Phenylephrine infusion for spinal-induced hypotension in elective cesarean delivery: Does preload make a difference?

Effect of pneumatic leg compression on phenylephrine dose for hypotension prophylaxis via variable rate infusion at cesarean delivery: an unblinded randomized controlled trial

BACKGROUND

Phenylephrine infusion is recommended to prevent spinal hypotension during cesarean delivery (CD) but may be associated with dose-dependent side effects. We hypothesized that adding intermittent pneumatic compression (IPC) of the lower legs to a variable-rate phenylephrine infusion will reduce the dose of phenylephrine required during CD.

METHODS

Seventy-six healthy women undergoing elective CD under combined spinal-epidural anesthesia were randomly assigned to IPC or control groups (n = 38 per group). After spinal anesthesia, IPC of the lower legs was initiated in the IPC group, and all women received a phenylephrine infusion starting at 25 μg·min-1 and increasing by 16.7 μg·min-1 for systolic blood pressure (SAP) < 90% baseline. If hypotension (SAP < 80% baseline) occurred, 100 μg phenylephrine bolus was administered. The primary outcome was the dose of phenylephrine per minute.

RESULTS

The dose of phenylephrine per minute (34.4 ± 7.3 μg·min-1 vs. 40.9 ± 9.5 μg·min-1, P = 0.001; mean difference -6.6 μg·min-1, 95% CI -10.5 to -2.7 μg·min-1) and the incidence of hypotension (24% vs. 55%, P = 0.005) were lower in the IPC group than in the control group. There were no significant differences between the two groups in the total dose of phenylephrine (603.2 ± 217.1 μg vs. 706.2 ± 247.5 μg, P = 0.058; mean difference -102.9 μg, 95% CI -209.4 to 3.5 μg), maternal side effects, or neonatal outcomes.

CONCLUSIONS

Intermittent pneumatic compression combined with a variable-rate phenylephrine infusion reduced the phenylephrine dose per minute and the incidence of hypotension during CD under spinal anesthesia.

Colloid coload versus crystalloid coload to prevent maternal hypotension in women receiving prophylactic phenylephrine infusion during caesarean delivery: a randomised controlled trial

BACKGROUND

The optimal fluid strategy to prevent maternal hypotension during caesarean delivery remains unclear. This study aim was to compare the incidence of post-spinal anaesthesia hypotension in women receiving either colloid or crystalloid coload in the setting of prophylactic phenylephrine infusion during caesarean delivery.

METHODS

Healthy mothers undergoing elective caesarean delivery under spinal anaesthesia were randomised to receive a rapid intravenous coload with 6% hydroxyethyl starch 130/0.4 10 mL/kg (colloid group) or balanced crystalloid solution (Plasma Solution A) 10 mL/kg (crystalloid group) during spinal anaesthesia. All women had a prophylactic phenylephrine infusion initiated at 25 μg/min immediately after the subarachnoid block and titrated to systolic blood pressure using a standardised protocol. The primary outcome was the incidence of hypotension (systolic blood pressure <80% of baseline) until delivery.

RESULTS

The incidence of hypotension was 50% in the colloid group and 62% in the crystalloid group (absolute difference, -12% [95% CI -33% to 9%]; relative risk, 0.8 [95% CI 0.56 to 1.14]; P=0.314). No significant difference between groups was found in the number of hypotensive episodes (median 0.5 [IQR 0 to 1] vs 1 [0 to 2], P=0.132) or phenylephrine dose (675 [IQR 425 to 975] μg vs 750 [625 to 950] μg, P=0.109). The incidence of severe hypotension, symptomatic hypotension, bradycardia, nausea, and the neonatal outcomes were not significantly different.

CONCLUSIONS

This study found no benefit of colloid coload compared with crystalloid coload for preventing maternal hypotension in the presence of prophylactic phenylephrine infusion during caesarean delivery.

Colloid preloading versus crystalloid preloading to prevent hypotension after spinal anesthesia for cesarean delivery: A protocol for systematic review and meta-analysis

BACKGROUND

Maternal hypotension is the most frequent complication of spinal anesthesia for cesarean delivery, and intravenous fluid preloading is a preventive measure. We aimed to assess the efficacy of colloids versus crystalloids for preloading to reduce the incidence of spinal anesthesia-induced hypotension and vasopressor requirement in healthy parturients during elective cesarean delivery.

METHODS

We searched the Cochrane Library, MEDLINE and EMBASE to identify all studies published to June, 2019, through OVID and PubMed. We included randomized controlled trials, comparing colloid preloading with crystalloid preloading in women having spinal anesthesia for cesarean delivery. Primary outcomes were the incidence of hypotension and vasopressor requirement. Secondary outcomes included nausea and/or vomiting, neonatal Apgar score, neonatal umbilical blood pH. We used standardized mean differences for expressing continuous outcomes and risk ratios for dichotomous outcomes. Random-effect model was performed to estimate the pooled risk ratios and standardized mean differences.

RESULTS

Thirty-three randomized controlled trials contributed data for this meta-analysis. Fewer women experienced hypotension in the colloid group compared with the crystalloid group (risk ratio: 0.72, 95% confidence interval: 0.63-0.82; 2566 women, 32 studies; P < .00001). The total ephedrine dose required was significantly lower with colloid preloading (standardized mean difference: -0.37, 95% CI: -0.64 to -0.09; 1472 women, 19 studies; P = .009). Colloid preloading was also associated with fewer phenylephrine requirement compared with crystalloid preloading (standardized mean difference: -0.54, 95% CI: -0.82 to -0.25; 169 women; P = .0002). The incidence of nausea and/or vomiting was significantly reduced with colloid preloading (risk ratio: 0.72, 95% CI: 0.55-0.95; 1601 women, 20 studies; P = .02). However, the incidence of 1-minute Apgar score < 7, umbilical artery pH < 7.2 and umbilical vein pH < 7.2 were not statistically different between groups.

CONCLUSIONS

Colloid preloading is superior to crystalloid preloading in reducing the incidence of hypotension induced by spinal anesthesia and vasopressor requirement in the healthy parturients undergoing elective cesarean delivery.The PROSPERO registration number: CRD42018096402.

Fluid loading therapy to prevent spinal hypotension in women undergoing elective caesarean section: Network meta-analysis, trial sequential analysis and meta-regression

BACKGROUND

Fluid loading is one of the recognised measures to prevent hypotension due to spinal anaesthesia in women scheduled for a caesarean section.

OBJECTIVE

We aimed to evaluate the current evidence on fluid loading in the prevention of spinal anaesthesia-induced hypotension.

DESIGN

Systematic review and network meta-analysis with trial sequential analysis and meta-regression.

DATA SOURCES

Medline, Epub, Embase.com (Embase and Medline), Cochrane Central, Web of Science and Google Scholar were used.

ELIGIBILITY CRITERIA

Only randomised controlled trials were used. Patients included women undergoing elective caesarean section who received either crystalloid or colloid fluid therapy as a preload or coload. The comparator was a combination of either a different fluid or time of infusion.

RESULTS

A total of 49 studies (4317 patients) were included. Network meta-analysis concluded that colloid coload and preload offered the highest chance of success (97 and 67%, respectively). Conventional meta-analysis showed that crystalloid preload is associated with a significantly higher incidence of maternal hypotension than colloid preload: risk ratio 1.48 (95% CI 1.29 to 1.69, P < 0.0001, I = 60%). However, this result was not supported by Trial Sequential Analysis. There was a significant dose-response effect for crystalloid volume preload (regression coefficient = -0.073), which was not present in the analysis of only double-blind studies. There was no dose-response effect for the other fluid regimes.

CONCLUSION

Unlike previous meta-analysies, we found a lack of data obviating an evidence-based recommendation. In most studies, vasopressors were not given prophylactically as is recommended. Studies on the best fluid regimen in combination with prophylactic vasopressors are needed. Due to official european usage restrictions on the most studied colloid (HES), we recommend crystalloid coload as the most appropriate fluid regimen.

TRIAL REGISTRATION

CRD42018099347.

Dissecting genetic factors affecting phenylephrine infusion rates during anesthesia: a genome-wide association study employing EHR data

BACKGROUND

The alpha-adrenergic agonist phenylephrine is often used to treat hypotension during anesthesia. In clinical situations, low blood pressure may require prompt intervention by intravenous bolus or infusion. Differences in responsiveness to phenylephrine treatment are commonly observed in clinical practice. Candidate gene studies indicate genetic variants may contribute to this variable response.

METHODS

Pharmacological and physiological data were retrospectively extracted from routine clinical anesthetic records. Response to phenylephrine boluses could not be reliably assessed, so infusion rates were used for analysis. Unsupervised k-means clustering was conducted on clean data containing 4130 patients based on phenylephrine infusion rate and blood pressure parameters, to identify potential phenotypic subtypes. Genome-wide association studies (GWAS) were performed against average infusion rates in two cohorts: phase I (n = 1205) and phase II (n = 329). Top genetic variants identified from the meta-analysis were further examined to see if they could differentiate subgroups identified by k-means clustering.

RESULTS

Three subgroups of patients with different response to phenylephrine were clustered and characterized: resistant (high infusion rate yet low mean systolic blood pressure (SBP)), intermediate (low infusion rate and low SBP), and sensitive (low infusion rate with high SBP). Differences among clusters were tabulated to assess for possible confounding influences. Comorbidity hierarchical clustering showed the resistant group had a higher prevalence of confounding factors than the intermediate and sensitive groups although overall prevalence is below 6%. Three loci with P < 1 × 10^-6 were associated with phenylephrine infusion rate. Only rs11572377 with P = 6.09 × 10^-7, a 3'UTR variant of EDN2, encoding a secretory vasoconstricting peptide, could significantly differentiate resistant from sensitive groups (P = 0.015 and 0.018 for phase I and phase II) or resistant from pooled sensitive and intermediate groups (P = 0.047 and 0.018).

CONCLUSIONS

Retrospective analysis of electronic anesthetic records data coupled with the genetic data identified genetic variants contributing to variable sensitivity to phenylephrine infusion during anesthesia. Although the identified top gene, EDN2, has robust biological relevance to vasoconstriction by binding to endothelin type A (ET_A) receptors on arterial smooth muscle cells, further functional as well as replication studies are necessary to confirm this association.