BJA Advance Access originally published online on May 23, 2006
British Journal of Anaesthesia 2006 97(2):200-207; doi:10.1093/bja/ael121
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Epidural catheter placement in children: comparing a novel approach using ultrasound guidance and a standard loss-of-resistance technique
1 Department of Anaesthesia and Intensive Care Medicine, Medical University of Vienna 1090 Vienna., Austria
2 Department of Anaesthesia, University of Cape Town, Red Cross Children's Hospital Klipfontein Road, Rondebosch 7700, Cape Town, South Africa
3 Division of Anaesthesia and Intensive Care Medicine, Gersthof Orthopedic Hospital 1180 Vienna, Austria
*Corresponding author: Department of Anaesthesia and Intensive Care Medicine, Medical University of Vienna, Waehringer Guertel 18–20, A-1090 Vienna. E-mail: peter.marhofer{at}meduniwien.ac.at
Accepted for publication April 3, 2006.
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Abstract |
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Background. We report a prospective, randomized study to evaluate ultrasound guidance for epidural catheter placement in children 0–6 yr of age.
Methods. Epidural catheters were placed at lumbar or thoracic cord levels in 64 children undergoing major surgery, using either ultrasonography or loss-of-resistance (LOR) for guidance. Using a 5–10 MHz linear ultrasound probe, the neuraxial structures were identified, the skin-epidural depth and epidural space was measured, the advancing epidural catheter visualized, and the spread of local anaesthetic verifying catheter position was confirmed. Epidural placement procedures were analysed for bone contacts and speed of execution. Children under 6 months were analysed separately.
Results. Epidural placement involved bone contacts in 17% of children in the ultrasound group and 71% of children in the LOR group (P<0.0001). Epidurals were executed more swiftly in the ultrasound group [162 (75) s vs 234 (138) s; P<0.01]. Children under 6 months revealed a 0.9 correlation between skin-epidural depth and body weight.
Conclusions. Ultrasonography is a useful aid to verify epidural placement of local anaesthetic agents and epidural catheters in children. Advantages include a reduction in bone contacts, faster epidural placement, direct visualization of neuraxial structures and the spread of local anaesthetic inside the epidural space. Ultrasound guidance requires additional training and good manual skills, and should only be used once experience in ultrasound-guided techniques of regional anaesthesia has been acquired.
Keywords: anaesthesia; paediatric; anaesthetic techniques; epidural; measurement techniques; ultrasonography
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Introduction |
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Epidural blockade in children, particularly neonates and infants, is challenging. Neuraxial analgesia for thoracic and abdominal surgery is known to offer compelling advantages in both adults1–3 and in children.4 5 In children, these advantages include improved haemodynamic stability,6 reduced need for postoperative ventilatory support,1 3 7 improved analgesia1 3 8 without the risk of opiate-induced respiratory depression and lower perioperative stress levels.9
Despite these advantages the routine use of epidural analgesia, particularly in newborns (preterm or term) is limited to a few centres. The most popular method for detecting the epidural space is the loss-of-resistance (LOR) technique, and is usually performed with the child under anaesthesia. The LOR approach has been associated with complications and adverse outcomes. These include dural puncture or more significantly neurological deficits as a result of unintentional spinal cord trauma.10–13 The LOR techniques rely on tactile sensation and are performed more or less ‘blind’, leaving the task of determining the position of the epidural cannula either to the physician's individual ability or radiographic studies. Recently electric stimulation has been used to confirm correct catheter placement but requires the use of specially designed catheters.14 15
Ultrasonography has been shown to improve the success rate and safety of a variety of peripheral regional anaesthesia techniques in children.16 17 As a logical consequence, ultrasound guidance should also facilitate continuous epidural anaesthesia, particularly in children, because of direct visualization of the spread of local anaesthetic inside the epidural space. A prospective randomized study was therefore designed to evaluate the feasibility, number of bone contacts and duration of performance of the block of using ultrasound guidance compared with the traditional LOR method for epidural catheter placement in newborns, infants and preschool children.
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Materials and methods |
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After obtaining approval from the local ethics committee and parental consent, we evaluated 64 children who were undergoing major abdominal or thoracic surgery, ranging from neonates to 6 yr of age. Children with neurological disorders, seizures, local infection, or coagulopathies were excluded.
Prior to induction of anaesthesia, the children were randomized to either one of two groups. In the study group, catheter placement was guided by direct ultrasound visualization. In the control group, the standard LOR technique was used. The randomization protocol was prepared outside the study centre and delivered in opaque envelopes that were sealed and sequentially numbered.
Oral midazolam 0.5 mg kg–1 was administered as premedication at the anaesthetist's discretion. Premedication was not given to children under 1 yr. General anaesthesia was induced using inhalation anaesthesia (halothane or sevoflurane) or i.v. with propofol 2–3 mg kg–1. After endotracheal intubation, anaesthesia was maintained with 1 minimum alveolar concentration halothane in either nitrous oxide and oxygen or air and oxygen. Neuromuscular blocking agents were given at the discretion of the anaesthesiologist. Fluid management included bolus administration of 10 ml kg–1 lactated Ringer's solution, followed by continuous infusion of lactated Ringer's solution as dictated by the surgery.
Intraoperative monitoring included ECG, heart rate, pulse oximetry, non-invasive blood pressure measurements and continuous end-tidal carbon dioxide concentrations. Urinary catheters and nasogastric tubes were placed as indicated.
Epidural catheter placement
Ultrasound group
Children were placed in a lateral position for epidural catheter placement. The level of epidural puncture was dictated by the surgical procedure. Both the puncture site and the ultrasound probe were aseptically prepared. Ultrasound imaging was performed by an assistant with a linear 5–10 MHz hockey-stick probe connected to a portable ultrasound unit (SonoSite 180plus, SonoSiteTM, Bothell, WA, USA). The probe was applied to obtain a paramedian, longitudinal view of the neuraxial structures (Fig. 1). This approach is in accordance with our previous pilot study of neuraxial ultrasound imaging in infants and children, which also showed that the dura can be visualized better than the flavum ligament.18 Consequently, the dura was used as main neuraxial reference structure in the ultrasound group. The sonographic measurements made from this paramedian and longitudinal view included the distances from skin to epidural space, from skin to dura, and the percentage of dura visible in the ultrasound image. The measuring points for skin–epidural distance and diameter of epidural space are illustrated in Figure 2.
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All epidural punctures were performed by one investigator using a 19 G epidural catheter set with a Tuohy 50 mm cannula and 24 G catheter (PajunkTM, Geisingen, Germany). On identifying the dura in the ultrasound image, the puncture was performed using a midline approach (medial direction relative to the ultrasound probe, Fig. 1). Our approach in this group was to directly observe the needle penetrating the ligamentum flavum and to confirm the entry of the local anaesthetic within the epidural space during continuous testing for LOR using levobupivacaine 0.25% (ChirocaineTM, Abbott, Roscrea, Ireland).
Once satisfied that the needle tip was correctly positioned within the epidural space, levobupivacaine 0.25% 0.2 ml kg–1 (ChirocaineTM, Abbott, Roscrea, Ireland) was injected. The spread of the local anaesthetic within the epidural space and the downward (forward) movement of the dura was taken to further confirm the correct placement of the epidural needle. After the initial injection of local anaesthetic in the epidural space through the Tuohy needle the epidural catheter was introduced. After introducing the epidural catheter, the actual position of the tip can be confirmed by sonographically monitoring the movement of the liquid within the epidural space or the movement of the dura as the epidural space is expanded by the injected local anaesthetic. This was done by injecting levobupivacaine 0.25% 0.2 ml kg–1 after introducing the epidural catheter 2–3 cm into the epidural space (Fig. 3). The catheter was then fixed with a sterile transparent adhesive dressing (Tegaderm).
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Control group
The epidural placement in this group was guided by the standard LOR technique using a midline approach. Air or saline was used for the LOR according to the anaesthesiologist's preference. Direct ultrasound imaging was not performed during the procedure but measurements were made prior to performing the epidural. Apart from this, the epidural was performed in the same position using the same skin preparation and epidural catheter kits as in the ultrasound group.
Once the epidural space had been identified using levobupivacaine 0.25%, 0.2 mg kg–1 of the same local anaesthetic was injected prior to inserting the catheter 2–3 cm within the epidural space. The needle was removed and a further levobupivacaine 0.25% 0.2 ml kg–1 was injected through the catheter. The catheter was fixed in the same manner.
After completion, the children were placed in a supine position, the patency of the catheter was checked, and the initial bolus dose was topped up to a total of levobupivacaine 0.25% 0.5–0.7 ml kg–1 at lumbar level; or 0.4–0.5 ml kg–1 at the thoracic level. A continuous infusion of levobupivacaine 0.125% (0.2 ml kg–1 h–1 at lumbar sites and 0.1 ml kg–1 h–1 at thoracic sites) was started during operation. All puncture sites were checked daily for inflammation or other adverse reactions. The epidural catheters were removed 2–3 days after surgery.
The same dosing regimen was applied in both groups.
Data collection during epidural placement
The following data and events were recorded in both groups during epidural placement: bone contact, blood aspiration, dural puncture, epidural failures and the time interval from initial skin puncture to catheter fixation. Additional parameters evaluated in the ultrasound group included: relative visibility of the dura mater (expressed as percentage of the ultrasound screen on which the image was visible), skin–epidural distance and diameter of the epidural space.
Evaluation of perioperative analgesia and rescue medication
Decreases in heart rate or blood pressure of >30% from baseline were considered to reflect hypotension or bradycardia. These events were managed with atropine 0.01 mg kg–1 (minimum dose 0.1 mg) or by fluid infusion. If unsuccessful, etilefrine (a potent 
agonist) 0.02 mg kg–1 was administered.
The surgical incision was made at least 15 min after placement of the epidural block. An increase in heart rate or blood pressure of more than 20% from baseline was considered to reflect inadequate analgesia and was managed by bolus administration of levobupivacaine 0.25% 0.3 ml kg–1 through the epidural catheter. If this was unsuccessful, the epidural block was considered to have failed, and i.v. fentanyl 3 µg kg–1 was administered. Those children requiring intraoperative i.v. pain therapy were excluded from further pain evaluation.
After surgery was completed, the children were extubated either immediately or, if cardiorespiratory conditions dictated, in the intensive care unit (ICU) when stabilized. All children were transferred to the ICU for postoperative management. Any complications associated with epidural anaesthesia (such as respiratory insufficiency, hypotonia, bradycardia or local infections) were carefully recorded and managed appropriately.
The efficacy of postoperative analgesia was assessed after extubation over 24 h using the observational pain scale (OPS). The OPS is based on five objective behavioural parameters: crying, facial expression, torso position, leg position and motor restlessness. Values of 1 (none), 2 (moderate) or 3 (severe) are assigned to each parameter. If two consecutive assessments yielded a cumulative score of 
11,17 a bolus of levobupivacaine 0.3 ml was administered via the epidural catheter or, if unsuccessful i.v. morphine was administered at a dose level of 0.1–0.2 mg kg–1.
Subgroup analysis of children <6 months
To date there are no data available on the use of ultrasound for epidural catheter placement in children under 6 months of age. This subgroup was therefore analysed separately. In addition to the above data, the skin–epidural space depth was measured and correlated to body weight.
Statistical analysis
Values are expressed as means and SDs, but where appropriate, they are expressed as medians with 25th and 75th percentiles. An independent t-test was used to analyse patient characteristic differences and time differences in the execution of the epidural block. Haemodynamic changes during surgery were analysed for intergroup differences by ANOVA for repeated measurements. The 
2-test was applied to compare both groups for suboptimal events (bone contacts, blood aspiration, dural perforations, failed punctures) and additional analgesic requirements (systemic analgesia during skin incision) using SPSS 11.1.2 software (SPSS Inc., Chicago, IL, USA). Results were considered to be statistically significant at P
0.05. Pearson's correlation coefficient was used to relate body weights to skin–epidural depths in children aged less than 6 months.
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Results |
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The patient characteristic data and epidural puncture level were similar in both groups (Table 1). Epidural placement was successful in all children irrespective of whether ultrasound guidance or LOR was used.
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Epidural catheters were placed more swiftly in the ultrasound group 234 (SD 138) s than in the control group 162 (SD 75). This difference was statistically significant (P<0.01). Bone contact occurred in 5 of 31 children (17%) in the ultrasound group and in 24 of 34 children (71%) in the control group (P<0.0001) while performing the epidural block. Blood was aspirated in one child in the control group. No dural puncture occurred in either group. Two children required supplementary intraoperative analgesia in the control group, while no additional analgesia was required in the ultrasound group. None of the children with successful intraoperative epidural analgesia required i.v. pain therapy in the postoperative period. Of 30, 26 children (87%) in the ultrasound group and 88% (30/34) in the control group were able to be extubated immediately after surgery. The difference was not statistically significant.
In two children in the control group an OPS score >11 in two consecutive measurements was observed in the recovery room (in one child immediately after admission and in another child after 60 min). Those children were successfully treated with i.v. morphine. None of the children in the ultrasound group required i.v. administration of morphine in the recovery room. Two children in both study groups received an epidural bolus of levobupivacaine 0.3 ml because of OPS scores >11 (ultrasound group: 60 and 240 min after admission in the recovery room; control group: 30 and 45 min after admission in the recovery room).
Heart rates were reduced in the order of 10% in the ultrasound group, while no such change was observed in the control group. This difference fell short of statistical significance. No significant change in arterial blood pressure was noted in either group.
There were 32 children under 6 months of age; 19 in the ultrasound group and 13 in the control group. These findings are summarized in Table 2. The correlation between skin–epidural depth and body weight in this subgroup is shown in Figure 4. The Pearson coefficient for the association between body weight and skin–epidural depth was 0.9. Data for children older than 6 months (32 children; 11 in the ultrasound and 21 in the control group) are presented in Table 3.
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one or more bone contacts; 
% of entire ultrasound image
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Discussion |
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Epidural anaesthesia in infants and neonates may pose significant challenges to anaesthesiologists because of subtle difficulties in identifying the epidural space in these patients. In addition, epidural catheters are sometimes difficult to advance.
Although the use of ultrasound-guided regional techniques in children is somewhat limited at present, its use is expected to broaden. Children may prove to be ideal subjects for ultrasound-guided nerve blocks because good quality images of peripheral nerves, and even the spinal cord, and their surrounding structures can be obtained in small children with modern ultrasound equipment. High frequency probes (7–15 MHz) produce good image resolution but penetration is limited. A trade off therefore exists between image resolution and tissue penetration. Deeper structures require lower frequencies but the resulting images are of lower resolution. The high frequency linear array transducer probes generate better images than the sector probes.18
In infants less than 6 months the posterior elements of the spinal canal are incompletely ossified allowing an acoustic window for sonographic imaging. With increasing age, the value of ultrasound imaging decreases as ossification increases and the depth of the epidural space and spinal cord increases. Direct visualization of neuraxial structures in children is a function of body weight18 and therefore skin–epidural depth. Of the various scanning perspectives, the paramedian longitudinal and the intervertebral axial planes offer the best views, but the size of these ultrasound windows also decreases with age.18 Thus, when using these probes, the reduced resolution beyond 3.5 cm limits accurate evaluation of spinal cord structures in children weighing more than approximately 25–30 kg. In neonates and infants under 6 months where there is little space between neuraxial structures, ultrasonography offers a unique opportunity to verify the epidural catheter has been correctly positioned by directly visualizing the spread of local anaesthetic inside the epidural space.
This study confirms that ultrasonography is a practical option for epidural catheter placement in children weighing between 0.95 and 23.3 kg. The advantages include direct visualization of all neuraxial structures by ultrasonography and fewer bone contacts during epidural catheter placement compared with a technique that relies purely on LOR. We also observed swifter execution of ultrasonographic-guided epidural catheter placement compared with the standard method, albeit the preparation time of the ultrasound equipment was not considered. Booting time, sterile preparation of the ultrasound probe and initial measurements take approximately 30 s.
In choosing to use an epidural block in neonates and small infants the risks and benefits should be taken into consideration. In experienced hands the risks are low, but any method aimed at reducing the risks would be an advantage. The advantage of epidural anaesthesia in children undergoing major abdominal or thoracic surgery include profound analgesia without respiratory depression, a reduced need for postoperative ventilation and a reduced stress response.5 9
Apart from anecdotal reports, very few severe complications have been reported in large studies.10–12 Giaufré and colleagues19 reported a complication rate of 3.7/1000 for the lumbar approach. None of these complications were considered serious and included dural puncture, intra-vascular injection, technical problems, overdosing and transient paraesthesia. Interestingly, despite the small numbers, Giaufré and colleagues19 reported no complications for the thoracic approach but suggested that the use of thoracic epidural was confined to experienced paediatric anaesthesiologists.
It is difficult to demonstrate that a particular technique with a relatively low complication rate can be made safer by a specific method such as using ultrasound guidance. Large numbers would be required to demonstrate clinical significance. However, we suggest that the safety of epidural anaesthesia can be greatly enhanced if the spread of local anaesthetic and the position of the catheter can be directly visualized.
The skin–epidural distance depth varies in the growing child. A number of formulae have been developed for estimating the skin–epidural distance20 21 but these are inaccurate in children under 6 months.21 The depth of epidural space can be established using ultrasonography as 70–100% of the dura mater is visible in newborns and infants up to 3 months of age. Although this visibility is increasingly reduced in older children it is still possible to calculate the distance from the skin to the dura. In this study good correlation between the distance determined clinically and that measured by ultrasound was demonstrated, particularly in children less than 6 months of age.
Although the neuraxial structures of all patients in this study were normal, ultrasound can also be used to locate the position of the conus medullaris and the dural sac. It can also be used to determine whether there is any hidden structural abnormality that may contraindicate the use of epidural blockade.
The position of the epidural catheter tip is an important factor in determining whether satisfactory epidural analgesia will be achieved. The exact location of the catheter tip can be verified radiographically or by using techniques such as electrical catheter stimulation15 22 23 or monitoring ECG changes.24 While some publications report acceptable success rates,15 others have not been shown to compare favourably with purely landmark-based techniques.25 The exact location of the catheter cannot be established with any certainty using the LOR technique. Caudal catheters can be passed to lumbar and thoracic cord levels.26 However, the success rates of this approach have been variable,27–29 particularly in children aged less than 2 yr.
Ultrasonography currently offers the only method whereby the position of the epidural cannula and catheter can be verified using non-invasive method albeit by using surrogate markers. Direct visualization of the catheter inside the epidural space has been reported.30 31 Rapp and colleagues30 relied on direct visualization to verify the catheter position in a recent non-comparative report in children older than 6 months. Some of these ultrasound images may have been misinterpreted though because an axial resolution of only 0.4 mm can be achieved with 7 MHz probe or 0.3 mm with 10 MHz probes.
For this reason it is more appropriate to use real-time imaging of surrogate markers for more accurate assessment of the catheter position. These surrogate markers include the epidural spread of local anaesthetic that clearly indicates whether the catheter tip is correctly positioned. Alternatively a puff of air injected through the needle or catheter can easily be seen ultrasonographically and can be used to verify its position. The position of the catheter can also be reviewed after operation at any time by simply injecting a small amount of local anaesthetic or saline under ultrasound visualization.
Although this study was not intended to compare the quality of analgesia, the postoperative analgesia was similar in both groups, although 2 of 34 children in the LOR group required supplementary i.v. analgesia while none was required in the ultrasound group. This may suggest that the two catheters in the control group were not optimally positioned, despite that the investigator did not detect technical problems during catheter placement.
Paediatric epidurals are possibly the most demanding application of ultrasound guidance. Despite all epidural catheters being correctly placed in this study, the 21% rate of bone contacts in the ultrasound group (compared with 54% in the LOR group) highlights the difficulty of performing this technique in clinical practice. These bone contacts occurred despite the experience that our study group has with ultrasound-guided regional anaesthesia, and despite the good visibility of neuraxial structures in the age group studied.18 A reliable explanation for bone contacts in the ultrasound group is the incomplete ossification in babies and therefore the impossibility to detect the exact dimension of the vertebrae in ultrasonography. The fact that we detected a 21% rate of bone contacts in children <6 months compared with only 9% in children 6 months confirms this hypothesis.
Practitioners are cautioned that epidural blocks in this age group are challenging and should only be placed by experienced paediatric anaesthetists who have undergone the necessary training and have developed the manual skills. However, the ultrasound technique can be safely applied in clinical practice once the required degree of familiarity has been reached. The described technique for placing epidural catheters in children includes the need for two experienced investigators, which could be construed as a possible disadvantage. It is true that additional knowledge and hand skills are prerequisites for a safe and effective performance of that technique, and paediatric anaesthetists are encouraged to acquire specific training in ultrasonographic-guided regional anaesthesia.
At the time of writing, a further 158 epidural catheters have been placed through lumbar and thoracic puncture sites in newborns, infants and children up to 6 yr of age at our department. No complications have occurred. Further studies are being conducted to establish whether ultrasound guidance reduces the complication rate in paediatric epidural anaesthesia compared with conventional LOR techniques.
In summary, this is the first study comparing ultrasound guidance with the traditional LOR technique for epidural anaesthesia. Direct visualization of the intraepidural spread of local anaesthetic is a reliable way to verify the position of the epidural catheter. In experienced hands, ultrasound guidance reduces both the duration of catheter placement and the risk of bone contacts.
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Acknowledgments |
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This collaborative study was performed at Red Cross Children's Hospital. We are indebted to EVN (Lower Austrian Energy Supply Corporation) for the portable ultrasound system (SonoSite 180plus) used in the study group.
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References |
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