This article is accompanied by the following Invited Commentary:
Lönnqvist P-A, Bösenberg AT. Anatomical dissections are not obsolete. Cadaver studies can still provide important information for regional anaesthesia. Eur J Anaesthesiol 2014; 31:303–304.
Regional anaesthesia for lower abdominal incisions (such as open inguinal hernia repair, hydrocoele repair, open appendicectomy, open varicocele repair, orchidopexy) can be achieved with spinal, epidural or peripheral regional blocks, such as ilioinguinal-iliohypogastric, transversus abdominis plane (TAP) and thoracolumbar paravertebral block (PVB). Peripheral regional blocks are often the technique of choice in paediatric patients because of the lower incidence of complications as compared with neuraxial methods,1–3 and the avoidance of adverse events such as hypotension and urinary retention.4–7 Data from the scientific literature show that PVB for anaesthesia of the lower abdomen is more effective and reliable than TAP block8 and ilioinguinal-iliohypogastric nerve block.9
The safety and efficacy of PVB was demonstrated in a meta-analysis examining thoracic PVB, which showed a comparable analgesic effect and a better complication profile of PVB as compared with epidural anaesthesia,6 as well as in reports focusing on PVB for abdominal wall anaesthesia.3,10
It is common practice when performing a PVB for abdominal wall anaesthesia to inject a certain volume of local anaesthetic solution into the paravertebral space at several levels in order to achieve anaesthesia of the corresponding dermatomes.4,11–13 There are a number of scientific publications however, showing the clinical efficacy of a single injection thoracic PVB14 and the possibility of local anaesthetic solution spread not only between thoracic segments of the paravertebral space, but also between thoracic and lumbar paravertebral spaces.15–18 There are data on the spread of local anaesthetics when performing thoracic PVB in both adults6,18–22 and children,23 but the nature of spread of local anaesthetic or injectate as part of a single injection thoracolumbar PVB has not yet been studied.
The aim of this study was to determine the pattern of injectate spread in infants’ paravertebral spaces, to check the feasibility of a single injection for PVB and to determine the optimal volume of injectate necessary to cover the paravertebral segments responsible for sensation of lower abdomen.
Approval was obtained from the Lviv Regional Children's Hospital Ethics Committee (Protocol #3, dated April 4, 2013, chairperson O. Burda, MD, PhD). Consent was obtained from the parents of all participants for dye injection and autopsy, including soft tissue dissection, but excluding dissection of spine. The study was conducted using 20 fresh, unembalmed infant cadavers including 12 males and eight females [median age at death 7 months (range 1 to 13 months), median body mass 4550 g (range 2100 to 8100 g)]. Cadavers were divided into five equal groups, depending on the amount of dye injected into paravertebral space (0.1, 0.2, 0.3, 0.4, and 0.5 ml kg−1). Unilateral injection of dye into the paravertebral space was performed prior to cadaveric dissection. The vertebral level was estimated by palpation of C7 spinous process and counting caudally. The PVB was performed under ultrasound guidance using a 5 to 10 MHz linear-array probe (SonoSite Titan; SonoSite Inc., Washington, USA). The thoracolumbar area was scanned with the cadaver in the prone position and the probe located in the transverse axis. The transverse process of the T12 vertebra and the psoas muscle were identified. A 10 cm, 20-gauge Quincke spinal needle (Becton-Dickinson, New Jersey, USA) was inserted laterally to the probe. The needle was advanced using a transverse, in-plane visualisation technique in a lateromedial direction until the needle tip appeared between the transverse process and dorsal aspect of the psoas muscle. At that point, a single shot of methylene blue dye 1% in distilled water was injected (Figs 1 and 2).
After dissection of the cadaver and removal of viscera, the spread of dye within the paravertebral space was studied. The primary outcome of the study was the total number of paravertebral segments stained after dye injection and the specific vertebral levels of cephalad and caudad spread of dye within the paravertebral space. Other data collected included the spread of dye to the intercostal spaces, anterior to the vertebral bodies and contralateral paravertebral space.
Statistical analysis was performed using STATISTICA 6.0 software (StatSoft Inc., Tulsa, USA). Pearson's correlation coefficient was calculated for the amount of dye injected and the stained segments of the paraverbetral space, anterior dye spread and contralateral dye spread.
All 20 cadavers were examined. The transverse processes of T12 vertebra and the psoas muscles were located ultrasonographically in all cases. Dye was present in the paravertebral spaces of all cadavers. The number of nerve roots, sympathetic ganglia and rami communicantes stained with dye correlated with injected volume. A typical picture of the observed dye spread is shown in Fig. 3.
Both cephalad and caudad spread of dye was observed in all cadavers. Cephalad spread was associated with thoracic spinal nerve root and intercostal space staining. Caudad spread was associated with lumbar plexus nerve root and dorsal surface of psoas muscle staining. Strong correlation was found between the volume of dye injected and the extent of its cephalad and caudad spread (r = 0.97, P < 0.05). The extent of paravertebral space staining in relation to injectate volume is shown in Fig. 4.
The number of spinal nerve roots surrounded with dye corresponded to the number of paravertebral segments involved. T11, T12 and L1 nerve roots were stained in all cases. Both anterior and contralateral spread of dye was observed, with an incidence correlating with dye volume (r = 0.88 and 0.89, respectively, P < 0.05). Dye was present in the intercostal spaces in all cases. The level of intercostal spread corresponded to the level of thoracic paravertebral space spread (Table 1).
There are controversies in the scientific literature about the anatomy of the paravertebral space, the possibility of injectate spread between thoracic and lumbar paravertebral spaces, and the number of injections needed to achieve adequate anaesthesia of the abdominal wall. Several studies advocate multiple injection techniques in PVB for thoracic and abdominal wall anaesthesia based on clinical and radiographic signs of superior distribution of local anaesthetic.3,13,24
Lönnqvist and Hildingsson25 described the T12 vertebral body and transverse processes as the ‘caudal boundary of the thoracic paravertebral space’ and insisted that local anaesthetic solution cannot spread caudally to the T12-L1 intervertebral disc due to the origin of the psoas muscle. Several studies, however, describe the connection of thoracic and lumbar paravertebral spaces. Thoracolumbar spread of injectate via the medial and lateral arcuate ligaments of the diaphragm to the retroperitoneal space in relation to the anterior surface of the psoas major and quadratus lumborum muscles was observed by Saito et al.26–28 The authors suggest that in this case, local anaesthetic effects may occur because of blockade of peripheral nerves originating from the lumbar plexus rather than blockade of spinal nerve roots. Tighe et al.29 noted that the endothoracic fascia divides the paravertebral space into two compartments: anterior subserous (extrapleural) and subendothoracic. As it continues inferiorly it runs with the fascia transversalis of the abdomen dorsal to the diaphragm through the medial and lateral arcuate ligaments and the aortic hiatus. Batra et al.30 hypothesised that this endothoracic fascia could be the anatomical basis for thoracolumbar injectate spread. The authors believe that injection of local anaesthetic in the lower thoracic paravertebral space posterior to the endothoracic fascia can lead to its spread inferiorly through the medial and lateral arcuate ligaments to the retroperitoneal space behind the fascia transversalis, where the lumbar spinal nerves lie.
The results of our study show that the thoracic and lumbar paravertebral spaces in infants are anatomically connected despite the presence of borders such as the origin of the psoas muscle (from vertebral bodies, lateral aspects of discs between them and transverse processes of T12-L5).25,31
Taking into account the fact that T10-L1 spinal nerve roots must be blocked to provide analgesia for lower abdominal surgery and based on the spread of dye within the paravertebral space after a single PVB injection at T12-L1, our study suggests that 0.2 to 0.3 ml kg−1 of local anaesthetic solution would provide adequate spread within the paravertebral space. Larger doses of local anaesthetic or a PVB at a more cephalad level, may be considered for regional anaesthesia for unilateral upper abdominal surgery.
The study by Lönnqvist and Hesser32 that included 18 paediatric patients, suggested 0.5 ml kg−1 of local anaesthetic as an optimal dose to cover at least five thoracic paravertebral segments. Our results show that smaller doses of 0.2 and 0.3 ml kg−1 were sufficient in all cases to cover five and six thoracolumbar segments, respectively. This discrepancy in suggested dosing may be because of the possible peculiarities of injectate spread in different age groups (neonates versus infants), because of different contrast media (dye versus radiopaque contrast) or because of bias from the small number of patients in our study.
The anatomical connection between the thoracic paravertebral and intercostal spaces and the extensive spread of dye to these spaces after PVB was shown by Cowie et al.16 and Burns et al.33 We also observed dye spread from paravertebral to intercostal spaces in all cases. Spread of injectate anterior to the vertebra is described by Lönnqvist and Hesser,32 Cowie et al.16 and Karmakar et al.18 and our data support their findings. Injectate spread to the contralateral paravertebral space is shown by Lönnqvist and Hesser,32 in a case report of Karmakar et al.34 and by Gadsden et al.35 Our study supports these data and suggests that the incidence of contralateral dye spread is volume dependent and that a bilateral block may be possible, especially when using high volumes of local anaesthetic.
Epidural spread of local anaesthetic through the intervertebral foraminae was also observed by Richardson and Lönnqvist.2 Some authors describe an incidence of epidural injectate spread of up to 40% after thoracic PVB in adults.16,35 It is unclear whether contralateral paravertebral dye spread in infants occurs through the epidural space or across the anterior surface of vertebral column, or both. We were unable to examine this aspect because of a lack of parental consent for spine dissection.
Data on paravertebral injectate spread in children and adolescents must be obtained to find out the nature of dye spread in these age groups and the feasibility of performing single injection thoracolumbar PVB for anaesthesia of the abdomen.
Thoracolumbar PVB at T12-L1 in infant cadavers leads to caudad and cephalad dye spread in a dose-dependent manner. Single injection thoracolumbar paravertebral blockade could be performed to provide regional anaesthesia of the lower abdomen in infants. This study suggests that a single injection of 0.2 to 0.3 ml kg−1 of local anaesthetic in the thoracolumbar paravertebral space could provide adequate coverage of the dermatomes of the lower abdomen.
Acknowledgements relating to this article
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