John Jeffrey Andrews

Consequences of misfilling contemporary vaporizers with desflurane

Desflurane is a volatile anaesthetic that combines low blood gas solubility (blood/gas partition coefficient =0.42 at 37° C), moderate potency (MAC = 6–7%), and high volatility (vapour pressure =681 mmHg at 20° C, boiling point = 23.5° C). The volatility and potency of desflurane prevent its safe use in vaporizers of traditional design. We present a mathematical model which demonstrates the potential for desflurane overdose if contemporary vaporizers are misfilled with desflurane. The most hazardous filling error occurs if an enflurane vaporizer is misfilled with desflurane. The calculated desflurane output of a misfilled enflurane vaporizer at a dial setting of 1% and a temperature of 22° C is 57.8%, or 9.6 MAC. For misfilled enflurane, isoflurane, and halothane vaporizers at dial settings equivalent to one MAC at 22° C, the calculated desflurane output is 14.0, 10.2, and 7.8 MAC, respectively. We conclude that the safe delivery of desflurane will require engineering safeguards, additional monitoring, and education of the anesthesia community.RésuméLe desflurane est un anesthésique volatil caractérisé par un degré de solubilité sanguine peu élevé (coefficientpartage sang/ gaz = 0,42 à 37° C), une puissance intermédiaire (MAC = 6–7%) et une volatilité élevée (pression de vapeur = 681 mmHg à 20° C, point d’ébullition =23,5° C). La volatilité et la puissance du desflurane préviennent son usage en toute sécurité dans les vaporisateurs utilisés actuellement. Nous présentons un modèle qui illustre pour le desflurane le danger de surdosage si on fait l’erreur de remplir les vaporisateurs actuels avec cet agent. Le débit calculé d’un vaporisateur à enflurane chargé au desflurane avec manette de calibrage règlé à 1%, à une température de 22° C, est de 57,8% ou 9,6 MAC. Pour les vaporisateurs d’enflurane, isoflurane et halothane à des ajustements de contrôle à 1 MAC, les débits calculés de desflurane le situent respectivement à 14,0, 10,2 et 7,8 MAC. Nous concluons que l’administration en toute sécurité du desflurane nécessitera des balises techniques, un monitorage supplémentaire et des études de la part des d’utilisateurs.

Comparison of tests for detecting leaks in the low-pressure system of anesthesia gas machines

Small leaks in the low-pressure system (LPS) of the anesthesia gas machine can cause hypoxia or patient awareness. We sought to determine the relative sensitivities of the various tests recommended for detecting LPS leaks before anesthesia. Special adapters were fashioned to create leaks of six different sizes in the LPS that were equivalent to the following: a single 25-, 22-, 20-, or 15-gauge needle, two 15-gauge needles, or a 2.5-mm endotracheal tube connector. With each leak condition, five different leak tests were performed on three each of the following machines: Ohmeda Modulus I [TM], Ohmeda Modulus II [R]-Plus, and North American Drager Narkomed (2A, 3 and 4), for a total of 54 leaks to be detected for each leak test (3 x 3 x 6). The number of leaks detected with each test was compared by Fishers exact test, P < 0.05 being considered significant. Only the negative pressure leak test detected all 54 leaks, a significant difference from the positive pressure test, which detected the least number of leaks, 28 (P < 0.05). Some leak tests are more suitable for specific anesthesia machines. Adoption of the negative pressure test as a universal LPS leak test may prevent the risks associated with using the wrong test for the particular anesthesia machine: hypoxic gas or patient awareness. (Anesth Analg 1997;84:179-84)

Bulk Liquid Oxygen Supply Failure

WE report an oxygen supply tank failure at our institution that occurred during the morning of a busy operating room schedule when medical center oxygen use was maximal.

Complications of inhaled anesthesia delivery systems

Inhaled anesthesia delivery systems (ADS) have evolved in the past 20 years from simple pneumatic machines to complex computer-controlled devices. For the purposes of this discussion, we will outline some of the potential complications that may result from the use of these systems. Because of the complexity of modern ADS, it is incumbent on the anesthesiologist to be cognizant of potential problems that may arise with their use. Even though it is now more difficult than ever for the practitioner to develop a comprehensive understanding of these machines, it remains essential for the safe practice of anesthesia. When the anesthesiologist understands the basic design differences between products from different manufacturers, it is more likely that the appropriate preoperative checks will be performed and that delivery of a safe anesthetic can be ensured. Although malpractice claims associated with anesthesia delivery systems are rare, when they do occur they may be severe, and they continue to occur. These complications may range in severity from mild hypercapnia to awareness and even death.

Dual causes of vaporizer aberrance lucidly separated.

Evaluation of the Tee 6 desflurane vaporizer using different, varying circuit carrier gases is reported by Johnston et al. (11. I agree that the performance of the Tee 6 “with a change in carrier gas closely resembles that for conventional variable-bypass vaporizers” (21, as regards discrepancies in steady-state plateau concentrations of halogenated vapors. The demonstrated reductions in desflurane concentrations do parallel “the proportional decrease in viscosity of the carrier gas” because of differences in “back pressure generated by restrictor Rl” (1). Thus the influence of carrier gas viscosity has been separately demonstrated, apart from the influence of carrier gas solubilify in reservoirs of liquid halogenated anesthetics, previously manifested concomitantly. The latter phenomenon is responsible for “transient peaks and valleys” (1,2) of vapor output from earlier models of Tee-type vaporizers. Daniel B. Gould, MD Department of Anesthesiology St. Louis Regional Medical Center St. Louis, MO 63112