Wing H. Kwok

Real-time ultrasound-guided paramedian epidural access: evaluation of a novel in-plane technique

BACKGROUND Current methods of locating the epidural space rely on surface anatomical landmarks and loss-of-resistance (LOR). We are not aware of any data describing real-time ultrasound (US)-guided epidural access in adults. METHODS We evaluated the feasibility of performing real-time US-guided paramedian epidural access with the epidural needle inserted in the plane of the US beam in 15 adults who were undergoing groin or lower limb surgery under an epidural or combined spinal-epidural anaesthesia. RESULTS The epidural space was successfully identified in 14 of 15 (93.3%) patients in 1 (1-3) attempt using the technique described. There was a failure to locate the epidural space in one elderly man. In 8 of 15 (53.3%) patients, studied neuraxial changes, that is, anterior displacement of the posterior dura and widening of the posterior epidural space, were seen immediately after entry of the Tuohy needle and expulsion of the pressurized saline from the LOR syringe into the epidural space at the level of needle insertion. Compression of the thecal sac was also seen in two of these patients. There were no inadvertent dural punctures or complications directly related to the technique described. Anaesthesia adequate for surgery developed in all patients after the initial spinal or epidural injection and recovery from the epidural or spinal anaesthesia was also uneventful. CONCLUSIONS We have demonstrated the successful use of real-time US guidance in combination with LOR to saline for paramedian epidural access with the epidural needle inserted in the plane of the US beam.

Ultrasound-guided lumbar plexus block through the acoustic window of the lumbar ultrasound trident

Lumbar plexus block (LPB) is frequently used in combination with an ipsilateral sacral plexus or sciatic nerve block for lower limb surgery. This is traditionally performed using surface anatomical landmarks, and the site for local anaesthetic injection is confirmed by observing quadriceps muscle contraction to peripheral nerve stimulation. In this report, we describe a technique of ultrasound-guided LPB that was successfully used, in conjunction with a sciatic nerve block, for anaesthesia during emergency lower limb surgery. The anatomy, sonographic features, technique of identifying the lumbar plexus, and the potential benefits of using this approach are discussed.

Ultrasound-Guided Regional Anesthesia

Abstract Peripheral nerve blocks are frequently performed in children to provide anesthesia or analgesia during the perioperative period. Success depends on the ability to accurately place the needle—and thereby the local anesthetic—close to the target nerve without causing injury to the nerve or adjacent structures. In the past, clinicians relied on anatomic landmarks, fascial clicks, loss of resistance, or nerve stimulation to position the needle in the vicinity of the nerve. Anatomic landmarks provide valuable clues to the position of the nerve, but they are surrogate markers, lack precision, vary among children of different ages, and may be difficult to locate in obese children. Even nerve stimulation, which has been recommended as the gold standard for nerve localization, may not always elicit a motor response and its use does not guarantee success or preclude complications. Moreover, the accuracy of needle placement cannot be predicted with any of these methods, which may lead to multiple attempts to place the needle that may result in pain and possibly an incomplete or failed nerve block. The use of ultrasound (US) to guide peripheral and central neuraxial blocks has improved both accuracy and safety in both adults and children. In this chapter, the basic principles of US imaging and the techniques of US-guided regional anesthesia (USGRA) in children are described and reviewed.

Regional hemodynamic changes after an axillary brachial plexus block: a pulsed-wave Doppler ultrasound study.

Background Brachial plexus block (BPB) causes vasodilatation and an increase in blood flow to the ipsilateral upper limb. However, no reports have comprehensively evaluated the regional hemodynamic changes after a BPB. Methods Eight healthy adult patients who were scheduled for elective hand surgery had an ultrasound-guided axillary BPB for anesthesia. Regional hemodynamic parameters were measured in the ipsilateral brachial artery, using pulsed-wave Doppler (PWD) ultrasound before the block (0 minute) and at regular intervals for 30 minutes after the block. Skin temperature on the dorsum of the ipsilateral hand was also recorded at the same time intervals. Regional hemodynamic parameters that were measured in the brachial artery included peak systolic velocity (PSV, cm/s), end-diastolic velocity (EDV, cm/s), mean velocity (V mean) and time-averaged mean velocity (TAVM, cm/s), ratio of PSV and EDV (S/D), diameter (d, cm), resistance index (RI), and pulsatility index (PI). Brachial artery blood flow (Q) was calculated as the product of TAVM and cross-sectional area. Results The ultrasound-guided axillary BPB was successful in all the patients studied. The earliest change after the BPB was a change in the morphology of the PWD spectral waveform from a triphasic to a monophasic waveform and an elevation in the diastolic blood flow velocity. Over time, there was also a significant increase in PSV, EDV, V mean, TAVM, d, brachial artery blood flow, and skin temperature and a decrease in S/D ratio, RI, and PI. Most of these changes were seen as early as 5 minutes after the block. The increase in EDV (3.7-fold) was the most notable change, and it was greater (P < 0.05) than the increase in PSV (1.5-fold) and V mean (2.8-fold). Conclusions Regional hemodynamic changes that occur after an axillary BPB include a change in the morphology of the PWD spectral waveform, arterial vasodilatation, an increase in blood flow velocity, and an increase in blood flow through the ipsilateral brachial artery.

Sonoanatomy relevant for lumbar plexus block in volunteers correlated with cross-sectional anatomic and magnetic resonance images.

Background Ultrasound imaging of the anatomy relevant for lumbar plexus block (LPB) is challenging because of its deep anatomic location and the “acoustic shadow” of the overlying transverse processes. A paramedian transverse scan (PMTS) of the lumbar paravertebral region with the ultrasound beam being insonated through the intertransverse space (ITS) and directed medially toward the intervertebral foramen (PMTS-ITS) may overcome the problem of the “acoustic shadow” and allow clear visualization of the anatomy relevant for LPB. This study assessed the feasibility of using PMTS-ITS for imaging the anatomy relevant for LPB in healthy volunteers. Methods Thirty young volunteers underwent a PMTS-ITS of the right lumbar paravertebral region. The sonoanatomy was defined in corresponding cadaver anatomic sections and magnetic resonance images. Visibility of the paravertebral structures in the sonograms was assessed by 4 independent observers using a 4-point Likert scale (0, not visible; 1, hardly visible; 2, well visible; 3, very well visible), and the mean total ultrasound visibility score (UVS; maximum score possible, 30) was determined. Overall ultrasound visibility was judged as good if the total UVS was greater than 20, average if it was 10 to 20, and poor if it was less than 10. Results Ultrasound imaging of the right lumbar paravertebral region at the L3-L4-L5 vertebral level was successfully performed through the PMTS-ITS scan window in all volunteers studied. The lumbar nerve root, lumbar paravertebral space, lumbar plexus, and the psoas compartment were delineated in 57%, 27%, 57%, and 87% of volunteers, respectively. Overall ultrasound visibility of the lumbar paravertebral structures was judged as “good” (mean [SD] total UVS, 20.4 [3]). Conclusions A PMTS-ITS can be used to image the sonoanatomy relevant for LPB including the lumbar nerve root, lumbar paravertebral space, lumbar plexus, and the psoas compartment.

Gelatin-Agar Lumbosacral Spine Phantom A Simple Model for Learning the Basic Skills Required to Perform Real-time Sonographically Guided Central Neuraxial Blocks

This report describes the preparation of a gelatin‐agar spine phantom that was used for spinal sonography and to practice the hand‐eye coordination skills required to perform sonographically guided central neuraxial blocks. The phantom was prepared by embedding a lumbosacral spine model into a mixture of gelatin and agar in a plastic box. Cellulose powder and chlorhexidine were also added to the mixture, after which it was allowed to solidify. Sonography of the osseous elements of the lumbosacral spine in the phantom was then performed, and their sonographic appearances were compared to those in volunteers. Simulated real‐time sonographically guided paramedian spinal needle insertions were also performed in the phantom. The texture and echogenicity of the phantom were subjectively comparable to those of tissue in vivo. The osseous elements of the spine in the phantom were clearly delineated, and their sonographic appearances were comparable to those seen in vivo in the volunteers. During the simulated sonographically guided spinal injections, the needle could be clearly visualized, but the phantom provided little tactile feedback. In conclusion, the gelatin‐agar spine phantom is a simple and inexpensive sonographic spine model that has a tissuelike texture and echogenicity. It can be used to study the osseous anatomy of the lumbar spine and practice the skills required to perform sonographically guided central neuraxial blocks.

Ultrasound-guided lumbar plexus block using a transverse scan through the lumbar intertransverse space: a prospective case series.

Background and Objectives A paramedian transverse scan (PMTS) can be used to delineate the anatomy relevant for ultrasound-guided lumbar plexus block (LPB) through the lumbar intertransverse space. This case series evaluated the feasibility of using the PMTS to guide LPBs for anesthesia. Methods After research ethics committee approval and written informed consent, 15 American Society of Anesthesiologists physical status 1 to III patients with body mass index of less than 35 kg/m2 scheduled for lower-extremity surgery received an ultrasound-guided LPB and a sciatic nerve block for anesthesia. The blocks were performed using the PMTS and in-plane needle insertion. Localization of the lumbar plexus was confirmed by obtaining quadriceps muscle twitch. Successful blocks were defined as adequate anesthesia for lower-extremity surgery in the sensory territory of the lumbar plexus. Results The articular process and psoas muscle were visualized on ultrasound in all 15 patients (mean age, 46.3 ± 20.4 years; body mass index, 22.2 ± 2.4 kg/m2), but the lumbar plexus was identified in two-thirds of the patients. Blocks were successfully performed in 14 (93%) of the 15 patients. Poor visibility in 1 patient (7%) precluded the use of ultrasound guidance. The needle was visualized in the psoas muscle in 14 patients (93%), whereas proper needle location was confirmed in all patients by nerve stimulation. Needle to lumbar plexus contact was delineated on ultrasound in 8 (53%) and 14 patients (93%), before and after injection of local anesthetic, respectively. Adequate anesthesia was accomplished in all patients within 30 minutes of injection. Conclusion Ultrasound-guided LPBs can be reliably accomplished using the PMTS.

Quantitative evaluation of the echo intensity of the median nerve and flexor muscles of the forearm in the young and the elderly

OBJECTIVES Musculoskeletal structures often appear brighter on imaging in the elderly, which makes it difficult to accurately delineate a peripheral nerve during ultrasound-guided regional anaesthetic procedures. The echo intensity of skeletal muscles is significantly increased in the elderly. However, there are no data comparing the echo intensity of peripheral nerves in the young and the elderly, which this study was designed to evaluate. METHODS 13 healthy, young volunteers (aged <30 years) and 11 elderly patients (aged >60 years) who were scheduled to undergo orthopaedic lower limb surgery were recruited. The settings of the ultrasound system were standardised and a high-frequency linear array transducer was used for the scan. A transverse scan of the median nerve (MN) and the flexor muscles (FMs) at the left mid-forearm was performed and three video loops of the ultrasound scan were recorded for each subject. Still images were captured from the video loops and normalised. Computer-assisted greyscale analysis was then performed on these images to determine the echo intensity of the MN and the FMs of the forearm. RESULTS The echo intensity of the MN and FMs of the mid-forearm was significantly increased in the elderly (p<0.005). There was also a reduction in contrast between the MN and the adjoining FM in the elderly (p = 0.04). CONCLUSION Under the conditions of this study, the MN and the FMs in the forearm appeared significantly brighter than those in the young, and there was a loss of contrast between these structures in sonograms of the elderly.

Congenital tracheoesophageal fistula

the prolonged/delayed emergence from general anesthesia. It is not clear why this occurred following a day-case procedure in which only short-acting agents were administered. We postulate that the absence of adipose tissue resulted in the brain being disproportionately affected by anesthetic agent. Sevoflurane has a relatively high fat-solubility coefficient (47) relative to other shortacting agents (desflurane – 19). The brain with its myriad of myelinated neurons consists of 60% fat. It is not clear whether this delayed emergence phenomenon is a feature of Berardinelli–Seip syndrome, or idiosyncratic to our patient. Were it to become clear from other correspondence that it is a feature of the syndrome, it would be advisable to avoid highly fatsoluble anesthetic agents. Desflurane would seem to be a rational choice of inhaled anesthetic, augmented where possible by a regional anesthetic technique.