In this author’s experience presurgical peritoneal fluid samples from uncomplicated uterine torsion cases have not revealed any values outside of the normal range. If neglected or misdiagnosed, mares may develop significant uterine compromise that results in changes in the composition of the peritoneal fluid. WBC counts in excess of 10,000 cells/μl in conjunction with total protein levels above 3.0 g/dl are cause for concern. When abnormalities are detected, the expense of a ventral midline celiotomy to evaluate the condition of the uterus may be justified. Alternatively, results of peritoneal fluid analysis may support a decision for euthanasia on economic grounds.
Normal Foaling Process
In prepartum animals and in mares with uncomplicated deliveries (oxytocin-induced or natural foaling), peritoneal fluid is clear to yellow unless it is red-tinged as a result of blood contamination. The WBC count in the postpartum samples may be increased compared with the prefoaling values, but should remain within the normal range for the laboratory. This slightly increased peritoneal fluid mononuclear cell count (WBC still <5000 cells/μd) seen in foaling mares may be caused by normal hemodynamic changes in the immediate postpartum period. When the fetus is delivered, pressure on the great vessels is removed and the volume of peritoneal fluid may decrease. Thus, the cellularity of the remaining fluid would be expected to increase. Although the WBC count in clinically normal postdystocia cases also remains at less than 5000 cells/μl, the increased cellularity is the result of an influx of neutrophils, probably in response to hyperemia and increased endothelial permeability. However, any bruising and inflammation within the uterine wall is generally not severe enough to cause leakage of protein-rich fluid. The TPr should remain at less than 2.5 g/dl.
It may be beneficial to obtain a peritoneal fluid sample from referred obstetric cases. In most instances the foal will be dead, and the fluid analysis will provide a baseline that can document preexisting conditions (e.g., uterine tear) before further vaginal intervention. Evidence of a laceration would warrant an immediate cesarean section. The duration of the dystocia before successful fetal extraction does not appear to affect the composition of the peritoneal fluid. In difficult obstetric cases that have been subjected to prolonged manipulations before referral to a veterinary hospital, the peritoneal fluid profile is generally not altered from the normal range. The author has managed cases with an emphysematous or macerated fetus in which the composition of the peritoneal fluid samples was not abnormal. Dystocia itself does not necessarily cause significant changes in the peritoneal fluid. If an experienced obstetrician performs the vaginal manipulations and/or fetotomy the fluid should remain grossly normal.
The author has studied the peritoneal fluid from more than 50 cases that remained clinically normal after resolution of a dystocia. None of the median values changed significantly in the peritoneal fluid of these postdystocia mares. However, although the median WBC counts remained within the laboratory reference limit (<5000 cells/μl), some mares did develop slightly increased cell counts. Although TPr exceeded normal limits (as high as 3.4 g/dl) in 3 cases, the cell count never exceeded 10,000 cells/μl in mares that remained clinically normal. The preponderance of neutrophils may reach 90% in some cases. Only one mare had more than one peritoneal value elevated on either day 1 or day 2. In this author’s experience, those mares that are destined to become clinically ill will have at least two of the TPr, WBC count, and percent neutrophil values significantly elevated above the normal reference range.
As might be expected, mares that experience postdystocia complications have significantly higher median peritoneal fluid values for TPr, WBC count, and percent neutrophils than do mares that make an uneventful recovery. The markedly increased WBC counts in the mares with uterine tears or with vaginal lacerations involving the peritoneal cavity will cause the peritoneal fluid to appear cloudy, with a dark orange color from the increased erythrocyte numbers. These cases are likely to have TPr, WBC count, and percent neutrophil values that exceed 3.0 g/dl, 15,000 cells/p.1, and 80%, respectively. WBC counts often exceed 50,000 to 100,000 cells/μl. A mare with a partial thickness uterine tear is unlikely to have elevated TPr or WBC counts immediately postpartum. However, the peritoneal fluid values may be increased within 2 to 3 days depending on the severity of the damage to the uterine wall.
The normal parturient process in the mare does not entail epithelial loss from the endometrium. An intact endometrium appears to be able to prevent absorption of endotoxin and bacteria, whereas devitalization permits diapedesis and peritoneal contamination. Peritonitis is likely to develop subsequent to severe necrotizing endometritis as areas of transmural necrosis extend through the myometrium to the uterine serosa. Complete perforation of the uterine wall is not necessary for peritonitis to develop if traumatic obstetric manipulations have damaged the uterine wall. However, recent research has proven that even a fetotomy procedure does not alter the composition of the postpartum peritoneal fluid if it is performed correctly.
Cases with rupture of the uterine artery and associated development of a broad ligament hematoma tend to have markedly elevated TPr values (as high as 5.0 g/dl), but the WBC count is likely to remain within the normal range (<5000 cells/μl). Broad ligament inflammation around a uterine artery hematoma may explain the high protein levels seen in these cases. Specific gravity values are inevitably increased if the TPr is elevated. A tear in the broad ligament subsequent to a uterine artery rupture invariably results in a bloody tap, with an elevated red blood cell count in the peritoneal fluid. Even if a clot has contained most of the hemorrhage within the broad ligament, there is often considerable blood loss into the peritoneal cavity. In this author’s opinion these mares should not be transported, because movement could destabilize the clot and prove fatal. Postpartum hemorrhage is discussed in detail in site.
Rupture of the mesocolon is unlikely to cause an immediate increase in the WBC count. However, the compromised segment of bowel soon loses its integrity and a massively increased WBC count (as high as 150,000 cells/μl) can occur within 48 hours as peritonitis ensues. An intussusception of the uterine horn can cause an elevated TPr (3.0 g/dl), but the WBC count tends to remain low unless necrosis has developed in more chronic cases. Retroperitoneal abscessation can be a life-threatening complication following a dystocia. Affected mares exhibit signs of toxemia, and the peritoneal fluid is likely to develop an increased TPr content (3.0-5.0 g/dl) and a massive increase in the WBC count (often exceeding 100,000 cells/μl). These retroperitoneal abscesses often develop from infected hematomas. Thus, retroperitoneal hematomas in a postpartum mare warrant prophylactic broad-spectrum antibiotic coverage.
Repeated abdominocentesis is indicated in cases where clinical signs suggest that a parturient related abdominal lesion may be present, because the peritoneal fluid constituents may change within hours. Several studies have shown that repeated abdominocentesis is not detrimental to the horse and does not cause significant changes in the peritoneal fluid composition. If indicated, a series of peritoneal fluid analyses may provide useful information about the progression and seriousness of the condition. A single, elevated peritoneal fluid value (either TPr, WBC, or percent neutrophils) is likely to be an incidental finding, whereas two or more elevated values may signal the onset of clinical abnormalities. This author’s clinical experience has been that if a postpartum peritoneal fluid sample has TPr greater than 3.0 g/dl in conjunction with WBC count greater than 15,000 cells/μl and a WBC differential count of greater than 80% neutrophils (especially if degenerative changes are present) then a potentially life-threatening lesion is likely. However, peritoneal fluid values should not be viewed in isolation. An abnormal peritoneal fluid analysis must be considered in conjunction with the history and clinical signs that are exhibited by the mare.