In the late 1960s, Wollman and Marx outlined the importance of fluid infusion to oppose the relative hypovolemia induced by spinal anesthesia.1 Since then, various fluid regimes have been proposed, but the results of the studies investigating the effects of prehydration on the incidence of hypotension after spinal anesthesia are not consistent. Some investigators reported beneficial effects or no effect of prehydration,2,3 whereas others described deleterious effects of prehydration with crystalloids, including pulmonary edema, tissue edema, and changes in the colloid osmotic pressure.4 Previous investigations have focused on the effect of prehydration on arterial blood pressure; data on the effect of hydration administered after the spinal block on the cardiac output (CO) are scarce. The effect of Trendelenburg position on preventing the hypotension after spinal anesthesia has also been studied by Miyabe et al.,5,6 who concluded that the Trendelenburg position could not prevent the decrease in systolic blood pressure (SAP) after spinal block. However, the effects of the Trendelenburg position after spinal anesthesia on CO have not been studied. In this study, we compared the effects of 3 different modes of increasing preload–Trendelenburg position, the infusion of 6% hydroxyethyl starch solution and the infusion of lactated Ringer’s solution–initiated immediately after spinal anesthesia, on changes in hemodynamics after spinal anesthesia, with CO as the primary outcome variable.
We studied 70 ASA class I-II patients older than 50 yr, scheduled for orthopedic hip or knee replacement surgery under spinal anesthesia. The study was approved by the National Medical Ethics Committee. Informed consent was obtained from each patient.
The patients fasted overnight. Premedication consisted of oral diazepam 10 mg 1 h before surgery. After arriving in the operating room, an IV line was placed and the patient was placed in the lateral position. Lumbar puncture was performed with a 25-gauge Sprotte needle at the L2–3 interspace, using the paramedian approach. Three milliliters of 0.5% plain bupivacaine (Marcaine 0.5% plain; Astra, Sodertalje, Sweden) was injected within 15 s with the needle aperture oriented in a cephalad direction. Patients were allocated randomly using a random number generator to one of the three treatment groups. In the Trendelenburg group, the patients were placed in the 15° head-down Trendelenburg position immediately after spinal anesthesia for 10 min, and then placed back in the horizontal position for immediate infusion of lactated Ringer’s solution (1000 mL within the next 20 min). In the hydroxyethyl starch group, the patients received 500 mL of 6% hydroxyethyl starch solution over 20 min starting immediately after spinal anesthesia. In the lactated Ringer’s group, the patients received 1000 mL of lactated Ringer’s solution over 20 min starting immediately after spinal anesthesia.
Hemodynamic measurements were started 5 min after placing the patient in the lateral position. The hemodynamic measurements were recorded for 45 min (for 15 min before and 30 min after the injection of the local anesthetic solution). CO was measured with the impedance cardiography method (NCCOM3; BoMed Medical Manufacturing, Irvine, CA). Data were recorded continuously and stored in an IBM-compatible computer. For data analysis and graphic presentation, CO data were averaged over 1 min intervals. Diastolic blood pressure (DAP) and SAP were measured every 2.5 min with an automated device (BCI 6004 monitor; BCI International, Waukesha, WI). Mean arterial blood pressure (MAP) (mm Hg) was calculated as follows:
Systemic vascular resistance (SVR) (in dynes · s · cm−5) was calculated as follows:
Level of sensory blockade was assessed by a blinded observer using a sponge immersed in ice-cold alcohol 30 min after the injection of the local anesthetic. Hypotension was defined as a decrease in SAP to ≤90 mm Hg or ≤70% of baseline and was treated with 5 mg of ephedrine IV Bradycardia was defined as heart rate slower than 55 bpm and was treated with 1 mg of atropine IV Complications including bradycardia and/or hypotension were recorded and treated according to the protocol.
Data were analyzed with the SPSS 12. Demographic data and baseline values were compared with one-way analysis of variance, the Kruskal Wallis test, and χ2 where appropriate. The analysis of variance for repeated measurements with Bonferroni correction was done to compare the hemodynamic effects among the three groups and to compare the hemodynamic data after spinal anesthesia with baseline values. P < 0.05 was considered statistically significant.
Sample size calculation to detect a difference in CO of 1 L/min (sd 1.3 L/min) among treatment groups with a probability level of 0.05 and a power of 0.80 yielded a sample size of 21 patients for each treatment group.
We randomized 73 patients. Three patients were excluded from data analysis due to a poor impedance signal, making it impossible to measure CO. Therefore, 70 patients were included in the analysis. There were no significant differences among the groups with respect to demographic data and the baseline hemodynamics, duration of surgery and the level of sensory block (Table 1).
There were no significant differences in CO among the groups (Table 2). In the Trendelenburg group, CO did not change while the patients were in the Trendelenburg position but increased significantly 20 (P = 0.04) and 30 min (P < 0.001) after the block compared to baseline (Table 2). In the hydroxyethyl starch group, CO increased significantly 10 min after the block (P = 0.001) and remained significantly increased until the end of measurements (30 min after the block P = 0.001) (Table 2). In the lactated Ringer’s group, CO increased significantly 10 (P < 0.001), 20 (P < 0.001), and 30 min (P = 0.013) after the block with respect to the values immediately before the block. In the period from the 20th to the 30th min after spinal anesthesia, CO statistically significantly decreased in the lactated Ringer’s group (P < 0.001) (Table 2).
In all 3 treatment groups, SAP decreased after the block with respect to baseline. SAP was significantly higher 10 (P = 0.025) and 20 min (P = 0.023) after the block in the lactated Ringer’s group in comparison with the Trendelenburg group (Table 2). MAP also significantly decreased after the block with respect to baseline values in all 3 treatment groups (P < 0.05) (Table 2). After the block, MAP was significantly higher in the lactated Ringer’s group in comparison with the Trendelenburg Group 10 (P = 0.032), 20 (P = 0.01), and 30 (P = 0.04) min after the spinal block (Table 2).
In all 3 groups, the SVR decreased significantly 10 (P < 0.001), 20 (P < 0.001), and 30 (P < 0.01) min after the spinal block compared to baseline (Table 2). In the lactated Ringer’s group, there was a significant increase in SVR from the 20th to the 30th min after the block (P < 0.05). Thirty minutes after the block there was a significant difference in SVR between Trendelenburg and lactated Ringer’s group (P = 0.009).
The time course of percent change in CO is shown in Figure 1. There was a statistically significant difference in percentage of change in CO between the Trendelenburg group and the lactated Ringer’s Group 10 min after spinal block (P = 0.01). The other differences among the three treatment groups in the percent of change in CO were not statistically significant. There was a statistically significant increase in percent of change in CO both 20 and 30 min after the block in all 3 groups (P < 0.01). Ten minutes after the block the percent of change in CO significantly increased only in the hydroxyethyl starch group (P = 0.001) and lactated Ringer’s group (P < 0.001), but not in the Trendelenburg group. In the period from the 20th to the 30th min after spinal anesthesia, the percent of change in CO statistically significantly decreased in the lactated Ringer’s group (P < 0.001). Fourteen patients developed complications (Table 3). There were no significant differences among groups.
We studied the influence of three different modes of increasing preload after spinal anesthesia on changes in hemodynamics, with CO as the primary outcome variable. CO was measured noninvasively with impedance cardiography. Although the absolute value of CO measured with the impedance cardiography method is controversial, its value for monitoring the trends of CO change has been accepted by most researchers.7–9 Since the method is noninvasive, it is often used to follow the trend in CO in spontaneously breathing, low-risk patients during spinal anesthesia in which invasive methods are ethically rarely justified.10,11 In studies comparing different drugs or measures that influence CO, comparing the trend in CO change among the study groups gives us more important information about the differences among the study groups than the comparison of absolute values. In addition, in our opinion, noninvasive measurement should always be favored in research if it provides the information we are searching for. In our study, the impedance cardiography method was also used as a trend monitor to noninvasively follow the trend in CO change after three different measures of preventing the decrease in CO after spinal anesthesia.
Few previous studies have evaluated the effect of preloading on CO. Casati et al.2 found that unilateral spinal anesthesia, performed with minimal doses of hyperbaric bupivacaine, resulted in a reduction in stroke volume and cardiac index in patients who did not receive crystalloid preload before spinal puncture. Marhofer et al.12 showed in elderly ASA 3 patients that the hypotension during spinal anesthesia was caused by a decrease in SVR index, but cardiac index did not change. They also observed a prophylactic effect of colloid solutions in attenuating “spinal anesthesia-induced” hypotension.
We studied the influence of three different fluid regimens on changes in CO after spinal anesthesia. The study has shown that the infusion of 1000 mL of lactated Ringer’s solution, 500 mL of 6% hydroxyethyl starch solution, and placing the patient in the Trendelenburg position after spinal block prevent the decrease of CO after spinal anesthesia. The changes in CO among the three study groups were not significant. However, the time course changes in CO were significant. In the lactated Ringer’s group and in the hydroxyethyl starch group, CO significantly increased with respect to the values immediately before the block. Kamenik and Eržen11 showed that CO decreased after spinal anesthesia in their group of patients who did not receive crystalloids as well as in the group of patients who received crystalloids before spinal anesthesia, whereas CO increased in the group of patients who received lactated Ringer’s solution at the time of spinal block. Our results are consistent with their work. We found that the infusion of 1000 mL of lactated Ringer’s solution and 500 mL of 6% hydroxyethyl starch solution, given at the time of spinal block, actually increased CO while the infusion was running. In addition, after stopping the infusion of 6% hydroxyethyl starch solution, CO remained significantly increased until the end of measurements. In the Trendelenburg group, CO did not change according to the value obtained immediately before the spinal block. By placing the patients in the 15° Trendelenburg position, we cannot increase CO after spinal anesthesia, but we can maintain CO at the value immediately before the block.
In our study, SAP and MAP decreased significantly after spinal anesthesia in all three treatment groups. In the lactated Ringer’s group, SAP was significantly higher as compared to the Trendelenburg Group 10 and 20 min after the block. Also, MAP was significantly higher in the lactated Ringer’s group compared to the Trendelenburg Group 10, 20, and 30 min after the block. These results show that, although by placing the patients in the Trendelenburg position we could prevent a decrease in CO, this group of patients was at higher risk of developing hypotension in comparison with the groups receiving volume infusion.
In our study, 11 patients (16%) became hypotensive. Buggy et al.,13 who defined hypotension accordingly, showed that regardless of prehydration (or type of solution administered), a high incidence of hypotension follows spinal anesthesia in normovolemic elderly patients undergoing elective procedures. In their study, the overall incidence of spinal anesthesia-induced hypotension was 49%, ranging from 39% in the colloid group to 62% in the crystalloid group. Donati et al.14 showed that prehydrating patients with colloids decreased the incidence of hypotension, but did not prevent the decrease of MAP. An important observation in our study was that moving patients from the Trendelenburg position back to the supine position can be hazardous. Although we can prevent the decrease in CO after spinal anesthesia by placing patients in the Trendelenburg position, all the adverse events in the Trendelenburg group happened just after placing the patients back in the supine position.
One possible way to decrease the hemodynamic effects of spinal anesthesia in our study would have been to use a lower dose of local anesthetic as shown by Asehnoune et al.9 We used 3 mL of 0.5% bupivacaine for spinal anesthesia. We decided to use this dose of local anesthetic because of the relatively long time period between the spinal puncture and the end of the surgical procedure, which was about 150 min.
In conclusion, Trendelenburg position, infusion of 6% hydroxyethyl starch solution or infusion of lactated Ringer’s solution, each prevented a decrease of CO from baseline after spinal anesthesia. Infusion of lactated Ringer’s solution and 6% hydroxyethyl starch solution immediately after spinal anesthesia not only prevents a decrease, but actually increases CO during the period of development of sympathetic block after spinal anesthesia. While the effects of the infusion of the lactated Ringer’s solution on CO are only transient, the effects of the infusion of 6% hydroxyethyl starch solution are extended throughout the study period (30 min after spinal block). Since the measurements in our study were terminated 30 min after spinal block, we do not know how long the effects of the infusion of 6% hydroxyethyl starch solution on CO would last during an operative procedure. Further studies are necessary to evaluate the duration of the effects of the infusion of colloids on CO and to evaluate the value of different colloids in maintaining CO after spinal anesthesia.
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© 2009 International Anesthesia Research Society
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