but the relationship between this protein and the high-affinity Ins(1,4,5)P3-binding sites of peripheral tissues is unclear. We compared the Ins(1,4,5)P3-binding sites of liver and cerebellum by measuring inhibition of specific Ins(1,4,[32P]5)P3 binding by various ligands under equilibrium conditions, and find that each ligand binds with similar affinity in the two tissues. Earlier studies in which Ins(1,4,5)P3 binding and Ca2+ mobilization were measured under different conditions demonstrated large differences between KD values for binding and EC50 values (concn. giving half-maximal effect) for Ca2+ release. We show here that, when measured under identical conditions, KD and EC50 values for four agonists are similar. Schild analysis of inhibition of Ins(1,4,5)P3 binding by ATP demonstrates a competitive interaction between the two at the liver Ins(1,4,5)P3-binding site, and this partly accounts for earlier discrepancies in binding and Ca2(+)-release data. We conclude that the high-affinity Ins(1,4,5)P3-binding site of hepatocytes is likely to be the receptor that mediates Ca2+ mobilization, and that this receptor is at present indistinguishable from that in cerebellum.

Molecular target sizes of inositol 1,4,5-trisphosphate receptors in liver and cerebellum.

Ins(1,4,5)P3 is the intracellular messenger that mediates the effects of many cell-surface receptors on intracellular Ca2+ stores. Although radioligand-binding studies have identified high-affinity Ins(1,4,5)P3-binding sites in many tissues, these have not yet been convincingly shown to be the receptors that mediate Ca2+ mobilization, nor is it clear whether there are differences in these binding sites between tissues. Here we report that Ins(1,4,5)P3 binds to a single class of high-affinity sites in both permeabilized hepatocytes (KD = 7.8 +/- 1.1 nM) and cerebellar membranes (KD = 6.5 +/- 2.4 nM), and provide evidence that these are unlikely to reflect binding to either of the enzymes known to metabolize Ins(1,4,5)P3. Furthermore, the rank order of potency of synthetic inositol phosphate analogues in displacing specifically bound Ins(1,4,5)P3 is the same as their rank order of potency in stimulating mobilization of intracellular Ca2+ stores, suggesting that the Ins(1,4,5)P3-binding site may be the physiological receptor. Radiation inactivation of the Ins(1,4,5)P3-binding sites of liver and cerebellum reveals that they have similar molecular target sizes: 257 +/- 36 kDa in liver and 258 +/- 20 kDa in cerebellum. We conclude that an Ins(1,4,5)P3-binding protein with a molecular target size of about 260 kDa is probably the receptor that mediates Ca2+ mobilization in hepatocytes, and our limited data provide no evidence to distinguish this from the cerebellar Ins(1,4,5)P3-binding protein.

A diacylglycerol kinase inhibitor, R59022, potentiates secretion by and aggregation of thrombin-stimulated human platelets.

The diacylglycerol kinase inhibitor R59022 (10 microM) potentiates secretion and aggregation responses in human platelets challenged with sub-maximal concentrations of thrombin. Potentiation correlates closely with increased formation of diacylglycerol, increased phosphorylation of a 40 kDa protein, a known substrate for protein kinase C, and with decreased formation of phosphatidic acid, the product of diacylglycerol kinase. Phosphorylation of myosin light chains, formation of inositol phosphates and the mobilization of Ca2+ by thrombin are not affected by R59022 (10 microM). These data support a role for protein kinase C in platelet aggregation and secretion, and provide further evidence that endogenous diacylglycerols bring about the activation of this enzyme. These data also add further argument against a role for phosphatidic acid in platelet activation.