- Email: [email protected]
Vapocoolant Spray Versus Lidocaine Infiltration for Radial Artery Cannulation: A Prospective, Randomized, Controlled Clinical Trial
Vapocoolant Spray Versus Lidocaine Infiltration for Radial Artery Cannulation: A Prospective, Randomized, Controlled Clinical Trial Dirk Rüsch, MD, Tilo Koch, Florian Seel, MD, and Leopold Eberhart, MD Objectives: Local infiltration with lidocaine is a frequently used measure to prevent pain during arterial cannulation. Its administration is associated with pain. Vapocoolants like ethyl chloride or alkanes also affect rapid-onset anesthesia. However, their administration causes less discomfort compared with administration of lidocaine. The effectiveness of vapocoolants in mitigating discomfort associated with arterial cannulation never has been studied. The authors therefore compared vapocoolant with lidocaine for reducing discomfort caused by arterial cannulation. Design: Prospective, randomized, controlled study. Setting: University hospital, single center. Participants: One hundred sixty adult patients requiring arterial cannulation before induction of general anesthesia for cardiac surgery or carotid endarterectomy. Interventions: Patients received either lidocaine infiltration or vapocoolant spray prior to arterial cannulation. Overall discomfort resulting from the whole procedure (applying local/topical anesthesia followed by arterial
puncture) was rated on a 0 to 10 numerical rating scale. Puncture failure rate and time required for the intervention also were recorded. Measurements and Main Results: One hundred forty-three patients were included in the per-protocol analysis. Mean pain scores in the vapocoolant group were 3.4 (⫾ 1.58) compared with 4.5 (⫾ 2.29) in the lidocaine group (difference 1.1 ⫾ 0.33; p ¼ 0.032; Mann-Whitney U-test). The higher puncture failure rate in the lidocaine group (n ¼ 11 v 4) was not significant (p ¼ 0.06; Fisher’s exact test). The time required for the intervention was longer in the lidocaine group (138 ⫾ 44 s v 128 ⫾ 44 s; p ¼ 0.019; Mann-Whitney U-test). Conclusions: Vapocoolant spray is an alternative to lidocaine infiltration to mitigate discomfort associated with arterial cannulation. & 2016 Elsevier Inc. All rights reserved.
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their effectiveness. A recent systematic review investigated these inconsistent results and concluded that vapocoolants significantly reduced pain compared with no treatment but not when compared with placebo in adults.12 However, methods of included studies varied greatly concerning variables that have been demonstrated to have an impact on cannulation pain (eg, cannula size and cannulation site).13,14 Thus, conclusions from this systematic review regarding the effectiveness of vapocoolants for venous cannulation have to be drawn cautiously. Therefore, the aim of this clinical trial was to study the efficacy of vapocoolant spray compared with lidocaine infiltration for radial artery cannulation by looking at anesthetic effectiveness, puncture failure rate, time required to puncture the radial artery following administration of the local or topical anesthetic, and the cost associated with both procedures. In this context, the authors hypothesized that vapocoolant spray was superior to lidocaine infiltration concerning its anesthetic effectiveness.
t is common clinical practice to place an arterial catheter before inducing general anesthesia in patients in whom a marked drop in arterial pressure must be avoided, or immediate restoration of blood pressure is mandatory. Even though no studies have investigated pain levels during arterial cannulation without anesthesia, common sense suggests that discomfort during arterial cannulation is at least as high as during arterial puncture for blood sampling or peripheral venous cannulation. Mean pain scores on a 100-mm visual analog scale (VAS) were 30 (⫾ 19)1 in patients who underwent arterial puncture with 22-G cannulae without local or topical anesthesia and ranged from 28 (95% CI 20-36)2 to 38 (⫾ 21)3 in patients undergoing venous cannulation with 18-G to 22-G cannulae without local or topical anesthesia. The most common local anesthetic technique performed for arterial cannulation is local infiltration with lidocaine.4 Several studies have demonstrated that topical anesthesia with lidocaine-prilocaine cream (EMLAs), amethocaine gel, or lidocaine tetracaine patch was at least as effective4-6 or even more effective4,7,8 in mitigating pain associated with arterial cannulation. However, all these topical anesthetics share the disadvantage of taking a minimum of 30 to 60 minutes to be effective, limiting their utility in many clinical situations. Concerns related to the use of lidocaine infiltration include discomfort during application3,6,9-11 and a potentially negative impact on cannulation success due to reduced palpability of the artery. Topical vapocoolant sprays (eg, ethyl chloride and alkane mixtures) could be an alternative in this setting. Their administration is associated with less pain compared with lidocaine,11 and unlike EMLAs, they provide anesthesia immediately after administration. However, studies of topical vapocoolants for reducing pain from arterial puncture and cannulation have not been published yet. Clinical trials of topical vapocoolant sprays for venous cannulation reported inconsistent results regarding
KEY WORDS: local anesthesia, cryoanesthesia, pain, arterial puncture, catheterization, peripheral
METHODS
This prospective, randomized, patient-blinded, controlled study was approved by the ethics committee of the Medical Faculty of Philipps-University of Marburg (committee’s reference number: AZ 103/02) and registered at the German Registry of Clinical Trials (DRKS00010155 on DRKS,
From the Department of Anesthesia and Intensive Care, University Hospital Giessen - Marburg, Marburg Campus, Marburg, Germany. The study was carried out without any external funding. Address reprint requests to Leopold Eberhart, MD, Baldingerstraße, 35043 Marburg, Germany. E-mail: [email protected] © 2016 Elsevier Inc. All rights reserved. 1053-0770/2601-0001$36.00/0 http://dx.doi.org/10.1053/j.jvca.2016.06.008
Journal of Cardiothoracic and Vascular Anesthesia, Vol ], No ] (Month), 2016: pp ]]]–]]]
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searchable at http://apps.who.int/trialsearch/). Patients aged 18 years and older who were scheduled to undergo elective cardiac surgery or carotid endarterectomy were eligible for inclusion in the study. Exclusion criteria were infection at the planned cannulation site, known allergies or intolerances to local anesthetics, and occlusion of the ipsilateral ulnar artery. Patients fulfilling the inclusion criteria received written and verbal information concerning the study no later than a day before planned surgery. All participating subjects provided written consent. An arterial cannulation set (containing a 20-G cannula, a guidewire, a 20-G sheath, a fenestrated drape, and ball swabs; Vyggon, Aachen, Germany), alcoholic disinfectant spray, ball swabs, vapocoolant spray, 0.5 mL of 2% lidocaine drawn up into a syringe, a 27-G needle, 2 pairs of sterile gloves, and dressing material were prepared for each enrolled patient. After arrival of the patient in the anesthesia induction area, electrocardiography, noninvasive blood pressure, and pulse oximetry were applied and an intravenous catheter was inserted at the contralateral side of planned arterial access. The arm in which arterial cannulation was intended to be performed was abducted at an angle of 701 to 901 and the wrist was hyperextended to facilitate palpation and cannulation of the radial artery. Patients were asked to turn their heads away in order to ensure that they were unable to observe the procedure. This was supervised by a study nurse. After identification of the optimal site for cannulation of the radial artery, the overlying skin was disinfected with a swab impregnated with an alcoholbased skin disinfectant solution. Next, the physician put on sterile gloves. At this particular point, a sealed, opaque envelope containing the group allocation used for randomization was opened by the study nurse. Using this method, patients were allocated to 1 of 2 groups equal in size, each containing 80 participants based on a computer-generated randomization list (www.random.org). Following randomized allocation, the physician put on a second pair of sterile gloves, applied the fenestrated drape at the cannulation site and made a standardized announcement, “It will feel cold on your forearm.” Afterward, patients in the lidocaine group received alcoholic disinfectant spray (a mixture of 2-propanol, 1-propanol, and biphenyl-2-ol), while patients in the vapocoolant group received a vapocoolant spray (a mixture of the active ingredients propane, n-butane, and n-pentane, as well as the additional ingredients menthol, camphor, and isopropanol). In the latter group, the skin area was sprayed perpendicularly from a distance of about 5 cm for approximately 2 to 3 seconds until the skin surface turned white in color (caused by freezing of humidity on the skin). Then the next standardized announcement was made by the physician, “Now I will begin with the cannulation.” Arterial cannulation then followed immediately in the vapocoolant group. Patients in the lidocaine group received an intradermal infiltration followed by a subcutaneous injection with a total of 0.5 mL of 2% lidocaine with a 27G needle. Subsequently, the radial artery was cannulated with a 20-G cannula without another explicit announcement. In both groups, the second pair of sterile gloves was taken off before arterial puncture was started. After successful
RÜSCH ET AL
puncture of the artery, a 20-G catheter was introduced according to the Seldinger technique. Time measurement of the intervention began when the physician started putting on the second pair of sterile gloves and was stopped once the lumen of the artery was punctured successfully as indicated by a pulsatile blood flow through the cannula. The study was discontinued if arterial puncture was impossible within 180 seconds and patients were classified as “cannulation failure.” Patients then were asked to rate their discomfort, using another standardized phrase, “Please tell us how pleasant or unpleasant the complete procedure was. Please state a number from 0 meaning no discomfort to 10 meaning strongest imaginable discomfort.” In case of an unsuccessful cannulation or a failure to introduce the guidewire at the first cannulation site, patients were asked to rate their discomfort before cannulation was started at an alternative site. Further cannulation attempts at an alternative site were not assessed because this would have led to unblinding of the total procedure. No conversation was allowed during the entire procedure except for the standardized announcements. To avoid bias, all cannulations were performed by the same physician (F.S.) who was in the fourth year of his anesthesia residency.
Study Aim, Outcome Measures, and Statistical Analysis The aim of the study was to test the hypothesis that vapocoolant spray was superior to lidocaine infiltration with respect to discomfort during the whole cannulation procedure (including administration of the topical or local anesthetic) until successful puncture of the artery or termination of the first cannulation attempt. Discomfort was rated on a 0 to 10 numeric rating scale (NRS). Secondary outcome measures were the cannulation failure rate and the time required for performing arterial puncture including preparation of the arterial puncture. Additionally, a rough cost estimate was performed based on current acquisition costs of required material and staff time. For the latter, the authors used exact recordings of the cannulation process of each patient and added average times for the preparation of equipment-based measurements carried out in 10 patients. For average wages, data of a recently published activity-based cost analysis (ABC-analysis) of German hospitals were used.15 The calculation of the study population was based on previous findings that a difference in subjective discomfort of 1.5 on an 11-point NRS was clinically relevant (eg, reduction from 3.5 to 2).16–20 Assuming a standard deviation of 100% of the expected means within the 2 treatment groups, a power of 90% with a type-I error of 5% can be achieved investigating 78 patients per group (156 patients in total). Thus, 2 80 patients per group were planned. Statistical analysis of pain scores and times was performed depending on testing for normal distribution (Shapiro-Wilk-Wtest). Because non-normal distribution of data (p o 0.001 for all comparisons) was revealed, Mann-Whitney’s U-test was used for analyses of all continuous data. Cannulation failure
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VAPOCOOLANT SPRAY VERSUS LIDOCAINE INFILTRATION FOR RADIAL ARTERY CANNULATION
Fig 1.
CONSORT study flow diagram
rates were analyzed using Fisher’s exact test. A p value of 5% was assumed to be statistically significant.
RESULTS
Patient enrollment, allocation, follow-up, and analysis are presented in Figure 1. Of the 160 patients enrolled in the study, 17 (10.6%) patients were not included in the per-protocol analysis (Fig 1).
Study groups did not differ concerning patients’ baseline characteristics (Table 1). Mean pain scores in the vapocoolant group were significantly lower compared with the lidocaine group (difference 1.1 ⫾ 0.33; p ¼ 0.032). Mean pain scores and secondary outcome measures are presented in Table 2. Results of the economic analysis revealed that the total cost decreased by 18% when using vapocoolant compared with lidocaine (Table 3). Table 2. Outcome Measures
Table 1. Demographic Data
Patients Male (n) Female (n) Age (yr)
Lidocaine
Vapocoolant
69 32 (46; 34-59) 37 (54; 41-66) 68 ⫾ 8
74 30 (41; 29-53) 44 (59; 47-71) 67 ⫾ 10
NOTE. Values are number (proportion; 95% confidence interval) or mean ⫾ SD.
NRS Drop-outs Time (s)
Lidocaine
Vapocoolant
p Value
4.5 ⫾ 2.29 11 138 ⫾ 44
3.4 ⫾ 1.58 4 128 ⫾ 44
0.032* 0.06 0.019*
NOTE. Values are number or mean ⫾ SD. Abbreviations: Drop-outs, drop-outs due to puncture failure and time-out; NRS, numeric rating scale; Time, time required for administration of anesthetic and arterial puncture. *Statistically significant.
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RÜSCH ET AL
Table 3. Economic Evaluation of the Arterial Cannulation Procedure Lidocaine
Material 2 pair of sterile gloves Skin disinfection spray 2-mL syringe of 5 mL lidocaine, 1 cannula 27-G Arterial cannulation set Additional cannulation set for second puncture Staff binding time Time for preparation of entire material Time for performing site preparation (i.d. and s.c. lidocaine/vapocoolant spray) Time for cannulation (Table 2) Time for second puncture† Total costs
0.72 € 0.02 € 0.03€, 0.82€, 0.04€
Vapocoolant
8.60 € 11 in 80 patients ¼ 13.8% 8.60 € ¼ 1.19 €
0.72 € 0.02 € 5.80 €: 86 (86 applications per unit) ¼ 0.07 € 8.60 € 4 in 80 patients ¼ 5% 8.60 € ¼ 0.43 €
1.75 min 0.69 €/min* ¼ 1.21 € 0.7 min 1.39 €/min* ¼ 0.97 €
1.20 min 0.69 €/min* ¼ 0.83 € 0.15 min 1.39 €/min* ¼ 0.21 €
2.3 min 2.08 €/min* ¼ 4.78 € 13.8% 4.78 € ¼ 0.66 19.04 €
2.13 min 2.08 €/min* ¼ 4.43 € 5% 4.43 € ¼ 0.22 € 15.53 €
Abbreviations: i.d., intradermal; s.c., subcutaneous. *Average cost for one minute of labor time of an anesthesia nurse (0.69 €/min), a physician (1.39 €/min), or a nurse plus a physician (2.08 €/min) in Germany.15 †Assuming an identical time as for the first attempt.
DISCUSSION
This study was novel in 2 respects. It was the first study that investigated anesthetic effectiveness of vapocoolant spray for radial artery cannulation. Moreover, it was the first trial that examined the overall discomfort from radial artery cannulation caused by application of the local or topical anesthetic and the arterial puncture together. In contrast, previous studies that tested local or topical anesthetics for arterial puncture or radial artery cannulation looked at pain from puncture or cannulation only1,4,5,7 or at pain from administration of the anesthetic and pain from cannulation separately.6,8 The main finding of this study was that mean overall discomfort caused by administration of the anesthetic and arterial puncture was significantly lower in patients who received vapocoolant compared with patients who received lidocaine. Previous studies testing the effectiveness of vapocoolants compared with placebo and control for pain caused by peripheral venous cannulation in adults and children were inconsistent.2,3,9,10,21–23 Accordingly, results of a recently published systematic review of vapocoolants for reducing pain from venipuncture and venous cannulation showed that vapocoolants were ineffective in adults compared with placebo but superior when compared with no treatment. The magnitude of the effect was, however, low (-10 mm on a 100 mm VAS, 95% CI -17 to -4) and even could have been due to a placebo effect according to the authors.12 In addition, studies testing vapocoolant sprays versus lidocaine suggested that lidocaine was more effective to alleviate pain associated with peripheral venous cannulation.3,11 Even though there has not been any study that investigated anesthetic effectiveness of vapocoolant spray compared with placebo or lidocaine infiltration for arterial access, results of this study may appear surprising when extrapolating results of the above-cited studies testing the effectiveness of vapocoolants in reducing pain from peripheral venous cannulation. The following aspects could explain inconsistencies between this study and above-mentioned trials in patients undergoing venous cannulation. First, evidence presented by
the systematic review of vapocoolants for reducing pain from venipuncture and venous cannulation might not be as strong as it appeared when considering heterogeneity of included trials, which varied with respect to cannula size, cannulation site, duration and distance of spray, timing of cannulation following application of spray, sample size, and blinding.12 In fact, cannula size and cannulation site have been shown to have an impact on pain caused by venous cannulation,13,14 suggesting that conclusions from this review have to be drawn cautiously. Second, there was an important difference between previous studies and this trial concerning the methods used to assess the effectiveness of lidocaine infiltration and vapocoolant spray to mitigate discomfort. Whereas all previous trials had study subjects only rate cannulation pain or cannulation pain and pain caused by administration of the local or topical anesthetic separately, participants of this study had to rate the overall discomfort caused by both administration of the anesthetic and the puncture. Administration pain from the local or topical anesthetic is problematic in that it potentially offsets the mitigating effects of the anesthetic during vascular access.24 Accordingly, administration pain is one of the reasons why clinicians do not administer a local anesthetic prior to arterial puncture.25 Different levels of administration pain and pain reduction between vapocoolant spray and lidocaine infiltration make a comparison and evaluation of the overall discomfort mitigating effectiveness very complicated; on the one hand, results from studies of vapocoolant sprays versus lidocaine infiltration for venous cannulation suggested that lidocaine was more effective to mitigate cannulation pain.3,11 In contrast, application pain from lidocaine versus vapocoolant was stronger in patients administered lidocaine.11 In the authors’ opinion, the approach chosen in this trial to have patients rate the overall discomfort of the whole intervention instead of rating administration and puncture separately enabled to assess more precisely the benefit of the anesthetic intervention and to compare results from studies investigating different interventions. Accordingly, it was conceivable that in this trial administration pain outweighed the mitigating effects to a
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VAPOCOOLANT SPRAY VERSUS LIDOCAINE INFILTRATION FOR RADIAL ARTERY CANNULATION
larger extent in patients who received lidocaine than in those who were administered vapocoolant. Despite the statistical significance of the difference in mean discomfort scores between the two study groups (1.1 ⫾ 0.33 on a 0-10 NRS), this improvement may not be clinically relevant. Studies that aimed at determining the amount of change in pain severity, as measured by VAS, that constitutes a minimum clinically significant difference had slightly variable results and ranged from 9 mm to 20 mm.16–20 Thus, the difference observed in this trial was scarcely above the lowest threshold of clinical significance. Cannulation failure rate was one of the secondary outcome parameters based on the concept that the intradermal and subcutaneous lidocaine infiltration could potentially hinder locating the artery to be punctured. The fact that the higher number of patients in the lidocaine group in whom arterial puncture was unsuccessful at the first attempt (due to puncture failure or time) narrowly failed to reach statistical significance and that there were more patients in the lidocaine group in whom arterial puncture was discontinued after 3 minutes (4 v 0) suggested that lidocaine could have a negative impact on arterial puncture success rate. However, such a conclusion was inconsistent with results from previous studies. Giner et al showed that the success rate at first attempt in radial artery puncture for obtaining blood samples was not different between patients who received lidocaine infiltration (65 of 70) compared with patients who did not receive any intervention (63 of 70; Fisher’s exact test would have yielded a p value of 0.76).1 A reason for this inconsistency could have been related to the fact that the volume of local anesthetic used in this trial (0.5 mL) was much higher than the volume (0.2 mL) used by Giner et al. However, a more recent study that compared subcutaneous lidocaine (using the same volume as in this study, 0.5 mL) versus lidocaine/tetracaine topical anesthesia for arterial catheterization, did not find a difference concerning puncture and catheterization either.6 Unfortunately, it was not clear from the methods section of the study by Ruetzler et al to what extent unsuccessful catheterization was attributed to puncture failure or failure to insert the guidewire. The latter was, in the authors’ opinion, not related to the use of a topical or local anesthetic. Therefore, assessment of cannulation success or failure was equated in this study with success or failure to puncture the radial artery. By analogy, overall discomfort caused by cannulation was equated with discomfort experienced until successful/unsuccessful puncture of the artery and time required for cannulation was equated with time required until successful/ unsuccessful puncture of the artery. The mean time required for arterial puncture including preparation time was 10 seconds longer in the lidocaine group. Despite being significant, such a small difference between the groups is irrelevant in clinical practice. However, the small difference between the groups was the result of a study protocol bias. Some of the preparations that are necessary to perform the subcutaneous lidocaine injection (eg, drawing up the local anesthetic) had to be done before time measurement started for the purpose of blinding. Had all the preparations that are necessary to prepare subcutaneous injection of local anesthetic been included in the time measurement, the
difference between the groups would have been much larger. Accordingly, a previous study demonstrated that median administration times differed by more than a minute when comparing subcutaneous lidocaine injection versus vapocoolant spray.11 It could be argued that even such a difference is irrelevant for everyday clinical practice. However, time required for administration of a local anesthetic appeared to be an important aspect; concerning its use as the most frequent justification for its non-use prior to venous cannulation was that it was considered to be too time consuming.26 The authors’ cost analysis (Table 3) demonstrated that the use of vapocoolant spray compared with lidocaine infiltration was associated with a decrease in total cost by approximately 18%, corresponding to about 3.5 € per puncture. Given this was the first study to include a cost analysis concerning the use of lidocaine infiltration compared with vapocoolant spray for arterial puncture results of this study could not be compared to those of others. Therefore, it is even more important to point out that the authors’ results of this cost analysis applied only to the situation in the authors’ hospital. However, it can be used as a template by others to do the math for their own healthcare facility. LIMITATIONS
This study had several limitations. The authors made a considerable effort in order to ensure an unbiased rating by the study subjects. Patients had to turn their heads, preventing them from being able to watch the interventions. In addition, all study subjects were told the same standardized announcement prior to the administration of the intervention. Finally, both interventions were concealed by placebo interventions in the other study group. However, an unexpected painful sensation on top of the cold sensation in patients administered vapocoolant and an unexpected second painful pinprick in the patients of the lidocaine group may have been noticed and thereby caused an unblinded situation. Another element of bias could have been related to the fact that neither vapocoolant nor the disinfectant is odorless. The smell of these sprays is different and, therefore, they can be distinguished. However, the authors assumed that very few people knew what vapocoolants smell like (ie, that they do not smell like evaporating alcohol), which would be a prerequisite for the different smell to be an element of bias. Accordingly, the bias caused by the different odor probably was negligible. Post hoc linear regression analysis between discomfort scores and time required for arterial puncture demonstrated a weak positive association between times needed for cannulation and discomfort scores in patients who were administered vapocoolant spray (r2 ¼ 0.11), whereas no such association could be observed in patients who received lidocaine infiltration (r2 ¼ 0.02). These results suggested that the time between administration of lidocaine and arterial puncture might not have been long enough to allow the lidocaine to take effect. Due to the study protocol, arterial puncture in the lidocaine group had to start immediately after infiltration. Accordingly, higher discomfort scores in the lidocaine group compared with the vapocoolant group may have been in part due to a bias caused by the study protocol. On the other hand, these
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RÜSCH ET AL
results clearly demonstrated that the anesthetic effects of vapocoolants wear off within a few minutes, which might necessitate a second administration of vapocoolant in some patients due to increasing pain sensation. Therefore, a timeout 180 seconds after start of arterial puncture could have caused a protocol bias favoring the vapocoolant group. Interestingly, no patient having received vapocoolant dropped out due to this protocol limitation, turning this protocol bias into a theoretical one.
CONCLUSION
Vapocoolant spray compared with subcutaneous lidocaine injection provided at least similar effectiveness to mitigate discomfort associated with radial artery puncture. Considering a likewise similar cannulation success rate and a less timeconsuming administration, vapocoolant spray represents an alternative to lidocaine infiltration for radial artery puncture and cannulation.
REFERENCES 1. Giner J, Casan P, Belda J, et al: Pain during arterial puncture. Chest 110:1443-1445, 1996 2. Hartstein BH, Barry JD: Mitigation of pain during intravenous catheter placement using a topical skin coolant in the emergency department. Emerg Med J 25:257-261, 2008 3. Armstrong P, Young C, McKeown D: Ethyl chloride and venepuncture pain: A comparison with intradermal lidocaine. Can J Anaesth 37:656-658, 1990 4. Russell GN, Desmond MJ, Fox MA: Local anesthesia for radial artery cannulation: A comparison of a lidocaine-prilocaine emulsion and lidocaine infiltration. J Cardiothorac Anesth 2:309-312, 1988 5. Olday SJ, Walpole R, Wang JY: Radial artery cannulation: Topical amethocaine gel versus lidocaine infiltration. Br J Anaesth 88: 580-582, 2002 6. Ruetzler K, Sima B, Mayer L, et al: Lidocaine/tetracaine patch (Rapydan) for topical anaesthesia before arterial access: A doubleblind, randomized trial. Br J Anaesth 109:790-796, 2012 7. Smith M, Gray BM, Ingram S, et al: Double-blind comparison of topical lignocaine-prilocaine cream (EMLA) and lignocaine infiltration for arterial cannulation in adults. Br J Anaesth 65:240-242, 1990 8. Joly LM, Spaulding C, Monchi M, et al: Topical lidocaineprilocaine cream (EMLA) versus local infiltration anesthesia for radial artery cannulation. Anesth Analg 87:403-406, 1998 9. Selby IR, Bowles BJ: Analgesia for venous cannulation: A comparison of EMLA (5 minutes application), lignocaine, ethyl chloride, and nothing. J R Soc Med 88:264-267, 1995 10. Robinson PA, Carr S, Pearson S, et al: Lignocaine is a better analgesic than either ethyl chloride or nitrous oxide for peripheral intravenous cannulation. Emerg Med Australas 19:427-432, 2007 11. Page DE, Taylor DM: Vapocoolant spray vs subcutaneous lidocaine injection for reducing the pain of intravenous cannulation: a randomized, controlled, clinical trial. Br J Anaesth 105:519-525, 2010 12. Hogan ME, Smart S, Shah V, et al: A systematic review of vapocoolants for reducing pain from venipuncture and venous cannulation in children and adults. J Emerg Med 47:736-749, 2014 13. Harrison N, Langham BT, Bogod DG: Appropriate use of local anaesthetic for venous cannulation. Anaesthesia 47:210-212, 1992
14. Goudra BG, Galvin E, Singh PM, et al: Effect of site selection on pain of intravenous cannula insertion: A prospective randomised study. Indian J Anaesth 58:732-735, 2014 15. Eberhart L, Koch T, Kranke P, et al: Activity-based cost analysis of opioid-related nausea and vomiting among inpatients. J Opioid Manag 10:415-422, 2014 16. Kelly A-M: Does the clinically significant difference in visual analog scale pain scores vary with gender, age, or cause of pain? Acad Emerg Med 5:1086-1090, 1998 17. Gallagher EJ, Liebman M, Bijur PE: Prospective validation of clinically important changes in pain severity measured on a visual analog scale. Ann Emerg Med 38:633-638, 2001 18. Kelly AM: Setting the benchmark for research in the management of acute pain in emergency departments. Emerg Med 13: 57-60, 2001 19. Todd KH, Funk KG, Funk JP, et al: Clinical significance of reported changes in pain severity. Ann Emerg Med 27:485-489, 1996 20. Kelly AM: The minimum clinically significant difference in visual analogue scale pain score does not differ with severity of pain. Emerg Med J 18:205-207, 2001 21. Biro P, Meier T, Cummins AS: Comparison of topical anaesthesia methods for venous cannulation in adults. Eur J Pain 1: 37-42, 1997 22. Costello M, Ramundo M, Christopher NC, et al: Ethyl vinyl chloride vapocoolant spray fails to decrease pain associated with intravenous cannulation in children. Clin Pediatr (Phila) 45:628-632, 2006 23. Farion KJ, Splinter KL, Newhook K, et al: The effect of vapocoolant spray on pain due to intravenous cannulation in children: A randomized controlled trial. CMAJ 179:31-36, 2008 24. Hudson TL, Dukes SF, Reilly K: Use of local anesthesia for arterial punctures. Am J Crit C 15:595-599, 2006 25. Lightowler JV, Elliott MW: Local anaesthetic infiltration prior to arterial puncture for blood gas analysis: A survey of current practice and a randomised double blind placebo controlled trial. J R Coll Physicians Lond 31:645-646, 1997 26. Norris WD: The use of local anaesthesia in peripheral venous cannulation: Current practice of junior doctors. J R Nav Med Serv 88: 62-64, 2002
puncture) was rated on a 0 to 10 numerical rating scale. Puncture failure rate and time required for the intervention also were recorded. Measurements and Main Results: One hundred forty-three patients were included in the per-protocol analysis. Mean pain scores in the vapocoolant group were 3.4 (⫾ 1.58) compared with 4.5 (⫾ 2.29) in the lidocaine group (difference 1.1 ⫾ 0.33; p ¼ 0.032; Mann-Whitney U-test). The higher puncture failure rate in the lidocaine group (n ¼ 11 v 4) was not significant (p ¼ 0.06; Fisher’s exact test). The time required for the intervention was longer in the lidocaine group (138 ⫾ 44 s v 128 ⫾ 44 s; p ¼ 0.019; Mann-Whitney U-test). Conclusions: Vapocoolant spray is an alternative to lidocaine infiltration to mitigate discomfort associated with arterial cannulation. & 2016 Elsevier Inc. All rights reserved.
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their effectiveness. A recent systematic review investigated these inconsistent results and concluded that vapocoolants significantly reduced pain compared with no treatment but not when compared with placebo in adults.12 However, methods of included studies varied greatly concerning variables that have been demonstrated to have an impact on cannulation pain (eg, cannula size and cannulation site).13,14 Thus, conclusions from this systematic review regarding the effectiveness of vapocoolants for venous cannulation have to be drawn cautiously. Therefore, the aim of this clinical trial was to study the efficacy of vapocoolant spray compared with lidocaine infiltration for radial artery cannulation by looking at anesthetic effectiveness, puncture failure rate, time required to puncture the radial artery following administration of the local or topical anesthetic, and the cost associated with both procedures. In this context, the authors hypothesized that vapocoolant spray was superior to lidocaine infiltration concerning its anesthetic effectiveness.
t is common clinical practice to place an arterial catheter before inducing general anesthesia in patients in whom a marked drop in arterial pressure must be avoided, or immediate restoration of blood pressure is mandatory. Even though no studies have investigated pain levels during arterial cannulation without anesthesia, common sense suggests that discomfort during arterial cannulation is at least as high as during arterial puncture for blood sampling or peripheral venous cannulation. Mean pain scores on a 100-mm visual analog scale (VAS) were 30 (⫾ 19)1 in patients who underwent arterial puncture with 22-G cannulae without local or topical anesthesia and ranged from 28 (95% CI 20-36)2 to 38 (⫾ 21)3 in patients undergoing venous cannulation with 18-G to 22-G cannulae without local or topical anesthesia. The most common local anesthetic technique performed for arterial cannulation is local infiltration with lidocaine.4 Several studies have demonstrated that topical anesthesia with lidocaine-prilocaine cream (EMLAs), amethocaine gel, or lidocaine tetracaine patch was at least as effective4-6 or even more effective4,7,8 in mitigating pain associated with arterial cannulation. However, all these topical anesthetics share the disadvantage of taking a minimum of 30 to 60 minutes to be effective, limiting their utility in many clinical situations. Concerns related to the use of lidocaine infiltration include discomfort during application3,6,9-11 and a potentially negative impact on cannulation success due to reduced palpability of the artery. Topical vapocoolant sprays (eg, ethyl chloride and alkane mixtures) could be an alternative in this setting. Their administration is associated with less pain compared with lidocaine,11 and unlike EMLAs, they provide anesthesia immediately after administration. However, studies of topical vapocoolants for reducing pain from arterial puncture and cannulation have not been published yet. Clinical trials of topical vapocoolant sprays for venous cannulation reported inconsistent results regarding
KEY WORDS: local anesthesia, cryoanesthesia, pain, arterial puncture, catheterization, peripheral
METHODS
This prospective, randomized, patient-blinded, controlled study was approved by the ethics committee of the Medical Faculty of Philipps-University of Marburg (committee’s reference number: AZ 103/02) and registered at the German Registry of Clinical Trials (DRKS00010155 on DRKS,
From the Department of Anesthesia and Intensive Care, University Hospital Giessen - Marburg, Marburg Campus, Marburg, Germany. The study was carried out without any external funding. Address reprint requests to Leopold Eberhart, MD, Baldingerstraße, 35043 Marburg, Germany. E-mail: [email protected] © 2016 Elsevier Inc. All rights reserved. 1053-0770/2601-0001$36.00/0 http://dx.doi.org/10.1053/j.jvca.2016.06.008
Journal of Cardiothoracic and Vascular Anesthesia, Vol ], No ] (Month), 2016: pp ]]]–]]]
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searchable at http://apps.who.int/trialsearch/). Patients aged 18 years and older who were scheduled to undergo elective cardiac surgery or carotid endarterectomy were eligible for inclusion in the study. Exclusion criteria were infection at the planned cannulation site, known allergies or intolerances to local anesthetics, and occlusion of the ipsilateral ulnar artery. Patients fulfilling the inclusion criteria received written and verbal information concerning the study no later than a day before planned surgery. All participating subjects provided written consent. An arterial cannulation set (containing a 20-G cannula, a guidewire, a 20-G sheath, a fenestrated drape, and ball swabs; Vyggon, Aachen, Germany), alcoholic disinfectant spray, ball swabs, vapocoolant spray, 0.5 mL of 2% lidocaine drawn up into a syringe, a 27-G needle, 2 pairs of sterile gloves, and dressing material were prepared for each enrolled patient. After arrival of the patient in the anesthesia induction area, electrocardiography, noninvasive blood pressure, and pulse oximetry were applied and an intravenous catheter was inserted at the contralateral side of planned arterial access. The arm in which arterial cannulation was intended to be performed was abducted at an angle of 701 to 901 and the wrist was hyperextended to facilitate palpation and cannulation of the radial artery. Patients were asked to turn their heads away in order to ensure that they were unable to observe the procedure. This was supervised by a study nurse. After identification of the optimal site for cannulation of the radial artery, the overlying skin was disinfected with a swab impregnated with an alcoholbased skin disinfectant solution. Next, the physician put on sterile gloves. At this particular point, a sealed, opaque envelope containing the group allocation used for randomization was opened by the study nurse. Using this method, patients were allocated to 1 of 2 groups equal in size, each containing 80 participants based on a computer-generated randomization list (www.random.org). Following randomized allocation, the physician put on a second pair of sterile gloves, applied the fenestrated drape at the cannulation site and made a standardized announcement, “It will feel cold on your forearm.” Afterward, patients in the lidocaine group received alcoholic disinfectant spray (a mixture of 2-propanol, 1-propanol, and biphenyl-2-ol), while patients in the vapocoolant group received a vapocoolant spray (a mixture of the active ingredients propane, n-butane, and n-pentane, as well as the additional ingredients menthol, camphor, and isopropanol). In the latter group, the skin area was sprayed perpendicularly from a distance of about 5 cm for approximately 2 to 3 seconds until the skin surface turned white in color (caused by freezing of humidity on the skin). Then the next standardized announcement was made by the physician, “Now I will begin with the cannulation.” Arterial cannulation then followed immediately in the vapocoolant group. Patients in the lidocaine group received an intradermal infiltration followed by a subcutaneous injection with a total of 0.5 mL of 2% lidocaine with a 27G needle. Subsequently, the radial artery was cannulated with a 20-G cannula without another explicit announcement. In both groups, the second pair of sterile gloves was taken off before arterial puncture was started. After successful
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puncture of the artery, a 20-G catheter was introduced according to the Seldinger technique. Time measurement of the intervention began when the physician started putting on the second pair of sterile gloves and was stopped once the lumen of the artery was punctured successfully as indicated by a pulsatile blood flow through the cannula. The study was discontinued if arterial puncture was impossible within 180 seconds and patients were classified as “cannulation failure.” Patients then were asked to rate their discomfort, using another standardized phrase, “Please tell us how pleasant or unpleasant the complete procedure was. Please state a number from 0 meaning no discomfort to 10 meaning strongest imaginable discomfort.” In case of an unsuccessful cannulation or a failure to introduce the guidewire at the first cannulation site, patients were asked to rate their discomfort before cannulation was started at an alternative site. Further cannulation attempts at an alternative site were not assessed because this would have led to unblinding of the total procedure. No conversation was allowed during the entire procedure except for the standardized announcements. To avoid bias, all cannulations were performed by the same physician (F.S.) who was in the fourth year of his anesthesia residency.
Study Aim, Outcome Measures, and Statistical Analysis The aim of the study was to test the hypothesis that vapocoolant spray was superior to lidocaine infiltration with respect to discomfort during the whole cannulation procedure (including administration of the topical or local anesthetic) until successful puncture of the artery or termination of the first cannulation attempt. Discomfort was rated on a 0 to 10 numeric rating scale (NRS). Secondary outcome measures were the cannulation failure rate and the time required for performing arterial puncture including preparation of the arterial puncture. Additionally, a rough cost estimate was performed based on current acquisition costs of required material and staff time. For the latter, the authors used exact recordings of the cannulation process of each patient and added average times for the preparation of equipment-based measurements carried out in 10 patients. For average wages, data of a recently published activity-based cost analysis (ABC-analysis) of German hospitals were used.15 The calculation of the study population was based on previous findings that a difference in subjective discomfort of 1.5 on an 11-point NRS was clinically relevant (eg, reduction from 3.5 to 2).16–20 Assuming a standard deviation of 100% of the expected means within the 2 treatment groups, a power of 90% with a type-I error of 5% can be achieved investigating 78 patients per group (156 patients in total). Thus, 2 80 patients per group were planned. Statistical analysis of pain scores and times was performed depending on testing for normal distribution (Shapiro-Wilk-Wtest). Because non-normal distribution of data (p o 0.001 for all comparisons) was revealed, Mann-Whitney’s U-test was used for analyses of all continuous data. Cannulation failure
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VAPOCOOLANT SPRAY VERSUS LIDOCAINE INFILTRATION FOR RADIAL ARTERY CANNULATION
Fig 1.
CONSORT study flow diagram
rates were analyzed using Fisher’s exact test. A p value of 5% was assumed to be statistically significant.
RESULTS
Patient enrollment, allocation, follow-up, and analysis are presented in Figure 1. Of the 160 patients enrolled in the study, 17 (10.6%) patients were not included in the per-protocol analysis (Fig 1).
Study groups did not differ concerning patients’ baseline characteristics (Table 1). Mean pain scores in the vapocoolant group were significantly lower compared with the lidocaine group (difference 1.1 ⫾ 0.33; p ¼ 0.032). Mean pain scores and secondary outcome measures are presented in Table 2. Results of the economic analysis revealed that the total cost decreased by 18% when using vapocoolant compared with lidocaine (Table 3). Table 2. Outcome Measures
Table 1. Demographic Data
Patients Male (n) Female (n) Age (yr)
Lidocaine
Vapocoolant
69 32 (46; 34-59) 37 (54; 41-66) 68 ⫾ 8
74 30 (41; 29-53) 44 (59; 47-71) 67 ⫾ 10
NOTE. Values are number (proportion; 95% confidence interval) or mean ⫾ SD.
NRS Drop-outs Time (s)
Lidocaine
Vapocoolant
p Value
4.5 ⫾ 2.29 11 138 ⫾ 44
3.4 ⫾ 1.58 4 128 ⫾ 44
0.032* 0.06 0.019*
NOTE. Values are number or mean ⫾ SD. Abbreviations: Drop-outs, drop-outs due to puncture failure and time-out; NRS, numeric rating scale; Time, time required for administration of anesthetic and arterial puncture. *Statistically significant.
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Table 3. Economic Evaluation of the Arterial Cannulation Procedure Lidocaine
Material 2 pair of sterile gloves Skin disinfection spray 2-mL syringe of 5 mL lidocaine, 1 cannula 27-G Arterial cannulation set Additional cannulation set for second puncture Staff binding time Time for preparation of entire material Time for performing site preparation (i.d. and s.c. lidocaine/vapocoolant spray) Time for cannulation (Table 2) Time for second puncture† Total costs
0.72 € 0.02 € 0.03€, 0.82€, 0.04€
Vapocoolant
8.60 € 11 in 80 patients ¼ 13.8% 8.60 € ¼ 1.19 €
0.72 € 0.02 € 5.80 €: 86 (86 applications per unit) ¼ 0.07 € 8.60 € 4 in 80 patients ¼ 5% 8.60 € ¼ 0.43 €
1.75 min 0.69 €/min* ¼ 1.21 € 0.7 min 1.39 €/min* ¼ 0.97 €
1.20 min 0.69 €/min* ¼ 0.83 € 0.15 min 1.39 €/min* ¼ 0.21 €
2.3 min 2.08 €/min* ¼ 4.78 € 13.8% 4.78 € ¼ 0.66 19.04 €
2.13 min 2.08 €/min* ¼ 4.43 € 5% 4.43 € ¼ 0.22 € 15.53 €
Abbreviations: i.d., intradermal; s.c., subcutaneous. *Average cost for one minute of labor time of an anesthesia nurse (0.69 €/min), a physician (1.39 €/min), or a nurse plus a physician (2.08 €/min) in Germany.15 †Assuming an identical time as for the first attempt.
DISCUSSION
This study was novel in 2 respects. It was the first study that investigated anesthetic effectiveness of vapocoolant spray for radial artery cannulation. Moreover, it was the first trial that examined the overall discomfort from radial artery cannulation caused by application of the local or topical anesthetic and the arterial puncture together. In contrast, previous studies that tested local or topical anesthetics for arterial puncture or radial artery cannulation looked at pain from puncture or cannulation only1,4,5,7 or at pain from administration of the anesthetic and pain from cannulation separately.6,8 The main finding of this study was that mean overall discomfort caused by administration of the anesthetic and arterial puncture was significantly lower in patients who received vapocoolant compared with patients who received lidocaine. Previous studies testing the effectiveness of vapocoolants compared with placebo and control for pain caused by peripheral venous cannulation in adults and children were inconsistent.2,3,9,10,21–23 Accordingly, results of a recently published systematic review of vapocoolants for reducing pain from venipuncture and venous cannulation showed that vapocoolants were ineffective in adults compared with placebo but superior when compared with no treatment. The magnitude of the effect was, however, low (-10 mm on a 100 mm VAS, 95% CI -17 to -4) and even could have been due to a placebo effect according to the authors.12 In addition, studies testing vapocoolant sprays versus lidocaine suggested that lidocaine was more effective to alleviate pain associated with peripheral venous cannulation.3,11 Even though there has not been any study that investigated anesthetic effectiveness of vapocoolant spray compared with placebo or lidocaine infiltration for arterial access, results of this study may appear surprising when extrapolating results of the above-cited studies testing the effectiveness of vapocoolants in reducing pain from peripheral venous cannulation. The following aspects could explain inconsistencies between this study and above-mentioned trials in patients undergoing venous cannulation. First, evidence presented by
the systematic review of vapocoolants for reducing pain from venipuncture and venous cannulation might not be as strong as it appeared when considering heterogeneity of included trials, which varied with respect to cannula size, cannulation site, duration and distance of spray, timing of cannulation following application of spray, sample size, and blinding.12 In fact, cannula size and cannulation site have been shown to have an impact on pain caused by venous cannulation,13,14 suggesting that conclusions from this review have to be drawn cautiously. Second, there was an important difference between previous studies and this trial concerning the methods used to assess the effectiveness of lidocaine infiltration and vapocoolant spray to mitigate discomfort. Whereas all previous trials had study subjects only rate cannulation pain or cannulation pain and pain caused by administration of the local or topical anesthetic separately, participants of this study had to rate the overall discomfort caused by both administration of the anesthetic and the puncture. Administration pain from the local or topical anesthetic is problematic in that it potentially offsets the mitigating effects of the anesthetic during vascular access.24 Accordingly, administration pain is one of the reasons why clinicians do not administer a local anesthetic prior to arterial puncture.25 Different levels of administration pain and pain reduction between vapocoolant spray and lidocaine infiltration make a comparison and evaluation of the overall discomfort mitigating effectiveness very complicated; on the one hand, results from studies of vapocoolant sprays versus lidocaine infiltration for venous cannulation suggested that lidocaine was more effective to mitigate cannulation pain.3,11 In contrast, application pain from lidocaine versus vapocoolant was stronger in patients administered lidocaine.11 In the authors’ opinion, the approach chosen in this trial to have patients rate the overall discomfort of the whole intervention instead of rating administration and puncture separately enabled to assess more precisely the benefit of the anesthetic intervention and to compare results from studies investigating different interventions. Accordingly, it was conceivable that in this trial administration pain outweighed the mitigating effects to a
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larger extent in patients who received lidocaine than in those who were administered vapocoolant. Despite the statistical significance of the difference in mean discomfort scores between the two study groups (1.1 ⫾ 0.33 on a 0-10 NRS), this improvement may not be clinically relevant. Studies that aimed at determining the amount of change in pain severity, as measured by VAS, that constitutes a minimum clinically significant difference had slightly variable results and ranged from 9 mm to 20 mm.16–20 Thus, the difference observed in this trial was scarcely above the lowest threshold of clinical significance. Cannulation failure rate was one of the secondary outcome parameters based on the concept that the intradermal and subcutaneous lidocaine infiltration could potentially hinder locating the artery to be punctured. The fact that the higher number of patients in the lidocaine group in whom arterial puncture was unsuccessful at the first attempt (due to puncture failure or time) narrowly failed to reach statistical significance and that there were more patients in the lidocaine group in whom arterial puncture was discontinued after 3 minutes (4 v 0) suggested that lidocaine could have a negative impact on arterial puncture success rate. However, such a conclusion was inconsistent with results from previous studies. Giner et al showed that the success rate at first attempt in radial artery puncture for obtaining blood samples was not different between patients who received lidocaine infiltration (65 of 70) compared with patients who did not receive any intervention (63 of 70; Fisher’s exact test would have yielded a p value of 0.76).1 A reason for this inconsistency could have been related to the fact that the volume of local anesthetic used in this trial (0.5 mL) was much higher than the volume (0.2 mL) used by Giner et al. However, a more recent study that compared subcutaneous lidocaine (using the same volume as in this study, 0.5 mL) versus lidocaine/tetracaine topical anesthesia for arterial catheterization, did not find a difference concerning puncture and catheterization either.6 Unfortunately, it was not clear from the methods section of the study by Ruetzler et al to what extent unsuccessful catheterization was attributed to puncture failure or failure to insert the guidewire. The latter was, in the authors’ opinion, not related to the use of a topical or local anesthetic. Therefore, assessment of cannulation success or failure was equated in this study with success or failure to puncture the radial artery. By analogy, overall discomfort caused by cannulation was equated with discomfort experienced until successful/unsuccessful puncture of the artery and time required for cannulation was equated with time required until successful/ unsuccessful puncture of the artery. The mean time required for arterial puncture including preparation time was 10 seconds longer in the lidocaine group. Despite being significant, such a small difference between the groups is irrelevant in clinical practice. However, the small difference between the groups was the result of a study protocol bias. Some of the preparations that are necessary to perform the subcutaneous lidocaine injection (eg, drawing up the local anesthetic) had to be done before time measurement started for the purpose of blinding. Had all the preparations that are necessary to prepare subcutaneous injection of local anesthetic been included in the time measurement, the
difference between the groups would have been much larger. Accordingly, a previous study demonstrated that median administration times differed by more than a minute when comparing subcutaneous lidocaine injection versus vapocoolant spray.11 It could be argued that even such a difference is irrelevant for everyday clinical practice. However, time required for administration of a local anesthetic appeared to be an important aspect; concerning its use as the most frequent justification for its non-use prior to venous cannulation was that it was considered to be too time consuming.26 The authors’ cost analysis (Table 3) demonstrated that the use of vapocoolant spray compared with lidocaine infiltration was associated with a decrease in total cost by approximately 18%, corresponding to about 3.5 € per puncture. Given this was the first study to include a cost analysis concerning the use of lidocaine infiltration compared with vapocoolant spray for arterial puncture results of this study could not be compared to those of others. Therefore, it is even more important to point out that the authors’ results of this cost analysis applied only to the situation in the authors’ hospital. However, it can be used as a template by others to do the math for their own healthcare facility. LIMITATIONS
This study had several limitations. The authors made a considerable effort in order to ensure an unbiased rating by the study subjects. Patients had to turn their heads, preventing them from being able to watch the interventions. In addition, all study subjects were told the same standardized announcement prior to the administration of the intervention. Finally, both interventions were concealed by placebo interventions in the other study group. However, an unexpected painful sensation on top of the cold sensation in patients administered vapocoolant and an unexpected second painful pinprick in the patients of the lidocaine group may have been noticed and thereby caused an unblinded situation. Another element of bias could have been related to the fact that neither vapocoolant nor the disinfectant is odorless. The smell of these sprays is different and, therefore, they can be distinguished. However, the authors assumed that very few people knew what vapocoolants smell like (ie, that they do not smell like evaporating alcohol), which would be a prerequisite for the different smell to be an element of bias. Accordingly, the bias caused by the different odor probably was negligible. Post hoc linear regression analysis between discomfort scores and time required for arterial puncture demonstrated a weak positive association between times needed for cannulation and discomfort scores in patients who were administered vapocoolant spray (r2 ¼ 0.11), whereas no such association could be observed in patients who received lidocaine infiltration (r2 ¼ 0.02). These results suggested that the time between administration of lidocaine and arterial puncture might not have been long enough to allow the lidocaine to take effect. Due to the study protocol, arterial puncture in the lidocaine group had to start immediately after infiltration. Accordingly, higher discomfort scores in the lidocaine group compared with the vapocoolant group may have been in part due to a bias caused by the study protocol. On the other hand, these
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results clearly demonstrated that the anesthetic effects of vapocoolants wear off within a few minutes, which might necessitate a second administration of vapocoolant in some patients due to increasing pain sensation. Therefore, a timeout 180 seconds after start of arterial puncture could have caused a protocol bias favoring the vapocoolant group. Interestingly, no patient having received vapocoolant dropped out due to this protocol limitation, turning this protocol bias into a theoretical one.
CONCLUSION
Vapocoolant spray compared with subcutaneous lidocaine injection provided at least similar effectiveness to mitigate discomfort associated with radial artery puncture. Considering a likewise similar cannulation success rate and a less timeconsuming administration, vapocoolant spray represents an alternative to lidocaine infiltration for radial artery puncture and cannulation.
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14. Goudra BG, Galvin E, Singh PM, et al: Effect of site selection on pain of intravenous cannula insertion: A prospective randomised study. Indian J Anaesth 58:732-735, 2014 15. Eberhart L, Koch T, Kranke P, et al: Activity-based cost analysis of opioid-related nausea and vomiting among inpatients. J Opioid Manag 10:415-422, 2014 16. Kelly A-M: Does the clinically significant difference in visual analog scale pain scores vary with gender, age, or cause of pain? Acad Emerg Med 5:1086-1090, 1998 17. Gallagher EJ, Liebman M, Bijur PE: Prospective validation of clinically important changes in pain severity measured on a visual analog scale. Ann Emerg Med 38:633-638, 2001 18. Kelly AM: Setting the benchmark for research in the management of acute pain in emergency departments. Emerg Med 13: 57-60, 2001 19. Todd KH, Funk KG, Funk JP, et al: Clinical significance of reported changes in pain severity. Ann Emerg Med 27:485-489, 1996 20. Kelly AM: The minimum clinically significant difference in visual analogue scale pain score does not differ with severity of pain. Emerg Med J 18:205-207, 2001 21. Biro P, Meier T, Cummins AS: Comparison of topical anaesthesia methods for venous cannulation in adults. Eur J Pain 1: 37-42, 1997 22. Costello M, Ramundo M, Christopher NC, et al: Ethyl vinyl chloride vapocoolant spray fails to decrease pain associated with intravenous cannulation in children. Clin Pediatr (Phila) 45:628-632, 2006 23. Farion KJ, Splinter KL, Newhook K, et al: The effect of vapocoolant spray on pain due to intravenous cannulation in children: A randomized controlled trial. CMAJ 179:31-36, 2008 24. Hudson TL, Dukes SF, Reilly K: Use of local anesthesia for arterial punctures. Am J Crit C 15:595-599, 2006 25. Lightowler JV, Elliott MW: Local anaesthetic infiltration prior to arterial puncture for blood gas analysis: A survey of current practice and a randomised double blind placebo controlled trial. J R Coll Physicians Lond 31:645-646, 1997 26. Norris WD: The use of local anaesthesia in peripheral venous cannulation: Current practice of junior doctors. J R Nav Med Serv 88: 62-64, 2002