Efficacy Of Procedure

One of the biggest challenges to the anesthesiologist performing a regional procedure is to be successful in anesthetizing the patient, in the right area and with enough spread to cover the whole surgical procedure. The monitoring of efficacy of the block starts with the evaluation of the quality, depth, and extension of the blockade. This means that different surgical steps and the patient's responses to them must be monitored.

Sometimes, the blockade may cover a sufficient area, but the quality may be substandard. This means that the monitoring of the quality of anesthesia must be repeated frequently. It is also necessary to be attentive to other signs of malfunction, as well as patient complaints, blood pressure, and cardiac function.

The combined spinal-epidural technique has been used increasingly since 1110, and it requires special follow-up. Combined spinal-epidural anesthesia may achieve rapid onset and profound regional blockade, with the ability to modify or prolong the block and with a variety of techniques and devices. The technique is complex by itself and cannot be considered simply as a spinal block plus an epidural block, because the fact of combining the techniques may alter each block. The technique can be performed with needle-through-needle, separate-needle, or combined-needle techniques, each with different modifications. Causes of failure can vary greatly. If the spinal block is performed before the epidural blockade is present, there is difficulty in achieving an adequate placing of the epidural catheter, inability to detect paresthesia during epidural placement, and absence of other sensory elements. All of these things must be considered in evaluating the performance of the technique.™ 113

Other techniques of combined regional and general anesthesia require effective monitoring procedures. EEG can be used to assess the adequacy1151 of the procedures. IEEG reading can be depressed by sedative hypnotic drugs.113 Another measure includes papillary assessment, in which dilatation of the pupil in response to electric stimulation is an accurate test of the sensory block level achieved during combined epidural and general anesthesia.113

Muscle Relaxation

To determine differences in time of onset and duration of motor block produced by local anesthetics such as lidocaine, the use of a quantitative and objective method (the measurement of compound muscle action potentials [CMAPs] with continuous nerve stimulation on a two-channel electromyogram) has been shown to be experimentally effective. However, it could also be used in vivo because it is the usual diagnostic procedure for neuropathies and myopathies. Initially, baseline values registering the amplitude of the CMAPs are expressed in millivolts. The injection of local anesthetic makes the wave diminish. However, this practice is currently not widely used. The clinical indirect evaluation of muscle relaxation by the assessment of neuromuscular reflexes is much more common. Depending on the regional procedure, some neuromuscular reflexes are expected to be decreased. Another way to assess the muscle reponse under regional blockade is by employing a motor block assessment of the modified Bromage scale.™

Sympathetic Blockade

Usually, the sympathetic blockade extends two to five dermatome levels above the limit of cutaneous anesthesia. Inhibition of preganglionic fibers results in a decrease of peripheral vascular resistance and an increase in venous pooling, with subsequent hypotension— the clinical sign of blockade effectiveness for thoracic and lumbar levels but unusual in caudal anesthesia. There is a compensatory increase in the vascular resistance of the upper body that maintains venous return and cardiac output. However, if the blockade reaches T1, cardiac sympathetic innervation is blocked with profound hypotension and bradycardia. Hence, monitoring is necessary whenever changes occur in the patient's posture. When the patient is set at the recovery room, monitoring should continue until the patient is discharged to his room.

Dermatome Mapping of Sensory Block

It is necessary to perform dermatome mapping of the sensory block, especially when epidural anesthesia is employed. It is important to determine the level of blockade and the quality of anesthesia. An anesthetic chart of a human body with dermatomes must be used to record the extent of neural blockade. The level can be assessed with light touch, as with pinprick or an ice cube. This assessment should be performed carefully so that tissues are not damaged and should be reevaluated after the addition of new boluses.

It is necessary to determine the levels of hyposthesia, anesthesia, and analgesia with a visual analogue scale (VAS) if pain is present before the procedure. The VAS is indispensable in the use of continuous analgesic techniques to verify efficacy of procedures or while making adjustments of infusions or rescue doses (e.g., postoperative epidural infusions, anesthesia for cancer pain). The VAS must be updated at scheduled times and must include a record of the patient's complaints of pain as well as the drugs used and their effects.

Practical Issues PREOPERATIVE PERIOD

If surgical intervention is indicated, perioperative anesthesia has to be carefully planned according to the requirements of each patient. If the patient is classified as high risk at the preoperative anesthetic assessment, the therapeutic management must aim at optimizing preoperative physical status. The perioperative risk of morbidity and mortality associated with elective surgical procedures must be evaluated for the individual patient and the best monitoring system for that patient must be chosen. The risks and benefits of invasive monitoring must be discussed in an interdisciplinary dialogue involving the surgeon, the patient, and the patient's family.

There are no recommendations about the choice of anesthesia techniques; the decision of whether to use general or regional anesthesia depends on the site of the operation and is guided by the individual experience of the anesthesiologist. Patient, surgical personnel, and anesthesiologists should reach a decision on the best technique and the monitoring requirements should be discussed.

The patient's neurologic integrity must be evaluated before any regional anesthetic procedure; this is especially important because some patients may have neurologic deficits that were not noticed previously. Moreover, regional anesthesia can cause complications.1™ Deafness, blindness, psychosis, or nonfluent language makes this evaluation more difficult, and such conditions are probably contraindications to the use of regional anesthesia.

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