Elective Cesarean Section: Its Impact on Neonatal Respiratory Outcome

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Physiologic events in the last few weeks of pregnancy coupled with the onset of spontaneous labor are accompanied by changes in the hormonal milieu of the fetus and its mother, resulting in preparation of the fetus for neonatal transition. Rapid clearance of fetal lung fluid is a key part of these changes, and is mediated in large part by transepithelial sodium reabsorption through amiloride-sensitive sodium channels in the alveolar epithelial cells, with only a limited contribution from mechanical factors and Starling forces. This article discusses the respiratory morbidity associated with elective cesarean section, the physiologic mechanisms underlying fetal lung fluid absorption, and potential strategies for facilitating neonatal transition when infants are delivered by elective cesarean section before the onset of spontaneous labor.

Section snippets

The changing landscape for human deliveries

Cesarean births rose for a 10th straight year in 2006 to a record 31.1% of all deliveries in the United States. This rate is more than 50% higher than in 1996 and is accompanied by a significant drop in the number of women attempting vaginal birth after a previous cesarean delivery (VBAC) (Fig. 1) [1]. Most of the overall increase can be attributed to the increase in the primary cesarean rates from 14.6% in 1996 to 20.3% in 2005. This rise in the primary cesarean rate coupled with the decrease

Maternal choice: “too posh to push”

Although difficult to quantify, it has been estimated that nearly 4% to 18% of all cesarean deliveries worldwide are done upon maternal request [17]. In the United States, cesarean delivery on maternal request is estimated to be between 2.6% and 5.5% [18]. A recent NIH state-of-the-science consensus seminar, Cesarean Delivery on Maternal Request, reiterates the assertion that maternal request is playing an increasingly important role in obstetricians' decisions to perform cesarean sections [19].

Respiratory morbidity in infants born by cesarean delivery

Several studies have documented the high incidence of respiratory distress and neonatal intensive care unit (NICU) admissions in infants born by cesarean delivery before the onset of spontaneous labor [12], [16], [21], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36], [37], [38], [39], [40], [41], [42], [43], [44], [45], [46], [47], [48], [49]. However, the incidence of birth asphyxia, trauma, and meconium aspiration is lower with cesarean delivery, and these advantages of elective

Role of retained fetal lung fluid in neonatal respiratory morbidity

The fetus has an interesting challenge presented to it at birth [64]. Often at short notice, sometimes with no notice at all, it is asked to rapidly clear its air spaces of the fluid that it has been secreting through much of the pregnancy. The ability of a neonate to self-resuscitate at birth after remaining “submerged” in fluid for much of its life is truly remarkable, considering that victims of near-drowning faced with similar amounts of fluid in the lungs do so poorly [64], [71], [72]. A

How is the fetal lung fluid cleared?

It is now clear that active sodium transport across the pulmonary epithelium drives liquid from lung lumen to the interstitium, with subsequent absorption into the vasculature [64], [81]. In the lung, sodium reabsorption is a two-step process [104]. The first step is passive movement of sodium from the lumen across the apical membrane into the cell through sodium-permeable ion channels. The second step is active extrusion of sodium from the cell across the basolateral membrane into the serosal

What causes the neonatal lung epithelium to switch to an absorptive mode?

Our basic science investigations have focused on physiologic changes that trigger the change in lung epithelia from a chloride-secretory to a sodium-reabsorption mode [64], [71], [81], [87], [113], [114]. Although several endogenous mediators, including catecholamines, vasopressin, and prolactin, have been proposed to increase lung fluid absorption, none explains this switch convincingly [111], [115]. Mechanical factors, such as stretch and exposure of the epithelial cells to air interface, are

Can rescue strategies work once an infant has become symptomatic?

Considerable evidence shows that high levels of endogenous catecholamines at birth may be important for accelerating alveolar fluid clearance [82], [85], [119]. We [115] have shown that β-agonists increase the activity of sodium channels in the lung through a cAMP-PKA–mediated mechanism. It is logical to conclude that, in the absence of an endogenous surge in fetal catecholamines, exogenous catecholamines should be effective in initiating fetal lung fluid clearance. However, recent studies show

If cesarean sections are here to stay, can we make them safer?

As mentioned earlier, delaying elective cesarean birth until 39 weeks seems to be the first logical step in reducing iatrogenic prematurity and excess risk of respiratory distress. Risk of respiratory distress and NICU admissions is inversely proportional to the gestational age. Recent analysis of the MFMU network cesarean section registry by Tito and colleagues confirms this. We believe that antenatal glucocorticoids, after having been introduced in 1972 to enhance fetal lung maturity, now

Summary

In the United States, a significant number of babies each year are delivered by cesarean delivery before onset of spontaneous labor. Although the occurrence of such complications as birth asphyxia, meconium aspiration, and hypoxic-ischemic encephalopathy is reduced, a significant number of these infants develop respiratory distress due to failed transition and may require additional treatments, such as ventilation, surfactant, inhaled nitric oxide, and ECMO. The need is urgent for preventive

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