Determination of the 90% effective dose (ED90) of phenylephrine for hypotension during elective cesarean delivery using a continual reassessment method

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.

Understanding Research Methods: Up-and-down Designs for Dose-finding

SUMMARY

For the task of estimating a target benchmark dose such as the ED50 (the dose that would be effective for half the population), an adaptive dose-finding design is more effective than the standard approach of treating equal numbers of patients at a set of equally spaced doses. Up-and-down is the most popular family of dose-finding designs and is in common use in anesthesiology. Despite its widespread use, many aspects of up-and-down are not well known, implementation is often misguided, and standard, up-to-date reference material about the design is very limited. This article provides an overview of up-and-down properties, recent methodologic developments, and practical recommendations, illustrated with the help of simulated examples. Additional reference material is offered in the Supplemental Digital Content.

Determination of the ED95 of intranasal sufentanil combined with intranasal dexmedetomidine for moderate sedation during endoscopic ultrasonography

BACKGROUND

Sedation during endoscopic ultrasonography (EUS) poses many challenges and moderate-to-deep sedation are often required. The conventional method to preform moderate-to-deep sedation is generally intravenous benzodiazepine alone or in combination with opioids. However, this combination has some limitations. Intranasal medication delivery may be an alternative to this sedation regimen.

AIM

To determine, by continual reassessment method (CRM), the minimal effective dose of intranasal sufentanil (SUF) when combined with intranasal dexmedetomidine (DEX) for moderate sedation of EUS in at least 95% of patients (ED₉₅).

METHODS

Thirty patients aged 18-65 and scheduled for EUS were recruited in this study. Subjects received intranasal DEX and SUF for sedation. The dose of DEX (1 μg/kg) was fixed, while the dose of SUF was assigned sequentially to the subjects using CRM to determine ED₉₅. The sedation status was assessed by modified observer’s assessment of alertness/sedation (MOAA/S) score. The adverse events and the satisfaction scores of patients and endoscopists were recorded.

RESULTS

The ED₉₅ was intranasal 0.3 μg/kg SUF when combined with intranasal 1 μg/kg DEX, with an estimated probability of successful moderate sedation for EUS of 94.9% (95% confidence interval: 88.1%-98.9%). When combined with intranasal 1 μg/kg DEX, probabilities of successful moderate sedation at each dose level of intranasal SUF were as follows: 0 μg/kg SUF, 52.8%; 0.1 μg/kg SUF, 75.4%; 0.2 μg/kg SUF, 89.9%; 0.3 μg/kg SUF, 94.9%; 0.4 μg/kg SUF, 98.0%; 0.5 μg/kg SUF, 99.0%.

CONCLUSION

The ED₉₅ needed for moderate sedation for EUS is intranasal 0.3 μg/kg SUF when combined with intranasal 1 μg/kg DEX, based on CRM.

Determination of the 90% Effective Dose of Phenylephrine Boluses to Treat Spinal Anesthesia-Induced Hypotension in Patients with Severe Preeclampsia during Cesarean Delivery: A Pilot Study

PURPOSE

Treatment of spinal anesthesia-induced hypotension in patients with severe preeclampsia assumes special concern as hypotension may further reduce placental perfusion. Phenylephrine is still the first-line vasopressor for treating spinal anesthesia-induced hypotension. However, the optimal dose of phenylephrine used as intravenous (IV) boluses in patients with severe preeclampsia has not been clearly determined. We aim to calculate the 90% effective dose (ED90) of phenylephrine as IV boluses for treating spinal anesthesia-induced hypotension in patients with severe preeclampsia undergoing cesarean delivery.

PATIENTS AND METHODS

Forty patients with severe preeclampsia were enrolled in this prospective sequential allocation dose-finding trial. Using the biased coin up-and-down (BCUD) method, all patients in our study received an IV bolus phenylephrine of either 40, 50, 60, 70, or 80 µg when the mean arterial pressure (MAP) decreased to less than 80% of the baseline level and the ED90 was determined. The primary outcome was the success of the assigned phenylephrine bolus to maintain the MAP at or above 80% of baseline value between the induction of spinal anesthesia and delivery of the fetus. Secondary outcomes included hypertension, nausea, vomiting, bradycardia, upper sensory level of anesthesia, umbilical blood gases, and Apgar score. Estimating of the ED90 with 95% confidence interval (CI) was achieved by isotonic regression method.

RESULTS

The ED90 of phenylephrine was estimated as 62.00 µg (95% CI=50.00-67.40 µg) using the isotonic regression method. No patients enrolled in our study experienced bradycardia and those patients who developed hypertension were all observed at the dose level 70 µg.

CONCLUSION

For clinical practice, we recommend that phenylephrine 60 µg may be both effective and safe for treatment of spinal anesthesia-induced hypotension in severe preeclampsia during cesarean delivery.

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).

Bolus dose of epinephrine for refractory post-arrest hypotension

Post-cardiac arrest hypotension is associated with worse outcomes. However, a significant proportion of patients may not be responsive to intravenous (IV) fluids, and vasopressor infusions require significant time to initiate. This case series describes the successful use of a bolus dose of epinephrine to rapidly treat IV fluid refractory hypotension among three patients in the post-arrest period. A bolus dose of epinephrine may be considered as a treatment for post-arrest hypotension that does not respond to IV fluids, but further studies should be performed prior to routine use.