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Use of vasopressors to manage spinal anesthesia-induced hypotension during cesarean delivery

Cesarean sections are commonly performed under spinal anesthesia, which can lead to hypotension, adversely affecting maternal and fetal outcomes. Hypotension following spinal anesthesia is generally defined as a blood pressure of 80-90% below the baseline value. Various strategies have been implemented to reduce the incidence of spinal anesthesia-induced hypotension. The administration of vasopressors is a crucial method for preventing and treating hypotension. In the past decade, phenylephrine, a primarily alpha-adrenergic agonist, has been the preferred vasopressor for cesarean sections. Recently, norepinephrine, a potent alpha-agonist with modest beta-agonist activity, has gained popularity owing to its advantages over phenylephrine. Vasopressors can be administered via a bolus or continuous infusion. Although administering boluses alone is simpler in a clinical setting, continuous prophylactic infusion initiated immediately after spinal anesthesia is more effective in reducing the incidence of hypotension. Tailoring the infusion dose based on the patient's body weight and adjusting the rate in response to blood pressure changes, in addition to using a prophylactic or rescue bolus, helps reduce blood pressure variability during cesarean sections under spinal anesthesia until neonatal delivery.

Comparative dose-response study on the infusion of norepinephrine combined with intravenous ondansetron versus placebo for preventing hypotension during spinal anesthesia for cesarean section: a randomised controlled trial

BACKGROUND

Ondansetron has been reported to attenuate the incidence of spinal anaesthesia-induced hypotension (SAIH) and norepinephrine requirement during caesarean section. However, no quantitative study has evaluated the extent of this effect. This study aimed to determine the dose-response of prophylactic infusion of norepinephrine to prevent SAIH in parturients who received intravenous ondansetron or placebo before spinal anaesthesia for caesarean section. The median effective dose (ED 50 ) and 90% effective dose (ED 90 ) were compared to evaluate the effect of ondansetron versus placebo on the norepinephrine requirement.

MATERIALS AND METHODS

One hundred fifty parturients undergoing caesarean section were randomized to receive either 0.1 mg/kg ondansetron (group O) or saline control (group C) 10 min before spinal anaesthesia. The parturients were randomly assigned to one of five different norepinephrine infusion groups: 0.02, 0.04, 0.06, 0.08 or 0.10 µg/kg/min. An effective infusion dose of norepinephrine was defined as non-occurrence of hypotension during the study period. The values for ED 50 and ED 90 of norepinephrine infusion were determined using probit regression. Differences between the two groups were evaluated by comparing the relative median potency with 95% CIs.

RESULTS

The ED 50 values were 0.033 (95% CIs, 0.024-0.043) µg/kg/min in group C and 0.021 (95% CIs, 0.013-0.029) µg/kg/min in group O. The ED 90 values were 0.091 (95% CIs 0.068-0.147) µg/kg/min in group C and 0.059 (95% CIs 0.044-0.089) µg/kg/min in group O, respectively. The estimate of the relative median potency for norepinephrine in group C versus group O was 0.643 (95% CIs, 0.363-0.956). The incidence of side effects was comparable between groups. No significant difference in neonatal outcomes.

CONCLUSION

Intravenous ondansetron 0.1 mg/kg before spinal anaesthesia significantly reduced the dose requirement of prophylactic norepinephrine infusion in parturients undergoing elective caesarean section. This finding is potentially useful for clinical practice and further research.

Determination of the Relative Potency of Norepinephrine and Phenylephrine Given as Infusions for Preventing Hypotension During Combined Spinal-Epidural Anesthesia for Cesarean Delivery: A Randomized Up-And-Down Sequential Allocation Study

Purpose: The relative potency of norepinephrine and phenylephrine given as boluses to treat hypotension during spinal anesthesia for cesarean delivery has been reported but few data are available for infusions. This study aimed to determine the relative potency of norepinephrine and phenylephrine when given by infusion for preventing hypotension during combined spinal-epidural anesthesia for cesarean delivery.

Methods: This was a prospective, randomized, double-blind, up-and-down sequential allocation study. Patients were randomly allocated to receive a prophylactic infusion of norepinephrine or phenylephrine started immediately after induction of anesthesia. The first patients received either norepinephrine 0.1 μg/kg/min or phenylephrine 0.5 μg/kg/min. An effective infusion rate was defined when no hypotension occurred before delivery. For each subsequent patient, the norepinephrine infusion rate was decreased or increased by 0.01 μg/kg/min or the phenylephrine infusion rate was decreased or increased by 0.05 μg/kg/min according to whether the infusion was effective or ineffective respectively in the previous patient. Values for the infusion rate that was effective in preventing hypotension in 50% of patients (ED50) for norepinephrine and phenylephrine were estimated using up-and-down sequential analysis and relative potency was estimated. Probit regression was used as a backup and sensitivity analysis.

Results: The ED50 values for norepinephrine and phenylephrine calculated by the up-and-down method were 0.061 (95% CI 0.054–0.068) μg/kg/min and 0.368 (95% CI 0.343–0.393) μg/kg/min respectively. The estimated relative potency ratio for ED50 for norepinephrine to phenylephrine was 6.03:1 (95% CI 5.26:1 to 6.98:1).

Conclusion: Under the conditions of this study, norepinephrine given by infusion was about 6 times more potent than phenylephrine. This information is useful for clinical practice and further comparative studies of norepinephrine versus phenylephrine.

Clinical Trial Registration:http://www.chictr.org.cn/showproj.aspx, identifier [ChiCTR2200056237]

Spinal hypotension in obstetrics: Context-sensitive prevention and management

Spinal hypotension during caesarean section remains a common complication, with important attendant maternal and fetal adverse outcomes. Research elucidating the mechanisms of spinal hypotension has led to the development and refinement of effective management strategies, with a particular emphasis on prophylactic vasopressor administration. This has proved effective in well-resourced settings, with maternal comfort and the elimination of nausea now considered the primary aim of treatment. In resource-limited settings, sophisticated strategies are not feasible due to insufficient equipment, staff, and expertise. Therefore, in these areas spinal hypotension remains an important cause of maternal and fetal morbidity and mortality. Translational, context-sensitive research in resource-limited settings has shown promise in implementing pragmatic strategies based on research from resource-rich environments. We review the current best practice for the prevention and treatment of spinal hypotension, with a special emphasis on effective strategies in resource-limited settings. We further suggest a research agenda to address the knowledge gap in specific contexts.

Comparison of norepinephrine and phenylephrine infusions for maintenance of haemodynamics following subarachnoid block in lower segment caeserean section

Background and Aims:

Phenylephrine is the vasopressor of choice in spinal anaesthesia–induced maternal hypotension. However, it results in reflex bradycardia and decrease in cardiac output (CO), an effect that is perhaps less evident with the use of norepinephrine. We sought to evaluate the effect of phenylephrine and norepinephrine infusion on maternal systolic blood pressure (SBP), heart rate (HR), intraoperative nausea vomiting (IONV) and fatal Apgar scores.

Methods:

A randomised double-blind study was conducted on 200 American Society of Anesthesiologists (ASA) II–III parturients undergoing caesarean section under subarachnoid block (SAB) who were randomised to two groups A and B to receive variable rate, manually controlled infusions of phenylephrine and norepinephrine targeting maintenance of SBP to 100% of the baseline value. Maternal haemodynamics especially episodes of hypotension, IONV and vasopressor consumption were observed and recorded.

Results:

A statistically significant trend of lower SBP was observed during the first 6 min following intrathecal injection in group A (P value – 0.000). Though a greater number of parturients experienced ≥1 episode of hypotension in Group A vs Group B (13% vs 9%), the difference was, however, statistically insignificant. The incidence of bradycardia was higher in group A than in group B (16% vs 1%) and was found to be statistically significant (P < 0.05). The episodes of hypertension, IONV, maternal vasopressor consumption and neonatal Apgar score were comparable among both the groups.

Conclusion:

A dilute solution of norepinephrine infusion is comparably efficacious to the current gold standard vasopressor phenylephrine in maintaining blood pressure following spinal anaesthesia for caesarean delivery, with a significantly lower incidence of bradycardia.

Determination of the ED50 and ED95 of intravenous bolus of norepinephrine for the treatment of hypotension during spinal anesthesia for cesarean delivery

Norepinephrine is considered as a potential alternative for blood pressure stabilization during spinal anesthesia for cesarean delivery, as it maintains a better maternal heart rate and cardiac output compared with phenylephrine. However, its use as a bolus dose for hypotension treatment remains largely unexplored. Therefore, the present study investigated the ED₅₀ and ED₉₅ of norepinephrine as a bolus for maternal hypotension during cesarean delivery. In the present prospective trial, 42 patients were enrolled for elective delivery under spinal anesthesia. The dose of norepinephrine was decided by the up-and-down sequential allocation method (UDM) with an initial dose of 0.075 µg/kg and a 0.025 µg/kg increment. The 42 patients received a bolus of norepinephrine when systolic blood pressure fell to <80% of baseline. The ED₅₀ was calculated by the sequential method and the probit regression model. The ED₉₅ was then calculated using the probit regression model. The ED₅₀ of norepinephrine, which was determined by the UDM, was 0.067 µg/kg (95% CI, 0.056–0.081). The probit regression model calculated an ED₅₀ of 0.072 µg/kg (95% CI, 0.056–0.088) and an ED₉₅ of 0.121 µg/kg (95% CI, 0.1–0.207). In summary, the present results suggested the ED₅₀ of a bolus norepinephrine for preventing hypotension in elective CD is 0.067 µg/kg (95% CI, 0.056–0.081), with an ED₉₅ of 0.121 µg/kg (95% CI, 0.1–0.207).

Systemic hemodynamic effects of norepinephrine versus phenylephrine in intermittent bolus doses during spinal anesthesia for cesarean delivery

Background

Norepinephrine, a potent α-adrenergic agonist with β-adrenergic effects, has recently emerged as a potential alternative to phenylephrine that does not lower cardiac output (CO) and heart rate (HR) during cesarean deliveries. We examined the systemic hemodynamic effects of both agents in this setting, using intermittent bolus doses to treat spinal anesthesia-induced hypotension.

Methods

A total of 56 parturients consenting to spinal anesthesia for elective cesarean delivery were randomly assigned to phenylephrine (100 μg/ml) or norepinephrine (5 μg/ml) intermittent bolus dosing. The primary study outcome was maternal normalized CO, examining and other hemodynamic variables, maternal side effects, and fetal outcomes secondarily.

Results

In terms of systolic blood pressure and HR, there were significant within-group differences over time (P < 0.001 and P < 0.001, respectively). Normalized CO and stroke volume (SV) also showed significant differences between groups (P < 0.001 and P = 0.002, respectively). In the phenylephrine group, normalized CO and SV declined (relative to baseline values) by as much as 13% and 9%, respectively; whereas in the norepinephrine group, normalized CO did not differ significantly from baseline, and SV increased up to 5% (relative to baseline). Normalized total peripheral resistance likewise displayed significant within-group differences over time (P < 0.001).

Conclusions

During elective cesarean delivery, intermittent bolus doses of norepinephrine proved effective for treating spinal anesthesia-induced hypotension, while maintaining CO and SV. No maternal complications or fetal effects were evident.

Effects of Vasoactive Medications and Maternal Positioning During Cesarean Delivery on Maternal Hemodynamics and Neonatal Acid-Base Status

Maternal hemodynamics, positioning, and anesthesia technique for cesarean delivery influence neonatal acid-base balance; direct effects from drugs that cross the placenta also have an influence. Spinal anesthesia limits fetal exposure to depressant drugs and avoids maternal airway instrumentation, but is associated with hypotension. Hypotension may be prevented/treated with vasopressors and intravenous fluids. Current evidence supports phenylephrine as the first-line vasopressor. Fifteen degrees of lateral tilt during cesarean delivery has been advocated to relieve vena caval obstruction, but routine use may be unnecessary in healthy nonobese women having elective cesarean delivery if maternal blood pressure is maintained near baseline.

Efficacy and safety of norepinephrine versus phenylephrine for the management of maternal hypotension during cesarean delivery with spinal anesthesia: A systematic review and meta-analysis

BACKGROUND

Phenylephrine is the current "gold standard' vasopressor used to treat maternal hypotension in women undergoing cesarean delivery with spinal anesthesia. Since 2015, various studies have explored the use of norepinephrine to manage maternal hypotension. We conducted this systematic review and meta-analysis of available randomized controlled trials (RCTs) to compare the efficacy and safety of norepinephrine and phenylephrine for the prevention and treatment of maternal hypotension.

METHODS

A systematic literature search was conducted using electronic databases, including PubMed, MEDLINE, Embase (Embase.com), and the Cochrane CENTRAL register of controlled trials. Parturients underwent cesarean delivery with spinal anesthesia and received norepinephrine to prevent or treat hypotension were considered. Maternal outcomes, including incidences of hypotension, hypertension, bradycardia, intraoperative nausea and vomiting (IONV), maternal cardiac output (CO), and blood pressure (BP) control precision, as well as neonatal Apgar scores and umbilical cord blood analyses, were compared between groups.

RESULTS

Three RCTs in 4 reports published between 2015 and 2018 were finally identified with a total of 294 parturients. We found there was no difference in effectiveness between norepinephrine and phenylephrine for the treatment of maternal hypotension (odds ratio [OR] 0.64; 95% confidence interval [CI] 0.37-1.10, P = .11), and there was no difference in the occurrence of hypertension (OR 0.74; 95% CI 0.33-1.62, P = .45). Of note, compared to the phenylephrine group, parturients in the norepinephrine group were less likely to experience bradycardia (OR 0.29; 95% CI 0.12-0.68, P = .005) and IONV (OR 0.54; 95% CI, 0.29-0.99, P = .04). Further, we did not observe a difference between the two vasopressors in the incidence of neonatal Apgar scores < 7 at 1  and 5 minutes or in umbilical vein (UV) blood gas. However, evidence is insufficient to draw conclusions regarding the greater maternal CO and better BP control precision with the use of norepinephrine.

CONCLUSION

This systematic review and meta-analysis shows norepinephrine provides similar efficacy to manage maternal hypotension compared to phenylephrine; additionally, showing advantage regarding certain side effects like bradycardia and IONV reduction. Accordingly, norepinephrine is a promising alternative to phenylephrine. However, before routine clinical application, more studies are warranted.

A Review of the Impact of Obstetric Anesthesia on Maternal and Neonatal Outcomes

Obstetric anesthesia has evolved over the course of its history to encompass comprehensive aspects of maternal care, ranging from cesarean delivery anesthesia and labor analgesia to maternal resuscitation and patient safety. Anesthesiologists are concerned with maternal and neonatal outcomes, and with preventing and managing complications that may present during childbirth. The current review will focus on recent advances in obstetric anesthesia, including labor anesthesia and analgesia, cesarean delivery anesthesia and analgesia, the effects of maternal anesthesia on breastfeeding and fever, and maternal safety. The impact of these advances on maternal and neonatal outcomes is discussed. Past and future progress in this field will continue to have significant implications on the health of women and children.

The Efficacy and Safety of Norepinephrine and Its Feasibility as a Replacement for Phenylephrine to Manage Maternal Hypotension during Elective Cesarean Delivery under Spinal Anesthesia

Maternal hypotension commonly occurs during spinal anesthesia for cesarean delivery, with a decrease of systemic vascular resistance recognized as a significant contributor. Accordingly, counteracting this effect with a vasopressor that constricts arterial vessels is appropriate, and the pure α-adrenergic receptor agonist phenylephrine is the current gold standard for treatment. However, phenylephrine is associated with dose-dependent reflex bradycardia and decreased cardiac output, which can endanger the mother and fetus in certain circumstances. In recent years, the older, traditional vasopressor norepinephrine has attracted increasing attention owing to its mild β-adrenergic effects in addition to its α-adrenergic effects. We search available literature for papers directly related to norepinephrine application in spinal anesthesia for elective cesarean delivery. Nine reports were found for norepinephrine use either alone or compared to phenylephrine. Results show that norepinephrine efficacy in rescuing maternal hypotension is similar to that of phenylephrine without obvious maternal or neonatal adverse outcomes, and with a lower incidence of bradycardia and greater cardiac output. In addition, either computer-controlled closed loop feedback infusion or manually-controlled variable-rate infusion of norepinephrine provides more precise blood pressure management than equipotent phenylephrine infusion or norepinephrine bolus. Thus, based on the limited available literature, norepinephrine appears to be a promising alternative to phenylephrine; however, before routine application begins, more favorable high-quality studies are warranted.

Prophylactic Norepinephrine Infusion for Preventing Hypotension During Spinal Anesthesia for Cesarean Delivery

BACKGROUND

The use of norepinephrine for maintaining blood pressure (BP) during spinal anesthesia for cesarean delivery has been described recently. However, its administration by titrated manually controlled infusion in this context has not been evaluated.

METHODS

In a double-blinded, randomized controlled trial, 110 healthy women having spinal anesthesia for elective cesarean delivery were randomly allocated to 1 of 2 groups. In group 1, patients received an infusion of 5 µg/mL norepinephrine that was started at 30 mL/h (2.5 µg/min) immediately after intrathecal injection and then manually adjusted within the range 0-60 mL/h (0-5 µg/min), according to values of systolic BP measured noninvasively at 1-minute intervals until delivery, with the objective of maintaining values near baseline. In group 2, no prophylactic vasopressor was given, and a bolus of 1 mL norepinephrine 5 µg/mL (5 µg) was given whenever systolic BP decreased to <80% of the baseline value. The study protocol was continued until delivery. The primary outcomes of the study were the incidence of hypotension and the overall stability of systolic BP control versus baseline compared using performance error calculations. In addition, the incidence and timing of hypotension were further compared using survival analysis.

RESULTS

Three patients were excluded from the analysis. Nine patients (17%) in group 1 had 1 or more episodes of hypotension versus 35 (66%) in group 2 (P < .001). Performance error calculations showed that on average, systolic BP was maintained closer to baseline (P < .001) in group 1. Survival curve analysis showed a significant difference between groups (log-rank test P < .001). Four patients in each group had a recorded heart rate <60 beats/min (P = .98). Despite a much greater rate of administration of norepinephrine in group 1 (median, 61.0 [interquartile range, 47.0-72.5] µg) versus group 2 (5.0 [0-18.1] µg) (P < .001), there was no difference in neonatal outcome as assessed by Apgar scores and umbilical cord blood gas analysis.

CONCLUSIONS

In patients having spinal anesthesia for elective cesarean delivery, a manually titrated infusion of 5 µg/mL of norepinephrine was effective for maintaining BP and decreasing the incidence of hypotension, with no detectable detrimental effect on neonatal outcome. Further investigation of the use of dilute norepinephrine infusions for routine use in obstetric patients is suggested.

A Random-allocation Graded Dose-Response Study of Norepinephrine and Phenylephrine for Treating Hypotension during Spinal Anesthesia for Cesarean Delivery

BACKGROUND

Norepinephrine has been investigated as a potential alterative to phenylephrine for maintaining blood pressure during spinal anesthesia for cesarean delivery with the advantage of less depression of maternal heart rate and cardiac output. However, the relative potencies of these two vasopressors have not been fully determined in this context.

METHODS

In a random-allocation, graded dose-response study, 180 healthy patients undergoing spinal anesthesia for elective cesarean delivery received a single bolus of norepinephrine in one of six different doses ranging from 4 to 12 µg or phenylephrine in one of six different doses ranging from 60 to 200 µg to treat the first episode of hypotension. The magnitude of response was measured as the percentage of full restoration of systolic blood pressure to the baseline value. Dose-response analysis was performed using nonlinear regression to derive four-parameter logistic dose-response curves, which were compared to determine relative potency.

RESULTS

Data were analyzed for 180 patients. The estimated ED50 values (dose giving a 50% response) were norepinephrine 10 µg (95% CI, 6 to 17 µg) and phenylephrine 137 µg (95% CI, 79 to 236 µg). The estimated relative potency ratio for the two drugs was 13.1 µg (95% CI, 10.4 to 15.8 µg).

CONCLUSIONS

Comparative dose-response analysis was completed for norepinephrine and phenylephrine given as a bolus to treat the first episode of hypotension in patients undergoing spinal anesthesia for cesarean delivery. The estimated dose equivalent to phenylephrine 100 µg was norepinephrine 8 µg (95% CI, 6 to 10 µg). These results may be useful to inform the design of future comparative studies.