Critical Care 2009, 13:R208

Hydroxyethyl starch (HES) solutions are widely used for volume replacement therapy but are also known to compromise coagulation, impair renal function and increase long-term mortality. To test the hypotheses that HES 130/0.4 has less adverse effects than HES 200/0.5 and exerts anti-inflammatory properties we compared the effects of HES130/0.4, HES200/0.5 and saline on in vitro haemostasis and pro-inflammatory platelet function.

Methods
Whole blood samples from healthy volunteers were mixed with 6% HES130/0.4, 10% HES200/0.5, or normal saline to achieve a final haemodilution rate of 10 % or 40 %. Haemostatic capacity was characterised by thromboelastography (ROTEM) and measurement for FXIIIa activity. Platelet activation and pro-inflammatory platelet functions were characterised by flow cytometry measuring the platelet activation marker CD62P and binding of fibrinogen to platelets as well as the formation of heterotypic platelet-leukocyte conjugates.

Results
Compared to saline, HES130/0.4 dose-dependently impaired formation and firmness of the fibrin clot but did not affect the fibrin-crosslinking activity of FXIIIa. At 40 % but not at 10 % haemodilution rate HES200/0.5 also increased platelet fibrinogen binding and both HES solutions increased expression of CD62P, the main receptor for platelet-leukocyte adhesion. HES130/0.4 but not HES200/0.5 increased formation of platelet-neutrophil conjugates and, to a lesser degree, platelet-monocyte conjugates.
HES130/0.4 impairs haemostasis and stimulates pro-inflammatory blood platelet function
Conclusions
Our data demonstrate that HES130/0.4 has similar adverse effects as HES200/0.5. In particular, both types of HES impair coagulation capacity and stimulate rather than attenuate pro-inflammatory platelet function.

Crit Care Med 1990;18:728

The incidence and consequences of fluid overload in the surgical ICU (SICU) have not been well defined, but may influence length of stay, days requiring mechanical ventilation, and mortality. Forty-eight consecutive patients admitted to our SICU were prospectively monitored for acute changes in weight and its impact on clinical management and outcome. When defined as a gain >10% from their preoperative or premorbid weight (or an approximately 20% increase in total body water), 40% of patients had fluid overload. Patients were divided into three groups: those who had gained <=10%, those with a weight gain between 11% and 20%, and those with >20% increase in weight. Significant differences were found with respect to vasopressor dependence, colloid administration, and mortality. When indexed by initial Acute Physiology and Chronic Health Evaluation (APACHE H) mortality prediction scores, all groups had similar degrees of illness. On average, presumably due to volume limitations, patients were inadequately nourished during 85% of their SICU stay. Our results suggest that the morbidity of fluid overload can be significant, and warrants a fresh look at the methods of intraoperative fluid resuscitation.

Br. J. Anaesth. 2009 103: 346-351

Fluid management guided by oesophageal Doppler monitor has been reported to improve perioperative outcome. Stroke volume variation (SVV) is considered a reliable clinical predictor of fluid responsiveness. Consequently, the aim of the present trial was to evaluate the accuracy of SVV determined by arterial pulse contour (APCO) analysis, using the FloTracTM/VigileoTM system, to predict fluid responsiveness as measured by the oesophageal Doppler.

Methods
Patients undergoing major abdominal surgery received intraoperative fluid management guided by oesophageal Doppler monitoring. Fluid boluses of 250 ml each were administered in case of a decrease in corrected flow time (FTc) to <350 ms. Patients were connected to a monitoring device, obtaining SVV by APCO. Haemodynamic variables were recorded before and after fluid bolus application. Fluid responsiveness was defined as an increase in stroke volume index >10%. The ability of SVV to predict fluid responsiveness was assessed by calculation of the area under the receiver operating characteristic (ROC) curve.

Results
Twenty patients received 67 fluid boluses. Fifty-two of the 67 fluid boluses administered resulted in fluid responsiveness. SVV achieved an area under the ROC curve of 0.512 [confidence interval (CI) 0.32–0.70]. A cut-off point for fluid responsiveness was found for SVV > 8.5% (sensitivity: 77%; specificity: 43%; positive predictive value: 84%; and negative predictive value: 33%).

Conclusions
This prospective, interventional observer-blinded study demonstrates that SVV obtained by APCO, using the FloTracTM/VigileoTM system, is not a reliable predictor of fluid responsiveness in the setting of major abdominal surgery.

Anesthesiology 2008;109:723-740

Replacement of assumed preoperative deficits, in addition to generous substitution of an unsubstantiated increased insensible perspiration and third space loss, plays an important role in current perioperative fluid regimens. The consequence is a positive fluid balance and weight gain of up to 10 kg, which may be related to severe complications. Because the intravascular blood volume remains unchanged and insensible perspiration is negligible, the fluid must accumulate inside the body. This concept brings into question common liberal infusion regimens. Blood volume after fasting is normal, and a fluid-consuming third space has never been reliably shown. Crystalloids physiologically load the interstitial space, whereas colloidal volume loading deteriorates a vital part of the vascular barrier. The endothelial glycocalyx plays a key role and is destroyed not only by ischemia and surgery, but also by acute hypervolemia. Therefore, undifferentiated fluid handling may increase the shift toward the interstitial space. Using the right kind of fluid in appropriate amounts at the right time might improve patient outcome.

Principles of perioperative fluid management have received increased interest in recent years within type and amount of crystalloid and colloid, the concept of individualized goal-directed cardiovascular optimization (GDT), and finally assessed on a procedure-specific basis. In this issue, Kimberger et al., investigated the underlying tissue mechanisms during GDT management with crystalloids or colloids for abdominal surgery with a colonic anastomosis. This elegant experimental study in pigs included detailed techniques of postsurgical assessments of conventional cardiovascular variables (blood pressure, heart rate, urinary output) and microcirculatory blood flow and tissue oxygen tension in healthy and perianastomotic colonic tissue. Three types of fluid management were instituted at the end of surgery: restricted Ringer lactate (RL) versus GDT RL or GDT colloid to achieve a mixed venous oxygen saturation (Svo₂) greater than 60%.

Anesthesiology 2009;110:496-504

The aim of this study was to compare the effects of goal-directed colloid fluid therapy with goal-directed crystalloid and restricted crystalloid fluid therapy on healthy and perianastomotic colon tissue in a pig model of colon anastomosis surgery.

Methods
Pigs (n = 27, 9 per group) were anesthetized and mechanically ventilated. A hand-sewn colon anastomosis was performed. The animals were subsequently randomized to one of the following treatments: R-RL group, 3 ml [middle dot] kg-1 [middle dot] h-1 Ringer lactate (RL); GD-RL group, 3 ml [middle dot] kg-1 [middle dot] h-1 RL + bolus 250 ml of RL; GD-C group, 3 ml [middle dot] kg-1 [middle dot] h-1 RL + bolus 250 ml of hydroxyethyl starch (HES 6%, 130/0.4). A fluid bolus was administered when mixed venous oxygen saturation dropped below 60%. Intestinal tissue oxygen tension and microcirculatory blood flow were measured continuously.

Results
After 4 h of treatment, tissue oxygen tension in healthy colon increased to 150 +/- 31% in group GD-C versus 123 +/- 40% in group GD-RL versus 94 +/- 23% in group R-RL (percent of postoperative baseline values, mean +/- SD; P < 0.01). Similarly perianastomotic tissue oxygen tension increased to 245 +/- 93% in the GD-C group versus 147 +/- 58% in the GD-RL group and 116 +/- 22% in the R-RL group (P < 0.01). Microcirculatory flow was higher in group GD-C in healthy colon.

Conclusions
Goal-directed colloid fluid therapy significantly increased microcirculatory blood flow and tissue oxygen tension in healthy and injured colon compared to goal-directed or restricted crystalloid fluid therapy.

Curr Opin Anaesthesiol 2009;22:100-108

Perioperative fluid management influences patient outcome. Vascular surgery unites various surgical procedures, mainly with a high impact on patients who often have relevant preexisting illnesses. There are only scarce data on this specialty, forcing the clinician to extrapolate existing data when planning perioperative fluid management. This review aims to summarize the underlying facts.

Recent findings
Perioperative insensible perspiration does not exceed 1 ml/kg per hour. A third space shift does not exist; therefore, its primary substitution is erroneous. Rather, a crystalloid fluid excess causes a tremendous shift towards the interstitial space. Colloidal volume effects are context sensitive, that is, only their use as a substitute when blood or plasma loss occurs leads to maintenance within the circulatory space. Colloidal hypervolaemia and surgical trauma both have the potential to deteriorate the vascular barrier, leading to plasma loss into the interstitial space. Current perioperative fluid therapy should aim to maintain normovolaemia of the individual body fluid compartments as far as possible. This might be achieved by combining a protocol-based replacement of extracellular losses (urinary output plus insensible perspiration) with isotonic balanced crystalloids and blood volume optimization using isooncotic colloids.

Summary
The basis of fluid therapy in vascular surgery is a careful differential indication of the respective classes of preparations. A goal-directed approach might help to avoid hypovolaemia.

Current Opinion in Anaesthesiology 2009;22:163-167

Plasma expanders are reviewed to determine their ability to restore microvascular function as a means for extending the transfusion trigger and delaying the use of blood transfusions. This outcome is currently achievable because of the emergence of a new understanding of optimal tissue function that prioritizes maintenance of functional capillary density, which results from the normalization of blood viscosity via the increase in plasma viscosity with new viscogenic colloids.

Recent findings
Use of viscous plasma expanders in experimental models of extreme hemodilution, hemorrhagic shock and endotoxemia shows that the limiting factor in anemia is not oxygen-carrying capacity but the decline of microvascular function due to the lowering of functional capillary density. In support of this hypothesis, we find that viscogenic colloids including high-molecular-weight starches, dextrans, polyvinylpyrrolidone, keratin and polyethylene glycol-conjugated albumin maintain or restore microvascular function in extreme hemodilution, polyethylene glycol-conjugated albumin yielding the best results.

Summary
Preclinical studies show that polyethylene glycol-conjugated albumin at concentrations in the range of 2-4% extends the transfusion trigger, providing the more extended and complete microvascular and systemic recovery from hemorrhagic shock, extreme hemodilution and endotoxemia, postponing the need of reestablish intrinsic blood oxygen-carrying capacity to hemoglobin concentrations lower than those associated with accepted transfusion triggers.

Critical Care 2009, 13:R40

Perioperative hypovolemia arises frequently and contributes to intestinal hypoperfusion and subsequent postoperative complications. Goal-directed fluid therapy (GDT) might reduce these complications. The aim of this study was to compare the effects of goal-directed administration of crystalloids and colloids on distribution of systemic, hepato-splanchnic and microcirculatory (small intestine) blood flow after major abdominal surgery in a clinically relevant pig model.

Methods
Twenty-seven pigs were anesthetized, mechanically ventilated and underwent open laparotomy. They were randomly assigned to one of the three following treatment groups: the restricted Ringer’s lactate group (R-RL, n=9) received 3 ml.kg-1.h-1 RL; the goal-directed RL group (GD-RL, n=9) received 3 ml.kg-1.h-1 RL and intermittent boluses of 250 ml RL and the goal-directed colloid group (GD-C, n=9) received 3 ml.kg-1.h-1 RL and boluses of 250 ml 6% hydroxyethyl starch (130/0.4). The two latter groups received a bolus infusion when mixed venous oxygen saturation (SvO2) was below 60% (lock out time 30 minutes). Regional blood flow was measured in the superior mesenteric artery and the celiac trunk. In the small bowel, microcirculatory blood flow was measured using laser Doppler flowmetry. Intestinal tissue oxygen tension was measured with intramural Clark-type electrodes.

Results
After 4 hours of treatment, arterial blood pressure, cardiac output, mesenteric artery flow and mixed oxygen saturation were significantly higher in groups GD-C and GD-RL than in group R-RL. Microcirculatory flow in the intestinal mucosa increased by 50% in GD-C but remained unchanged in the other two groups. Likewise, tissue oxygen tension in the intestine increased by 30% in GD-C but remained unchanged in GD-RL and decreased by 18% in the R-RL group. Mesenteric venous glucose concentrations were higher and lactate levels lower in group GD-C compared with the two crystalloid groups.

Conclusions
Goal-directed colloid administration markedly increased microcirculatory blood flow in the small intestine and intestinal tissue oxygen tension after abdominal surgery. In contrast, goal-directed crystalloid and restricted crystalloid administrations had no such effects. Additionally, mesenteric venous glucose and lactate concentrations suggest that intestinal cellular substrate levels were higher in the colloid-treated than in the crystalloid-treated animals. These results support the notion that perioperative goal-directed therapy with colloids might be beneficial during major abdominal surgery.

Acta Anaesthesiol Scand 2008; 52: 522–29

Pre-operative fasting is assumed to cause a deficit in intravascular blood volume (BV), as a result of ongoing urine production and insensible perspiration. Standard regimes consist of volume loading prior or simultaneous to any anaesthetic procedure to minimise the risk of hypotension. However, fluid overload in the context of major abdominal surgery has been shown to deteriorate patient outcome. Our study aimed to quantify total intravascular BV after fasting by direct measurements and to compare it with calculated normal values in comparable non-fasted patients.

Methods
After 10 h of fasting, total plasma volume (PV) and red cell volume (RCV) were measured via the double-label technique (indocyanine green dilution and erythrocytes labelled with fluorescein, respectively) following induction of general anaesthesia in 53 gynaecological patients suffering from malignoma of the cervix. The corresponding normal values were calculated individually from age, body height and body weight.

Results
Measured BV, RCV and PV after fasting were 4123±589, 1244±196 and 2879±496 ml, respectively. The differences to the corresponding calculated normal values were not significant (3882±366, 1474±134 and 2413±232 ml, respectively). The measured haematocrit reflected a slight anaemic state (0.35±0.03).

Conclusion
Our data suggest that even after prolonged pre-operative fasting, cardio-pulmonary healthy patients remain intravascularly normovolaemic. Therefore, hypotension associated with induction of general or neuraxial anaesthesia should perhaps be treated with moderate doses of vasopressors rather than with undifferentiated volume loading

Acta Anaesthesiol Scand 2009;108:311-317

It is unknown whether an intra-operative colloid infusion alters the dynamics of a crystalloid load administered post-operatively.

Methods
Ten patients received 12.5 ml/kg of Ringer’s lactate over 30 min 1–3 days before and 4 h after laparoscopic cholecystectomy, during which 10 ml/kg of a colloid solution, hydroxyethylstarch (HES 130/0.4), was infused. The total body clearance of the pre- and post-operative test infusions was taken as the ratio between the urinary excretion and the Hb-derived dilution of venous plasma over 150 min. The plasma clearance of the infused fluid was calculated using volume kinetics based on the plasma dilution alone. The pre-operative plasma clearance was compared with the post-operative plasma clearance and patients served as their own control.

Results
The urinary excretion averaged 350 ml for the pre-operative infusion and 612 ml post-operatively, which corresponds to 46% and 68% of the pre- and post-operative infusions, respectively. The total body clearance of the crystalloid fluid was 30 ml/min before surgery and 124 ml/min after surgery (P<0.01). The plasma clearance, as obtained from the plasma dilution alone, was 28 and 412 ml/min, respectively. The maximal increase in plasma volume was 410 ml pre-operatively vs. 220 ml post-operatively.

Conclusions
Infusion of a colloid solution in combination with a crystalloid during laparoscopic cholecystectomy increased the plasma clearance of a post-operative crystalloid infusion.

Anesth Analg 2009 108: 616-622

Recent studies have emphasized the importance of perioperative fluid restriction. However, fluid restriction regimens may increase the likelihood of insufficient perioperative fluid administration or may result in excess intravascular crystalloid replacement. We postulate that the use of transesophageal echocardiography may reduce the amount of crystalloid administered during open and laparoscopic colorectal surgery.

Methods
Fifteen ASA I and II patients scheduled for open colorectal surgery, and 15 patients scheduled for laparoscopic surgery were studied. Lactated Ringer’s solution was infused during the procedures. Left ventricular end diastolic volume index (LVEDVI) and cardiac index were assessed throughout surgery and used to guide the rate of lactated Ringer’s solution administration. Statistical analysis was performed with Student’s t-test for unpaired samples.

Results
The rate of crystalloid administration required to maintain baseline LVEDVI and cardiac index was 5.9 ± 2 mL · kg^–1 · h^–1 for open surgery and 3.4 ± 0.8 mL · kg^–1 · h^–1 for laparoscopic surgery (P < 0.01). This slower rate for laparoscopic surgery was offset by the longer surgical duration.

Conclusion
The rate of crystalloid solution to maintain baseline LVEDVI and cardiac index was greater in open surgery than laparoscopic surgery, and lower than commonly recommended for colorectal surgery.

NHS National Library of Health

From October 2006 the Association of Surgeons of Great Britain and Ireland, SARS, BAPEN Medical, the Intensive Care Society, the Association for Clinical Biochemistry and the Renal Association nominated core members of a steering committee who came together to establish consensus for good perioperative fluid prescribing. Concern arose from a high incidence of postoperative sodium and water overload, and evidence to suggest that preventing or treating this, by more accurate fluid therapy, would improve outcome.

BJA 2008;101:761-768

Stroke volume variation (SVV) is able to predict adequately the individual response to fluid loading. Our objective was to assess whether the SVV measured by a new algorithm (VigileoTM; FlotracTM) can predict fluid responsiveness.

Methods
Forty mechanically ventilated patients undergoing liver transplantation, who needed volume expansion (VE), were included. VE was done with albumin (4%) 20 mlxBMI over 20 min. SVV, pulse pressure variation (PPV), central venous pressure (CVP), and pulmonary artery occlusion pressure (PAOP) were measured immediately before and after VE. Cardiac output (CO) measured by transthoracic echocardiography (CO-TTE) was used to define responder patients if CO increased by 15% or more after VE, or non-responder otherwise. CO obtained with the pulmonary artery catheter (CO-PAC) and with Vigileo (CO-Vigileo) were also recorded.

Results
Five patients were excluded. Seventeen patients were responders (Rs) and 18 were non-responders (NRs). Before VE (i) SVV and PPV were higher in Rs and (ii) CVP and PAOP were lower in Rs. Baseline SVV and PPV correlated with change in CO induced by VE (respectively, r2=0.72, P<0.0001; r2=0.84, P<0.0001). An SVV threshold of >10% discriminated Rs with a sensitivity of 94% and a specificity of 94%. After VE, the decrease in SVV was significantly correlated with the increase in CO (r2=0.51; P<0.0001). There was no difference between the area under the ROC curves of SVV and PPV. After VE, the change in CO-Vigileo was closely correlated with change in CO-TTE (r2=0.74, P<0.0001) and with change in CO-PAC (r2=0.77, P<0.0001).

Conclusions
The SVV obtained by the Vigileo system may be used as a predictor of fluid responsiveness in patients with circulatory failure after liver transplantation. CO-Vigileo is able to track the change in CO induced by VE.

BJA 2009;102:221-226

This study tested the circulatory effectiveness of post-trauma administration of a large intravascular volume expander, hydroxyethyl starch 130/0.4 (HES), vs standard lactated Ringer’s solution (RL).

Methods
Liver injury was inflicted in 14 pigs [31 (4) kg; mean (SD)] and treatment simulated an acute pre-hospital event: after a standard first-respond delay (7 min), volume administration was provided in three phases to simulate increasing intravascular access. In the first two phases, the fluid was administered either by HES or by RL and, during the last phase, all animals received HES to stabilize the intravascular volume.

Results
The liver trauma severed an equal number of 1–3 mm diameter blood vessels [1.4 (0.6)] and after 7 min, the blood loss was 184 (127) ml and mean arterial pressure had decreased by 19 (13) mm Hg (P<0.01). The intravascular volume expansion effect was 115 (25)% for HES and 76 (21)% for RL (P<0.05), yet oxygen uptake was maintained in zero of seven vs three of seven pigs and the survival was three of seven vs seven of seven, respectively (P<0.05). In these animals, the initial administration of HES provoked uncontrolled bleeding, whereas the administration of RL was associated with attenuated bleeding: total blood loss 2455 (1919) vs 311 (208) ml, respectively (P<0.01), reflecting that bleeding ceased in six of the pigs administered RL.

Conclusions
After injury, the intravascular volume expanding effect of HES was larger than that for RL. However, initial administration of HES provoked uncontrolled haemorrhage, suggesting that prioritizing intravascular volume expansion did not result in stabilization of the circulation after haemorrhage.

Intensive Care Med 2008:34;2157-2168

Crystalloids, artificial and natural colloids have been opposed as representing different strategies for shock resuscitation, but it may be relevant to distinguish fluids based on their oncotic characteristics. This study assessed the risk of renal adverse events in patients with shock resuscitated using hypooncotic colloids, artificial hyperoncotic colloids, hyperoncotic albumin or crystalloids, according to physician’s choice.

Participants and setting
International prospective cohort study including 1,013 ICU patients needing fluid resuscitation for shock. Patients suffering from cirrhosis or receiving plasma were excluded.

Measurements and results
Influence of different types of colloids and crystalloids on the occurrence of renal events (twofold increase in creatinine or need for dialysis) and mortality was assessed using multivariate analyses and propensity score. Statistical adjustment was based on severity at the time of resuscitation, risks factor for renal failure, and on variables influencing physicians’ preferences regarding fluids. A renal event occurred in 17% of patients. After adjustment on potential confounding factors and on propensity score for the use of hyperoncotic colloids, the use of artificial hyperoncotic colloids [OR: 2.48 (1.24–4.97)] and hyperoncotic albumin [OR: 5.99 (2.75–13.08)] was significantly associated with occurrence of renal event. Overall ICU mortality was 27.1%. The use of hyperoncotic albumin was associated with an increased risk of ICU death [OR: 2.79 (1.42–5.47)].

Conclusions
This study suggests that harmful effects on renal function and outcome of hyperoncotic colloids may exist. Although an improper usage of these compounds and confounding factors cannot be ruled out, their use should be regarded with caution, especially because suitable alternatives exist.
See the Editorial by PM Honorel, O Joannes-Boyau and W Boer: Hyperoncotic colloids in shock and risk of renal injury: enough evidence for a banning order?

Crit Care Med 2008;36:3001-3007

Measures of arterial pulse pressure variation and left ventricular stroke volume variation induced by positive-pressure breathing vary in proportion to preload responsiveness. However, the accuracy of commercially available devices to report dynamic left ventricular stroke volume variation has never been validated.

Methods
We compared the accuracy of measured arterial pulse pressure and estimated left ventricular stroke volume reported from two Food and Drug Administration-approved aortic flow monitoring devices, one using arterial pulse power (LiDCOplus(TM)) and the other esophageal Doppler monitor (HemoSonic(TM)). We compared estimated left ventricular stroke volume and their changes during a venous occlusion and release maneuver to a calibrated aortic flow probe placed around the aortic root on a beat-to-beat basis in seven anesthetized open-chested cardiac surgery patients.

Results
Dynamic changes in arterial pulse pressure closely tracked left ventricular stroke volume changes (mean r2 .96). Both devices showed good agreement with steady-state apneic left ventricular stroke volume values and moderate agreement with dynamic changes in left ventricular stroke volume (esophageal Doppler monitor -1 +/- 22 mL, and pulse power -7 +/- 12 mL, bias +/- 2 sd). In general, the pulse power signals tended to underestimate left ventricular stroke volume at higher left ventricular stroke volume values.

Conclusion
Arterial pulse pressure, as well as, left ventricular stroke volume estimated from esophageal Doppler monitor and pulse power reflects short-term steady-state left ventricular stroke volume values and tract dynamic changes in left ventricular stroke volume moderately well in humans.

Critical Care 2008,12:232

This review summarises key research papers in the fields of cardiology and intensive care published during 2007 in Critical Care. To create a context and for comparison with the papers described in the review, we cite studies on the same subject published in other journals. The papers have been grouped into four categories: venous oximetry, cardiac surgery, perioperative fluid optimisation, and haemodynamic monitoring.

Br. J. Anaesth. 2008;101:141-150

The advent of balanced solutions for i.v. fluid resuscitation and replacement is imminent and will affect any specialty involved in fluid management. Part of the background to their introduction has focused on the non-physiological nature of ‘normal’ saline solution and the developing science about the potential problems of hyperchloraemic acidosis. This review assesses the physiological significance of hyperchloraemic acidosis and of acidosis in general. It aims to differentiate the effects of the causes of acidosis from the physiological consequences of acidosis. It is intended to provide an assessment of the importance of hyperchloraemic acidosis and thereby the likely benefits of balanced solutions.

Clin Sci 2003;104:17-24

In this double-blind crossover study, the effects of bolus infusions of 0.9% saline (NaCl) and Hartmann’s solution on serum albumin, haematocrit and serum and urinary biochemistry were compared in healthy subjects. Nine young adult male volunteers received 2-litre intravenous infusions of 0.9% saline and Hartmann’s solution on separate occasions, in random order, each over 1h. Body weight, haematocrit and serum biochemistry were measured pre-infusion and at 1h intervals for 6h. Biochemical analysis was performed on pooled post-infusion urine. Blood and plasma volume expansion, estimated by dilutional effects on haematocrit and serum albumin, were greater and more sustained after saline than after Hartmann’s solution (P<0.01). At 6h, body weight measurements suggested that 56% of the infused saline was retained, in contrast with only 30% of the Hartmann’s solution. Subjects voided more urine (median: 1000 compared with 450ml) of higher sodium content (median: 122 compared with 73mmol) after Hartmann’s than after saline (both P = 0.049), despite the greater sodium content of the latter. The time to first micturition was less after Hartmann’s than after saline (median: 70 compared with 185min; P = 0.008). There were no significant differences between the effects of the two solutions on serum sodium, potassium, urea or osmolality. After saline, all subjects developed hyperchloraemia (>105mmol/l), which was sustained for >6h, while serum chloride concentrations remained normal after Hartmann’s (P<0.001 for difference between infusions). Serum bicarbonate concentration was significantly lower after saline than after Hartmann’s (P = 0.008). Thus excretion of both water and sodium is slower after a 2-litre intravenous bolus of 0.9% saline than after Hartmann’s solution, due possibly to the more physiological [Na+]/[Cl-] ratio in Hartmann’s solution (1.18:1) than in saline (1:1) and to the hyperchloraemia caused by saline.