Coagulation Profile Changes Due to Thromboprophylaxis and Platelets in Trauma Patients at High-Risk for Venous Thromboembolism

We hypothesize there are coagulation profile changes associated both with initiation of thromboporphylaxis (TPX) and with change in platelet levels in trauma patients at high-risk for venous thromboembolism (VTE). A total of 1203 trauma intensive care unit patients were screened with a VTE risk assessment profile. In all, 302 high-risk patients (risk assessment profile score ≥ 10) were consented for weekly thromboelastography. TPX was initiated between initial and follow-up thromboelastography. Seventy-four patients were analyzed. Upon admission, 87 per cent were hypercoagulable, and 81 per cent remained hypercoagulable by Day 7 (P = 0.504). TPX was initiated 3.4 ± 1.4 days after admission; 68 per cent received unfractionated heparin and 32 per cent received low-molecular-weight heparin. The VTE rate was 18 per cent, length of stay 38 (25-37) days, and mortality of 17.6 per cent. In all, 76 per cent had a rapid clotting time at admission versus 39 per cent at Day 7 (P < 0.001); correcting from 7.75 (6.45-8.90) minutes to 10.45 (7.90-15.25) minutes (P < 0.001). At admission, 41 per cent had an elevated maximum clot formation (MCF) and 85 per cent had at Day 7 (P < 0.001); increasing from 61(55-65) mm to 75(69-80) mm (P < 0.001). Platelets positively correlated with MCF at admission (r = 0.308, R(2) = 0.095, P = 0.008) and at Day 7 (r = 0.516, R(2) = 0.266, P < 0.001). Change in platelet levels correlated with change in MCF (r = 0.332, R(2) = 0.110, P = 0.005). In conclusion, hypercoagulability persists despite the use of TPX. Although clotting time normalizes, MCF increases in correlation with platelet levels. As platelet function is a dominant contributor to sustained trauma-evoked hypercoagulability, antiplatelet therapy may be indicated in the management of severely injured trauma patients.

Liquid plasma use during "super" massive transfusion protocol

BACKGROUND

A massive transfusion protocol (MTP) presents a logistical challenge for most blood banks and trauma centers. We compare the ratio of packed red blood cells (PRBC) and plasma transfused over serial time points in those requiring MTP (10-30 U PRBC/24 h) to those requiring "super" MTP (S-MTP; >30 U PRBC/24 h) and test the hypothesis that changes in allocation of blood products with use of readily transfusable liquid plasma (LP) improves the ratio of PRBC and plasma during S-MTP.

MATERIALS AND METHODS

All transfused trauma patients (n = 1305) from January 01, 2009-April, 03, 2015 were reviewed. PRBC:plasma ratio was compared for MTP (n = 277) and S-MTP (n = 61) patients, before and after the availability of LP at our institution. Data are reported as mean ± standard deviation or median (interquartile range).

RESULTS

Age was 41 ± 19 y, 52% blunt mechanism, injury severity score 32 ± 16, and 46.3% mortality. In 24 h, requirements were 17 (14) U PRBC and 10 (11) U plasma, with a PRBC:plasma of 1.6 (0.8). Within the first hour, PRBC:plasma for S-MTP versus MTP was 2.1:1 versus 1.7:1 (P = 0.017). With LP, S-MTP patients received significantly lower PRBC:plasma at the first hour (P < 0.001). Before institutional changes, PRBC:plasma positively correlated with PRBC transfused at hour 1 (r = 0.410, R(2) = 0.168, P < 0.001); after institutional changes and the advent of LP, there was no correlation (r = 0.177, R(2) = 0.031, P = 0.219).

CONCLUSIONS

Within the first hour of transfusion, units of PRBC transfused positively correlated with PRBC:plasma, and patients receiving S-MTP had higher PRBC:plasma than those receiving MTP. Changes in our institution's MTP protocol to include LP improved the early PRBC:plasma transfused in patients requiring S-MTP.

Does obesity affect outcomes of adult burn patients?

BACKGROUND

Obesity negatively affects outcomes after trauma and surgery; results after burns are more limited and controversial. The purpose of this study was to determine the effect of obesity on clinical and economic outcomes after thermal injury.

METHODS

The National Inpatient Sample was queried for adults from 2005-2009 with International Classification of Diseases-9 codes for burn injury. Demographics and clinical outcomes of obese and nonobese cohorts were compared. Univariate and multivariate analysis using logistic regression models were performed. Data are expressed as median (interquartile range) or mean ± standard deviation and compared at P < 0.05.

RESULTS

In 14,602 patients, 3.3% were obese (body mass index ≥30 kg/m(2)). The rate of obesity increased significantly by year (P < 0.001). Univariate analysis revealed significant differences between obese and nonobese patients in incidence of wound infection (7.2% versus 5.0%), urinary tract infection (7.2% versus 4.6%), deep vein thrombosis in total body surface area (TBSA) ≥10% (3.1% versus 1.1%), pulmonary embolism in TBSA ≥10% (2.3% versus 0.6%), length of stay [6 d (8) versus 5 d (9)], and hospital costs ($10,122.12 [$18,074.72] versus $7892.07 [$17,191.96]) (all P < 0.05). Death occurred less frequently in the obese group (1.9% versus 4%, P = 0.021). Significant predictors of grouped adverse events (urinary tract infection, wound infection, deep vein thrombosis, and pulmonary embolism) on multivariate analysis include obesity, TBSA ≥20%, age, and black race (all P ≤ 0.05).

CONCLUSIONS

Obesity is an independent predictor of adverse events after burn injury; however, obesity is associated with decreased mortality. Our findings highlight the potential clinical and economic impact of the obesity epidemic on burn patients nationwide.

Hypercoagulability and venous thromboembolism in burn patients

To our knowledge, this is the first comprehensive review on the subject of venous thromboembolism (VTE) and hypercoagulability in burn patients. Specific changes in coagulability are reviewed using data from thromboelastography and other techniques. Disseminated intravascular coagulation in burn patients is discussed. The incidence and risk factors associated with VTE in burn patients are then examined, followed by the use of low-molecular-weight heparin thromboprophylaxis and monitoring techniques using antifactor Xa levels. The need for large, prospective trials in burn patients is highlighted, especially in the areas of VTE incidence and safe, effective thromboprophylaxis.

Initial hematocrit predicts the use of blood transfusion in the pediatric trauma patient

PURPOSE

Initial hematocrit (Hct) is generally not considered a marker of acute blood loss because it is assumed that physiologic response of fluid conservation to hemorrhage is delayed. We challenged this idea by theorizing that admission Hct correlates with conventional signs of shock and predicts the use of blood transfusion during resuscitation of pediatric trauma patients.

METHODS

Data from 1928 pediatric admissions (<18 years) at a Level I trauma center (2000-2012) were compared using standard statistical analyses and logistic regression modeling to identify factors associated with blood transfusion during initial trauma resuscitation.

RESULTS

Overall mortality rate was 3.5%, with a transfusion rate of 10.7%. Factors significantly associated with transfusion were initial Hct, Glasgow Coma Score, base deficit, and injury severity score (all p<0.001). Initial Hct is a stronger predictor for transfusion (area under receiver operator curve (AUC: 0.728) compared to age-specific tachycardia (AUC: 0.689), age-specific hypotension (AUC: 0.673), and altered mental status (AUC: 0.654)). On multivariate analysis, initial Hct was an independent predictor (OR [95% CI]: 2.94 [1.56, 5.52]) along with hypotension (6.37 [2.95, 13.8]), base deficit (4.14 [1.38, 12.4]), and tachycardia (3.07 [1.62, 5.81]).

CONCLUSIONS

Initial Hct correlates significantly with conventional signs of shock and is a strong independent predictor for blood transfusion with better predictability than other clinical factors.

Trauma induced hypercoagulablity in pediatric patients

PURPOSE

Coagulation changes in pediatric trauma patients are not well defined. To fill this gap, we tested the hypothesis that trauma evokes a hypercoagulable response.

METHODS

A prospective observational study was conducted in hospitalized patients (age 8months to 14years) admitted for trauma or elective surgery. Informed consent was obtained from the parents and informed assent was obtained in patients 7years of age or older. Coagulation changes were evaluated on fresh whole blood using thromboelastography (TEG) and on stored plasma using assays for special clotting factors.

RESULTS

Forty three patients (22 trauma, median injury severity score =9; and 21 uninjured controls) were evaluated. For trauma vs control, prothrombin time (PT) was higher by about 10% (p<0.001), but activated partial thromboplastin time was not altered. TEG clotting time (R;p=0.005) and fibrin cross-linking were markedly accelerated (K time, alpha angle; p<0.001) relative to the control patients. d-Dimer, Prothrombin Fragment 1+2, and Plasminogen Activator Inhibitor-1 were all elevated, whereas Protein S activity was reduced (all p<0.01). Importantly, a large fraction of TEG values and clotting factor assays in the pediatric control group were outside the published reference ranges for adults.

CONCLUSION

A hypercoagulable state is associated with minor trauma in children. More work is needed to determine the functional significance of these changes and to establish normal pediatric reference ranges.

Do all trauma patients benefit from tranexamic acid?

BACKGROUND

This study tested the hypothesis that early routine use of tranexamic acid (TXA) reduces mortality in a subset of the most critically injured trauma intensive care unit patients.

METHODS

Consecutive trauma patients (n = 1,217) who required emergency surgery (OR) and/or transfusions from August 2009 to January 2013 were reviewed. At surgeon discretion, TXA was administered at a median of 97 minutes (1-g bolus then 1-g over 8 hours) to 150 patients deemed high risk for hemorrhagic death. With the use of propensity scores based on age, sex, traumatic brain injury (TBI), mechanism of injury, systolic blood pressure, transfusion requirements, and Injury Severity Score (ISS), these patients were matched to 150 non-TXA patients.

RESULTS

The study population was 43 years old, 86% male, 54% penetrating mechanism of injury, 25% TBI, 28 ISS, with 22% mortality. OR was required in 78% at 86 minutes, transfusion was required in 97% at 36 minutes, and 75% received both. For TXA versus no TXA, more packed red blood cells and total fluid were required, and mortality was 27% versus 17% (all p < 0.05). The effects of TXA were similar in those with or without TBI, although ISS, fluid, and mortality were all higher in the TBI group. Mortality associated with TXA was influenced by the timing of administration (p < 0.05), but any benefit was eliminated in those who required more than 2,000-mL packed red blood cells, who presented with systolic blood pressure of less than 120 mm Hg or who required OR (all p < 0.05).

CONCLUSION

For the highest injury acuity patients, TXA was associated with increased, rather than reduced, mortality, no matter what time it was administered. This lack of benefit can probably be attributed to the rapid availability of fluids and emergency OR at this trauma center. Prospective studies are needed to further identify conditions that may override the benefits from TXA.

LEVEL OF EVIDENCE

Therapeutic study, level IV.

Vasopressor use during emergency trauma surgery

Most evidence suggests early vasopressor use is associated with death after trauma, but no previous study has focused on patients requiring emergency operative intervention (OR). We test the hypothesis that vasopressors are harmful in this population. Records from 746 patients requiring OR from July 2009 to March 2013 were retrospectively reviewed and stratified based on vasopressor use (epinephrine [EPI], phenylephrine, ephedrine, norepinephrine, dobutamine, vasopressin) or no vasopressor use. Vasopressors were administered to 225 patients (30%) during OR; 59 patients (8%) received multiple vasopressors. Patients who received vasopressors were older, more severely injured, had worse vital signs, and increased mortality rate (all P < 0.001). EPI was independently associated with mortality (odds ratio, 6.88; P = 0.001). If patients who received EPI were excluded, there was no difference in mortality between those who received vasopressors alone or in combination and those that did not (5 vs 6%, P = 0.523), although multiple markers of injury severity were worse. We conclude that vasopressor use is relatively common in the most severely injured patients requiring OR and is associated with mortality. EPI is most often used for cardiac arrest, whereas other vasopressors are used for their vasoconstrictive properties. This suggests that, except for EPI, vasopressors during OR are not independently associated with mortality.

Long-term coagulation changes after resection of thoracoabdominal malignancies

BACKGROUND

The purpose of this study was to evaluate the long-term coagulation status of patients undergoing malignancy resection.

STUDY DESIGN

A prospective observational trial was conducted with informed consent in 52 patients (age 66 ± 10 years and 60% male) with thoracoabdominal tumors (pancreas [n = 18, 35%], esophagus [n = 13, 25%], liver [n = 7, 14%], stomach [n = 6, 12%], bile duct [n = 3, 6%], retroperitoneal [n = 3, 6%], and duodenum [n = 2, 4%]) with 6- to 12-month follow-up. Coagulation was evaluated with rotational thromboelastography (ROTEM) on whole blood and with a panel of hemostatic markers on stored plasma.

RESULTS

Maximum clot firmness (MCF) in the intrinsic, extrinsic, and fibrinogen pathways increased immediately postoperatively and then decreased by 9.2 ± 4.1 months (p < 0.05). Markers of thrombin generation (prothrombin fragment 1 + 2, fibrinolysis [D-dimer], and endothelial activation [coagulation factor VIII]) were elevated at all time points. The ROTEM pattern depended on histologic type and cancer location. All esophageal tumors were adenocarcinoma and demonstrated similar patterns to the overall population, with MCF differences over time in all 3 pathways (all p < 0.05). Regarding tumors of the pancreas or liver, there were no statistically significant differences when comparing all 3 time periods, but there were time-related differences when evaluating only primary adenocarcinomas of the liver (all p < 0.05). Three patients (6%) developed venous thromboembolism (VTE) and had decreased clot formation time, increased angle, and increased MCF (all p < 0.05).

CONCLUSIONS

Cancer patients at risk for VTE can be identified with a point-of-care ROTEM test and may benefit from additional anticoagulation. Biomarkers reflecting different functional hemostasis activity groups (fibrinolysis, thrombin generation, and endothelial activation) confirm the ongoing prothrombotic state. The ROTEM demonstrated increased hypercoagulability postoperatively, which returned to baseline in long-term follow-up. Reversal of cancer-induced hypercoagulability occurred in some patients and varied with tumor histology and location.

Pre-existing hypercoagulability in patients undergoing potentially curative cancer resection

BACKGROUND

Rotational thromboelastometry (ROTEM) is a new point-of-care test that allows a rapid and comprehensive evaluation of coagulation. We were among the first to show that ROTEM identifies baseline hypercoagulability in 40% of patients with intra-abdominal malignancies and that hypercoagulability persists for ≥1 month after resection. The purpose of this follow-up study was to confirm and extend these observations to a larger population in outpatient preoperative clinics. The hypothesis is that pre-existing hypercoagulability is present in patients undergoing surgery for malignant disease and that coagulation status varies by tumor type.

METHODS

After informed consent, preoperative blood samples were drawn from patients undergoing exploratory laparotomies for intra-abdominal malignancies and analyzed with ROTEM.

RESULTS

Eighty-two patients were enrolled, including 72 with a confirmed pathologic diagnosis and 10 age-matched controls with benign disease. The most common cancers involved the pancreas (n = 23; 32%), esophagus (n = 19; 26%), liver (n = 12; 17%), stomach (n = 7; 10%), and bile ducts (n = 5; 7%). Preoperative hypercoagulability was detected in 31% (n = 22); these patients were more likely to have lymphovascular invasion (88% vs 50%; P = .011), perineural invasion (77% vs 36%; P = .007), and stage III/IV disease (80% vs 62%; P = .039). More patients with pancreatic tumors (9/23, 39%) were hypercoagulable than with esophageal (3/19, 16%) or liver (2/13, 15%, P = .034) tumors. When only resectable malignancies were considered, clot formation was more rapid (low clot formation time, high alpha) with enhanced maximum clot strength (high maximum clot firmness) in pancreatic versus esophageal or liver cancers and in all cancers versus those with benign disease.

CONCLUSION

Preoperative hypercoagulability can be identified with ROTEM and is associated with lymphovascular/perineural invasion and advanced-staged disease in cancer. Compared with other tumor types, pancreatic adenocarcinomas have the greatest risk for hypercoagulability.

Change in hematocrit during trauma assessment predicts bleeding even with ongoing fluid resuscitation

This study tests the hypothesis that a change in hematocrit (ΔHct) during initial trauma work-up is as reliable as conventional vital signs for detecting bleeding, even with ongoing fluid resuscitation. Consecutive trauma patients admitted to a Level I trauma center receiving two Hct measurements during initial resuscitation between January 2010 and January 2011 were stratified based on estimated blood loss greater than 250 mL (bleeding) or nonbleeding. Sensitivity, specificity, and receiver operating characteristic curves were calculated for systolic blood pressure (SBP), heart rate, base deficit, and ΔHct. In 168 (72%) nonbleeding versus 64 (28%) bleeding patients, age and gender were similar. Arrival SBP was highly specific (90 to 99%) but poorly sensitive (13 to 31%) for detecting bleeding. Combinations of vital signs increased specificity, albeit at the expense of sensitivity. For bleeding versus nonbleeding patients (all receiving resuscitation fluid), ΔHct was 9.0 versus 1.8, ΔHct/liter was 4.8 versus 1.5, and ΔHct/liter/hour was 2.8 vs 0.6 (all P < 0.001). Only SBP (area under the curve [AUC] 0.608 to 0.695) and ΔHct (AUC 0.731 to 0.921) were significant for identifying bleeding with ΔHct 6 or greater being the best predictor (sensitivity 89%, specificity 95%, AUC 0.921). During ongoing fluid resuscitation of a trauma victim, ΔHct is the single most reliable indicator of continuing blood loss. A ΔHct 6 or greater during initial resuscitation is highly suspicious for ongoing blood loss, but even lesser changes have predictive value. Altogether, these results support the idea that fluid shifts are rapid after hemorrhage and Hct can be valuable during initial trauma assessment.

Admission hematocrit and transfusion requirements after trauma

BACKGROUND

The decision to transfuse packed RBCs (PRBC) during initial resuscitation of trauma patients is based on physiologic state, evidence for blood loss, and potential for ongoing hemorrhage. Initial hematocrit (Hct) is not considered an accurate marker of blood loss. This study tests the hypothesis that admission Hct is associated with transfusion requirements after trauma.

METHODS

From June to December 2008, data from 1,492 consecutive admissions at a Level I trauma center were retrospectively reviewed to determine whether initial Hct was associated with PRBC transfusions. From October 2009 through October 2011, data from 463 consecutive transfused patients were retrospectively reviewed to determine whether Hct correlated with number of PRBC units received.

RESULTS

Packed RBC transfusion was not correlated with heart rate and was more highly correlated with Hct (r = -0.45) than with systolic blood pressure or base deficit (r = -0.32 or r = -0.26). Hematocrit was a better overall predictor than systolic blood pressure (sensitivity 45% vs 29%, specificity 94% vs 98%, area under receiver operator characteristic curve 0.71 vs 0.64). Lower Hct was associated with hypotension, more advanced shock, higher blood loss, and increased transfusion of PRBC, plasma, platelets, or cryoprecipitate (all, p < 0.01).

CONCLUSION

Admission Hct is more strongly associated with the PRBC transfusion than either tachycardia, hypotension, or acidosis. Admission Hct is also correlated with 24-hour blood product requirements in those receiving early transfusions. These findings challenge current thinking and suggest that fluid shifts are rapid after trauma and that Hct can be important in initial trauma assessment.

Insertion of central venous catheters induces a hypercoagulable state

BACKGROUND

Central venous catheters (CVCs) increase the risk of venous thromboembolism. We have previously demonstrated that pulmonary artery catheters are associated with a hypercoagulable state in an animal model and in patients. The purpose of this study is to determine whether the insertion of a CVC is associated with a similar response.

METHODS

ANIMAL

7F femoral artery catheters were placed in healthy anesthetized swine (N = 16). Serial arterial blood samples were drawn immediately before and after an 8.5F jugular vein CVC and then for 3 hours after CVC removal. Samples were analyzed using kaolin-activated thromboelastography (TEG) at precisely 2 minutes. Human: An institutional review board-approved prospective observational trial was conducted, with informed consent, in patients with critical illness (N = 8) at a Level I trauma center. Blood was drawn from indwelling arterial catheters immediately before and 60 minutes after CVC insertion. Samples were stored in sodium citrate for 15 minutes before TEG. Routine and special coagulation tests were performed on stored samples in the hospital pathology laboratory.

RESULTS

Insertion of a CVC decreased TEG clotting time (R) by 55% in swine and by 29% in humans (p < 0.001 and 0.019, respectively). Initial clot formation time (K) was reduced by 41% in swine and by 36% in humans (p = 0.003 and 0.019). Fibrin cross-linking (α) was accelerated by 28% in swine and by 17% in humans (p = 0.007 and 0.896), but overall clot strength (maximum amplitude) was not affected. There was no change in routine or special coagulation factors, including von Willebrand factor, antithrombin III, prothrombin time, international normalized ratio, or activated partial thromboplastin time. In animals, the hypercoagulable TEG response was persistent for 3 hours after CVC removal and was prevented by pretreatment with enoxaparin (n = 4) but not heparin (n = 2).

CONCLUSION

In healthy swine and patients with critical illness, a systemic hypercoagulable state occurred after CVC insertion, and this may partially account for an increased risk of venous thromboembolism. However, because the sample size was small and not powered to detect changes in coagulation proteins, no inferences can be made about the mechanism for the hypercoagulable response.

Effect of hetastarch bolus in trauma patients requiring emergency surgery

If blood products are not available, current military guidelines recommend a hetastarch bolus (HEX, Hextend 6% hetastarch in lactated electrolyte buffer, www. hospira.com) for initial treatment of hypovolemic shock in the field. We previously reported that a HEX bolus plus standard of care (SOC = crystalloid plus blood products) was safe during initial resuscitation in 1714 trauma patients. This study tests the hypothesis that HEX+SOC is more effective than SOC alone for volume expansion in trauma patients requiring urgent operation.

METHODS

From July 2009 to August 2010, the records from all adults who required emergency surgery within 4 hours of admission were screened for a retrospective cohort observational study. Burns, and those with primary neurosurgical or orthopedic indications, were excluded. The study population was comprised of 281 patients with blunt (n = 72) or penetrating (n = 209) trauma; 141 received SOC and 140 received SOC+HEX in the emergency room only (ER, n = 81) or the ER and operating room (OR, n = 59). Each case was reviewed with waiver of consent.

RESULTS

After penetrating injury, with SOC, the injury severity score was 17 and mortality was 12%; the corresponding values in the HEX(ER) and HEX(OR) groups were 19?21 and 8%, but these apparent differences did not reach significance. However, in patients receiving HEX, initial heart rate was higher, base deficit was lower, and hematocrit was lower (consistent with relative hypovolemia), even though blood product requirements were reduced, and urine output was greater (all p < 0.05). These effects were absent in patients with blunt trauma. Platelet consumption was higher with HEX after either penetrating (p = 0.004) or blunt trauma (p = 0.045), but coagulation tests were unchanged.

CONCLUSION

HEX is safe for initial resuscitation in young patients who required urgent operation after penetrating trauma, but there was no apparent effect after blunt trauma. A bolus of HEX reduced transfusion requirements without inducing coagulopathy or causing renal dysfunction, but a randomized controlled trial is necessary to eliminate the possibility of selection bias.

Nicardipine reverses vasoactivity associated with University of Wisconsin solution in the rat peripheral circulation

BACKGROUND

The rapid uniform delivery of University of Wisconsin solution (UW) to the microcirculation may be compromised by its vasoactivity.

METHODS

In 2 different rodent models, we tested whether UW-mediated vasoconstriction could be reversed with nicardipine.

RESULTS

In the perfused, splanchnic circulation, intravascular control solutions (lactated Ringers [LR], Hextend [HEX], histidine-tryptophan-ketoglutarate [HTK]) or UW (± nicardipine) evoked pressure changes in 3 protocols (series 1; n = 35). In the cremaster muscle, topical control solutions or UW (± nicardipine) evoked vascular responses measured by video microscopy in 4 protocols (series 2; n = 47). In series 1A, 37°C UW increased perfusion pressure, but there was no change caused by LR, HEX, or HTK. In series 1B, 4°C UW caused a similar, albeit transient, increase. In series 1C, nicardipine reversed 37°C UW-mediated vasoconstriction in a dose-related manner. In series 2A, UW caused a 30%-59% constriction that varied with arteriolar branching order. In series 2B, the recovery from UW-induced vasoconstriction varied with duration of exposure, but nicardipine fully reversed residual vasoconstriction. In series 2C, cold and warm UW were equipotent, near maximal, vasoconstrictors. In series 2D, UW potentiated no-reflow.

CONCLUSION

UW causes a potent temperature-independent vasoconstriction by a calcium-mediated mechanism and this effect can be mitigated with nicardipine.

Hemodynamic and metabolic efficacy of dopamine versus norepinephrine in a brain-dead swine model

We tested the hypothesis that hepatosplanchnic and systemic hemodynamics are improved with equi-effective doses of dopamine (DA) versus norepinephrine (NE) in a brain-dead swine model. Pigs (n = 18) were anesthetized and ventilated. Brain death was induced by epidural balloon inflation, hypoventilation, and hypoxia. After 30 minutes, mechanical ventilation was restored without anesthesia. During 60 and until 480 minutes, half received DA (10 microg/kg/minute) and half received NE (0.1 microg/kg/minute) titrated to a mean arterial pressure (MAP) > 60 mm Hg with supplemental fluid to maintain a central venous pressure > 8 mm Hg. Hemodynamics, hepatic laser Doppler blood flow, and hepatic and gastric tissue oxygenation with near-infrared spectroscopy were continuously monitored. Serial blood samples were analyzed for blood gases and electrolytes, coagulation changes, and serum chemistries. Balloon inflation caused brain death and autonomic storm, and 8 of 18 were nonsurvivors. After 30 minutes, the MAP, mixed venous O(2) saturation, and partial pressure of arterial oxygen values decreased to 37 +/- 2 mm Hg, 38 +/- 4, and 49 +/- 8 mm Hg, respectively. Serum lactate increased to 5.4 +/- 0.7 mM. Among survivors (n = 10), MAP stabilized with either pressor. Urine output was maintained (>1 mL/kg/hour), but creatinine increased >30% with respect to the baseline. Tachyphylaxis developed with NE but not with DA (P < 0.05). Cardiac index was higher with DA versus NE (P < 0.05). There were no differences in stroke volume, metabolic indices, or liver blood flow. Liver tissue O(2) was higher with DA versus NE at 8 hours (P < 0.05). Coagulation tests and liver enzymes were similar with NE versus DA (P > 0.05). In conclusion, after brain death, cardiac index and hepatic oxygenation were significantly improved with equi-effective doses of DA versus NE.

Heart rate variability index in trauma patients

BACKGROUND

Heart rate variability (HRV) changes often reflect autonomic dysfunction with high sensitivity, but the specificity is also low. There are several different methods for measuring HRV, but interpretation is often complex, and the units are not interchangeable. For these reasons, HRV monitoring is not routinely used in many clinical situations. We hypothesized that the specificity of HRV as a screening tool for trauma patients could be improved by controlling some of the confounding influences using multiple logistic regression.

METHODS

A prospective observational trial with waiver of consent was performed in 243 healthy student volunteers and 257 trauma patients, in the resuscitation bay and intensive care units of a Level I trauma center, who received computed axial tomography (CT) scans of the head as part of the initial work up. Electrocardiogram results were recorded for 5 minutes. HRV was defined by SD of normal R-R intervals (SDNN5) and by root mean square of successive differences of R-R intervals (RMSSD5). A head CT scan was considered positive (+) if there were abnormalities in the parenchyma (diffuse axonal injury or contusion), vasculature (intraparenchymal, subdural, or epidural hemorrhage), and/or structural or bony components (fractures of the face or cranium).

RESULTS

In volunteers, SDNN5 was 73 +/- 15 (M +/- SD) milliseconds, compared with 42 +/- 22, 31 +/- 19, 28 +/- 17, and 12 +/- 8 milliseconds in, CT(-) patients with no sedation (n = 82), CT(-) with sedation (n = 60), CT(+) with no sedation (n = 55), and CT(+) with sedation (n = 60), respectively. The differences between trauma, sedation, and CT categories were significant (all p < 0.001). RMSSD5 differences were similar and also highly significant (all p < 0.001). For both SDNN5 and RMSSD5, in each category, there was wide overlap in the range of values, and strong inverse correlations with heart rate (all p < 0.001). Using multiple logistic regression in a subset with no missing data (n = 194), an index was derived from ln(SDNN5) adjusted for six confounding factors. With a negative predictive value held constant at 0.90, compared with ln(SDNN5) alone, the stepwise addition of heart rate, sedation, age, gender, and blood pressure progressively improved the specificity of the HRV index from 0.56 to 0.77, positive predictive value from 0.55 to 0.68, and efficiency from 0.68 to 0.80. This index was then normalized (0-100 scale) for ease of interpretation.

CONCLUSIONS

(1) Several factors alter HRV in patients; (2) when HRV was indexed for some of these factors, its specificity and efficiency were improved for predicting a discrete pathologic state in trauma patients, i.e. (+) or (-) cranial CT scans; (3) the algorithm can incorporate other factors to further refine the diagnostic and/or prognostic ability of HRV as a noninvasive clinical tool; (4) this concept should be applicable to any other HRV measurement technique or outcome.

Lung contusion: pathophysiology and management

Management of severe pulmonary contusion is a challenge for clinicians. The incidence of adult respiratory distress syndrome (5-20%), pneumonia (5-50%), and mortality (5-10%) associated with traumatic lung injury has changed little in the past three decades. Therapeutic options are limited to basic supportive measures such as mechanical ventilation, positive end expiratory pressure, invasive cardiopulmonary monitoring, analgesics and aggressive pulmonary hygiene. Presently, no pharmacological agents can prevent the progressive respiratory embarrassment that is associated with the natural history of the disease, but several drugs have been tested in the laboratory. The purpose of this brief review is to summarize information published since January 2000 related to the clinical management and pathophysiology of lung contusion.