Peribulbar versus Retrobulbar Anesthesia forOphthalmic Surgery
An Anatomical Comparison of Extraconal and Intraconal InjectionsJacques Ripart, M.D., Ph.D.,* Jean-Yves Lefrant, M.D., Ph.D.,† Jean-Emmanuel de La Coussaye, M.D., Ph.D.,‡Dominique Prat-Pradal, M.D., Ph.D.,§ Bruno Vivien, M.D.,i Jean-Jacques Eledjam, M.D.#
Background: Peribulbar and retrobulbar anesthesia havelong been opposed on the basis of the existence of an intermus-cular membrane, which is supposed to separate the intraconalfrom the extraconal spaces in a water-tight fashion. A localanesthetic injected outside the cone should spread through thisseptum to reach the nerves to be blocked. The existence of thisseptum is questioned. The aim of this study was to compare thespread of a colored latex dye injected intraconally or extraco-nally to simulate both retrobulbar and peribulbar anesthesia.
Methods: The authors used 10 heads from human cadavers.For each head, one eye was injected intraconally, and the othereye was injected extraconally. The heads were then frozen andsectioned into thin slices following various planes. They werethen photographed and observed.
Results: There was no evidence of the existence of an inter-muscular septum separating the intraconal and extraconalspaces. Those two spaces appeared to be part of a commonspreading space, the corpus adiposum of the orbit.
Conclusions: These results are in accord with the fact thatclinical studies were not able to clearly demonstrate that retro-bulbar anesthesia is more efficient than peribulbar anesthesia.On the basis of a similar clinical efficacy of the two techniquesas a result of similar spreading of the local anesthetic injected,and a potentially higher risk of introducing the needle into themuscular cone, the authors recommend replacing retrobulbaranesthesia with peribulbar anesthesia.
REGIONAL anesthesia is standard for most ophthalmicprocedures. Retrobulbar anesthesia (RBA) has long beenthe choice technique for ophthalmic surgery.1–4 Itconsists of injecting a small volume of local anesthetic(3–4 ml) into the muscular cone. To prevent blinking, anadditional facial nerve block is required to obtain akine-sia of the orbicularis muscle of the lid, the only muscle ofwhich motor innervation is located outside the cone.However, complications of RBA have led many anesthe-siologists to turn to peribulbar anesthesia (PBA). PBA,
which consists of introducing a needle into the extraco-nal space, should theoretically be safer than RBA. PBAwas formally described in 1986.5–8 It is based on the“tissue compartment principle”9: “a needle is insertedinto a compartment and the local anesthetic injectedspreads by virtue of its pressure and volume throughoutthe compartment.” A relatively high volume of localanesthetic is injected into the extraconal space (usually8–12 ml). The local anesthetic injected into the extraco-nal space must spread to the intraconal space to provideadequate anesthesia and akinesia of the globe. RBA andPBA have been opposed on the basis of the existence ofthe so-called intermuscular membrane (IMM) (fig. 1)which is supposed to separate the intraconal space fromthe extraconal space in a watertight fashion. Anatomi-cally, this membrane, as a barrier impairing the spread ofthe local anesthetic, should make PBA less efficient thanRBA. However, the reality of the existence of this sep-tum remains controversial.10,11 From a clinical point ofview, there is a lack of evidence to assume that RBA ismore efficient than PBA.12–20 Moreover, in an anatomicstudy in live patients, Ropo et al.21 demonstrated thatthe local anesthetic injected into both spaces (ie, intra-conal and extraconal) was able to flow freely from onespace to the other. Ortiz et al.22 found similar resultsusing tomodensitometry in human cadavers. The aim ofthis anatomic study performed on human cadavers wastherefore conducted to describe precisely and compare thespread of a solution injected using both techniques and toassess precisely the existence—or not—of the IMM.
Materials and Methods
InjectionsTen human heads separated from the trunks were
used. For each head, two different injections of a coloredlatex dye were randomly performed. One eye was allo-cated to receive an extraconal injection simulating PBA(five right eyes and five left eyes), and the other eye wasallocated to receive an intraconal injection simulatingRBA (five right eyes and five left eyes). All injectionswere performed by the same anesthesiologist (J. R.)experienced in both techniques in live patients andcadavers. All of the RBA injections were performed atthe same site, using the technique described by Hamil-ton.2 A transcutaneous approach of the needle was usedinstead of a transconjunctival approach. A 30-mm 24-gauge needle was bent at 15 mm from the bevel at an
* Staff Anesthesiologist, i Resident in Anesthesiology, # Professor of Anesthe-siology and Chief, Département Anesthésie-Douleur, † Staff Anesthesiologist,‡ Professor of Anesthesiology and Chief, Département Urgence-Réanimation,§ Associate Professor, Laboratoire d’anatomie.
Received from the Laboratoire d’Anatomie, Faculté de médecine, and Dépar-tements Anesthésie-Douleur et Urgence-Réanimation, Centre Hospitalier Univer-sitaire, Nimes, France. Submitted for publication January 18, 2000. Accepted forpublication July 25, 2000. Supported by the Association pour la recherche enanesthésie réanimation and the Association pour la recherche en morphologieexpérimentale, Centre Hospitalier Universitaire de Nimes, Nimes, France. Presentedat the 23rd Annual Meeting of the American Society of Regional Anesthesia, Seattle,Washington, May 14–17, 1998, and the 40th National Congress of the French Societyof Anesthesiology and Intensive Care, Paris, France, September 25–28, 1997.
Address correspondence to Dr. Ripart: Département d’Anesthésie-Douleur,Hopital Caremeau, Centre Hospitalier Universitaire Nimes, 5 rue Hoche, 30029Nimes Cedex 09, France. Address electronic mail to: [email protected] will not be available from the authors. Individual article reprints may bepurchased through the Journal Web site, www.anesthesiology.org.
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angle of 10°. The needle was inserted at the junction ofthe lateral and the medial thirds of the margin of theorbital floor on a vertical line drawn from the lateral partof the iris. It was advanced posteriorly to 15 mm andthen redirected slightly medially and upward to 30 mm,where 4 ml latex dye was injected. We chose a 24-gaugeinstead of the more frequently used 25-gauge needlebecause of the viscosity of latex, which occasionallypolymerizes and obstructs smaller needles. All of thePBA injections were performed using a 24-gauge 25-mmneedle, with a volume of 6 ml, using the three differentsites of introduction of the needle commonly used incurrent practice.6 Four injections were performed at theinferotemporal site, which is the same site as for RBA,
with the needle directed strictly posteriorly to a depth of25 mm.6 Three injections were performed at the supero-nasal site, approximately at the junction of medial andmiddle thirds of the margin of the orbital roof, with theneedle directed posteriorly to a maximum depth of25 mm.5–8 The remaining three injections were per-formed at the medial canthus, using the medial com-partment block technique described by Hustead et al.:the needle was directed posteriorly to the depth of15 mm.2,23,24 Specially prepared latex was used, diluted to50% in water, with natural blue pigments. The speed ofinjection was standardized for both injections as 1 ml/10 s.
Anatomic TechniqueImmediately after the end of the injection, the heads
were deeply frozen at a temperature of 218°C for 48 h
Fig. 1. Supposed location of the intermuscular membrane(IMM). Semischematic view of a fontal section of a human orbit,passing just posteriorly to the posterior pole of the globe. 1 5optic nerve; 2 5 lateral rectus muscle; 3 5 inferior rectus mus-cle; 4 5 medial rectus muscle; 5 5 superior rectus muscle; 6 5levator palpebrae superioris muscle; 7 5 superior oblique mus-cle; 8 5 intermuscular membrane. (Redrawn with permissionfrom Rouviére et al.39 and Koziol.40)
Table 1. Peribulbar (Extracone) Injections: Spread of the Latex
HeadNo. Side Injection
Plane ofSections IMMS
DiffusionScore IFS Comments
1 R IT H 2 1 12 R IT C 2 1 1 Partial intravenous
injection3 L IT S 0 0 04 L IT C 0 0 05 L SN C 2 0 0 Partial subtenon6 L SN H 0 0 0 Lateral rectus
muscle7 R SN S 0 0 08 R MC C 1 0 19 R MC H 2 1 1
10 L MC S 4 1 1
R 5 right eye, L 5 left eye; IT 5 inferotemporal; SN 5 superonasal, MC 5medial canthus; H 5 horizontal (transverse) section; C 5 coronal (frontal)section; S 5 sagittal section; IMMS 5 intermuscular membrane score (from 0[evidence there is no membrane in the four quadrants] to 8 [total evidencethere is a barrier to the dye spread at the supposed place where the septumlies]); diffusion score 5 presence of latex in the space not injected (i.e.,extraconal space); IFS 5 intracone filling score by latex (0 5 total or massive,1 5 incomplete or partial, 2 5 not at all). For details, see text.
Table 2. Retrobulbar (Intracone) Injections: Spread of theLatex
HeadNo. Side
Plane ofSections IMMS
DiffusionScore IFS Comments
1 L H 1 0 0 Lateral rectus muscle2 L C 0 0 03 R S 1 0 04 R C 0 0 05 R C * * *6 R H * * *7 L S 0 0 08 L C * * *9 L H 1 0 1
10 R S 0 0 0
All injections were performed using the same approach, i.e., inferotemporal.L 5 left eye; R 5 right eye; H 5 horizontal (transverse) section; C 5 coronal(frontal) section; S 5 sagittal section; IMMS 5 intermuscular membrane score(from 0 [evidence there is no membrane in the four quadrants] to 8 [totalevidence there is a barrier to the dye spread at the supposed place where theseptum lies]); diffusion score 5 presence of latex in the space not injected(i.e., intraconal space); IFS 5 intracone filling score by latex (0 5 total ormassive, 1 5 incomplete or partial, 2 5 not at all). *Excluded from analysis.For further details, see text.
Table 3. Comparison of IFS after Retrobulbar (Intracone 5RBA) and Peribulbar (Extracone 5 PBA) Injections
HeadNo.
Side of RBAInjection
Site of PBAInjection
Plane ofSections IFS:RBA IFS:PBA
1 L IT H 0 12 L IT C 0 13 R IT S 0 04 R IT C 0 05 R SN C * 06 R SN H * 07 L SN S 0 08 L MC C * 19 L MC H 1 1
10 R MC S 0 1
All RBA injections were performed using the same approach, i.e., inferotem-poral. The PBA injections used three different approaches: inferotemporal (IT),superonasal (SN), and medial canthus (MC).
L 5 left eye; R 5 right eye; H 5 horizontal (transverse) section; C 5 coronal(frontal) section; S 5 sagittal; IFS 5 intracone filling score by latex (0 5 totalor massive, 1 5 incomplete or partial, 2 5 not at all). *Excluded from analysis.For further details, see text.
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Fig. 2. Human head injected with blue latex (no. 4): coronal section passing just posterior to the posterior pole of the eyeball (similarto fig. 1). (A) Right orbit injected with 3.5 ml into the intraconal space via an inferotemporal approach (retrobulbar anesthesia).(B) Left orbit injected with 6 ml latex into the inferotemporal quadrant of the extraconal space (peribulbar anesthesia). (A’ andB’) Semischematic view of A and B with the superimposed place where the intermuscular membrane should be (dottedline). * 5 Approximate site of injection; 1 5 optic nerve; 2 5 lateral rectus muscle; 3 5 inferior rectus muscle; 4 5 medial rectusmuscle; 5 5 superior rectus muscle–levator palpebrae superioris muscle complex; 6 5 superior oblique muscle. Note the spread oflatex from one space to the other, through the supposed intermuscular membrane, resulting in a very similar picture after bothinjections.4™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™
Fig. 3. Human head injected with blue latex (no. 3): sagittal section passing through the eyeball, just laterally to the optic nerve. (A)Right eye injected with 3.5 ml into the intraconal space via an inferotemporal approach (retrobulbar anesthesia). (B) Left orbitinjected with 6 ml latex into the inferotemporal quadrant of the extraconal space (peribulbar anesthesia). (A’ and B’) Semischematicview of A and B with the superimposed place where the intermuscular membrane should be (dotted line). 1 5 superior rectusmuscle–levator palpebrae superioris muscle complex; 2 5 lateral rectus muscle (sectioned); 3 5 inferior oblique muscle (outside thecone). Note the spread of latex from one space to the other, through the supposed intermuscular membrane, resulting in a verysimilar picture after both injections.4™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™
Fig. 4. Human head injected with blue latex (no. 7): sagittal section passing through the eyeball and the optic nerve. (A) Left orbitinjected with 4 ml into the intraconal space via an inferotemporal approach (retrobulbar anesthesia). (B) Right orbit injected with6 ml of latex via the superonasal quadrant of the extraconal space (peribulbar anesthesia). (A’ and B’) (Semischematic view of A andB with the superimposed place where the intermuscular membrane should be (dotted line). 1 5 optic nerve; 2 5 inferior rectusmuscle; 3 5 superior rectus muscle–levator palpebrae superioris muscle complex; 4 5 lateral rectus muscle (cross-sectioned). Notethe spread of latex from one space to the other, through the supposed intermuscular membrane, resulting in a very similar pictureafter both injections.4™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™
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or more. They were then sliced with an electric saw in5-mm sections in various planes: three in a horizontalplane (one for each site of PBA injections), three in asagittal plane (one for each site of PBA injections), andfour in a coronal plane (two for inferotemporal site, onefor superonasal, and one for medial canthus). Therefore,for each site of injection of PBA, there were at least threeeyes injected and cut following the three differentplanes. For each head, the eye injected using the RBAtechnique was cut following the same plane as the sec-ond eye injected with PBA. They were then rewarmedto ambient temperature, washed, photographed, andobserved.
Analysis of the Anatomic ViewsThree scores were used for the analysis of the spread.
All were scored by two independent investigators (J. R.and another anesthesiologist who was not involved inthe study and who was unfamiliar with eye blocks). IMMscore was used to quantify the evidence of the IMMexistence for each eye. A 0–2-point scale was used foreach of the four quadrants (A 5 superotemporal; B 5superonasal; C 5 inferonasal; D 5 inferotemporal): 0 5evidence of inexistence of the IMM (free spreadingof the dye clearly identified from one space to the other);1 5 no evidence of the existence or absence of the IMM(unclear spread or no dye in this quadrant); and 2 5evidence of the existence of the IMM (spreading of thedye from one space to the other clearly impaired by abarrier located on the supposed place of the IMM withstagnation of the dye on the border of this barrier). Theglobal IMM score was the sum of the four quadrantsscores and ranged from 0 (total evidence of inexistenceof the septum) to 8 (total evidence of the existence ofthe septum). Regarding the final location of the dye, foreach eye, the spreading of the dye from the space whereit was injected to the other space was scored as follows:0 5 massive; 1 5 moderate or partial; 2 5 not at all,whatever the track identified for this spread. This wasscored to compare the pertinence of the oppositionbetween the two techniques of injections (RBA andPBA). Finally, as an index corresponding to clinical effi-cacy, the presence or absence of latex dye in the mus-cular cone was assessed using the intraconal fillingscore: 0 5 massive or total filling of the intraconal spaceby the latex dye; 1 5 partial or incomplete filling of theintraconal space by the latex dye; 2 5 absolutely no latexin the intraconal space.
Statistical AnalysisComparison of intraconal filling score between intra-
conal and extraconal injections was performed with thechi-square test.
Results
The site of injection was identified as being well lo-cated in all but three cases, which were excluded from
the analysis: in one case of RBA (no. 8), the injection wasinadvertently performed extraconally; in one case ofRBA, although the injection was located in the attendedspace, an intravenous injection precluded any otherspread of the latex (no. 5); in the third case, because ofan unsuspected fracture of the orbital floor, the needletook a false track, resulting in an injection in the maxil-lary sinus (no. 6).
In one case (PBA no. 2), although the injection waslocated in the right space, it appeared that part of thelatex was injected intravenously, with subsequentspread to the cavernous sinus. This case was not ex-cluded from the analysis because part of the latex spreadinto the extraconal space. No intraarterial injection wasidentified. In two cases, some latex was found in the sheathof the lateral rectus muscle: one RBA (no. 1) and one PBA(no. 6), possibly indicating an intramuscular injection. Inno case was a brain-stem spread of the dye identified.
Tables 1 and 2 summarize the scores of latex spreadafter simulated PBA and RBA, respectively. Table 3shows the individual comparisons of intraconal fillingscore between RBA and PBA injections. The only statis-tical comparison was intraconal filling score, whichshowed no significant difference between the filling ofthe intraconal space after both RBA and PBA. In no casewas there clear evidence of an IMM impairing spread of thelatex: all individual IMM scores were less than 3, except forone that was 4 (RBA no. 10). In the latter case, the scorewas 1 (no evidence or unclear) for each quadrant.
Three views of both eyes of the same heads showingtypical spread of the dye are shown in figures 2–4. In allcases of RBA and PBA, the spread of the dye from theinjection site was observed in all directions of the space.It was mainly guided by the small septa network thatsegments the whole adipose tissue of the orbit. Therewas no evidence of the existence of any intermuscularseptum that clearly separated the intraconal and extra-conal spaces. In fact, the final location of the dye wasvery similar between PBA and RBA. In all the injectionsbut one PBA (no. 10), there was a spread from one spaceto another through the gaps between the adjacent pairsof rectus muscles. It appeared that the intraconal andextraconal spaces are not separated, but rather are twoparts of one single space, the corpus adiposum of theorbit. In all cases, spread of the dye appeared to becaused by pressure of injection and guided only by thesepta framework in all directions of the space, with anuncertain pattern, sometimes filling the whole orbit andsometimes not.
Discussion
In this anatomic comparison between retrobulbar andperibulbar injections, we were unable to confirm theexistence of any intermuscular septum separating intra-conal from extraconal spaces. The colored dye spread
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very similarly after both injections throughout the adi-pose tissues of the orbit in an uncertain and sometimesheterogeneous fashion.
Extrapolation from Cadaver to Live PatientsSome concern may be expressed about extrapolating
results from cadavers to live patients. In fact, the anat-omy is the same. The high viscosity of latex led us to useneedles of relatively large diameter that are currentlyused in live patients.5–7 A second problem is that thelatex we used was more viscous than the local anestheticmixture and quickly polymerizes after injection and be-comes unable to spread, whereas local anesthetic maycontinue to spread over a few minutes. Therefore, latexmight spread incompletely. In fact, in two previous stud-ies, we injected orbits of human cadavers with similarlatex and fluid hydrophylic contrast media for tomoden-sitometry, respectively.25,26 The conclusions of thosetwo studies were very similar, with the exception of amore complete spread of the dye with the contrastmedia than with latex. Therefore, if there is a differenceof spread caused by viscosity of the latex dye, it is morelimited with latex than with local anesthetic. This shouldnot modify our conclusions. Another frequently usedcolored dye is methylene blue, which spreads very easilythroughout adipose tissues. Hustead et al.27 performedsuch an injection, which resulted in an orbit totally filledwith blue: “...the dye has distributed throughout most ofthe orbit. Neither the needle track nor the point ofinjection can be deduced.” We felt that using a very fluidsolution would not be discriminative enough to identifyan IMM if it exists.
Effect of VolumeOne can argue that we did not inject the same volume
in RBA than in PBA. Those volumes were determinedfrom current clinical practice. Indeed, all the nervesresponsible of the sensory, motor, and autonomic inner-vation of the eyeball transit through the intraconal space,with the exception of the branch of the facial nerve,which is responsible for the motor innervation of theorbicularis muscle of the lids. Therefore, the local anes-thetic injected via any technique (i.e., RBA or PBA) mustspread into the cone to block them. That is why the localanesthetic injected extraconally has a longer way tospread from the site of injection to the target nerves tobe blocked. Obviously, increasing the volume injected isa means of compensating for this need for morespreading.
ComplicationsOne point of interest is intravenous injection with
subsequent filling of the cavernous sinus (10% both forRBA and PBA). Because of the low volumes used in eyes,an inadvertent intravenous injection is unlikely to pro-duce signs of systemic toxicity. One can assume that
such an intravenous injection is frequently unrecognizedbecause of a lack of symptoms. By contrast, an intraar-terial injection with a subsequent back flow to the inter-nal carotid artery is a clearly identified complication.28
This generally leads to immediate seizures. Such an in-traarterial injection was not identified in our work. An-other complication is the occurrence of postoperativestrabismus. We observed spread of the latex into thefascial sheath of a muscle in one case of RBA and in onePBA. We assumed that the risk for inadvertent injury toa rectus muscle remains significant for both techniques.
Although uncommon, many other complications havebeen described after PRA: ptosis, globe perforation, op-tic nerve injury, and brain-stem anesthesia. In thepresent study we did not observe an injection that mightbe correlated with one of these complications. All thecomplications were fist described after RBA, and subse-quently after a PBA. Some of them obviously require theintraconal positioning of the needle and should not oc-cur after PBA, such as optic nerve injury or arterialretrobulbar hemorrhage.29 This implies that some in-tended PBAs turn out, in fact, to be RBAs. Indeed, sometechniques are not clearly identified as RBA or PBA, andprovided that the needle is directed to the cone, chang-ing its depth of insertion can change a PBA into a RBA.30
We did not encounter such a misplacement of the nee-dle, but we experienced an inadvertent PBA in place ofa intended RBA. Moreover, in one case of intended PBA,an inadvertent episcleral (sub-Tenon) injection was ob-served, which may occur in clinical practice withoutalways being recognized as the only sign is the occur-rence of a chemosis.25,26,31–34 Therefore, even whenperforming PBA, the needle is sometimes very close tothe eyeball, which may be inadvertently perforated.
There are no comparative studies to confirm that com-plications occur less frequently with PBA than with RBA.This is probably because of the very low frequency ofthose complications, with a lack of power of small-sizedcomparative studies. Although this has to be confirmed,we assume that PBA should theoretically lead to a lowerrisk of complications.35
Clinical Implications: Compared Efficacy ofRetrobulbar and Peribulbar AnesthesiaThe main finding of this work was to confirm that PBA
and RBA correspond to the same final location of thelocal anesthetic. This is in agreement with the results ofRopo et al.21, who described the same spread after PBAand RBA in live patients using computed tomodensito-metry. Ortiz et al.22 found similar results after injecting asimulated PBA in cadavers and evaluating the spread ofthe dye using tomodensitometry. Moreover, increasingthe volume injected with the RBA technique may pro-vide an efficient motor blockade of the orbicularis of thelids.13,31,36,37 This implies that the local anestheticspreads through the extraconal space before reaching
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the lids, as after PBA. Many investigators are convinced,mainly based on personal experience or retrospectivenonrandomized studies, that RBA is more efficient thanPBA.6,14,29 However, to our knowledge, most random-ized studies were not able to clearly demonstrate a ben-efit of RBA over PBA in terms of akinesia or onset ofblock. Ali-Melkkilä et al.38 compared RBA and PBA in 300patients and found rates of additional block of 13% and35%, respectively. In another similar study, the sameinvestigators were unable to confirm those results, withrates of reinjection between 11% and 19%.12 Demediuket al.13 observed rates of need for reinjection of 31% and33% after PBA and RBA, respectively. Murdoch15 found a3% rate of unsatisfactory blocks after PBA as comparedwith 10% with RBA. Saunders et al.16 failed to find adifference of efficacy between RBA and PBA, as didShriver et al.,17 who found rates of reinjection of 4.4%and 6.8% for RBA and PBA, respectively. Similarly, nodifference was observed by Weiss and Deichman,18 withreinjection rates of 28% for PBA and 21% for RBA. Fi-nally, Whitsett et al.19 found no difference between PBAand RBA, with reinjection rates of 11% and 8%, respec-tively. The fact that the reinjection rate varies in theseseries from 4% to 28% is not surprising. Those variationsprobably reflect the fact that the efficacy of the blocks isoperator-dependent rather than technique-dependent,and especially that the exigency of the surgeon regard-ing total akinesia may vary dramatically from one insti-tution to another. However, the absence of clear evi-dence of difference between the two techniques is inagreement with the same spread of the dye after bothtechniques we observed in our study.
In conclusion, our work confirms that intraconal andextraconal spaces largely communicate. In fact, RBA andPBA correspond to the same spread of the dye. This is inagreement with a similar efficacy of both techniquesobserved in clinical practice. Theoretically, the puncturerisk is lower in PBA than in RBA. Therefore, the combi-nation those two facts should be considered as an argu-ment for replacing RBA with PBA in current practice.
The authors thank Margaret Manson, Laboratory of Physiology and Anesthesia,for reviewing the manuscript, and Michel Bossy, Laboratory of Anatomy, CentreHospitalier Universitaire, Nimes, France, for helpful technical assistance.
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