The delivery rate accuracy of portable infusion pumps used for continuous regional analgesia

Portable pumps used for local anesthetic infusion during continuous regional analgesia are gaining acceptance. These pumps are often used for ambulatory patients who are medically unsupervised throughout most of the infusion. However, the performance of these pumps, which infuse potentially toxic medication, has not been independently investigated. We investigated the flow rate accuracy, consistency, and profiles of various portable pumps often used for local anesthetic infusion during continuous regional analgesia. By using a computer/scale combination within a laboratory to record infusion rates, 6 pumps were tested with their flow regulators at expected (30 degrees-32 degrees C) and increased (34 degrees-36 degrees C) temperatures. Infusion rate accuracy differed significantly among the pumps, exhibiting flow rates within +/-15% of their expected rate for 18%-100% of their infusion duration. An increase in temperature also affected pumps to differing degrees, with infusion rates increasing from 0% to 25% for each model tested. These results suggest that factors such as flow rate accuracy and consistency, infusion profile, and temperature sensitivity should be considered when choosing and using a portable infusion pump for local anesthetic administration.

IMPLICATIONS

Portable pumps often used for local anesthetic infusion during continuous regional analgesia exhibit varying degrees of delivery rate accuracy and consistency. Furthermore, increases in temperature result in an increased infusion rate for various pumps investigated. These factors should be taken into consideration when choosing and using a portable infusion pump.

[Ultrasound in local anaesthesia. Part I: technical developments and background]

The localisation of the nerve to be blocked is one of the special challenges in local anaesthesia. Since the first time local anaesthesia procedures were carried out approximately 100 years ago, the basic limitations of this method have always been the unsatisfactory success rate and the specific risks involved. Even by variation of the access route to the various nerves and use of different identification methods, no ideal blockade technique has been found which allows a 100% success rate and at the same time reduces the risks to a minimum. The clinical introduction of various aids, such as nerve stimulation or Doppler sonography, have brought no statistically significant advantages despite showing clear improvements. In recent years there has been a trend towards local anaesthesia in perioperative care due to the proven advantages and range of possibilities. Several working groups have developed methods for the sonographic identification of nerves or the epidural space and to an exact placing of needles or catheters from the information obtained. In this way the application of catheters and the injection of local anaesthetic agents can be carried out in an accurate and controlled manner. Although sonography is a procedure which has been used in local anaesthesia for over 10 years, there are at present only few practising local anaesthetists who can use this method. However, interest in this method is growing especially due to the aspect of quality assurance. Organising committees have established that this method will be the future direction. Perhaps even the prediction of Alon P. Winnie for ultrasound-guided local anaesthesia will become true: "Sooner or later someone will make a sufficiently close examination of the anatomy involved, so that exact techniques will be developed."

A modification of the inter-cuff technique of IVRA for use in knee arthroscopy

PURPOSE

To describe a modified approach to intravenous regional anesthesia (IVRA) for operations on the knee joint.

CLINICAL FEATURES

A 52-yr-old male presenting for knee arthroscopy was anesthetized by IVRA using only 40 mL of lidocaine 0.5%. After performing IVRA in the routine way an additional below knee tourniquet was used and inflated after local anesthetic exsanguination towards the knee. Operation was performed without the need for further analgesic.

CONCLUSION

The technique allowed the use of a small anesthetic volume for IVRA on the lower limb, thus decreasing the potential risk of local anesthetic toxicity.

Use of a simple forearm tourniquet as an adjunct to an intravenous regional block

Intravenous regional anesthesia (IVRA) is a well-recognized technique for producing anesthesia during surgical procedures of the extremities. It has been suggested that the application of a tourniquet to the forearm may improve the quality of the block. The purpose of this investigation was to determine whether the application of a forearm tourniquet would accelerate onset time and improve the density and quality of an intravenous regional block. Twenty volunteer subjects were enrolled and randomly assigned in this crossover investigation. Control subjects received a standard IVRA technique; experimental subjects received IVRA technique with the application of a simple forearm tourniquet. Pain was elicited by means of an electrical stimulus, and assessments were performed using a 100-mm Visual Analogue Scale (VAS). Paired t tests were used to examine differences between groups on the variables studied. It was noted that the arm with the tourniquet had a shorter time for the onset of anesthesia (P = .0008) and had lower 10-minute VAS tolerance (P = .0469). This investigation suggests that the application of a simple forearm tourniquet as an adjunct to IVRA provides a more rapid onset of anesthesia than when no tourniquet is applied and may improve the density and quality of the block.

Supraclavicular regional anaesthesia revisited--the bent needle technique

A new technique for achieving brachial plexus anaesthesia through the supraclavicular fossa is described. Its objectives are to minimize risk to the lung and provide for continuous as well as single-shot options. The plexus is approached through the lateral aspect of the supraclavicular fossa, and a bend in the shaft of the needle permits the tip of the needle to be directed tangential to the chest wall. An audit of 572 cases associated with the development of this technique is presented.

Quantitative comparison of leakage under the tourniquet in forearm versus conventional intravenous regional anesthesia

We compared the quantitative leakage between forearm and conventional IV regional anesthesia (IVRA). Forearm IVRA remains unpopular because of the theoretical risk of local anesthetic leakage through the interosseous vessels. IVRA was simulated on the forearm or arm during two separate, randomized sessions using a double tourniquet in 14 volunteers. A radiolabeled substance, DISIDA (99m Tc-disofenin) with a structure similar to lidocaine, was injected instead of local anesthetic. Volumes of 0.4 mL/kg (maximum 25 mL), were used for forearm IVRA and 0.6 mL/kg (maximum 45 mL) for conventional IVRA. A gamma camera recorded radioactivity levels in the limb distal to the tourniquet every 30 s while the tourniquet was inflated (25 min) and for 20 min postdeflation. The leakage of radiolabeled substance during inflation was similar in both groups, 6%+/-12% (mean +/- SD) from the forearm and 10%+/-20% from the upper arm. After deflation, mean loss of radioactivity was higher in conventional IVRA, 70%+/-7% vs 57%+/-11% and 82%+/-5% vs 69%+/-11% at 3 and 20 min, respectively (P < 0.001). We conclude that forearm IVRA results in tourniquet leakage comparable to conventional IVRA and is potentially safer because the required dose of local anesthetic is smaller.

IMPLICATIONS

Using a tourniquet on the forearm for IV regional anesthesia does not increase the risk of drug leakage. This is potentially a safer technique compared with conventional IV regional anesthesia because a much smaller dose of local anesthetic is required.

Adverse effects of regional anaesthesia in children

True complications of regional block procedures pertain to the performance of the block technique and the local anaesthetic. Such complications include lesions caused by the device used, and many of these complications can be avoided by using specifically designed devices.Complications related to the local anaesthetic solution mainly consist of local and systemic complications. Local toxicity has mainly been reported in adults following spinal administration of 5% lidocaine (lignocaine), a drug that is not usually used in children. Systemic toxicity consists of CNS and cardiovascular complications, methaemoglobinaemia and allergic reactions. Systemic toxicity has special features in children, especially in those <1 year old. Infants have a much higher free serum concentration of local anaesthetics than older children and adults, and are more prone to the deleterious effects of local anaesthetics. Additionally, as regional blocks are usually performed under general anaesthesia in children, signs of CNS toxicity may be concealed. Because of their higher heart rate, newborns and infants are thought to be more prone to the phasic block produced by tertiary amine agents such as bupivacaine than are adults. Serum concentrations at which bupivacaine (and etidocaine) exert cardiac toxicity seem to be similar to those producing CNS toxicity. As there is an increased threshold for CNS toxicity in infants plus an increased (or equal) sensitivity to bupivacaine cardiotoxicity, cardiac signs may not be preceded by any sign of CNS toxicity. Cardiac complications include: (i) arrhythmias with high degree conduction block, major QRS widening, torsade de pointes, and ventricular tachycardia related to re-entry phenomena; and (ii) major vascular collapse favoured by a concomitant decrease in the myocardial contractile force. Other complications of regional block procedures result from poor selection of agent, and inadequate safety precautions and monitoring of the patient, especially during the postoperative period. There are 2 other groups of disorders often reported as complications of regional anaesthetics: (i) effects that were not anticipated by the anaesthetist because of a lack of knowledge of all the consequences of the technique used; and (ii) complications attributed to a concomitant regional block procedure but with no established, sometimes even improbable, causal link with the regional technique. The overall morbidity of regional anaesthesia in children is low. Sound selection of local anaesthetics, insertion routes and block procedures, together with appropriate and careful monitoring, should prevent any major undesirable effects and enable regional anaesthesia to be a well tolerated and effective tool to overcome pain associated with minimal morbidity.

Regional anesthesia equipment checkout recommendations: a case report and discussion

The use of an apparatus checkout list is common in medicine and anesthesia. After being involved in a case in which the separation of a spinal introducer hub from its shaft during subarachnoid block required surgical removal of the retained shaft, a search for related cases was undertaken. The Medline database from 1966 to 1997 was used to identify defects and problems related to centroneuraxis equipment. Using these data, a regional anesthesia equipment checkout list of six recommendations was created in the spirit of other anesthesia checkout lists. The recommendations are to (1) ensure the proper fit and length between the needle and its stylet (particularly if using resterilized needles), (2) check for defects in the needle hub and shaft union by applying axial traction to the hub, (3) flush the needle with the distal end occluded, checking for defects in the hub-shaft junction or in the shaft itself, (4) check for malalignment between the needle hub and shaft, (5) examine the catheter for consistency in diameter and ensure the catheter can be introduced into the needle, and (6) flush the catheter, checking for the presence, patency, and location of distal holes. These recommendations must undergo further review before they are accepted as a practice standard.

A review of regional blocks for the foot

The blocking of the posterior tibial, sural, saphenous, superficial peroneal, and the deep peroneal nerves with possible alternative approaches is discussed. Digital blocks, Mayo blocks, and intravenous regional anesthesia are also discussed. The placement of the tourniquet above the ankle but below the calf muscles will avoid deep muscle pain. Lidocaine and bupivacaine cause vasodilatation in the foot.

[Techniques of local anesthesia in the area of the head]

In the head and neck region, many procedures can be performed under local anesthesia. The anesthetic agent can be applied onto the surface of the skin or mucosa (surface anesthesia), it can be infiltrated into the tissue to be treated, or it can be used to block the regional sensory nerve (conduction anesthesia). In this paper, the most important techniques for local anesthesia of the face are presented as a short clinical guide.

[Axillary plexus catheter block in childhood and adolescence]

During the past two years (1994 and 1995), eight patients with the average age of eleven and a half years (four to fifteen years) received continuous axillary plexus anaesthesia subsequent to severe injuries of their upper extremities. The advantage of intra-, peri-, and postoperative anaesthesia and postoperative pain management are presented as a case report.

[Interscalene brachial plexus catheter for anesthesia and postoperative pain therapy. Experience with a modified technique]

OBJECTIVES

This study was conducted to evaluate a modified technique of interskalene brachial plexus anaesthesia (ISB) and postoperative catheter analgesia for shoulder surgery. The original method described by Winnie bears some rare but life-threatening complications (inadvertent subarachnoid or intra-arterial injection, pneumothorax).

MATERIALS AND METHODS

Ninety-one patients with chronic rheumatoid arthritis who were scheduled for open or closed shoulder surgery received a modified ISB with catheter insertion. The injection site was more cephalad than that described by Winnie and the cannula was directed towards the junction between the medial and lateral third of the clavicle. Intra- and postoperative management, complications, and patients' satisfaction were recorded and evaluated.

RESULTS

Implementation of ISB was possible in all cases, however, 3% of these presented technical problems. Anaesthesia with 300 mg mepivacaine 1% was successful in 94% of patients without and in 96% with augmentation after an average of 32 min; 10% of the patients suffered a drop in blood pressure after being placed in the beach-chair position for surgery. Postoperatively, all patients received 20 ml bupivacaine 0.25% for pain management via the catheter; 11% needed an additional analgesic drug. The catheter was removed after an average of 5 days. Signs of superficial local infection were noticed in 8 cases. Side effects occurred in 13% as Horner's syndrome, in 6.5% as recurrent laryngeal nerve block, and in 3.3% as phrenic nerve block. The acceptance of this anaesthetic technique among the patients was very high (96.7%).

CONCLUSION

We consider the modified ISB with catheter a safe and effective procedure for anaesthesia and postoperative pain management of open and closed shoulder surgery.

Long-tapered double needle used to reduce needle stick nerve injury

BACKGROUND AND OBJECTIVES

Needle trauma may cause peripheral nerve injuries during performance of peripheral nerve block.

METHODS

Four types of 21-gauge needles for regional anesthesia were compared: a beveled nerve block needle (Quincke type); a short-tapered needle with a side orifice (Whitacre type); a long-tapered needle with a side orifice (Sprotte type); and a long-tapered double needle combining an inner pencil-point fine needle with an outer truncated conical needle (a new type). This new needle was developed to reduce the potential for nerve injury while retaining a suitable flow rate of anesthetic solution and the ability to inject the solution precisely at the point of paresthesia elicited by the tip. Each type of needle was used to produce puncture injuries to rabbit sciatic nerves. Eighteen specimens were studied within each needle group. The beveled needle was used to produce two different types of nerve injuries by inserting it either transverse or longitudinal to the nerve fibers. Each histologic specimen of the nerve with the needle puncture was surface-stained with hematoxylin-eosin and Bodian's method. Subsequently, the number of damaged axons was histomorphologically counted and statistically evaluated.

RESULTS

Both long-tapered needles produced significantly fewer transected axons than the beveled needle inserted with the bevel longitudinal to the nerve fibers.

CONCLUSIONS

The long-tapered needles produced the least number of transected nerve fibers after sciatic nerve puncture.