Objective-To examine the accuracy and precision of isoflurane and sevoflurane anesthetic vaporizers. Sample Population-5 identcal isoflurane and 5 identical sevoflurane vaporizers. Procedures-Oxygen flow rates from 0.02 to 10 L/min were used with different vaporizer dial settings. Agent concentrations were measured at the common gas outlet by use of a refractometer. Accuracy was defined as the difference between measured agent concentrations, and dial settings were expressed as a percentage of the applied dial settings. Precision was defined as SD of the measured agent concentrations for each combination of dial setting and flow. Results-Isoflurane values were generally greater than the dial settings. Accuracy of the isoflurane vaporizer was > 20% when 0.6% and 1% was dialed. Accuracy of the sevoflurane vaporizer was always within +/- 20% but decreased at 0.02 L/min flow and at combinations of high flow and high dial settings. Overall precision of the isoflurane vaporizer was better than that of the sevoflurane vaporizer. Conclusions and Clinical Relevance-A possible explanation for the inaccuracy of the isoflurane vaporizer may be that it was manufactured to be accurate with air but not oxygen, which must be accounted for when using the vaporizer with oxygen, especially with nonrebreathing systems. The sevoflurane vaporizer may not deliver accurate agent concentrations at high flow and high dial settings. Both vaporizers are suitable for clinical use with a wide range of oxygen flow rates if these precautions are properly addressed.

Objective--To evaluate the efficacy of coumaphos, an organophosphate (OP) acaricide, at concentrations up to 2 times higher than the highest concentration required by the US Eradication Program against all stages of an OP-resistant strain of Boophilus microplusin experimentally infested cattle. Animals--16 tick-naïve 200-kg female Hereford calves. Procedure--Four groups of cattle (4 calves/group) were all infested with Boophilus ticks 3 times before treatment. Each group was treated with coumaphos as follows: group 1, at 0.165% active ingredient (AI); group 2, at 0.299% AI; group 3, at 0.566% AI; and group 4, not treated. Following treatment, ticks were collected for 21 days. Ticks collected 1 to 7, 8 to 14, and 15 to 21 days after treatment were considered adults, nymphs, and larvae, respectively, at time of treatment. Results--Overall control at 0.165, 0.299, and 0.566% AI was 52.9, 75.8, and 89.7%, respectively. Control of adults ranged from 4.3% at 0.165% AI to 73.5% at 0.566% AI. Control of nymphs ranged from 60.6% at 0.165% AI to 97.3% at 0.566% AI. Control of larvae was > 98% at all coumaphos concentrations. Conclusions and Clinical Relevance--All coumaphos concentrations failed to provide acceptable control for use in the US Eradication Program against OPresistant ticks. Treatment was least effective against adults and most effective against larvae. Even at 0.566% AI (2 times higher than required by the US Eradication Program), ticks were not eradicated, placing the United States at risk from dispersing cattle harboring viable ticks to uninfested areas.