Therapeutic anticoagulation using heparin in early phase severe coronavirus disease 2019: A retrospective study

a b s t r a c t

Background: Although several reports recommend the use of systemic anticoagulation therapy in patients with severe coronavirus disease 2019 (COVID-19) pneumonia, appropriate target population and timing of adminis- tration are unknown. We assessed association between therapeutic anticoagulation administration with unfrac- tionated heparin and outcomes in patients with severe COVID-19 pneumonia, assuming that anticoagulant administration effects are influenced by therapy timing.

Methods: This retrospective observational study included severe COVID-19 patients requiring mechanical venti-

lation in a tertiary emergency critical care hospital intensive care unit (ICU) in Japan from May 1, 2020 to Septem- ber 30, 2021. All included patients were divided into early and late-phase administration groups based on therapeutic anticoagulant administration timing (<=5 and >5 days, respectively, after commencing oxygen ther- apy). Primary outcomes (in-hospital mortality and adverse events related to anticoagulation therapy) and sec- ondary outcomes [veno-venous extracorporeal membrane oxygenation , ventilator-free days (VFD), and ICU-free days] were compared between groups using univariate and multivariate models.

Results: Of 198 included patients 104 (52.5%) and 94 (47.5%) were in early-phase and late-phase administration groups, respectively. Although background characteristics were similar between the groups, the early-phase ad- ministration group had a significantly lower in-hospital mortality rate (3.8% vs. 27.7%; p < 0.001), lower Adverse event rates (1.9% vs. 12.8%; p < 0.001), significantly longer VFD and ICU-free days, and lower ECMO rates, than the late-phase administration group, in the multivariate model.

Conclusions: Late administration of therapeutic-dose anticoagulation in patients with severe COVID-19 pneumo- nia was significantly associated with worse outcomes than early administration.

(C) 2022 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY license (http://


List of abbreviations

1. Introduction

APACHE II Acute Physiology and Chronic Health Evaluation

COVID-19 coronavirus disease 2019

CRP C-reactive protein

ECMO extracorporeal membrane oxygenation

FDP fibrin-fibrinogen degradation product

ICU intensive care unit

PaO2/FiO2 arterial oxygen partial pressure to fractional inspired oxygen RCT randomized control trial

SARS-CoV-2 severe acute respiratory syndrome coronavirus disease 2 SOFA Sequential Organ Failure Assessment

UFH unfractionated heparin

VFD ventilator-free days

* Corresponding author at: Tokyo Medical and Dental University, 1-5-45, Yushima, Bunkyo-ku, Tokyo 113-0034, Japan.

E-mail address: [email protected] (W. Takayama).

The coronavirus disease 2019 (COVID-19) pandemic, an ongoing Public health problem, has caused the death of more than 4.8 million people worldwide, as of the end of September 2021 [1]. COVID-19 in- duces a cytokine storm that activates a coagulation cascade, resulting in coagulopathy and thrombotic phenomena, which leads to Multiple organ dysfunction and high mortality [2]. The inflammation and throm- bosis associated with endothelial dysfunction and hypercoagulability lead to an increased risk of micro (or macro) vascular thrombosis [3,4]. Thus, guidelines from several medical organizations recommend the use of anticoagulation therapy in patients with COVID-19 [5].

A large cohort study [6,7] reported that the use of anticoagulation at Therapeutic doses may be associated with a reduced risk of mortality among hospitalized patients with COVID-19. Although a recent ran- domized control trial (RCT) has reported that therapeutic-dose


0735-6757/(C) 2022 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

anticoagulation did not decrease the mortality rate and the number of organ support free days, the severity of included patients was relatively low, and the date of onset of symptoms was not considered [8]. Mean- while, another recent RCT demonstrated a clear benefit of therapeutic dose anticoagulation for non-critically ill patients with COVID-19 [9]. Therefore, the appropriate target population and timing of the adminis- tration of therapeutic anticoagulants are still under debate.

Based on this background, in the present study, we assessed the as- sociation between the administration of therapeutic-dose anticoagulant therapy and the outcomes in patients with severe COVID-19 pneumo- nia, assuming that the effects of therapeutic anticoagulant administra- tion are affected by the timing of the therapy.

  1. Methods
    1. Study design and setting

This was a single-center retrospective observational study con- ducted at the intensive care unit (ICU) of a tertiary emergency critical care hospital in Tokyo. The medical records of patients with COVID-19 with severe pneumonia who were admitted between May 1, 2020, and September 30, 2021, were reviewed. All patients with COVID-19 who underwent mechanical ventilation at our hospital received thera- peutic doses of heparin during the study period. Clinical outcomes were compared between patients who received therapeutic doses of heparin in the early and late phases of COVID-19 treatment. The study was approved by the institutional review board of our hospital (ap- proval number: M2020-130). The board waived the need for written in- formed consent given the retrospective nature of the study.

    1. Patient population

Consecutive patients with severe COVID-19 requiring mechanical ventilation who were admitted to ICU of Tokyo Medical and Dental Uni- versity Hospital in Japan were included. A diagnosis of COVID-19 diag- nosis was made based on the findings of a nasopharyngeal swab test for severe acute respiratory syndrome coronavirus disease 2 (SARS- CoV-2) using real-time reverse transcriptase-polymerase chain reaction in all patients. We excluded patients with ‘do not attempt resuscitation’ orders [including veno-venous Extracorporeal membrane oxygenation and Renal replacement therapy ], those who had received systemic anticoagulant therapy at intubation time, and patients with missing or insufficient data regarding the study variables.

    1. Patient management

Patients with COVID-19 were transferred to the ICU and underwent mechanical ventilation if they could not maintain an arterial oxygen partial pressure to fractional inspired oxygen (PaO2/FiO2) ratio of less than 200 after oxygen therapy in our hospital. All included patients received unfractionated heparin within the first 6 h after ICU ad- mission, and their activated partial thromboplastin time was monitored and maintained at 1.5 to 2.5 times that of the control. During the study period, when anticoagulation therapy-related adverse events occurred, or the patients were discharged from the ICU, these therapies were dis- continued immediately.

    1. Data collection

Data were collected by trained medical doctors, and a standard ab- straction form was used to ensure uniform data handling. Collected data were monitored, and suspected outliers were confirmed or corrected by other chart abstractors. The following information was ret- rospectively collected from the patients’ medical records: age, sex, body mass index, date of disease onset, date of oxygen therapy, history of an- ticoagulant and/or Antiplatelet therapy, smoking history, Charlson

Comorbidity Index score [10], administration of ECMO, drug treatment for COVID-19, and status on hospital discharge (i.e., dead or alive). The clinical course, length of ventilation, and ICU stay for each patient were also recorded. Furthermore, we collected laboratory results such as D-dimer, fibrin-fibrinogen degradation products (FDP), white blood cell count, and C-reactive protein levels. All blood samples evalu- ated in this study were obtained after the institution of mechanical ven- tilation and before administering anticoagulation therapy. For all included patients, the worst Sequential Organ Failure Assessment and Acute physiology and chronic health evaluation II scores within the first 24 h of mechanical ventilation were assessed.

    1. Definitions and outcome measures

In this study, severe COVID-19 pneumonia was defined as an acute need for invasive mechanical ventilation. The “early-phase administra- tion group” was defined as patients who received therapeutic anticoag- ulation within 5 days after the commencement of oxygen therapy, while the “late-phase administration group” was defined as those who received it 6 days or after, based on the fact that almost all patients who need oxygen therapy require hospitalization. A cut-off value of “5 days” was determined as the median number of days from oxygen ther- apy administration to therapeutic anticoagulation administration. The date of disease onset was defined as the day that the symptoms were ob- served. COVID-19-related sepsis was defined as life-threatening organ dysfunction caused by a dysregulated host response to infection, accord- ing to the 2016 Third International Consensus Definition [11]. Secondary infection was diagnosed when patients showed clinical symptoms or signs of pneumonia, urinary tract infection, or central line-associated bloodstream infection; or when patients had a positive culture of a new pathogen from blood, lower respiratory tract (qualified sputum or endotracheal aspirate), or urine specimens after ICU admission [12].

We defined the primary efficacy outcome as in-hospital mortality. The primary Safety outcomes included anticoagulation therapy-related adverse events, defined as any of the following events: (1) hemoglobin level < 7 g/dL and any red blood cell transfusion, (2) at least two units of red blood cell transfusion within 48 h, or (3) clinical diagnosis of major bleeding (defined as symptomatic intracranial hemorrhage or hemor- rhage requiring surgical or radiological intervention). Secondary out- comes were defined as the administration of ECMO, ventilator-free days (VFD) 28 days after admission, and ICU-free days within the first 28 days after admission.

    1. Statistical analysis

In the univariate analysis, continuous variables were compared using Student’s t-test or the Mann-Whitney U test. Categorical variables were compared using the ?2 test or Fisher’s exact test, as appropriate. First, using a multivariable logistic regression model, we evaluated the interaction between therapeutic-dose anticoagulant therapy and the days from commencement of oxygen therapy to the anticoagulant ther- apy for the primary outcome, to determine whether the timing of ther- apeutic anticoagulation influenced the outcomes. We incorporated age and SOFA score, which are known a priori to be associated with out- comes in patients with severe COVID-19 pneumonia [13-15], and se- lected variables based on clinical plausibility and the number of outcomes (10 events per variable rule) as covariates in the multivariate model. Second, we divided the enrolled patients into two groups: the early-phase administration group (<=5 days after the commencement of oxygen therapy) and the late-phase administration group (>5 days after the commencement of oxygen therapy) based on the median number of days from oxygen therapy administration to therapeutic an- ticoagulation administration. We then compared the characteristics, se- verity, and outcomes of both groups. Furthermore, we divided the enrolled patients into two groups based on the another cut-off value (7 days) and performed a sensitivity analysis of the primary and

Image of Fig. 1

Fig. 1. Patient flow diagram.

COVID-19, coronavirus disease 2019; ICU, intensive care unit; DNR, do not attempt resuscitation.

secondary outcomes. All statistical analyses were conducted using R software (version 4.1.1; R Foundation for Statistical Computing, Vienna, Austria). Statistical significance was set at p < 0.05.

  1. Results

The patient Selection process is shown in Fig. 1. Among 606 poten- tially eligible patients with COVID-19, 198 (32.7%) patients with severe pneumonia underwent mechanical ventilation during the study period. Of these, 104 (52.5%) patients were treated with therapeutic anticoagu- lation in the early phase. Table 1 shows the main clinical characteristics, laboratory data at the initiation of mechanical ventilation, the worst Clinical scores during the first 24 h after intubation, and the adminis- tered drugs during the ICU stay. The patients’ laboratory data and sever- ity scores were similar between the two groups. However, D-dimer and CRP levels, FDP, and severity scores tended to be higher in the late- phase administration group. Although the patients in both groups re- ceived similar treatments, the frequency of clinical complications was significantly higher in the late-phase administration group than in the early phase administration group. Table 2 provides the univariate anal- ysis results for the outcomes between the early- and late-phase admin- istration groups. Compared with the late-phase administration group, the early phase administration group had a significantly lower in- hospital mortality rate [4 (3.8%) vs. 26 (27.7%) patients; p < 0.001] and a lower rate of anticoagulation therapy-related adverse events [2 (1.9%) vs. 12 (12.8%) patients; p < 0.001]. Furthermore, compared to the late-phase administration group, the early phase administration group had significantly longer VFD and ICU-free days and lower rates of ECMO therapy.

The p-value for the interaction between therapeutic-dose anticoagu-

lant therapy and the days from the commencement of oxygen therapy to the anticoagulant therapy for in-hospital mortality was 0.004, indi- cating that the effect of therapeutic-dose anticoagulation was signifi- cantly affected by the duration from oxygen therapy to the commencement of therapeutic-dose anticoagulation therapy. Table 3 presents the multivariate logistic regression analysis results adjusted for age and SOFA score. The late-phase administration of therapeutic- dose anticoagulants, compared to early phase administration, was sig- nificantly associated with higher in-hospital mortality, rates of adverse events, rates of ECMO administration, and shorter VFD and ICU-free days. Supplementary Tables 1, 2 and 3 show the result of the sensitivity analysis wherein the patients were grouped according to different criteria. The results were similar to the main findings.

  1. Discussion

In this retrospective observational study, we found that the timing of therapeutic anticoagulation therapy significantly influenced the out- comes in 198 patients with COVID-19 pneumonia requiring mechanical ventilation. Furthermore, our findings indicated that late administration compared to early administration of therapeutic-dose anticoagulation was significantly associated with higher in-hospital mortality, adverse events, and ECMO administration, as well as shorter VFD and ICU-free days. To the best of our knowledge, this is the first study to report the association between the timing of therapeutic dose anticoagulation and outcomes in patients with severe COVID-19 pneumonia.

In COVID-19 pneumonia, despite anticoagulant prophylaxis or ther- apy, several studies have reported life-threatening arterial or venous thrombosis, including frequent severe Pulmonary embolisms [16,17]. Such disease characteristics have led to the Empirical treatment of pa- tients with severe COVID-19 with heparin at therapeutic doses than at the usual thromboprophylaxis doses [18]. In addition to its known anti- coagulant properties, heparin has been reported to have potential ther- apeutic effects in severe lung inflammation, impaired pulmonary Gas exchange, and high viral load [19-21]. Because SARS-CoV-2 infection causes an excessive inflammatory response that may lead to coagula- tion hyperactivity, anticoagulation therapy using heparin is expected to have positive effects on the outcomes based on potential antiviral mechanisms [21] in addition to anticoagulative effects. However, the optimal anticoagulant regimen remains unknown. A recent RCT did not support the hypothesis that routine therapeutic dose anticoagula- tion benefits patients with severe COVID-19 pneumonia [8], possibly because the net effect of anticoagulation on clinical outcomes may de- pend on the timing of initiation in relation to disease course or severity. Further RCTs considering the timing of commencement are warranted to assess the effects of therapeutic anticoagulation.

In severe COVID-19 pneumonia cases, dramatic changes in the coag- ulation/fibrinolytic status on illness days 7-10 have been reported, where the status is changed from a hypofibrinolytic state to a hyper- fibrinolytic state [22,23]. In this respect, late administration of therapeutic-dose anticoagulation in patients with severe COVID-19 could influence the fibrinolytic state, increasing bleeding risk. However, since the underlying mechanisms of the late-phase administration of therapeutic anticoagulation could not be elucidated by our clinical data, further research is warranted to reveal the differences in the effect between the early and late phases in patients with severe COVID-19.

Lymphopenia has been reported in most patients with severe COVID-19 pneumonia [24], and immunosuppression is more obvious in severe cases than in mild cases [25]. In severe cases, immunosuppres- sion has been reported to develop after more than 7 days of illness onset [26]. In this study, we found that the prevalence of secondary infection in the late-phase administration group was higher than that in the early-phase administration group (22.3% vs. 3.8%). Previous studies re- ported high mortality in patients with COVID-19 with secondary infec- tions [27,28], and the higher incidence of secondary infection observed in the late-phase administration group might have affected the out- comes in this study. Although details regarding the immune effect of heparin and the immune status of the patients could not be assessed in the present study, the immune effect, in addition to the anticoagulative effect, might have influenced the worse outcomes in the late-phase administration group.

The present study had several limitations. First, this was a retrospec- tive observational study conducted at a single hospital with a limited sample size. Accordingly, the number of variables used in the multivar- iate analysis had to be limited, and there is a risk of residual confounding and type II error. Additional research is necessary to provide more defin- itive data, including large-scale studies adjusted for covariates. Second, we did not consider the coronavirus variant type or the days from dis- ease onset to therapeutic anticoagulation administration, which could influence the outcomes and coagulation state. Third, patients who had

Table 1

Comparison of characteristics and laboratory data at ICU admission between the early-phase and the late-phase administration groups.

All patients

Early-phase administration

Late-phase administration

p value

(n = 198)

group (n = 104)

group (n = 94)


Age (y), median [IQR]

62 [52-75]

59 [50-73]

66 [55-77]


Male, n (%)

167 (84.3)

87 (83.7)

80 (85.1)


Body mass index (kg/m2), median [IQR]

26.3 [24.2-27.9]

26.8 [24.9-28.4]

25.5 [23.9-28.1]


History of smoking, n (%)

93 (47.0)

50 (48.7)

44 (46.8)


History of anticoagulant and/or antiplatelet therapy, n (%)

35 (17.7)

19 (18.3)

16 (17.0)


Days from the oxygen therapy to the administration of mechanical ventilation, median [IQR]

5 [4-6]

5 [3-5]

7 [5-11]


8 [7-10]

6 [5-7]

10 [8-13]


Days from illness onset to the administration of mechanical ventilation, median [IQR]

Laboratory data

D-dimer level, median [IQR]

3.5 [2.2-6.1]

2.4 [1.5-5.8]

4.3 [2.4-6.8]


Fibrin-fibrinogen degradation products, median [IQR]

7.1 [5.8-9.6]

5.8 [4.3-7.3]

8.2 [6.6-10.8]


White blood cell count (/ul), median [IQR]

9200 [7400-10,800]

10,500 [8100-11,800]

7400 [6400-8600]


C-reactive protein (mg/dl) level, median [IQR]

5.6 [3.4-7.8]

4.0 [3.1-7.2]

7.4 [3.9-9.8]


Clinical scores

SOFA score, median [IQR]

4 [3-5]

4 [3-5]

5 [3-5]


APACHE II score, median [IQR]

15 [11-16]

12 [11-15]

16 [11-17]


Treatment drugs Favipiravir, n (%)

82 (41.4)

42 (40.4)

40 (42.6)


Tocilizumab, n (%)

85 (42.3)

48 (46.2)

37 (39.4)


Remdesivir, n (%)

75 (37.9)

38 (36.5)

37 (39.4)


Baricitinib, n (%)

41 (20.7)

23 (22.1)

18 (19.1)


Nafamostat mesylate, n (%)

24 (12.1)

13 (12.5)

11 (11.7)


Corticosteroid, n (%)

196 (99.0)

103 (99.0)

93 (98.9)


Clinical complications

Severe sepsis, n (%)

96 (48.5)

31 (29.8)

65 (69.1)


Secondary infection, n (%)

25 (12.6)

4 (3.8)

21 (22.3)


ICU, intensive care unit; IQR, interquartile range; SOFA, Sequential Organ Failure Assessment; APACHE II, Acute Physiology and Chronic Health Evaluation.

Table 2

Treatment outcomes of both groups.

All patients

Early-phase administration

Late-phase administration

p value

(n = 198)

group (n = 104)

group (n = 94)

Primary outcomes

In-hospital mortality, n (%)

30 (15.2)

4 (3.8)

26 (27.7)


Anticoagulation therapy-related adverse events, n (%)

14 (7.1)

2 (1.9)

12 (12.8)


Secondary outcomes ECMO, n (%)

20 (10.1)

3 (2.9)

17 (18.9)


VFD, median days [IQR]

15 [8-19]

17 [12-21]

11 [6-18]


ICU-free days, median days [IQR]

13 [3-17]

15 [10-18]

8 [4-15]


ECMO, extracorporeal membrane oxygenation; VFD, ventilator-free days; ICU, intensive care unit; IQR, interquartile range;

Table 3

Multivariate analysis of the impact of the late-phase therapeutic anticoagulation.

already received anticoagulants and/or Antiplatelet agents were ex- cluded from this study. The proportions were similar between the two

Primary outcome

Adjusted odds

ratio [95% CI]

Adjusted difference [95% CI]

p value

groups in our study (early-phase administration group, 18.3% vs. late- phase administration group, 17.0%), although these agents could influ- ence the coagulable state and anticoagulation sensitivity.

Despite these limitations, we showed a novel and significant associa-

In-hospital mortality 8.86 [5.45-11.3] – <0.001

tion between the timing of therapeutic anticoagulation therapy and the

Anticoagulation therapy-related adverse events

Secondary outcomes

6.34 [3.35-8.13] – <0.001

outcomes in patients with severe COVID-19 pneumonia. Further large- scale research is necessary to confirm the results of the present study.

ECMO 7.82 [4.15-9.92] – <0.001

VFD -4.7 [-6.9-1.6] <0.001

ICU-free days – -4.1 [-7.0-2.1] <0.001

CI, confidence interval; ECMO, extracorporeal membrane oxygenation; VFD, ventilator- free days; ICU, intensive care unit.

  1. Conclusion

The results of this study suggest that late administration of therapeutic-dose anticoagulation in patients with COVID-19 pneumonia

requiring mechanical ventilation was significantly associated with worse outcomes compared to early administration. Further studies are necessary to validate our results.

Ethics approval and consent to participate

The study was approved by the institutional review board of our hospital (approval number: M2020-130). The board waived the need for written informed consent because the study was retrospective.

Consent for publication

This study was approved by the institutional review board, and writ- ten informed consent was waived because of the retrospective design.

Availability of data and materials

The datasets analyzed in this study are not publicly available due to privacy issues, but are available from the corresponding author upon reasonable request.

Funding sources

Not applicable.


This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Authors’ contributions

WT, AE, and YO participated in the study conception and design, data collection, and drafting of the manuscript. All authors read and approved the final manuscript.

Credit authorship contribution statement

Wataru Takayama: Writing – review & editing, Writing – original draft, Validation, Supervision, Resources, Project administration, Meth- odology, Investigation, Data curation, Conceptualization. Akira Endo: Data curation, Investigation, Validation, Writing – review & editing. Yasuhiro Otomo: Writing – review & editing, Validation, Supervision.

Declaration of Competing Interest

The authors declare that they have no competing interests.


The authors thank all patients and their families, physicians, nurses, and staff.

Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi. org/10.1016/j.ajem.2022.05.031.


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