Cardiovascular Alterations in the Parturient Undergoing Cesarean Delivery With Neuraxial Anesthesia

Katherine W Arendt; Jochen D Muehlschlegel; Lawrence C Tsen

Disclosures

Expert Rev of Obstet Gynecol. 2012;7(1):59-75. 

In This Article

Hemodynamic Changes During Cesarean Delivery With Neuraxial Anesthesia

Hemodynamic changes during CD with neuraxial anesthesia occur during prehydration, block onset and birth. The greatest hemodynamic changes occur with block onset, which can lead to maternal hypotension, decreased uterine blood flow, maternal nausea and vomiting and, potentially, fetal compromise. Studies documenting the changes that occur with prehydration, block onset and birth are generally not designed to show statistical significance between events and, consequently, only selected values and trends can be discussed. Furthermore, there are a myriad of confounding factors including patient positioning, vasopressor administration, and local anesthetic solutions containing epinephrine that make these data difficult to analyze.

Prehydration/Cohydration

Hydration prior to neuraxial placement ('prehydration') or at the time of neuraxial block administration ('co-loading') is performed to correct hypovolemia and prevent hypotension after the initiation of neuraxial anesthesia.[44,45] The type of fluid (colloid vs crystalloid), the overall volume administered, the timing in relation to neuraxial blockade and the speed at which it is delivered all affect the efficacy of hydration in preventing hypotension. Neither prehydration nor co-loading can reliably prevent hypotension following neuraxial blockade,[46–49] although other benefits may be realized; an increase in maximal uterine artery blood flow has been observed with prehydration despite the absence of maternal MAP increases.[50]

It has been suggested that the prevention of neuraxial anesthesia-induced hypotension is dependent on a fluid bolus sufficient enough to significantly increase intravascular volume, and subsequently CO.[51] Rapid administration of fluid in term parturients prior to neuraxial techniques does increase CO; however, the response is dependent on alterations in HR and SV that are quite variable. One study demonstrated that the administration of 1 l of lactated Ringers (LR) solution 15 min prior to neuraxial anesthesia increased CO by 20% (from 6.50 to 7.83 l/min), with the HR increasing from 77.6 to 81.9 bpm and the SV increasing from 84.2 to 95.4 ml.[52] A second study, using LR solution in a mean volume of 805 ml as prehydration, observed a 10% increase in CO (from 7.01 to 7.70 l/min) with a relatively stable HR (83–82 bpm) but a significant increase in SV from 84 to 95 ml.[53] A similar study using 1 l of LR as prehydration resulted in an 11% increase in CO (5.2–5.8 l/min), an unchanged HR and a significant increase in SV from 63.3 to 70.5 ml.[54] A final study using 10 ml/kg of 6% hydroxyethyl starch (HES) as prehydration noted an increase in CO (cardiac index increasing 12% from 3.2 to 3.6 l/min/m2) and HR (74–89 bpm), but a decreasing stroke index from 42.2 to 40.2 ml/m2.[40] Summarizing these studies, an increase in CO is observed with prehydration; however, the relative contributions of HR and SV are variable.

The magnitude of CO increase is related to the fluid type, as well as the amount of hydration. Furthermore, the amount of fluid that remains intravascular may be associated with the incidence of hypotension. In a study comparing 1.5 l LR to 0.5 l HES to 1 l HES as prehydration prior to neuraxial blockade for CD, Ueyama and colleagues demonstrated that the amount of prehydration that remains intravascular (as measured by indocyanine green blood concentration monitored though noninvasive pulse spectrophotometry) is significantly correlated to the increase in CO; moreover, the incidence of hypotension was reduced in the group with the greatest increase in CO.[51] The authors demonstrated that in the 1.5 l LR, 0.5 l HES and 1.0 l HES groups, the volume of infused solution remaining in the intravascular space was 0.43 ± 0.20 l, 0.54 ± 0.14 l and 1.03 ± 0.21 l, respectively; and the increase in CO was 11% (from 5.4 ± 1.0 to 6.0 ± 1.0 l/min), 15% (from 5.4 ± 1.0 to 6.2 ± 0.6 l/min) and 43% (from 5.1 ± 1.0 to 7.3 ± 1.1 l/min), respectively. The percentage of blood volume increase significantly correlated to the increase in CO (r2 = 0.838; p < 0.001). The incidence of hypotension after spinal anesthesia was 75% in the 1.5 l LR group, 58% for the 0.5 l HES group and only 17% for the 1.0 l HES group. In summary, 1.0 l of HES preload increased the intravascular volume and CO significantly more effectively than 1.5 l LR or 0.5 l HES; the incidence of 1 h post spinal hypotension was also reduced in this group.

Overall, colloid solutions have been found to be more effective than crystalloid solutions in prehydration to prevent hypotension,[55] especially when at least 1 l of HES is used.[51] However, the use of colloid solutions prior to uterine evacuation and subsequent autotransfusion has been questioned by some, with the risk of potential pulmonary edema, allergies to colloidal solutions and the costs of the solutions cited.[56] Interestingly, recent studies have demonstrated that initiating a rapid infusion of crystalloid at the time of neuraxial blockade administration (i.e., 'co-loading') is as effective as prehydration with crystalloid in preventing hypotension;[45,57] however, when colloid is used as a co-load versus for prehydration, there are no differences in the incidence of hypotension or vasoactive medications use.[48,58] Therefore, crystalloid solutions are more beneficial in preventing hypotension when used as a co-load instead of as prehydration, whereas colloid solutions can be as beneficial when used in either of these time frames. As a result of these studies, the use of a rapid co-load of crystalloid solution through a moderately large intravenous line during performance of a neuraxial technique for CD is a viable option.

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