Clinical Trial: Predicting Hypotension Related to Spinal Anesthesia

Study Status: Completed
Recruit Status: Completed
Study Type: Observational

Official Title: Predicting Hypotension Resistant to Phenylephrine (PE) Infusion in Elective Cesarean Delivery (CD)

Brief Summary: This study aims to identify women at risk of low blood pressure (hypotension) after the usual cesarean anesthetic - a spinal anesthetic. Hypotension may be caused by dehydration. We believe we can predict who will get hypotension by using two anesthesia monitors together with a passive leg raise (PLR) (legs elevated after a period spent reclining). The PLR will cause a shift of blood from the legs to the heart, and the monitors will detect the heart's response to tell if a subject is dehydrated. We want to see if these dehydration tests can also predict hypotension after a spinal anesthetic.

Detailed Summary:

We aim to predict the development of spinal anesthesia related hypotension in subjects already receiving a prophylactic infusion of phenylephrine (PE) who are having a cesarean delivery (CD). Hypotension arising in this fashion may signify that a subject is actually relatively fluid-deplete, and might benefit from intravenous (IV) fluid replacement. We will observe the association between hypotension and results of pre-anesthesia tests with two non-invasive monitors used in conjunction with a dynamic cardiovascular fluid challenge (by using a passive leg raise (PLR) maneuver). The use of any therapeutic intervention such as a fluid infusion would be the object of a subsequent study.

We propose that a minority of parturients present for elective CD being relatively fluid deplete. It is our hypothesis that the characteristics of passive leg raise (PLR) induced changes in the plethysmography variability index (PVI generated by the Masimo Radical 7™) and cardiac output (CO as derived from the Non Invasive Cardiac Output Monitor (NICOM) produced by Cheetah Medical™) will identify these subjects and that without large volume fluid administration they are likely to develop hypotension despite the use of a prophylactic PE infusion

Justification: Hypotension is the most common cause of spinal anesthesia related morbidity in cesarean delivery. Hypotension is very common and without treatment can affect over 80% of women. The mechanism is usually twofold: Firstly preload to the right ventricle (RV) is reduced as a result of venodilation from spinal sympathetic blockade. Unfortunately attempting to improve preload by infusion of IV fluid alone doesn't make much difference to the rates of hypotension (only 16% reduction in one large study). The second mechanism results from afterload reduction through arterial vasodilation
Sponsor: University of British Columbia

Current Primary Outcome:

  • Passive leg raise related cardiac output change and correlation with presence of phenylephrine infusion resistant hypotension [ Time Frame: One hour prior to scheduled cesarean delivery ]
  • Passive leg raise related plethysmography variability index change and correlation with presence of phenylephrine infusion resistant hypotension [ Time Frame: One hour prior to scheduled cesarean delivery ]


Original Primary Outcome: Same as current

Current Secondary Outcome:

  • Baseline plethysmography variability index, plethysmography index and systemic vascular resistance values and correlation with presence of phenylephrine infusion resistant hypotension [ Time Frame: From administration of spinal anesthetic to delivery of infant ]
  • Passive leg raise related plethysmography variability index and cardiac output change and correlation with severe phenylephrine resistant hypotension [ Time Frame: One hour prior to scheduled cesarean delivery ]
    Defined as requirement of 3 or more rescue bolus doses of vasopressor/anticholinergic according to intervention protocol
  • Passive leg raise related plethysmography variability index and cardiac output change and correlation with hypotension associated with bradycardia [ Time Frame: One hour prior to scheduled cesarean delivery ]
  • Presence of phenylephrine infusion associated side effects [ Time Frame: From administration of spinal anesthetic to delivery of infant ]
    Hypertension or normotensive bradycardia associated with phenylephrine infusion use
  • Presence of recurrent (3 or more) episodes of phenylephrine infusion associated side effects [ Time Frame: From administration of spinal anesthetic to delivery of infant ]
  • Maternal cardiac output and systemic vascular resistance changes following spinal anesthesia [ Time Frame: From administration of spinal anesthesia to delivery of infant ]
  • Umbilical cord gases [ Time Frame: At delivery of infant ]
  • Apgar scores at 1 and 5 minutes [ Time Frame: At delivery of infant ]


Original Secondary Outcome: Same as current

Information By: University of British Columbia

Dates:
Date Received: January 18, 2011
Date Started: January 2011
Date Completion:
Last Updated: February 10, 2012
Last Verified: February 2012