Association of hemodilution and blood pressure in uncontrolled bleeding

Platelet-derived- Extracellular Vesicles Promote Hemostasis and Prevent the Development of Hemorrhagic Shock

Every year more than 500,000 deaths are attributed to trauma worldwide and severe hemorrhage is present in most of them. Transfused platelets have been shown to improve survival in trauma patients, although its mechanism is only partially known. Platelet derived-extracellular vesicles (PEVs) are small vesicles released from platelets upon activation and/or mechanical stimulation and many of the benefits attributed to platelets could be mediated through PEVs. Based on the available literature, we hypothesized that transfusion of human PEVs would promote hemostasis, reduce blood loss and attenuate the progression to hemorrhagic shock following severe trauma. In this study, platelet units from four different donors were centrifuged to separate platelets and PEVs. The pellets were washed to obtain plasma-free platelets to use in the rodent model. The supernatant was subjected to tangential flow filtration for isolation and purification of PEVs. PEVs were assessed by total count and particle size distribution by Nanoparticle Tracking Analysis (NTA) and characterized for cells of origin and expression of EV specific-surface and cytosolic markers by flow cytometry. The coagulation profile from PEVs was assessed by calibrated automated thrombography (CAT) and thromboelastography (TEG). A rat model of uncontrolled hemorrhage was used to compare the therapeutic effects of 8.7 × 10⁸ fresh platelets (FPLT group, n = 8), 7.8 × 10⁹ PEVs (PEV group, n = 8) or Vehicle (Control, n = 16) following severe trauma. The obtained pool of PEVs from 4 donors had a mean size of 101 ± 47 nm and expressed the platelet-specific surface marker CD41 and the EV specific markers CD9, CD61, CD63, CD81 and HSP90. All PEV isolates demonstrated a dose-dependent increase in the rate and amount of thrombin generated and overall clot strength. In vivo experiments demonstrated a 24% reduction in abdominal blood loss following liver trauma in the PEVs group when compared with the control group (9.9 ± 0.4 vs. 7.5 ± 0.5 mL, p < 0.001>). The PEV group also exhibited improved outcomes in blood pressure, lactate level, base excess and plasma protein concentration compared to the Control group. Fresh platelets failed to improve these endpoints when compared to Controls. Altogether, these results indicate that human PEVs provide pro-hemostatic support following uncontrolled bleeding. As an additional therapeutic effect, PEVs improve the outcome following severe trauma by maintaining hemodynamic stability and attenuating the development of ischemia, base deficit, and cardiovascular shock.

Defining Dogma: Quantifying Crystalloid Hemodilution in a Prospective Randomized Control Trial with Blood Donation as a Model for Hemorrhage

BACKGROUND

The concept of hemodilution after blood loss and crystalloid infusion is a surgical maxim that remains unproven in humans. We sought to quantify the effect of hemodilution after crystalloid administration in voluntary blood donors as a model for acute hemorrhage.

STUDY DESIGN

A prospective, randomized control trial was conducted in conjunction with community blood drives. Donors were randomized to receive no IV fluid (noIVF), 2 liters of normal saline (NS), or 2 liters lactated Ringer's (LR) after blood donation. Blood samples were taken before donation of 500 mL of blood, immediately after donation, and after IV fluid administration. Hemoglobin (Hgb) was measured at each time point. Hemoglobin measurements between time points were compared between groups using standard statistical tests and the Bonferroni correction for multiple comparisons. Statistical significance was set at p ≤ 0.0167.

RESULTS

Of 165 patients consented, 157 patients completed the study. Average pre-donation Hgb was 14.3 g/dL. There was no difference in the mean Hgb levels after blood donation between the 3 groups (p > 0.05). Compared with the control group, there was a significant drop in Hgb in the crystalloid infused groups from the post-donation level to post-resuscitation (13.2 vs 12.1 vs 12.2 g/dL, p < 0.0001). A formula was created to predict hemoglobin levels from a given estimated blood loss (EBL) and volume replacement (VR): Hemodilution Hgb = (mean pre-donation Hgb - hemorrhage Hgb drop - equilibration hemoglobin drop - resuscitation Hgb drop) = Mean pre-donation Hgb - [(EBL/TBV)*l] - [(EBL/TBV)*h] - [(VR/TBV)*r], l = 5.111g/dL = blood loss coefficient, h = 6.722 g/dL = equilibration coefficient, r = 2.617g/dL = resuscitation coefficient.

CONCLUSIONS

This study proves the concept of hemodilution and derived a mathematical relationship between blood loss and resuscitation. These data may help to estimate response of hemoglobin levels to blood loss and fluid resuscitation in clinical practice.

Pancreatoduodenectomy and the risk of complications from perioperative fluid administration

BACKGROUND

The dogma of administering sufficient intravenous fluids aggressively to avoid under-resuscitation has recently been challenged. Evidence suggests that excessive perioperative fluid administration may be associated with negative clinical outcomes in gastrointestinal surgery. This study examines the impact of fluid administration on perioperative outcomes in patients undergoing pancreatoduodenectomy (PD).

METHODS

A retrospective analysis of 202 patients undergoing PD between January 2004 and August 2015 was performed. A cut-off value of 10 mL/kg/h was applied (low fluid group: <10 mL/kg/h versus high fluid group: ≥10 mL/kg/h).

RESULTS

There were 76 patients in the low fluid group and 126 patients in the high fluid group. Both groups had comparable age, American Society of Anesthesiologists score and preoperative morbidity rates. Patients in the high fluid group received significantly more total fluids, crystalloids and colloids intraoperatively (P < 0.0001, P < 0.0001 and P = 0.013, respectively) without a significant difference in estimated blood loss (P = 0.586). The net fluid balance on post-operative day 0 was also significantly higher in the high fluid group (P < 0.0001). The mortality rate was 0% in the cohort. Major morbidity rate was 46.1% and 44.4% in low and high fluid groups, respectively (P = 0.836). Reoperation rate was 5.3% for the low fluid group and 1.6% for the high fluid group (P = 0.136). There were no significant differences between the groups for any of the individual complications.

CONCLUSION

This study did not identify a difference in post-operative outcomes between the low and high fluid regime in patients undergoing PD.

Thromboelastography predictive of death in trauma patients

OBJECTIVES

To determine if thromboelastography (TEG) is predictive of patient outcomes following traumatic injury.

METHODS

A retrospective review of 131 patients with pelvic trauma admitted to a Level II trauma center was conducted over four years from 1 January 2009 to 31 December 2012. Patients were identified retrospectively from a prospectively collected database of acute pelvic trauma (n = 372). Eligible patients were identified from billing/coding data as having fractures of the acetabulum, iliac wing or sacral alae. Patients with incomplete TEG data were excluded (n = 241), as were patients with pathological fractures. TEG clotting variables and traditional clotting variables were recorded.

RESULTS

Evaluation of TEG data revealed 41 patients with abnormal clotting times (TEG R). TEG R > 6 was an independent risk factor for death (OR, 16; 95%CI 5.4-53; P = 0.0001). The death rate was 52% in patients with TEG R values ≥6 (n = 13/25). There was no significant association between traditional clotting markers and death rate.

CONCLUSIONS

TEG reaction time value, representing the time of initial clot formation, was the only hematologic marker predictive of mortality in patients with pelvic trauma. Delay in reaction time was associated with a significantly increased death rate, independent of injury severity. The death rate association was not observed with traditional markers of clotting. Future prospective studies may be warranted to determine the presentation and significance of TEG abnormalities when resuscitating patients with orthopaedic trauma.