Combined superficial peroneal and saphenous nerve block for ascending venography

0 1992 Elsevier Science Publishers

56

EURRAD

European Journal of Radiology, 14 (1992) 56-59 B.V. All rights reserved. 0720-048X/92/$05.00

00203

Combined superficial peroneal and saphenous nerve block for ascending venograpby Stavros Mussurakis Department of DiagnosticRadiology,HippokrationGeneral Hospital,Athens. Greece (Received

Key words: Venography,

1 May 1991; accepted after revision 4 June 1991)

regional anaesthesia;

Nerve block, peroneal nerve; Nerve block, saphenous

nerve

Abstract

Needle insertions into the veins of the dorsum of the foot are an overlooked source of pain and discomfort during ascending venography. As a solution to this problem a regional anaesthetic technique is presented, the combined superficial peroneal and saphenous nerve block, after being studied prospectively on 42 patients referred for bilateral venography. The nerve blocks were always performed unilaterally. At the end of each bilateral study patients were asked to express a preference for one of the two venograms, on the basis of pain and discomfort from the needle insertions. Ofthe 42 patients, 27 (64.3 %) opted for venography with regional anaesthesia, 9 (21.4%) for venography without regional anaesthesia, while 6 (14.3%) did not state a definite preference. As shown by the sign test, preference for venography with regional anaesthesia was highly significant. By observing the reactions of the patients during the needle insertions, the radiologist classified arbitrarily the pain produced in each individual venogram as minimal, moderate or severe. The statistical significance of these observations was verified with the chi-squared test for trend and the sign test. In addition to diminishing effectively the pain from the venography needle, this simple technique proved to be safe and causing negligible discomfort. It is recommended for all patients who are apprehensive or have already experienced considerable pain on a first unsuccessful venipuncture attempt, or when multiple punctures are expected because of lack of suitable veins or presence of oedema.

Introduction

Methods

Ascending venography, the ‘gold standard’ in the diagnosis of venous pathology of the lower extremities, has well-documented inherent disadvantages. Concern focuses on specific phlebographic complications, that is, the pain in the calf during the injection of contrast medium, the consequences of contrast extravasation and the induction of thrombosis. Meanwhile, another source of potentially considerable pain and discomfort to the patient is totally ignored. Introduction of a needle into a vein of the dorsum of the foot can sometimes prove among the most painful needle insertions performed in radiology. As a solution to this problem a regional anaesthetic technique is presented, the combined superficial peroneal and saphenous nerve block for use in ascending venography.

During a two-year period, 42 patients originally referred for bilateral ascending venography were included in the study. There were 19 men and 23 women, with a mean age of 58 years (age range: 21-84 years). Informed consent was obtained from all patients. Regional anaesthesia was always performed unilaterally, after selecting randomly the extremity to be examined first and the foot to be anaesthetized. As a local anaesthetic, lignocaine solution 1 y0 without adrenaline was used, in 10 ml syringes fitted with 27-gauge needles. Throughout the blocking procedure the patients were in the supine position and, therefore, unable to see which foot was actually blocked. To ensure single-blinding and eliminate response bias even further, patients were not informed whether none, one or both feet were about to be blocked. Although they were notified when consented that local anaesthesia might be applied during the procedure, neither the exact

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Mussurakis,

M.D.,

185 Bellhagg

details of the anaesthetic technique nor the sites of infiltration were revealed to them. The minimal discomfort caused by the very fine 27 G needles helped notably in reaching the required degree of singleblinding. For the superficial peroneal nerve block, the puncture was performed about 6 cm above the tip of the lateral malleolus, 2 cm lateral to the palpable anterior border of the tibia. A volume of 5-10 ml of local anaesthetic solution was infiltrated subcutaneously, from the anterior midpoint of the leg to the superior aspect of the lateral malleolus. A double needle passage with slow continuous infiltration was sufficient. To block the saphenous nerve, a small skin wheal was raised immediately above and anterior to the medial malleolus, and 3-5 ml of local anaesthetic were infiltrated subcutaneously around the great saphenous vein. In this location aspiration was essential to avoid inadvertent intravenous injection. The entire blocking procedure never required more than a few minutes and then venography was carried out, using for the venipuncture either a 23-gauge butterfly-type needle or a 22-gauge intravenous cannula, but never both on the same patient. At the end of each bilateral study patients were asked to express a preference for one of the two venograms, on the basis of pain and discomfort from the needle insertions. By decoding the answers a series of three choices was formed, i.e., venography with or without regional anaesthesia, or no particular preference. The findings were evaluated with the sign test. In addition, by observing the patient reactions during the needle insertion(s), the radiologist classified arbitrarily the pain produced in each individual venogram as minimal, moderate or severe. These observations were analysed with the chi-squared test for trend and the sign test. Results Of the 42 patients, 27 (64.3 %) opted for venography with regional anaesthesia, 9 (21.4%) for venography without regional anaesthesia, while 6 (14.3%) were unwilling to state a specific preference. A well-suited method of analysis is the sign test. After the continuity correction, the standardized normal deviate is z = 2.83. There is little doubt that patients favoured venography with regional anaesthesia (P = 0.0047). The difference between the proportions of definite preferences is 42.9% (95% confidence limits: 16.8x-68.92). The results from the radiologist’s subjective estimation of the severity of pain are shown in Table 1. The columns of the table correspond to different categories of a qualitative variable, i.e., the severity of pain, which

TABLE 1 Classification of the severity of pain produced by the insertion(s) of the needle during each individual venogram, according to the subjective estimation ofthe radiologist, for the examinations performed with and without regional anaesthesia. Magnitude

of pain

minimal

moderate

Venography with regional anaesthesia

29

10

3

42

Venography without regional anaesthesia

12

22

8

42

Total

41

32

11

84

severe

total

can be ordered but not readily assigned a numerical value. An appropriate method for the analysis of these data is the chi-squared test for trend. The equally spaced scores of 1,2 and 3 are assigned to the severity of pain, producing a xtrend = 11.72 on one D.F. (P = 0.0006). Alternatively, since data from the classification of pain come from matched pairs of observations on the same subjects, the sign test may be used. Once more, scores of 1, 2 and 3 are assigned to the severity of pain and the standardized normal deviate, after the continuity correction, is now, z = 3.23 (P = 0.0012). Finally, it should be noted that none of the patients had any complications related to the blocking procedure. Discussion The major obstacle to the wider acceptance of venography in clinical practice has been the invasive nature of the procedure. An overlooked source of potentially substantial, if brief, pain and discomfort to the patient is the insertion of the venography needle. There are several reasons justifying this pain [ 11. The skin of the dorsum ofthe foot can be thick and relatively impenetrable. To enter a superficial vein, the needle has to follow a long parallel course through the richly innervated subcutaneous tissues. Multiple punctures are often necessary, as here veins tend to be thin, fragile and hard to locate, while they may be completely obscured by acute or chronic oedema. On the other hand, neither local anaesthesia nor sedation is used in ascending venography as in other angiographic procedures. The solution to this problem may be found in regional anaesthetic techniques. A nerve block involves the extraneural injection of local anaesthetic at some point in the course of the

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nerve [ 21. The solution reaches the nerve by diffusion and loss of sensation results in the region supplied by the branches distal to the infiltration site. Nerve blocks in the foot and ankle are long-established, though not widely practised regional anaesthetic techniques [ 3-61. Apart from the study of Lieberman and Kaplan [ 11, they are nothing short of unknown to radiologists. In the present study, the combined superficial peroneal and saphenous nerve block diminished effectively or even eliminated the pain from the venography needle. This simple technique proved to be safe, caused negligible discomfort and did not anaesthetize the plantar surface of the foot or create motor deficiency. Virtually complete anaesthesia of the skin of the dorsum of the foot was achieved and it was not necessary to block the sural or the deep peroneal nerve, as most of the dorsum of the foot and toes is innervated by the superficial peroneal nerve. The saphenous and sural nerves supply the medial and lateral aspects of the foot respectively, while the deep peroneal nerve supplies only the first interdigital cleft [7,8]. There is a degree of overlapping in the distributions of cutaneous nerves. As a result, while blocking a nerve produces complete anaesthesia at the centre of its territory, reduced sensation may remain at the periphery. This difficult to define overlap has led us to modify the superficial peroneal nerve block described by Lieberman and Kaplan [ 11, by combining it with the saphenous nerve block. The modification appears to be well justified, since the vessels which are the most suitable for venography, that is, the dorsomedial vein of the great toe and the group of parallel superficial veins crossing the medial border of the foot, all lie in the transition area innervated by both superficial peroneal and saphenous branches [7,8]. As far as the validity of the results is concerned, sufficient precautions were taken to avoid the introduction of significant bias in the study. The duration of the trial was decided in advance, on the basis of the typical rate of referrals for bilateral venograms in the department. The adopted study design, the within group (paired) comparisons, is very powerful statistically as it has all the advantages of the cross-over design but none of the disadvantages. Double-blinding was not feasible, as it would be impossible to keep the radiologist performing the venograms and assessing the severity of pain produced by the needle insertions in ignorance of the blocking procedure. The total number of venipuncture attempts before a successful cannulation could be achieved, the occurrence of contrast extravasation with the consequent need for a new cannulation and the presence of oedema were undoubtedly sources of considerable variation. Randomization,

however, should have eliminated the effects of variability of this type. Other methods of regional anaesthesia also exist, though they are not suitable for venography. Field blocks take advantage of the subcutaneous course of somatosensory branches. The region of interest is encircled with local anaesthetic, the solution being distributed subcutaneously where the nerves pass before they ramify [ 21. No attempt is made to anaesthetize individual nerves. In venography, the easiest way to achieve a field block would be to surround the ankle with a ring of local anaesthetic at the level of the malleoli, yet this would be too distressing for the patient and time-consuming for the radiologist. Another method would be to inject a wheal of local anaesthetic solution over the vein selected for puncture, but even a tiny skin wheal can obscure the vein, while a new wheal is required for every puncture attempted at a different site [I]. When the needle touches a sensory nerve, a paraesthesia in the nerve distribution occurs, a manoeuvre that is occasionally used in regional anaesthesia for tracing nerves. This technique is not to be recommended, since intraneural injections are painful, may cause frank nerve damage and are often followed by prolonged neuralgia. Acute, shooting type pain referred to the distribution of the nerve being blocked indicates intraneural position of the needle and the injection should be stopped immediately. Moreover, because of the anaesthesia, the patient may not feel an extravasation of the contrast medium and the radiologist must observe the venipuncture site carefully throughout the contrast injection. The primary objection should be whether the technique is in fact necessary. After all, venography is considered a minor angiographic procedure, and the nerve blocks demand additional, if small, intervention. Nevertheless, rather than advocate routine use of the technique, it is recommended that it be reserved for those patients who are apprehensive or have already experienced considerable pain on a first unsuccessful venipuncture attempt, and for those instances where multiple punctures are expected because of lack of suitable veins or presence of oedema. Under these circumstances, the addition of regional anaesthesia can make ascending venography more acceptable to patient and radiologist alike. References 1 Lieberman RP, Kaplan PA. Superficial peroneal nerve block for leg venography. Radiology 1987; 165: 578-579 2 Adriani J (ed). Labat’s regional anaesthesia. Techniques and

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clinical applications. Philadelphia: W.B.Saunders Company, 1967: 54-76 Lofstrom B. Nerve block at the ankle. In: Eriksson E, ed. Illustrated handbook in local anaesthesia. London: Lloyd-Luke (Medical Books) Ltd., 1979: 112-115 Bridenbaugh PO. The lower extremity: Somatic blockade. In: Cousins MJ, Bridenbaugh PO, eds. Neural blockade in clinical anaesthesia and management of pain. Philadelphia: J.B.Lippincott Company, 1980: 335-339

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Raj P, Pai U. Techniques of nerve blocking. In: Raj P, ed. Handbook of regional anesthesia. New York: Churchill Livingstone, 1985: 198-202 Scott DB. Techniques of regional anaesthesia. Norwalk, Connecticut: Appleton & Lange/Mediglobe, 1989: 134-141 Sarrafian SK. Anatomy of the foot and ankle. Philadelphia: J.B.Lippincott Company, 1983: 313-332 Williams PL, Warwick R, Dyson M, Bannister LH (eds). Gray’s anatomy. Edinburgh: Churchill Livingstone, 1989: 1140-1153