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BACKGROUND: Hypotension associated with spinal anesthesia for cesarean section is still a clinical problem. Colloid solutions seem preferable to crystalloid solutions for preloading. In most studies the overall rate of hypotension is reported. Few studies have, however, investigated the maternal and neonatal consequences of different levels of maternal hypotension. METHODS: In this randomized, double-blinded study 110 patients presenting for elective cesarean section received either 1000 ml acetated Ringer's solution or 1000 ml 3% dextran 60 solution immediately before spinal anesthesia. The effect on overall hypotension, clinically significant hypotension (hypotension associated with maternal discomfort defined as nausea, retching/vomiting, dizziness or chest symptoms) and severe hypotension (systolic arterial pressure <80 mmHg) was studied. RESULTS: Dextran reduced the incidence of overall hypotension from 85 to 66% (P=0.03), reduced the incidence of clinically significant hypotension from 60 to 30% (P=0.002) and reduced the incidence of severe hypotension from 23 to 3.6% (P=0.004) compared to Ringer's solution. There were neither differences in neonatal outcome between treatment groups nor between neonates grouped after severity of maternal hypotension. CONCLUSION: Clinically significant hypotension seems to be a more suitable outcome variable than overall hypotension. The protective effect of the colloid solution increased with increased severity of hypotension.

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OBJECTIVE: To assess the accuracy of the diffusible indicators heavy water and thermal indicator in the measurement of extravascular lung water (EVLW). DESIGN: Cardiac output (CO), mean transit time and EVLW for the two diffusible indicators were measured. CO for indocyanine green, gravimetric EVLW and the calculated mean transit time for a diffusible indicator were used as independent reference variables. CO, mean transit time and EVLW for the two diffusible indicators were compared to the reference variables and the percentage error for each measured variable was calculated for each bolus injection. SETTING: 6 sheep with healthy lungs and 6 with pulmonary oedema in a research laboratory. INTERVENTIONS: CO was altered with positive end-expiratory pressure and dobutamine. MEASUREMENTS: All indicators were given together in a bolus through a central venous line. Indicators were detected simultaneously in the aorta, and CO, mean transit time and EVLW were measured. EVLW was measured gravimetrically (EVLWgrav) postmortem. RESULTS: In the combination of a low CO and a large distribution volume, heavy water and thermal indicator produced a large number of slow wash-out curves. These curves were abolished from further analysis. The mean errors in CO and mean transit time for heavy water were close to zero and independent of the distribution volume; the product EVLW was close to EVLWgrav. The mean error in thermodilution CO measured in the aorta was close to zero but dependent on the distribution volume. The mean error in mean transit time for the thermal indicator was 36% and dependent on the distribution volume. Their product EVLW overestimated EVLWgrav by 70%. CONCLUSIONS: The results obtained for heavy water confirmed the theoretical basis of the indicator dilution method. The mean transit time for the thermal indicator was not proportionate to its distribution volume. The magnitude of this error prevents the calculation of an anatomically defined EVLW using a catheter-mounted thermistor in the aorta.

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1. This study aimed at enhancing the clearance of experimental hydrostatic pulmonary oedema in dogs using hypertonic-hyperoncotic solution (HHS) and furosemide. 2. Anaesthetized dogs (n = 20) were mechanically ventilated with a positive end-expiratory pressure of 10 cmH2O (1.0 kPa). 3. Hydrostatic pulmonary oedema was induced by inflating a balloon inserted into the left atrium and simultaneously infusing isotonic saline rapidly. Oedema formation was terminated by deflating the balloon and reducing the infusion rate. 4. Four groups were studied: A, control; B, furosemide; C, HHS and D, HHS+furosemide. HHS, 6 ml kg-1, was given as a bolus injection and furosemide, 1 mg kg-1, intravenously as a bolus followed by an infusion of 0.5 mg kg-1 h-1. All dogs were studied for 4 h. 5. Serum osmolarity, plasma colloid oncotic pressure and diuresis in groups C and D (HHS groups) substantially increased; haemoglobin concentration decreased and pulmonary arterial wedge pressure remained constant. 6. Despite the combination of these factors favouring fluid flux from the extravascular to the intravascular compartment, extravascular lung water measured with the double indicator dilution technique decreased no faster in the HHS groups than in the two other groups (from over 26 to approximately 19 ml kg-1 in groups A, C and D and to 14.7 in group B (only furosemide)). 7. This was confirmed by postmortem gravimetric measurements of extravascular lung water; A, 11.0 +/- 5.7; B, 9.7 +/- 3.3; C, 10.5 +/- 3.1 and D, 10.6 +/- 1.8 g kg-1. 8. We speculate that mechanisms other than effective Starling gradients and enhanced diuresis might define a maximal rate of pulmonary oedema clearance.

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The study aimed to establish whether furosemide given intravenously improved resorption of hydrostatic pulmonary oedema in 14 dogs mechanically ventilated with positive end-expiratory pressure (PEEP). Hydrostatic pulmonary oedema was created by simultaneous inflation of a left atrial balloon and rapid intravenous infusion of isotonic saline. The hydrostatic process was terminated by deflating the balloon and reducing the infusion rate. A PEEP of 10 cmH2O (1.0 kPa) was applied in all animals; in seven, furosemide was administered (diuretic group), 1 mg/kg intravenously as a bolus followed by an infusion of 0.5 mg/kg per hour, while the remaining seven dogs served as a control group. All dogs were studied for a period of 4 h. The extravascular lung water measured with the double indicator dilution technique was 28.3 +/- 3.8 (diuretic group) and 28.2 +/- 6.8 ml/kg (control group) during maximum oedema. It was reduced to 16.4 +/- 2.2 (diuretic group) vs 19.8 +/- 3.7 ml/kg (control group) after 4 h of resorption, P less than 0.05. Postmortem gravimetric values of extravascular lung water were 9.1 +/- 3.4 (diuretic group) vs 12.6 +/- 5.0 g/kg (control group). In the diuretic group the urinary output increased threefold, and haemoglobin and serum protein concentrations were higher than in the control group. There was a significantly greater decrease in cardiac output and central blood volume in the diuretic group. In conclusion, furosemide given intravenously improved lung fluid resorption in hydrostatic pulmonary oedema, probably by increasing the plasma colloid osmotic pressure.

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The reliability of the double-indicator dilution technique (dye/cold) for measuring extravascular lung water (EVLW) has been studied in lung-healthy dogs after pleural fluid injection of saline (up to 20 ml/kg) during mechanical ventilation at zero and 10 cmH2O (1.0 kPa) end-expiratory pressure (ZEEP and PEEP, respectively). Pleural fluid injection had no effect on EVLW at either ZEEP or PEEP. PEEP induced changes in cardiac output, and reduced both the intravascular (dye) and the thermal indicator volumes, but with no effect on the calculated EVLW. It is concluded that pleural fluid up to 20 ml/kg and ventilation with PEEP of 10 cmH2O (1.0 kPa) do not affect the reliability of the double-indicator dilution technique for measuring extravascular lung water in the dog.

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