Floria F. Ng

Prevention of hypotension during spinal anesthesia for cesarean delivery: an effective technique using combination phenylephrine infusion and crystalloid cohydration.

Background: Many methods for preventing hypotension during spinal anesthesia for cesarean delivery have been investigated, but no single technique has proven to be effective and reliable. This randomized study studied the efficacy of combining simultaneous rapid crystalloid infusion (cohydration) with a high-dose phenylephrine infusion. Methods: Nonlaboring patients scheduled to undergo elective cesarean delivery received an intravenous infusion of 100 &mgr;g/min phenylephrine that was started immediately after spinal injection and titrated to maintain systolic blood pressure near baseline values until uterine incision. In addition, patients received infusion of lactated Ringers solution that was given either rapidly (group 1, n = 57) or at a minimal maintenance rate (group 0, n = 55). Maternal hemodynamic changes and neonatal condition were compared. Results: Six patients were excluded from analysis. Only 1 of 53 patients (1.9% [95% confidence interval, 0.3–9.9%]) in group 1 experienced hypotension versus 15 of 53 patients (28.3% [95% confidence interval, 18.0–41.6%]) in group 0 (P = 0.0001). Compared with group 0, patients in group 1 had greater values for the following: serial measurements of systolic blood pressure (P = 0.02), minimum recorded systolic blood pressure (P = 0.0002), and minimum recorded heart rate (P = 0.013). Total phenylephrine consumption was smaller in group 1 compared with group 0 (P = 0.008). Neonatal outcome and maternal side effects were similar between groups. Conclusions: Combination of a high-dose phenylephrine infusion and rapid crystalloid cohydration is the first technique to be described that is effective for preventing hypotension during spinal anesthesia for cesarean delivery.

Placental transfer and fetal metabolic effects of phenylephrine and ephedrine during spinal anesthesia for cesarean delivery.

Background:Use of ephedrine in obstetric patients is associated with depression of fetal acid-base status. The authors hypothesized that the mechanism underlying this is transfer of ephedrine across the placenta and stimulation of metabolism in the fetus. Methods:A total of 104 women having elective Cesarean delivery under spinal anesthesia randomly received infusion of phenylephrine (100 &mgr;g/ml) or ephedrine (8 mg/ml) titrated to maintain systolic blood pressure near baseline. At delivery, maternal arterial, umbilical arterial, and umbilical venous blood samples were taken for measurement of blood gases and plasma concentrations of phenylephrine, ephedrine, lactate, glucose, epinephrine, and norepinephrine. Results:In the ephedrine group, umbilical arterial and umbilical venous pH and base excess were lower, whereas umbilical arterial and umbilical venous plasma concentrations of lactate, glucose, epinephrine, and norepinephrine were greater. Umbilical arterial Pco2 and umbilical venous Po2 were greater in the ephedrine group. Placental transfer was greater for ephedrine (median umbilical venous/maternal arterial plasma concentration ratio 1.13 vs. 0.17). The umbilical arterial/umbilical venous plasma concentration ratio was greater for ephedrine (median 0.83 vs. 0.71). Conclusions:Ephedrine crosses the placenta to a greater extent and undergoes less early metabolism and/or redistribution in the fetus compared with phenylephrine. The associated increased fetal concentrations of lactate, glucose, and catecholamines support the hypothesis that depression of fetal pH and base excess with ephedrine is related to metabolic effects secondary to stimulation of fetal &bgr;-adrenergic receptors. Despite historical evidence suggesting uteroplacental blood flow may be better maintained with ephedrine, the overall effect of the vasopressors on fetal oxygen supply and demand balance may favor phenylephrine.

A Randomized Double-Blinded Comparison of Phenylephrine and Ephedrine Infusion Combinations to Maintain Blood Pressure During Spinal Anesthesia for Cesarean Delivery: The Effects on Fetal Acid-Base Status and Hemodynamic Control

BACKGROUND: Phenylephrine and ephedrine are both used to maintain arterial blood pressure during spinal anesthesia for cesarean delivery. Usually, either drug is given alone but several previous studies have described combining the drugs. However, the effect of varying the proportion of vasopressors in such combinations has not been reported. METHODS: One-hundred-twenty-five parturients having spinal anesthesia for elective cesarean delivery were randomized to receive an IV infusion of phenylephrine and ephedrine combined in one of five different concentration ratios. Assuming phenylephrine 100 μg to be approximately equipotent to ephedrine 8 mg, the groups contained the proportional potency equivalent of 100%, 75%, 50%, 25% or 0% of phenylephrine and 0%, 25%, 50%, 75% or 100%, respectively, of ephedrine. The infusions were adjusted to maintain systolic blood pressure (SBP) near baseline until uterine incision. Hemodynamic changes and umbilical cord blood gases were compared. RESULTS: As the proportion of phenylephrine decreased and proportion of ephedrine increased among the groups, the following significant trends were detected: the incidences of hypotension and nausea/vomiting increased, the median magnitude of deviations of SBP above or below baseline and the bias for SBP to be above baseline increased, maternal heart rate was faster, fetal pH and base excess decreased, umbilical arterial oxygen content decreased and umbilical venous Po2 increased. CONCLUSIONS: When varying combinations of phenylephrine and ephedrine were given by infusion to maintain arterial blood pressure during spinal anesthesia for cesarean delivery, as the proportion of phenylephrine decreased and the proportion of ephedrine increased, hemodynamic control was reduced and fetal acid-base status was less favorable. Combinations of phenylephrine and ephedrine appear to have no advantage compared with phenylephrine alone when administered by infusion for the prevention of hypotension associated with spinal anesthesia for cesarean delivery.

Maternal and neonatal effects of remifentanil at induction of general anesthesia for cesarean delivery: a randomized, double-blind, controlled trial.

Background:Use of remifentanil during general anesthesia for cesarean delivery has been described, but its maternal and neonatal effects have not been investigated by a controlled study. Methods:In a randomized, double-blind, controlled study, patients undergoing elective cesarean delivery received an intravenous bolus of 1 &mgr;g/kg remifentanil (n = 20) or saline (n = 20) immediately before induction of general anesthesia. The authors compared maternal hemodynamic changes and neonatal condition and measured plasma concentrations of remifentanil. Results:The maximum increase in systolic arterial pressure from baseline after induction was smaller in the remifentanil group (median, 9 [range, −17 to 31] mmHg) compared with the control group (42 [6–73] mmHg, median difference, 33 mmHg; 95% confidence interval of difference, 23–45 mmHg; P < 0.0001). Maximum recorded values were smaller in the remifentanil group compared with the control group for systolic and mean arterial pressure and maternal heart rate. Apgar scores and time to sustained respiration were similar between groups. Two neonates in the remifentanil group were considered clinically depressed at birth and were given a single dose of naloxone. Remifentanil crossed the placenta with an umbilical venous/maternal arterial concentration ratio of 0.73 (SD, 0.17) and an umbilical arterial/umbilical venous concentration ratio of 0.60 (0.23). Conclusions:A single bolus of 1 &mgr;g/kg remifentanil effectively attenuated hemodynamic changes after induction and tracheal intubation. However, remifentanil crosses the placenta and may cause mild neonatal depression and thus should be used for clear maternal indications when adequate facilities for neonatal resuscitation are available.

Prophylactic phenylephrine 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 comparison of patients' and health care professionals' preferences for symptoms during immediate postoperative recovery and the management of postoperative nausea and vomiting.

In this study we sought to examine the differences in patients’ and health care professionals’ preferences for symptoms during immediate postoperative recovery and the management of postoperative nausea and vomiting (PONV). The key differences between symptoms during immediate postoperative recovery (PONV, sedation, and pain) and management of PONV (prophylaxis, efficacy of antiemetic, and extra cost) were used to develop 14 scenarios in a questionnaire. Fifty-two health care professionals (anesthesiologists and recovery room nurses) and 200 women undergoing elective gynecological surgery were recruited (overall response rate, 97%). From patients’ and health care professionals’ perspectives, conjoint analysis showed that the most important attribute for immediate postoperative recovery was a reduction in the risk of PONV. Health care professionals placed more importance on postoperative sedation than patients did. They were more concerned about the cost of the antiemetic to the patient than the patients were themselves. There was no preference for a policy of effective treatment versus routine prophylaxis. This study shows that there were small differences in the importance of pain, sedation, efficacy of the antiemetic, and extra cost of treatment between patients and health care professionals.

Randomized double-blinded comparison of norepinephrine and phenylephrine for maintenance of blood pressure during spinal anesthesia for cesarean delivery.

Background:During spinal anesthesia for cesarean delivery, phenylephrine can cause reflexive decreases in maternal heart rate and cardiac output. Norepinephrine has weak &bgr;-adrenergic receptor agonist activity in addition to potent &agr;-adrenergic receptor activity and therefore may be suitable for maintaining blood pressure with less negative effects on heart rate and cardiac output compared with phenylephrine. Methods:In a randomized, double-blinded study, 104 healthy patients having cesarean delivery under spinal anesthesia were randomized to have systolic blood pressure maintained with a computer-controlled infusion of norepinephrine 5 &mgr;g/ml or phenylephrine 100 &mgr;g/ml. The primary outcome compared was cardiac output. Blood pressure heart rate and neonatal outcome were also compared. Results:Normalized cardiac output 5 min after induction was greater in the norepinephrine group versus the phenylephrine group (median 102.7% [interquartile range, 94.3 to 116.7%] versus 93.8% [85.0 to 103.1%], P = 0.004, median difference 9.8%, 95% CI of difference between medians 2.8 to 16.1%). From induction until uterine incision, for norepinephrine versus phenylephrine, systolic blood pressure and stroke volume were similar, heart rate and cardiac output were greater, systemic vascular resistance was lower, and the incidence of bradycardia was smaller. Neonatal outcome was similar between groups. Conclusions:When given by computer-controlled infusion during spinal anesthesia for cesarean delivery, norepinephrine was effective for maintaining blood pressure and was associated with greater heart rate and cardiac output compared with phenylephrine. Further work would be of interest to confirm the safety and efficacy of norepinephrine as a vasopressor in obstetric patients.

A double blinded randomised placebo-controlled study of intramuscular pethidine for pain relief in the first stage of labour

Objective  It has recently been suggested that systemic pethidine is ineffective in relieving labour pain. This study aims to evaluate the analgesic efficacy of pethidine in labour.

Supplementary oxygen for emergency Caesarean section under regional anaesthesia

BACKGROUND Controversy still exists if the administration of supplementary oxygen to patients having emergency Caesarean section (CS) under regional anaesthesia is beneficial or potentially harmful. Therefore, in a prospective double-blinded study, we randomized patients having emergency CS under regional anaesthesia to receive either air or 60% oxygen until delivery and compared the effects on fetal oxygenation and lipid-peroxidation in the mother and baby. METHODS We recruited 131 women having emergency CS under regional anaesthesia. Either 21% (air group) or 60% oxygen (oxygen group) was administered using a Venturi-type facemask until delivery. We compared the oxygen exposure duration, umbilical arterial (UA) and venous (UV) blood gases and oxygen content, and plasma concentration of 8-isoprostane. Subanalysis was performed according to whether or not fetal compromise was considered present. RESULTS Data from 125 patients were analysed. For the oxygen group vs the air group, there were greater values for UA PO(2) [mean 2.2 (SD 0.5) vs 1.9 (0.6) kPa, P=0.01], UA O(2) content [6.6 (2.5) vs 4.9 (2.8) ml dl(-1), P=0.006], UV PO(2) [3.8 (0.8) vs 3.2 (0.8) kPa, P<0.0001], and UV O(2) content [12.9 (3.5) vs 10.4 (3.8) ml dl(-1), P=0.001]. There was no difference between the groups in maternal, UA, or UV 8-isoprostane concentration. Apgar scores and UA pH were similar between the groups. Similar changes were observed regardless of whether fetal compromise was considered present (n=37) or not (n=88). CONCLUSIONS Breathing 60% oxygen during emergency CS under regional anaesthesia increased fetal oxygenation with no associated increase in lipid-peroxidation in the mother or fetus.

Randomized comparison of closed-loop feedback computer-controlled with manual-controlled infusion of phenylephrine for maintaining arterial pressure during spinal anaesthesia for Caesarean delivery

BACKGROUND Closed-loop feedback computer-controlled infusion has not been described for administering phenylephrine to maintain arterial pressure (AP) during spinal anaesthesia for caesarean delivery. We aimed to compare AP control using this automated system with a previously described manual infusion system. METHODS We randomly allocated 222 healthy subjects having spinal anaesthesia for scheduled caesarean delivery to have systolic AP maintained near baseline with phenylephrine (100 µg ml(-1)) by computer-controlled infusion utilizing a proportional algorithm or manual-controlled infusion utilizing an on-off algorithm. AP control was assessed by comparing the proportion of systolic AP measurements within ±20% of baseline and by performance error (PE) calculations. RESULTS A total of 212 subjects finished the study. In the computer-control group, 97% of systolic AP recordings fell within ±20% of baseline compared with 95% in the manual-control group (P=0.0004). For computer-control compared with manual-control, wobble was smaller [median 3.5 (inter-quartile range 2.5-4.8)% vs 4.2 (3.3-5.9)%, P=0.003], but there was no difference in the median PE [2.9 (0.3-4.7)% vs 1.9 (0-4.2)%], median absolute PE [4.7 (3.5-5.6)% vs 4.7 (3.8-6.7)%], or divergence [-0.01 (-0.03-0)% vs -0.06 (-0.26-0.08)%]. Fewer interventions per subject for controlling AP were required in the computer-control group [2 (2-2) vs 10 (8-13), P<0.001]. There were no differences in measured clinical outcomes. CONCLUSIONS Within the constraints of the studied algorithms, closed-loop feedback computer-controlled phenylephrine infusion provided better AP control with fewer interventions required compared with manual-controlled infusion.