The Effect of Fluids on Aortic VTI During C-section

Study Overview
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Brief Summary
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Pregnancy is associated with a myriad of physiologic changes, including expansion of blood volume, decrease in oncotic pressure, and increased cardiac output. The obstetric population is associated with intrapartum hemorrhage. Accordingly, it is important to have an accurate method to assess fluid status in intrapartum patients. The use of standard volume assessment tools including arterial lines and central venous catheters is limited given the brevity of obstetric procedures and the morbidity of these techniques on the awake patients, and the costs. Non-invasive methods to assess volume status (carotid dopplers, direct measurement of blood loss, bio-impedance devices) are imperfect. Echocardiography is an attractive tool to measure fluid status in experienced operators such as anesthesiologists. IVC diameter and variation of aortic velocity time integral are two measures that can be obtained via echocardiography and been studied in spontaneously breathing patients. The purpose of this study is to determine whether these measurements can be used in the assessment of volume status in the laboring patient.

Detailed Description
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Pregnancy is associated with a myriad of physiologic changes, including expansion of blood volume, decrease in oncotic pressure, and increased cardiac output. Comorbidities including maternal hypertension, renal or cardiac disease may further complicate the assessment of volume status and are associated with increased risks related to fluid administration (c). In addition, the majority of obstetric patients receive neuraxial analgesia or anesthesia to facilitate both vaginal and operative delivery. These techniques are associated with hemodynamic changes including maternal hypotension secondary to a decrease in SVR and CO. These changes may in turn be associated with a reduction in placental blood flow affecting fetal outcome, and may also cause maternal nausea, vomiting and dizziness. Further, the obstetric population is high risk for intrapartum hemorrhage. As such, it is critical to have an accurate method to assess fluid status in intrapartum patients. The use of invasive volume assessment tools including arterial lines and central venous catheters is limited given the brevity of obstetric procedures, the morbidity of these invasive techniques for the awake patient, and the associated time and costs (b). Non-invasive methods that assess volume status in the obstetric population include techniques such as direct measurement of blood loss (g), carotid dopplers (c), bio-impedence devices (f); However these methods have been shown to be imperfect and are not widely used. Echocardiography is a non-invasive, widely-available tool that can provide rapid information for experienced operators such as anesthesiologists. Respiratory variations in inferior vena cava diameter (IVCd) and variation in aortic velocity time integral (∆VTI) following passive leg raise have been extensively studied in spontaneously breathing patients. IVCd has been shown to predict fluid responsiveness, however requires a high threshold (>40-50% collapsibility) to detect a difference. IVCd may also change with diaphragmatic motion, thus results may be confounded if the patient becomes tachypneic (d) or is spontaneously breathing (g). In contrast, aortic velocity time integral (∆VTI) may be a more sensitive indicator of volume status. Lamia et al showed a 12% change in VTI as 77% sensitive and 100% specific for a 15% change in cardiac output following 500 mL volume expansion in ICU patients with shock (both spontaneously breathing and mechanically ventilated, e). While there are some studies of IVC collapsibility in the obstetric population, there are limited data on VTI as a measure of volume status in laboring patients. The purpose of this study is to determine whether the aortic velocity time integral (VTI) is influenced by intravascular fluid administration during cesarean section. Secondary aims include determining whether inferior vena cava diameter (IVCd), blood pressure, and heart rate are influenced by intravascular fluid administration during cesarean section. Additionally, total amount of vasopressor agents administered during the procedure will be recorded.

Official Title
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The Influence of Intravascular Fluid Administration on Aortic Velocity Time Integral in Obstetric Patients Undergoing Cesarean Section

Conditions
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Pregnancy Related, Hemorrhage, Fluid Overload, Labor Complication

Intervention / Treatment
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* Drug: lactated ringers


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: healthy nulliparous or multiparous pregnant women with a term (>37 weeks gestation) age 18-35 singleton pregnancy scheduled for Cesarean delivery with planned neuraxial spinal or combined spinal epidural anesthesia American Society for Anesthesiologists physical status 2 Exclusion Criteria: Patients without ability to provide informed consent American Society for Anesthesiologists physical status 3 or 4 Emergency cesarean section BMI>40 Known cardiac and pulmonary comorbidities including chronic hypertension, preeclampsia, gestational hypertension, diabetes, asthma, renal disease Age > 35

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 35 Years

Sexes Eligible for Study
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Female

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| 0 mL crystalloid<br>These are the measurements (aortic velocity time integral, inferior vena cava diameter, vital signs) that will be taken at time 0, at which time 0 mL of fluids will have been administered. | Drug: lactated ringers<br>* the intervention is one liter fluid bag of lactated ringers which is routinely used as a fluid coload for spinal anesthesia. All patients will receive the same amount of fluids however this will be paused at various time points in order to perform the echocardiogram.<br>* Other names: crystalloid;|
| 250 mL crystalloid.<br>These are the measurements (aortic velocity time integral, inferior vena cava diameter, vital signs) that will be taken at time 1, after the spinal has been placed and approximately 250 mL fluids has been administered. | Drug: lactated ringers<br>* the intervention is one liter fluid bag of lactated ringers which is routinely used as a fluid coload for spinal anesthesia. All patients will receive the same amount of fluids however this will be paused at various time points in order to perform the echocardiogram.<br>* Other names: crystalloid;|
| 500 mL crystalloid<br>These are the measurements (aortic velocity time integral, inferior vena cava diameter, vital signs) that will be taken at time 2, at which time 500 mL of fluids will have been administered. | Drug: lactated ringers<br>* the intervention is one liter fluid bag of lactated ringers which is routinely used as a fluid coload for spinal anesthesia. All patients will receive the same amount of fluids however this will be paused at various time points in order to perform the echocardiogram.<br>* Other names: crystalloid;|
| 1000 mL crystalloid<br>These are the measurements (aortic velocity time integral, inferior vena cava diameter, vital signs) that will be taken at time 3, at which time 1000 mL of fluids will have been administered. | Drug: lactated ringers<br>* the intervention is one liter fluid bag of lactated ringers which is routinely used as a fluid coload for spinal anesthesia. All patients will receive the same amount of fluids however this will be paused at various time points in order to perform the echocardiogram.<br>* Other names: crystalloid;|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| aortic velocity time integral | the percent change in aortic velocity time integral as measured by transthoracic echo | at baseline measure, right after spinal placement (250mL LR), at 500mL LR infusion, and at 1 L LR infusion (approximately 20mins) | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| inferior vena cava collapsibility | the percent change in diameter of inferior vena cava as measured by transthoracic echo | at baseline measure, right after spinal placement (250mL LR), at 500mL LR infusion, and at 1 L LR infusion (approximately 20mins) | 
| change in systolic blood pressure | percent change in systolic blood pressure | every 2.5 mins for 20 mins (when 1L LR is administered) once the pt has a spinal placement | 
| change in heart rate | percent change in heart rate | every 2.5 mins for 20 mins (when 1L LR is administered) once the pt has a spinal placement | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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obstetrics, fluid responsiveness, fluid resuscitation