21 General Principles for Performing Peripheral Blocks
21.1 Essential Components Necessary for Proper Aseptic Technique
Although the risk of infection with “single-shot” nerve blocks is relatively small, a strictly sterile technique must nevertheless be observed. There has been one documented case of a fatal necrotizing fasciitis due to single-shot axillary block (Nseir et al 2004). Mandatory preparation for the therapist includes as a minimum hand scrub, mask, cap, and sterile surgical gloves and carefully spraying and wiping the skin with alcoholic disinfectants, paying meticulous attention to the prescribed contact time.
Much higher demands must be made when placing peripheral nerve catheters for continuous administration of local anesthetic. Peripheral regional pain catheters carry a substantial risk of infection (see Chapter 22).
The strictest hygienic standards are required for dealing with continuous regional pain catheters.
The guidelines on hygiene in the administration and subsequent care of regional block techniques are clearly defined (Morin et al 2006). Essential aspects are:
Hand-washing is mandatory for all personnel involved before starting the procedure.
Wearing a mask and cap is mandatory for all personnel involved in the procedure wearing a sterile gown is recommended.
For skin areas rich in sebaceous glands (neck, axilla, groin), the alcoholic disinfectant must have a contact time of 10 minutes; alcohol solutions with a higher percentage of ethanol achieve the required reduction of bacteria on the skin in areas rich in sebaceous glands after 2.5 minutes (Cutasept med F, see manufacturer′s information)
After patient positioning, it is recommended to use generous spray disinfection of the puncture site before starting the other preparations for placing a continuous block.
The site chosen must be kept wet with the disinfectant for the entire contact time.
After another hand-washing, sterile gowning and gloving, and preparation of the sterile field, the initial spray disinfection must be repeated as a wipe disinfection several times.
Sterile draping of the planned insertion site should include a widespread area and should not obscure anatomical landmarks and a clear view of the expected response (Fig. 21.1).
After fixation of the catheter, the insertion site must be covered with a sterile dressing. The date and time of catheter placement must be noted (see “Complications of Peripheral Nerve Catheters for Pain Management” in Chapter 22).
21.2 General Principles of Informed Consent, Positioning and Monitoring
Anesthesia-related mortality has fallen markedly in recent decades and is today estimated at 1 death per 10,000 anesthesia procedures. Many incidents of complications during both general and regional anesthesia can be avoided. An important requirement is judicious preparation and monitoring and early identification of a problematic situation.
A requirement for every regional anesthesia is the patient′s legally effective informed consent. In day surgery or in the outpatient pain clinic, continuous peripheral block techniques can be performed and continued successfully on an outpatient basis (Rawal et al 1997, Rawal 2000). However, the basic conditions (getting home, side effects, etc.) must be carefully discussed and evaluated with the patient and if necessary the relatives or family doctor should also be involved. Besides the anesthetist′s competence, the facilities and equipment are of fundamental importance in regional anesthesia. The treatment room should have a calm atmosphere, be of adequate size, and allow the patient to be placed in suitable positions.
Emergency medications, the possibility of ventilation and intubation, and also a defibrillator must be available. Every patient should have an IV line and basic monitoring (ECG, blood pressure monitoring).
In addition to monitoring of the vital parameters, assessment and monitoring of the onset, distribution, and quality of the nerve block is required. The procedure and sequence should be documented.
21.2.1 Patient Informed Consent before Peripheral Nerve Blocks
The procedure of a peripheral nerve block must be explained to the patient. It is important also to mention the possibility of an incomplete block and discuss further procedures in this case. General anesthesia should always be considered, so information must also be provided about this.
A regional block can be planned as a supplement to general anesthesia in major surgery, particularly when continuous peripheral nerve analgesia is planned or for postoperative pain management. Whether sedation is desired for performance of the block must be discussed.
As well as specific complications of the technique (e.g., Horner syndrome, pneumothorax), the patient must be generally informed about toxic reactions caused by the local anesthetic and about possible nerve injuries. Hematomas and false aneurysms can also occur after vascular puncture. If continuous peripheral techniques are planned, the risk of infection must be described. It must be pointed out to the patient that some problems can become apparent only after the end of the block (e.g., infection, pneumothorax). The patient should be instructed to report problems of any kind.
For continuous procedures of the lower limb, the patient must be informed of the possible risk of falling on getting up as a result of the impaired motor and sensory function and depth perception (Muraskin et al 2007, Ilfeld et al 2010). There is a risk of injury (see also Chapter 22). The patient should get up only with assistance at the start!
The most comfortable position possible should be ensured for the patient. Positioning aids (cushions, pads, etc.) can facilitate the procedure. Position-related injuries in particular must be avoided. Attention must be paid to regions particularly at risk (e.g., ulnar nerve in the ulnar sulcus; common fibular nerve distal to the head of the fibula). Pressure-free positioning of the limb must also be ensured in the postoperative period. This applies especially to continuous techniques. Special pads and splints are available (Fig. 21.2).
In premedicated or sedated patients, an additional (abdominal) positioning strap may be useful in the operative area to secure the patient in order to avoid unintended falls.
Many patients want sedation and this requires special attention and monitoring by the anesthetist. Pulse oximetry should be ensured in sedated patients in addition to ECG and blood pressure monitoring; ECG monitoring of the depth of sedation may be useful (Fig. 21.3).
Oscillometric automatic blood pressure measurement has become well established in clinical practice. Monitoring of circulation during regional anesthesia can be expanded, depending on the risk classification of the patient and the type of operation.
There should be continuous ECG monitoring during the performance of a regional anesthesia block and perioperatively. Together with blood pressure monitoring and pulse oximetry, the ECG is the basis of monitoring patients under regional anesthesia.
Perioperative monitoring of ventilation during regional anesthesia is usually just clinical (visual and acoustic). With indirect measurement of ventilation by means of pulse oximetry, the consequences of reduced alveolar ventilation are identified with a marked delay, particularly when oxygen is being given (hypercapnic normoxia). Additional monitoring of spontaneous respiration (at least as a trend) can be performed by measuring end-expiratory CO2. To do this, a CO2 line is placed close to the patient′s nose under the oxygen mask. Transcutaneous monitoring and CO2 measurement is now possible (TOSCA) (Fig. 21.4).
The importance of pulse oximetry during regional anesthesia is uncontroversial. It has a key position in the monitoring of vital functions through the indirect monitoring of circulation and ventilation. Low oxygen levels that are not consistent with the clinical impression may indicate methemoglobinemia if prilocaine was used as local anesthetic. Vasoconstriction is a limiting factor of pulse oximetry.
Monitoring of body temperature is indicated particularly in elderly patients, in prolonged operations, and when there is increased blood loss. In regional anesthesia with a marked sympathetic block, heat redistribution occurs and the insulating function of the periphery (vasoconstriction) is eliminated. In addition, the patient finds the cool room temperature (air conditioning) unpleasant. Adequate warming is therefore recommended during prolonged operations. Convection warming systems are regarded as particularly suitable (e.g., Warm Touch from Covidien GmbH; Bair Hugger from Arizant).
21.3 Technical Aids for Performing Peripheral Nerve Blocks
21.3.1 Vascular Doppler Sonography
Doppler ultrasound is used in regional anesthesia for orientation of the course of blood vessels and to avoid vascular puncture. It can be extremely helpful especially in difficult anatomical situations. With different acoustic transducers, the small and very handy devices that are now available can show both superficial (8 MHz) and very deep (4 MHz) veins and arteries (Fig. 21.5).
Example of suitable Doppler devices: handydop by Kranzbühler, Huntleigh, Elcat.
Ultrasound scanning is described in detail in Chapter 1.
21.3.3 Surface Thermometer
Depending on the proportion of sympathetic fibers, blockade of peripheral nerves leads to regional sympathetic block. The proportion of sympathetic fibers is very high in the brachial plexus and the sciatic nerve, for instance. The effects of the block can be checked very well by monitoring the skin temperature. As the C-fibers (postganglionic sympathetic fibers) are blocked first, a rise in skin temperature distal to the site of the block is an early indication of the onset of the block. The rise in skin temperature is 2 to 8° Celsius depending on the baseline and can be measured quickly and easily with a surface thermometer.
A suitable thermometer (adjustable to surface temperature) is, for example, First Temp Genius, Sherwood Medical (Fig. 21.6).
21.3.4 Peripheral Nerve Stimulation
The need for peripheral nerve stimulation (PNS) in performing conduction anesthesia continues to be controversial (Schwarz et al 1998). Regional anesthesia can also be performed successfully without nerve stimulation. This applies particularly for techniques that for anatomical reasons (common fascial sheath around the nerves) allow a loss-of-resistance technique (e.g., axillary plexus anesthesia). PNS can then be used for additional orientation.
However, use of a nerve stimulator should be mandatory in difficult anatomical situations and in nerve blocks involving a large skin–nerve distance (e.g., sciatic nerve). PNS is particularly indicated for nerves with predominantly motor fibers (e.g., femoral nerve), as paresthesia cannot always be produced because of lack of sensory fibers, which means an increased risk of injuries to the nerve. In purely motor neurons, an overproportionate incidence of intraneural injection can be expected (Urmey 1997, Graf and Martin 2001). In these structures, the block can be performed in combination with ultrasound guidance.
PNS cannot be regarded as a substitute for anatomical knowledge, but it is a valuable aid for precise localization of the nerve.
Adjustable constant current
Monophasic rectangular output pulse
Adjustable pulse duration (0.1–1.0 ms)
Adjustable current intensity (0–5.0 mA)
Digital display of actual current value
Stimulating frequency 1–2 Hz
Alarm when circuit is interrupted
Alarm when impedance is too high
Alarm on internal device error
Outputs clearly assigned
Reliable instructions for use, stating tolerated deviations
Numerous animal experiments and clinical trials using ultrasound have shown that the concept of a clear relationship between the level of stimulus current and the pulse width, on the one hand, and the distance of the needle to the nerve on the other hand, must be reconsidered (Gurnaney et al 2007, Rigaud et al 2008, Tsai et al 2008, Tsui et al 2008, Robards et al 2009, Li et al 2011).
It has been shown that a response at less than 0.2 mA/0.1 ms was always associated with an intraneural needle position, but on the other hand no response was produced despite intraneural needle position up to a stimulation current of 1.7 mA/0.1 ms in some cases (Tsai et al 2008). Several studies show that stimulation at lower levels (< 0.5 mA/0.1 ms) offers no advantage with respect to the position of the needle in comparison with higher stimulation currents. An intraneural injection cannot be definitely ruled out even at stimulation currents greater than 0.5 mA/0.1 ms, but is less likely than at lower stimulation currents less than 0.5 mA/0.1 ms (Gurnaney et al 2007, Rigaud et al 2008, Robards et al 2009).
A dramatic increase in electrical resistance can be an indication of an intraneural needle position (Tsui et al 2008). Experimental reversal of the current flow (the cathode is conventionally used for stimulation) leads to a valid correlation between stimulation current and needle–nerve distance (Li et al 2011).
Practical Notes on the Use of the Nerve Stimulator
The pulse duration is given as “ms” for millisecond. Note: In Anglo-American usage, the pulse duration is sometimes given as µsec (0.1 ms = 100 µsec).
When the nerve stimulator is operated after perforation of the skin, it should first be ensured, using a low amplitude, that the needle tip is not already in the vicinity of the nerve, as uncontrolled muscle contractions might occur otherwise. The subsequent search for the nerve begins at a current amplitude of 1.0 mA and a pulse width of 1.0 ms or 0.1 ms with decreasing current.
As soon as contractions in the key muscle are produced, the nerve stimulator is switched to the shorter pulse (0.1 ms). The current concept that the pulse width of 1 ms inherently would be substantially more uncomfortable has not been confirmed. Rather, it is the total energy applied (i.e., the product of current times pulse width: E [nC] = I [mA] × t [µs]) which is responsible for the discomfort felt by the patient (Hadzic et al 2004). Nevertheless, if at all possible the pulse width should be kept at 0.1 ms since only this level permits fine-tuning of the distance between needle tip and nerve (Neuburger et al 2001).
Injection at a response below 0.5 mA and a pulse width of 0.1 ms should be avoided.
Practical clinical experience has shown that a response at 0.2 to 0.3 mA/1.0 ms often corresponds to a response of 1 mA/0.1 ms (Neuburger et al 2001).
In patients with polyneuropathy (e.g., diabetes mellitus), it is useful to select a longer pulse (1.0 ms).
A minimum distance between the electrode and stimulation needle has not been established. When nerve stimulators with adjustable stabilized current output are used, the site of placement of the cutaneous electrode appears to be unimportant for the function of the nerve stimulator (Hadzic 2004).
For the stimulation level desired (≤ 0.5–0.7 mA, 0.1 ms), the administration of saline or local anesthetics will change the electric field and, compared with the administration of glucose 5%, will therefore result in immediate adverse effects on, or even loss of, the response (Tsui et al 2004, Neuburger et al 2005, Tsui and Kropelin 2005). Knowing this, so-called “multiple injection” techniques have to be regarded critically, since the response of the nerve stimulator may be significantly impaired after an initial injection of saline or local anesthetic at the puncture site (Neuburger et al 2005).
Contrary to the statements of the manufacturers, PNS can also be used in patients with implanted cardiac pacemakers/defibrillators (Kaiser and Neuburger 2010). However, it should be ensured that the pacemaker aggregate, the cardiac electrodes, and the heart are not on the line connecting the skin electrode to the stimulation needle. The indication should be made strictly and the options of nerve stimulation/ultrasound should be weighed. Cardiac arrest was reported in one case study (Engelhardt et al 2006).
21.3.5 Needles and Catheters
Needles insulated on the shaft and conductive at the tip (monopolar or unipolar) are used as stimulation needles with the nerve stimulator. For ultrasound-guided blocks, specially processed surfaces allow better visualization with ultrasound even at steeper puncture angles (Chapter 1). There are needles for single-shot techniques and for continuous techniques.
The major difference in the design of the tip of the needle is between needles with a bevel (15°, 30°; Fig. 21.8), Tuohy needles, and pencil-point needles. Pencil-point and Tuohy needles make it possible to advance the catheter in a certain direction in continuous techniques.
Statements on the advantages and disadvantages of different types of needles with respect to potential injuries are limited mainly to animal tests (Selander et al 1977, Hirasawa et al 1990, Selander 1993, Steinfeldt et al 2010a, 2010b, 2011).
There are no clinical trials on advantages and disadvantages of different types of needles with respect to potential nerve damage. The decision as to which type of needle to use therefore remains at the discretion of the user.
There are two techniques, which differ in both material and procedure, for catheter insertion:
Needles with a surrounding plastic cannula (Fig. 21.8): These are needles inside a plastic indwelling cannula that make it possible to guide the indwelling cannula to the nerve. After successful placement and removal of the needle, a catheter is advanced 3 to 5 cm beyond the tip of the indwelling cannula. The indwelling cannula is then removed.
Needles for the “catheter-through-needle” technique (Fig. 21.9): These are needles through which, after successful placement, a catheter can be advanced directly about 3 cm beyond the tip of the needle. The needle is then removed.
Needle with steel stylet.
A needle with a plastic indwelling part is a special type of needle with a not hollow bored, solid steel stylet and 45° bevel and rounded edges (18 G/20 G) (KombiPlex B, Pajunk; Fig. 21.10). This needle can be used for a single-shot perivascular plexus block or femoral nerve block as well as to place a catheter for a continuous procedure. For a single-shot block, the indwelling plastic part can be left until the end of the operation; for a continuous block, the indwelling plastic part must be removed after the catheter is advanced.
Due to the solid stylet with the 45° bevel, the loss of resistance when the connective tissue is penetrated is felt clearly (Fig. 21.10).
Examples of Needles for Single-Shot Blocks with Electrical Insulation (Noninsulated Needle Tips as “Contact Point”)
Stimuplex D needles (B. Braun) with 15° bevel (20 G/22 G/23 G/25 G, 35/40/55/70/80/120/150 mm) and 30° bevel (22 G, 40/50/80 mm).
Stimuplex Ultra needles (B. Braun) with 30° bevel (20 G/22 G, 35/50/80/150 mm) with echogenic marking (suitable for ultrasound).
UniPlex needles (Pajunk, UPK) with Sprotte tip (22G/24G/25G, 40/50/70/90/150 mm) or bevel (20 G/21 G/24 G/25 G, 25/35/40/50/80/100/120/150 mm).
SonoPlex needles (Pajunk) with Sprotte tip (22 G/24 G, 40/50/70/90 mm) or bevel tip (20 G/21 G/22 G/24 G, 25/40/50/80/100/120/150 mm) with “cornerstone” reflectors and NanoLine coating (suitable for ultrasound).