Objective
To investigate the extent and risk factors for hypotension among women undergoing elective cesarean section, and whether maternal hypotension has any impact on perinatal infant outcome.
Study Design
Retrospective analysis of data on 919 mother-infant pairs after elective cesarean section that involved the use of regional anesthetic. Data collection included information on maternal blood pressure during the cesarean section procedure and any infant perinatal complications.
Results
Nearly one-half of the mothers underwent a decrease in their mean arterial blood pressure by ≥30%. The risk factors for hypotension included preoperative hypertension, older age, type of spinal anesthesia, and a higher infant birthweight. A drop in the maternal mean arterial blood pressure exceeding 30% or even 50% compared with the preoperative value was not found to predict any perinatal complications.
Conclusion
Despite a very high prevalence of maternal hypotension during cesarean sections, term infants tend to tolerate this placental blood perfusion challenge without any major sequel.
Cesarean section (CS) accounts for 20-25% of all births in Israel and more than 30% of all births in the United States (National Center for Health Statistics 2005). Many CSs are elective because of a previous CS, multiple pregnancy, breech presentation of the fetus, estimation of high fetal weight, maternal medical conditions, maternal request, and others. Anesthetic used in elective CS is mostly regional (epidural or spinal); 1 well-documented and common effect of regional anesthesia is maternal hypotension. Hypotension results from temporary sympathectomy leading to reduced preload (increased venous capacitance and pooling of blood volume in the splanchnic bed and lower extremities) and reduced afterload (decreased systemic vascular resistance), causing lower maternal mean arterial blood pressure (MABP) and reduced uteroplacental perfusion. Several studies have shown that the rate of hypotension is higher for spinal anesthesia compared with the epidural route, whereas others have shown similar rates of hypotension, but appearing earlier and more rapidly in the former. The various available medical interventions for preventing hypotension were not found to be consistently effective. The common preventive approach is the prophylactic use of intravenous (IV) fluid before regional anesthesia, after hypotension has begun evolving, combining the fluid with vasopressor medications, such as ephedrine and neosynephrine, as needed, and increasing the IV fluid administration as needed.
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The effect of maternal hypotension on the fetus’s condition could be important, but this has not been investigated in depth. In fact, the fetus is rarely monitored at this stage of the surgical procedure. A number of studies found a higher rate of acidemia in cord blood of infants born to mothers who gave birth under general anesthesia compared with regional anesthesia, and higher rates in spinal compared with epidural anesthesia, presumably because of decreased placental blood flow.
It is well established that term infants born by elective CS are at a higher risk for having respiratory distress develop after birth compared with infants born by vaginal delivery. To the best of our knowledge, no studies have been performed to evaluate the clinical outcome of newborn infants born by elective CS under regional anesthesia that caused maternal hypotension. This study was designed to evaluate the risk factors, rate, and extent of maternal hypotension after regional anesthesia for elective CS, and to document the short-term clinical outcome of term newborn infants born to mothers who underwent elective CS and had severe vs milder degrees of hypotension develop.
Materials and Methods
We retrospectively reviewed the retrieved data on newborn infants and their mothers who gave birth at the Sheba Medical Center (≈10,000 deliveries per year) in Israel during a 15-month period (May 2006 through July 2007). All mothers who gave birth at term (gestational age [GA], 37-42 completed weeks) by an elective CS with regional anesthetic (either spinal or epidural) were included. Excluded were mothers who had multiple pregnancy and infants with major congenital malformations. The data recorded on the computerized system of the obstetrics operation room included maternal age, number of parity and gravida, indications for CS, type of anesthetic (spinal or epidural), blood pressure parameters on admission and thereafter during the administration of anesthetic throughout the operation until delivery, and medications and volume of IV fluid needed during the procedure. All details were recorded until the infant’s delivery (maternal hypotension after the infant was delivered was not recorded). Blood pressure (BP) was measured noninvasively at 1-minute intervals beginning 1 minute after regional anesthetic was given. In case of ≥10% drop in MABP, IV fluids were given at a rate of 1 L/h. If a further drop of ≥20% occurred, either ephedrine (5-15 mg) or neosynephrine (50 μg) was given.
The data collected from the infant’s medical files included GA, birthweight (BW), sex, Apgar score, the need for a pediatrician to be present (not routine protocol during elective CSs in our institution), postnatal complications, the need for oxygen or antibiotic treatment, the rate of phototherapy, or feeding intolerance.
Statistical analysis
Continuous variables were compared by using analysis of variance. Categorical variables were compared using the Pearson χ 2 test or Fisher exact test. A P value of ≤ .05 was considered significant. Logistic regression was used to determine those variables that were most significantly associated with maternal hypotension. In addition, we used logistic regression to determine risk factors for short-term neonatal outcome, such as a low Apgar score and respiratory distress.
The institutional research ethics board at the Chaim Sheba Medical Center approved the study.
Results
During the study period, 13,309 infants were born at our center, of which 12,136 were born at term. Of the latter group, 2878 (23.7%) were born by CS for any indication. After excluding the cases that did not fulfill the study criteria (ie, emergency CS, multiple pregnancy, use of general anesthetic, and infants with congenital major malformations), there were 981 mother-infant pairs, of whom another 62 were dropped because data on BP before or during CS were not available. The remaining 919 mother-infant pairs comprised the study group and their characteristics are listed in Table 1 .
| Characteristics | Value | Range |
|---|---|---|
| Maternal data | ||
| Age, y | 34.3 ± 5 | 19–56 |
| Deliveries, n | 2.4 ± 1.3 | 1–11 |
| Diseases | ||
| Hypertension | 40 (4.4) | |
| Diabetes | 128 (13.9) | |
| Anesthesia type | ||
| Spinal, n (%) | 742 (80.7) | |
| Epidural, n (%) | 177 (19.3) | |
| Infant data | ||
| Gestational age, wk | 38.3 ± 0.9 | 37–42 |
| Birthweight, g | 3299 ± 457 | 1965–4765 |
| Male sex, n (%) | 473 (51.5) | |
| Apgar at 1-min <7, n (%) | 9 (1) | |
| Meconium-stained amniotic fluid, n (%) | 19 (2) | |
| Pediatrician in attendance, n (%) | 66 (7.2) | |
| Respiratory distress, n (%) | 55 (6) | |
| Oxygen need for >24 h, n (%) | 13 (1.4) | |
| Days to discharge | 3.8 ± 1.5 | 2–16 |
The rate of maternal diabetes was relatively high (13.9%) compared with the rate of diabetes among all mothers in labor in our institution (5.4%). Only 2% of our studied cases had meconium-stained amniotic fluid. There was a 1% rate of a low Apgar (<7) score at 1 minute, followed by normal scores at 5 minutes.
A total of 427 (46.5%) of the mothers experienced a drop in their MABP of ≥30% compared with their pre-CS BP. The comparison of mothers whose BP dropped by ≥30% with those whose BP dropped <30% is shown in Table 2 . More women in the former group were older, received spinal anesthetic, had a preoperative diagnosis of hypertension, had a higher preoperative MABP, had a higher maximal heart rate (HR) during the operation, received a higher fluid volume, and needed antihypotensive medications during the CS. The 2 groups were similar for other maternal diseases or medications (data not shown) as well as the numbers of deliveries ( Table 2 ).
| Characteristics | MABP drop ≥30% n = 427 | MABP drop <30% n = 492 | P value |
|---|---|---|---|
| Maternal data | |||
| Age, y | 34.7 ± 5 | 33.8 ± 5.1 | .007 |
| Deliveries, median (IQR) | 2 (1-3) | 2 (2-3) | .2 |
| Diseases | |||
| Hypertension | 25 (5.9) | 15 (3) | .051 |
| Diabetes | 67 (15.7) | 61 (12.4) | .15 |
| Anesthesia, n (%) | .044 | ||
| Spinal | 357 (83.6) | 385 (78.3) | |
| Epidural | 70 (16.4) | 107 (21.7) | |
| Preoperative MABP | 108 ± 13.5 | 101 ± 13 | < .001 |
| Lowest MABP during surgery | 61 ± 11.5 | 82 ± 10.5 | < .001 |
| Maximum heart rate | 130.6 ± 20 | 125 ± 17.6 | < .001 |
| Mean iV volume during surgery, mL | 1606.8 ± 599 | 1425.6 ± 514 | < .0001 |
| IV fluid volumes during surgery, n (%) | < .0001 | ||
| ≤1.5 L | 195 (47) | 275 (59) | |
| 1.5-2.5 L | 197 (47.5) | 182 (39.1) | |
| ≥2.5 L | 23 (5.5) | 9 (1.9) | |
| Antihypotensive medications during CS, n (%) a | 275 (64.4) | 143 (29.1) | < .001 |
| Infant data | |||
| Gestational age, wk | 38.3 ± 0.9 | 38.3 ± 0.9 | .62 |
| Birthweight, g | 3337 ± 434 | 3267 ± 474 | .02 |
| Male sex, n (%) | 214 (50.1) | 259 (52.7) | .43 |
| Apgar at 1-min <7, n (%) | 5 (1.2) | 4 (0.8) | .74 |
| Meconium-stained amniotic fluid, n (%) | 9 (2.1) | 10 (2) | > .99 |
| Pediatrician attendance at surgery, n (%) | 35 (8.2) | 31 (6.3) | .3 |
| Respiratory distress, n (%) | 25 (5.9) | 30 (6.1) | .89 |
| Oxygen treatment, n (%) | 23 (5.4) | 30 (6.1) | .67 |
| Oxygen >24 h, n (%) | 5 (1.2) | 8 (1.6) | .59 |
| Days to discharge (IQR) | 3 (3-4) | 3 (3-4) | .21 |
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