The Pleth Variability Index and Hypotension at Caesarean Under Spinal.
Condition: Caesarean Section
MeSH terms: Hypotension
Study type: Observational

Summary: 
      During a caesarean section the blood pressure is usually measured every few minutes and it
      may fall too quickly to be detected in a timely fashion by this intermittent means. The
      monitor the Masimo Rainbow SET® (MRS) uses a peg attached to a finger to detect (amongst
      other things) the flow of blood through it. One of the measures it takes is called the Pleth
      Variability Index (PVI) which (unlike standard blood pressure measurement) it measures
      continuously. The investigators would like to try the MRS on patients to see if the PVI can
      be used to predict falls in blood pressure.
    

Detailed description: 
      BACKGROUND: When a baby is delivered by a surgical procedure (a Caesarean Section) the women
      will usually have a spinal anaesthetic. With a spinal anaesthetic local anaesthetic is
      injected into the spinal fluid to make the woman numb from her chest to her feet and this
      allows her to be comfortable but awake during the birth. One of the common side effects of a
      spinal anaesthetic is that the woman's blood pressure may fall making her feel unwell and
      (rarely) causing stress to the unborn baby. During a caesarean section the blood pressure is
      usually measured every few minutes and it may fall too quickly to be detected in a timely
      fashion by this intermittent means. The monitor the Masimo Rainbow SET® (MRS) uses a peg
      attached to a finger to detect (amongst other things) the flow of blood through it. One of
      the measures it takes is called the Pleth Variability Index (PVI) which (unlike standard
      blood pressure measurement) it measures continuously. The investigators have used the MRS on
      one of their patients who was having a caesarean section under a spinal anaesthetic and the
      PVI was seen to change before the patients blood pressure fell. Because this was only one
      case they would like to try the MRS on some more patients to see if the PVI can be used to
      predict falls in blood pressure. To keep a close eye on the blood pressure they would use
      another monitor called a finometer. A finometer measures blood pressure continuously by means
      of a small cuff that is placed around a finger. The finometer should allow them to follow
      changes in blood pressure more closely and see how these affect the PVI reading.

      AIMS: The aim of this study is to see whether changes in PVI happen before a fall in blood
      pressure when a woman is having a spinal anaesthetic for a caesarean section.

      METHODOLOGY: The women will have exactly the same anaesthetic as they would have had if they
      were not in the study. The investigators will simply be using two pieces of equipment (the
      MRS and the Finometer) to see what happens when and if the blood pressure falls.

      EXPECTED OUTCOMES: The investigators hope that they will find that the PVI changes before the
      blood pressure falls significantly.

      IMPLICATIONS: If this study were to be promising then the investigators could go on to
      perform another study where they use the MRS to help them decide when to give drugs and
      intravenous fluids to stop the blood pressure from falling.
    

Observational model: Cohort
Time perspective: Prospective
Sampling method: Non-Probability Sample
Study population: 
        Patients with a singleton uncomplicated pregnancy presenting for elective caesarean section
        under spinal anaesthesia where surgery and anaesthesia are anticipated to be uncomplicated.