A breathtaking and bloodcurdling story of coagulation and inflammation in acute lung injury

The effect of nebulized heparin on clinical outcomes in mechanically ventilated patients: a meta-analysis and review of the literature

OBJECTIVE

To determine the relationship between use of nebulized heparin and clinical outcomes in mechanically ventilated patients.

METHODS

The Medline, Embase, Web of Science, Cochrane Library, and PubMed databases were searched for relevant randomized controlled trials (RCTs), published between database inception and May 2022. Primary outcomes were intensive care unit (ICU) length of stay and in-hospital mortality; secondary outcomes included duration of mechanical ventilation, ventilator-free days (VFDs) in 28 days, and length of hospitalization. The study protocol was registered on PROSPERO (registration No: CRD42022345533).

RESULTS

A total of eight RCTs (651 patients) were included. Nebulized heparin was associated with reduced ICU length of stay (six studies; mean difference [MD] -1.10, 95% confidence interval [CI] -1.87, -0.33, I2 = 76%), reduced duration of mechanical ventilation (two studies; MD -2.63, 95% CI -3.68, -1.58, I2 = 92%) and increased VFDs in 28 days (two studies; MD 4.22, 95% CI 1.10, 7.35, I2 = 18%), without increased incidence of adverse events, such as bleeding; but was not associated with a reduction in length of hospitalization (three studies; MD -1.00, 95% CI -2.90, -0.90, I2 = 0%) or in-hospital mortality (five studies; odds ratio 1.10, 95% CI 0.69, 1.77, I2 = 0%).

CONCLUSION

Nebulized heparin reduces ICU length of stay and duration of mechanical ventilation in mechanically ventilated patients, but has no effect on length of hospitalization or mortality.

Knockdown of TFPI-Anchored Endothelial Cells Exacerbates Lipopolysaccharide-Induced Acute Lung Injury Via NF-κB Signaling Pathway

As activation of the coagulation system is both a consequence and contributor to acute lung injury (ALI), pulmonary coagulopathy has become a potential target for therapeutic intervention in ALI patients. We investigated the effects and possible mechanisms of endothelial cell (EC)-anchored tissue factor pathway inhibitor (TFPI) on lipopolysaccharide (LPS)-induced ALI in mice. To assess the effect of EC-anchored TFPI deletion on ALI indices, TFPI knockout (cKO) mice were generated. Mice were instilled by direct intratracheal injection LPS for the preparation of an ALI model. Evans blue dye (EBD) was injected intravenously 2 h prior to animal sacrifice (48 h post-LPS). Lungs were fixed for histopathology and the prepared tissue was homogenized or used to extract bronchoalveolar lavage fluid (BALF) or detect EBD concentration. TFPI knockdown mice with ALI were compared to wild-type (WT) mice with ALI to assess the effect of TFPI on endothelial barrier function and inflammation. TFPI deletion markedly exacerbated LPS histopathological changes in lung, and the LPS changes in protein, EBD extravasation, proinflammatory cytokines TNF-α, IL-1β, and IL-6 in BALF in lung. The number and infiltration of white blood cells (WBCs) from BALF and lung tissue of TFPI cKO mice with LPS-challenged ALI was increased compared to WT mice with LPS-challenged ALI. We also found further increased toll-like receptor 4 and nuclear factor kappa-light-chain-enhancer of activated B cells activation and additional expression of vascular cell adhesion molecule 1 and reduction of angiotensin converting enzyme 2 expression in TFPI cKO+LPS mice compared with WT+LPS mice. Endothelial-specific TFPI deficiency promoted LPS-induced pulmonary inflammation and endothelial barrier permeability possibly via toll-like receptor 4-mediated nuclear factor kappa-light-chain-enhancer of activated B cells signaling pathway activation.

Nebulized heparin for patients under mechanical ventilation: an individual patient data meta-analysis

Pulmonary coagulopathy is a characteristic feature of lung injury including ventilator-induced lung injury. The aim of this individual patient data meta-analysis is to assess the effects of nebulized anticoagulants on outcome of ventilated intensive care unit (ICU) patients. A systematic search of PubMed (1966-2014), Scopus, EMBASE, and Web of Science was conducted to identify relevant publications. Studies evaluating nebulization of anticoagulants in ventilated patients were screened for inclusion, and corresponding authors of included studies were contacted to provide individual patient data. The primary endpoint was the number of ventilator-free days and alive at day 28. Secondary endpoints included hospital mortality, ICU- and hospital-free days at day 28, and lung injury scores at day seven. We constructed a propensity score-matched cohort for comparisons between patients treated with nebulized anticoagulants and controls. Data from five studies (one randomized controlled trial, one open label study, and three studies using historical controls) were included in the meta-analysis, compassing 286 patients. In all studies unfractionated heparin was used as anticoagulant. The number of ventilator-free days and alive at day 28 was higher in patients treated with nebulized heparin compared to patients in the control group (14 [IQR 0-23] vs. 6 [IQR 0-22]), though the difference did not reach statistical significance (P = 0.459). The number of ICU-free days and alive at day 28 was significantly higher, and the lung injury scores at day seven were significantly lower in patients treated with nebulized heparin. In the propensity score-matched analysis, there were no differences in any of the endpoints. This individual patient data meta-analysis provides no convincing evidence for benefit of heparin nebulization in intubated and ventilated ICU patients. The small patient numbers and methodological shortcomings of included studies underline the need for high-quality well-powered randomized controlled trials.

Nebulized anticoagulants for acute lung injury - a systematic review of preclinical and clinical investigations

Background

Data from interventional trials of systemic anticoagulation for sepsis inconsistently suggest beneficial effects in case of acute lung injury (ALI). Severe systemic bleeding due to anticoagulation may have offset the possible positive effects. Nebulization of anticoagulants may allow for improved local biological availability and as such may improve efficacy in the lungs and lower the risk of systemic bleeding complications.

Method

We performed a systematic review of preclinical studies and clinical trials investigating the efficacy and safety of nebulized anticoagulants in the setting of lung injury in animals and ALI in humans.

Results

The efficacy of nebulized activated protein C, antithrombin, heparin and danaparoid has been tested in diverse animal models of direct (for example, pneumonia-, intra-pulmonary lipopolysaccharide (LPS)-, and smoke inhalation-induced lung injury) and indirect lung injury (for example, intravenous LPS- and trauma-induced lung injury). Nebulized anticoagulants were found to have the potential to attenuate pulmonary coagulopathy and frequently also inflammation. Notably, nebulized danaparoid and heparin but not activated protein C and antithrombin, were found to have an effect on systemic coagulation. Clinical trials of nebulized anticoagulants are very limited. Nebulized heparin was found to improve survival of patients with smoke inhalation-induced ALI. In a trial of critically ill patients who needed mechanical ventilation for longer than two days, nebulized heparin was associated with a higher number of ventilator-free days. In line with results from preclinical studies, nebulization of heparin was found to have an effect on systemic coagulation, but without causing systemic bleedings.

Conclusion

Local anticoagulant therapy through nebulization of anticoagulants attenuates pulmonary coagulopathy and frequently also inflammation in preclinical studies of lung injury. Recent human trials suggest nebulized heparin for ALI to be beneficial and safe, but data are very limited.