Discussion Questions

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  What were the objectives of the study?

  
  
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  How were the study and control groups defined?

  
  
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  What were the primary and secondary outcomes?

  
  
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  How was sample size of the study determined?

  
  
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  What are the key findings of the study?

  
  
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  What are the strengths and limitations of the study?

  
  
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  How generalizable are the findings of the study?

  
  
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  Will this study change your practice?

Introduction

The most recent estimate reveals that the cesarean delivery rate in the United States is at an all-time high: 31.8% of births in 2007. That statistic confers instant relevance on a new study by Maayan-Metzger and colleagues. While it is well known that maternal hypotension can occur after regional anesthesia, especially spinal anesthesia, there is a paucity of data on its frequency and severity—and almost none on outcomes in neonates born to women who develop hypotension. After weighing the study’s potential contribution to the literature, journal club members wished they had thought of performing a study like this one.

Sean C. Blackwell, MD and George A. Macones, MD, MSCE

Study Design

Blackwell: What were the objectives of the study?

Nguyen: The objectives were to determine the frequency and severity of maternal hypotension among women undergoing elective cesarean delivery; to evaluate risk factors for the development of hypotension; and to determine the frequency of adverse short-term neonatal outcomes following maternal hypotension.

Blackwell: What was the study design?

Lee: This was a historic cohort study of women undergoing elective cesarean delivery at a single medical center, Sheba Medical Center, in Ramat-Gan, Israel, over a 15-month period from 2006-2007. Data were derived from a computerized hospital data system for the obstetrical operating room.

Blackwell: What were the eligibility criteria?

Lee: Inclusion criteria were term pregnancy (37-42 weeks), elective cesarean delivery, and use of regional anesthesia (epidural or spinal). Women with multiple gestations or fetuses with major congenital malformations were excluded.

Blackwell: How did the authors define the study and control groups, and what was the rationale for these definitions?

Lee: The primary comparison was based on changes in maternal mean arterial blood pressure (MABP) at any time during the cesarean section compared to the pre-cesarean MABP. Women who had a decrease in MABP of less than 30% were compared to those who had a decrease of ≥30%. A second comparison was made between women whose MABP dropped by ≥50% and those with a change of less than 50%.

Although reductions of 30% and 50% seem large, the authors don’t provide justification or prior data for these thresholds.

Blackwell: Do you think MABP changes of ≥30 and ≥50% are clinically meaningful?

Pacheco: MABP is calculated as 2 times the diastolic blood pressure (DBP) plus the systolic blood pressure (SBP) divided by 3 [MABP= (2 x DBP + SBP)/3]. On average, an MABP >50 mmHg is necessary for adequate brain perfusion and 80 mmHg is needed for renal perfusion.

Yes, in my experience, I would expect to see some clinical effects with decreases of these magnitudes. Given that this was a healthy population, even with a total study sample size of 919 women, it might be difficult to find differences in severe complications due to their rare frequency.

Blackwell: Are there normal values for MABP in pregnancy or for a pregnant woman at term?

Pacheco: I’m not aware of normative data—at least we don’t use pregnancy-adjusted values in our intensive care units at UTMB. We extrapolate the values from the nonpregnant state.

Blackwell: What clinical factors were available for risk factor analysis?

Lee: Maternal age, gravidity, parity, gestational age, cesarean indications, regional anesthesia type, and maternal medical complications, such as hypertension and diabetes.

Blackwell: What was the sample size of the study, and do you think that was adequate to address the research questions?

Chiossi: No a priori sample size calculation or power analysis was performed. It is possible that the sample size was determined based on the practical aspects of the availability of the data. Given that this was an exploratory study mainly intended to provide frequency and risk factor data, the current sample size seems reasonable. However, if the study had primarily been performed to compare neonatal outcomes, then the absence of such calculations combined with the lack of differences in neonatal morbidity would be an issue. Because this is a term population of mostly healthy mother-infant pairs, the rarity of important adverse outcomes would necessitate a much larger sample size to address that question.