Brachial plexus block (BPB) can lead to vasodilatation and increased blood flow in the ipsilateral arm,1 which could be beneficial for vascular re-construction2 and severe forearm ischaemia.3 However, it is not known which specific nerves among the musculocutaneous, radial, ulnar and median nerves innervate the radial and ulnar arteries. We therefore conducted a randomised controlled trial to identify which nerve block would lead to an increase in blood flow through the radial and ulnar arteries.
This double-blind randomised controlled study was approved by the Institutional Review Board of the Second Affiliated Hospital and Yuying Children Hospital of Wenzhou Medical University, 109 Xueyuang xi Road, Wenzhou, China [Ref 2009(002), 2 February 2009, Chairman Professor Qinquan Lian] and was registered at Clinicaltrials.gov with the identifier NCT02139982 on 28 May 2014.
Between March and December 2012, patients undergoing upper limb surgery were screened for inclusion in the trial. Informed consent was obtained from each patient included in the study. Eligible patients were randomly assigned to one of four groups according to selective nerve blockade (SNB) of the brachial plexus [Group MC (musculocutaneous), Group UL (ulnar), Group RA (radial) and Group ME (median)] using computer-generated (Microsoft Excel 2010) random numbers placed in sealed envelopes.
Patients received a selective nerve block (MC, UL, RA or ME) in the axillary region using ultrasound combined with neurostimulation, and 5 ml of ropivacaine 0.5% (Naropin, Astra-Zeneca, Sweden) were injected. Thirty minutes after SNB, when all study data had been captured, all patients receive scheduled axillary BPB for surgery; the other three nerves of the axillary brachial plexus were blocked with the same method of SNB. A separate study investigator, blinded to the protocol and patient allocation, completed the haemodynamic measurements at all-time points: before insertion of blockade (baseline, T0), 30 min after SNB (T2) and 30 min after the entire brachial plexus had been blocked (T3). Time-averaged maximum velocity (TAMAX) and cross-sectional area (CSA) of the ulnar and radial artery were measured 1 cm proximal to the ulnar or radial styloid process using Pulsed-wave Doppler ultrasound and B-mode imaging (DC-6, Mindray Medical International Limited, China). Blood flow (BF) was calculated from the formula BF = TAMAX × CSA × 60. The relative change in regional blood flow was calculated from the formula ΔBF = (BFT1−BFT0)/(BFT2−BFT0).
Our pilot study that showed the mean ± SD radial and ulnar artery blood flow increased three-fold (from 33.3 ± 19.5 to 102.1 ± 54.5 ml min−1) when measured 30 min after SNB or BPB. We estimated that six patients in each group would give the study a power of 80% (P < 0.05). Data are presented as mean ± SD or median (Inter-Quartile Range). Results were compared using Kruskal-Wallis H nonparametric test for relative change in regional blood flow among different groups and repeated measures analysis for the measurements at different time points. Statistical significance was defined as P < 0.05.
Seventy six patients were screened, 35 patients were eligible and three patients did not give informed consent. Consequently, 32 patients were included in the study. Relative changes in regional blood flow are shown in Fig. 1. The greatest relative change of blood flow through the radial artery occurred in Group ME (P < 0.05). The changes in Group RA were less (P < 0.05) and there were no significant changes in Groups MC or UL. Relative change of blood flow through the ulnar artery in Group UL was greater than in the other three groups (P < 0.05); there were no significant changes in groups MC, ME or RA. In summary, median nerve block resulted in a greater increase in blood flow through the radial artery than did radial nerve block, and only ulnar nerve block increased blood flow through the ulnar artery (Fig. 1).
Our study data showed that only the median nerve block resulted in a significant increase of the CSA of the radial artery and only the ulnar nerve block resulted in increased CSA of the ulnar artery, indicating that the radial artery may be innervated by only the median nerve, whereas the ulnar artery is innervated only by the ulnar nerve. Previous anatomical studies in the forearm demonstrated that the radial artery receives branches from the median nerve,4 superficial branch of the radial nerve or lateral antebrachial cutaneous5 nerve and that the ulnar artery receives a branch of the ulnar nerve.4 However, a study by Lange et al.6 measured the temperature of skin after SNB and reached the same conclusion as ours. The exact pathway of sympathetic innervation to the radial artery remains unclear and further research is required. Blocking the median or ulnar nerve specifically may be beneficial for micro-vascular surgery to produce vasodilatation and increased blood flow.
The limitations of our study are that maximum haemodynamic effects of SNB may not be achieved 30 min after SNB or BPB, and we do not know whether SNB causes a slight effect on the sympathetic fibres of neighbouring nerves.
In conclusion, selective ulnar and median nerve block resulted in arterial vasodilatation, an increase in blood flow velocity and blood flow through the ulnar artery and radial artery, respectively. Selective radial nerve block resulted in only a slight increase in blood flow through the radial artery. Selective musculocutaneous nerve block did not change the haemodynamics of either artery.
Acknowledgements relating to this article
Assistance with the study: we would like to thank Professor Weiyang Gao, Head of Hand Surgery, for designing this study.
Financial support and sponsorship: this work was funded by the Health and Family Planning Commission of Zhejiang Province, China, Grant No. 2009A145 and The Recruitment Program of Global Experts, China.
Conflict of interest: none.
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