Introduction
Trauma-related injuries are one of the most common reasons for emergency department (ED) admissions. In the United States, it was reported that 17% (22 million) of the annual 130 million ED admissions in all age groups and 48% of the patients under 30 were due to trauma. Reference Villaveces, Mutter, Owens and Barrett1 Trauma is the third leading cause of death following cancer and cardiovascular diseases in all age groups and is the most common cause of death under the age of 45. Reference Hardaway2 According to World Health Organization (WHO; Geneva, Switzerland) estimates, approximately five million people die from trauma-related injuries each year, and this number is expected to increase by 2020. Reference Mbanjumucyo, George and Kearney3
The shock caused by intravascular volume depletion is the most important cause of morbidity and mortality in multi-trauma patients. Reference Stewart, Myers and Dent4 Blood pressure, heart rate, urine output, and physical examination signs are the first steps, but they are unreliable parameters to determine the shock at an early stage. In some conditions, such as depressed level of consciousness, the diagnosis and treatment may be delayed, resulting in increased morbidity and mortality. Currently, base deficit (BD), lactate levels, the shock index (SI), perfusion index, Reference Ozakin, Yazlamaz, Kaya, Karakilic and Bilgin5 and caval index Reference de Valk, Olgers, Holman, Ismael, Ligtenberg and ter Maaten6 are generally recognized as new parameters of shock.
Different diagnostic methods have been elucidated to determine the intravascular volume depletion and hypovolemia in multi-trauma patients. These methods are pulse indicates continuous cardiac output, ultrasound to measure the degree of variation of the vena cava inferior, Reference Monge García, Gil Cano and Díaz Monrové7–Reference Yanagawa, Sakamoto and Okada9 global end-diastolic volume index, Reference Michard, Alaya, Zarka, Bahloul, Richard and Teboul10 and measuring the flatness index of the inferior vena cava (IVC). Jeffrey and Federle described the collapsed IVC on computed tomography (CT) images as strong evidence of hypovolemia of trauma patients; Reference Jeffrey and Federle11 Johnson, et al and Nguyen, et al showed that a flat IVC on initial abdominal CT scan has a significant correlation with other known markers of shock and is an independent predictor of mortality in severely injured trauma patients. Reference Johnson, Garwe and Albrecht12,Reference Nguyen, Plurad and Bricker13
The purpose of the study was to determine whether the flatness index of IVC could be used to predict the intravascular volume status in multi-trauma patients, and to establish its correlations between vital and shock parameters such as lactate and BDs, and the relationship between SI and Revised Trauma Score (RTS).
Materials and Methods
Selection of Patients
This prospective, cross-sectional study was conducted in the Adult ED of Eskisehir Osmangazi University (Eskisehir, Turkey) from December 1, 2017 through September 5, 2018. The required number from power calculation of volunteers was determined to be at least 324 to limit the error to five percent and obtain a confidence level of 95%. This study included adult multi-trauma patients (>18 years) who were admitted to the ED and underwent a thoracoabdominal CT. Exclusion criteria of the study were: pregnancy, death before CT scan, failure to obtain written consent, contrast allergy, intubation before CT scan, and patients with known medical histories such as right ventricular failure, right ventricular hypertension, tricuspid valve disease, pericardial pathologies, anticoagulant medication use, known bleeding disorder, and other trauma patients without tomography indication. Also, Class IV hemorrhages could not be included in the study because they were unstable for tomography and were directly transferred to the operating room.
Ethics Committee and Written Consent
The study was conducted in accordance with the amended Declaration of Helsinki and was approved by the Research Ethics and Review Board of the University Medical Centre (number: 34-29/06/2017). Written consent was obtained after the fact given that the thoracoabdominal CT was already indicated based on the mechanism of injury and/or physical examination findings, from the patients or their first-degree relatives, depending on their level of consciousness and cooperation.
Data Collection
The demographic features of the patients (age/gender), comorbidities, trauma mechanisms, vital signs, laboratory (hemoglobin, hematocrit, pH, lactate, and BD), and shock parameters such as SI, RTS, and class of hemorrhage obtained at the time of ED evaluation were recorded. The flatness index of IVC was calculated according to the literature and recorded. Non-probability technique was used in patient selection. Clinical outcomes included the need for hospital admission, the need for blood/fluid replacement, surgery and intubation, and in-hospital death within 24 hours. Multi-trauma patients were defined according to “The Definition of Polytrauma: The Need for International Consensus.”Reference Butcher and Balogh14
Shock Index (SI)
Shock index was calculated at the time of ED admission by dividing the heart rate per minute by the systolic blood pressure (SBP).Reference Allgöwer and Burri15
Revised Trauma Score (RTS)
The RTS was scored using coded values according to the literature and recorded (Table 1).Reference Manoochehry, Vafabin, Bitaraf and Amiri16,Reference Champion, Sacco, Copes, Gann, Gennarelli and Flanagan17
Table 1. Revised Trauma Score
Abbreviations: RTS, Revised Trauma Score; GCS, Glasgow Coma Scale; SBP, systolic blood pressure; RR, respiratory rate.
Estimated Class of Hemorrhage
The estimated class of hemorrhage was determined and recorded by the fourth-year emergency medicine resident according to the classification in Advanced Trauma Life Support (ATLS) 10th edition.
Imaging Procedure
After the clinical evaluation, the patient was taken to the radiology unit, which was 30 meters from the trauma resuscitation area. Radiographic contrast agent containing 90mL of iohexol was given intravenously, and thoracoabdominal CT imaging was performed via Siemens SOMATOM Perspective 128-slice CT scanner device (2015 model; Siemens Healthcare GmbH; Erlangen, Germany). Patients were told to hold their breath during the scanning procedure, without deep inspiration or expiration, according to the literature.Reference Jeffrey and Federle11 The scanning procedure lasted for about 23 seconds. Using this CT images, the outlet of the left renal vein from the left kidney was marked in the axial plane. Then, the point where the left renal vein flows into IVC was detected. The IVC transverse and anteroposterior diameters were measured as 5mm (one section) above this point in the axial plane by a radiology physician in accordance with similar studies.Reference Barber, Touska and Negus18,Reference Li, Zhang, Wang and Zhang19 The transverse diameter and the anteroposterior diameter (Figure 1) of the IVC were measured just above the renal veins. Then, the flatness index of IVC was calculated by dividing IVC transverse diameter by IVC anteroposterior diameter and recorded. In different studies, IVC flatness index was measured from different areas. This point was selected since traces of the left renal vein disappeared in this section and there was no other large vascular structure draining into the IVC above this point. “FLAT” IVC was defined as diameter less than 2cm and “FAT” IVC when the vein was equal or larger than 2cm.
Figure 1. Method Used for Measuring the Flatness Index of IVC.
Abbreviations: AP, Anteroposterior; T, Transvers; IVC, inferior vena cava.
Statistical Analysis
IBM SPSS Statistics for Windows, Version 20.0 (IBM Corp; Armonk, New York USA) was used for all statistical analyses. The patients’ demographic features were presented through descriptive statistical information such as number, percentage, and standard deviation (SD). Shapiro-Wilk test was used to show the normal distribution of the flatness index of IVC. The Mann-Whitney U and Kruskal-Wallis tests were used to determine the factors associated with the flatness index of IVC. The Spearman Correlation Analysis was used for comparing the continuous data with each other.
Results
There were 66,987 patients over the age of 18 admitted to the adult ED during the study period. Of these patients, 14,865 were assessed as trauma and 1,224 were assessed as multi-trauma patients. Three hundred sixty-five of these multi-trauma patients were indicated for a thoracoabdominal CT. Thirty-eight patients were excluded from the study for the reasons mentioned in Figure 2.
Figure 2. Flow-Chart of the Patients.
Abbreviations: ER, emergency room; CT, computerized tomography.
A total of 327 patients were included in the study. Of all the patients, 229 (70.0%) were male and the mean age was 40.90 (SD = 17.93; median: 37; min:1 - max: 95). Of the trauma mechanisms, 299 (91.4%) were blunt and 28 (8.6%) were penetrating. Motor vehicle accidents, falling from a height, and motorcycle accidents were the most common trauma mechanisms, respectively.
The mean value of the flatness index of IVC of the patients was 2.09cm (CI 95%, 1.97-2.22) and the median value was 1.75cm [IQR 25-75: 1.50-2.21], as shown in Table 2 (IVC transverse diameter average as 3.0cm [SD = 4.8]; range: 1.57-4.67cm and anteroposterior diameter average as 1.67cm [SD = 0.57]; range: 0.33-3.30cm).
Table 2. Mean and Median Values of the Flatness Index of IVC in the Study Group
Abbreviations: CI, confidence interval; IQR, interquartile range; IVC, inferior vena cava.
As shown in Table 3, there were no significant relations between the flatness index of IVC and gender (P = .134) and trauma mechanisms (P = .701). However, the flatness index of IVC was found to be related with the vital parameters obtained during the ED evaluation. The flatness index of IVC was significantly higher in patients with SBP ≤90mmHg (P = .015), diastolic blood pressure (DBP) ≤60mmHg (P = .019), heart rate >100 beats/min (P = .049), and/or SpO2 ≤94% (P <.001).
Table 3. Relationship Between the Flatness Index of IVC Values with Gender, Trauma Mechanisms, and Vital Parameters
Note: Mann Whitney U test was used for P values.
Abbreviations: IVC, inferior vena cava; SBP, systolic blood pressure; DBP, diastolic blood pressure; HR, heart rate.
When comparing the flatness index of IVC with the laboratory parameters, the flatness index of IVC was found to be significantly higher in patients with lactate ≥2mmol/l (P = .043). However, the flatness index of IVC was not significantly related to hemoglobin, hematocrit, and BD values. According to the ATLS classification of hemorrhage table, 11 patients (3.4%) were in Class III hemorrhage, and the flatness index of IVC was significantly higher (P = .003) in these patients when compared to the patients in Class I and Class II hemorrhage (Table 4). The SI was analyzed and categorized into two groups as ≥0.9 and as <0.9. In 65 (19.9%) patients, SI was ≥0.9 and the flatness index of IVC was significantly higher (P = .026) in this group than in the group of patients with SI <0.9 (Table 4).
Table 4. Relationship Between the Flatness Index of IVC with the Laboratory Parameters and Shock Index
Abbreviation: IVC, inferior vena cava.
a Mann Whitney U test was used.
b Kruskal Wallis test was used.
A weak positive correlation was determined between lactate level with the flatness index of IVC; a weak negative correlation was found between Glasgow Coma Scale (GCS) and RTS with the flatness index of IVC (for each of them, P <.05; Table 5).
Table 5. Correlations Between the Flatness Index of IVC with Age and Laboratory Parameters
Abbreviation: IVC, inferior vena cava.
Discussion
Despite considerable advances in the medical and technological fields, trauma still remains a significant public health problem. Trauma is very common in the youth and productive individuals, which negatively impacts the society causing both labor and financial loss. According to these data, approximately one-half of the patients were under the age of 40 and 70% of them were male. Studies show that the average age of individuals undergoing trauma is continuously increasing. However, existing data prove that trauma is still more common in the younger population, particularly in men.Reference Aldrian, Koenig, Weninger, Vécsei and Nau20–Reference Jm22 Exposure of younger males to trauma can be explained by the fact that they spend more time in traffic, get more involved in business and industrialization fields, and engage in adventure and risk-related activities. In this study, the majority of trauma mechanisms were blunt traumas. Among them, traffic accidents and falling from a height were the most common reasons. Similar to this study, other studies have also reported these two incidents as the primary causes of trauma, both in Turkey and world-wide.Reference Abbasi, Mousavi, Taheri Akerdi, Niakan, Bolandparvaz and Paydar23 In addition to the technological, demographic, and developmental levels of the societies studied, the reasons such as the geographical location of the hospitals and the differences in their work areas may have led to changes in the ranking of trauma mechanisms. Irrespective of the reported rankings, traffic accidents are one of the most important causes of trauma and remain a global public health problem.
All shock types may be seen in multi-trauma patients, but the most common type is hemorrhagic shock. Particularly, early-stage shock may be seen in 16%-70% of hemodynamically stable conditions at their first admissions to the ED and is a condition associated with poor prognosis and high mortality in the event of delayed or missed diagnosis.Reference Blow, Magliore, Claridge, Butler and Young24,Reference Claridge, Crabtree, Pelletier, Butler, Sawyer and Young25 The most effective way to decrease mortality in the presence of shock in patients undergoing trauma is to recognize the shock at an early stage.Reference Hardaway2 Early, effective treatment and appropriate fluid management are essential to increase survival in these patients. Reference Stewart, Myers and Dent4 Although physical examination, vital signs and laboratory parameters, and response to the initial treatment may detect the presence of shock, it is not always possible. Furthermore, a single vital or laboratory parameter is not often sufficient to indicate shock.
The preferred imaging modality is CT in patients with trauma, Reference Yanagawa, Sakamoto and Okada9 according to trauma guidelines in hemodynamically stable patients. In addition to the recognition of solid organ damage, it has been found that the flatness index of IVC measurement can be used as a method to determine the intravascular volume status. Reference Johnson, Garwe and Albrecht12,Reference Nguyen, Plurad and Bricker13,Reference Citilcioglu, Sebe and Oguzhan Ay26 In trauma studies, the flatness index of IVC measurement via CT was found to be a useful method for determining the severity of the injury, recognizing the presence of an early-stage hypovolemic shock, and the need for aggressive resuscitation. It has been reported that the flattened IVC may be a sign of significant blood loss, and hemodynamic monitorization should be performed more carefully in these patients. Reference Jeffrey and Federle11,Reference Nguyen, Plurad and Bricker13 Studies also reported that the presence of flattened IVC is an independent predictor of mortality associated with other known shock parameters in trauma patients and may be used as a hypovolemic shock indicator. Reference Johnson, Garwe and Albrecht12,Reference Li, Zhang, Wang and Zhang19 In this study, there was no significant relationship between the flatness index of IVC and the demographical characteristics of the patients and the trauma mechanisms. Similar to this study, other studies have shown that there is no significant relationship between the flatness index of IVC and the demographic characteristics such as gender, age, and trauma types. Reference Johnson, Garwe and Albrecht12,Reference Nguyen, Plurad and Bricker13,Reference Li, Zhang, Wang and Zhang19 Hypovolemic shock can be seen in all trauma patients, regardless of gender or trauma mechanism. The flatness index of IVC shall also increase in case of intravascular volume depletion independent of gender or trauma mechanism. Therefore, the flatness index of IVC can be regarded as a parameter which is independent of gender or trauma mechanism.
On comparing the vital signs with the flatness index of IVC, the flatness index of IVC was higher in patients with SBP ≤90mmHg, DBP ≤60mmHg, heart rate >100 beats/min, and SpO2 ≤94%. Similar to these findings, SBP was found to be significantly lower in patients with increased flatness index of IVC. Reference Nguyen, Plurad and Bricker13 Contrary to these results, a study indicated that there was no relationship between the flatness index of IVC and SBP and heart rate. Reference Johnson, Garwe and Albrecht12 However, in both studies, mechanically ventilated patients were included. Recent studies have shown that, in mechanically ventilated patients, IVC diameter does not show atrial pressure accurately. Reference Citilcioglu, Sebe and Oguzhan Ay26,Reference Lorsomradee, Lorsomradee, Cromheecke, ten Broecke and De Hert27 Therefore, the performed measurements may not indicate the actual flatness index of IVC, as incorrect measurement of IVC diameter might be obtained due to the increased intrathoracic pressure in these patients. Although publications show that the blood parameters (such as hemoglobin, hematocrit, pH, BD, and lactate) correlate with the flatness index of IVC, in this study, the flatness index of IVC was only related with the blood lactate levels. Reference Nguyen, Plurad and Bricker13,Reference Liao, Lin, Lu, Foo, Guo and Chen28 However, this relationship couldn’t be corroborated by hemoglobin or hematocrit values. This may be due to the fact that the clinically stable patients were selected for CT imaging and only the blood parameters, obtained at the time of ED admission, were compared with the flatness index of IVC.
In this study, the flatness index of IVC was higher in patients with Class III hemorrhagic shock compared to the patients in Class I or Class II hemorrhagic shock. As the class of hemorrhagic shock increases, the morbidity and mortality rates increase. Since the flatness index of IVC shows a linear correlation with the class of hemorrhagic shock, this value can be used as a parameter to detect shock. There is no study in the literature reporting the relationship between the class of hemorrhagic shock and the flatness index of IVC, warranting further research. Class IV hemorrhage was not included in this study, because there was no included patient in this stage. This situation can be explained by the early arrival to the scene and appropriate treatment of the patients by Emergency Medical Services, the rapid delivery of the patients to the center without any deterioration of the clinical status, and the rapid transfer of unstable patients directly to the operating room or intensive care unit without CT scanning.
In this study, the flatness index of IVC correlated with GCS and RTS, but not with SI. When SI is categorized as ≥0.9 and <0.9, the flatness index of IVC was significantly higher in patients with SI ≥0.9. Studies reported that the flatness index of IVC was directly proportional to SI, inversely proportional to RTS, and did not correlate with GCS. Reference Johnson, Garwe and Albrecht12,Reference Nguyen, Plurad and Bricker13,Reference Li, Zhang, Wang and Zhang19 Both GCS and RTS are reliable scoring systems that predict the morbidity and mortality in trauma patients. It is also known that SI reflects the presence of shock better than heart rate or blood pressure alone. The correlation of the flatness index of IVC with these scoring systems suggests that this value can be used as a new indicator of mortality and morbidity in trauma patients.
There is no widely accepted cut-off value for the flatness index of IVC. One study reported that the cut-off value was ≥1.9 with the highest sensitivity and specificity (sensitivity = 52%; specificity = 88%), discharging rates were lower, mortality rates were higher, and mortality occurred in the early period with high flatness index; this study also reported that the mortality rates were eight-times greater in these patients, even after adjustment for other confounding factors. Reference Johnson, Garwe and Albrecht12 The presence of hypovolemic shock received as a reference, and the optimal diagnostic cut-off value for the flatness index of IVC with the highest sensitivity and specificity (sensitivity = 3.5%; specificity = 86.2%) was 3.02. Reference Li, Zhang, Wang and Zhang19 Variation in these cut-off values may be due to the fact that measurements were made through different sections and in different numbers, and also due to assuming different clinical features as reference in the studies.
Limitations
There are several limitations in this study. The research had a small sample size that only reflected a local region. There was an inability to perform serial IVC flattening index measurements in terms of response to fluid therapy. All the measurements were made by an emergency radiology specialist, but these measurements were not correlated by emergency physicians. Prospective research studies with a larger number of patients are needed to verify the practical value of this method. Patients with CT indication and undergoing imaging were included in the study. The effect of IVC flatness index on mortality could not be determined due to insufficient number of patients with Stage 4 shock and exitus.
Conclusion
Various CT findings were defined to determine the hypovolemic shock in patients with multi-trauma. However, the majority of these findings have not been widely accepted. Measurement of the flatness index of IVC by CT is an easily understood, measured, and practical method. It may be used as a helpful method to determine the intravascular volume status in multi-trauma patients. It may also be used as a new vital parameter in these patients. Further research in this field is required to ascertain these findings.
Author Contributions
Nazlı O. Yazlamaz: Article writer and data collection; Engin Ozakın: Article supervision, statistical analysis correction; Betul T. Bastug: Radiological imaging and evaluation; Evvah Karakilic: Review of the literature; Nurdan Acar: Review of the literature; Filiz Baloglu Kaya: Data collection; and Rusengul Koruk: Data collection.
Conflicts of interest
none
