CHAPTER 185 Rescuing Foals during Dystocia
During dystocia in mares, minutes count. If dystocia is not relieved rapidly, the chances of the foal surviving quickly diminish. A series of techniques designed to rescue the fetal foal during labor through fetal resuscitation have been collectively termed EXIT (ex utero intrapartum treatment). The goal of fetal resuscitation during dystocia is to maintain the foal and buy time for correction of the dystocia either by vaginal manipulations (controlled vaginal delivery) or cesarean section. This should be followed by resuscitation to revive the foal that is failing the birth transition.
Irrespective of the nature of the circumstances of the dystocia, survival of the fetal foal is inversely related to the length of second-stage labor. Recent advances attempting to shorten stage 2 labor have focused primarily on developing dystocia correction protocols, with efforts directed at attempting the most successful therapeutic manipulations while still moving refractory cases toward definitive correction by cesarean section in a timely manner. EXIT complements these protocols by initiating resuscitation while the foal is still in the birth canal. If EXIT techniques can be applied successfully, the foal can be rescued and the need for haste is obviated, allowing more time for safely correcting the dystocia.
Resuscitation of the fetal foal can begin even before the foal is fully engaged in the birth canal. Although most dystocia cases are not anticipated, as soon as it is apparent that stage 2 of labor might be prolonged, the mare should be started on intranasal oxygen insufflation. The countercurrent pattern of equine placental perfusion facilitates an increase in maternal partial pressure arterial oxygen (PaO2) and ensures maximum transfer of oxygen to the fetus wherever placental perfusion is maintained. A second method of increasing oxygen delivery to the fetus over the short term is rapid expansion of the mare’s vascular volume with crystalloid fluid administration. This is vital if the mare’s perfusion is compromised because placental perfusion can be severely compromised. In women, even if perfusion is not compromised, a rapid increase in maternal plasma volume transiently but significantly increases oxygen delivery to the fetus. The combination of maternal oxygen insufflation and fluid therapy are important steps in fetal resuscitation that can be undertaken even before the foal enters the birth canal.
The most effective EXIT technique is intubation and ventilation of the foal while it is still in the birth canal. The equipment needed to perform EXIT is identical to that needed for birth resuscitation. Although no special equipment is needed, minor modifications can make the procedure easier. Required equipment includes an appropriate-sized endotracheal tube (7- to 10-mm internal diameter, 55 cm long, cuffed tube) and self-inflating bag-valve device. Useful but optional equipment includes a capnograph or other carbon dioxide detector, extension tubing fitting between the self-inflating bag and the endotracheal attachment/valve, polyethylene tubing with a syringe adaptor long enough to deliver drugs to the trachea beyond the endotracheal tube, and a source of oxygen. A long intravenous catheter, such as a 24-inch Intracath (16-gauge, 24-inch Intracath, Desert Pharmaceutical Deseret Pharmaceuticals Inc., Sandy, UT 84070), which can be protected by its plastic sleeve and kept clean between uses, makes a convenient drug-administration catheter. An extension tube, which can be made from ventilator tubing, inserted between the self-inflating bag and valve complex attached to the endotracheal tube, enables ventilation of the foal when its head is well within the birth canal without introducing excessive dead space to the system. All the usual resuscitation drugs should be available; epinephrine and vasopressin are the most important.