Intravenous Ondansetron to Attenuate the Hypotensive, Bradycardic Response to Spinal Anesthesia in Healthy Parturients

Study Overview
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Brief Summary
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The investigators hypothesize that given prophylactically, intravenous ondansetron will attenuate the drop in blood pressure and heart rate frequently seen after spinal anesthesia. Eighty-six American Society of Anesthesiologists (ASA) physical status I or II in preoperative patient assessment, parturients age of 18 to 45 years scheduled to undergo elective caesarean section will be enrolled. Patients will be randomized to 2 groups: the ondansetron group, receiving 8 mg intravenous ondansetron diluted in 10 mL of saline; or the placebo group, who were administered 10 mL of saline given 5 minutes prior to performing the spinal anesthetic. Investigational Pharmacy will randomize and dispense study drug. Baseline measurements of vital signs will be taken. Otherwise standard management will then be used: Patients must be NPO for 8 hours Pulse oximetry, EKG monitoring, noninvasive blood pressure at a minimum of every 3 minutes, more frequently if decided by the provider. Standard lumbar puncture in a sitting position the L3-L4 or L4-L5 Whitacre pencil-point, 25 gauge Injectate: 2 mL of 0.75% hyperbaric bupivacaine, 100 mcg preservative free morphine, 20 mcg fentanyl Immediately after completing the subarachnoid injection, patients will be laid supine with left lateral uterine displacement The sensory level of anesthesia will be assessed in the standard fashion every five minutes using ice. The motor component will tested using the Bromage scale for spinal anesthesia (0, no paralysis; 1, inability to lift the thigh [only knee/feet]; 2, inability to flex the knee [only feet]; 3, inability to move any joint in the legs).

Detailed Description
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Over the last 30 years, regional anesthesia has emerged as the method of choice for elective caesarean section because it avoids risks involved in managing the airway of the parturient and has the added significant benefit of mother being awake for the birth of her child. Indeed, this changing practice patterns is thought to have lead to a significant drop in anesthesia related maternal morbidity and mortality. At the same time, regional anesthesia is associated with both minor and significant risk. Most common among these effects is hypotension and bradycardia, occurring in 33% and 13% of cases, respectively. In the pregnant patient, supine positioning required for surgery is associated hypotension due to aortocaval compression by the gravid uterus in 8% of patients, even without spinal anesthesia. During caesarean section, the combination of these factors can lead to hypotension include decreased placental blood flow, impaired fetal oxygenation and fetal acidosis. Maternal symptoms of low blood pressures include nausea, vomiting, dizziness, and decreased consciousness. This situation has lead to dozens of publications seeking to prevent or minimize the hypotensive response. Hypotension after a spinal is initially due to a blockade of sympathetic fibers leading to a drop in systemic vascular resistance. Spinal-induced bradycardia is multifactorial but is in part due to the Bezold-Jarisch Reflex (BJR). This reflex is mediated by serotonin receptors within the wall of the ventricle in response to systemic hypotension. These receptors, the 5HT3 subtype, cause an increase efferent vagal signaling when bound by serotonin released during hypovolemic states, clinically leading to bradycardia and further hypotension. Ondansetron, a widely used anti-emetic and serotonin antagonist, has been safely used to blunt the BJR, resulting in less bradycardia and hypotension first in animals and later in humans undergoing spinal anesthesia. , Use During Pregnancy: The FDA labels ondansetron as a class B. Studies in pregnant rats and rabbits at doses up to 70 times higher than clinically used doses revealed no evidence of impaired fertility or harm to the fetus due to ondansetron. There are, however, few prospective studies in pregnant women. Nevertheless, the drug is widely used has a long safety history for use in pregnancy and during anesthesia for caesarean section.

Official Title
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IRB-HSR# 14583: Intravenous Ondansetron to Attenuate the Hypotensive, Bradycardic Response to Spinal Anesthesia in Healthy Parturients

Conditions
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Hypotension, Pregnancy

Intervention / Treatment
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* Drug: ondansetron
* Drug: placebo


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Elective Caesarean section Consent to be in the study Age 18-45 ASA 1 or 2 Exclusion Criteria: Patient refusal Patients with known allergy to ondansetron will be excluded Contraindications to spinal anesthetic Known Coagulopathy (acquired e.g. anticoagulation or existing such as liver disease; using patient history, physical examination to determine bleeding risks, a platelet count under 100 or a PT INR over 1.4) Severely altered anatomy (e.g. post surgical changes) Existing neurological deficits (Women with a history of migraine or tension headache will be allowed to enroll. More severe conditions with daily life limiting symptoms will be excluded. Examples include epilepsy, pseudotumor cerebri, prior stroke with persistent neurologic deficits, or any motor or sensory neuropathy with existing deficits) Skin infection overlying site

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 45 Years

Sexes Eligible for Study
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Female

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Prevention
Allocation: Randomized
Intervention Model: Parallel Assignment
Masking: Triple


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: ondansetron<br>ondansetron 8 mg IV will be administered prior to placement of the spinal anesthesia | Drug: ondansetron<br>* Ondansetron 8mg IV or placebo will be administered prior to placement of the spinal anesthetic<br>* Other names: epidural;|
| Placebo Comparator: Placebo<br>Ondansetron 8 mg IV or Placebo will be administered prior to placement of the spinal anesthestic | Drug: placebo<br>* placebo or ondansetron 8mg IV will be administered prior to placement of the spinal anesthetic<br>* Other names: epidural;|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Number of Participants with Adverse Events as a Measure of Safety and Tolerability | hypotension & bradycardia will be recorded from the placement of the spinal through the end of surgical c-section | day 1 | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| dosage of vasopressors administered | vasopressors administered during surgery | day one | 
| number of episodes of nausea |  | 24 hours after surgery | 
| occurrence & intensity of itching |  | 24 hours after surgery | 
| pain scores reported by the patient |  | 24 hours after surgery | 
| dosage of anticholinergics administered |  | 24 hours after surgery | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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c-section, Hypotension after spinal anesthesia for C-section