Abomasal Displacement in Cows – Measurement of Oxygen Saturation of the Abomasal Wall
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KeywordsOxygen Saturation Pulse Oximetry Pulse Oximeter Oximetry Probe Monitor Oxygen Saturation
The monitoring of intestinal oxygen saturation by means of a pulse oximeter is routinely applied in human medicine during surgery of the gastrointestinal tract to evaluate the disturbance of perfusion and assess tissue viability. To some extent, this technique has been applied in veterinary medicine. The purpose of this study was to test the technique in cattle and to describe the influence of gas volume and intraluminal pressure of the displaced abomasum on oxygen saturation of the organ.
The study was performed on 35 cows suffering from left or right abomasal displacement (LDA, 20 cows; RDA (torsions ≥ 180°, 15 cows). The cows, ages 2,5 to 7 years, were a cross between the local dairy cow breed (Schwarzbuntes Milchrind) and Holstein-Friesian.
A pulse oximeter (CardiocapII-CG) was used to monitor oxygen saturation on the displaced abomasum and, as a comparison, on the rumen. The pulse oximetry probe was attached to the highest point of the gas-filled vault of the abomasum and the most caudal aspect of the dorsocaudal ruminal sack (transmission pulse oximetry). The gas pressure was measured by cannulating a needle (diameter 2,1 mm,) and a non-compressible tube connected to the electronic manometer (BMT 401). The gas volume was measured by aspirating the complete gas volume with an aspirator (GF 80) and pipelining the gas into a water-filled container to displace the water. The displaced water volume was registered as the indirect gas volume.
The oxygen saturation of the abomasal wall was lower in cows with right abomasal volvulus (79,4%) than in cows with LDA (83,8%). In comparison to the abomasum, the oxygen saturation of the dorsal rumen was 89,1% in cows with LDA and 89,5% in cows with RDA. The oxygen saturation in cows with LDA did not correlate to the gas pressure nor to the gas volume of the displaced abomasum. In cows with RDA, the oxygen saturation correlated negatively to the gas volume (rs = -0,16) and to the gas pressure (rs = -0,15).
The average intraluminal pressure and the abomasal gas volume in cows with LDA (6,04 ± 2,16 mmHg respectively 7,98 ± 2,041) was significantly lower than in cows with RDA (12,86 ± 5,60 mmHg respectively 11,53 ± 3,861). The weak correlation between gas pressure and gas volume can be a result of other factors which influence the intraabdominal pressure and volume, like ruminal content or tension of the abdominal wall. Factors causing the relatively weak correlation between gas pressure and volume on one hand and the oxygen saturation on the other hand might be the unknown time lapse (in most cases) between the beginning of the abomasal displacement and the admission into the clinic, the imprecise degree of disturbance in the motility and the unknown amount of fluid in the abomasum.
The application of pulse oximetry to the gastrointestinal tract in cattle during laparotomy is feasible and requires a short amount of time. In the cows in this study, the measured oxygen saturation indicated that the perfusion of the displaced abomasum was altered in LDA as well as in RDA. Probable reasons for this disturbance are the impact of pressure caused by the content of gas and fluid to the abomasal wall, the compression of the blood vessels due to the distension of the abomasal wall and the influence of the displacement or torsion of the abomasum itself on the the vessels in the omentum. Severe disturbances in perfusion have to be expected in cases of right abomasal displacement where severe torsions of the abomasum are present. This technique can be useful to establish a prognosis and metaphylactic therapeutic efforts to prevent reperfusions injuries, paralytic postoperative ileus, and abomasal atony.
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