Robert V. Johnston

Cryotherapy for Postoperative Pain Relief Following Knee Arthroplasty

Ninety consecutive patients undergoing primary knee arthroplasty received local cryotherapy 72 hours after surgery for pain relief. Thermal-pad circulating temperatures were randomly assigned to 50 degrees, 60 degrees, or 70 degrees F (room temperature). Pain relief was monitored using patient-controlled analgesia machines. The amount of morphine received and number of attempts per hour were statistically analyzed with relation to temperature group, age, sex, weight, side, and diagnosis. The amount of morphine injected was positively correlated to the number of attempts per hour and moderately correlated to body weight. There was no correlation between thermal-pad temperature or any other parameter and the amount of morphine injected after surgery.

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.

The effects of carrier gas composition on the performance of the Tec 6 desflurane vaporizer

The new Tec 6 desflurane vaporizer is an electrically heated, pressurized, electromechanically coupled dual-circuit blender. We hypothesized that carrier gas viscosity should affect the electromechanical coupling of the fresh gas and vapor circuits, and that desflurane output should vary with different carrier gases. In the first portion of the study, the performance of eight vaporizers was evaluated using a constant dial setting of 10% desflurane with four different carrier gases and three different fresh gas flow rates. In the second portion of the study, the carrier gas flow rate was maintained at 1, 5, or 10 L/min, and vaporizer output was analyzed at all integer dial settings from 1% to 18%. Vaporizer output was highest when oxygen was the carrier gas and lowest when nitrous oxide was the carrier gas. This effect was accentuated at low fresh gas flow rates and correlated with carrier gas viscosity. At a flow rate of 1.0 L/min with a constant dial setting of 10%, the averaged output from vaporizers was 10.3 ± 0.66, 9.4 ± 0.58, 8.7 ± 0.52, and 8.1 ± 0.44 vol% for 100% oxygen, air, 30% oxygen plus 70% nitrous oxide, and 100% nitrous oxide, respectively. With 100% nitrous oxide as the carrier gas at a flow rate of 1.0 L/min, the vaporizer delivered 2 vol% less than the dial setting at dial settings in excess of 12%. Differences between the analyzed concentration and the dial setting were most pronounced with high concentrations of nitrous oxide at low fresh gas flow rates.

Photodeactivation of ethyl violet: a potential hazard of Sodasorb®

Breathing circuit cannisters containing functional CO2 absorbent are critical to prevent rebreathing CO2 during general anesthesia using closed or semiclosed breathing systems. Ethyl violet is the indicator dye added to Sodasorb to indicate impending exhaustion of the absorbent. A case of CO2 rebreathing due to failure of ethyl violet indicator in exhausted Sodasorb was encountered. Laboratory investigation demonstrated that dye failure could result from photodeactivation caused by fluorescent lights. Using a fixed intensity fluorescent light source and quantitative spectrophotometric analysis, a highly significant dose-response relationship was demonstrated between duration of light exposure and the decrease in ethyl violet concentration. After 24 h of fluorescent light exposure with a received flux density of 46 nwatts/cm2 at 254 nm, the concentration of functional ethyl violet remaining in pulverized Sodasorb was 16% of the baseline value. Furthermore, using multiple light sources of various intensities, the greater the intensity of light, the more rapid the rate of decline of the ethyl violet concentration. It is recommended to minimize the problem by using ultraviolet filters and incorporating additional ethyl violet in Sodasorb. Finally, ethyl violet undergoes temporal deactivation after a Sodasorb container is opened, even if it is stored in the dark.

Reflex sympathetic dystrophy after clavicle fracture: Case report

Reflex sympathetic dystrophy (RSD) of the anterior chest wall is a rare entity. A MEDLINE search in all languages of the worlds literature from 1966 to the present yielded no report of the association of clavicle fracture with this pain syndrome. Two cases are presented and the anatomic variations of the supraclavicular nerves in relation to the clavicle are discussed.

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