Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, V5A 1S6, Canada.
Research and Clinical Innovation, Royal Centre for Defence Medicine, Birmingham, UK.
Clin Auton Res. 2023 Dec;33(6):673-689. doi: 10.1007/s10286-023-00972-8. Epub 2023 Aug 17.
Vasovagal syncope (VVS), or fainting, is frequently triggered by pain, fear, or emotional distress, especially with blood-injection-injury stimuli. We aimed to examine the impact of intravenous (IV) instrumentation on orthostatic tolerance (OT; fainting susceptibility) in healthy young adults. We hypothesized that pain associated with IV procedures would reduce OT.
In this randomised, double-blind, placebo-controlled, cross-over study, participants (N = 23; 14 women; age 24.2 ± 4.4 years) underwent head-up tilt with combined lower body negative pressure to presyncope on three separate days: (1) IV cannulation with local anaesthetic cream (EMLA) (IV + EMLA); (2) IV cannulation with placebo cream (IV + Placebo); (3) sham IV cannulation with local anaesthetic cream (Sham + EMLA). Participants rated pain associated with IV procedures on a 1-5 scale. Cardiovascular (finger plethysmography and electrocardiogram; Finometer Pro), and forearm vascular resistance (FVR; brachial Doppler) responses were recorded continuously and non-invasively.
Compared to Sham + EMLA (27.8 ± 2.4 min), OT was reduced in IV + Placebo (23.0 ± 2.8 min; p = 0.026), but not in IV + EMLA (26.2 ± 2.2 min; p = 0.185). Pain was increased in IV + Placebo (2.8 ± 0.2) compared to IV + EMLA (2.0 ± 2.2; p = 0.002) and Sham + EMLA (1.1 ± 0.1; p < 0.001). Orthostatic heart rate responses were lower in IV + Placebo (84.4 ± 3.1 bpm) than IV + EMLA (87.3 ± 3.1 bpm; p = 0.007) and Sham + EMLA (87.7 ± 3.1 bpm; p = 0.001). Maximal FVR responses were reduced in IV + Placebo (+ 140.7 ± 19.0%) compared to IV + EMLA (+ 221.2 ± 25.9%; p < 0.001) and Sham + EMLA (+ 190.6 ± 17.0%; p = 0.017).
Pain plays a key role in predisposing to VVS following venipuncture, and our data suggest this effect is mediated through reduced capacity to achieve maximal sympathetic activation during orthostatic stress. Topical anaesthetics, such as EMLA, may reduce the frequency and severity of VVS during procedures requiring needles and intravascular instrumentation.
血管迷走神经性晕厥（VVS），又称晕厥，常由疼痛、恐惧或情绪困扰引发，尤其是与血液-注射-损伤刺激有关。我们旨在研究静脉（IV）操作对健康年轻成年人直立耐受力（OT；晕厥易感性）的影响。我们假设与 IV 程序相关的疼痛会降低 OT。
在这项随机、双盲、安慰剂对照、交叉研究中，参与者（N=23；14 名女性；年龄 24.2±4.4 岁）在 3 天内分别接受三种不同的头高位倾斜合并下体负压至预晕厥：（1）用局部麻醉乳膏（EMLA）进行 IV 插管（IV+EMLA）；（2）用安慰剂乳膏进行 IV 插管（IV+安慰剂）；（3）用局部麻醉乳膏进行假 IV 插管（Sham+EMLA）。参与者使用 1-5 级量表对与 IV 程序相关的疼痛进行评分。心血管（手指容积描记法和心电图；Finometer Pro）和前臂血管阻力（FVR；肱动脉多普勒）反应连续无创记录。
与 Sham+EMLA（27.8±2.4 分钟）相比，IV+安慰剂（23.0±2.8 分钟；p=0.026）的 OT 降低，但 IV+EMLA 组（26.2±2.2 分钟；p=0.185）未降低。与 IV+EMLA（2.0±2.2）和 Sham+EMLA（1.1±0.1）相比，IV+安慰剂（2.8±0.2）的疼痛增加（p=0.002 和 p<0.001）。与 IV+EMLA（87.3±3.1 bpm）和 Sham+EMLA（87.7±3.1 bpm）相比，IV+安慰剂（84.4±3.1 bpm）的直立心率反应更低（p=0.007 和 p=0.001）。与 IV+EMLA（+221.2±25.9%）和 Sham+EMLA（+190.6±17.0%）相比，IV+安慰剂（+140.7±19.0%）的最大 FVR 反应降低（p<0.001 和 p=0.017）。
疼痛在静脉穿刺后引发 VVS 中起着关键作用，我们的数据表明，这种效应是通过在直立应激时降低达到最大交感神经激活的能力介导的。局部麻醉剂，如 EMLA，可能会减少需要针和血管内仪器的操作过程中 VVS 的频率和严重程度。
