Article, Cardiology

When to activate a multidisciplinary team for an acute abdominal aortic aneurysm?

a b s t r a c t

Background: It is often difficult to determine when a multidisciplinary aneurysm team should be summoned based on the (often limited) pre-hospital information provided Method: We performed a retrospective cohort study of patients brought to our hospital between January 1st 2013 and October 1st 2014 by the emergency medical services (EMS) with a clinical suspicion of an acute AAA. Within this group we compared patients with a documented acute AAA and without an acute AAA in order to identify patient characteristics that could be used for the development of evidence based activation criteria for multidis- ciplinary acute aneurysm teams.

Results: Of the 63 patients presented by the EMS with a clinical suspicion of an acute AAA, 16 had an acute AAA. The optimal age cut-off value to discriminate patients with- from patients without an acute AAA was 70 years, whereas the optimal cut-off systolic blood pressure was 137 mmHg. “Age N 70” (LR+ 2.6 [1.8-3.8], “SBP b 137mm Hg” (LR+ 2.6 [1.5-4.9], the “presence of diaphoresis ” (LR+ 2.5 [1.7-3.8] and a “prior history of AAA” (LR+ 2.9 [1.5-5.7] were independent predictors of the presence of an acute AAA. The presence of any of these factors increased the pre-test probability of an acute AAA to N 50%.

Conclusion: Pre-hospital information regarding the patient’s age, history (known AAA), blood pressure and gen- eral appearance (presence of diaphoresis) can be useful when EMS services announce the arrival of a patient with suspected acute AAA in order to improve appropriate triage and minimize time to definitive care.

(C) 2016

Introduction

Abdominal aortic aneurysms (AAA) are relatively common, affecting between 2 and 8% of males over the age of 60. [1] Most AAA’s expand gradually without symptoms. However, with expansion of the aneurys- mal sac, the aneurysm can compress lumbar and aortic nerves causing lower back- abdominal or Scrotal pain. These symptomatic aneurysms (sAAA) have a high risk of rupture. Despite advances in treatment over the past years with the introduction of endovascular aneurism re- pair (EVAR), the mortality of a ruptured AAA (rAAA) remains 80-90%.

? Source of support/funding: None.

* Corresponding author at: Department of Emergency Medicine, Medical Centre Leeu- warden, Henry Dunantweg 2, 8934 AD Leeuwarden, the Netherlands. Tel.: +31 582866666.

E-mail addresses: [email protected] (M. Maltha), [email protected] (A. Visser), [email protected] (T. Sandjer), [email protected] (A.K. Jahrome),

[email protected] (T.W.F. Vink), [email protected], [email protected] (E. ter Avest).

Approximately 30% of all patients with a rAAA die before reaching hos- pital and 40% of the patients who reach the hospital die without under- going surgery. [2] A recently published Norwegian study of Reite et al. reported a lower mortality (68%), which might reflect advancements in treatment options that have become available over the last couple of years. [3] Previous studies have demonstrated that a longer time from symptom onset to definitive treatment is associated with a higher mortality of rAAA. [4,5]. Therefore, it is of utmost importance to recog- nize acute Abdominal aneurysms (either sAAA of rAAA) timely, in order to be able to transport patients to appropriate hospitals where all resources for definitive treatment are available [6,7,8]. Ideally, in these hospitals a multidisciplinary acute aneurysm team is timely in- formed and present in the ED when the patient is presented, in order to expedite both the diagnostic process and the shared decision- making concerning the various treatment options.

The activation of such a Multidisciplinary team (consisting of an

emergency physician, vascular surgeon, anesthetist and an interven- tional radiologist) is part of most dedicated aneurysm Care pathways. However, it is often difficult to determine when such a team should be summoned based on the (often limited) pre-hospital information

http://dx.doi.org/10.1016/j.ajem.2016.05.006

0735-6757/(C) 2016

provided. Diagnosing acute AAA can be challenging with physical examination alone, since signs and symptoms are often not specific.

[9] The guidelines of the vascular society of the UK suggest that a

rAAA should be considered in patients over the age of 50 with abdomi- nal/back pain and hypotension, and in patients with a known AAA with symptoms of either Abdominal or back pain or hypotension/ collapse. [10] However, the classic triad of a palpable mass, hypotension and abdominal and/or back pain is present in only 25-50% of the sub- jects [11], and patients may have completely normal vital signs as a con- sequence of retroperitoneal containment of hematoma. Therefore acute AAA is often misdiagnosed [12], resulting in either unnecessary activa- tion (overtriage) or too late activation (undertriage) of the multidisci- plinary team.

This study aims to identify patient characteristics for patients with symptomatic or Ruptured aortic aneurysms that could be used to reduce time to definitive care and improve appropriate triage to centres with appropriate capabilities based on pre-hospital information provided by the EMS.

Methods

Study design and subjects

We performed a retrospective cohort study of all patients brought to our hospital between January 1st 2013 and October 1st 2014 by the emergency medical services (EMS) with a clinical suspicion of an acute AAA.

Hospital and EMS services

Our study was undertaken in the Medical Center Leeuwarden, a large teaching hospital with 25.000 ED visits yearly, staffed by emergen- cy physicians and residents. The medical Center Leeuwarden is a region- al center for vascular surgery with 7 vascular surgeons and 3 interventional radiologists on call 24/7. Treatment capabilities include TEVAR, FEVAR and EVAR. Around 80 acute and elective AAA’s are treat- ed on a yearly basis, either by Endovascular aneurysm repair or by sur- gical repair. Patients were brought to the ED by two independent EMS services. In the Netherlands there are 25 regional ambulance services, appointed by the ministry of health to be responsible for EMS care in that particular region. Medical command of the ambulance services is done by a dedicated EMS doctor. In line with governmental policy, am- bulances in our region are able to present within 15 minutes after an emergency call is made. All ambulances are staffed with a driver and a highly skilled ambulance nurse. Nurses have completed the full training required to be registered as a nurse in the Netherlands, with additional training and certification in anesthesia, intensive care, cardiac care, or emergency medicine, after which they have an additional year of ambu- lance training before they qualify as a registered ambulance nurse. EMS nurses are capable and authorized to administer iv medication (except vasopressor perfusors) and to perform endotracheal intubation when needed. They were not trained to use bedside ultrasonography. Both ambulance services work with an electronic patient chart named EDAZ wherein the Ambulance nurses note the patients’ history, findings on physical examinations, and any given treatments. In their charts they have to indicate specifically if they suspect a patient of an acute AAA (yes/no). This was already part of the chart before we initiated this study. Whether or nor the nurse indicates if he/she has a suspicion on acute AAA is based on their clinical gestalt and not forced by any pre- defined patient characteristics or Vital parameters.

Data acquisition

Pre-hospital data were collected using the electronic charts of the ambulance service. Based on recommendations of the European society of vascular surgery [13] we choose to abstract the following variables

from the pre-hospital electronic patient files: Age, first recorded pre- hospital blood pressure, AVPU score, oxygen saturation, pain (NRS) score, and pulse frequency, presence of a palpable abdominal Pulsatile mass, duration of pain (acute or chronic), onset of pain (acute or slowly progressive), presence of Limb ischemia, presence of diaphoresis, pres- ence of syncope, prior history of (untreated) AAA and the presence of any known Cardiovascular risk factors: history of vascular disease (pe- ripheral, coronary, or cerebral), hypertension, smoking, diabetes and dyslipidemia. Final diagnosis was determined using the hospital elec- tronic patient records, using both Radiology reports and operation re- ports. All data were retrieved by two investigators (MM and AV) according to the recommendations of Gilbert et al. [14].

Outcome measures

Primary outcome was defined as the diagnostic accuracy of various pre-hospital patient characteristics to predict a correct pre- hospital diagnosis of acute AAA (either symptomatic- or ruptured). Symptomatic AAA was defined as the presence of an AAA (diameter N 3 cm) determined with CT-angiography with abdominal/back/flank pain or limb ischemia that could be attributed to the aneurysm. Rup- tured AAA was defined as tearing of the wall of an abdominal aneurysm (diameter N 3cm) with extravasation of blood outside the adventitial layer of the vessel. Final diagnosis was determined either by CT- angiography or peri-operative.

Ethics

As our study only involved retrospective evaluation of routinely re- corded patient data, this type of study was determined to be exempt re- search by the ethical review board of our institution.

Statistical analysis

Data are represented as mean (95% CI) unless stated otherwise. Missing data are reported in the results section according to the STROBE guideline [15]. Comparisons between patients with- and with- out acute AAA were done using Student’s t-test, Mann-Whitney U-test or Fisher’s exact test as appropriate. Univariate correlation analysis using point biserial Correlation coefficients (continuous and categorical data) and phi coefficients (dichotomous data) was carried out to evalu- ate the Prognostic ability of various variables to discriminate between subjects with- and without acute AAA. A multivariate logistic regression analysis with backward selection procedures was carried out to investi- gate which variables with an r N 0.2 contributed independently to the prediction of the presence of an acute AAA. To avoid problems with (multi) co-linearity, systolic blood pressure (SBP) was chosen over dia- stolic blood pressure (DBP) as representative of the pertinent parameter (blood pressure) entering the multivariate model. optimal cut-off values to discriminate between subjects with- and without an acute AAA were determined for the continuous variables age and SBP under the condition of equal “cost” of misclassification of cases and non- cases. Likelihood ratio’s, sensitivities and specificities were calculated for the optimal cut off values, and probabilities of the presence of an acute AAA for these cut-off points were determined using logistic re- gression analysis. A p-value b 0.05 was considered statistically signifi- cant. All statistical analysis were done with SPSS 23.0 for Apple statistical package (SPSS Inc, Chicago, Illinois, USA) and Vasarstats sta- tistical software (Vassar college, Poughkeepsie, New York, USA).

Results

Study population

During the study period a total of 14.684 patients were transported to our hospital by the EMS services. Of the 63 patients presented by

the EMS services with a presumed acute AAA, 2 had a symptomatic AAA and 14 had a ruptured AAA. In the remaining 47 patients, no AAA was present. Most prevalent Alternative diagnoses in the group of patients without acute AAA were aortic dissection (n= 5) and constipation (n= 5). Table 1 shows the characteristics of patients presumed to have an acute AAA by EMS personnel.

Patients who turned out to have an acute AAA after evaluation in the hospital were older than patients who did not have an acute AAA (78 [74-82] vs. 67 [63.-70] years, p b 0.001). Furthermore, they had a lower average pre-hospital SBP (104 [85-123] vs. 151 [141- 161] mmHg, p b 0.001), were more often profound diaphoretic (87.5 vs. 36.2%, pb 0.001), and had more often an untreated AAA in their his- tory (62.5 vs. 21.3%, p =0.004). Although there was a trend towards a higher incidence of syncope and lower oxygen saturation levels in pa- tients with an acute AAA compared to patients without an acute AAA, statistical significance was not reached for these parameters. Limb is- chemia wasn’t noticed in any of the patients. The presence of a pulsatile Abdominal mass was presumed to be present in 2 patients with- and 2 patients without an acute AAA.

Patient characteristics associated with an acute AAA

Univariate correlation analysis revealed that “age”, “SBP”, “DBP”, “oxygen saturation”, “presence of diaphoresis” and a “prior history of AAA” were all significantly correlated to a correct pre-hospital diagnosis of the presence of an acute AAA with an r N 0.2. When a multivariate model was constructed, “age”, “SBP”, “presence of diaphoresis ” and a “prior history of AAA” remained independent predictors of the presence of an acute AAA, with a total adjusted R [2] of 0.50 ( Table 2).

The optimal SBP cut-off to discriminate patients with- and without an acute AAA was determined to be 137 mmHg, whereas the optimal age-cut-off was 70 years. Positive- and negative likelihood ratio’s, sensi- tivities and specificities for these optimal cut off values as well as for the presence of “diaphoresis” and “prior history of AAA” are given in Table 3.

Probabilities of acute AAA

Probabilities of the presence of an acute AAA were calculated for all (optimal cut off values of) variables that were independently predictive

Table 2

Multivariate model of patient characteristics predicting a correct pre-hospital diagnosis of an acute AAA.

Variable

r

Std. ?

p

Adjusted R2?

DBP

-0.36

NA

NA

NA

Oxygen saturation

0.23

NA

NA

NA

SBP

-0.51

-0.27

0.016

0.25

Age

0.46

0.29

0.007

0.12

Diaphoresis present

0.49

0.34

0.002

0.08

History of AAA

0.39

0.25

0.018

0.05

SBP, systolic blood pressure; AAA, abdominal aortic aneurism. * denotes absolute increase in R [2] when entered in the model. NA; did not enter final model.

of the presence of an acute AAA. 16 out of 34 subjects aged N 70 years had an acute AAA (probability 47%), whereas none of the 29 subjects aged b 70 had an acute AAA. 28 subjects had a SBP b 137 mmHg, of which 14 had an acute AAA (probability 50%), whereas the probability of an acute AAA in the subjects with a SBP N 137 mmHg was only 6%. Of the 33 patients with profound diaphoresis, 15 had an acute AAA (probability 45%), whereas only 1 patient without diaphoresis had an acute AAA (probability 3%). 20 subjects had a known AAA in their histo- ry. 10 of them had an acute AAA (probability 50%), whereas this proba- bility was only 14% when no known AAA was present. In our population 15 patients had a SBPN 137 mmHg in the absence of diaphoresis and without a history of AAA. When subjects had a SBPN 137 mmHg in the absence of diaphoresis and without a history of AAA, the probability of an acute AAA in our population was 0%. 7 patients were older than 70, had a SBPb 137, were diaphoretic and had a history of AAA. All of these patients turned out to have an acute AAA (Table 3).

Discussion

To the best of our knowledge, this is the first study to demonstrate the potential of pre-hospital data for the early identification of patients with an acute AAA. Using prehospital data might result in a more appro- priate use of available resources and a better outcome for the patient by minimising overtriage and preventing undertriage at the same time [16,17]. This is especially important since aneurysm surgery has become more and more centralised in higher volume centres over the past

Table 1

Baseline characteristics of subjects transported by the Emergency Medical Service with a presumed AAA, stratified by final diagnosis.

No acute AAA (n=47)

Acute AAA (n=16)

N Missing

p

Demographics

Age (Y)

66.5 (63.1-69.8)

78.1 (74.1-82.1)

0

b0.001

Sex, male, n (%)

31 (66.6)

13 (81.3)

0

0.35

Vital signs

SBP (mmHg)

151 (141-161)

104 (85-123)

6

b0.001

DBP (mmHg)

92 (83-101)

69 (56-82)

6

0.009

Heart rate (bpm)

75 (68-83)

84 (73-95)

3

0.22

Oxygen saturation (%)

93 (91-96)

87 (81-94)

8

0.09

AVPU-score (n)

0

0,16

Alert

46 (97,9)

14 (77,5)

Verbal/Pain/Unresponsive

1 (2.1)

2 (12.5)

Symptoms/physical exam, Acute pain?

38 (80.9)

12 (75.0)

0

0.72

Diaphoresis

17 (36.2)

14 (87.5)

2

b0.001

Syncope

7 (14.9)

6 (37.5)

0

0.08

Comorbidity

Hypertension

26 (55.3)

7 (43.8)

0

0.56

Smoking (yes)

8 (20.5)

3 (37.5)

16

0.37

Diabetes Mellitus

7 (14.9)

2 (12.5)

0

1.00

Vascular disease

16 (34)

9 (56.3)

0

0.15

History of AAA

10 (21.3)

10 (62.5)

0

0.004

History of treated AAA

3 (6.4)

5 (31.3)

0

0.65

All data are represented as mean (%). AAA, abdominal aortic aneurism; SBP, systolic blood pressure; DBP, diastolic blood pressure; NRS= Numeric rating scale (1-10); AVPU score: A = alert, V = responsive to verbal, P = responsive to pain, U = unresponsive; * “acute” is defined as a maximum perceived pain score within 30 minutes after complaints have started.

Table 3

Diagnostic accuracy indices of various pre-hospital patient characteristics to predict a correct diagnosis of an acute AAA.

Cut-off value

LR-

LR +

Sensitivity % (95% CI)

Specificity % (95% CI)

SBP

b137

0.3 (0.1-0.9)

2.6 (1.5-4.9)

85 (54-97)

75 (59-86)

Age (Y)

N 70

0

2.6 (1,8-3.8)

100 (76-100)

62 (46-75)

Diaphoresis

NA

0.1 (0.02-0.7)

2.5 (1.7-3.8)

93(66-100)

63(47-76)

History of AAA

NA

0.5 (0.3-0.9)

2.9 (1.5-5.7)

63(36-84)

79 (64-89)

SBP, systolic blood pressure; (R)AAA, (ruptured) abdominal aortic aneurism; LR -, negative likelihood ratio; LR+, positive likelihood ratio.

decade in most Developing countries [18]. This places a High demand on resources in regional centres receiving all patients that are suspected of an acute AAA [19]. So ideally prehospital parameters should be both specific and sensitive and discriminate those subjects who benefit most from a multidisciplinary team approach.

In our study we investigated subjects in whom EMS personnel suspected an acute aneurysm to be present. Whereas previous studies showed that the incidence of an acute AAA is low, with around 10.6% per 100.000 person years [20], the a-priori chance of the presence of an acute AAA in our selected population with a clinical suspicion of an acute AAA by EMS personnel was as high as 25%. This could be attributed to the accurate clinical gestalt of our ambulance personnel. However, we are not aware of any previous studies about the accuracy of EMS gestalt re- garding a correct diagnosis of acute AAA, making it hard to place this num- ber in perspective. Despite the high a-priori chance of the presence of an acute AAA, we were still able to identify pre-hospital factors that increased the a-priori chance of the presence of an acute AAA considerably. “AgeN 70”, “SBPb 137”, “presence of diaphoresis” and the “presence of a known AAA” were all in dependent predictors of the presence of an acute AAA. The presence of any of these factors increased the pre-test probability of an acute AAA to N 50%. When all of these factors were pres- ent, the probability of an acute AAA rose to 100%. When team activation would occur only when all these factors are present, there would be a sig- nificant percentages undertriage (9 out of 16 acute abdominal aortic aneu- rysms missed). Therefore, it seems prudent to activate a multidisciplinary aneurysm team when any of these factors is reported by EMS services when they announce the arrival of a patient they suspect of an acute AAA. For subjects with a known AAA in their history, this is in agreement with current guidelines wherein it is recognised that a clinical diagnosis of acute AAA should be considered in any patient aged N 50 or with a known AAA and symptoms of either abdominal/back pain or hypoten- sion/collapse. [10] However, we demonstrate that the optimal age cut- off derived under the condition of equal costs of misqualification to dis- criminate patients with- and without an acute AAA in our population was as high as 70 years. The mean age of the patients with an acute AAA (78 years) in our study was comparable to previous studies [21,22]. Using the currently advocated age cut-off of 50 years used in most guidelines would have resulted in significant over-triage in our study since 58 out of 63 patients were aged over 50 years and only 16

of them truly had an acute AAA.

Although hemodynamic instability has been shown to be the main prognostic clinical factor of a bad outcome in various studies [21,23,24], hypotension is only present in a minority (22%) of patients with an acute AAA [22]. Therefore, it comes at no surprise that an opti- mal SBP cut off value as high as 137 mmHg was derived from our study population to discriminate patients with- and without an acute AAA. Pa- tients with systolic blood pressures N 137 mmHg had a very low proba- bility of an acute AAA, especially when diaphoresis was absent and no history of AAA was present. In these patients, it could be advocated to postpone multidisciplinary team activation until the patient is present- ed in the hospital and diagnostic studies (e.g. FAST-exam) are per- formed to exclude AAA.

A promising tool to improve pre-hospital triage might be the use of pre-hospital ultrasound . A Study of Heegard et al [25] showed that EMS paramedics can adequately perform a FAST exam after a training pro- gram of only 6 hours.

Limitations

Our study has several limitations. First, inherent to the retrospective design of our study, we had to cope with missing data. Especially infor- mation regarding the presence or absence of limb ischemia or a pulsatile abdominal mass was lacking. Since previous studies demonstrated that the presence of these factors is an accurate predictor of the presence of an acute AAA, inclusion of this parameter in the final multivariate model might have influenced the predictive properties of the parameters cur- rently incorporated in the multivariate model. Second, our study popu- lation was relatively small. As a result, confidence intervals of the diagnostic accuracy indices for the different parameters are relatively wide and our model was only able to predict 50% of the variability of our outcome variable. It should be anticipated that absolute cut off- values for age (70 years) and SBP (137mmHg) would not have been ex- actly the same when more patients would have been available to in- clude in our model. Furthermore, recommendations to activate- or not activate a team based on the provided information in this study can not simply be extrapolated to other populations with e.g. a higher or lower baseline prevalence of acute AAA or less/better trained EMS ser- vices. Generalizability of results to US system with less trained EMS ser- vices is therefore limited. Finally, activation criteria for multidisciplinary aneurysm teams should always be balanced with local available re- sources, and can thereby vary considerably from hospital to hospital, as is the case for traumateam activations [26].

With an acute abdominal aortic aneurysm prevalence of 25% in our population, and the generally accepted rule of thumb of 10 events per candidate predictor, it is fully clear that our study does not have suffi- cient power for building a full scale prognostic model. However, we did identify appropriate candidate predictors. Larger prospective stud- ies are warranted to confirm our results before any solid recommenda- tions can be made about which pre-hospital parameters should be obtained to improve appropriate triage.

In conclusion

Pre-hospital information regarding the patient’s age, history (known AAA), blood pressure and general appearance (presence of diaphoresis) can be useful when EMS services announce the arrival of a patient with suspected acute AAA in order to improve appropriate triage and mini- mize time to definitive care.

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