Pathophysiology and treatment of coagulopathy in massive hemorrhage and hemodilution

Massive blood loss in elective spinal and orthopedic surgery: Retrospective review of intraoperative transfusion strategy

OBJECTIVE

To evaluate the perioperative dynamics of hematologic changes and transfusion ratio in patients undergoing a major spinal surgery accompanied with massive bleeding defined as blood loss >5 liters.

DESIGN

Retrospective cohort study.

SETTING

Operating room of a university-affiliated hospital.

PATIENTS

Adult patients who underwent elective neurosurgical, orthopedic, or combined spinal surgical procedure between 2008 and 2012.

METHODS

Patients who underwent a major spinal or orthopedic surgery and who experienced major bleeding (>5 L) during surgery were identified and selected for final analysis. The following information was analyzed: demographics, clinical diagnoses, hematologic parameters, estimated intraoperative blood loss, blood product transfusions, and survival 1 year after surgery.

RESULTS

During the study period, 25 patients, who underwent 28 spinal procedures, experienced intraoperative blood loss >5 L. Mean patient age was 50.5 years and 56.4% were males. The majority of patients underwent procedures to manage spinal metastases. Median estimated intraoperative blood loss was 11.25 L (IQR 6.35-22 L) and median number of units (U) transfused was 24.5 U (IQR 14.0-32.5 U) of packed red blood cells (RBCs), 24.5 U (IQR 14.0-34.0 U) of fresh frozen plasma (FFP), and 4.5 U (IQR 3.0-11.5 U) of platelets (PLTs). The blood product transfusion ratio was 1 and 4 for RBC:FFP, and RBC:PLT, respectively. Hematocrit, hemoglobin, PLTs, partial thromboplastin, prothrombin time, INR, and, fibrinogen varied significantly throughout the procedures. However, acid-base status did not change significantly during surgery. Patients' survival at 1 year was 79.17%.

CONCLUSION

Our results indicate that a 1:1 RBC:FFP and 4:1 RBC:PLT transfusion ratio was associated with significant intraoperative variations in coagulation variables but stable intraoperative acid-base parameters. This transfusion ratio helped clinicians to achieve postoperative coagulation parameters not significantly different to those at baseline. Future studies should assess if more liberal transfusion strategies or point of care monitoring might be warranted in patients undergoing spinal surgery at risk of major blood loss.

Multivariable predictors of substantial blood loss in children undergoing craniosynostosis repair: implications for risk stratification

BACKGROUND

Operative treatment of craniosynostosis is associated with substantial blood loss, often requiring transfusion of packed red blood cells (PRBC) and coagulation products.

AIMS

The aim of this prospective study was to analyze thromboelastographic (TEG) parameters and platelet fibrinogen product to determine predictors of substantial blood loss, and the need for PRBC transfusion and coagulation products.

METHODS

With IRB approval, we enrolled 120 children undergoing craniosynostosis repair with a standardized anesthetic, fluid management, and TEG measurements at predefined times. Outcomes of interest were intraoperative blood loss, and need for PRBC transfusion and coagulation products. Multivariable logistic regression and receiver operating characteristic (ROC) curve analysis was applied to determine independent predictors of substantial blood loss and need for coagulation products.

RESULTS

One hundred and eighteen children were included in the analysis. Forty-four required PRBC transfusion (median 26 ml·kg(-1) ; IQR: 22-42) with median blood loss of 56 ml·kg(-1) (IQR: 43-83). Factors associated with the PRBC transfusion included type of surgery, duration of surgery, and three TEG parameters, α-angle, MA, and K-time (all P < 0.001). A predictive algorithm was developed by subgroup analysis of cranial vault reconstruction (CVR) patients for substantial intraoperative blood loss (defined as ≥60 ml·kg(-1) ) and need for coagulation products with ROC-derived cut-off values: platelet fibrinogen product, <343; α-angle, <62°; MA, <55 mm; K-time, >2.1 min. The best prognostic combination included at least two of these four predictors (sensitivity 89%, specificity 90%). Multivariable regression identified MA as the only independent predictor of coagulation product administration (P < 0.001) and ROC analysis identified MA <46 mm as the optimal cut-off (sensitivity 86%, specificity 94%).

CONCLUSIONS

Risk for substantial intraoperative blood loss can be assessed using TEG parameters and platelet fibrinogen product, whereas the need for coagulation products is strongly related to low MA. Patients susceptible to substantial blood loss can be risk stratified based on their TEG/platelet fibrinogen product profile.

Importance of fibrinogen in dilutional coagulopathy after neurosurgical procedures: A descriptive study

BACKGROUND AND AIMS

The routine management of coagulopathy during surgery involves assessing haemoglobin, prothrombin time (PT), activated partial thromboplastin time (aPTT) and platelets. Correction of these parameters involves administration of blood, fresh frozen plasma and platelet concentrates. The study was aimed at identifying the most common coagulation abnormality during neurosurgical procedures and the treatment of dilutional coagulopathy with blood components.

METHODS

During 2 years period, all adult patients undergoing neurosurgical procedures who were transfused two or more units of red cells were prospectively evaluated for the presence of a coagulopathy. PT, aPTT, platelet count and fibrinogen levels were estimated before starting a component therapy.

RESULTS

After assessing PT, aPTT, platelet count and fibrinogen levels following two or more blood transfusions, thirty patients were found to have at least one abnormal parameter that required administration of a blood product. The most common abnormality was a low fibrinogen level, seen in 26 patients; this was the only abnormality in three patients. No patient was found to have an abnormal PT or aPTT without either the fibrinogen concentration or platelet count or both being low.

CONCLUSION

Low fibrinogen concentration was the most common coagulation abnormality found after blood transfusions for neurosurgical procedures.

Prothrombin Complex Concentrates for Bleeding in the Perioperative Setting

Prothrombin complex concentrates (PCCs) contain vitamin K-dependent clotting factors (II, VII, IX, and X) and are marketed as 3 or 4 factor-PCC formulations depending on the concentrations of factor VII. PCCs rapidly restore deficient coagulation factor concentrations to achieve hemostasis, but like with all procoagulants, the effect is balanced against thromboembolic risk. The latter is dependent on both the dose of PCCs and the individual patient prothrombotic predisposition. PCCs are approved by the US Food and Drug Administration for the reversal of vitamin K antagonists in the setting of coagulopathy or bleeding and, therefore, can be administered when urgent surgery is required in patients taking warfarin. However, there is growing experience with the off-label use of PCCs to treat patients with surgical coagulopathic bleeding. Despite their increasing use, there are limited prospective data related to the safety, efficacy, and dosing of PCCs for this indication. PCC administration in the perioperative setting may be tailored to the individual patient based on the laboratory and clinical variables, including point-of-care coagulation testing, to balance hemostatic benefits while minimizing the prothrombotic risk. Importantly, in patients with perioperative bleeding, other considerations should include treating additional sources of coagulopathy such as hypofibrinogenemia, thrombocytopenia, and platelet disorders or surgical sources of bleeding. Thromboembolic risk from excessive PCC dosing may be present well into the postoperative period after hemostasis is achieved owing to the relatively long half-life of prothrombin (factor II, 60-72 hours). The integration of PCCs into comprehensive perioperative coagulation treatment algorithms for refractory bleeding is increasingly reported, but further studies are needed to better evaluate the safe and effective administration of these factor concentrates.

Impact of Preemptive Fibrinogen Concentrate on Transfusion Requirements in Liver Transplantation: A Multicenter, Randomized, Double-Blind, Placebo-Controlled Trial

We hypothesized that preemptive fibrinogen administration to obtain an initial plasma level of 2.9 g/L would reduce transfusion requirements in liver transplantation. A randomized, multicenter, hemoglobin-stratified, double-blind, fibrinogen-versus-saline-controlled trial was conducted. The primary end point was the percentage of patients requiring red blood cells. We evaluated 51 patients allocated to fibrinogen and 48 allocated to saline; the primary end point was assessed using data for 92 patients because the electronic record forms were offline for three patients in the fibrinogen group and four in the saline group. We injected a median of 3.54 g fibrinogen preemptively in the fibrinogen group. Nine patients in the saline group (20.9%) required fibrinogen at graft reperfusion (compared with one patient [2.1%] in the fibrinogen group; p = 0.005). Blood was transfused to 52.9% (95% confidence interval [CI] 42.5-63.3%) in the fibrinogen group and 42.74% (95% CI 28.3-57.2%) in the saline group (p = 0.217). Relative risk for blood transfusion was 0.80 (95% CI 0.57-1.13). Thrombotic events occurred in one patient (2.1%) and five patients (11.4%) in the fibrinogen and saline groups, respectively. Seven patients (14.6%) in the fibrinogen group and nine (20.3%) in the saline group required reoperation. Preemptive administration of fibrinogen concentrate did not influence transfusion requirements.

Ex vivo recapitulation of trauma-induced coagulopathy and preliminary assessment of trauma patient platelet function under flow using microfluidic technology

BACKGROUND

Relevant to trauma-induced coagulopathy diagnostics, microfluidic assays allow controlled hemodynamics for testing of platelet and coagulation function using whole blood.

METHODS

Hemodilution or hyperfibrinolysis was studied under flow with modified healthy whole blood. Furthermore, platelet function was also measured using whole blood from trauma patients admitted to a Level I trauma center. Platelet deposition was measured with PPACK-inhibited blood perfused over collagen surfaces at a wall shear rate of 200 s, whereas platelet/fibrin deposition was measured with corn trypsin inhibitor-treated blood perfused over tissue factor (TF)/collagen.

RESULTS

In hemodilution studies, PPACK-treated blood displayed almost no platelet deposition when diluted to 10% hematocrit with saline, platelet-poor plasma, or platelet-rich plasma. Using similar dilutions, platelet/fibrin deposition was essentially absent for corn trypsin inhibitor-treated blood perfused over TF/collagen. To mimic hyperfibrinolysis during trauma, exogenous tissue plasminogen activator (50 nM) was added to blood before perfusion over TF/collagen. At both venous and arterial flows, the generation and subsequent lysis of fibrin were detectable within 6 minutes, with lysis blocked by addition of the plasmin inhibitor, ε-aminocaproic acid. Microfluidic assay of PPACK-inhibited whole blood from trauma patients revealed striking defects in collagen response and secondary platelet aggregation in 14 of 21 patients, whereas platelet hyperfunction was detected in three of 20 patients.

CONCLUSION

Rapid microfluidic detection of (1) hemodilution-dependent impairment of clotting, (2) clot instability because of lysis, (3) blockade of fibrinolysis, or (4) platelet dysfunction during trauma may provide novel diagnostic opportunities to predict trauma-induced coagulopathy risk.

Four-Group Classification Based on Fibrinogen Level and Fibrin Polymerization Associated With Postoperative Bleeding in Cardiac Surgery

Fibrinogen and fibrin formation have a key role in perioperative hemostasis. The aim of this study is to examine the association of postoperative hemostasis with a combined evaluation of the fibrinogen level and fibrin polymerization in cardiac surgery. We retrospectively classified 215 consecutive cardiac surgery patients into 4 groups (Fuji-san classification) that were divided by fibrinogen level <150 mg/dL (ie, hypofibrinogenemia) and fibrinogen thromboelastometry value at 10 minutes with rotational thromboelastometry <6 mm (ie, low fibrin polymerization) at the warming of cardiopulmonary bypass. Four groups resulted; group I, the acceptable range (n = 85); group II, only hypofibrinogenemia (<150 mg/dL, ≥6 mm, n = 63); group III, hypofibrinogenemia and low fibrin polymerization (<150 mg/dL, <6 mm, n = 60); and group IV, only low fibrin polymerization (≥150 mg/dL, <6 mm, n = 7). The risk of chest tube drainage volume greater than 500 mL within the first 24 hours after surgery (with group I as the reference) was increased in group II (odds ratio [OR], 3.3; 95% confidence interval [CI], 1.5-7.4; P < .01) and group III (OR, 8.5; 95% CI, 3.5-21.7; P < .01), and the risk greater than 1000 mL (with group I as the reference) was increased in group III (OR, 4.0; 95% CI, 1.1-17.3; P = .03) and group IV (OR, 23.1; 95% CI, 3.2-201.0; P < .01). Intraoperative blood transfusions were decreased by 24.5%, after stratifying the starting amount of fresh frozen plasma by the 4-group classification in the recent consecutive 65 (30.2%) patients ( P < .01). The 4-group classification is associated with postoperative bleeding and may improve the quality of perioperative blood transfusion in cardiac surgery.

Massive obstetric hemorrhage: Current approach to management

Massive obstetric hemorrhage is a major cause of maternal mortality and morbidity worldwide. It is defined (among others) as the loss of>2,500ml of blood, and is associated to a need for admission to critical care and/or hysterectomy. The relative hemodilution and high cardiac output found in normal pregnancy allows substantial bleeding before a drop in hemoglobin and/or hematocrit can be identified. Some comorbidities associated with pregnancy can contribute to the occurrence of catastrophic bleeding with consumption coagulopathy, which makes the situation even worse. Optimization, preparation, rational use of resources and protocolization of actions are often useful to improve outcomes in patients with postpartum hemorrhage. Using massive obstetric hemorrhage protocols is useful for facilitating rapid transfusion if needed, and can also be cost-effective. If hypofibrinogenemia during the bleeding episode is identified, early fibrinogen administration can be very useful. Other coagulation factors in addition to fibrinogen may be necessary during postpartum hemorrhage replacement measures in order to effectively correct coagulopathy. A hysterectomy is recommended if the medical and surgical measures prove ineffective.

Dynamic and quantitative assessment of blood coagulation using optical coherence elastography

Reliable clot diagnostic systems are needed for directing treatment in a broad spectrum of cardiovascular diseases and coagulopathy. Here, we report on non-contact measurement of elastic modulus for dynamic and quantitative assessment of whole blood coagulation using acoustic radiation force orthogonal excitation optical coherence elastography (ARFOE-OCE). In this system, acoustic radiation force (ARF) is produced by a remote ultrasonic transducer, and a shear wave induced by ARF excitation is detected by the optical coherence tomography (OCT) system. During porcine whole blood coagulation, changes in the elastic property of the clots increase the shear modulus of the sample, altering the propagating velocity of the shear wave. Consequently, dynamic blood coagulation status can be measured quantitatively by relating the velocity of the shear wave with clinically relevant coagulation metrics, including reaction time, clot formation kinetics and maximum shear modulus. The results show that the ARFOE-OCE is sensitive to the clot formation kinetics and can differentiate the elastic properties of the recalcified porcine whole blood, blood added with kaolin as an activator, and blood spiked with fibrinogen.

Reducing transfusion requirements in liver transplantation

Liver transplantation (LT) was historically associated with massive blood loss and transfusion. Over the past two decades transfusion requirements have reduced dramatically and increasingly transfusion-free transplantation is a reality. Both bleeding and transfusion are associated with adverse outcomes in LT. Minimising bleeding and reducing unnecessary transfusions are therefore key goals in the perioperative period. As the understanding of the causes of bleeding has evolved so too have techniques to minimize or reduce the impact of blood loss. Surgical “piggyback” techniques, anaesthetic low central venous pressure and haemodilution strategies and the use of autologous cell salvage, point of care monitoring and targeted correction of coagulopathy, particularly through use of factor concentrates, have all contributed to declining reliance on allogenic blood products. Pre-emptive management of preoperative anaemia and adoption of more restrictive transfusion thresholds is increasingly common as patient blood management (PBM) gains momentum. Despite progress, increasing use of marginal grafts and transplantation of sicker recipients will continue to present new challenges in bleeding and transfusion management. Variation in practice across different centres and within the literature demonstrates the current lack of clear transfusion guidance. In this article we summarise the causes and predictors of bleeding and present the evidence for a variety of PBM strategies in LT.

Investigation into the effects of antioxidant-rich extract of Tamarindus indica leaf on antioxidant enzyme activities, oxidative stress and gene expression profiles in HepG2 cells

The leaf extract of Tamarindus indica L. (T. indica) had been reported to possess high phenolic content and showed high antioxidant activities. In this study, the effects of the antioxidant-rich leaf extract of the T. indica on lipid peroxidation, antioxidant enzyme activities, H₂O₂-induced ROS production and gene expression patterns were investigated in liver HepG2 cells. Lipid peroxidation and ROS production were inhibited and the activity of antioxidant enzymes superoxide dismutase, catalase and glutathione peroxidase was enhanced when the cells were treated with the antioxidant-rich leaf extract. cDNA microarray analysis revealed that 207 genes were significantly regulated by at least 1.5-fold (p < 0.05) in cells treated with the antioxidant-rich leaf extract. The expression of KNG1, SERPINC1, SERPIND1, SERPINE1, FGG, FGA, MVK, DHCR24, CYP24A1, ALDH6A1, EPHX1 and LEAP2 were amongst the highly regulated. When the significantly regulated genes were analyzed using Ingenuity Pathway Analysis software, “Lipid Metabolism, Small Molecule Biochemistry, Hematological Disease” was the top biological network affected by the leaf extract, with a score of 36. The top predicted canonical pathway affected by the leaf extract was the coagulation system (P < 2.80 × 10⁻⁶) followed by the superpathway of cholesterol biosynthesis (P < 2.17 × 10⁻⁴), intrinsic prothrombin pathway (P < 2.92 × 10⁻⁴), Immune Protection/Antimicrobial Response (P < 2.28 × 10⁻³) and xenobiotic metabolism signaling (P < 2.41 × 10⁻³). The antioxidant-rich leaf extract of T. indica also altered the expression of proteins that are involved in the Coagulation System and the Intrinsic Prothrombin Activation Pathway (KNG1, SERPINE1, FGG), Superpathway of Cholesterol Biosynthesis (MVK), Immune protection/antimicrobial response (IFNGR1, LEAP2, ANXA3 and MX1) and Xenobiotic Metabolism Signaling (ALDH6A1, ADH6). In conclusion, the antioxidant-rich leaf extract of T. indica inhibited lipid peroxidation and ROS production, enhanced antioxidant enzyme activities and significantly regulated the expression of genes and proteins involved with consequential impact on the coagulation system, cholesterol biosynthesis, xenobiotic metabolism signaling and antimicrobial response.

A national common massive transfusion protocol (MTP) is a feasible and advantageous option for centralized blood services and hospitals

BACKGROUND

A common national MTP was jointly implemented in 2011 by the national blood service (Blood Services Group) and seven participating acute hospitals to provide rapid access to transfusion support for massively haemorrhaging patients treated in all acute care hospitals.

METHODS

Through a systematic clinical workflow, blood components are transfused in a ratio of 1:1:1 (pRBC: whole blood-derived platelets: FFP), together with cryoprecipitate for fibrinogen replacement. The composition of components for the MTP is fixed, although operational aspects of the MTP can be adapted by individual hospitals to suit local hospital workflow. The MTP could be activated in support of any patient with critical bleeding and at risk of massive transfusion, including trauma and non-trauma general medical, surgical and obstetric patients.

RESULTS

There were 434 activations of the MTP from October 2011 to October 2013. Thirty-nine per cent were for trauma patients, and 30% were for surgical patients with heavy intra-operative bleeding, with 25% and 6% for patients with gastrointestinal bleeding and peri-partum haemorrhage, respectively. Several hospitals reported reduction in mean time between request and arrival of blood. Mean transfusion ratio achieved was one red cell unit: 0·8 FFP units: 0·8 whole blood-derived platelet units: 0·4 units of cryoprecipitate. Although cryoprecipitate usage more than doubled after introduction of MTP, there was no significant rise in overall red cells, platelet and FFP usage following implementation.

CONCLUSION

This successful collaboration shows that shared transfusion protocols are feasible and potentially advantageous for hospitals sharing a central blood provider.

[Fluid resuscitation in hemorrhage]

How fluid resuscitation has to be performed for acute hemorrhage situations is still controversially discussed. Although the forced administration of crystalloids and colloids has been and still is practiced, nowadays there are good arguments that a cautious infusion of crystalloids may be initially sufficient. Saline should no longer be used for fluid resuscitation. The main argument for cautious fluid resuscitation is that no large prospective randomized clinical trials exist which have provided evidence of improved survival when fluid resuscitation is applied in an aggressive manner. The explanation that no positive effect has so far been observed is that fluid resuscitation is thought to boost bleeding by increasing blood pressure and dilutional coagulopathy. Nevertheless, national and international guidelines recommend that fluid resuscitation should be applied at the latest when hemorrhage causes hemodynamic instability. Consideration should be given to the fact that damage control resuscitation per se will neither improve already reduced tissue perfusion nor hemostasis. In acute and possibly rapidly progressing hypovolemic shock, colloids can be used. The third and fourth generations of hydroxyethyl starch (HES) are safe and effective if used correctly and within prescribed limits. If fluid resuscitation is applied with ongoing re-evaluation of the parameters which determine oxygen supply, it should be possible to keep fluid resuscitation restricted without causing undesirable side effects and also to administer a sufficient quantity so that survival of patients is ensured.

The effect of 0.9% saline versus plasmalyte on coagulation in patients undergoing lumbar spinal surgery; a randomized controlled trial

INTRODUCTION

In multi-level lumbar spinal fusion surgery yielding a large amount of blood loss, choice of fluid for volume resuscitation is an important issue since it can influence acid-base status, coagulation, and patients' outcome. This study compared the effect of plasmalyte to 0.9% saline on coagulation assessed by rotation thromboelastometry (ROTEM) and acid-base balance in the aforementioned patients.

METHODS

Fifty patients were randomly allocated to receive either 0.9% saline or plasmalyte during operation and until postoperative 12 h. ROTEM was performed at 10 min after anesthetic induction and end of surgery. Arterial blood gas analyses were serially performed from 10 min after anesthetic induction until postoperative 12 h. Fluid balance, blood loss, and transfusion requirement were assessed.

RESULTS

ROTEM variables showed sporadic deterioration in both groups after surgery without intergroup differences. Intraoperatively, arterial pH, base excess, and bicarbonate concentrations were lower and serum chloride concentrations were higher in the 0.9% saline group compared with the plasmalyte group. The differences in base excess and bicarbonate concentrations persisted until postoperative 12 h. Fluid balance, blood loss, and transfusion requirement were similar between the groups while urine output was greater in the plasmalyte group compared with the 0.9% saline group (3.2 ± 1.6 ml/kg/h vs. 1.8 ± 1.1 ml/kg/h, p = 0.001).

CONCLUSION

In contrast to plasmalyte, fluid therapy with 0.9% saline resulted in transient hyperchloremic acidosis in patients undergoing multi-level lumbar spinal fusion, while coagulation assessed by ROTEM analysis and the amount of blood loss were similar between the groups.

Prediction of Post-Weaning Fibrinogen Status during Cardiopulmonary Bypass: An Observational Study in 110 Patients

Background

After cardiac surgery with cardiopulmonary bypass (CPB), acquired coagulopathy often leads to post-CPB bleeding. Though multifactorial in origin, this coagulopathy is often aggravated by deficient fibrinogen levels.

Objective

To assess whether laboratory and thrombelastometric testing on CPB can predict plasma fibrinogen immediately after CPB weaning.

Patients / Methods

This prospective study in 110 patients undergoing major cardiovascular surgery at risk of post-CPB bleeding compares fibrinogen level (Clauss method) and function (fibrin-specific thrombelastometry) in order to study the predictability of their course early after termination of CPB. Linear regression analysis and receiver operating characteristics were used to determine correlations and predictive accuracy.

Results

Quantitative estimation of post-CPB Clauss fibrinogen from on-CPB fibrinogen was feasible with small bias (+0.19 g/l), but with poor precision and a percentage of error >30%. A clinically useful alternative approach was developed by using on-CPB A10 to predict a Clauss fibrinogen range of interest instead of a discrete level. An on-CPB A10 ≤10 mm identified patients with a post-CPB Clauss fibrinogen of ≤1.5 g/l with a sensitivity of 0.99 and a positive predictive value of 0.60; it also identified those without a post-CPB Clauss fibrinogen <2.0 g/l with a specificity of 0.83.

Conclusions

When measured on CPB prior to weaning, a FIBTEM A10 ≤10 mm is an early alert for post-CPB fibrinogen levels below or within the substitution range (1.5–2.0 g/l) recommended in case of post-CPB coagulopathic bleeding. This helps to minimize the delay to data-based hemostatic management after weaning from CPB.

Higher fibrinogen concentrations for reduction of transfusion requirements during major paediatric surgery: A prospective randomised controlled trial

BACKGROUND

Hypofibrinogenaemia is one of the main reasons for development of perioperative coagulopathy during major paediatric surgery. The aim of this study was to assess whether prophylactic maintenance of higher fibrinogen concentrations through administration of fibrinogen concentrate would decrease the volume of transfused red blood cell (RBCs).

METHODS

In this prospective, randomised, clinical trial, patients aged 6 months to 17 yr undergoing craniosynostosis and scoliosis surgery received fibrinogen concentrate (30 mg kg(-1)) at two predefined intraoperative fibrinogen concentrations [ROTEM(®) FIBTEM maximum clot firmness (MCF) of <8 mm (conventional) or <13 mm (early substitution)]. Total volume of transfused RBCs was recorded over 24 h after start of surgery.

RESULTS

Thirty children who underwent craniosynostosis surgery and 19 children who underwent scoliosis surgery were treated per protocol. During craniosynostosis surgery, children in the early substitution group received significantly less RBCs (median, 28 ml kg(-1); IQR, 21 to 50 ml kg(-1)) compared with the conventional fibrinogen trigger of <8 mm (median, 56 ml kg(-1); IQR, 28 to 62 ml kg(-1)) (P=0.03). Calculated blood loss as per cent of estimated total blood volume decreased from a median of 160% (IQR, 110-190%) to a median of 90% (IQR, 78-110%) (P=0.017). No significant changes were observed in the scoliosis surgery population. No bleeding events requiring surgical intervention, postoperative transfusions of RBCs, or treatment-related adverse events were observed.

CONCLUSIONS

Intraoperative administration of fibrinogen concentrate using a FIBTEM MCF trigger level of <13 mm can be successfully used to significantly decrease bleeding, and transfusion requirements in the setting of craniosynostosis surgery, but not scoliosis.

CLINICAL TRIAL REGISTRY NUMBER

ClinicalTrials.gov NCT01487837.

Fibrinogen measurements in plasma and whole blood: a performance evaluation study of the dry-hematology system

BACKGROUND

An accurate and rapid determination of fibrinogen level is important during hemorrhage to establish a timely hemostatic intervention. The accuracy of fibrinogen measurements may be affected by the specific methodology for its determination, fluid therapies, and anticoagulant agents. The dry-hematology method (DRIHEMATO®) is a novel approach to determine fibrinogen levels in plasma and whole blood based on thrombin-activated coagulation time. We hypothesized that plasma or whole blood fibrinogen level using the dry-hematology method would be similar to those measured with conventional plasma fibrinogen assays.

METHODS

Acquired hypofibrinogenemia was modeled by serial dilutions of blood samples obtained from 12 healthy volunteers. Citrated whole blood samples were diluted with either normal saline, 5% human albumin, or 6% hydroxyethyl starch to achieve 25%, 50%, and 75% volume replacement. The dry-hematology method, the Clauss method, the prothrombin time (PT)-derived method, determination of antigen levels, and thromboelastometric fibrin formation were compared in plasma or whole blood samples. The effect of heparin on each assay was examined (0 to 6 IU/mL). Comparisons of dry-hematology and other methods were also conducted using ex vivo samples obtained from cardiac surgical patients (n = 60).

RESULTS

In plasma samples, there were no significant differences between dry-hematology and the Clauss method, while dry-hematology showed lower fibrinogen levels compared with PT-derived and antigen level methods. The dry-hematology method yielded acceptable concordance correlation coefficients (Pc) with the Clauss method, the PT-derived method, and fibrinogen antigen levels (Pc = 0.91-0.99). The type of diluents and heparin affected the results of the PT-derived method and thromboelastometric assay, but not the dry-hematology method. In cardiac surgical patients, the overall correlation in fibrinogen levels between dry-hematology and the other methods was comparable to the results from in vitro dilution experiments. The dry-hematology reported higher fibrinogen values in whole blood compared with those measured in plasma samples, but hematocrit adjustment decreased the bias between whole blood and plasma samples from 73 mg/dL (95% prediction interval: 40, 106) to -13 mg/dL (95% prediction interval: -35, 8.5).

CONCLUSIONS

This study demonstrated that fibrinogen levels can be accurately assessed by the dry-hematology method in plasma and the results are not affected by heparin or colloids. For whole blood fibrinogen measurements by dry-hematology, hematocrit adjustment is necessary to compensate for dynamic changes in hematocrit in perioperative bleeding settings.

Massive transfusion and massive transfusion protocol

Haemorrhage remains a major cause of potentially preventable deaths. Rapid transfusion of large volumes of blood products is required in patients with haemorrhagic shock which may lead to a unique set of complications. Recently, protocol based management of these patients using massive transfusion protocol have shown improved outcomes. This section discusses in detail both management and complications of massive blood transfusion.

Coagulation testing in the perioperative period

Perioperative coagulation management is a complex task that has a significant impact on the perioperative journey of patients. Anaesthesia providers play a critical role in the decision-making on transfusion and/or haemostatic therapy in the surgical setting. Various tests are available in identifying coagulation abnormalities in the perioperative period. While the rapidly available bedside haemoglobin measurements can guide the transfusion of red blood cells, blood product administration is guided by many in vivo and in vitro tests. The introduction of newer anticoagulant medications and the implementation of the modified in vivo coagulation cascade have given a new dimension to the field of perioperative transfusion medicine. A proper understanding of the application and interpretation of the coagulation tests is vital for a good perioperative outcome.

Correction of hypothermic and dilutional coagulopathy with concentrates of fibrinogen and factor XIII: an in vitro study with ROTEM

BACKGROUND

Fibrinogen concentrate treatment can improve coagulation during massive traumatic bleeding. The aim of this in vitro study was to determine whether fibrinogen concentrate, or a combination of factor XIII and fibrinogen concentrates, could reverse a haemodilution-induced coagulopathy during hypothermia.

METHODS

Citrated venous blood from 10 healthy volunteers was diluted in vitro by 33% with 130/0.42 hydroxyethyl starch (HES) or Ringer's acetate (RAc). The effects of fibrinogen concentrate corresponding to 4 gram per 70 kg, or a combination of the same dose of fibrinogen with factor XIII (20 IU per kg), were measured using rotational thromboelastometry (ROTEM). The blood was analysed at 33°C or 37°C with ROTEM EXTEM and FIBTEM reagents. Clotting time (CT), clot formation time (CFT), alpha angle (AA) and maximal clot formation (MCF) were recorded.

RESULTS

Fibrinogen with or without factor XIII improved all ROTEM parameters in either solution irrespective of temperature, with the exception of EXTEM-AA and EXTEM-CFT in HES haemodilution. Fibrinogen increased FIBTEM-MCF more in the samples diluted with RAc than HES, particularly in presence of factor XIII.

CONCLUSIONS

Fibrinogen improved in vitro haemodilution-induced coagulopathy at both 33°C and 37°C, though more efficiently after crystalloid than HES haemodilution. Factor XIII had an additional effect on FIBTEM-MCF, but only after crystalloid dilution.

New approaches to obstetric hemorrhage: the postpartum hemorrhage consensus algorithm

PURPOSE OF REVIEW

Postpartum hemorrhage is increasingly frequent and a major contributor to maternal morbidity and mortality. Although individual steps, such as coagulation or surgical management, have been reviewed, there is little information on treatment algorithms.

RECENT FINDINGS

A treatment algorithm for postpartum hemorrhage was developed by the experts from three different specialties and from three countries. The algorithm describes symptoms, diagnosis, general measurements, medication, and organizational aspects.

SUMMARY

The algorithm is thought to serve as a template for local adaptation. It will hopefully improve the management of postpartum hemorrhage.

Is there a place for crystalloids and colloids in remote damage control resuscitation?

Crystalloids and colloids are used in prehospital fluid resuscitation to replace blood loss and preserve tissue perfusion until definite surgical control of bleeding can be achieved. However, large volumes of fluids will increase bleeding by elevating blood pressure, dislodging blood clots, and diluting coagulation factors and platelets. Hypotensive fluid resuscitation strategies are used to avoid worsening of uncontrolled bleeding. This is largely supported by animal studies. Most clinical evidence suggests that restricting fluid therapy is associated with improved outcome. Remote damage control resuscitation emphasizes the early use of blood products and restriction of other fluids to support coagulation and tissue oxygenation. Controversy regarding the optimal choice and composition of resuscitation fluids is ongoing. Compared with crystalloids, less colloid is needed for the same expansion of intravascular volume. On the other hand, colloids may cause coagulopathy not only related to dilution. The most important advantage of using colloids is logistical because less volume and weight are needed. In conclusion, prehospital fluid resuscitation is considered the standard of care, but there is little clinical evidence supporting the use of either crystalloids or colloids in remote damage control resuscitation. Alternative resuscitation fluids are needed.

[Management of postpartum hemorrhage (PPH): algorithm of the interdisciplinary D-A-CH consensus group PPH (Germany - Austria - Switzerland)]

Postpartum hemorrhage (PPH) is one of the main causes of maternal deaths even in industrialized countries. It represents an emergency situation which necessitates a rapid decision and in particular an exact diagnosis and root cause analysis in order to initiate the correct therapeutic measures in an interdisciplinary cooperation. In addition to established guidelines, the benefits of standardized therapy algorithms have been demonstrated. A therapy algorithm for the obstetric emergency of postpartum hemorrhage in the German language is not yet available. The establishment of an international (Germany, Austria and Switzerland D-A-CH) "treatment algorithm for postpartum hemorrhage" was an interdisciplinary project based on the guidelines of the corresponding specialist societies (anesthesia and intensive care medicine and obstetrics) in the three countries as well as comparable international algorithms for therapy of PPH.The obstetrics and anesthesiology personnel must possess sufficient expertise for emergency situations despite lower case numbers. The rarity of occurrence for individual patients and the life-threatening situation necessitate a structured approach according to predetermined treatment algorithms. This can then be carried out according to the established algorithm. Furthermore, this algorithm presents the opportunity to train for emergency situations in an interdisciplinary team.

Role of prothrombin complex concentrate in perioperative coagulation therapy

Prothrombin complex concentrate (PCC) is a term to describe pharmacological products that contain lyophilized, human plasma-derived vitamin K-dependent factors (F), FII, FVII, FIX, FX, and various amounts of proteins C and S. PCCs can be rapidly reconstituted in a small volume (20 ml for about 500 international units (IU)) at bedside and administered regardless of the patient's blood type. PCCs are categorized as 4-factor PCC if they contain therapeutic amounts of FVII, and 3-factor PCC when FVII content is low. In addition, activated PCC which contains activated FVII and FX with prothrombin is available for factor VIII bypassing therapy in hemophilia patients with inhibitors. Currently, 4-factor PCC is approved for the management of bleeding in patients taking warfarin, but there has been increasing use of various PCCs in the treatment of acquired perioperative coagulopathy unrelated to warfarin therapy and in the management of bleeding due to novel oral anticoagulants. There is also an ongoing controversy about plasma transfusion and its potential hazards including transfusion-related lung injury (TRALI). Early fixed ratio plasma transfusion has been implemented in many trauma centers in the USA, whereas fibrinogen concentrate and PCC are preferred over plasma transfusion in some European centers. In this review, the rationales for including PCCs in the perioperative hemostatic management will be discussed in conjunction with plasma transfusion.

Usefulness of standard plasma coagulation tests in the management of perioperative coagulopathic bleeding: is there any evidence?

Standard laboratory coagulation tests (SLTs) such as prothrombin time/international normalized ratio or partial thromboplastin time are frequently used to assess coagulopathy and to guide haemostatic interventions. However, this has been challenged by numerous reports, including the current European guidelines for perioperative bleeding management, which question the utility and reliability of SLTs in this setting. Furthermore, the arbitrary definition of coagulopathy (i.e. SLTs are prolonged by more than 1.5-fold) has been questioned. The present study aims to review the evidence for the usefulness of SLTs to assess coagulopathy and to guide bleeding management in the perioperative and massive bleeding setting. Medline was searched for investigations using results of SLTs as a means to determine coagulopathy or to guide bleeding management, and the outcomes (i.e. blood loss, transfusion requirements, mortality) were reported. A total of 11 guidelines for management of massive bleeding or perioperative bleeding and 64 studies investigating the usefulness of SLTs in this setting were identified and were included for final data synthesis. Referenced evidence for the usefulness of SLTs was found in only three prospective trials, investigating a total of 108 patients (whereby microvascular bleeding was a rare finding). Furthermore, no data from randomized controlled trials support the use of SLTs. In contrast, numerous investigations have challenged the reliability of SLTs to assess coagulopathy or guide bleeding management. There is actually no sound evidence from well-designed studies that confirm the usefulness of SLTs for diagnosis of coagulopathy or to guide haemostatic therapy.

Treatment with fibrinogen γ-chain peptide-coated, adenosine 5'-diphosphate-encapsulated liposomes as an infusible hemostatic agent against active liver bleeding in rabbits with acute thrombocytopenia

BACKGROUND

We evaluated the hemostatic efficacy of H12-(adenosine 5'-diphosphate [ADP])-liposomes in the setting of active liver bleeding in rabbits with dilutional thrombocytopenia after massive transfusion.

STUDY DESIGN AND METHODS

Acute thrombocytopenia (platelet [PLT] count < 50 × 10(9) /L) was induced in rabbits by repeated blood withdrawal and isovolemic transfusion of autologous washed red blood cells. Liver hemorrhage was initiated by a penetrating liver injury. Subsequently, the animals received tamponade treatment for the liver hemorrhage for 5 minutes and were intravenously administered H12-(ADP)-liposomes with PLT-poor plasma (PPP), PLT-rich plasma (PRP), PPP alone, H12-(phosphate-buffered saline [PBS])-liposome/PPP, or H12-(ADP)-liposomes/PPP plus fibrinogen concentrate during the tamponade.

RESULTS

Administration of H12-(ADP)-liposomes/PPP rescued 60% of the rabbits from the liver hemorrhage; PRP administration rescued 50%. In contrast, rabbits receiving PPP or H12-(PBS)-liposome/PPP achieved only 10 or 17% survival, respectively, for the first 24 hours. H12-(ADP)-liposomes/PPP as well as PRP consistently reduced bleeding volumes and shortened clotting times (CTs) in comparison to PPP administration. Specifically, bleeding volumes in the initial 5 minutes averaged 11 mL (H12-(ADP)-liposomes/PPP) and 17 mL (PRP) versus 30 mL (PPP; p < 0.05); CTs averaged 270 and 306 seconds versus 401 seconds (p < 0.05). H12-(ADP)-liposomes were observed at the bleeding site with thrombus formation, suggesting an induction of thrombi. Neither macro- nor microthrombi were detected in the lung, kidney, spleen, or liver in rabbits treated with H12-(ADP)-liposomes. Supplementation of fibrinogen to H12-(ADP)-liposomes/PPP did not significantly improve rabbit survival.

CONCLUSIONS

H12-(ADP)-liposomes might be a safe and effective therapeutic tool during damage control surgery for trauma patients with acute thrombocytopenia and massive bleeding.

Improvements in patient blood management for pediatric craniosynostosis surgery using a ROTEM(®) -assisted strategy - feasibility and costs

BACKGROUND

Moderate to severe intraoperative bleeding and the presence of acquired coagulopathy remain serious problems in the management of major pediatric craniosynostosis surgery. After implementation of a ROTEM(®) -assisted patient blood management (PBM) strategy, using primarily purified coagulation factor concentrates, feasibility and costs of this new regimen were analyzed.

METHODS

Retrospective analysis of all consecutive children who underwent primary elective major craniofacial surgery for craniosynostosis repair was carried out at the Children's University Hospital, Zurich, between 2007 and 2013. Laboratory workup and transfusion requirements were compared.

RESULTS

A total of 47 children (36 in the historic group and 11 after implementation of PBM) were analyzed. Although all patients in this study needed transfusion of red blood cell concentrates, there was a total avoidance of perioperative transfusion of fresh frozen plasma and a reduction in transfused platelets (one of nine children vs nine of 36 children in the historic group) after implementation of the PBM strategy. Based on a predefined ROTEM(®) threshold in the PBM group (FibTEM MCF <8 mm), administration of fibrinogen concentrate was necessary in all of these children. The mean total costs per patient consisting of transfused allogeneic blood products and coagulation factor concentrates were reduced by 17.1% after implementation of PBM (1071.82 EUR per patient before vs 888.93 EUR after implementation).

CONCLUSIONS

The implementation of a ROTEM(®) -assisted PBM is feasible and is associated with a considerable reduction in intraoperative transfusion requirements and thereby a decrease in transfusion-related direct costs.

Bleeding management for pediatric craniotomies and craniofacial surgery

Pediatric patients when undergoing craniotomies and craniofacial surgery may potentially have significant blood loss. The amount and extent will be dictated by the nature of the surgical procedure, the proximity to major blood vessels, and the age, and weight of the patient. The goals should be to maintain hemodynamic stability and oxygen carrying capacity and to prevent and treat hyperfibrinolysis and dilutional coagulopathy. Over transfusion and transfusion-related side effects should be minimized. This article will highlight the pertinent considerations for managing massive blood loss in pediatric patients undergoing craniotomies and craniofacial surgery. North American and European guidelines for intraoperative administration of fluid and blood products will be discussed.

A 2014 Update on Coagulation Management for Cardiopulmonary Bypass

Coagulopathy after cardiac surgery with cardiopulmonary bypass is a serious complication that may result in massive bleeding requiring transfusion of significant amounts of blood products, plasma, and platelets. In addition to increased patient morbidity and mortality it is associated with longer hospital stay and increased resource utilization. The current review discusses aspects in cardiopulmonary bypass–induced coagulopathy with emphasis on point-of-care testing and individualized “goal-directed” therapy in patients who develop excessive bleeding after cardiac surgery.

Fibrinogen concentrate administration attributes to significant reductions of blood loss and transfusion requirements in thoracic aneurysm repair

Background

Repair of thoracic aortic aneurysm (TAA) is often associated with massive hemorrhage aggravated by dilutional coagulopathy with severe hypofibrinogenemia. Although only fresh frozen plasma (FFP) is available for acquired hypofibrinogenemia in Japan, the hemostatic effect of FFP has not been enough for dilutional coagulopathy in TAA surgery. There are increasing reports suggesting that fibrinogen concentrate may be effective in controlling perioperative bleeding and reducing transfusion requirements.

Methods

We retrospectively analyzed the hemostatic effect of fibrinogen concentrate compared with FFP in total 49 cases of elective TAA surgery. In 25 patients, fibrinogen concentrate was administered when the fibrinogen level was below 150 mg/dL at the cardiopulmonary bypass (CPB) termination. The recovery of fibrinogen level, blood loss, and transfused units during surgery were compared between cases of this agent and FFP (n = 24).

Results

We observed rapid increases in plasma fibrinogen level and subsequent improvement in hemostasis by administration of fibrinogen concentrate after CPB termination. The average volume of total blood loss decreased by 64% and the average number of transfused units was reduced by 58% in cases of fibrinogen concentrate given, in comparison with cases of only FFP transfused for fibrinogen supplementation.

Conclusions

In patients showing severe hypofibrinogenemia during TAA surgery, timely administration of fibrinogen concentrate just after removal from CPB is effective for hemostasis, and therefore in reducing blood loss and transfused volumes.

Management of hemorrhage in cardiothoracic surgery

Bleeding is an important issue in cardiothoracic surgery, and about 20% of all blood products are transfused in this clinical setting worldwide. Transfusion practices, however, are highly variable among different hospitals and more than 25% of allogeneic blood transfusions have been considered inappropriate. Furthermore, both bleeding and allogeneic blood transfusion are associated with increased morbidity, mortality, and hospital costs. In the past decades, several attempts have been made to find a universal hemostatic agent to ensure hemostasis during and after cardiothoracic surgery. Most drugs studied in this context have either failed to reduce bleeding and transfusion requirements or were associated with severe adverse events, such as acute renal failure or thrombotic/thromboembolic events and, in some cases, increased mortality. Therefore, an individualized goal-directed hemostatic therapy ("theranostic" approach) seems to be more appropriate to stop bleeding in this complex clinical setting. The use of point-of-care (POC) transfusion and coagulation management algorithms guided by viscoelastic tests such as thromboelastometry/thromboelastography in combination with POC platelet function tests such as whole blood impedance aggregometry, and based on first-line therapy with fibrinogen and prothrombin complex concentrate have been associated with reduced allogeneic blood transfusion requirements, reduced incidence of thrombotic/thromboembolic and transfusion-related adverse events, and improved outcomes in cardiac surgery. This article reviews the current literature dealing with the management of hemorrhage in cardiothoracic surgery based on POC diagnostics and with specific coagulation factor concentrates and its impact on transfusion requirements and patients' outcomes.

A calcium-containing electrolyte-balanced hydroxyethyl starch (HES) solution is associated with higher factor VIII activity than is a non-balanced HES solution, but does not affect von Willebrand factor function or thromboelastometric measurements--results of a model of in vitro haemodilution

BACKGROUND

Hydroxyethyl starch (HES) is known to impair blood coagulation. The impact of calcium-containing, balanced carrier solutions of HES on coagulation is controversial. We investigated the effects of increasing degrees of haemodilution with modern 6%, electrolyte-balanced HES vs non-balanced HES on coagulation in vitro, and compared the balanced HES to a balanced crystalloid solution for an internal control.

MATERIALS AND METHODS

Blood samples from ten healthy volunteers were diluted in vitro by 20%, 40% and 60% with either calcium-containing balanced 130/0.42 HES, non-balanced 130/0.4 HES or balanced crystalloid. In all samples, blood counts, prothrombin time ratio, activated partial thromboplastin time, ionized calcium, factor VIII activity, von Willebrand factor antigen, von Willebrand factor collagen binding activity, and von Willebrand factor activity were determined, and activated rotational thromboelastometry (EXTEM and FIBTEM assays) was performed.

RESULTS

Haemodilution impaired coagulation in a dilution-dependent manner as determined by both conventional laboratory assays and thromboelastometry. Ionized calcium increased with balanced HES (p≤0.004), but decreased with non-balanced HES (p≤0.004). Prothrombin time ratio (p≤0.002) and factor VIII levels (p=0.001) were better preserved with balanced HES than with non-balanced HES in dilutions ≥40%. Thromboelastometry showed no differences between values in blood diluted with the balanced or non-balanced HES.

DISCUSSION

In vitro, a balanced calcium-containing carrier solution of 6% HES 130/0.42 preserved coagulation better than did non-balanced HES 130/0.4 as quantified by conventional coagulation assays, but not in activated thromboelastometry. One explanation could be the increased ionized calcium levels after dilution with calcium-containing carrier solutions.

Restoring hemostasis: fibrinogen concentrate versus cryoprecipitate

Fibrinogen plays a key role in the coagulation process, and therefore maintaining adequate quantities of fibrinogen is an essential step in achieving satisfactory hemostasis in patients with acquired hypofibrinogenemia. Potential options for treating acquired hypofibrinogenemia in patients with uncontrolled bleeding include the use of cryoprecipitate or fibrinogen replacement therapy. This review provides a brief overview of the hemostatic process and the methods for assessing coagulopathy and discusses the efficacy and safety of cryoprecipitate and fibrinogen concentrate in restoring fibrinogen levels, achieving hemostasis and reducing transfusion requirements in different patient populations requiring rapid hemostasis. Other issues relevant to the clinical use of these agents in restoring hemostasis, including variations in product composition, preparation time and cost, are also examined.

Therapeutic rather than prophylactic platelet transfusion policy for severe thrombocytopenia during liver transplantation

Platelet transfusion (PTx) has been identified as an important risk factor for morbidity and mortality after liver transplantation (LTx). Our aim was to evaluate the safety of therapeutic rather than prophylactic PTx policy in severe thrombocytopenic patients undergoing LTx. Recipients of LTx were divided into two groups: group I (GI) (n = 76) platelet count (PC) ≥ 50 × 10(9)/l and group II (GII) PC < 50 × 109/l (n = 76). Platelets were transfused following a thromboelastometry protocol and clinical signs of diffuse bleeding. Both groups were compared regarding hemoglobin (Hb), international normalized ratio (INR), fibrinogen level, blood loss (BL), blood products required, percentage of bloodless surgery, duration of mechanical ventilation, ICU stay, and vascular complications. Each group was further subdivided according to PTx into (GI NPTx and GII NPTx) with no platelet transfusion (NPTx) and (GI PTx and GII PTx) received PTx. These subgroups were further compared for some variables. Base line Hb was significantly higher while INR was significantly lower in GI.75% avoided PTx in GII. Comparisons of BL, packed red blood cells (PRBCs), and cryoprecipitate transfusion were insignificant. Fresh frozen plasma (FFP) transfusion was higher and the percentage of bloodless surgery was lower in GII. In GII, PC increased after start of surgery. Two cases of hepatic artery thrombosis in GI and one in GII were recorded. Recovery of platelets was quicker, and duration of mechanical ventilation and ICU stay was shorter in NPTx patients regardless the base line PC. Cut-off values of PC 30 × 10(9)/l (with sensitivity 73.7% and specificity 78.8%, p < 0.01), BL of 3750 ml in GI (sensitivity of 75% and specificity of 69%, p < 0.01) and of 3250 ml in GII (sensitivity of 84.2% and specificity of 87.7% (p < 0.01)) could indicate the need of PTx. With therapeutic approach, 75% of patients in GII could avoid unnecessary PTx with its hazards without excessive bleeding. PC in GII increased intraoperatively, PTx may lead to delayed recovery of platelets, increased duration of mechanical ventilation and ICU stay. The given cut-off values may help to guide PTx.