We installed two waste gas scavenging systems into the operating room. This was simple and inexpensive, as the ICU is contiguous with the operating room.
An adequate scavenging device can be made by connecting the exhaust port of the ventilator to a T- piece that is attached to a 3-L reservoir bag. Wall suction is applied to the remaining limb of the T-piece until the reservoir bag partially fills with each breath, but never fully collapses. Leaks are readily detectable, since isoflurane has a characteristic pungent odor.
Since this is a nonrebreathing system, a great deal of isoflurane is vaporized hourly. The cost for 24 h of continuous use is high, but it is partially offset by decreased use of other sedatives and muscle relaxants.
Most authors have suggested that an anesthesiologist should be in constant attendance of the patient, since isoflurane is unfamiliar to most critical care personnel. This is extremely difficult to organize, particularly if the drug is used for prolonged periods. We have dealt with this problem by providing educational material to the nurses in the ICU, supplemented by bedside educational sessions for the nurse caring for the patient. An anesthesiologist (R.G.J.) initiated therapy with the drug and titrated the dose by increments of 0.5 percent until the PIP decreased, the BP fell, or a concentration of 2.5 percent was reached. If the BP fell, saline solution or albumin was infused until the BP increased to an acceptable level. The isoflurane concentration was then increased again at 0.5 percent increments. Once the patient was in stable condition while receiving a given concentration for one hour, the anesthesiologist was no longer in constant attendance. The nursing supervisors, who received more in-depth instruction, and who were experienced ICU nurses, were allowed to vary the concentration by increments of 0.5 percent. When the PIP began to decline, the isoflurane concentration was kept constant for several hours. Attempts were then made to decrease the concentration until reaching the minimal concentration that resulted in lower airway pressures, clinical improvement, and improved ventilation. The nurses were instructed to immediately discontinue the isoflurane treatment if the patients became severely hypotensive or if arrhythmias occurred. This circumstance never arose. During maintenance with isoflurane, narcotics were given for painful procedures and muscle relaxants were used if the patients coughed or became asynchronous with the ventilator. The nurse was in constant attendance at the bedside to guard against accidental ventilator disconnection or loss of airway control.
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When PIP was less than 40 cm H20 for several hours, and clinical assessment revealed marked improvement, isoflurane treatment was discontinued while an intensivist was present. Awakening was surprisingly rapid, occurring in 20 to 60 minutes. This is predicted theoretically and confirmed in one other case report. If bronchospasm worsened during awakening, the isoflurane dose was increased to its former level with rapid relief.
In a patient who is unresponsive to maximal conventional therapy for status asthmaticus, isoflurane may be the drug of choice for additional therapy. Its relatively mild side effects, lack of toxicity, sedative action, and ease of administration are significant advantages. Further clinical trials would seem to be indicated.