Original article 1
The prehospital intravenous access assessment: a prospective study on intravenous access failure and access delay in prehospital emergency medicine Johannes Prottengeiera, Matthias Albermanna, Sebastian Heinricha, Torsten Birkholza, Christine Gallb and Joachim Schmidta Objectives Intravenous access in prehospital emergency care allows for early administration of medication and extended measures such as anaesthesia. Cannulation may, however, be difficult, and failure and resulting delay in treatment and transport may have negative effects on the patient. Therefore, our study aims to perform a concise assessment of the difficulties of prehospital venous cannulation. Methods We analysed 23 candidate predictor variables on peripheral venous cannulations in terms of cannulation failure and exceedance of a 2 min time threshold. Multivariate logistic regression models were fitted for variables of predictive value (P < 0.25) and evaluated by the area under the curve (AUC > 0.6) of their respective receiver operating characteristic curve. Results A total of 762 intravenous cannulations were enroled. In all, 22% of punctures failed on the first attempt and 13% of punctures exceeded 2 min. Model selection yielded a three-factor model (vein visibility without tourniquet, vein palpability with tourniquet and insufficient ambient lighting) of fair accuracy for the prediction of puncture failure (AUC = 0.76) and a structurally congruent model of four factors (failure model factors plus vein
Introduction The intravenous administration of fluids and medication is one of the key concepts in emergency medicine. The ideal time for the establishment of intravenous access, however, remains highly disputed and possible delays of up to 5 min owed to intravenous access [1,2] are one of the reasons why many paramedic-based Emergency Medical Service (EMS) systems favour cannulations in the emergency department – especially in severe trauma [3]. In a physician-staffed EMS system (presently instated in Germany), the range of prehospital therapies is considerably broader and intravenous access is standard in severe missions, when a physician is present. However, the potential benefits of an extended prehospital treatment must not be given away by undue time consumption for venous cannulation. The literature states that approximately one out of four patients will need more than one attempt for intravenous access in a prehospital situation [4,5] and the fact that 0969-9546 Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
visibility with tourniquet) for the exceedance of the 2 min threshold (AUC = 0.80). Conclusion Our study offers a simple assessment to identify cases of difficult intravenous access in prehospital emergency care. Of the numerous factors subjectively perceived as possibly exerting influences on cannulation, only the universal – not exclusive to emergency care – factors of lighting, vein visibility and palpability proved to be valid predictors of cannulation failure and exceedance of a 2 min threshold. European Journal of Emergency Medicine 00:000–000 Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved. European Journal of Emergency Medicine 2015, 00:000–000 Keywords: difficult peripheral intravenous access, invasive procedure, prehospital emergency medicine, venous cannulation a Department of Anaesthesiology, Erlangen University Hospital and bDepartment of Medical Informatics, Biometry and Epidemiology, Friedrich-Alexander University Erlangen, Erlangen, Germany
Correspondence to Johannes Prottengeier, MD, Department of Anaesthesiology, Erlangen University Hospital, Krankenhausstrasse 12, 91054 Erlangen; Germany Tel: + 49-9131-85-42332; fax: + 49-9131-85-36147; e-mail: [email protected] Received 24 February 2015 Accepted 4 June 2015
prehospital intravenous access can be challenging is recognized in guidelines by Germany’s Anaesthesia and Intensive Care Society and the European Resuscitation Council [6,7]. These state that alternative routes of application (especially the intraosseous access) should be considered in critically ill emergency patients after three unsuccessful attempts at intravenous cannulation or if more than 2 min have passed for these attempts. In addition, these guidelines suggest a pre-emptive use of alternatives (again intraosseous access) in situations where cannulation failure seems likely. However, although predictors for a difficult intravenous access have been investigated for in-hospital settings [8–12], only little data are available on the special environment of prehospital emergency care. In summary, there is a profound lack of evidence to base the above-mentioned prediction of success on anything but one’s own gut feeling. The aim of this prospective, prehospital study was to identify factors influencing successful cannulation and to DOI: 10.1097/MEJ.0000000000000291
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2 European Journal of Emergency Medicine 2015, Vol 00 No 00
present a concise assessment to identify in advance those scenarios and patients where cannulation will possibly be unsuccessful and/or considerably delayed – before timeconsuming and painful attempts at cannulation fail. Such an assessment could provide evidence-based criteria for crew resource management, responsibly guide towards more invasive alternatives of vascular access and save valuable time in prehospital treatment.
selection, odds ratios were calculated and the area under the corresponding receiver operating characteristic (ROC) curve was derived as a measure of predictive accuracy. For comparison, a further reduced model containing only those variables with an area under the curve (AUC) more than 0.6 was fitted. The outcome addressing the excess of the 2 min time limit is addressed analogously.
Methods
Results
The University of Erlangen-Nuremberg’s ethics committee approved this study and waived the need for a formal informed consent from patients because of the anonymous and purely observational nature of our study. We documented in detail a large cohort of peripheral venous cannulations that were performed by physicians of the EMS stationed at the Erlangen University Hospital. In the German EMS system, selected severe cases of prehospital emergencies are handled by specially trained emergency physicians – assisted by paramedics. The establishment of intravenous access and the application of intravenous medications are standard in prehospital treatment. At our institution, all senior anaesthesiology faculty serve as EMS physicians in addition to their clinical practice in our department, conducting a little over 3500 missions annually.
A total of 797 intravenous cannulations were documented. Thirty-five punctures in children younger than 14 years old were excluded as a subgroup with special considerations, but insufficient group size. Of a total of 762 enroled cannulations, 78% were successful on first attempt. In 14% of cases, two attempts were required, and three or more in 8%, respectively. Model selection yielded a model of fair accuracy (AUC = 0.78) with eight influencing factors (Table 2), of which only three (vein visibility without tourniquet, vein palpable with tourniquet and insufficient lighting) had a predictive accuracy of AUC more than 0.6. Success rates corresponding to the different parameters are shown in Table 3.
A total of 797 accesses were documented through an online questionnaire – right after each mission. EMS Physicians were trained beforehand on the contents of the questionnaire and the situational assessment required – thus gaining a ‘quasi prospective’ evaluation of the cannulation procedure despite the ex-post perspective of online documentation. Cannulations were analysed in terms of 23 candidate predictor variables in relation to each mission, patient and invasive procedure (Table 1). These variables were gathered from previous investigations into intrahospital access failure and discussions within a multidisciplinary group of paramedics, emergency physicians, emergency department nurses and senior anaesthetists from Erlangen University Hospital. We analysed our data for two outcomes of interest. First was the successful intravenous placement at the first attempt. Second was any time consumption for the procedure of cannulation exceeding 2 min – as defined by the Consensus on Cardiopulmonary Resuscitation [7]. Statistics
Statistical analysis was carried out using SAS, 9.3 (SAS Institute, Cary, North Carolina, USA). The outcome of interest was addressed by logistic regression. In a stepwise approach, candidate predictive variables were first evaluated by a univariate logistic regression (Table 1). Variables likely to influence the outcome – represented by a P-value less than 0.25 from univariate regression – were subjected to multivariable logistic regression. For variables remaining in the model after backward
In 13% of cases, cannulation took more than 2 min and in 4% of cases, it took more than 5 min. Model selection yielded a model of good accuracy (AUC = 0.81) with seven influencing factors (Table 2), of which four (vein visibility with and without tourniquet, vein palpable with tourniquet and insufficient lighting) had a predictive accuracy of AUC more than 0.6. For the model of cannulation failure, the process of simplification through removal of mediocre factors (type of mission, patient exsiccation, local soft tissue oedema/ swelling, patient unrest and vein visibility with tourniquet) resulted in a much simpler but nonetheless accurate prediction rule (Fig. 1). In analogy, second-rate factors (patient age, centralization of circulation and local soft tissue oedema or swelling) were excluded from the time-threshold model of prediction (Fig. 2). In summary, two structurally congruent statistical models were obtained: puncture failure can be predicted by assessing the three factors of (1) Vein visibility without tourniquet. (2) Vein palpability with tourniquet and (3) Sufficiency of ambient lighting, resulting in an area under the ROC curve of 0.7555. The prediction model of exceedance of a 2 min time threshold is augmented by an additional predictive factor of (4) Vein visibility with tourniquet, towards an AUC (ROC) of 0.8011.
Discussion The prehospital establishment of intravenous access is controversial despite many years of practice [13,14]. Possible benefits comprise early administration of medication and extended treatment such as emergency anaesthesia. The major disadvantage is a significant time
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PHIVA-assessment Prottengeier et al. 3
Table 1
Univariate regression of predictor variables Outcome: success/failure of intravenous cannulation on first attempt Odds ratio estimate [point estimate (95% CI)]
Variable Patient sex (reference: female) Patient age, categorized by quartiles (years) 1 (< 49) 2 (≥49) 3 (≥69) 4 (>81)
P-value*
Outcome: undercut/exceedance of the 2 min time limit
Included in multivariable logistic regression model
Odds ratio estimate [point estimate (95% CI)]
P-value*
Included in multivariable logistic regression model
0.61 (0.43–0.86)
0.0051
Yes
0.73 (0.48–1.11)
0.1413
Yes
1 vs. 4
1.12 (0.69–1.82)
0.7011
No
1.34 (0.77–2.32)
0.0542
Yes
2 vs. 4 3 vs. 4 1 vs. 4
1.15 (0.7–1.9) 0.89 (0.56–1.42) 1.57 (0.63–3.93)
Yes
2.29 (1.22–4.3) 1.72 (0.97–3.04) 1.34 (0.47–3.78)
0.0032
Yes
2 vs. 4 3 vs. 4 Type of mission: cardiopulmonary resuscitation Type of mission: medical Type of mission: neurological Type of mission: trauma Vein visible without tourniquet Vein visible without tourniquet Vein visible with tourniquet Vein palpable with tourniquet Centralization, shock Puncture site soft tissue oedema/ swelling Dehydration/exsiccosis Hypothermia Puncture site: local injuries Puncture site: local dirt Puncture site: other alterations to skin aspect Surroundings: limited space Surroundings: dark/insufficient ambient lighting Agitated patient Procedure performed inside ambulance Mode of tourniquet 1 vs. 2 1 = Tourniquet by quick release tourniquet 2 = Tourniquet by blood pressure cuff 3 = No tourniquet 2 vs. 3 Size of intravenous cannula
2.24 (1.46–3.43) 2.38 (1.49–3.81) 0.37 (0.18–0.78)
0.0085
Yes
2.46 (1.47–4.12) 2.26 (1.29–3.95) 0.64 (0.25–1.59)
0.3322
No
1.13 (0.8–1.6) 0.84 (0.55–1.29) 1.21 (0.76–1.94) 0.22 (0.15–0.31) 0.24 (0.15–0.38) 0.22 (0.13–0.39) 0.19 (0.13–0.27) 0.32 (0.2–0.5) 0.25 (0.14–0.46)
0.4778 0.4374 0.4166 < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001
No No No Yes Yes Yes Yes Yes Yes
0.95 (0.62–1.45) 0.98 (0.57–1.68) 1.28 (0.71–2.29) 0.14 (0.09–0.22) 0.23 (0.13–0.44) 0.12 (0.07–0.22) 0.21 (0.14–0.33) 0.27 (0.16–0.45) 0.17 (0.09–0.32)
0.8007 0.9435 0.4125 < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001
No No No Yes Yes Yes Yes Yes Yes
0.52 (0.34–0.81) 0.32 (0.19–0.55) 0.46 (0.2–1.07) 0.67 (0.32–1.43) 0.66 (0.45–0.97)
0.0039 < 0.0001 0.0698 0.3018 0.0365
Yes Yes Yes No Yes
0.59 (0.35–1) 0.38 (0.21–0.69) 0.45 (0.18–1.17) 0.42 (0.19–0.93) 0.47 (0.3–0.74)
0.0521 0.0015 0.1013 0.0316 0.0010
Yes Yes Yes Yes Yes
0.37 (0.25–0.53) 0.3 (0.21–0.43)
< 0.0001 < 0.0001
Yes Yes
0.42 (0.27–0.64) 0.29 (0.19–0.45)
< 0.0001 < 0.0001
Yes Yes
0.43 (0.29–0.65) 1.23 (0.82–1.85)
< 0.0001 0.3087
Yes No
0.4 (0.25–0.65) 1.36 (0.82–2.27)
0.0002 0.2388
Yes Yes
0.75 (0.21–2.68)
0.4693
No
0.4 (0.05–3.05)
0.4548
No
0.99 (0.26–3.72) 1.74 (1.34–2.25)
< 0.0001
BMI categorized 1 (< 18.5) 2 (≥18.5) 3 (≥25) 4 (≥30)
0.0005
No (see the Discussion section)
0.52 (0.06–4.21) 2.11 (1.53–2.92)
< 0.0001
No (see the Discussion section)
Candidate predictor variables are analysed for the outcomes of both puncture success/failure and undercut/exceedance of the 2 min time threshold. The odds ratio estimate and P-value are presented for a univariate logistic regression. Variables selected for the multivariate modelling are marked accordingly. CI, confidence interval. *Overall P-value for categorical data.
delay for hospital admission because of the time cost for the procedure itself [1–3]. The overall failure rate of cannulation in our study was 22% at the first attempt and 8% at the second attempt. These results are in general agreement with previous investigations into peripheral venous access [4,15–17].
However, we considered the issue of time delay in the establishment of peripheral access of even greater significance. Although an unsuccessful puncture may be considered a mere nuisance, the resulting timely delay in administering emergency medication might be the real calamity. Guidelines by the European Resuscitation Council reflect on this issue and set the benchmark for
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4 European Journal of Emergency Medicine 2015, Vol 00 No 00
Table 2
Results for models found by backward selection Outcome Successful intravenous placement on first attempt [point estimate (95% Wald-CI)] Area under ROC curve
Model Vein visible without tourniquet Vein visible with tourniquet Vein palpable with tourniquet Dark/insufficient ambient lighting Puncture site soft tissue oedema/ swelling Dehydration/exsiccosis Agitated patient Type of mission: cardiopulmonary resuscitation Centralisation/shock Patient age, categorized in quartiles
0.78 0.67 0.57 0.68 0.63 0.55
Odds ratio estimates
(0.74–0.82) (0.63–0.71) (0.54–0.60) (0.63–0.72) (0.59–0.67) (0.52–0.58)
0.49 0.49 0.28 0.49 0.50
0.54 (0.51–0.58) 0.57 (0.53–0.60) 0.53 (0.51–0.55)
Excess of the 2 min time limit [point estimate (95% Wald-CI)] Area under ROC curve
NA (0.31–0.76) (0.25–0.99) (0.18–0.43) (0.32–0.74) (0.25–1.0)
0.81 0.72 0.62 0.67 0.64 0.58
Odds ratio estimates
(0.77–0.87) (0.68–0.77) (0.57–0.66) (0.62–0.73) (0.58–0.69) (0.54–0.62)
0.60 (0.36–0.99) 0.56 (0.35–0.91) 0.41 (0.16–1.1)
0.35 0.27 0.38 0.53 0.37
NA (0.20–0.61) (0.14–0.55) (0.22–0.64) (0.32–0.89) (0.18–0.78)
Not included Not included Not included
Not included Not included
0.596 (0.55–0.64) 0.53 (0.47–0.60)
0.46 (0.25–0.83) 0.91 (0.73–1.14)
CI, confidence interval; NA, not available; ROC, receiver operating characteristic.
Success rates according to values of predictor variables with relevant AUC
Table 3
Fig. 1
1.00
Outcome Successful intravenous placement on first attempt (overall success rate: 78%)
Variable Value Success rate Vein visible without tourniquet Yes 87 No 59 Vein visible with tourniqueta Yes 80 No 47 Vein palpable with tourniquet Yes 86 No 53 Dark/insufficient ambient lighting Yes 84 No 61
Successful undercut of the 2 min time limit (overall success rate: 87%)
0.75 95% CI
Success rate
95% CI
0.84–0.90 0.53–0.65
94 70
0.92–0.96 0.64–0.76
0.77–0.83 0.34–0.61
89 51
0.87–0.92 0.37–0.65
0.83–0.88 0.45–0.60
92 70
0.89–0.94 0.63–0.77
0.81–0.87 0.54–0.68
75 91
0.68–0.81 0.88–0.93
Success rate is represented as %. AUC, area under the curve; CI, confidence interval. a Relevant AUC only for outcome ‘Undercut of the 2 min time threshold’.
Sensitivity
Predictor variables with relevant AUC
0.50
0.25
0.00 0.00
0.25
0.50 1− Specificity
0.75
1.00
ROC curve (area)
the establishment of intravenous access in emergencies at 2 min [6,7]. In our study, 13% of cannulation procedures took more than 2 min and 4% took even more than 5 min, respectively. These results indicate that not only puncture failure but a significant time delay is common with intravenous access and strategies for the improvement of these techniques in emergency medicine are urgently needed.
Receiver operating characteristic (ROC) curves of the reduced model for the outcome parameter: ‘successful intravenous placement on first attempt.’
The vast number of candidate variables gathered from the structured discussions within our university’s team of experienced emergency care providers indicates the personal perception of a variety of factors that are subjectively suspected to exert influences on invasive procedures. However, statistical analysis of our large cohort produced rather sobering results. Despite the truly unique environment of an emergency scene, the most common approach to a venous puncture site as it is
practiced in any other field of medicine proves to be valid: the general visibility of a vein and its palpability after tourniquet are the most valuable predictors for cannulation success and speed. The importance of vein visibility is underlined by the influence of insufficient lighting (a certain contributor to poor visibility) and the effect of a second assessment of vein visibility after
Model (0.7555) Vein visible without tourniquet (0.6731) Vein palpable with tourniquet (0.6731) Dark ambient lighting (0.6302)
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PHIVA-assessment Prottengeier et al. 5
Interestingly, the physicians’ subjective assessment of expected puncture difficulties [categories 1 (extremely easy) to 10 (extremely difficult)] was also a reliable predictive factor for puncture failure. Univariate logistic regression found a fair predictive accuracy (AUC = 0.78).
Fig. 2
1.00
Sensitivity
0.75
0.50
0.25
0.00 0.00
0.25
0.50 1− Specificity
0.75
1.00
ROC curves (area) Model (0.8011) Vein visible without tourniquet (0.7239) Vein visible with tourniquet (0.6176) Vein palpable with tourniquet (0.6738) Dark ambient lighting (0.6376) Receiver operating characteristic (ROC) curves for the reduced model for the outcome parameter: ‘excess of the 2 min time limit’.
tourniquet as derived from the time-threshold model. Trivial as this might seem, it underlines the general significance of puncture site inspection. The abundance of other variables that we investigated was either not associated with puncture failure and delay or was inferior in its predictive power compared with the simple threeitem and four-item models. In summary, our short but comprehensive evaluation tool will reliably anticipate cannulation failure and timely delay: caution is advised if veins are not readily visible or palpable after tourniquet. We did not formulate a scoring system as we believed that this was not suitable for a mere three-item or a fouritem prediction model. In a similar manner, a recent study by Riker et al. [10] has simplified previous multifactorial paediatric prediction rules into a three-factor scoring system without forfeiting accuracy. Predictors in the Riker model are: (1) Vein visible with tourniquet in place. (2) Vein palpable with tourniquet in place (Vein characteristics without tourniquet were not considered in this study.) and (3) Child’s age. In contrast to these results, our data do not suggest an influence of patient age. It may be argued that the special developmental aspects of infancy and childhood are without significance in an adult, already grown-up population.
As a side note, our data did confirm the conjecture described by Frisch and colleagues, who discovered that an increasing catheter size was associated positively with successful intravenous placement. Frisch and colleagues had argued that this might be explained by the fact that paramedics would probably choose a larger size of cannula when they assumed that cannulation success was more likely to be achieved. Univariate logistic regression for our data set also showed a significant relation between catheter size and success at first attempt (for our data: P = 0.0001, odds ratio = 1.68 with confidence interval = 1.29–2.18). However, inclusion of this variable in the multivariable logistic regression model with the covariates listed in Table 2 yielded a nonsignificant association (P = 0.47, odds ratio = 1.12 with confidence interval =0.82–1.53), indicating that the association between successful cannulation and catheter size is a consequence of confounding. Naturally, there are limitations to this observational study. First, all surveys based on questionnaires might be influenced by a subjective selection bias. Second, the mode of operation, especially the anatomical site of cannulation, was neither randomized nor restricted to one predefined vein. A biased choice of puncture site is possible as procedural tactics endorse cannulation attempts in a centripetal sequence (proximal haematoma or vascular leakage after failed punctures may render further, more peripheral sites useless). More peripheral veins are usually easier to visualize but also smaller in diameter compared with more proximal vessels. Cannulation failure may therefore be confounded by inadequate puncture site selection. Third, in this single-centre study, the participating physicians were all from a very similar professional background with comparable training in venous puncture and secondary techniques such as the intraosseus access. We therefore refrained from an analysis of providers’ factors on the clinical endpoints of our study. A future multicentre investigation could possibly investigate whether the professional background (paramedics vs. physicians of different clinical disciplines) could identify further factors of predictive value for cannulation. Such a multicentre design could also explore the influence of tactical consideration of EMS missions (e.g. time and distance to next hospital in relation to severity of disorder or injury) on cannulation attempts. Furthermore, we excluded all paediatric patients from our study. This was necessary as the subgroup of paediatric patients was too small for analysis. However, it is this subgroup of patients that is known to lead to the highest degree in anxiety in EMS providers and is infamous for difficulties in the
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6 European Journal of Emergency Medicine 2015, Vol 00 No 00
establishment of intravenous access [18,19]. A future study focusing on this precarious group of patients would therefore be most welcome but, because of the low frequency of prehospital venous cannulation in children, would have to be implemented using a much larger multicentre approach.
2 3
4
5
Conclusion
Cannulation failure and time delay should be avoided by implementing our short and comprehensive puncture assessment to save valuable time in prehospital treatment. Under sufficient lighting, a short assessment of vein visibility and vein palpability (with tourniquet) should be performed. If the vein is neither visible nor palpable, the likelihood of failure increases significantly to 46% and there is a 30% chance of more than 2 min of delay. Once rated as a difficult venous access scenario, immediate consequences should be as follows:
6
7
8
9
10
(1) Punctures should only be performed by the most experienced and most able team member. (2) Clear communication of time frames and numbers of trials for conventional venous cannulations. (3) Adequate step-up to secondary alternatives, especially intraosseus access, as indicated by recent guidelines.
11 12
13
If indecisive, one should feel free to – most unscientifically – rely on one’s own gut feeling as such an assessment is a valuable predictor of success.
14
15
Acknowledgements The authors thank all participating EMS Physicians for their contributions to our intravenous access database.
16
17
Conflicts of interest
There are no conflicts of interest.
18
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The prehospital intravenous access assessment: a prospective study on intravenous access failure and access delay in prehospital emergency medicine Johannes Prottengeiera, Matthias Albermanna, Sebastian Heinricha, Torsten Birkholza, Christine Gallb and Joachim Schmidta Objectives Intravenous access in prehospital emergency care allows for early administration of medication and extended measures such as anaesthesia. Cannulation may, however, be difficult, and failure and resulting delay in treatment and transport may have negative effects on the patient. Therefore, our study aims to perform a concise assessment of the difficulties of prehospital venous cannulation. Methods We analysed 23 candidate predictor variables on peripheral venous cannulations in terms of cannulation failure and exceedance of a 2 min time threshold. Multivariate logistic regression models were fitted for variables of predictive value (P < 0.25) and evaluated by the area under the curve (AUC > 0.6) of their respective receiver operating characteristic curve. Results A total of 762 intravenous cannulations were enroled. In all, 22% of punctures failed on the first attempt and 13% of punctures exceeded 2 min. Model selection yielded a three-factor model (vein visibility without tourniquet, vein palpability with tourniquet and insufficient ambient lighting) of fair accuracy for the prediction of puncture failure (AUC = 0.76) and a structurally congruent model of four factors (failure model factors plus vein
Introduction The intravenous administration of fluids and medication is one of the key concepts in emergency medicine. The ideal time for the establishment of intravenous access, however, remains highly disputed and possible delays of up to 5 min owed to intravenous access [1,2] are one of the reasons why many paramedic-based Emergency Medical Service (EMS) systems favour cannulations in the emergency department – especially in severe trauma [3]. In a physician-staffed EMS system (presently instated in Germany), the range of prehospital therapies is considerably broader and intravenous access is standard in severe missions, when a physician is present. However, the potential benefits of an extended prehospital treatment must not be given away by undue time consumption for venous cannulation. The literature states that approximately one out of four patients will need more than one attempt for intravenous access in a prehospital situation [4,5] and the fact that 0969-9546 Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
visibility with tourniquet) for the exceedance of the 2 min threshold (AUC = 0.80). Conclusion Our study offers a simple assessment to identify cases of difficult intravenous access in prehospital emergency care. Of the numerous factors subjectively perceived as possibly exerting influences on cannulation, only the universal – not exclusive to emergency care – factors of lighting, vein visibility and palpability proved to be valid predictors of cannulation failure and exceedance of a 2 min threshold. European Journal of Emergency Medicine 00:000–000 Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved. European Journal of Emergency Medicine 2015, 00:000–000 Keywords: difficult peripheral intravenous access, invasive procedure, prehospital emergency medicine, venous cannulation a Department of Anaesthesiology, Erlangen University Hospital and bDepartment of Medical Informatics, Biometry and Epidemiology, Friedrich-Alexander University Erlangen, Erlangen, Germany
Correspondence to Johannes Prottengeier, MD, Department of Anaesthesiology, Erlangen University Hospital, Krankenhausstrasse 12, 91054 Erlangen; Germany Tel: + 49-9131-85-42332; fax: + 49-9131-85-36147; e-mail: [email protected] Received 24 February 2015 Accepted 4 June 2015
prehospital intravenous access can be challenging is recognized in guidelines by Germany’s Anaesthesia and Intensive Care Society and the European Resuscitation Council [6,7]. These state that alternative routes of application (especially the intraosseous access) should be considered in critically ill emergency patients after three unsuccessful attempts at intravenous cannulation or if more than 2 min have passed for these attempts. In addition, these guidelines suggest a pre-emptive use of alternatives (again intraosseous access) in situations where cannulation failure seems likely. However, although predictors for a difficult intravenous access have been investigated for in-hospital settings [8–12], only little data are available on the special environment of prehospital emergency care. In summary, there is a profound lack of evidence to base the above-mentioned prediction of success on anything but one’s own gut feeling. The aim of this prospective, prehospital study was to identify factors influencing successful cannulation and to DOI: 10.1097/MEJ.0000000000000291
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2 European Journal of Emergency Medicine 2015, Vol 00 No 00
present a concise assessment to identify in advance those scenarios and patients where cannulation will possibly be unsuccessful and/or considerably delayed – before timeconsuming and painful attempts at cannulation fail. Such an assessment could provide evidence-based criteria for crew resource management, responsibly guide towards more invasive alternatives of vascular access and save valuable time in prehospital treatment.
selection, odds ratios were calculated and the area under the corresponding receiver operating characteristic (ROC) curve was derived as a measure of predictive accuracy. For comparison, a further reduced model containing only those variables with an area under the curve (AUC) more than 0.6 was fitted. The outcome addressing the excess of the 2 min time limit is addressed analogously.
Methods
Results
The University of Erlangen-Nuremberg’s ethics committee approved this study and waived the need for a formal informed consent from patients because of the anonymous and purely observational nature of our study. We documented in detail a large cohort of peripheral venous cannulations that were performed by physicians of the EMS stationed at the Erlangen University Hospital. In the German EMS system, selected severe cases of prehospital emergencies are handled by specially trained emergency physicians – assisted by paramedics. The establishment of intravenous access and the application of intravenous medications are standard in prehospital treatment. At our institution, all senior anaesthesiology faculty serve as EMS physicians in addition to their clinical practice in our department, conducting a little over 3500 missions annually.
A total of 797 intravenous cannulations were documented. Thirty-five punctures in children younger than 14 years old were excluded as a subgroup with special considerations, but insufficient group size. Of a total of 762 enroled cannulations, 78% were successful on first attempt. In 14% of cases, two attempts were required, and three or more in 8%, respectively. Model selection yielded a model of fair accuracy (AUC = 0.78) with eight influencing factors (Table 2), of which only three (vein visibility without tourniquet, vein palpable with tourniquet and insufficient lighting) had a predictive accuracy of AUC more than 0.6. Success rates corresponding to the different parameters are shown in Table 3.
A total of 797 accesses were documented through an online questionnaire – right after each mission. EMS Physicians were trained beforehand on the contents of the questionnaire and the situational assessment required – thus gaining a ‘quasi prospective’ evaluation of the cannulation procedure despite the ex-post perspective of online documentation. Cannulations were analysed in terms of 23 candidate predictor variables in relation to each mission, patient and invasive procedure (Table 1). These variables were gathered from previous investigations into intrahospital access failure and discussions within a multidisciplinary group of paramedics, emergency physicians, emergency department nurses and senior anaesthetists from Erlangen University Hospital. We analysed our data for two outcomes of interest. First was the successful intravenous placement at the first attempt. Second was any time consumption for the procedure of cannulation exceeding 2 min – as defined by the Consensus on Cardiopulmonary Resuscitation [7]. Statistics
Statistical analysis was carried out using SAS, 9.3 (SAS Institute, Cary, North Carolina, USA). The outcome of interest was addressed by logistic regression. In a stepwise approach, candidate predictive variables were first evaluated by a univariate logistic regression (Table 1). Variables likely to influence the outcome – represented by a P-value less than 0.25 from univariate regression – were subjected to multivariable logistic regression. For variables remaining in the model after backward
In 13% of cases, cannulation took more than 2 min and in 4% of cases, it took more than 5 min. Model selection yielded a model of good accuracy (AUC = 0.81) with seven influencing factors (Table 2), of which four (vein visibility with and without tourniquet, vein palpable with tourniquet and insufficient lighting) had a predictive accuracy of AUC more than 0.6. For the model of cannulation failure, the process of simplification through removal of mediocre factors (type of mission, patient exsiccation, local soft tissue oedema/ swelling, patient unrest and vein visibility with tourniquet) resulted in a much simpler but nonetheless accurate prediction rule (Fig. 1). In analogy, second-rate factors (patient age, centralization of circulation and local soft tissue oedema or swelling) were excluded from the time-threshold model of prediction (Fig. 2). In summary, two structurally congruent statistical models were obtained: puncture failure can be predicted by assessing the three factors of (1) Vein visibility without tourniquet. (2) Vein palpability with tourniquet and (3) Sufficiency of ambient lighting, resulting in an area under the ROC curve of 0.7555. The prediction model of exceedance of a 2 min time threshold is augmented by an additional predictive factor of (4) Vein visibility with tourniquet, towards an AUC (ROC) of 0.8011.
Discussion The prehospital establishment of intravenous access is controversial despite many years of practice [13,14]. Possible benefits comprise early administration of medication and extended treatment such as emergency anaesthesia. The major disadvantage is a significant time
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PHIVA-assessment Prottengeier et al. 3
Table 1
Univariate regression of predictor variables Outcome: success/failure of intravenous cannulation on first attempt Odds ratio estimate [point estimate (95% CI)]
Variable Patient sex (reference: female) Patient age, categorized by quartiles (years) 1 (< 49) 2 (≥49) 3 (≥69) 4 (>81)
P-value*
Outcome: undercut/exceedance of the 2 min time limit
Included in multivariable logistic regression model
Odds ratio estimate [point estimate (95% CI)]
P-value*
Included in multivariable logistic regression model
0.61 (0.43–0.86)
0.0051
Yes
0.73 (0.48–1.11)
0.1413
Yes
1 vs. 4
1.12 (0.69–1.82)
0.7011
No
1.34 (0.77–2.32)
0.0542
Yes
2 vs. 4 3 vs. 4 1 vs. 4
1.15 (0.7–1.9) 0.89 (0.56–1.42) 1.57 (0.63–3.93)
Yes
2.29 (1.22–4.3) 1.72 (0.97–3.04) 1.34 (0.47–3.78)
0.0032
Yes
2 vs. 4 3 vs. 4 Type of mission: cardiopulmonary resuscitation Type of mission: medical Type of mission: neurological Type of mission: trauma Vein visible without tourniquet Vein visible without tourniquet Vein visible with tourniquet Vein palpable with tourniquet Centralization, shock Puncture site soft tissue oedema/ swelling Dehydration/exsiccosis Hypothermia Puncture site: local injuries Puncture site: local dirt Puncture site: other alterations to skin aspect Surroundings: limited space Surroundings: dark/insufficient ambient lighting Agitated patient Procedure performed inside ambulance Mode of tourniquet 1 vs. 2 1 = Tourniquet by quick release tourniquet 2 = Tourniquet by blood pressure cuff 3 = No tourniquet 2 vs. 3 Size of intravenous cannula
2.24 (1.46–3.43) 2.38 (1.49–3.81) 0.37 (0.18–0.78)
0.0085
Yes
2.46 (1.47–4.12) 2.26 (1.29–3.95) 0.64 (0.25–1.59)
0.3322
No
1.13 (0.8–1.6) 0.84 (0.55–1.29) 1.21 (0.76–1.94) 0.22 (0.15–0.31) 0.24 (0.15–0.38) 0.22 (0.13–0.39) 0.19 (0.13–0.27) 0.32 (0.2–0.5) 0.25 (0.14–0.46)
0.4778 0.4374 0.4166 < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001
No No No Yes Yes Yes Yes Yes Yes
0.95 (0.62–1.45) 0.98 (0.57–1.68) 1.28 (0.71–2.29) 0.14 (0.09–0.22) 0.23 (0.13–0.44) 0.12 (0.07–0.22) 0.21 (0.14–0.33) 0.27 (0.16–0.45) 0.17 (0.09–0.32)
0.8007 0.9435 0.4125 < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001
No No No Yes Yes Yes Yes Yes Yes
0.52 (0.34–0.81) 0.32 (0.19–0.55) 0.46 (0.2–1.07) 0.67 (0.32–1.43) 0.66 (0.45–0.97)
0.0039 < 0.0001 0.0698 0.3018 0.0365
Yes Yes Yes No Yes
0.59 (0.35–1) 0.38 (0.21–0.69) 0.45 (0.18–1.17) 0.42 (0.19–0.93) 0.47 (0.3–0.74)
0.0521 0.0015 0.1013 0.0316 0.0010
Yes Yes Yes Yes Yes
0.37 (0.25–0.53) 0.3 (0.21–0.43)
< 0.0001 < 0.0001
Yes Yes
0.42 (0.27–0.64) 0.29 (0.19–0.45)
< 0.0001 < 0.0001
Yes Yes
0.43 (0.29–0.65) 1.23 (0.82–1.85)
< 0.0001 0.3087
Yes No
0.4 (0.25–0.65) 1.36 (0.82–2.27)
0.0002 0.2388
Yes Yes
0.75 (0.21–2.68)
0.4693
No
0.4 (0.05–3.05)
0.4548
No
0.99 (0.26–3.72) 1.74 (1.34–2.25)
< 0.0001
BMI categorized 1 (< 18.5) 2 (≥18.5) 3 (≥25) 4 (≥30)
0.0005
No (see the Discussion section)
0.52 (0.06–4.21) 2.11 (1.53–2.92)
< 0.0001
No (see the Discussion section)
Candidate predictor variables are analysed for the outcomes of both puncture success/failure and undercut/exceedance of the 2 min time threshold. The odds ratio estimate and P-value are presented for a univariate logistic regression. Variables selected for the multivariate modelling are marked accordingly. CI, confidence interval. *Overall P-value for categorical data.
delay for hospital admission because of the time cost for the procedure itself [1–3]. The overall failure rate of cannulation in our study was 22% at the first attempt and 8% at the second attempt. These results are in general agreement with previous investigations into peripheral venous access [4,15–17].
However, we considered the issue of time delay in the establishment of peripheral access of even greater significance. Although an unsuccessful puncture may be considered a mere nuisance, the resulting timely delay in administering emergency medication might be the real calamity. Guidelines by the European Resuscitation Council reflect on this issue and set the benchmark for
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4 European Journal of Emergency Medicine 2015, Vol 00 No 00
Table 2
Results for models found by backward selection Outcome Successful intravenous placement on first attempt [point estimate (95% Wald-CI)] Area under ROC curve
Model Vein visible without tourniquet Vein visible with tourniquet Vein palpable with tourniquet Dark/insufficient ambient lighting Puncture site soft tissue oedema/ swelling Dehydration/exsiccosis Agitated patient Type of mission: cardiopulmonary resuscitation Centralisation/shock Patient age, categorized in quartiles
0.78 0.67 0.57 0.68 0.63 0.55
Odds ratio estimates
(0.74–0.82) (0.63–0.71) (0.54–0.60) (0.63–0.72) (0.59–0.67) (0.52–0.58)
0.49 0.49 0.28 0.49 0.50
0.54 (0.51–0.58) 0.57 (0.53–0.60) 0.53 (0.51–0.55)
Excess of the 2 min time limit [point estimate (95% Wald-CI)] Area under ROC curve
NA (0.31–0.76) (0.25–0.99) (0.18–0.43) (0.32–0.74) (0.25–1.0)
0.81 0.72 0.62 0.67 0.64 0.58
Odds ratio estimates
(0.77–0.87) (0.68–0.77) (0.57–0.66) (0.62–0.73) (0.58–0.69) (0.54–0.62)
0.60 (0.36–0.99) 0.56 (0.35–0.91) 0.41 (0.16–1.1)
0.35 0.27 0.38 0.53 0.37
NA (0.20–0.61) (0.14–0.55) (0.22–0.64) (0.32–0.89) (0.18–0.78)
Not included Not included Not included
Not included Not included
0.596 (0.55–0.64) 0.53 (0.47–0.60)
0.46 (0.25–0.83) 0.91 (0.73–1.14)
CI, confidence interval; NA, not available; ROC, receiver operating characteristic.
Success rates according to values of predictor variables with relevant AUC
Table 3
Fig. 1
1.00
Outcome Successful intravenous placement on first attempt (overall success rate: 78%)
Variable Value Success rate Vein visible without tourniquet Yes 87 No 59 Vein visible with tourniqueta Yes 80 No 47 Vein palpable with tourniquet Yes 86 No 53 Dark/insufficient ambient lighting Yes 84 No 61
Successful undercut of the 2 min time limit (overall success rate: 87%)
0.75 95% CI
Success rate
95% CI
0.84–0.90 0.53–0.65
94 70
0.92–0.96 0.64–0.76
0.77–0.83 0.34–0.61
89 51
0.87–0.92 0.37–0.65
0.83–0.88 0.45–0.60
92 70
0.89–0.94 0.63–0.77
0.81–0.87 0.54–0.68
75 91
0.68–0.81 0.88–0.93
Success rate is represented as %. AUC, area under the curve; CI, confidence interval. a Relevant AUC only for outcome ‘Undercut of the 2 min time threshold’.
Sensitivity
Predictor variables with relevant AUC
0.50
0.25
0.00 0.00
0.25
0.50 1− Specificity
0.75
1.00
ROC curve (area)
the establishment of intravenous access in emergencies at 2 min [6,7]. In our study, 13% of cannulation procedures took more than 2 min and 4% took even more than 5 min, respectively. These results indicate that not only puncture failure but a significant time delay is common with intravenous access and strategies for the improvement of these techniques in emergency medicine are urgently needed.
Receiver operating characteristic (ROC) curves of the reduced model for the outcome parameter: ‘successful intravenous placement on first attempt.’
The vast number of candidate variables gathered from the structured discussions within our university’s team of experienced emergency care providers indicates the personal perception of a variety of factors that are subjectively suspected to exert influences on invasive procedures. However, statistical analysis of our large cohort produced rather sobering results. Despite the truly unique environment of an emergency scene, the most common approach to a venous puncture site as it is
practiced in any other field of medicine proves to be valid: the general visibility of a vein and its palpability after tourniquet are the most valuable predictors for cannulation success and speed. The importance of vein visibility is underlined by the influence of insufficient lighting (a certain contributor to poor visibility) and the effect of a second assessment of vein visibility after
Model (0.7555) Vein visible without tourniquet (0.6731) Vein palpable with tourniquet (0.6731) Dark ambient lighting (0.6302)
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PHIVA-assessment Prottengeier et al. 5
Interestingly, the physicians’ subjective assessment of expected puncture difficulties [categories 1 (extremely easy) to 10 (extremely difficult)] was also a reliable predictive factor for puncture failure. Univariate logistic regression found a fair predictive accuracy (AUC = 0.78).
Fig. 2
1.00
Sensitivity
0.75
0.50
0.25
0.00 0.00
0.25
0.50 1− Specificity
0.75
1.00
ROC curves (area) Model (0.8011) Vein visible without tourniquet (0.7239) Vein visible with tourniquet (0.6176) Vein palpable with tourniquet (0.6738) Dark ambient lighting (0.6376) Receiver operating characteristic (ROC) curves for the reduced model for the outcome parameter: ‘excess of the 2 min time limit’.
tourniquet as derived from the time-threshold model. Trivial as this might seem, it underlines the general significance of puncture site inspection. The abundance of other variables that we investigated was either not associated with puncture failure and delay or was inferior in its predictive power compared with the simple threeitem and four-item models. In summary, our short but comprehensive evaluation tool will reliably anticipate cannulation failure and timely delay: caution is advised if veins are not readily visible or palpable after tourniquet. We did not formulate a scoring system as we believed that this was not suitable for a mere three-item or a fouritem prediction model. In a similar manner, a recent study by Riker et al. [10] has simplified previous multifactorial paediatric prediction rules into a three-factor scoring system without forfeiting accuracy. Predictors in the Riker model are: (1) Vein visible with tourniquet in place. (2) Vein palpable with tourniquet in place (Vein characteristics without tourniquet were not considered in this study.) and (3) Child’s age. In contrast to these results, our data do not suggest an influence of patient age. It may be argued that the special developmental aspects of infancy and childhood are without significance in an adult, already grown-up population.
As a side note, our data did confirm the conjecture described by Frisch and colleagues, who discovered that an increasing catheter size was associated positively with successful intravenous placement. Frisch and colleagues had argued that this might be explained by the fact that paramedics would probably choose a larger size of cannula when they assumed that cannulation success was more likely to be achieved. Univariate logistic regression for our data set also showed a significant relation between catheter size and success at first attempt (for our data: P = 0.0001, odds ratio = 1.68 with confidence interval = 1.29–2.18). However, inclusion of this variable in the multivariable logistic regression model with the covariates listed in Table 2 yielded a nonsignificant association (P = 0.47, odds ratio = 1.12 with confidence interval =0.82–1.53), indicating that the association between successful cannulation and catheter size is a consequence of confounding. Naturally, there are limitations to this observational study. First, all surveys based on questionnaires might be influenced by a subjective selection bias. Second, the mode of operation, especially the anatomical site of cannulation, was neither randomized nor restricted to one predefined vein. A biased choice of puncture site is possible as procedural tactics endorse cannulation attempts in a centripetal sequence (proximal haematoma or vascular leakage after failed punctures may render further, more peripheral sites useless). More peripheral veins are usually easier to visualize but also smaller in diameter compared with more proximal vessels. Cannulation failure may therefore be confounded by inadequate puncture site selection. Third, in this single-centre study, the participating physicians were all from a very similar professional background with comparable training in venous puncture and secondary techniques such as the intraosseus access. We therefore refrained from an analysis of providers’ factors on the clinical endpoints of our study. A future multicentre investigation could possibly investigate whether the professional background (paramedics vs. physicians of different clinical disciplines) could identify further factors of predictive value for cannulation. Such a multicentre design could also explore the influence of tactical consideration of EMS missions (e.g. time and distance to next hospital in relation to severity of disorder or injury) on cannulation attempts. Furthermore, we excluded all paediatric patients from our study. This was necessary as the subgroup of paediatric patients was too small for analysis. However, it is this subgroup of patients that is known to lead to the highest degree in anxiety in EMS providers and is infamous for difficulties in the
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6 European Journal of Emergency Medicine 2015, Vol 00 No 00
establishment of intravenous access [18,19]. A future study focusing on this precarious group of patients would therefore be most welcome but, because of the low frequency of prehospital venous cannulation in children, would have to be implemented using a much larger multicentre approach.
2 3
4
5
Conclusion
Cannulation failure and time delay should be avoided by implementing our short and comprehensive puncture assessment to save valuable time in prehospital treatment. Under sufficient lighting, a short assessment of vein visibility and vein palpability (with tourniquet) should be performed. If the vein is neither visible nor palpable, the likelihood of failure increases significantly to 46% and there is a 30% chance of more than 2 min of delay. Once rated as a difficult venous access scenario, immediate consequences should be as follows:
6
7
8
9
10
(1) Punctures should only be performed by the most experienced and most able team member. (2) Clear communication of time frames and numbers of trials for conventional venous cannulations. (3) Adequate step-up to secondary alternatives, especially intraosseus access, as indicated by recent guidelines.
11 12
13
If indecisive, one should feel free to – most unscientifically – rely on one’s own gut feeling as such an assessment is a valuable predictor of success.
14
15
Acknowledgements The authors thank all participating EMS Physicians for their contributions to our intravenous access database.
16
17
Conflicts of interest
There are no conflicts of interest.
18
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