Abstract
Regional anesthesia has undergone a great deal of growth in recent years, due in part to the ability of peripheral nerve blockade to treat pain without the administration of opioids, and the resultant avoidance of their systemic side effects, such as respiratory depression, sedation, nausea, and constipation. In addition to this advantage, adequate control of acute pain as can be achieved with regional techniques prevents the central sensitization that can result in chronic (including phantom limb) pain. Reduced exposure to opioids also decreases the risk of physical dependence and addiction. Regional techniques have also been demonstrated to reduce hospital length of stay.
Regional anesthesia has undergone a great deal of growth in recent years, due in part to the ability of peripheral nerve blockade to treat pain without the administration of opioids, and the resultant avoidance of their systemic side effects, such as respiratory depression, sedation, nausea, and constipation. In addition to this advantage, adequate control of acute pain as can be achieved with regional techniques prevents the central sensitization that can result in chronic (including phantom limb) pain. Reduced exposure to opioids also decreases the risk of physical dependence and addiction. Regional techniques have also been demonstrated to reduce hospital length of stay.
Regional anesthesiologists in modern urban settings are accustomed to practicing with near-unlimited resources, including high-tech equipment, but in austere settings with limited resources, a few adjustments to practice must be considered.1–4 Despite limitations, regional anesthetic techniques can still be performed; in fact, in the resource-constrained environment (e.g. no anesthesia machines are available for general anesthesia cases, lack of end-tidal gas monitoring, limited trained nurses for post-anesthesia care, etc.), regional techniques may become preferred. Health care workers in disaster circumstances must preserve precious supplies, and regional anesthesia can vastly extend the ability to respond through the conservation of pain medications and nursing support. Nerve blocks can take seconds to minutes to perform, and if long-acting medications are available, they will be effective for several hours, not only conserving resources, but also reducing complications. For example, in individuals who may have broken ribs, a serratus anterior plane block (or PECS II block) can be performed to alleviate this pain and help to reduce probability of hypoxemia or respiratory failure due to hypoventilation from splinting and poor respiratory mechanics.
In the OR, regional anesthetic techniques allow for decreased turnover time between patients; in the PACU, they shorten time needed to reach discharge criteria by improving pain control pain and obviating opioid side effects of sedation, nausea, and vomiting.
Limitations in the following facets of regional anesthesia performance in a disaster or other low-resource environment will be discussed, along with suggestions for how to perform a nerve block despite them:
Medications
Monitors
Equipment
Supplies
Documentation
Patient information
Limitations in Medications
Local Anesthetics
We recommend using the smallest volume and most dilute concentration of local anesthetic needed to provide either analgesia or anesthesia, depending on the goals of the anesthesiologist.
Studies have been performed to identify the minimum effective concentration (MEC) for ropivacaine, bupivacaine, lidocaine, and mepivacaine in various blocks as well as the minimum effective volume (MEV) for various blocks.
Usage of the MEC and MEV of local anesthetic will help to conserve supply of medication in the resource-constrained environment. This will also reduce the risk of local anesthetic toxicity in patients whose weight is uncertain, in the event of inadvertent intravascular injection, or when rescue medications are not readily available.
It should be borne in mind that all blocks may not require a “recommended” volume if ultrasound guidance is used to visualize adequate spread of local anesthetic. MEC and MEV which have been published in the literature are shown in Tables 24.1 and 24.2.
| Block type | Type of local | Volume | MEC >90 | Citation |
|---|---|---|---|---|
| Supraclavicular | Ropivacaine | 40 ml | 0.257% | 5 |
| Axillary block | Bupivacaine | 20 ml | 0.241% | 6 |
| Femoral | Lidocaine | 15 ml | 0.93% | 7 |
| Femoral | Ropivacaine | 15 ml | 0.167% | 8 |
| Subgluteal sciatic | Mepivacaine | 30 ml | 1.12% | 9 |
| Popliteal sciatic | Mepivacaine | 30 ml | 1.98% | 9 |
MEC 90 is the concentration at which >90% of patients underwent a surgical procedure without supplementation of analgesia or anesthesia. All studies were done with ultrasound-guidance.
| Block type | Type of local | Volume | MEV >90 | Citation |
|---|---|---|---|---|
| Interscalene | Ropivacaine | 7 ml | 0.75% | 10 |
| Interscalene | Bupivacaine | 0.95 ml | 0.5% | 11 |
| Infraclavicular | Lidocaine | 14 ml | 2% | 12 |
| Supraclavicular | Mepivacaine | 17 ml | 1.5% | 13 |
| Supraclavicular | 1:1 lidocaine levobupivacaine | 23 ml |
| 14 |
| Supraclavicular (elderly) | 1:1 lidocaine levobupivacaine | 11.9 ml |
| 14 |
| Axillary brachial plexus | Lidocaine | 1 ml /nerve | 2% | 15 |
| Axillary brachial plexus | Bupivacaine | 1.56 ml /nerve | 0.5% | 16 |
| Axillary brachial plexus | Lidocaine | 23 ml perivascular | 1.5% | 17 |
| Popliteal sciatic | Ropivacaine | 8.9 ml | 0.75% | 18 |
| Popliteal sciatic |
| 13.3 ml |
| 19 |
| Popliteal sciatic | Ropivacaine | 16 ml | 0.5% | 20 |
MEV has been studied with several different ultrasound-guided nerve blocks and local anesthetics at varying concentrations. MEV 90 or greater for surgical anesthesia is summarized in this table.
Limitations in Monitoring
Vital Signs During Block Placement
ASA standards for monitoring state that during a regional or local anesthetic without sedation (which is what we recommend), adequacy of ventilation of the patient should be continually observed by qualitative clinical signs. Adequacy of circulation can be assessed by manual observation of a pulse or auscultation of heart sounds, if needed.21
Continual monitoring in the form of constant meaningful communication and assessment of mental status can be used as secondary indicators of adequate circulation and oxygen saturation, as both are required to maintain mental status and phonation.
Due to the possible limited availability of monitoring equipment such as pulse oximeters, non-invasive blood pressure cuffs (either manual or automatic), and electrocardiography, we recommend that sedation not be administered for the placement of regional anesthetics in circumstances where vital signs cannot be ascertained and the patient cannot be monitored for a length of time sufficient for the sedating medications to resolve.
Limitations in Equipment
Many articles have been published in the emergency medicine literature about the value of ultrasound-guided regional anesthetic (USGRA) techniques in disaster or combat circumstances. This is readily accepted by health care providers, who can appreciate the value of an anesthetized limb vs the dangers of systemic opioids and other pain medications.
USGRA will be preferable in this setting, if available. Use of ultrasound has been shown to reduce necessary volume and concentration to achieve a successful nerve block,22 allowing conservation of local anesthetic in an environment where resupply may be difficult.
USGRA will also help to avoid toxicity in a patient whose weight may not be known for calculation of a maximum dosage, by allowing the anesthesiologist to use a lower volume and concentration of local anesthetic.
Ultrasound has also been shown to be associated with a reduced rate of complications, such as vascular puncture and paresthesia.22
In addition, with the availability and usage of USGRA, the practitioner can also utilize point-of-care ultrasound (PoCUS) for diagnostic techniques, including focused cardiac, lung, and abdominal exams. PoCUS can be used to identify contraindications to specific peripheral blocks, such as ruling out contralateral pneumothorax and evaluating excursion of the contralateral lung/diaphragm before performing proximal brachial plexus blocks associated with hemidiaphragmatic paresis. Further discussion of PoCUS is beyond the scope of this chapter, but its potential usefulness in a disaster or other low-resource environment is immense.
▪ Proximal brachial plexus blocks are fraught with potential contraindications. Due to risk of phrenic nerve block resulting in hemidiaphragmatic paresis, certain patients with respiratory or neuromuscular disorders may not tolerate the reduction in forced vital capacity. Contraindications to these blocks include severe COPD, severe pulmonary hypertension, myasthenia gravis, contralateral vocal cord paralysis, and contralateral lung or thoracic pathology such as pleural effusion, hemothorax, or pneumothorax. PoCUS can be used to rule out effusions, hemothorax, pneumothorax, and vocal cord paralysis.
Ultrasound will not always be available, particularly in high-demand, low-resource situations; therefore, facility with a peripheral nerve stimulator can be crucial in localizing nerves and placing peripheral blocks. However, usage of the peripheral nerve stimulator for block placement, especially in fractured extremities, should be done with caution. Not only can this technique be exquisitely painful for the patient, but it can also lead to closed-to-open fracture conversion necessitating debridement.
Landmark-based techniques can also be used for certain blocks, and can be employed when both forms of guidance are unavailable.
▪ For block procedure description, both for ultrasound and landmark-based techniques, please see Table 24.3.
Related posts:
Chapter 5 – Inhaled Anesthetics and Draw-Over Devices in Disaster Response
Chapter 4 – Total Intravenous Anesthesia in Disaster Medicine
Chapter 14 – Considerations When Working with Children and Families
Chapter 15 – Chemical and Radiologic Exposures in Trauma and Disasters
Chapter 23 – Pharmacy in Disaster Anesthesia
Chapter 12 – High-Altitude Physiology and Anesthesia
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