Determining the accuracy of Base deficit in diagnosis of intra-Abdominal injury in patients with blunt

abdominal trauma^?

Mani Mofidi MD?, Abbas Hasani MD, Nahid Kianmehr MD

Department of Emergency Medicine, Hazrat Rasool-e-Akram Hospital, Iran University of Medical Sciences and Health Services, Tehran, Iran

Received 14 March 2009; revised 24 June 2009; accepted 25 June 2009

Abstract

Background: blunt abdominal trauma is a leading cause of morbidity and mortality among all age groups. A multiplicity of diagnostic modalities exists to evaluate the abdomen. We sought to assess the diagnostic performance of base deficit (BD) in identifying intra-abdominal injury in patients with blunt abdominal trauma.

Methods: A prospective, nonrandomized series of patients with blunt abdominal trauma admitted into the 2 emergency departments was investigated from September 2007 to September 2008. Arterial blood samples were analyzed. According to BD, the patients were divided into 2 groups: group 1 who had a BD of -6 or lower and group 2 who had a BD more than -6. Ultrasonography, computed tomographic scan, or laparotomy was performed to find intra-abdominal injury. Follow-up at 7 days by telephone interview was obtained on patients who were discharged.

Results: A total of 400 patients were enrolled, with a mean (SD) age of 34.8 +- 17.1 years. Two hundred sixty-eight (67%) of them were male. Seventy-six (19%) of patients had a BD of -6 or lower. Sixty- eight (17%) of them showed to have intra-abdominal injury with a BD of approximately -8.7 +- 3.2, compared with patients without intra-abdominal injury, -0.4 +- 0.1. Patients with a BD of -6 or lower achieved more laparotomy and blood transfusion compared with patients with a BD more than -6. On receiver operating characteristic curve analysis, the cutoff point of -6 was obtained with sensitivity and specificity of 88.2% and 95.2% and with positive and negative predictive values of 79% and 97.5%, respectively. None of outpatients had abdominal problem in telephone follow-up.

Conclusions: These data show that the BD is an early available important indicator to identify intra- abdominal injury in patients with blunt abdominal trauma, as well as a high transfusion requirement.

(C) 2010

^? The authors are indebted to the Iran University of Medical Sciences and Health Services for financial support.

* Corresponding author. Tel.: +98 2166518098; fax: +98 66525327.

E-mail address: [email protected] (M. Mofidi).

Introduction

Blunt abdominal trauma is a leading cause of morbidity and mortality among all age groups [1]. The most common causes of blunt abdominal trauma are from motor vehicle accidents and automobile-pedestrian accidents [2].

0735-6757/$ - see front matter (C) 2010 doi:10.1016/j.ajem.2009.06.002

Table 1 advantages and disadvantages of Diagnostic strategies
Modality	Advantages	Disadvantages
Lab Studies	Repeatable	Low sensitivity
		Low specificity
		Time consuming
Phx	Repeatable	Low accuracy in head injury, alcohol and drug intoxication
DPL	Good in unstable patients	Complications
	Sensitive to bowel perforations	False-positive results
Sonography	Accurate	Low accuracy in overweight people
	Portable	Unable to show retroperitoneal space
	Poses no radiation or contrast hazard
CT scan	Accurate	Costly
	Show retroperitoneal space	Needs patient stability
		side effects of dye
		Modest sensitivity in pancreas and small bowel injuries
DPL indicates Diagnostic peritoneal lavage; Phx, physical examination.

Identification of serious intra-Abdominal pathology is a supreme challenge to the emergency specialist’s clinical acumen. Many injuries may not manifest during the initial assessment and treatment period. Mechanisms of injury often result in other Associated injuries that may divert the physician’s attention from potentially life-threatening intra- abdominal pathology [3].

Traditional vital signs, although specific, are not highly sensitive for hemorrhage detection [4]. Routine evaluating tools such as Lab Studies [5,6], physical examination [7-9], diagnostic peritoneal lavage [10,11], ultrasonography [12], and computed tomographic (CT) scan [13-15] have some advantages and disadvantages for abdominal evaluation, which are shown in Table 1.

Inadequate tissue perfusion causes metabolic acidosis due to anaerobic metabolism. Base deficit (BD) as a metabolic parameter is a highly sensitive indicator of blood loss by measuring tissue perfusion. An increased BD can be an early harbinger of hemorrhagic shock. Some studies showed that a BD of -6 or lower is strongly associated with the need for early transfusion and shock-related complications [16].

In a prospective series of acutely injured patients, BD was predictive of survival for the past 24 hours [17,18]. Previous studies have shown that BD is a good indicator of mortality even in a context of normalized vital signs [19], which can predict life-threatening injury in trauma patients [20]. Low BD should alert the clinician to the presence of potentially lethal injuries or uncompensated shock [21].

The purpose of this study was to evaluate the diagnostic performance of BD in identifying intra-abdominal injury in patients with blunt abdominal trauma.

Methods

We conducted a prospective; nonrandomized study of trauma patients to evaluate the accuracy of BD in diagnosis of intra-abdominal injury in blunt abdominal trauma patients. Inclusion criteria are shown in Table 2.

Four hundred eligible trauma patients were enrolled during the study period of September 2007 to September 2008 from 2 emergency departments (EDs) of urban, university-affiliated hospitals with emergency medicine residency program.

All patients had initial vital signs measured. One milliliter of arterial blood was obtained from enrolled patients. The following data were extracted from the medical record: age, sex, vital signs, the results of arterial blood gas (pH, HcO2, Po₂, PcO2, and BD), findings in Abdominal ultrasonography, CT scan or laparotomy (presence of free fluid), and need for blood transfusion. All of the patients received abdominal ultrasonography and CT scan, except unstable patients who were transferred to operating room because of having free fluid on sonography. According to BD, the patients were divided into 2 groups: group 1 who had BD less than or equal to -6 and group 2 who had a BD more than -6.

Finally, outpatients who were discharged after a few hours had a telephone call with their permissions from ED after a week and were asked about any abdominal problems thereafter.

A statistical analysis was performed by means of the Fisher exact and ?2 tests, with a P value less than .05 considered as significant. The model of logistic regression was performed for variables predicting the probability of

Table 2 Inclusion and exclusion criteria Inclusion

Any patients with blunt abdominal trauma

Exclusion

External bleeding Hemothorax

Elapsing 4 h after trauma and incidental ABG alcohol consumption

ABG indicates arterial blood gas.

Variables	Pediatrics (n = 12)	Pregnant women (n = 3)
BD <=-6	2	1
Intra-abdominal injury	2	1
Laparotomy	1	1
Blood transfusion	2	1

being free fluid. Analysis was done using SPSS 15 for windows (SPSS, Chicago, Ill). Informed consent was obtained from the patients who were included in this study. Five subjects did not sign the consent form and were excluded from the study.

Table 3 Measured variables of patients

Variables Result

Age (y), mean +- SD 34.8 +- 17.1 Sex (male) 268 (67) Unconscious 62 (15) Head trauma 102 (25) Intoxicated (opium) 20 (5) Time of measuring blood gas (min), 81 +- 44 mean +- SD SBP (mm Hg), mean +- SD 118 +- 24 DBP (mm Hg), mean +- SD 68 +- 14 Pulse rate, mean +- SD 91.5 +- 14.4/min PcO2 (mm Hg), mean +- SD 37.8 +- 7.0 Po2 (mm Hg), mean +- SD 94.8 +- 8.7 BD <=-6 76 (18) Abdominal injury 68 (17) Retroperitoneal bleeding 12 (3) Blood transfusion 56 (14) Laparotomy 48 (12)

Values are in n (%), unless otherwise indicated. Unconscious: Glasgow Coma Scale b9. DBP indicates diastolic blood pressure; SBP, systolic blood pressure.

Results

The study included 400 patients presented, with a mean (SD) age of 34.8 (17.1) years (range, 8-80 years), of whom 268 (67%) were male. Data were extracted from the medical records (Table 3). It was found that increasing pulse rate and decreasing BD predicted the probability of positive free fluid well (Table 4). Sixty-eight (17%) of patients had free fluid on ultrasonography, CT scan, or laparotomy. These patients showed a BD of approximately -8.73 +- 3.25 compared with cases without free fluid, -0.41 +- 0.17; P = .0001. Forty-eight cases achieved laparotomy, of whom 44 (91%) were in group 1; P = .0001. Nearly 56 (14%) of patients undergone blood transfusion as needed (52 cases in group 1 vs 4 cases in group

Table 4 The model of logistic regression for variables predicting the probability of being free fluid

Variables	B	P	Odds ratio
Pco2	-.029	.788	0.971
BD	-.809	.008	0.445
Pulse rate	.100	.032	1.106
Systolic pressure	-.015	.613	0.985
Constant	-12.075	.102	0.000
R2 = 0.488.

2; P = .0001) Twelve patients had retroperitoneal bleeding, of whom all showed BD equal or less than -6.

The outcomes of pediatrics and pregnant women are shown in Table 5. There were 3 cases in these groups with a BD of -6 or lower. All of them had Intra-abdominal injuries and undergone blood transfusion.

Table 5 Special groups

On receiver operating characteristic curve analysis, the cutoff point of -6 was obtained with sensitivity, specificity, positive predictive value, and negative predictive value of 88.2%, 95.2%, 79%, and 97.5%, respectively. The area under the curve was 0.039 (95% confidence interval, -0.024 to 0.102) and P = .0001. No one of the patients who were discharged home within 6 hours of observation had abdominal complaint on the seventh day of follow-up.

Discussion

Corresponding to our findings, a BD more than -6 provides a probability of more than 95% for the absence of intra-abdominal bleeding. Conversely, BD of -6 or lower and increased pulse rate indicate that there is a markedly enhanced risk for intra-abdominal bleeding. Hence, decreased BD and/or increased pulse rate was highly sensitive for detecting patients with internal bleeding, which is congruent with other studies [22,23], although both of these research focused on BD and one of them [22] chose a BD of -4 or lower. There are some relationships that have been previously established between injury severity and BD. Base deficit has been found to be associated with patient mortality, hypotension, and need for resuscitation [24].

Davis et al [25] studied 200 trauma patients and demonstrated that BD is a useful guide for volume resuscitation in them. They found that an increase of the BD despite fluid resuscitation was an important clue for ongoing hemorrhage.

Randolph et al [26] have shown that 37% of trauma patients with an admission BD of -5 or lower died. Of the 13 patients who died, 8 cases never cleared their BD.

In this study, a BD of -6 or lower had sensitivity of approximately 88.2% compared with ultrasonography, 76.5%. The latter is due to the fact that ultrasonography is not likely to detect most retroperitoneal or pelvic injuries [27]. However, ultrasonography has a positive predictive value of approximately 100% and nearly equal negative predictive value with BD for detecting free fluid [28].

Finally, BD correlates well with blood transfusion and laparotomy requirements (68.4% of patients with BD <=-6 indicated for blood transfusion compared with only 1.2% of patients with BD N-6, and 57.9% of patients with BD <=-6 indicated for laparotomy compared with only 1.2% of patients with BD N-6). Therefore, this study confirms that patients with blunt abdominal trauma whose BD is equal or less than -6 are more prone to laparotomy and blood transfusion, which is congruent with the survey findings of Davis et al [16]. Ultrasonography and diagnostic peritoneal lavage cannot identify occult injuries such as retroperitoneal bleeding. In our study, 12 cases had retroperitoneal bleeding, and 100% of them showed a BD of -6 or lower. This finding is very important, but relying on it needs more research with more cases.

Another interesting finding was about pediatrics and pregnant women who we often do not want to expose to radiation. All of these patients whose BDs were equal or less than -6 had intra-abdominal bleeding and undergone blood transfusion. This fact shows the importance of BD in these groups.

Advanced Trauma Life Support has many protocols for managing trauma patients, but its discussion about BD (in diagnose and treatment of hemorrhagic shock) is very short and incomplete. It is seems that our findings and other researches can complete this part.

A normal BD does not exclude intra-abdominal injury in blunt trauma patients, but the presence of a BD equal or less than -6 should be considered a strong indication for abdominal evaluation. The results of our study demonstrated that a BD of - or lower 6 has high sensitivity and specificity for detecting free intra-peritoneal fluid in patients with blunt abdominal trauma, as well as a high transfusion requirement and laparotomy in these patients.

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