Plasma Transfusion in Major Vascular Surgery: a Danish Nationwide Registry Study
Conditions: Aortic Aneurysm, Abdominal, Arterial Occlusive Diseases
Sponsor: Naestved Hospital

Plasma to red blood cell transfusion ratios in open abdominal aortic 
surgery: detailed statistical analysis plan 
 
Document version date: 2020-10-09 
ClinicalTrials.gov identifier: NCT04514575. 
 
 
Authors: 
Anders Møller1, Nikolaj Eldrup2, Jørn Wetterslev3, Henrik Hjalgrim4, Klaus Rostgaard4, Dorthe 
Hellemann1, Henning Bay5, and Ole Birger Pedersen6. 
 
Affiliations: 
1Department of Anesthesia and Intensive care Næstved-Slagelse, Slagelse Hospital, Denmark; 
2Department of Vascular Surgery, Rigshospitalet, Copenhagen, Denmark; 3Copenhagen Trial Unit, 
Center for Clinical Intervention Research, Rigshospitalet, Copenhagen, Denmark; 4Department of 
Epidemiology, Statens Seruminstitut, Copenhagen, Denmark; 5Department of Anesthesia, Zealand 
University Hospital Roskilde, Denmark; 6Department of Clinical Immunology, Næstved Hospital, 
Denmark. 
 
Corresponding author 
Anders Møller, Department of Anesthesia and Intensive Care, Slagelse Hospital, Fælledvej 11, DK-
4200 Slagelse, Denmark. E-mail: dr.andersm@gmail.com. Phone +45 51 22 81 21. 
 
 
 

Background 
• Major blood loss is frequent in open repair of ruptured and intact abdominal aortic aneurysm 
(AAA) as well as in aorto-bifurcated prosthesis insertion due to aortoiliac occlusive disease. 
• Major blood loss is associated with death, post-operative complications and coagulopathy.  
• Data from randomized trials in trauma patients indicate that a high plasma to red blood cell 
(RBC) transfusion ratio reduces 30-day mortality(1, 2) (Holcomb 2015, Sperry 2018).  
• No randomized trial data are available for the AAA population(3) (Desborough 2015). 
• Observational data demonstrate, that a high plasma:RBC transfusion ratio associates to a 
lower 30 day mortality. However, the reports are based on small cohorts of 78-165 patients(4-
7) (Mesar 2017, Montan 2016, Mell 2010, Johansson 2007), short term outcomes and lack 
information on major adverse events such as cardiac and respiratory. 
• The Danish Vascular Registry (DVR), covering 1996-2018, contains data on approx. 4,400 
ruptured and 8,200 intact (elective/symptomatic) AAA repairs, and 5,400 open aortoiliac 
repairs due to occlusive disease. Expected count 1997-2018: 17,000. 
• The Danish Transfusion Database (DTDB), covering 1997-2018, contains information on units 
of RBCs, plasma and platelets transfused. A unique patient identification number (CPR) allows 
merging of all data set. 
Objective 
To identify whether resuscitation with a high plasma to RBC ratio associates to improves survival 
in open abdominal aortic surgery as compared to a low plasma to RBC-ratio. 
 
Material and method 
• Population:  
Open abdominal aortic surgery 
• Intervention: 
“High FFP”: FFP to RBC unit ratio of 2:3 to 3:3 (0.7 - 1.0) 
• Comparison: 
“Low FFP”:  FFP to RBC unit ratio of 0:3 to 1:3 (0.0 - 0.3) 
• Outcome:  
All-cause mortality 90 days following surgery 
 
Inclusion criteria: 
1. Open abdominal aortic repair of either 
o intact (elective or symptomatic) AAA 

o ruptured AAA 
o aorto-iliac occlusive disease with the insertion of aorto-bifurcated prosthesis 
2. Requiring massive transfusion defined as 
o > 10 units of any blood product1 transfused on the same date (DTDB) 
 
1 = Allogeneic packed RBCs, FFP, cryoprecipitate, or platelets. 
Cryoprecipitate will account for 4 units of FFP in the FFP:RBC ratio. 
Data sources are noted in parenthesis. 
Exclusion criteria: 
- 
Surgery time limited to < 50 minutes (DVR) 
- 
No prosthesis inserted (DVR) AND 
  
operation date (DVR) equal to the death date (CPR) 
 
Excluding patients with surgery time less than 50 minutes or cases where no prosthesis has been 
inserted is expected to minimize survival bias from patients exsanguinating in the operation 
theater before blood products can be delivered. Intentionally, it may also exclude patients where 
surgery was considered futile and halted. 
 
Protocol amendment 2020-10-09:  
In the original protocol version, patients receiving 6 > RBC units during surgery, or > 15 units 
within two calendar days, would also fulfill the second inclusion criteria. We have removed these 
two criteria and confined the definition of massive transfusion (i.e., the second inclusion criteria) 
to 10 blood products or more transfused on the day of surgery. The old criteria would otherwise 
introduce bias. First, patients receiving > 6 RBC transfusions during surgery, but less than 10 units 
total on the same day, could only be included in the low FFP group because the maximal ratio 
would be 6 RBC : 3 FFP (ratio of 0.5). Two, including patients who received > 15 units within two 
calendar days, would introduce immortal time bias. These patients would be immortal by 
definition on the day of surgery, or they would not receive blood products on the 1st postoperative 
day. 
 

Data sources 
CPR, Danish Civil Registration System. 
DNPR, Danish National Patient registry. 
DVR, Danish Vascular registry. 
DPDB, The Danish national Prescription DataBase. 
 
Statistical analysis 
Our primary analysis will be a stratified cox regression model. 
Stratification 
• type of surgery/condition (ruptured AAA vs intact AAA vs aorto-iliac occlusive disease, source: 
DVR) 
• sex (CPR) 
• surgical center (Rigshospitalet vs. Gentofte vs. Slagelse vs. Odense vs. Kolding vs. Aarhus vs. 
Viborg vs. Aalborg, source: DVR) 
Covariate adjustment 
• calendar time (DVR) 
• age (CPR) 
• Carlson comorbidity index score (DNPR) 
• Priority (Acute vs. Sub-acute vs. Elective, source: DVR) 
• Use of anti-thrombotic drugs (DPDB). A covariate of 4 levels: 
The ATC code is noted in parenthesis. 
1) None vs.  
2) Anti-platelet therapy 
- 
acetylsalicylic acid (B01AC06) or  
- 
dipyridamole (B01AC07, eg. persantin or asasantin) 
3) Anti-platelet therapy “thienopyridines-like drugs” 
- 
clopidogrel (B01AC04) or  
- 
ticagrelor (B01AC24, eg. Brilique) or  
- 
prasugrel (B01AC22, eg. Efient) 
Comment: patients prescribed thienopyridines in combination with aspirin 
will be included in this “thienopyridine anti-platelet group 3” 
4) Anti-coagulant therapy 
- 
Vitamin K antagonists (B01AA, eg. warfarin or phenprocoumon (B01AA04) 

- 
Low-molecular weight heparine (B01AB01-10) 
- 
Direct thrombin inhibitors (B01AE, eg. Pradaxa/Dabigatran) 
- 
Direct factor Xa inhibitors (B01AF, eg. Rivaroxaban/Xarelto) 
Comment: patients prescribed both anticoagulant- and antiplatelet therapy 
and will be included in this “Anti-coagulant group 4” 
 
 
Additional analyses 
1. Stratify the population into 4 groups according to the total transfusion requirement 
a. patients receiving <10 units of any blood product < 24 hrs or 11-15 units < 48 hrs. vs.  
b. patients receiving 11-15 units of any blood product < 24 hrs. or 16-20 units < 48 hrs. vs.  
c. patients receiving 16-20 units of any blood product < 24 hrs. or 21-25 units < 48 hrs. vs. 
d. patients receiving more than 20 units of any blood product < 24 hrs. or more than 25 
units < 48 hrs. 
2. Outcome predicted by a joint function (general interaction) of total plasma transfusion and 
total blood cell transfusion will be assessed in an exploratory way by inspection and by 
agnostic modelling in the mold of Multivariate Adaptive Regression Splines (MARS) and 
recursive partitioning, i.e. Classification And Regression Trees (CART).  
3. Redefine intervention and control group as 4th and 1st quartile of FFP:RBC ratio. Initially, we 
will divide the population into 4 groups according to quartiles and compared the population 
below 1st quartile with the population above the 4th quartile, which will define the low vs. the 
high FFP group, resp. However, to allow for stratification for operation type (ruptured AAA vs. 
intact AAA vs. occlusive disease) it may be necessary to adjust the percentile cut to retain 
power in the analyses. For instance, the population may be cut according to tertiles, or, if 
there is sufficient data, cut by quintiles (5 groups) or deciles (10 groups). 
4. Confine the population to patient with blood loss above 50 % of total blood volume (calculated 
by Naddler’s equation accounting for sex, weight and height). If height and weight are not 
available, the registered blood loss must exceed 2 L in females and 2.5 L in males. 
5. Adjusting exclusively for calendar year, sex, age, Charlson’s comorbidity index score, and 
center (ie, excluding priority and antithrombotic therapy). 
 

Missing data 
We won’t have missing data on total units of blood products transfused as this is an inclusion 
criterion. All remaining covariates are discrete, and we will include missing data as a separate 
parameter (factor level). 
 
Statistical significance level 
We will apply Bonferroni adjustment of the significance level to control for multiple testing. 
With one primary and four secondary outcomes, only a P value below 0.01 (0.05/5) will be 
considered statistically significant. A P value between 0.01 and 0.05 will be considered borderline 
significant.  
 
Outcomes 
Primary outcome 
1. 90-day all-cause mortality 
Secondary outcomes 
2. 30-day all-cause mortality 
3. 1-year all-cause mortality 
4. Death or any major adverse event at 90-days (DNPR): 
A. Major adverse cardiovascular events “MACE” [ICD10-codes] 
§ acute myocardial infarction [DI21.0-23.9, DT817Y2] 
§ stroke [DI60-64.9, DT817Y1] (and DVR) 
§ non-fatal cardiac arrest [DI460] 
B. Major adverse respiratory events 
§ Adult respiratory distress syndrome [DJ80] 
§ pulmonary edema [DJ81]  
§ pulmonary embolism [DI26, DT817D] 
C. Major adverse vascular event  
§ bowel ischemia [DK550C-H] (and DVR) 
§ vascular reoperation for deep rebleeding or thrombus or embolus [KPWE, 
KPWG], lower-limb fasciotomy [KNGM09, KNHM09, KNFM09] or explorative 
laparotomy [KJAH00] (and DVR) 

§ major lower limb amputation [KNE-HQ] (and DVR) 
§ acute limb ischemia requiring intervention (DVR) 
D. Other 
§ renal replacement therapy [BJFD, DZ992] (and DVR) 
§ AB0-incompatibility reaction [DT803] 
§ Rhesus-incompatibility reaction [DT804] 
§ Hemorrhage and hematoma complicating a procedure, not elsewhere classified 
[T810, DT810G, DT810E] 
5. Days alive outside hospital within 90 days (DNPR and CPR). 
 
 

Figure 1. Time overlap of registries 
 
*Not all centers go back to 1997. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Danish National Patient Registry (DNPR)
1977-2018
-All somatic hospital 
admissions since 1977
-All hospital outpatient 
and emergency visits 
since 1995, including 
dates of admission and 
discharge, and 
discharge diagnoses
Danish Vascular Registry (DVR)
1996-2018
-Descriptive patient 
data (ig., age, sex, 
height, and weight and 
comorbidity)
-Surgery specifics (ig., 
surgical center, type of 
operation)
-Outcome variables for 
inhospital 
complications
Danish Transfusion 
Database (DTDB)
1997(2005)*-2018
-Units of allogenic 
blood transfusions
-operations/treatment,
-hemoglobin level and 
coagulation factor level.
1st registry 
study 
(descriptive) 
 
           2nd registry     
           study 
        (FFP transfusion) 

Figure 2. Grouping the study population. 
 
 
1. 
Holcomb JB, Tilley BC, Baraniuk S, Fox EE, Wade CE, Podbielski JM, et al. Transfusion 
of plasma, platelets, and red blood cells in a 1:1:1 vs a 1:1:2 ratio and mortality in patients with 
severe trauma: the PROPPR randomized clinical trial. Jama. 2015;313(5):471-82. 
2. 
Sperry JL, Guyette FX, Adams PW. Prehospital Plasma during Air Medical Transport in 
Trauma Patients. The New England journal of medicine. 2018;379(18):1783. 
3. 
Desborough M, Sandu R, Brunskill SJ, Doree C, Trivella M, Montedori A, et al. Fresh 
frozen plasma for cardiovascular surgery. The Cochrane database of systematic reviews. 
2015(7):CD007614. 
4. 
Johansson PI, Stensballe J, Rosenberg I, Hilslov TL, Jorgensen L, Secher NH. Proactive 
administration of platelets and plasma for patients with a ruptured abdominal aortic aneurysm: 
evaluating a change in transfusion practice. Transfusion. 2007;47(4):593-8. 
5. 
Mell MW, O'Neil AS, Callcut RA, Acher CW, Hoch JR, Tefera G, et al. Effect of early 
plasma transfusion on mortality in patients with ruptured abdominal aortic aneurysm. Surgery. 
2010;148(5):955-62. 
6. 
Mesar T, Larentzakis A, Dzik W, Chang Y, Velmahos G, Yeh DD. Association Between 
Ratio of Fresh Frozen Plasma to Red Blood Cells During Massive Transfusion and Survival Among 
Patients Without Traumatic Injury. JAMA Surg. 2017;152(6):574-80. 
7. 
Montan C, Hammar U, Wikman A, Berlin E, Malmstedt J, Holst J, et al. Massive Blood 
Transfusion in Patients with Ruptured Abdominal Aortic Aneurysm. European journal of vascular 
and endovascular surgery : the official journal of the European Society for Vascular Surgery. 2016.