How to Use EXIT (Ex-Utero Intra-Partum Treatment) to Rescue Foals During Dystocia

Beginning resuscitation of the foal while still in the birth canal can establish viability and may rescue some foals which otherwise would not survive a dystocia.

1. Introduction

The explosive nature of parturition in the mare makes dystocia a life-threatening event for both the mare and the foal [1-4]. The duration of stage II labor has an inverse relationship with foal survival rate. Recent attempts to increase foal survival rates have concentrated on shortening stage II with development of protocols using a well-coordinated dystocia team to minimize time spent until a definitive solution is found and the use of controlled vaginal delivery to rapidly relieve dystocia [1,5]. We have used another technique designed to support foals during a dystocia, called EXIT (ex-utero intra-partum treatment), allowing for survival of the foal during a prolongation of stage II and thus rescuing the foal, relieving the haste to correct the dystocia and allowing for more time to safely correct the dystocia. EXIT was developed by one of us (J.E.P.) as an evolution of birth resuscitation in the early 1990s, but despite the introduction of the technique at a number of forums, it has not become widely known [6-11].

2. Materials and Methods

The equipment needed to perform EXIT is identical to that needed for birth resuscitation. Necessary equipment includes the following:an endotracheal tube appropriate for the breed (usually a 7- to 10-mm internal diameter 55-cm cuffed endotracheal tube [a]), self-inflating bag-valve device [b], a capnograph [c] or other carbon dioxide detectors [d], and oxygen. During a dystocia, if the nose presents in the pelvic canal and is palpable or if the nares are external, intubation should be attempted. Placement of the tube can be checked by passing the hand to the level of the cranial esophagus and insuring that the tube has not been inadvertently placed in the esophagus. Once the airway is secured and the cuff is inflated, the capnograph tube adaptor should be placed between the endotracheal tube and the self-inflating bag and ventilation initiated. If the foal's nose is too far in the canal to allow direct attachment of the self-inflating bag, an extension tube with a central oxygen line to eliminate dead space can be used. The use of EXIT and inflation of the lungs during dystocia does not seem to interfere with the correction of the dystocia.

Once ventilation is initiated, the capnograph can be used to monitor cardiac output [11], ensuring that the foal is alive. Initially, in all cases, a low level of CO2 will be detected (4 - 8 torr) as residual levels are washed out of the lungs. If the foal is alive, ventilation will induce transition from placental circulation to pulmonary circulation, and the end tidal carbon dioxide (ETCO2) will increase. In the compromised foal, the ETCO2 may be as low as 8 - 20 torr, but in the healthy foal and those responding to resuscitation, the ETCO2 will increase to 40 - 60 torr. When ventilation is not limiting, the level of ETCO2 correlates with cardiac output [11].

3. Results and Discussion

The EXIT technique was a natural evolution of early birth resuscitation. In the early 1990s, because our clinic's case load of high-risk pregnancy cases increased, it became the senior author's (J.E.P.) standard operating procedure to be ready to begin aggressive birth resuscitation at the moment of birth. Opportunities arose when birth resuscitation was begun in severely compromised foals before complete delivery, when the head had been delivered, but delivery of the rest of the foal was delayed. Further opportunities arose when foals with bilateral front limb contracture would present with the nose exposed, allowing easy intubation. Successes in these situations led to seeking the nares when it was still in the birth canal and the development of the EXIT procedure. The term EXIT was first coined in human medicine in the 1990s to describe techniques used to maintain gas exchange and monitor fetal viability when circumstances demanded a delay in stage II labor as fetal problems are corrected [12]. We adopted this terminology because it describes the goal of our therapeutic interventions as well. Since that time, the term EXIT in human medicine has been used to describe a series of procedures largely aimed at prolonging placental gas exchange during delayed parturition [13,14], so currently, the term EXIT has different implications in human and veterinary medicine.

In 1997, when our clinic developed a dystocia management protocol, EXIT became a formal component in the management of all dystocia cases. In this setting, EXIT has not only served as a rescue technique but also as a method to determine the viability of the foal. Part of the compensatory response of the hypoxic fetus is suppression of movement to conserve oxygen for vital function [15]. This makes assessment of viability by detection of movement even in response to noxious stimulus difficult. Using movement as a sign of viability, hypoxia-suppressed fetuses can easily be assumed dead. Using EXIT combined with capnography, viability can be more accurately assessed. As long as the endotracheal tube is placed properly, fetal foals with no detectable ETCO2 are dead, those with low ETCO2 have low cardiac output and are experiencing significant distress, and those with normal or high ETCO2 are viable and likely to survive. In a series of 11 foals that received EXIT during correction of dystocia, 4 were confirmed dead before birth, and 7 were successfully resuscitated [5]. During correction of dystocia if fetal demise is confirmed, fetal manipulations can be performed with less haste. If the fetus is found viable through successful EXIT, fetal manipulations can be performed with less haste because EXIT will support fetal life until delivery, and the main reason for haste, preserving the foal's life, has been ensured. Although EXIT seems to have a favorable effect on the short-term or long-term outcome in those foals confirmed viable when the airway is secured, the number of cases we have studied are small, and firm conclusions will have to await additional cases with controls.

Another advantage of EXIT in situations where general anesthesia is necessary to correct dystocia because of the need to perform controlled vaginal delivery or cesarean section is the redirection of placental blood flow to the lungs. Once EXIT initiates pulmonary ventilation, there is a decrease in placental blood flow. This seems to be associated with rise in fetal pO2, but the exact mechanism is unclear [16]. Although the use of oxygen during birth resuscitation remains controversial, its role in redirection of placental blood flow is one reason in favor of its use during EXIT. The advantage of reduced placental blood flow is decrease transfer of anesthetic agents and other drugs from maternal circulation to the fetus. Although difficult to quantitate, antidotal experience shows a remarkable reduction in neonatal depression after delivery by cesarean section when EXIT is performed throughout the surgery.

As referral centers develop dystocia management protocols and expertise in handling dystocia cases, a limiting factor in success can be the travel distance to the referral center [5]. Another possible role for EXIT is to maintain fetal viability during shipment. EXIT is only possible if the nares are palpable in the birth canal and intubation is successful, which excludes a percentage of dystocia cases. If EXIT can be initiated at the farm, the successful referral radius for a center with a dystocia team may be significantly increased. In these cases, the only necessary equipment would be an endotracheal tube and a self-inflating bag. Oxygen would not be necessary. A carbon dioxide detector would be useful to reassure proper endotracheal placement and a viable foal, but it too would not be necessary, because transport of the mare for correction of dystocia would be necessary, regardless of the viability of the foal.

EXIT procedures provide the luxury of time to correct dystocia, a means to assess fetal viability, a means to rescue fetal foals during dystocia, and a means to increase the successful referral radius. During equine dystocia, the use of EXIT should be considered.

Footnotes

1. Global Veterinary Products, Inc., New Buffalo, MI 49117.
2. Ambu-bag; Ambu, Inc., Glen Burnie, MD 21060.
3. SurgiVet; Advantex International B.V., 5602 BK Eindhoven, The Netherlands.
4. Nellcor Easy Cap II; Nellcor, Pleasanton, CA 94588.