Volume Kinetics of Ringer's Solution in Hypovolemic Volunteers

Background: The amount of Ringer's solution needed to restore normal blood volumes is thought to be three to five times the volume of blood lost. This therapy can be optimized by using a kinetic model that takes accounts for the rates of distribution and elimination of the infused fluid.

Methods: The authors infused 25 ml/kg Ringer's acetate solution into 10 male volunteers who were 23 to 33 yr old (mean, 28 yr) when they were normovolemic and after 450 ml and 900 ml blood had been withdrawn. One-volume and two-volume kinetic models were fitted to the dilution of the total venous hemoglobin and plasma albumin concentrations.

Results: Withdrawal of blood resulted in a progressive upward shift of the dilution-time curves of both markers. The two-volume model was statistically justified in 56 of the 60 analyzed data sets. The hemoglobin changes indicated that the body fluid space expanded by the infused fluid had a mean total volume of 10.7 l (+/- 0.9 SEM). The elimination rate constant (k (r)) decreased with the degree of hypovolemia and was 133 ml/min (22 ml/min [SEM]), 100 ml/min (39 ml/min [SEM]), and 34 ml/min (7 ml/min [SEM]), respectively (P < 0.01). Plasma albumin indicated a slightly larger body fluid space expanded by the infused fluid, but kr was less (P < 0.02). Hypovolemia reduced the systolic and diastolic blood pressures by approximately 10 mmHg (P < 0.05).     

Volume Kinetic Analysis of the Distribution of 0.9% Saline in Conscious versus Isoflurane-anesthetized Sheep

Background: The distribution and elimination of 0.9% saline given by intravenous infusion has not been compared between the conscious state and during inhalational anesthesia.

Methods: Six adult sheep received an intravenous infusion of 25 ml/kg of 0.9% saline over 20 min in the conscious state and also during isoflurane anesthesia and mechanical ventilation. The distribution and elimination of infused fluid were studied by volume kinetics based on serial analysis of hemoglobin dilution in arterial blood and by mass balance that incorporated volume calculations derived from volume kinetic analysis and measurements of urinary volumes.

Results: The mass balance calculations indicated only minor differences in the time course of plasma volume expansion between the conscious and anesthetized states. However, isoflurane anesthesia markedly reduced urinary volume (median, 9 vs. 863 ml;P < 0.03). In conscious sheep, the central and peripheral volume expansion predicted by volume kinetics agreed well with the calculations based on mass balance. However, during isoflurane anesthesia and mechanical ventilation, calculation using volume kinetic analysis of the variable kr, an elimination factor that, in conscious humans and sheep, is closely related to urinary excretion, represented both urinary excretion and peripheral accumulation of fluid. This suggests that the previous assumption that kr approximates urinary excretion of infused fluid requires modification, i.e., kr simply reflects net fluid movement out of plasma.     

Volume kinetic analysis of the distribution of 0.9% saline in conscious versus isoflurane-anesthetized sheep

BACKGROUND: The distribution and elimination of 0.9% saline given by intravenous infusion has not been compared between the conscious state and during inhalational anesthesia. METHODS: Six adult sheep received an intravenous infusion of 25 ml/kg of 0.9% saline over 20 min in the conscious state and also during isoflurane anesthesia and mechanical ventilation. The distribution and elimination of infused fluid were studied by volume kinetics based on serial analysis of hemoglobin dilution in arterial blood and by mass balance that incorporated volume calculations derived from volume kinetic analysis and measurements of urinary volumes. RESULTS: The mass balance calculations indicated only minor differences in the time course of plasma volume expansion between the conscious and anesthetized states. However, isoflurane anesthesia markedly reduced urinary volume (median, 9 vs. 863 ml; P < 0.03). In conscious sheep, the central and peripheral volume expansion predicted by volume kinetics agreed well with the calculations based on mass balance. However, during isoflurane anesthesia and mechanical ventilation, calculation using volume kinetic analysis of the variable kr, an elimination factor that, in conscious humans and sheep, is closely related to urinary excretion, represented both urinary excretion and peripheral accumulation of fluid. This suggests that the previous assumption that kr approximates urinary excretion of infused fluid requires modification, i.e., kr simply reflects net fluid movement out of plasma. CONCLUSIONS: In both conscious and anesthetized, mechanically ventilated sheep, infusion of 0.9% saline resulted in minimal expansion of plasma volume over a 3-h interval. In conscious sheep, infused 0.9% saline was rapidly eliminated from the plasma volume by urinary excretion; in contrast, the combination of isoflurane anesthesia and mechanical ventilation reduced urinary excretion and promoted peripheral accumulation of fluid.     

Effects of different catecholamines on the dynamics of volume expansion of crystalloid infusion

BACKGROUND: The authors studied the influence of alpha, beta, and dopaminergic catecholamines on blood volume expansion in conscious normovolemic sheep before, during, and after a bolus infusion of a crystalloid. METHODS: A 0.9% NaCl bolus (24 ml/kg in 20 min) was infused in four paired experiments each: no drug, dopamine infusion (50 microg . kg . min), isoproterenol infusion (0.1 microg . kg . min), and phenylephrine infusion (3 microg . kg . min). Blood volume expansion was calculated by the dilution of blood hemoglobin concentration. RESULTS: Dopamine had little effect on peak blood volume expansion (12.7 +/- 0.9 ml/kg) compared with 0.9% NaCl (13.0 +/- 2.7 ml/kg); in contrast, isoproterenol augmented blood volume expansion (18.5 +/- 1.8 ml/kg), and phenylephrine reduced blood volume expansion (8.9 +/- 1.4 ml/kg). Two hours after the 0.9% NaCl bolus, sustained blood volume expansion was greatest in the isoproterenol protocol (12.2 ml/kg), whereas the dopamine protocol (6.8 ml/kg) remained similar to the control protocol (4.1 ml/kg), and the phenylephrine protocol had a net volume loss (-1.9 ml/kg). Some blood volume expansion differences were attributed to changes in renal function as phenylephrine infusion increased urinary output, whereas isoproterenol was associated with antidiuresis. However, dopamine caused diuresis and sustained augmentation of blood volume. CONCLUSION: Catecholamines can alter the intravascular volume expansion of fluid therapy. beta-Receptor (isoproterenol) stimulation augmented blood volume expansion, whereas alpha (phenylephrine) stimulation reduced blood volume expansion. Combined dopaminergic, beta, and possibly alpha stimulation with dopamine augmented blood volume expansion and cardiac output while inducing diuresis.     

Elimination rate constant describing clearance of infused fluid from plasma is independent of large infusion volumes of 0.9% saline in sheep

BACKGROUND: The purpose of this study was to determine the influence of varying large crystalloid infusion volumes, ranging from a volume that has been safely administered to volunteers to a volume that greatly exceeds a practical volume for studies in normovolemic humans, of rapidly infused 0.9% saline on the elimination rate constant in sheep. METHODS: Six sheep underwent three randomly ordered, 20 min, intravenous infusions of 0.9% saline in volumes of 25 ml/kg, 50 ml/kg and 100 ml/kg. Repeated measurements of arterial plasma dilution were analyzed using the volume kinetic approach to determine the apparent volumes of the central (V1) and peripheral (V2) body fluid spaces, the elimination rate constant (kr) describing clearance from the central fluid space and the rate constant (kt) for the diffusion of fluid between the central and the peripheral fluid spaces. The latter constant was split in to two constants, one describing flow out from the central fluid space and one describing flow into the central fluid space. Urinary output was measured in all sheep. RESULTS: kr was comparable at each infused volume (38.3 +/- 4.5, 32.2 +/- 4.2, and 36.7 +/- 7.0 ml/min, respectively, in the 25 ml/kg, 50 ml/kg, and 100 ml/kg protocols). However, for the largest infusion, other kinetic parameters were influenced by the magnitude of the infusion. V2 was significantly increased (P < 0.05) and the area under the dilution-time curve divided by the infused volume was 20% lower for the largest infusion (P < 0.03). Although urinary output increased as the infusion volume increased, only 59% of the administered volume had been excreted at 180 min after the 100 ml/kg infusion as compared with approximately 90% after the other two infusions (P < 0.01). CONCLUSIONS: Elimination from the central fluid space of large, rapidly infused volumes of saline solution is independent of infused volume. Larger volumes are apparently cleared from the central fluid space (V1) by expansion of a peripheral volume (V2) as renal excretion fails to increase in proportion to the volume of infused fluid.     

Albumin extravasation and tissue washout of hyaluronan after plasma volume expansion with crystalloid or hypooncotic colloid solutions

BACKGROUND: Intravascular volume expansion is followed by loss of fluid from the circulation. The extravasation of albumin in this readjustment is insufficiently known. METHODS: Twelve male volunteers participated, each in three separate sessions, in a controlled, randomised, open fashion. They received one of the following: albumin 40 g/L,(7.1 mL/kg, i.e. 500 mL per 70 kg); Ringer's acetate (21.4 mL/kg), or dextran 30 g/L (7.1 mL/kg). The fluids were infused during 30 min and the subjects were followed for 180 min. ECG, arterial oxygen saturation and non-invasive arterial pressure were recorded. Haemoglobin, haematocrit, serum albumin and osmolality, plasma colloid osmotic pressure and hyaluronan concentration were determined in venous samples. RESULTS: The serum albumin concentration decreased (P < 0.05, anova) following Ringer's acetate or dextran, whereas serum osmolality was unchanged in all groups. The colloid osmotic pressure decreased (P < 0.05) after the Ringer solution. The blood volume increase was estimated from the decrease in haemoglobin concentration and did not differ between the three fluids. The cumulated extravasation of albumin was largest following albumin (10.4 +/- 5.4 g, mean +/- SD), less following dextran (5.6 +/- 5.0 g) and negligible in the Ringer group (0.5 +/- 10.0 g; P < 0.05 against albumin). However, the Ringer solution increased the plasma concentration of hyaluronan drastically. CONCLUSIONS: Infusion of hypotonic colloidal solutions entails net loss of albumin from the vascular space. This is not the case after Ringer's acetate. Increased interstitial hydration from the latter fluid is followed by lymphatic wash out of hyaluronan.     

Elimination Rate Constant Describing Clearance of Infused Fluid from Plasma Is Independent of Large Infusion Volumes of 0.9% Saline in Sheep

Background: The purpose of this study was to determine the influence of varying large crystalloid infusion volumes, ranging from a volume that has been safely administered to volunteers to a volume that greatly exceeds a practical volume for studies in normovolemic humans, of rapidly infused 0.9% saline on the elimination rate constant in sheep.

Methods: Six sheep underwent three randomly ordered, 20 min, intravenous infusions of 0.9% saline in volumes of 25 ml/kg, 50 ml/kg and 100 ml/kg. Repeated measurements of arterial plasma dilution were analyzed using the volume kinetic approach to determine the apparent volumes of the central (V1) and peripheral (V2) body fluid spaces, the elimination rate constant (kr) describing clearance from the central fluid space and the rate constant (kt) for the diffusion of fluid between the central and the peripheral fluid spaces. The latter constant was split in to two constants, one describing flow out from the central fluid space and one describing flow into the central fluid space. Urinary output was measured in all sheep.

Results: kr was comparable at each infused volume (38.3 +/- 4.5, 32.2 +/- 4.2, and 36.7 +/- 7.0 ml/min, respectively, in the 25 ml/kg, 50 ml/kg, and 100 ml/kg protocols). However, for the largest infusion, other kinetic parameters were influenced by the magnitude of the infusion. V2 was significantly increased (P < 0.05) and the area under the dilution-time curve divided by the infused volume was 20% lower for the largest infusion (P < 0.03). Although urinary output increased as the infusion volume increased, only 59% of the administered volume had been excreted at 180 min after the 100 ml/kg infusion as compared with approximately 90% after the other two infusions (P < 0.01).     

Urinary excretion as an input variable in volume kinetic analysis of Ringer's solution

The disposition of fluid given by i.v. infusion can be studied by fitting one-volume and two-volume kinetic models to the fractioned dilution of blood haemoglobin and serum albumin concentrations over time. However, the two-volume model is sometimes associated with a high standard error in estimating the size of the secondary (peripheral) body fluid space, V2. To examine if a fixed elimination rate constant (kr) determined by urinary excretion can be used to make the model more stable, we infused Ringer's acetate 25 ml kg-1 over 30 min in 15 male volunteers (mean age 35 yr). A fixed kr increased the total residual error when curve-fitting was applied according to the one-volume model. The two-volume model was improved when there was a strong within- patient covariance between kr and V2 (r2 < or = -0.98). The size of V2 was 10 litre when the fixed and model-generated values of kr agreed fully.      

Hydroxyethyl starch 120, dextran 70 and acetated Ringer''s solution: hemodilution, albumin, colloid osmotic pressure and fluid balance following replacement of blood loss in pigs

Twenty healthy pigs weighing 12-17 kg were anesthetized and the small intestines were exteriorized into saline-moistened gauze. During a 2-h period 4% of the animals' body weight was bled through an arterial cannula in six increments and replaced immediately by the fluid tested: hydroxyethyl starch 120 (HES, Plasmafusin, Orion Corp., Mw 120,000), dextran 70 (DEX) and Ringer's acetate (RA). The amount of fluid infused for replacement of blood loss was equal to the amount of blood withdrawn in the colloid groups but fourfold in the RA group. Five non-bled pigs served as controls. After the hemodilution the laparotomy was closed and the animals received only 5% dextrose (2 ml/kg/min) during a 5-h follow-up period. The synthetic colloids caused a more effective dilution of hemoglobin and albumin than did RA. The colloid osmotic pressure (COP) was well maintained by the plasma substitutes but decreased in the RA group to 64% of the initial values. A stable urinary output and no edema formation was found in the HES and DEX groups. The RA animals were unable to excrete the excess crystalloid, which resulted in a strikingly positive fluid balance persisting throughout the study. Thus, the synthetic colloids were superior to RA in expansion of the plasma volume, maintenance of the COP and prevention of fluid accumulation. The effect of the two colloids was similar except that COP was slightly better maintained during the follow-up period in animals which received HES 120.     

Volume kinetics of Ringer solution after surgery for hip fracture

PURPOSE: To study the time course of volume changes during and after infusion of Ringer's solution in elderly patients after a standardised trauma. METHODS: The kinetics of 12.5 ml.kg-1 Ringer's solution infused over 30 min were studied in ten patients one day after surgery for hip fracture (mean age, 70 yr) and in an age- and sex-matched control group. Hemodilution, as measured every five minutes for 90 min, was used to calculate the size of the fluid space expanded by the fluid (V) and the elimination rate constant (kr). The baseline fluid balance status in the patients and the controls was compared by bioelectrical impedance analysis. RESULTS: The size of V was 4.1 +/- 0.51 (mean +/- SEM) in the patients and 3.4 +/- 0.21 in the controls (P:NS) while the corresponding results for kr were 85 +/- 12 and 166 +/- 27 ml.min-1, respectively (P < 0.04). Bioelectrical impedance analysis showed that the extracellular fluid space and the total body water volumes did not differ between the two groups. Computer simulations based on the data obtained for V and kr indicate that trauma increases the dilution of the plasma volume and the retention of fluid in response to slow and moderate infusion rates, while these indices of short-term changes in fluid balance remain the same in the two groups during very rapid infusion of Ringer's solution. CONCLUSION: A slower elimination rate increased dilution of plasma and retention of fluid when Ringer's solution was infused in elderly trauma patients.     

Effects of Different Catecholamines on the Dynamics of Volume Expansion of Crystalloid Infusion

Background: The authors studied the influence of [alpha], [beta], and dopaminergic catecholamines on blood volume expansion in conscious normovolemic sheep before, during, and after a bolus infusion of a crystalloid.

Methods: A 0.9% NaCl bolus (24 ml/kg in 20 min) was infused in four paired experiments each: no drug, dopamine infusion (50 [mu]g [middle dot] kg-1 [middle dot] min-1), isoproterenol infusion (0.1 [mu]g [middle dot] kg-1 [middle dot] min-1), and phenylephrine infusion (3 [mu]g [middle dot] kg-1 [middle dot] min-1). Blood volume expansion was calculated by the dilution of blood hemoglobin concentration.

Results: Dopamine had little effect on peak blood volume expansion (12.7 +/- 0.9 ml/kg) compared with 0.9% NaCl (13.0 +/- 2.7 ml/kg); in contrast, isoproterenol augmented blood volume expansion (18.5 +/- 1.8 ml/kg), and phenylephrine reduced blood volume expansion (8.9 +/- 1.4 ml/kg). Two hours after the 0.9% NaCl bolus, sustained blood volume expansion was greatest in the isoproterenol protocol (12.2 ml/kg), whereas the dopamine protocol (6.8 ml/kg) remained similar to the control protocol (4.1 ml/kg), and the phenylephrine protocol had a net volume loss (-1.9 ml/kg). Some blood volume expansion differences were attributed to changes in renal function as phenylephrine infusion increased urinary output, whereas isoproterenol was associated with antidiuresis. However, dopamine caused diuresis and sustained augmentation of blood volume.     

Kinetics and Extravascular Retention of Acetated Ringer's Solution during Isoflurane or Propofol Anesthesia for Thyroid Surgery

Background: In sheep, isoflurane causes extravascular accumulation of infused crystalloid fluid. The current study evaluates whether isoflurane has a greater tendency than propofol to cause extravascular retention in surgical patients.

Methods: Thirty patients undergoing thyroid surgery lasting for 143 +/- 32 min (mean +/- SD) received an intravenous infusion of 25 ml/kg acetated Ringer's solution over 30 min. Anesthesia was randomized to consist of isoflurane or propofol supplemented by fentanyl. The distribution and elimination of the infused fluid was estimated using volume kinetics based on the fractional dilution of blood hemoglobin over 150 min. Extravascular retention of infused fluid was taken as the difference between the model-predicted elimination and the urinary excretion. The sodium and fluid balances were measured.

Results: The fractional plasma dilution increased gradually to approximately 30% during the infusion and thereafter remained at 15-20%. Urinary excretion averaged 11% of the infused volume. Mean arterial pressure was 10 mmHg lower in the isoflurane group (P < 0.001). The excess fluid volumes in the central and peripheral functional body fluid spaces were virtually identical in the groups. The sum of water losses by evaporation and extravascular fluid retention amounted to 2.0 +/- 2.5 ml/min for isoflurane and 2.2 +/- 2.1 ml/min for propofol. The sodium balance refuted that major fluid shifts occurred between the extracellular and intracellular spaces.     

Epidural anesthesia, hypotension, and changes in intravascular volume

BACKGROUND: The most common side effect of epidural or spinal anesthesia is hypotension with functional hypovolemia prompting fluid infusions or administration of vasopressors. Short-term studies (20 min) in patients undergoing lumbar epidural anesthesia suggest that plasma volume may increase when hypotension is present, which may have implications for the choice of treatment of hypotension. However, no long-term information or measurements of plasma volumes with or without hypotension after epidural anesthesia are available. METHODS: In 12 healthy volunteers, the authors assessed plasma (125I-albumin) and erythrocyte (51Cr-EDTA) volumes before and 90 min after administration of 10 ml bupivacaine, 0.5%, via a thoracic epidural catheter (T7-T10). After 90 min (t = 90), subjects were randomized to administration of fluid (7 ml/kg hydroxyethyl starch) or a vasopressor (0.2 mg/kg ephedrine), and 40 min later (t = 130), plasma and erythrocyte volumes were measured. At the same time points, mean corpuscular volume and hematocrit were measured. Systolic and diastolic blood pressure, heart rate, and hemoglobin were measured every 5 min throughout the study. Volume kinetic analysis was performed for the volunteers receiving hydroxyethyl starch. RESULTS: Plasma volume did not change per se after thoracic epidural anesthesia despite a decrease in blood pressure. Plasma volume increased with fluid administration but remained unchanged with vasopressors despite that both treatments had similar hemodynamic effects. Hemoglobin concentrations were not significantly altered by the epidural blockade or ephedrine administration but decreased significantly after hydroxyethyl starch administration. Volume kinetic analysis showed that the infused fluid expanded a rather small volume, approximately 1.5 l. The elimination constant was 56 ml/min. CONCLUSIONS: Thoracic epidural anesthesia per se does not lead to changes in blood volumes despite a reduction in blood pressure. When fluid is infused, there is a dilution, and the fluid initially seems to be located centrally. Because administration of hydroxyethyl starch and ephedrine has similar hemodynamic effects, the latter may be preferred in patients with cardiopulmonary diseases in which perioperative fluid overload is undesirable.     

The effect of acetate ringer solution, 6% hydroxyethyl starch saline and 20% mannitol solution on the serum concentration of propofol continuously infused

Changes in serum concentrations of propofol after administration of three different fluids were investigated in 42 scheduled surgical patients. Anesthesia was induced with propofol 2 mg.kg-1 and maintained with constant rate infusion of propofol 6 mg.kg-1.hr-1. After achieving a stable depth of anesthesia, 5 ml.kg-1 of acetate Ringer's solution, 6% hydroxyethyl starch saline solution or 20% mannitol solution was infused in 15 minutes. Blood samples each 2 ml were taken before and 0, 5, 15, 30 and 60 minutes after fluid treatment. We measured hemoglobin and hematocrit of the samples for calculating the dilution rate of the plasma with infusion treatment, and determined the serum concentration of propofol by HPLC-spectrofluorometry. After administration of each fluid, the serum concentrations of propofol decreased significantly to 17 +/- 15, 25 +/- 10 and 35 +/- 8%, respectively (mean +/- SEM). The dilution rate of the plasma from the fractional change in blood hemoglobin increased to 0.08 +/- 0.02, 0.24 +/- 0.03, and 0.36 +/- 0.03, respectively. Administration of mannitol might markedly increase distribution volume of propofol, and this can be attributed to osmotic action of mannitol and resultant expansion of extracellular fluid volume. The results of the present investigation suggest that this pharmacokinetic change decreased the concentration of propofol more significantly in mannitol treatment patients than in Ringer's solution or 6% hydroxyethyl starch saline treatment patients.     

Postoperative complications after blood replacement with or without plasma. A trial in elective surgery

A prospective, controlled and randomized study of 275 patients undergoing major surgery was performed to investigate if postoperative complications were influenced by restrictive use of plasma to replace operative blood loss. All patients were given 6% dextran (Macrodex) for thromboprophylaxis and haemodilution. The "Dextran Group" received equal amounts of 6% dextran and electrolyte solution as substitution for plasma loss. The need for red-cell transfusion (60% suspension in saline-adenine-glucose-mannitol storage medium) averaged 5.8 units in this group and 5.2 in the "Plasma Group". The respective mean totals of infused plasma and dextran were 400 ml and 1,383 ml in the Dextran Group, compared with 1,099 and 619 ml in the Plasma Group. The mean total electrolyte infusion in the first postoperative week was c. 7,500 ml in both groups. Serum albumin decreased considerably in both groups, but significantly more in the Dextran Group. The incidence and pattern of postoperative complications were similar in both groups. When blood loss is up to 50-60% of the total volume, Macrodex can be used in preference to plasma, unless administration of plasma protein is specifically indicated.     

Kinetics and extravascular retention of acetated ringer's solution during isoflurane or propofol anesthesia for thyroid surgery

BACKGROUND: In sheep, isoflurane causes extravascular accumulation of infused crystalloid fluid. The current study evaluates whether isoflurane has a greater tendency than propofol to cause extravascular retention in surgical patients. METHODS: Thirty patients undergoing thyroid surgery lasting for 143 +/- 32 min (mean +/- SD) received an intravenous infusion of 25 ml/kg acetated Ringer's solution over 30 min. Anesthesia was randomized to consist of isoflurane or propofol supplemented by fentanyl. The distribution and elimination of the infused fluid was estimated using volume kinetics based on the fractional dilution of blood hemoglobin over 150 min. Extravascular retention of infused fluid was taken as the difference between the model-predicted elimination and the urinary excretion. The sodium and fluid balances were measured. RESULTS: The fractional plasma dilution increased gradually to approximately 30% during the infusion and thereafter remained at 15-20%. Urinary excretion averaged 11% of the infused volume. Mean arterial pressure was 10 mmHg lower in the isoflurane group (P < 0.001). The excess fluid volumes in the central and peripheral functional body fluid spaces were virtually identical in the groups. The sum of water losses by evaporation and extravascular fluid retention amounted to 2.0 +/- 2.5 ml/min for isoflurane and 2.2 +/- 2.1 ml/min for propofol. The sodium balance refuted that major fluid shifts occurred between the extracellular and intracellular spaces. CONCLUSIONS: The amount of evaporation and extravascular retention of fluid was small during thyroid surgery, irrespective of whether anesthesia was maintained by isoflurane or propofol.     

Influence of Liberal versus Restrictive Intraoperative Fluid Administration on Elimination of a Postoperative Fluid Load

Background: Previously, the authors found "liberal" fluid administration (approximately 3 l Ringer's lactate [RL]) to improve early rehabilitation after laparoscopic cholecystectomy, suggesting functional hypovolemia to be present in patients receiving "restrictive" fluid administration (approximately 1 l RL). Because volume kinetic analysis after a volume load may distinguish between hypovolemic versus normovolemic states, the authors applied volume kinetic analysis after laparoscopic cholecystectomy to explain the difference in outcome between 3 and 1 l RL.

Methods: In a prospective, nonrandomized trial, the authors studied 20 patients undergoing laparoscopic cholecystectomy. Ten patients received 15 ml/kg RL (group 1) and 10 patients received 40 ml/kg RL (group 2) intraoperatively. All other aspects of perioperative management were standardized. A 12.5-ml/kg RL volume load was infused preoperatively and 4 h postoperatively. The distribution and elimination of the fluid load was estimated using volume kinetic analysis.

Results: Patient baseline demographics and intraoperative data did not differ between groups, except for intraoperative RL, having a median of 1,118 ml (range, 900-1,400 ml) in group 1 compared with a median of 2,960 ml (range, 2,000-3,960 ml) in group 2 (P < 0.01). There were no significant preoperative versus postoperative differences in the size of the body fluid space expanded by infused fluid (V), whereas the clearance constant kr was higher postoperatively versus preoperatively (P = 0.03). The preoperative versus postoperative changes in volume kinetics including V were not different between the two groups.     

Influence of "liberal" versus "restrictive" intraoperative fluid administration on elimination of a postoperative fluid load

BACKGROUND: Previously, the authors found "liberal" fluid administration (approximately 3 l Ringer's lactate [RL]) to improve early rehabilitation after laparoscopic cholecystectomy, suggesting functional hypovolemia to be present in patients receiving "restrictive" fluid administration (approximately 1 l RL). Because volume kinetic analysis after a volume load may distinguish between hypovolemic versus normovolemic states, the authors applied volume kinetic analysis after laparoscopic cholecystectomy to explain the difference in outcome between 3 and 1 l RL. METHODS: In a prospective, nonrandomized trial, the authors studied 20 patients undergoing laparoscopic cholecystectomy. Ten patients received 15 ml/kg RL (group 1) and 10 patients received 40 ml/kg RL (group 2) intraoperatively. All other aspects of perioperative management were standardized. A 12.5-ml/kg RL volume load was infused preoperatively and 4 h postoperatively. The distribution and elimination of the fluid load was estimated using volume kinetic analysis. RESULTS: Patient baseline demographics and intraoperative data did not differ between groups, except for intraoperative RL, having a median of 1,118 ml (range, 900-1,400 ml) in group 1 compared with a median of 2,960 ml (range, 2,000-3,960 ml) in group 2 (P<0.01). There were no significant preoperative versus postoperative differences in the size of the body fluid space expanded by infused fluid (V), whereas the clearance constant kr was higher postoperatively versus preoperatively (P=0.03). The preoperative versus postoperative changes in volume kinetics including V were not different between the two groups. CONCLUSIONS: Elimination of an intravenous fluid load was increased after laparoscopic cholecystectomy per se but not influenced by the amount of intraoperative fluid administration.     

Bolus injection of Ringer's solution and dextran 1 kDa during induction of spinal anesthesia

BACKGROUND: Arterial hypotension following induction of spinal anesthesia is difficult to prevent with infusion fluids. In a randomized, unblinded and controlled study we evaluated whether a rapid fluid administration planned according to volume kinetic analysis is followed by a more stable blood pressure. METHODS: Spinal anesthesia was induced in 75 surgical patients, using one of three different fluid regimens: intravenous 'bolus injection' of 5 ml kg(-1) of Ringer's acetate over 3 min, 2 ml kg(-1) of low-molecular weight (1 kDa) dextran over 3 min, or a constant-rate infusion of 15 ml kg(-1) of Ringer's acetate over 40 min (controls). The kinetics of the fluid was studied in five patients in each group and also in eight volunteers. RESULTS: The decrease in mean arterial pressure averaged 28%, 27% and 26%, respectively, and was fully developed 16 min after the induction. The height of the block, but not the fluid programme, correlated with the hypotension. Nausea or near-fainting associated with marked hypotension or bradycardia was recorded in none, five (20%) and two (8%) of the patients, respectively. Both bolus injections were followed by translocation of fluid from the peripheral tissues to the bloodstream, which maintained the plasma dilution at about 10% for at least 30 min until surgery began. CONCLUSION: A brisk infusion of Ringer's solution or dextran 1 kDa over 3 min was followed by the same decrease in arterial pressure as a longer and 3-5-times larger infusion of Ringer's solution over 40 min during induction of spinal anesthesia.