CHAPTER 65Prefoaling and Postfoaling Complications
COLIC IN THE PERIPARTURIENT MARE
Abdominal pain following delivery of a foal is normal in most mares. Uterine contractions that persist after foaling and expulsion of fetal membranes may be accompanied by some degree of discomfort, occasional rolling, and mild signs of distress. Judgment of the severity of postpartum pain is important so that more serious causes are not overlooked.1 When examining periparturient mares showing signs of abdominal pain there are a number of complications to consider; these include rupture of the cecum or colon, colonic torsion and ischemic necrosis of the small colon2 as well as uterine torsion, rupture of the urinary bladder and internal hemorrhage from rupture of the utero-ovarian or middle uterine artery.2 In one study looking at postpartum death in mares, gastrointestinal disorders were the second most common cause, the majority being from perforation of the cecum.3 Although many mares may eat less on their own as parturition nears,4 one management technique that may reduce the incidence of gastrointestinal rupture is the reduction of roughage intake in the last few days prepartum.5
Broodmares late in gestation and after parturition appear to be at greater risk of large colon torsion than other horses.6 This is likely due to the stretched abdominal musculature, which permits greater movement of the colon. The large late-gestational uterus may induce repositioning of the colon or partially obstruct the right ventral colon, leading to gas retention and eventually to torsion.7
Segmental ischemic necrosis of the descending colon can occur with rectal prolapse in which more than 30 cm of the rectum is prolapsed. Any condition causing tenesmus, including parturition, with or without dystocia, can lead to prolapse.7 Some mares may suffer mesocolon tears without rectal prolapse. These cases are difficult to distinguish from the mild pain associated with uterine involution.8 There is extensive collateral blood supply to the small colon; if the injured segment is limited, there may be sufficient blood supply to maintain intestinal viability. However, the compromised area may undergo fibrosis with subsequent narrowing of the lumen, which predisposes the horses to small colon impactions.7 Exploratory celiotomy is recommended in cases of suspected mesocolon rupture. Although a left flank approach is possible,2 the recommended approach is ventral midline7 in order to fully evaluate the lesion and to allow resection and anastomosis of the small colon, if indicated. If the lesion is inaccessible, a permanent colostomy may be indicated.7
PERIPARTURIENT HEMORRHAGE
Rupture of a Major Vessel
Clinical Signs and Diagnosis
The middle uterine, utero-ovarian, and external iliac arteries are the major vessels that supply blood to the uterus. Though any of these may rupture, uterine artery rupture is most common.9,10 The vessel may rupture at any point in its course; however, the middle third is the usual site.9 In a study of postpartum deaths, almost 40% were due to uterine artery rupture.3 Incidence and severity of angiosis in endometrial vessels increases with the number of previous pregnancies and age.11 Long-standing changes in the elastic and collagen fibers may predispose to rupture. These changes have been described as senile degenerative changes.9 A correlation of low serum copper levels with artery rupture has been documented,12 and low copper may account for vessel fragility in aged mares.13 There appears to be a predilection for the right-side uterine vessel rupture.3,14 This may be because the cecum displaces the uterus to the left, which places increased tension on the vessels in the right broad ligament. This condition may occur in dystocia, as well as routine deliveries.3,4 Although hemorrhage may occur before, during, or after parturition, the first 24 hours postpartum is the most common time frame.15
Heart rate and mucus membrane color should be monitored in mares with dystocia. Though the mucus membrane color may not initially change, eventually the membranes will become pale and blanched. Mares may be very tachycardic with heart rates up to 140 beats per minute. Clinical signs may proceed very quickly. The mare may be found dead or moribund during or after birth.16 If the blood is contained within the broad ligament, the bleed may be self-limiting as a hematoma develops within the broad ligament. These mares may be trembling and show signs of pain, likely due to stretching of the broad ligament.3,15 Although rectal palpation can confirm a diagnosis of a hematoma developing in the broad ligament, this is often very painful to the mare and may be enough to cause fatal elevation of the mare’s blood pressure.16 The total protein and packed cell volume will likely not change immediately due to a relative loss of erythrocytes and plasma. Splenic contraction may also temporarily increase the hematocrit.17 Abdominal ultrasound examination and abdominocentesis are of diagnostic value to confirm that hemorrhage has occurred.16 Treatment of these mares may include conservative management or more aggressive medical therapy for shock, and it is up to the clinician to decide which approach to take based on the circumstances at hand. Surgical exploration to attempt repair of the vessel is contraindicated.
Treatment
Conservative management includes stall rest in a quiet, dark area with minimal disturbance. It is often best to leave the foal in the stall to keep the mare as quiet as possible.17 Sedatives should be used with caution (especially acetylpromazine) because they may exacerbate hypovolemic shock.15,16 The goal of conservative therapy is to reduce arterial pressure and encourage platelet-fibrin plug formation to seal the rent in the vessel wall.16
Although aggressive intravenous fluid volume replacement will elevate the blood pressure, in some instances it may be warranted and has proven successful to save valuable mares.3,16,17 Initial emergency therapy should include 2 to 3 L hypertonic saline followed by 10 to 20 L lactated Ringer’s solution over a period of 2 to 4 hours. An alternative to hypertonic saline would be the use of colloids such as plasma or hetastarch.17 Supplemental oxygen via nasal insufflation at 5 to 10 L/min may also be initiated during the resuscitative period.16 If the hematocrit continues to drop to less than 15%, whole blood transfusions (6 to 8 L over several hours) may be necessary.17
In addition to fluid volume replacement, flunixin meglumine (1.1 mg/kg) should be administered to reduce the inflammatory cascade, as well as to improve the comfort level of the mare.16 Low-dose oxytocin (10 to 20 IU) may be useful to promote uterine involution. This may decrease the weight of the uterus and the tension on the ligaments, as well as decreasing the blood supply to the uterus.16,18 Higher doses may induce a colic episode that could turn into fatal hemorrhage and should be avoided. If the mare survives the initial hemorrhagic crisis, broad-spectrum antibiotics are indicated to protect the mare from multiorgan failure that may be secondary to ischemic/reperfusion damage,17 as well as to prevent infection of the hematoma.19
Aminocaproic acid is an antifibrinolytic amino acid used in human medicine. The drug binds reversibly to plasminogen and therefore blocks the binding of plasminogen to fibrin and its activation and transformation to plasmin. Through this mechanism, there is inhibition of tissue fibrinolysis and a stabilization of clots.20 Conjugated estrogens can shorten prolonged bleeding times in humans; however, there is no documentation of the effect of these drugs in horses. The mechanism of conjugated estrogens on the bleeding time is unknown.20 There is a delayed onset of action, though the duration of effect in humans is 10 to 15 days. The conjugated estrogens are useful for long-lasting hemostasis but may not be of benefit in the acute hemorrhagic crisis. Anecdotal reports suggest that a single intravenous dose of naloxone (8 mg) may be efficacious in reducing hemorrhage. However, data have been extrapolated from small animals, and evidence of effect in horses is lacking.4,15,17 Historically, 10% buffered formalin given intravenously was considered to aid hemostasis. Recent studies were not able to prove any effect of formalin on coagulation parameters or bleeding times in normal horses.21 Because of the lack of evidence of efficacy in horses, these drugs should be used with caution.
UTERINE TORSION
Uterine torsion is an infrequent cause of equine dystocia, estimated at 5% to 10% of all serious equine obstetric problems.22 The underlying cause of uterine torsion is unknown; however, vigorous fetal movement, sudden falls, and a large fetus in a small volume of fluid have been proposed as contributing factors.23 Uterine torsion in the mare occurs less frequently than in the cow; however, there is a greater degree of difficulty in resolving the torsion, and the survival rate is lower in horses.24
Mares with torsions commonly present with signs of colic, with a duration of 6 hours to several days25; however, there are reports of chronic torsions of 2 to 8 weeks’ duration.26,27 The stage of gestation may range from 7 months to term, though in one report most were at 9.6 months.28
Clinical signs are the result of abdominal pain and include restlessness, sweating, anorexia, frequent urination, sawhorse stance, looking at the flank, and kicking at the abdomen.15 Rectal temperature and heart and respiratory rates are typically within normal ranges or only slightly elevated.29
Diagnosis
Diagnosis of uterine torsion is based on physical examination and rectal palpation findings. In contrast to the cow, equine uterine torsions rarely involve the cervix; therefore vaginal examination is often not diagnostically helpful.15 Upon rectal palpation, the broad ligaments are tense and spiraling in the direction of the torsion. Some authors believe the torsion is more common in a clockwise direction,24 whereas others believe there is no difference in occurrence.25 In the case of a clockwise torsion, the right uterine ligament is strongly stretched and runs immediately downward under the uterine body. The left ligament runs from its origin, over the body of the uterus to the right of the abdomen. Palpation of the ovaries may aid in identifying the broad ligaments. Any mare in the third trimester that is showing signs of colic should be palpated for uterine torsion. Depending on the stage of pregnancy and the degree and site of the torsion, there may be some constriction of the small colon, which could impede the ability of the palpator to perform a complete rectal examination.28,29 In these cases the viability of the fetus, the integrity of the uterus, or the direction of the torsion may be difficult to determine.28 Treatment should be initiated immediately upon diagnosis of uterine torsion to increase the chances for fetal and maternal survival.23
Treatment
Nonsurgical
If the mare is term and the cervix is dilated, manual detorsion through the cervix may be attempted. This usually is possible only if the torsion is less than 270 degrees.29 A well-lubricated arm may be passed into the uterus to grasp the foal ventrolaterally and rock the fetus back and forth until the fetus and uterus roll into correct position.23 Following correction of the torsion, the mare should begin second-stage labor; however, this may be delayed due to vascular congestion and edema and reduced uterine contractility.29 In some cases of advanced pregnancy, a torsion may go unrecognized and an assisted delivery is attempted. If this occurs, there is a high incidence of uterine rupture and subsequent maternal death due to hemorrhage or peritonitis.24,29
If the mare is preterm, has a closed cervix, or the vagina or cervix is involved in the torsion, an alternate method of correction is recommended. Rolling an anesthetized mare can be used to correct a uterine torsion in the last trimester of pregnancy; however, it is not recommended near term because of the increased risk of uterine rupture.30
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