Analysis of platlet function in the setting of controlled trauma in dogs using a whole blood electrical impedance platelet aggregometer
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Post-traumatic hemorrhage remains one of the leading causes of human deaths, accounting for 30 to 56 percent of pre-hospital post-traumatic deaths. Research focus has been centered around acute traumatic coagulopathy, with little focus regarding the role of platelet function. Despite having a normal platelet count, platelet dysfunction has been noted in 45.5 percent of human trauma patients at admission, and in 91 percent of cases at some point during their hospitalization. The suspected mechanism of action is an immediate platelet activation in response to tissue injury, which may induce a prolonged refractory state, known as "platelet exhaustion". The purpose of this study was to establish a reference interval for a Chrono-Log whole-blood electrical impedence aggregometer, as well as evaluate immediate postoperative platelet function in dogs undergoing ovariohysterectomy. Forty healthy dogs from 1 to 6 years of age, with no history of congenital coagulopathy, recent surgeries, or illnesses within the last month were enrolled to establish a reference interval. All animals had a normal physical examination, complete blood count (CBC) with a platelet count greater than 200,000/L, and chemistry panel within a week of enrollment. Patients were excluded if they received any medication known to alter platelet function (e.g., non-steroidal anti-inflammatory drugs, steroids, general anesthesia, tranquilizers, fatty acid supplements, or diets with omega-3 fatty acids) in the previous 14 days. Electrical whole blood impedence aggregometry was performed with collagen (2 ug/mL) and adenosine diphosphate (ADP, 10 uM and/or 20 uM), evaluating lag time, amplitude, slope, and area under the curve. Inclusion and exclusion criteria were the same for 20 dogs that underwent ovariohysterectomy. Diagnostics performed in dogs undergoing ovariohysterectomy included a CBC with a platelet count greater than 200,000/L, serum biochemistries, coagulation panel (prothrombin time and partial thromboplastin time), fibrinogen concentration, and physical examination within the week prior to surgery. Samples for platelet aggregometry and fibrinogen were collected preoperatively and immediately postoperatively. We hypothesized that there would be evidence of immediate postoperative platelet dysfunction using ADP and collagen as platelet agonists. Our data was consistent with previously published research, which showed that normal, healthy dogs inconsistently respond to ADP as an agonist in vitro. In addition, the inability to compare dogs to a hospital derived, population-based reference interval and, therefore, the need to use the individual dog as its' own control have been previously published in the literature. Therefore, we were unable to compare the ovariohysterectomy dogs to a reference interval to determine evidence of platelet dysfunction, nor were we able to make any inferences regarding ADP. Our data was not normally distributed, and we were limited in the number of samples that reacted to ADP as an agonist (ADP 10 uM, n equals 4; ADP 20 uM, n equals 6). Therefore, we performed a signed rank test with a one-sided alternative for collagen (n equals 20), comparing pre-operative and postoperative values. The data revealed a statistically significant difference in preoperative and postoperative values for amplitude and area under the curve, as well as fibrinogen concentration. However, given the modest sample size, a clinical relationship between pre-operative and postoperative fibrinogen could not be assumed and this data should be further analyzed in future studies with larger sample sizes. In conclusion, our data revealed that platelets may have an impaired response to collagen immediately postoperatively in patients undergoing an ovariohysterectomy. Additional studies are needed to understand how this information impacts this population of dogs further in the postoperative period, as well as the role of fibrinogen and ADP in dogs with surgical trauma.