Local anaesthetic toxicity after bilateral thoracic paravertebral block in patients undergoing coronary artery bypass surgery.

We conducted a small pilot observational study of the effects of bilateral thoracic paravertebral block (BTPB) as an adjunct to perioperative analgesia in coronary artery bypass surgery patients. The initial ropivacaine dose prior to induction of general anaesthesia was 3 mg/kg, which was followed at the end of the surgery by infusion of ropivacaine 0.25% 0.1 ml/kg/hour on each side (e.g. total 35 mg/hour for a 70 kg person). The BTPB did not eliminate the need for supplemental opioids after CABG in the eight patients studied. Moreover, in spite of boluses that were within the manufacturer's recommendation for epidural and major nerve blocks, and an infusion rate that was only slightly higher than what appeared to be safe for epidural infusion, potentially toxic total plasma ropivacaine concentrations were common. We also could not exclude the possibility that the high ropivacaine concentrations were contributing to postoperative mental state changes in the postoperative period. Also, one patient developed local anaesthetic toxicity after the bilateral paravertebral dose. As a result, the study was terminated early after four days. The question of whether paravertebral block confers benefits in cardiac surgery remains unanswered. However, we believe that the bolus dosage and the injection rate we used for BTPB were both too high, and caution other clinicians against the use of these doses. Future studies on the use of BTPB in cardiac surgery patients should include reduced ropivacaine doses injected over longer periods.

Lumbar neuraxial anatomical changes throughout pregnancy: a longitudinal study using serial ultrasound scans.

This observational study was designed to investigate the anatomical changes of the lumbar spine over the course of pregnancy using serial ultrasound scans. We performed paramedian scans on 58 women at the L2-3, L3-4 and L4-5 levels; these were done at four periods of 11+0-13+6, 19+0-23+0, 28+0-32+0 and 38+0-40+0 weeks gestation. At each intervertebral level, the length of the interlaminar space, length of the visible intervertebral posterior dura and depth of the posterior dura mater from the skin were measured. The length of the interlaminar space and length of the visible intervertebral posterior dura mater were longer, and the depth of the posterior dura mater was shallower, with ascending spinal interspace. The depth of the posterior dura mater increased during pregnancy, although it plateaued between the third and fourth measurement periods. The other spinal measurements were not affected by gestation. These findings indicate that the L2-3 level is the most appropriate puncture site for epidural anaesthesia in pregnant women. Our results ought to be embraced as a departure point towards developing neuraxial insertion techniques guided or aided by ultrasound.

Does circumferential spread of local anaesthetic improve the success of peripheral nerve block?

BACKGROUND: The relation between the pattern of local anaesthetic (LA) spread and the quality of peripheral nerve block is unclear. METHODS: Twenty-one volunteers were randomized to receive a median nerve block with intended circumferential or intended non-circumferential spread of LA. Different predetermined volumes and needle placement techniques were used to produce the different patterns of LA spread. Volumetric, multiplanar 3D ultrasound imaging was performed to evaluate the pattern and extent of LA spread. Sensory block was assessed at predetermined intervals. RESULTS: Complete circumferential spread of LA was achieved in only 67% of cases in the intended circumferential study group and in 33% of cases in the intended non-circumferential group. Block success was similar (90%) and independent of whether circumferential or non-circumferential spread of the LA was achieved. All block failures (n=4) occurred in the intended non-circumferential group with low volumes of LA. The onset of sensory block (independent of group allocation) was faster with circumferential spread of LA [median (IQR) onset time, 15 (8; 20) min] compared with non-circumferential spread of LA [median (IQR) onset time, 20 (15; 30) min]. More LA was used for circumferential blocks [median (IQR) volume of LA 2.8 (1.3; 3.6) vs 1.3 (1.1; 2.4) ml]. CONCLUSIONS: Even under optimal conditions, it was not possible to achieve circumferential spread of LA in all intended cases. The success of median nerve block seems to be independent of the pattern of LA spread. CLINICAL TRIAL REGISTRATION: DRKS 00003826.

Multiplanar 3D ultrasound imaging to assess the anatomy of the upper airway and measure the subglottic and tracheal diameters in adults.

OBJECTIVE: To evaluate the feasibility of using three-dimensional (3D) ultrasound to assess the anatomy of the airway. METHODS: 11 young volunteers were recruited for 3D ultrasound and MRI of the airway. 3D ultrasound data were obtained from the level of the true vocal cords, cricoid cartilage and upper trachea. Multiplanar 3D ultrasound images were rendered and compared visually with corresponding MRI and cadaver anatomical sections. The anteroposterior (AP) and transverse diameter of the subglottic space and transverse diameter of the upper trachea were also measured in the 3D ultrasound and MR images and compared. RESULTS: The airway anatomy was clearly delineated in the multiplanar 3D ultrasound images. It was also possible to identify the cricothyroid junction, and a simple method to measure the AP diameter of the subglottic space using this landmark is described. We were also able to accurately measure the transverse diameter of the upper trachea, but the transverse diameter of the subglottic space was overestimated using ultrasound. There was a strong correlation for the AP diameter measurement (r=0.94, p<0.05) and moderate correlation for the transverse diameter measurement (r=0.82, p=0.002) of the subglottic space, and a strong correlation for the transverse diameter measurement (r=0.91, p<0.05) of the upper trachea, in the ultrasound and MR images. CONCLUSION: The anatomy of the adult airway can be assessed using 3D ultrasound. It can also be used to accurately measure the AP diameter of the subglottic space and the transverse diameter of the upper trachea. ADVANCES IN KNOWLEDGE: This is the first report to describe the use of 3D ultrasound to evaluate the anatomy of the upper airway and accurately measure the AP diameter of the subglottic space and the transverse diameter of the upper trachea.

Assessment of the spine with CT and MRI prior to interspinous/interlaminar spinal procedures: a pictorial review.

Imaging of the spine is increasingly available, whether as dedicated spine examinations or as studies that include the spine in the images obtained (e.g. CT abdomen). This pictorial review discusses imaging of the spine with CT and MRI and how prior review of this imaging can be helpful with potentially difficult spinal procedures. Pathologies illustrated include osteoarthritis, scoliosis, inflammatory spondyloarthropathies and post-operative spines.

Sonoanatomy relevant for ultrasound-guided central neuraxial blocks via the paramedian approach in the lumbar region.

OBJECTIVES: The use of ultrasound to guide peripheral nerve blocks is now a well-established technique in regional anaesthesia. However, despite reports of ultrasound guided epidural access via the paramedian approach, there are limited data on the use of ultrasound for central neuraxial blocks, which may be due to a poor understanding of spinal sonoanatomy. The aim of this study was to define the sonoanatomy of the lumbar spine relevant for central neuraxial blocks via the paramedian approach. METHODS: The sonoanatomy of the lumbar spine relevant for central neuraxial blocks via the paramedian approach was defined using a "water-based spine phantom", young volunteers and anatomical slices rendered from the Visible Human Project data set. RESULTS: The water-based spine phantom was a simple model to study the sonoanatomy of the osseous elements of the lumbar spine. Each osseous element of the lumbar spine, in the spine phantom, produced a "signature pattern" on the paramedian sagittal scans, which was comparable to its sonographic appearance in vivo. In the volunteers, despite the narrow acoustic window, the ultrasound visibility of the neuraxial structures at the L3/L4 and L4/L5 lumbar intervertebral spaces was good, and we were able to delineate the sonoanatomy relevant for ultrasound-guided central neuraxial blocks via the paramedian approach. CONCLUSION: Using a simple water-based spine phantom, volunteer scans and anatomical slices from the Visible Human Project (cadaver) we have described the sonoanatomy relevant for ultrasound-guided central neuraxial blocks via the paramedian approach in the lumbar region.

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.

Generation of hydrogen rich gas through fluidized bed gasification of biomass.

The objective of this study was to investigate the process of generating hydrogen rich syngas through thermo chemical fluidized bed gasification of biomass. The experiments were performed in a laboratory scale externally heated biomass gasifier. Rice husk had been taken as a representative biomass and, steam had been used as the fluidizing and gasifying media. A thermodynamic equilibrium model was used to predict the gasification process. The work included the parametric study of process parameters such as reactor temperature and steam biomass ratio which generally influence the percentage of hydrogen content in the product gas. Steam had been used here to generate nitrogen free product gas and also to increase the hydrogen concentration in syngas with a medium range heating value of around 12 MJ/Nm3.

Right thoracic paravertebral anaesthesia for percutaneous radiofrequency ablation of liver tumours.

OBJECTIVES: Percutaneous radiofrequency ablation (PRFA) of liver tumours performed under local anaesthesia and intravenous sedation can cause severe pain to patients. This prospective study evaluated the efficacy of a right thoracic paravertebral block (TPVB) for anaesthesia and analgesia during PRFA of liver tumours. METHODS: 20 patients, aged 44-74 years, with liver malignancies received a multiple injection TPVB at the T6-10 levels 30 min before the PRFA. An intravenous infusion of propofol (3-5 mg kg(-1) h(-1)) was administered to patients who requested to be sedated and intravenous fentanyl (25 µg bolus) was administered as rescue analgesia. Pain during the TPVB and PRFA was assessed using a numerical rating scale (NRS; 0, no pain; 10, worst imaginable pain). Patients were also assessed for residual pain and analgesic consumption during the 24 h after the intervention. RESULTS: The TPVB was well tolerated and produced ipsilateral sensory anaesthesia with satisfactory spread (median (range); 8 (6-11) dermatomes). The PRFA procedure caused mild pain (mean (standard deviation, SD); NRS 1.4 (1.9)) during the insertion of the ablation needle and the peak pain intensity during the therapeutic burn was moderate (mean (SD); NRS 5.0 (3.3)) in severity. During the 24 h after the PRFA, patients reported minimal pain and consumed very few analgesics. The mean (SD) satisfaction score (0, totally dissatisfied; 10, very satisfied) of the patients was 8.9 (1.1) and that of the radiologists was 8.8 (1.4). CONCLUSION: A right TPVB is safe and effective for anaesthesia and analgesia during PRFA of malignant liver tumours.

The analgesic efficacy of continuous wound instillation with ropivacaine after open hepatic surgery.

The analgesic efficacy of continuous local anaesthetic wound instillation after open hepatic surgery was evaluated. Forty-eight patients scheduled for elective liver surgery were assigned to receive either ropivacaine 0.25% or saline infusion at 4 ml.h(-1) for 68 h via two multi-orifice indwelling catheters placed within the musculo-fascial layer before skin closure; plasma ropivacaine concentrations were measured during the infusion. Supplemental analgesia was provided by intravenous patient-controlled analgesia morphine. Patients in the ropivacaine group had decreased mean (SD) total morphine consumption (58 (30) mg vs 86 (44) mg, p = 0.01) and less pain at rest as well as after spirometry at 4, 12, 24, 48 and 72 h postoperatively (p < 0.01). Forced vital capacity was reduced postoperatively in both groups, but the reduction was greater in the saline group at 12 and 24 h (p = 0.03). The mean plasma concentration of ropivacaine increased to 2.05 (0.78) µg.ml(-1) at the point when the infusion was terminated.

A technique that may improve the reliability of endobronchial blocker positioning during adult one-lung anaesthesia.

We describe a novel technique, previously applied to small children, for adult one-lung anaesthesia in which a single-lumen endotracheal tube is used with an endobronchial balloon blocker The main aims of the technique are to reduce the likelihood of cephalad displacement of the balloon into the trachea and to facilitate directional placement of the endobronchial balloon. We present five illustrative cases of one-lung anaesthesia in patients of adult size, in which the endotracheal tube-endobronchial balloon technique was considered preferable to the use of a double-lumen tube technique. The situations included difficult intubation, need for postoperative ventilation, a tortuous trachea and an unexpected need to perform one-lung anaesthesia. The technique involved deliberate placement of the endotracheal tube tip near the carina to block cephalad dislodgement of the blocker The chance of the balloon blocking the endotracheal tube tip could be further reduced by having the intraluminal endobronchial balloon blocker emerge through the Murphy eye.

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.

Placing the tip of the endotracheal tube at the carina and passing the endobronchial blocker through the Murphy eye may reduce the risk of blocker retrograde dislodgement during one-lung anaesthesia in small children.

We present nine cases of one-lung anaesthesia in small children and infants in which a novel technique was used to reduce the risk of endobronchial blocker retrograde dislodgement. The technique involved threading the stem of the blocker through the Murphy eye of the endotracheal tube (ETT) and deliberately passing the tip of the ETT all the way to the carina. The tip of the ETT blocked any retrograde movement of the blocker.

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.

Closed-loop feedback computer-controlled infusion of phenylephrine for maintaining blood pressure during spinal anaesthesia for caesarean section: a preliminary descriptive study.

We describe the novel use of a closed-loop feedback computer-controlled infusion of phenylephrine for maintaining blood pressure in 53 patients having spinal anaesthesia for elective caesarean section. A simple on-off algorithm was used that activated an intravenous phenylephrine infusion at 100 microg.min(-1) when systolic blood pressure was less than or equal to baseline and stopped the infusion when systolic blood pressure exceeded baseline. Up to uterine incision, 94.6% of all systolic blood pressure measurements were within the range (baseline +/- 20%). Seven patients (13.2%) had one or more episodes of hypotension (systolic blood pressure < 80% of baseline) and 23 patients (37.7%) had one or more episodes of hypertension (systolic blood pressure > 120% of baseline). No patient had nausea or vomiting and in no case was umbilical arterial blood pH < 7.2. Calculated system performance parameters were comparable with those of previously published closed-loop systems and provide a reference for the potential development and comparison of more advanced algorithms.

Ultrasound-guided sciatic nerve block: description of a new approach at the subgluteal space.

Sciatic nerve block is frequently used for anaesthesia or analgesia during orthopaedic foot surgery and there are several different approaches to the sciatic nerve. This report describes a new approach to the sciatic nerve using ultrasound. Local anesthetic was injected into the 'subgluteal space' under ultrasound guidance which was effective in producing sciatic nerve block in a small series of five patients. The anatomy, sonographic features, technique of identifying the subgluteal space, and potential advantages of this approach to the sciatic nerve are discussed.