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      A definition of normovolaemia and consequences for cardiovascular control during orthostatic and environmental stress

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          Abstract

          The Frank–Starling mechanism describes the relationship between stroke volume and preload to the heart, or the volume of blood that is available to the heart—the central blood volume. Understanding the role of the central blood volume for cardiovascular control has been complicated by the fact that a given central blood volume may be associated with markedly different central vascular pressures. The central blood volume varies with posture and, consequently, stroke volume and cardiac output ( \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \dot{Q} $$\end{document} ) are affected, but with the increased central blood volume during head-down tilt, stroke volume and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \dot{Q} $$\end{document} do not increase further indicating that in the supine resting position the heart operates on the plateau of the Frank–Starling curve which, therefore, may be taken as a functional definition of normovolaemia. Since the capacity of the vascular system surpasses the blood volume, orthostatic and environmental stress including bed rest/microgravity, exercise and training, thermal loading, illness, and trauma/haemorrhage is likely to restrict venous return and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \dot{Q} $$\end{document} . Consequently the cardiovascular responses are determined primarily by their effect on the central blood volume. Thus during environmental stress, flow redistribution becomes dependent on sympathetic activation affecting not only skin and splanchnic blood flow, but also flow to skeletal muscles and the brain. This review addresses the hypothesis that deviations from normovolaemia significantly influence these cardiovascular responses.

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          Most cited references176

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          Effects of intravenous fluid restriction on postoperative complications: comparison of two perioperative fluid regimens: a randomized assessor-blinded multicenter trial.

          To investigate the effect of a restricted intravenous fluid regimen versus a standard regimen on complications after colorectal resection. Current fluid administration in major surgery causes a weight increase of 3-6 kg. Complications after colorectal surgery are reported in up to 68% of patients. Associations between postoperative weight gain and poor survival as well as fluid overload and complications have been shown. We did a randomized observer-blinded multicenter trial. After informed consent was obtained, 172 patients were allocated to either a restricted or a standard intraoperative and postoperative intravenous fluid regimen. The restricted regimen aimed at maintaining preoperative body weight; the standard regimen resembled everyday practice. The primary outcome measures were complications; the secondary measures were death and adverse effects. The restricted intravenous fluid regimen significantly reduced postoperative complications both by intention-to-treat (33% versus 51%, P = 0.013) and per-protocol (30% versus 56%, P = 0.003) analyses. The numbers of both cardiopulmonary (7% versus 24%, P = 0.007) and tissue-healing complications (16% versus 31%, P = 0.04) were significantly reduced. No patients died in the restricted group compared with 4 deaths in the standard group (0% versus 4.7%, P = 0.12). No harmful adverse effects were observed. The restricted perioperative intravenous fluid regimen aiming at unchanged body weight reduces complications after elective colorectal resection.
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            Effect of salt and water balance on recovery of gastrointestinal function after elective colonic resection: a randomised controlled trial.

            Low concentrations of albumin in serum and long gastric emptying times have been returned to normal in dogs by salt and water restriction, or a high protein intake. We aimed to determine the effect of salt and water balance on recovery of gastrointestinal function after elective colonic resection in human beings. We randomly allocated ten patients to receive postoperative intravenous fluids in accordance present hospital practice (> or = 3 L water and 154 mmol sodium per day) and ten to receive a restricted intake (< or = 2 L water and 77 mmol sodium per day). All patients had no disease other than colonic cancer. The primary endpoint was solid and liquid-phase gastric emptying time, measured by dual isotope radionuclide scintigraphy on the fourth postoperative day. Secondary endpoints included time to first bowel movement and length of postoperative hospital stay. Analysis was by intention to treat. Median solid and liquid phase gastric emptying times (T(50)) on the fourth postoperative day were significantly longer in the standard group than in the restricted group (175 vs 72.5 min, difference 56 [95% CI 12-132], p=0.028; and 110 vs 73.5 min, 52 [9-95], p=0.017, respectively). Median passage of flatus was 1 day later (4 vs 3 days, 2 [1-2], p=0.001); median passage of stool 2.5 days later (6.5 vs 4 days, 3 [2-4], p=0.001); and median postoperative hospital stay 3 days longer (9 vs 6 days, 3 [1-8], p=0.001) in the standard group than in the restricted group. One patient in the restricted group developed hypokalaemia, whereas seven patients in the standard group had side-effects or complications (p=0.01). Positive salt and water balance sufficient to cause a 3 kg weight gain after surgery delays return of gastrointestinal function and prolongs hospital stay in patients undergoing elective colonic resection.
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              Effect of intraoperative fluid management on outcome after intraabdominal surgery.

              The debate over the correct perioperative fluid management is unresolved. The impact of two intraoperative fluid regimes on postoperative outcome was prospectively evaluated in 152 patients with an American Society of Anesthesiologists physical status of I-III who were undergoing elective intraabdominal surgery. Patients were randomly assigned to receive intraoperatively either liberal (liberal protocol group [LPG], n = 75; bolus of 10 ml/kg followed by 12 ml x kg(-1) x h(-1)) or restrictive (restrictive protocol group [RPG], n = 77; 4 ml x kg(-1) x h(-1)) amounts of lactated Ringer's solution. The primary endpoint was the number of patients who died or experienced complications. The secondary endpoints included time to initial passage of flatus and feces, duration of hospital stay, and changes in body weight, hematocrit, and albumin serum concentration in the first 3 postoperative days. The number of patients with complications was lower in the RPG (P = 0.046). Patients in the LPG passed flatus and feces significantly later (flatus, median [range]: 4 [3-7] days in the LPG vs. 3 [2-7] days in the RPG; P < 0.001; feces: 6 [4-9] days in the LPG vs. 4 [3-9] days in the RPG; P < 0.001), and their postoperative hospital stay was significantly longer (9 [7-24] days in the LPG vs. 8 [6-21] days in the RPG; P = 0.01). Significantly larger increases in body weight were observed in the LPG compared with the RPG (P < 0.01). In the first 3 postoperative days, hematocrit and albumin concentrations were significantly higher in the RPG compared with the LPG. In patients undergoing elective intraabdominal surgery, intraoperative use of restrictive fluid management may be advantageous because it reduces postoperative morbidity and shortens hospital stay.
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                Author and article information

                Contributors
                +31-20-5662371 , +31-20-5669158 , j.j.vanlieshout@amc.uva.nl
                Journal
                Eur J Appl Physiol
                European Journal of Applied Physiology
                Springer-Verlag (Berlin/Heidelberg )
                1439-6319
                1439-6327
                7 January 2010
                7 January 2010
                May 2010
                : 109
                : 2
                : 141-157
                Affiliations
                [1 ]Special Medical Care, Department of Internal Medicine, Academic Medical Center, University of Amsterdam, Rm F7-205, PO Box 22700, 1100 DE Amsterdam, The Netherlands
                [2 ]Laboratory for Clinical Cardiovascular Physiology, Heart Failure Research Center, Academic Medical Center, Amsterdam, The Netherlands
                [3 ]Department of Anaesthesia, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark
                [4 ]Section of Surgical Pathophysiology, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark
                Author notes

                Communicated by Susan Ward.

                Article
                1346
                10.1007/s00421-009-1346-5
                2861179
                20052592
                5b0d81a4-602f-4928-9dda-d3e76e70ebab
                © The Author(s) 2010
                History
                : 22 December 2009
                Categories
                Review Article
                Custom metadata
                © Springer-Verlag 2010

                Anatomy & Physiology
                syncope,blood pressure,exercise,stroke volume,cardiac output,volume
                Anatomy & Physiology
                syncope, blood pressure, exercise, stroke volume, cardiac output, volume

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