Both groups had similar preinduction SBP and heart rates (HR). However, after spinal anesthesia minimum SBP was significantly lower and maximum HR higher in the LR group Table 2. Also, the incidence of hypotension was significantly higher in Group LR than in Group H and hypotension occurred earlier in Group LR Table 2; Figure 1. When only the first 15 min after spinal anesthesia are considered, the difference in the incidence of hypotension was even greater (Group LR 85% vs Group H 35%; P < 0.003). Group LR required more doses of ephedrine Table 2 indicating more recurrent episodes of hypotension. There was also a trend for group LR to receive a larger volume of additional IV fluid before delivery, but this difference was not significant Table 2.
Although mean SBP values were higher and mean HR values lower in Group H throughout the study Figure 1, repeated-measures analysis of variance did not demonstrate a significant difference between the groups. This is probably because patients were excluded from analysis when they received additional ephedrine. Thus, the patients with the greatest hemodynamic instability were not represented in ongoing comparisons of blood pressure and pulse over time.
Nausea after induction of spinal anesthesia was a minor problem and occurred with similar frequency in both groups. Only three patients in each group reported any nausea at 10 min, and only one in each group had a nausea score of 3 at any time. Nausea, when it occurred, was only transient. Neonatal outcome was excellent and similar in both groups Table 3. Only one neonate in each group had a 1-min Apgar score less than 7, and none had a 5-min score less than 7. Arterial and venous umbilical cord blood gases did not reveal significant acidosis in any neonate, and there were no differences between the groups in mean values Table 3. When neonates were grouped as to whether their mothers were hypotensive, there were also no differences in the umbilical cord blood gases.
In this study, patients receiving hetastarch had a lower incidence of hypotension and a lower HR after spinal anesthesia than those receiving only crystalloid. This is consistent with the findings of others who have compared colloid and crystalloid fluid administration prior to spinal anesthesia. Malthru et al.  found no hypotension (defined as systolic blood pressure less than 100 mm Hg) when patients received 15 mL/kg of 5% albumin prior to spinal anesthesia for cesarean section. The control group, which received 15 mL/kg of 5% dextrose in LR, had a 29% incidence of hypotension. In males having spinal anesthesia for transurethral resection of the prostate, Baraka et al.  reported an 11% incidence of hypotension after administration of 7 mL/kg of 3% gelatin compared with 52% after the same volume of crystalloid. In a preliminary report, Sharma et al.  recently observed that patients given 500 mL of hetastarch had a 21% incidence of hypotension after spinal anesthesia with lidocaine for postpartum tubal ligation compared to a 55% incidence in patients given 1000 mL of LR.
The more stable hemodynamic status observed after colloid administration probably relates to their remaining in the intravascular compartment longer than crystalloids. Extravascular redistribution of crystalloids may be so rapid that it may be impossible to infuse them fast enough to maintain intravascular volume and avoid hypotension during spinal anesthesia . Colloid solutions contain large molecules that do not immediately redistribute throughout the extracellular fluid compartment. Therefore, they should not decrease plasma colloid oncotic pressure (COP) as much as crystalloid solutions and intravascular volume should be better maintained [10,11]. Wennberg et al.  reported that COP decreased by only 1.7 mm Hg after preloading with 3% dextran 70 before epidural anesthesia for cesarean section, compared with a 5.6 mm Hg decrease after preloading with LR. In the same study population, Ramanathan et al.  found that a preload of 5% albumin given with LR decreased COP by 2 mm Hg compared with a 4-mm Hg decrease after LR alone; preloading with 25% albumin and LR actually increased COP by 2 mm Hg.
In addition to helping prevent hypotension, maintaining a higher plasma COP should result in less tissue edema provided capillary permeability remains normal. Although Wennberg et al.  found less lung water after dextran as compared with LR, Ramanathan et al.  found no differences in the aveolar-arterial oxygen difference or pulmonary morbidity (incidence of cough, rales, and fever) between parturients receiving colloids versus those receiving crystalloid. However, as patients in the latter study were young, healthy women, it is questionable whether significant pulmonary pathology would have been expected after a 2-L fluid load.
The incidence of hypotension in both groups in the current study was higher than in other studies of spinal anesthesia for cesarean section. For example Malthru et al.  reported no hypotension after colloid infusion, whereas we had an incidence of 45%. This may be a result of the larger colloid volume (1 L of albumin) used by Malthru et al. compared with the 500 mL hetastarch we administered. Rout et al.  reported a 43% incidence of hypotension in patients preloaded with only 20 mL/kg of crystalloid, whereas our LR group received a 30-mL/kg preload, yet had an 85% incidence of hypotension. In Rout et al.'s study  patients who received no fluid had a 71% incidence of hypotension, a lower incidence than in our patients who received a large crystalloid administration. There may be several reasons for the higher incidence of hypotension in the current study. First, opioids were not added to the local anesthetic in either of the other two studies. We added both morphine and fentanyl, which may increase the incidence of hypotension . Second, we used a larger dose of local anesthetic (hyperbaric bupivacaine 12 mg) than did Rout et al.  (isobaric bupivacaine 7.5 mg) or Malthru et al.  (hyperbaric tetracaine 6-8 mg). The larger local anesthetic dose might be expected to cause a higher block and a more extensive sympathectomy than smaller doses. In support of this hypothesis, our patients had a higher average sensory block level than did those in Malthru et al's study  (T3-4 vs T6-8, respectively). However, Rout et al.  reported similar sensory block levels to ours. A third hypothesis to explain our higher incidence of hypotension is that the relatively large preload given our LR group may, paradoxically, have caused more hypotension. Although most studies [12,14,15] have demonstrated less hypotension after crystalloid before spinal anesthesia, Carvalho et al.  found a greater incidence of hypotension after volume loading with a 20 mL/kg vs a 10 mL/kg preload of LR. They postulated that the larger fluid load diluted plasma proteins, lowering COP to a greater extent than the smaller volume, resulting in greater extravasation of fluid into the extracellular fluid compartment. Finally, definitions of hypotension varied among the different studies, so that it may be inappropriate to directly compare their incidences of hypotension.
Despite a significant difference in the incidence and severity of hypotension in the LR group, neonatal outcome was uniformly good in both groups. This reflects the experience that transient decreases in blood pressure, rapidly treated with ephedrine, do not usually affect fetal acid-base status [17,18]. Although in parturients nausea often accompanies hypotension, the incidence in this study was very low. Few hypotensive patients became nauseated, and this was unaffected by the type of fluid preload. The metoclopramide given preoperatively and the prophylactic ephedrine probably played a major role in preventing nausea and vomiting .
No adverse reactions to hetastarch occurred in this study and no serious reactions have occurred during several years of routine use in our obstetric service. Although the incidence of allergic reactions with artificial colloids can be high, severe anaphylactic or anaphylactoid reactions have been rare with hetastarch [one case in 16,405 infusions ]. Thus, we believe that it is safe to use hetastarch on a routine basis.
Although hetastarch is cheaper than albumin ($50 versus $67 for 500 mL), it is still much more expensive than LR ($1 per L). Considering that neonatal outcome was similar in both the crystalloid and colloid groups, is it appropriate to use hetastarch routinely instead of crystalloid alone as a preload before spinal anesthesia for cesarean section? It is not likely that clinical trials with small sample sizes will demonstrate outcome differences between patients preloaded with colloid versus crystalloid, nor is it likely that a large, multicenter clinical trial will be conducted to answer this question. However, it is well known that prolonged or severe maternal hypotension can cause serious adverse fetal and neonatal effects . Furthermore, spinal anesthesia can cause profound hypotension and bradycardia which on occasion has resulted in death . The incidence or severity of such life-threatening events might conceivably be reduced by the routine use of colloid preloads. As hypotension carries potentially serious consequences for both the mother and fetus, we believe that, despite its cost, hetastarch is warranted in this circumstance.
1. McCrae AF, Wildsmith JAW. Prevention and treatment of hypotension during central neural block. Br J Anaesth 1993;70:672-80.
2. Malthru M, Rao TLK, Kartha RK, et al. Intravenous albumin administration for prevention of spinal hypotension during cesarean section. Anesth Analg 1980;59:655-8.
3. Baraka AS, Taha SK, Ghabach MB, et al. Intravascular administration of polymerized gelatin versus isotonic saline for prevention of spinal-induced hypotension. Anesth Analg 1994;78:301-5.
4. Prough DS, Kramer G. Medium starch, please. Anesth Analg 1994;79:1034-5.
5. Tonnessen T, Tollofsrud S, Kongsgaard UE, et al. Colloid osmotic pressure of plasma replacement fluids. Acta Anaesthesiol Scand 1993;37:424-6.
6. Murray AM, Morgan M, Whitwam JG. Crystalloid versus colloid for circulatory preload for epidural Caesarean section. Anaesthesia 1989;44:463-6.
7. Karinen J, Rasanen J, Paavilainen T, et al. Uteroplacental and fetal haemodynamics and cardiac function of the fetus and newborn after crystalloid and colloid preloading for extradural Caesarean section anaesthesia. Br J Anaesth 1994;73:751-7.
8. Sharma S, Sidawi E, Gambling D, et al. Hetastarch versus lactated Ringer's preload: prevention of hypotension following spinal anesthesia [abstract]. Anesth Analg 1995;80(Suppl):S431.
9. Rout CC, Akoojee SS, Rocke DA. Rapid administration of crystalloid preload does not decrease the incidence of hypotension after spinal anaesthesia for elective caesarean section. Br J Anaesth 1992;68:394-7.
10. Wennberg E, Frid I, Haljamae H, et al. Comparison of Ringer's acetate with 3% dextran 70 for volume loading before extradural caesarean section. Br J Anaesth 1990;65:654-60.
11. Ramanathan S, Masih A, Rock I, et al. Maternal and fetal effects of prophylactic hydration with crystalloids or colloids before epidural anesthesia. Anesth Analg 1983;62:673-8.
12. Rout CC, Rocke DA, Levin J, et al. A reevaluation of the role of crystalloid preload in the prevention of hypotension associated with spinal anesthesia for elective cesarean section. Anesthesiology 1993;79:262-9.
13. Ward ME, Kliffer AP, Gambling DR, et al. Effect of combining fentanyl with morphine/bupivacaine for elective C/S under spinal [abstract]. Anesthesiology 1993;79:A1023.
14. Wollman SB, Marx GF. Acute hydration for prevention of hypotension of spinal anesthesia in parturients. Anesthesiology 1968;29:374-80.
15. Clark RB, Thompson DS, Thompson CH. Prevention of spinal hypotension associated with cesarean section. Anesthesiology 1976;45:670-4.
16. Carvalho JCA, Mathias RS, Senra WG, et al. Maternal, fetal, and neonatal consequences of acute hydration during epidural anesthesia for C-section [abstract]. Reg Anesth 1993;18(Suppl):19.
17. Corke BC, Datta S, Ostheimer GW, et al. Spinal anaesthesia for caesarean section. The influence of hypotension on neonatal outcome. Anaesthesia 1982;37:658-62.
18. Caritis SN, Abouleish E, Edelstone DI, et al. Fetal acid-base state following spinal or epidural anesthesia for cesarean section. Obstet Gynecol 1980;56:610-5.
19. Lussos SA, Bader AM, Thornhill ML, et al. The antiemetic efficacy and safety of prophylactic metoclopramide for elective cesarean delivery during spinal anesthesia. Reg Anesth 1992;17:126-30.
20. Ring J, Messmer K. Incidence and severity of anaphylactoid reactions to colloid volume substitutes. Lancet 1977;1:466-9.
21. Hollmen AI, Jouppila R, Koivisto M, et al. Neurologic activity of infants following anesthesia for cesarean section. Anesthesiology 1978;48:350-6.
© 1995 International Anesthesia Research Society
22. Caplan RA, Ward RJ, Posner K, et al. Unexpected cardiac arrest during spinal anesthesia: a closed claims analysis of predisposing factors. Anesthesiology 1988;68:5-11.