Can Augmentation Index (AIx) be Used to Predict Hypotension After Spinal Anesthesia?
Condition: Hypotension; Cesarean Delivery
MeSH terms: Hypotension
Study type: Interventional

Summary: 
      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.
    

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.
    

Intervention name(s): AIx measurement with a Sphygmacor TM; AIx measurement with a Sphygmacor TM
Intervention type(s): Device; Device
Intervention description(s): 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.; 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
Allocation: Non-Randomized
Intervention model: Parallel Assignment
Masking: Double (Participant, Investigator)
Primary purpose: Prevention
Keywords: Cesarean delivery; hypotension; Augmentation Index; Pulse Wave analysis; spinal anesthesia; Hypotension following spinal anesthesia for cesarean delivery