Chapter 5 – Inhaled Anesthetics and Draw-Over Devices in Disaster Response

Abstract

Chapter 5 Inhaled Anesthetics and Draw-Over Devices in Disaster Response

Carlton Brown

Inhaled anesthetics remain the primary pharmacologic agents for administering general anesthesia in current surgical practices. Anesthesia providers enjoy familiarity and extensive experience with these inhaled agents in the context of modern anesthesia delivery equipment. In providing anesthetic care during disasters, providers will often have access to the same technically sophisticated anesthetic vaporization and monitoring systems typical of modern, brick-and-mortar hospital facilities. For example, anesthetic care rendered after a focal mass casualty event in an urban area would likely be done with a reliable supply of pharmaceutical agents, modern anesthetic machines, modern monitors, and reliable electricity. Even in rare circumstances of regional natural disasters where local healthcare facilities have lost electricity, water, or other infrastructure support, it is still often possible to transfer patients to facilities in adjacent geographic areas where these services remain intact. In this context, the use of inhaled anesthetics in disaster response is likely to be simply a direct extension of our daily practices. “No one gets smarter in a disaster,” and our use of familiar equipment, familiar agents, in familiar settings, and with familiar patient flow patterns yields the highest probability of successful anesthetic outcomes. In the anesthetic care of patients in disaster settings, it is incumbent that providers not augment the misery and mortality of the actual disaster with any additional morbidity or mortality from their anesthetic care. As disaster triage directs patients into surgical care, the availability of the most sophisticated anesthetic care – familiar anesthetic equipment, agents, resources, and providers – should be part of that decision-making process.

In those rare circumstances where surgical care must be undertaken in very austere conditions, providers should carefully consider the advantages and disadvantages of delivering inhaled anesthetics and the concomitant need of airway manipulation and ventilation that generally accompanies them. Even for extensive surgical procedures, there are often alternatives to inhaled anesthetics. Total intravenous anesthesia (TIVA), intravenous or intramuscular ketamine, or regional anesthetic techniques may offer safer and more efficient resource utilization for austere surgical care. TIVA, typically with propofol, can be administered if necessary with only gravity fed IV and a mini-dripper. Ketamine, either IV or IM, can allow the completion of remarkably extensive surgical procedures while maintaining spontaneous ventilation and hemodynamic stability. Regional anesthetics often avoid airway issues and offer extremely efficient use of pharmaceutical resources. By example, a 30 ml vial of preservative-free 0.75% bupivacaine may yield as many as 15 isobaric spinal anesthetics. For procedures on the lower extremities or even into the abdomen up to the diaphragm, spinal anesthesia is a reasonable alternative to inhaled general anesthesia. Procedures on the upper extremities can be done with modest amounts of local anesthetic in regional plexus blocks. Trauma involving extremity injuries as seen in natural disasters is often amenable to regional anesthetics. Before anesthesia providers commit themselves and their patients to unfamiliar inhaled anesthetics delivered through unfamiliar equipment, a careful risk–benefit analysis should be considered given these alternative techniques for supporting surgical care.

Absent global apocalypse, modern anesthesia disaster resources and equipment are often delivered within a day or two of the primary event, even into extremely remote areas. These resources include readily transportable, scaled-down versions of commercial anesthesia machines that have many of the modern safety features appropriate for inhaled anesthetic delivery. These “field anesthesia machines” combine a small footprint, minimal logistic demands, and some intrinsic monitoring capabilities to provide safe inhaled anesthetic delivery. The US military currently issues and supports the Draeger Fabius Tiro “M” model for deployable use. This is only one of many such compact “field machines” available worldwide. Many of these machines are capable of providing PEEP, triggered and controlled ventilation, air dilution, and other features now considered part of normal contemporary anesthetic practice. As the care of trauma patients often involves penetrating wounds, crush injuries, and thoraco-abdominal surgery, these ventilator modes are most useful. The ability of these portable anesthesia machines to measure exhaled carbon dioxide is particularly important for assessing adequacy of ventilation and persistence of cardiac output. End-tidal inhaled anesthetic agent measurement is very helpful both in avoiding over-dosage and optimally timing emergence. Combined with a small portable monitor, these “field anesthesia machines” allow safe inhaled anesthetic delivery outside of a traditional hospital setting. Whenever possible, providers involved in disaster relief should become familiar with the machines with which they will practice prior to deployment. Both carefully reading the operator’s manual and some prior clinical experience are highly recommended, as some of these devices may have limited capabilities or unique characteristics (hidden on–off switches). Patient safety dictates familiarity with these machines before use in a high-stress disaster setting. Although comparable in safety to hospital equipment, these machines require reliable compressed gas supplies and electricity, and their vaporizers are typically agent-specific. These resources may be problematic in the most austere of locations. The decision to deliver inhaled anesthetics should consider availability of these machines, provider familiarity (or time available to learn their proper use), availability and reliability of infrastructure resources, and availability of inhaled anesthetic agents compatible with agent-specific vaporizers.

Disaster anesthesia often involves care of trauma patients, and most anesthesia providers are familiar with the relative advantages and disadvantages of inhaled anesthetics in this population (Box 5.1). The hemodynamic effects of inhaled anesthetics as sole agents may be clinically limiting. Modern fluoro-methyl ether anesthetics are vaso-depressant largely through decreases in systemic vascular resistance. This can be offset in part by using nitrous oxide in lieu of higher doses of these ethers. In field anesthesia, however, nitrous oxide may be either unavailable or inappropriate at altitude. The use of intravenous narcotics such as fentanyl may also allow reduced doses of inhaled drugs, but the availability of controlled substances in field settings may be problematic for both logistical and regulatory reasons. The absence of nitrous oxide or readily available intravenous narcotics may be a substantial change in practice for many anesthesia providers.