Transfusion-associated circulatory overload in a pediatric intensive care unit: different incidences with different diagnostic criteria

Estimating the incidence of transfusion-associated circulatory overload using active surveillance: A systematic review and meta-analysis

BACKGROUND

Transfusion-associated circulatory overload (TACO) is an adverse event that is the leading cause of transfusion-related death. It is underrecognized, and the aim of this study was to synthesize the available evidence from active surveillance studies to estimate its incidence.

STUDY DESIGN AND METHODS

This study is a systematic review and meta-analysis of publications reporting TACO incidence using active surveillance. A research librarian searched Medline and Embase, identifying publications between January 1991 and June 2024. Studies reporting TACO either by patient, blood component (red blood cells [RBCs], platelets, or plasma) or transfusion episode were identified, and all patient settings were eligible. A random effects model estimated TACO incidence, and potential sources of heterogeneity were evaluated using meta-regression.

RESULTS

Twenty-two studies met eligibility criteria and were included for analysis. The rate per patient was 22.2/1000 (95% CI: 16.2-29.2) based on 21 studies. The rate estimate of TACO among total blood components (RBCs, plasma, and platelets combined) reported in 10 studies was 2.2/1000 units transfused (95% CI: 1.2-3.5/1000). There was substantial between-study variation in rates and more recent studies tended to report higher rates. Although the platelet point estimate was higher than the point estimates for RBCs and plasma, the confidence intervals overlapped. Only two studies reported TACO rates per transfusion episode and the pooled estimate was 6.3/1000 (95% CI: 1-16.3/1000), about three times greater than the overall per unit estimate.

DISCUSSION

Clinicians should consider quantitative risks of important transfusion-related harms, such as TACO, when making the decision to transfuse.

Red blood cell transfusion management for people undergoing cardiac surgery for congenital heart disease

BACKGROUND

Congenital heart disease is the most common neonatal congenital condition. Surgery is often necessary. Patients with congenital heart disease are potentially exposed to red cell transfusion preoperatively, intraoperatively and postoperatively when admitted for cardiac surgery. There are a number of risks associated with red cell transfusion that may increase morbidity and mortality.

OBJECTIVES

To evaluate the association of red blood cell transfusion management with mortality and morbidity in people with congenital heart disease who are undergoing cardiac surgery.

SEARCH METHODS

We searched multiple bibliographic databases and trials registries, including the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (Ovid), Embase (Ovid), CINAHL (EBSCOhost), Transfusion Evidence Library, ClinicalTrials.gov and the World Health Organization (WHO) ICTRP. The most recent search was on 2 January 2024, with no limitation by language of publication.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) comparing red blood cell transfusion interventions in patients undergoing cardiac surgery for congenital heart disease. Participants of any age (neonates, paediatrics and adults) and with any type of congenital heart disease (cyanotic or acyanotic) were eligible for inclusion. No comorbidities were excluded.

DATA COLLECTION AND ANALYSIS

Two of five (AA, CK, KW, SB, SF) review authors independently extracted data and assessed the risk of bias in the trials. We contacted study authors for additional information. Two review authors (CK, KW) used GRADE methodology to assess evidence certainty for critical outcomes and comparisons.

MAIN RESULTS

We identified 19 relevant trials. The trials had 1606 participants, all of whom were neonates or children. No trials were conducted in the preoperative period or with adults. The trials compared different types of red blood cell transfusions. No trial compared red blood cell transfusion versus no red blood cell transfusion. None of the trials was at low risk of bias overall. Eight trials had a high risk of bias in at least one domain, most commonly, blinding of participants and personnel. For our critical outcomes, we judged the certainty of the evidence based on GRADE criteria to be low or very low. Five trials (497 participants) compared a restrictive versus a liberal transfusion-trigger. It is very uncertain whether a restrictive transfusion-trigger has an effect on all-cause mortality in the short-term (0 to 30 days post-surgery) (risk ratio (RR) 1.12, 95% confidence interval (CI) 0.42 to 3.00; 3 RCTs, 347 participants; very low certainty evidence) or long term (31 days to two years post-surgery) (RR 0.33, 95% CI 0.01 to 7.87; 1 RCT, 60 participants; very low certainty evidence). The evidence is also very uncertain on the incidence of severe adverse cardiac events (RR 1.00, 95% CI 0.73 to 1.37; 2 RCTs, 232 participants) and infection (RR 0.81, 95% CI 0.47 to 1.39; 2 RCTs, 232 participants) (both very low certainty evidence). A restrictive transfusion-trigger may have little to no effect on the duration of mechanical ventilation (mean difference (MD) -1.65, 95% CI -3.51 to 0.2; 2 RCTs, 168 participants; low-certainty evidence) or of ICU stay (MD 0.15, 95% CI -0.72 to 1.01; 3 RCTs, 228 participants, low-certainty evidence). Five trials (231 participants) compared washed red blood cells in CPB prime versus unwashed red blood cells in CPB prime. Washing red blood cells in CPB prime may have little to no effect on all-cause mortality in the short term (0 to 30 days post-surgery) (RR 0.25, 95% CI 0.03 to 2.18; 2 RCTs, 144 participants) or long term (31 days to 2 years post-surgery) (RR 0.50, 95% CI 0.05 to 5.38; 1 RCT, 128 participants) (both low-certainty evidence). The evidence is very uncertain about the effect of washed CPB prime on severe cardiac adverse events (RR 0.88, 95% CI 0.47 to 1.64), infection (RR 1.00, 95% CI 0.50 to 1.99) and duration of ICU stay (MD -0.3, 95% CI -4.32 to 3.72) (1 RCT, 128 participants; very low certainty evidence). Two trials (76 participants) compared crystalloid (bloodless) CPB prime versus red-blood-cell-containing CPB prime. It is very uncertain whether bloodless prime has an effect on the duration of mechanical ventilation (median 8.0 hours, interquartile range (IQR) 6.8 to 9.0 hours versus median 7.0 hours, IQR 6.0 to 8.0 hours; 1 RCT, 40 participants) or duration of ICU stay (median 23.0 hours, IQR 21.8 to 41.5 hours versus median 23.5 hours, IQR 21.0 to 29.0 hours; 1 RCT, 40 participants) (both very low certainty evidence). Two trials (160 participants) compared ultrafiltration of CPB prime versus no ultrafiltration. It is very uncertain whether ultrafiltration of CPB prime has an effect on all-cause mortality in the short term (0 to 30 days post-surgery) (RR not estimable; 1 RCT, 50 participants; very low certainty evidence). Ultrafiltration may reduce the duration of mechanical ventilation (MD -16.00, 95% CI -25.00 to -7.00) and the duration of ICU stay (MD -0.6, 95% CI -0.84 to -0.36) (1 RCT, 50 participants; low-certainty evidence). One trial (59 participants) compared retrograde autologous CPB prime versus standard CPB prime. It is very uncertain whether retrograde autologous CPB prime has an effect on the duration of mechanical ventilation (MD 0.02, 95% CI -0.03 to 0.07) or duration of ICU stay (MD 0, 95% CI -0.01 to 0.01) (1 RCT, 59 participants; very low certainty evidence). One trial (178 participants) compared 'fresh' (not near expiry date) versus 'old' (near expiry date) red blood cell transfusion but did not report on our outcomes.

AUTHORS' CONCLUSIONS

No randomised controlled trial compared red blood cell transfusion against no red blood cell transfusion in people with congential heart disease undergoing cardiac surgery. There are only small, heterogeneous trials in children that compare different forms of red blood cell transfusion, and there are no trials at all in adults. There is therefore insufficient evidence to accurately assess the association of red blood cell transfusion with the morbidity and mortality of patients with congenital heart disease undergoing cardiac surgery. It is possible that trial outcomes are affected by the presence or absence of cyanosis, so this should be considered in future trial design. Further adequately powered, high-quality trials in both children and adults are required.

Assessing Differential Transfusion Requirements for Children with Congenital Malformations vs. Pediatric Acute Abdomen Emergencies

BACKGROUND AND OBJECTIVES

This retrospective study aimed to evaluate the efficacy of preoperative blood transfusions in correcting anemia for pediatric patients with congenital malformations (CMs) versus those with acute abdomen (AA) conditions. The study hypothesized that the response to transfusions might vary significantly between these groups due to the differences in the underlying pathology and clinical status.

METHODS

The study included 107 pediatric patients admitted to Timisoara 'Louis Turcanu' Emergency Hospital for Children between January 2015 and May 2023, who required blood transfusions for preoperative anemia. Hemoglobin (HGB), hematocrit (HCT), and red blood cell counts (RBC) were assessed at admission, 48 h post-transfusion, and at discharge. Statistical analyses, including Student's t-test, Pearson correlation, and chi-square tests, were utilized to compare outcomes between the groups. The study population was divided into 53 children with CM and 54 with AA.

RESULTS

Initial analyses showed that children with CM had statistically significantly higher baseline HGB (8.54 ± 1.00 g/dL vs. 7.87 ± 1.02 g/dL, p = 0.001) and HCT (26.07 ± 3.98% vs. 23.95 ± 2.90%, p = 0.002) compared to those with AA. Post-transfusion, children with CM exhibited a greater increase in HGB, with the highest increases noted in patients with central nervous system defects (mean increase of 3.67 g/dL, p = 0.038). In contrast, the increases in HGB for children with AA were less pronounced, with the highest being 2.03 g/dL in those with peritonitis (p = 0.078).

CONCLUSIONS

No significant gender differences were noted in response to transfusion. Children with congenital malformations respond more effectively to preoperative blood transfusions compared to those with acute abdomen conditions. These findings suggest that differential transfusion strategies may be required based on the underlying medical condition to optimize the management of preoperative anemia in pediatric patients. Tailoring transfusion approaches according to specific patient needs and conditions could enhance clinical outcomes and resource utilization in pediatric surgical settings.

Developments in Transfusion Medicine: Pulmonary Transfusion Reactions and Novel Blood Cell Labeling Techniques

Staying updated on advancements in transfusion medicine is crucial, especially in critical care and perioperative setting, where timely and accurate transfusions can be lifesaving therapeutic interventions. This narrative review explores the landscape of transfusion-related adverse events, focusing on pulmonary transfusion reactions such as transfusion-associated circulatory overload (TACO) and transfusion-related acute lung injury (TRALI). TACO and TRALI are the leading causes of transfusion-related morbidity and mortality; however, specific treatments are lacking. Understanding the current incidence, diagnostic criteria, pathogenesis, treatment, and prevention strategies can equip clinicians to help reduce the incidence of these life-threatening complications. The review discusses emerging pathogenic mechanisms, including the possible role of inflammation in TACO and the mechanisms of reverse TRALI and therapeutic targets for TACO and TRALI, emphasizing the need for further research to uncover preventive and treatment modalities. Despite advancements, significant gaps remain in our understanding of what occurs during transfusions, highlighting the necessity for improved monitoring methods. To address this, the review also presents novel blood cell labeling techniques in transfusion medicine used for improving monitoring, quality assessment, and as a consequence, potentially reducing transfusion-related complications. This article aims to provide an update for anesthesiologists, critical care specialists, and transfusion medicine professionals regarding recent advancements and developments in the field of transfusion medicine.

Blood banking considerations in pediatric trauma

ABSTRACT

Transfusion of blood products to a hemorrhaging pediatric trauma patient requires seamless partnership and communication between trauma, emergency department, critical care, and transfusion team members. To avoid confusion and delays, understanding of blood banking principles and mutually agreed upon procedures and policies must be regularly updated as knowledge evolves. Because pediatric patients require specialized considerations distinct from those in adults, this brief review covers transfusion principles, policies, and procedures specific to the resuscitation of pediatric trauma patients.

Factors associated with postoperative respiratory conditions and critical outcomes on pediatric liver transplantation: A single-center experience

BACKGROUND

Orthotopic liver transplantation (OLT) is an established therapeutic option for pediatric end-stage liver disease (PELD). The postoperative respiratory conditions of OLT recipients may be associated with subsequent clinical outcomes including length of stay (LOS) in the pediatric intensive care unit (PICU). This study aimed to characterize the postoperative respiratory conditions, associated factors, and outcomes after pediatric OLT.

METHODS

Clinical data of children receiving OLT from July 2014 to July 2020 were retrospectively collected. Postoperative respiratory conditions were defined as time to extubation, significant pleural effusion, and initial postoperative PaO2/FiO2 ratio. Logistic and multiple regressions were applied to analyze the associations among clinical factors, postoperative respiratory conditions, and clinical outcomes.

RESULTS

Twenty-two patients with median age of 1.4-year-old (range: 25 days to 12 years old) were analyzed. Mortality within 28 days was 4.5% and median LOS in the PICU was 18 days. Of 22 patients, 11 patients (50.0%) were extubated over 24 hours after surgery, and 8 patients (36.4%) required drainage for pleural effusions. Longer LOS in the PICU were noted in patients extubated over 24 hours (p = 0.008), complicated with significant pleural effusions (p = 0.02) after surgery, and having low initial postoperative PaO2/FiO2 (<300 mmHg) (p = 0.001). Among clinical factors, massive intraoperative blood transfusion (>40 mL/kg) was significantly associated with prolonged intubations, significant pleural effusions, low initial postoperative PaO2/FiO2, and prolonged LOS in the PICU (>14 days). The initial postoperative PaO2/FiO2 significantly depended on age, disease severity (PELD score), and whether the patient received massive intraoperative blood transfusion.

CONCLUSION

Pediatric patients of OLT with poor postoperative respiratory conditions including low initial PaO2/FiO2 ratio, extubation over 24 hours or significant pleural effusions have longer LOS in the PICU, and the requirement of massive intraoperative transfusion was a risk factor for both poor postoperative respiratory conditions and prolonged LOS in the PICU.

Transfusion practices in a large cohort of hospitalized children

BACKGROUND

While previous studies have described the use of blood components in subsets of children, such as the critically ill, little is known about transfusion practices in hospitalized children across all departments and diagnostic categories. We sought to describe the utilization of red blood cell, platelet, plasma, and cryoprecipitate transfusions across hospital settings and diagnostic categories in a large cohort of hospitalized children.

STUDY DESIGN AND METHODS

The public datasets from 11 US academic and community hospitals that participated in the National Heart Lung and Blood Institute Recipient Epidemiology and Donor Evaluation Study-III (REDS-III) were accessed. All nonbirth inpatient encounters of children 0-18 years of age from 2013 to 2016 were included.

RESULTS

61,770 inpatient encounters from 41,943 unique patients were analyzed. Nine percent of encounters involved the transfusion of at least one blood component. RBC transfusions were most common (7.5%), followed by platelets (3.9%), plasma (2.5%), and cryoprecipitate (0.9%). Children undergoing cardiopulmonary bypass were most likely to be transfused. For the entire cohort, the median (interquartile range) pretransfusion laboratory values were as follows: hemoglobin, 7.9 g/dl (7.1-10.4 g/dl); platelet count, 27 × 10⁹ cells/L (14-54 × 10⁹ cells/L); and international normalized ratio was 1.6 (1.4-2.0). Recipient age differences were observed in the frequency of RBC irradiation (95% in infants, 67% in children, p < .001) and storage duration of RBC transfusions (median storage duration of 12 [8-17] days in infants and 20 [12-29] days in children, p < .001).

CONCLUSION

Based on a cohort of patients from 2013 to 2016, the transfusion of blood components is relatively common in the care of hospitalized children. The frequency of transfusion across all pediatric hospital settings, especially in children undergoing cardiopulmonary bypass, highlights the opportunities for the development of institutional transfusion guidelines and patient blood management initiatives.

Frequency and timing of all-cause deaths in visits involving suspected transfusion reactions, and the significance of cardiopulmonary disturbances

BACKGROUND/OBJECTIVES

Transfusion reactions (TRs) may cause or contribute to death. Cardiopulmonary TRs are distressing, and collectively account for most transfusion fatalities, though the degree to which they alter survival more broadly is unclear. Deaths (and their timing) after TRs may provide further insights.

MATERIALS/METHODS

Adult (tri-hospital network) haemovigilance data (2013-2016) recorded referrals with conclusions ranging from unrelated to transfusion (UTR) to entities such as: septic TRs, serologic/haemolytic reactions, transfusion-associated circulatory overload (TACO), transfusion-associated dyspnoea (TAD), transfusion-related acute lung injury (TRALI), allergic transfusion reaction (ATR), and others. For (in- or out-patient) visits involving suspected TRs (VISTRs), all-cause mortalities (% [95% confidence interval]) and associated time-to-death (TTD) (median days, [interquartile range]) were compared. Diagnoses were defined inclusively (possible-to-definite) or strictly (probable-to-definite).

RESULTS

Of 1144 events, rank order VISTR mortality following (possible-to-definite) TRs, and associated TTDs, were led by: DHTR 33% [6-19], 1 death at 123d; TRALI 32% [15-54], 6 deaths: 3d [2-20]; BaCon 21% [14-31], 17 deaths: 10d [3-28]; TACO 18% [12-26], 23 deaths: 16d [6-28]; TAD 17% [11-26]: 18 deaths, 6d [3-12]. Higher-certainty TRs ranked similarly (DHTR 50% [9-91]; BaCon 29% [12-55], 4 deaths: 12d [3-22]; and TACO 25% [16-38], 15 deaths: 21d [6-28]). VISTR mortality after TACO or TRALI significantly exceeded ATR (3·3% [2·4-5·8], P < 0·00001) but was not different from UTR events (P = 0·3).

CONCLUSIONS

Only half of cardiopulmonary TRs constituted high certainty diagnoses. Nevertheless, cardiopulmonary TRs and suspected BaCon marked higher VISTR mortality with shorter TTDs. Short (<1 week) TTDs in TAD, BaCon or TRALI imply either contributing roles in death, treatment refractoriness and/or applicable TR susceptibilities in the dying.

Pediatric Hemovigilance and Adverse Transfusion Reactions

Some types of transfusion reactions occur more frequently in the pediatric than the adult population. Allergic reactions are the most common, followed by nonhemolytic transfusion reactions; male children seem most susceptible to such reactions. Platelets are often implicated and pulmonary reactions are understudied in children. Clinical sequelae in neonates, such as bronchopulmonary dysplasia/chronic lung disease and intraventricular hemorrhage, have received increasing attention in relation to transfusion. There is a need to better understand the pathophysiology of transfusion reactions in neonatal and pediatric populations so preventive strategies can be undertaken. There is also a need for robust hemovigilance systems.

Transfusion outcome for volume- and plasma-reduced platelet concentrates for pediatric patients

BACKGROUND AND OBJECTIVES

Plasma reduction in platelet concentrate (PC) products has been reported to prevent large volume load and transfusion-related adverse reactions (TRARs). However, volume reduction might be associated with a poor transfusion response because of a deterioration in platelet (PLT) quality. Because PLT quality control and transfusion responses for recently washed PCs using PLT additive solutions are superior, we investigated the clinical safety and transfusion efficacy of volume-reduced washed PCs in pediatric patients.

MATERIALS AND METHODS

We prepared a simplified resuspended PC product (RPC) as a washed PC. Regular RPC (R-RPC) included equivalent volumes of bicarbonate Ringer's solution and anticoagulant citrate dextrose solution A (BRS-A) as the resuspension solution. Half RPC (H-RPC) was prepared by adding a half volume of BRS-A. Twenty-four pediatric patients were scheduled for transfusions with R-RPC and H-RPC up to 4 times. R-RPC was transfused 42 times into 24 patients. H-RPC was transfused 41 times into 23 patients.

RESULTS

Neither product was observed to cause TRARs. Although the calculated PLT recovery for H-RPC was significantly reduced, the posttransfusion corrected count increment (24 h) did not differ. Moreover, similar results were observed for vital signs during transfusion.

CONCLUSION

Volume-reduced washed PC can be transfused without causing TRARs, differences in vital signs, or inferior transfusion responses. Volume-reduced washed PC also provides the advantages of shortened transfusion times and reduced volume loads. Although a standard technique for stable resuspension is necessary, volume-reduced washed PC may be a beneficial option for children, including neonates, or individuals with cardiovascular or renal problems.

Transfusion in children with acute respiratory distress syndrome

Transfusion is a frequent treatment in pediatric patients with acute respiratory distress syndrome (PARDS) although evidence to support transfusion decision-making is lacking. The purpose of this review is to review the current state of knowledge on the issue of transfusion in children with PARDS and to detail the possible beneficial effects and potential deleterious impacts of transfusion in this patient population. Based on the current literature and recent guidelines, a restrictive red blood cell (RBC) transfusion strategy (avoidance of transfusion when the haemoglobin level is above 7 g/dL) is indicated in stable patients without severe PARDS, as these were excluded from the large trials. In children with severe PARDS, further research is needed to determine if factors other than the haemoglobin level might guide RBC transfusion decision-making by better characterizing the presence of low oxygen delivery (DO₂). Additionally, appropriate indications for prophylactic transfusion of hemostatic products (plasma or platelets) in children with PARDS are lacking.

Adverse transfusion reactions in transfused children

Transfusion in paediatrics requires specific guidelines, because child physiology and pathology differ significantly as compared to adults. Adverse transfusion reactions in transfused children also vary in type and frequency, but there is a better understanding of these reactions in adults than in children. However, for the most frequent adverse transfusion reactions, the overall prevalence is higher in children than in adults, with the exception of post-transfusion red blood cell alloimmunisation, which is lower, excluding patients with haemoglobinopathies. In several studies, allergic reactions were the most frequently reported adverse transfusion reaction in paediatrics, and the platelet concentrate the most frequently implicated blood product. Early diagnosis of certain adverse transfusion reactions such as haemosiderosis, is essential in order to initiate the best therapy and obtain a good clinical outcome. The prevention of adverse transfusion reactions in children is required, but needs further clinical studies in paediatrics. Lastly, changes in technology, policy and clinical practices will improve transfusion safety in children.

Transfusion-Associated Circulatory Overload in ICUs: A Scoping Review of Incidence, Risk Factors, and Outcomes

Transfusion-associated circulatory overload is the most frequent serious adverse transfusion reaction, with an incidence close to 1% of transfused patients in the general adult population. Patients in ICUs are probably more at risk of transfusion-associated circulatory overload as they are more frequently transfused and associated with more comorbidities. However, the epidemiology of transfusion-associated circulatory overload in ICU is not well characterized, leading to a risk of underdiagnosis.

OBJECTIVES

We conducted a scoping review to describe the incidence, risk factors, and outcomes of transfusion-associated circulatory overload in PICU and adult ICU.

DATA SOURCES

PubMed, Ovid Medline, Ovid All EBM Reviews, Ovid Embase, and EBSCO CINAHL COMPLETE.

STUDY SELECTION

Two reviewers independently screened each article for inclusion criteria. Studies were eligible if they reported data on incidence, risk factors, or outcomes of transfusion-associated circulatory overload in at least 10 ICU patients.

DATA SYNTHESIS

Among 5,926 studies identified, nine were included. Five studies were prospective, and four were retrospective. The definition of transfusion-associated circulatory overload varied among studies. The pooled incidence of transfusion-associated circulatory overload was of 5.5% (95% CI, 2.6-9.4%) in adult ICUs (four studies, 2,252 patients, high heterogeneity). In PICUs, two studies (345 patients) reported 0 cases, and a third study (136 patients) reported variable incidences between 1.5% and 76%, depending on diagnostic criteria. Risk factors for transfusion-associated circulatory overload included positive fluid balance, the number and type of products transfused, rate of transfusion, and cardiovascular and renal comorbidities. Transfusion-associated circulatory overload was associated with increased ICU and hospital lengths of stay, whereas the association with mortality was not consistent.

CONCLUSIONS

Transfusion-associated circulatory overload is frequent in ICU patients and is associated with adverse outcomes. The lack of a pediatric-adjusted definition of transfusion-associated circulatory overload may lead to a risk of underdiagnosis of this condition in PICUs. Further research is warranted to improve the knowledge of transfusion-associated circulatory overload and the safety of transfusion in ICU patients.

Transfusion-associated circulatory overload and transfusion-related acute lung injury

Transfusion-associated circulatory overload (TACO) and transfusion-related acute lung injury (TRALI) are syndromes of acute respiratory distress that occur within 6 hours of blood transfusion. TACO and TRALI are the leading causes of transfusion-related fatalities, and specific therapies are unavailable. Diagnostically, it remains very challenging to distinguish TACO and TRALI from underlying causes of lung injury and/or fluid overload as well as from each other. TACO is characterized by pulmonary hydrostatic (cardiogenic) edema, whereas TRALI presents as pulmonary permeability edema (noncardiogenic). The pathophysiology of both syndromes is complex and incompletely understood. A 2-hit model is generally assumed to underlie TACO and TRALI disease pathology, where the first hit represents the clinical condition of the patient and the second hit is conveyed by the transfusion product. In TACO, cardiac or renal impairment and positive fluid balance appear first hits, whereas suboptimal fluid management or other components in the transfused product may enable the second hit. Remarkably, other factors beyond volume play a role in TACO. In TRALI, the first hit can, for example, be represented by inflammation, whereas the second hit is assumed to be caused by antileukocyte antibodies or biological response modifiers (eg, lipids). In this review, we provide an up-to-date overview of TACO and TRALI regarding clinical definitions, diagnostic strategies, pathophysiological mechanisms, and potential therapies. More research is required to better understand TACO and TRALI pathophysiology, and more biomarker studies are warranted. Collectively, this may result in improved diagnostics and development of therapeutic approaches for these life-threatening transfusion reactions.