Can Augmentation Index (AIx) be Used to Predict Hypotension After Spinal Anesthesia?

January 22, 2013 updated by: University of British Columbia

Pulse Wave Analysis and Augmentation Index Changes Associated With Neuraxial Anesthesia in the Parturient

A fall in blood pressure (hypotension) occurs in one third of spinal anesthetics administered to pregnant patients undergoing cesarean delivery. However, predicting which patients will experience hypotension following spinal anesthesia has proven difficult. Pulse wave analysis is a repeatable and reproducible method for investigation of cardiovascular function. A device called a SphygmacorTM can be used to measure pulse. The pulse measurement is called the Augmentation Index (AIx). AIx has been useful in detecting risks associated with blood pressure changes after complex surgery in patients with heart and blood vessel disease. In this study the investigators wish to see if it is possible to predict if a subject will experience hypotension based on her AIx measurement preoperatively.

Study Overview

Status

Completed

Conditions

Intervention / Treatment

Detailed Description

At BC Women's Hospital (BCWH), anesthesiologists give spinal anesthesia for most elective cesarean deliveries. When the spinal medication is given, blood vessels expand in reaction to the spinal medication causing blood pressure to fall. If a patient experiences this common reaction, the anesthesiologist would administer some medications to restore blood pressure to normal. They do this to protect the blood supply to the placenta and to the baby.

It is not known why this happens in some people and not in others. The way blood circulates through the body can provide information about changes occurring in the body. Pulse measurements are a simple way of providing physicians with important clinical information about patient health.

A device called a SphygmacorTM can be used to measure a pulse. The pulse measurement is called the Augmentation Index (AIx). AIx has been useful in detecting risks associated with blood pressure changes after complex surgery in patients with heart and blood vessel disease. In our study we wish to see if AIx can predict a normal patient's risk of hypotension after spinal anesthesia. If a trend between AIx and the onset of hypotension after spinal anesthesia can be found, anesthesiologists can more effectively prevent and treat hypotension by being able to predict whether it will occur.

Consenting subjects will have their blood pressure and AIx measurement taken prior to surgery.

Surgery will commence as per usual practice at BCWH. If hypotension occurs after the spinal anesthesia, anesthesiologist will treat as per usual practice.

Following recruitment and data collection on the first 30 subjects we will review their anesthetic records to assess whether they became hypotensive or not (systolic BP > 20% from baseline). This will give us two groups. Group 1 will be those subjects who developed hypotension, and Group 2 will be those subjects who did not develop hypotension. We will then look at the preoperative measured AIx to determine whether there is a baseline difference between the two groups. A threshold value of the AIx with the best sensitivity and specificity for prediction of hypotension will then be determined.

The second part of the study will then use the threshold AIx value found from the subjects who developed hypotension from the first 30 subjects to prospectively predict hypotension after spinal anesthesia in another 60 subjects.

Study Type

Interventional

Enrollment (Actual)

56

Phase

  • Not Applicable

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Locations

  • Canada
    • British Columbia
      • Vancouver, British Columbia, Canada
        • BC Women's Hospital Dept of Anesthesia

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

19 years to 45 years (Adult)

Accepts Healthy Volunteers

No

Genders Eligible for Study

Female

Description

Inclusion Criteria:

  • All women undergoing elective or urgent cesarean delivery under spinal anesthesia
  • Singleton Pregnancy
  • Greater than 37 weeks gestation
  • Healthy subjects with ASA 1 & 2 classification of health
  • Potential subjects need to be able to read and understand English unless independent (non-partner) translator available

Exclusion Criteria:

  • ASA 3 or above
  • Emergency cesarean delivery for fetal heart rate abnormalities
  • Cesarean delivery under general, epidural, or combined spinal epidural anesthesia
  • Maternal age <19 years
  • Maternal infection
  • Mothers with vascular disease - including hypertension/pre-eclampsia
  • Mothers with Diabetes Mellitus
  • Polyhdramnios
  • Multiple Pregnancy
  • Height < 150cm or > 180cm
  • BMI > 40

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Prevention
  • Allocation: Non-Randomized
  • Interventional Model: Parallel Assignment
  • Masking: Double

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Active Comparator: 1
Subjects that experience hypotension after spinal anesthesia.
Device: AIx measurement with a Sphygmacor TM
All subjects will have their AIx measured prior to surgery. After 30 subjects are recruited, they will be split into 2 groups. Group 1 will be those subjects who developed hypotension, and Group 2 will be those subjects who did not develop hypotension. We will then look at the preoperative measured AIx to determine whether there is a baseline difference between the two groups. A threshold value of the AIx with the best sensitivity and specificity for prediction of hypotension will then be determined.
Device: AIx measurement with a Sphygmacor TM
The second part of the study will then use the threshold AIx value found from the subjects who developed hypotension from the first 30 subjects to prospectively predict hypotension after spinal anesthesia in another 60 subjects
Active Comparator: 2
Subjects that do not experience hypotension after spinal anesthesia.
Device: AIx measurement with a Sphygmacor TM
All subjects will have their AIx measured prior to surgery. After 30 subjects are recruited, they will be split into 2 groups. Group 1 will be those subjects who developed hypotension, and Group 2 will be those subjects who did not develop hypotension. We will then look at the preoperative measured AIx to determine whether there is a baseline difference between the two groups. A threshold value of the AIx with the best sensitivity and specificity for prediction of hypotension will then be determined.
Device: AIx measurement with a Sphygmacor TM
The second part of the study will then use the threshold AIx value found from the subjects who developed hypotension from the first 30 subjects to prospectively predict hypotension after spinal anesthesia in another 60 subjects

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Time Frame
Occurrence of hypotension following spinal anesthesia. Defined as systolic BP > 20% from baseline.
Time Frame: 1 week
1 week

Secondary Outcome Measures

Outcome Measure
Time Frame
Augmentation Index as measured by the SphygmacorTM preoperatively; Bradycardia requiring pharmacological treatment; Ephedrine requirement; Phenylephrine requirement; Block Height; Nausea/vomiting
Time Frame: 1 week
1 week

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

University of British Columbia

Collaborators

Children's & Women's Health Centre of British Columbia

Investigators

  • Principal Investigator: Vit Gunka, MD, FRCPC, University of British Columbia
  • Study Director: James Shannon, FCARSCI MSc, University of British Columbia

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start

March 1, 2009

Primary Completion (Actual)

March 1, 2010

Study Completion (Actual)

March 1, 2010

Study Registration Dates

First Submitted

April 3, 2009

First Submitted That Met QC Criteria

April 17, 2009

First Posted (Estimate)

April 20, 2009

Study Record Updates

Last Update Posted (Estimate)

January 23, 2013

Last Update Submitted That Met QC Criteria

January 22, 2013

Last Verified

January 1, 2013

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • H08-03019

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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