1Department of Anaesthesia and General Intensive Care, University Hospital of Vienna, Waehringer Guertel 1820, A-1090 Vienna, Austria. 2Department of Anaesthesia and General Intensive Care, Hospital of Korneuburg, Wiener Ring 35, A-2100 Korneuburg, Austria*Corresponding author
Accepted for publication: June 28, 2000
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Abstract |
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Br J Anaesth 2000; 85: 8413
Keywords: measurement techniques, ultrasound
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Introduction |
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Methods |
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After application of standard monitoring, including ECG, non-invasive arterial pressure and pulse oximetry, all patients were sedated with midazolam 13 mg iv. Women were placed on their side, with the side to be blocked uppermost, and were scanned with a HewlettPackard scanner with a 7.5 MHz linear array probe. The transverse process was located and its distance from the skin and the distance of the parietal pleura from the skin were determined. The scanning head was placed at 90° to the skin in all planes, 3.5 cm from the anatomical midline at the level of the cephalad end of the spinous process of T4. The transverse process and the parietal pleura were located by ultrasonography.
The skin was sterilized and then it and underlying structures were locally infiltrated with 3 ml of 2% lidocaine. The needle used for infiltration was inserted at 90° to the skin in all planes to strike the transverse process; the distance from the skin to the bony contact was marked on the needle and subsequently measured with a ruler. Angle corrections, if required to reach the bony contact, were recorded. Paravertebral block was performed 3.5 cm from the anatomical midline, as proposed by Eason and Wyatt.3 A 22 gauge spinal needle (Terumo spinal needle; Terumo Corporation, Tokyo, Japan) was inserted 3.5 cm from the anatomical midline at the level of the cephalad end of the spinous process of T4. The needle was advanced at 90° to the skin in all planes to strike the transverse process or the head of the rib. It was then directed over the top of the bony structure. The technique of loss of resistance to normal saline injection was used to identify the paravertebral space after the needle passed the costotransverse ligament. The depth was marked on the needle and the distance was measured with a ruler. After negative aspiration, a test dose of 5 ml of 0.5% bupivacaine with 1:200 000 epinephrine was administered incrementally. A single injection of 0.3 ml of 0.5% bupivacaine kg1 (maximum dose 150 mg) with 1:200 000 epinephrine was performed in all patients. The duration of injection of the local anaesthetic was 120 s. The puncture of the paravertebral space was performed in all cases by the same anaesthetist, who was blinded to the results of the ultrasonographic measurements. The patients body position was unchanged from the beginning of the ultrasonographic measurements until the block was finished. The angle deviation of the needle from the horizontal line was noted in order to calculate the angle correction of the sonographic distance: (i.e. needle distance=sonographic distance/cosine angle deviation). Angle deviation was measured with a protractor held on the patients skin.
The pinprick method and thermographic spread were used to assess the extent of analgesia. Paravertebral blocks with a thermographic spread (sympathetic block) of <4 dermatomes or loss of pinprick sensation of <3 dermatomes were taken to indicate incorrect puncture. Ipsilateral warming was recorded using an infrared temperature scanner (Dermatemp, Exergen, Watertown, MA, USA). Patients with insufficient paravertebral block were excluded from study evaluation. A chest X-ray was performed in all patients after surgery to exclude pleural puncture.
Patients characteristics and all distances are presented as mean (range). Correlations were calculated by the Spearman rank test.
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Results |
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Discussion |
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Although accidental pleural puncture is rare,2 paravertebral block is still considered potentially dangerous by many anaesthetists,4 so the technique is performed infrequently. However, some centres specialized in this block consider it the regional anaesthesia of choice for unilateral thoracic or abdominal surgery.4 Using ultrasound to visualize anatomical landmarks, it may be possible to improve the safety of the block.
The transverse process is an important landmark when one is performing paravertebral block. However, it can be difficult to locate in obese patients or in cases of vertebral abnormality, so the risk of pleural puncture may be higher in these patients. The finding that the apparent distances from the skin to the bony contact when measured using the needle method were greater than angle-corrected sonographic measurements may be explained by tangential contact of the transverse process or by skin compression with the scanning head. This compression might in part explain the relatively small differences between the distance to the paravertebral space and the angle-corrected ultrasound distance to the parietal pleura. Another explanation could be the quite lateral approach to the wedge-shaped paravertebral space of 3.5 cm laterally from the anatomical midline.
Ultrasound scanning of the transverse process and the parietal pleura provides accurate assessment of the maximum needle insertion depth to avoid pleural puncture and enables calculation of the depth to the paravertebral space. Prior knowledge of the depth to the paravertebral space should make paravertebral block easier to perform.
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References |
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2 Lönnqvist PA, MacKenzie J, Soni AK, Conacher ID. Paravertebral blockade: failure rate and complications. Anaesthesia 1995; 50: 81315[ISI][Medline]
3 Eason MJ, Wyatt R. Paravertebral thoracic blocka reappraisal. Anaesthesia 1979; 34: 63842[ISI][Medline]
4 Richardson J, Sabanathan S. Thoracic paravertebral analgesia. Acta Anaesthesiol Scand 1995; 39: 100515[ISI][Medline]