Comparison of Non-Invasive Mean Arterial Blood Pressure Measurements at the Arm and Ankle During Elective Cesarean Delivery.

Background Spinal anesthesia during elective cesarean delivery requires close monitoring of blood pressure to prevent maternal hypotension and decreased fetal perfusion. After birth, skin-to-skin contact offers several benefits, including improved well-being for the baby and support for breastfeeding initiation. The standard non-invasive blood pressure (BP) cuff on the arm can hinder comfortable and optimal positioning of the mother-infant dyad. This study aims to determine whether blood pressure measured by a non-invasive cuff on the ankle, five minutes after birth, is comparable to the standard measurement taken on the arm.

Objectives

Primary Objective:

Demonstrate a similar MAP between arm and ankle blood pressure measurements 5 minutes after birth

Secondary Objectives:

• Difference in MAP between arm and ankle BP before neuraxial anesthesia, in the waiting room
• Difference in MAP between arm and ankle BP five minutes after neuraxial anesthesia
• Assess maternal comfort and ease of skin-to-skin contact with each BP cuff. Four yes/no questions will be asked postoperatively in the recovery room.

Methods 110 term pregnant women (35 weeks and over) scheduled for elective cesarean delivery under neuraxial anesthesia will be recruited. Each patient will have a non-invasive BP cuff on the arm and another on the ankle. BP will be measured simultaneously at both sites before entering the operating room, five minutes after spinal anesthesia, and five minutes after birth.

Study Design Prospective, controlled, observational.

Study Population Pregnant women scheduled for elective cesarean section with a single fetus of 35 weeks or more of gestational age.

Exclusion: Women with preeclampsia or gestational hypertension, preterm pregnancy (< 35 weeks), urgent cesarean, cesarean under general anesthesia.

Sample Size 110 patients.

Study Duration 12 months.

Study Center Centre Hospitalier Universitaire Sainte-Justine (CHUSJ), Montreal, Quebec, CANADA.

Adverse Events Side effects of standard practice.

Hypothesis (Detailed) The investigators hypothesize that the use of the ankle BP cuff is a valid method for measuring blood pressure in elective cesarean section, meaning the MAP at the ankle will be equivalent to the MAP at the arm, five minutes after birth.

Objectives (Detailed)

Primary:

Assess equivalence between MAP measured by BP cuff at the arm and at the ankle five minutes after birth during elective cesarean under neuraxial anesthesia.

Secondary:

• Equivalence of MAP between arm and ankle BP before neuraxial anesthesia, in the waiting room
• Equivalence of MAP between arm and ankle BP five minutes after neuraxial anesthesia
• Assess maternal comfort and ease of skin-to-skin application with each BP cuff. Four yes/no questions will be asked postoperatively in the recovery room :

1. Did the arm BP cuff cause you discomfort or pain?
2. Did the ankle BP cuff cause you discomfort or pain?
3. Did the arm BP cuff limit your ability to hold your newborn as you wished?
4. Did the ankle BP cuff limit your ability to hold your newborn as you wished?

Methodology Population The target population will be adult pregnant women scheduled for elective cesarean at CHU Sainte-Justine. Eligibility will be determined by the inclusion and exclusion criteria below.

Inclusion Criteria:

• Age ≥ 18 years
• Women scheduled for elective cesarean under neuraxial anesthesia at CHU Sainte-Justine
• American Society of Anesthesiologists Physical Status I-III
• Singleton pregnancy
• Gestation ≥ 35 weeks
• BMI < 40
• Able to consent in French or English

Exclusion Criteria:

• Cesarean under general anesthesia
• Multiple pregnancy
• Prematurity < 35 weeks gestation
• Major fetal abnormalities
• Morbid obesity (BMI ≥ 40)
• Active labor
• Emergency cesarean
• Prisoners
• Peripheral vascular disease requiring medication or treatment
• Hypertensive diseases requiring medication
• Inability to place BP cuff on ankle (amputation, dysmorphism, etc.)
• Complications requiring significant hemodynamic support (transfusions, inotropes, multiple vasopressors, etc.)

Outcomes BP will be the only clinical outcome. It will be measured simultaneously at different times at the arm (standard care) and left ankle (research objective).

• Pre-spinal anesthesia: Supine with wedge under right hip in the operating room waiting area. BP taken twice; the average MAP will be considered baseline.
• 5 min post-spinal anesthesia: With 15-degree left uterine tilt.
• 5 min after birth: Primary objective. The arm BP cuff will be placed on the arm opposite the main peripheral IV, per standard practice. The leg BP cuff will be placed on the left ankle. Cuff size will be measured per AHA guidelines.

Co-interventions Neuraxial anesthesia will be administered per CHU Sainte-Justine standard practice by the attending anesthesiologist. Hypotension prevention will also follow standard practice. After spinal anesthesia, 1 liter of lactated Ringer's as a co-load and a phenylephrine infusion will be started. Phenylephrine will be titrated to keep MAP within normal limits for the patient (+/- 20% of baseline MAP from waiting room measurements). Clinical decisions will be based only on arm BP (standard), not ankle BP (research). Uterine atony prevention will follow standard practice and at the anesthesiologist's discretion. Shivering will be treated with 30 mcg IV dexmedetomidine after birth if shivering occurs. Fetal and neonatal monitoring will follow standard practices for elective cesarean at CHU Sainte-Justine.

Data Collection

MAP data will be collected using a standardized data collection form. The following data will also be collected:

• Demographics: age, weight, height, gestational age, gravida, para, reason for cesarean
• Systolic, diastolic, and mean BP before neuraxial anesthesia, 5 min after neuraxial anesthesia, and 5, 10, 15, 20 min after birth
• Incidence of shivering
• Incidence of shivering treated with dexmedetomidine
• Yes/no responses to the four Drake 2013 questions postoperatively
• Newborn Apgar score
• Newborn weight

Statistical Analysis Maternal and newborn demographic parameters (e.g., age, weight, height, BMI, gravida and parity, gestational age, fetal morphology and weight, obstetric factors), clinical parameters (e.g., shivering, BP at different times) will be summarized using descriptive statistics (mean, standard deviation, median, quartile, frequencies, proportions). Categorical data will be presented as counts and proportions. The main analysis will compare the difference between the two MAP measurements taken five minutes after birth. A Bland-Altman analysis will estimate the mean bias and 95% limits of agreement, with 95% confidence intervals. A Deming regression will also estimate proportional bias, with 95% confidence intervals. Secondary analyses will include similar analyses for other time points. Additionally, a multivariable mixed linear regression model will assess the association between measurement differences and time, adjusted for confounding factors measured before surgery (age, fasting hours, weight). Random intercepts and slopes will be estimated for each patient.

Data collection and Analysis All the necessary information obtained throughout this research is considered confidential information and will be obtained by the investigators and will be secured in a locked drawer file and transcribed manually into an electronic secure data set (a secure Excel sheet) for data analysis that will only be accessible by the investigators. Data will be obtained directly from the patient, from their medical files (registry of CHU Sainte-Justine, Dossier Santé Québec, and other hospital files if necessary) and from the study. Only the investigators will perform data analyses, such as Bland-Altman analyses, and interpret the results. No adverse events are expected in this study, but the investigators will nonetheless monitor for possible bruising, skin damage, nerve damage, and blood clots (theoretically possible but not clinically observed) and will alert clinical caretakers if observed.

Sample Size Calculation Based on previous observations, the distribution of arm MAP is 78.3, SD 7.1. Preliminary work in a non-obstetric population of 250 patients found arm MAP of 96.34 ± 11.71 mmHg. Based on this data, the investigators postulate a mean difference of 0 and SD of 6. To observe 95% of differences within a 15 mmHg agreement limit at alpha 0.05 and 80% power, 108 patients are needed. The investigators will recruit 110 to account for possible measurement issues.

Ethical Considerations Recruitment Patients will be approached by their obstetrician during pregnancy follow-up regarding the existence of a research project. They will be met upon arrival in the operating room waiting area. Consent will be explained and obtained before surgery. The study's implications will be explained, and questions will be answered. It will be explained that consent will not affect their care. Patients may withdraw consent at any time and will then receive standard treatment.

Risks and Benefits

Expected Benefits:

This study offers no direct benefit to participants.

Risks:

No discomfort is expected for participants, as they will be treated per standard care, and the addition of an ankle BP cuff may only cause slight discomfort at the first measurement before neuraxial anesthesia.