Anesthesia Techniques



Anesthesia Techniques


Warren C. Hammert



INTRODUCTION

A variety of anesthetic techniques can be used effectively for upper extremity surgery. Most upper extremity surgical cases can be performed using regional anesthesia, monitored anesthesia care (MAC) and/or local. These anesthetic choices have advantages over general anesthesia, such as decreased incidence of postoperative nausea and vomiting, better pain control, and greater cardiovascular stability, and earlier discharge. General anesthesia for upper extremity surgery is the same as for other anatomical regions and will not be discussed in this chapter.

The choice of anesthesia is dependent on the duration and type of procedure, anatomical location, and surgeon and patient preference. Although the surgeon will not perform all regional blocks, he/she should be familiar with the techniques and advantages/disadvantages of different techniques and the anatomy of peripheral nerves.

A description of the various local anesthetics and their pharmacology is found in Chapter 12.


TOXICITY


Local Reactions

The perineurium acts as a barrier, preventing high concentrations of anesthetics from reaching the intraneural structures. This protective perineurium makes direct toxicity rare without an intraneural injection. Injection directly into the nerve produces an intense pain response and must be avoided. Care must be taken when injecting around peripheral nerves in patients under general, deep sedation, or with proximal nerve blockade as they will not elicit the pain response and inadvertent intraneural injection could occur.


Systemic Reactions

Central nervous system (CNS) and cardiovascular system toxicity are dose and time dependent; most severe reactions are a result of intravascular injection. The quicker the plasma levels rise, the greater the chance systemic problems will occur. Initial CNS symptoms are tinnitus, metallic taste, light-headedness, and perioral numbness. With higher levels, muscle twitching, tremors, tonic-clonic seizures, loss of consciousness, and respiratory arrest may occur. Benzodiazepines will raise the CNS threshold and can be used to terminate seizure activity. Protection of the airway with intubation and ventilation to ensure oxygenation is paramount in caring for patients with CNS toxicity.1

Cardiovascular toxicity is less common than CNS toxicity, but occurs as a result of decrease in myocardial peripheral smooth muscle conduction. There is prolongation of conduction, increasing the PR and QRS intervals, along with suppression of the sinoatrial and atrioventricular nodes, causing bradycardia, conduction block, and cardiac arrest. Bupivacaine has greater cardiotoxicity than lidocaine. Similar to CNS toxicity, intubation and mechanical ventilation, followed by Advanced Cardiac Life Support (ACLS) protocol for resuscitation, should be instituted.1


ADDITIVES


Sodium Bicarbonate

Sodium bicarbonate can be added to local anesthetic solutions to increase the rate of onset and decrease the pain at the injection site.1


Preservatives

Antimicrobial preservatives, such as methylparaben and ethylparaben, are often added to multidose vials. Anesthetics with these additives can be used for local infiltration, but should not be used for IV regional (bier block) anesthesia or spinal/epidural anesthesia. Antioxidants such as sodium ethylenediaminetetraacetic acid can be added to prevent oxidation and slow their degradation.1


Epinephrine

Epinephrine is commonly added to local anesthetics. It functions by increasing the time of onset, limits the systemic absorption, and thus increasing the maximum dose, and increases the duration of action (Chapter 12). It is commonly used in concentrations of 1:200,000 (range 1:100,000 to 1:400,000).2

Historically, it was taught that epinephrine should not be used in the hand or finger for fear of vasoconstriction and finger necrosis. A critical look at the evidence indicates that case reports are mostly prior to the 1950s and associated with procaine and cocaine injections with epinephrine.3 The current evidence clearly demonstrates that epinephrine can be safely used in the fingers.3,4,5,6,7,8,9 If reperfusion is delayed, 0.5% phentolamine mesylate can be used to reverse the effects of epinephrine. It is injected locally, reversibly blocking the alpha-1 receptors, and causing vasodilation.10,11 Phentolamine has a short half-life, so repeat injection may be necessary.


REGIONAL ANESTHESIA

Brachial plexus blocks can be used for most procedures in the upper extremity. These can be used as the sole anesthetic agent, or combined with sedation or general anesthesia, depending on the patient, surgeon, and anesthesiologist preference. Chan et al. compared infraclavicular block anesthesia with general anesthesia and demonstrated an increase in time to begin the surgical portion of the case. The block took 5 to 10 minutes to perform and 15 to 25 minutes to reach a level for surgical stimulation.12 The trade-off for this increased time to begin the procedure is decreased recovery time, leading to faster discharge, elimination of anesthetic gases, and thus, less potential for nausea and vomiting, and better early postoperative pain relief. Of course, the onset of pain will occur as the block wears off and this may be in the middle of the night, making it important to instruct the patient on use of postoperative pain medications. The most efficient use of regional anesthesia is a system where the anesthesiologists can perform the block about 30 minutes prior to starting the procedure to allow adequate time for the block to take effect. This can be performed in a designated area, such as a “block area or room,” to allow the most efficient use of the operating room.

Brachial plexus blocks can be performed at four anatomical sites: two above the clavicle (interscalene and supraclavicular), one below (infraclavicular), and one in the arm (axillary). Ultrasound or nerve stimulation is commonly used to assist with localization of the needle, increasing safety and effectiveness of the block.2


Interscalene

The interscalene block allows for anesthesia at a proximal level, away from the lung, making this location good for
shoulder surgery with a low incidence of pneumothorax. Anesthesia of the inferior trunk (C7-T1) may be incomplete, necessitating ulnar nerve block for procedures involving the elbow, wrist, and hand.13

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Jun 26, 2016 | Posted by in General Surgery | Comments Off on Anesthesia Techniques
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