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 assess the accuracy of isoflurane, halothane, and sevoflurane vaporizers during high oxygen flow and at maximum dial settings at room temperature and to test sevoflurane vaporizers similarly during heating and at low-fill states.
Sample—5 isoflurane, 5 halothane, and 5 sevoflurane vaporizers.
Procedures—Vaporizers were tested at an oxygen flow of 10 L/min and maximum dial settings for 15 minutes under various conditions. All 3 vaporizer types were filled and tested at room temperature (21° to 23°C). Filled sevoflurane vaporizers were wrapped with circulating hot water (42°C) blankets for 2 hours and tested similarly, and near-empty sevoflurane vaporizers were tested similarly at room temperature. During each 15-minute test period, anesthetic agent concentration was measured at the common gas outlet with a portable refractometer and temperature of the vaporizer wall was measured with a thermistor.
Results—For each vaporizer type, anesthetic agent concentrations and vaporizer wall temperatures decreased during the 15-minute test period. Accuracy of isoflurane and halothane vaporizers remained within the recommended 20% (plus or minus) deviation from dial settings. Heated and room-temperature sevoflurane vaporizers were accurate to within 23% and 11.7% (plus or minus) of dial settings, respectively. Sevoflurane vaporizers at low-fill states performed similarly to vaporizers at full-fill states.
Conclusions and Clinical Relevance—Under these study conditions, the isoflurane and halothane vaporizer models tested were accurate but the sevoflurane vaporizers were not. Sevoflurane vaporizer accuracy was not affected by fill state but may be improved with vaporizer heating; measurements of inspired anesthetic agent concentrations should be obtained during the use of heated vaporizers.
Objective—To assess agreement between anesthetic agent concentrations measured by use of an infrared anesthetic gas monitor (IAGM) and refractometry.
Sample—4 IAGMs of the same type and 1 refractometer.
Procedures—Mixtures of oxygen and isoflurane, sevoflurane, desflurane, or N2O were used. Agent volume percent was measured simultaneously with 4 IAGMs and a refractometer at the common gas outlet. Measurements obtained with each of the 4 IAGMs were compared with the corresponding refractometer measurements via the Bland-Altman method. Similarly, Bland-Altman plots were also created with either IAGM or refractometer measurements and desflurane vaporizer dial settings.
Results—Bias ± 2 SD for comparisons of IAGM and refractometer measurements was as follows: isoflurane, −0.03 ± 0.18 volume percent; sevoflurane, −0.19 ± 0.23 volume percent; desflurane, 0.43 ± 1.22 volume percent; and N2O, −0.21 ± 1.88 volume percent. Bland-Altman plots comparing IAGM and refractometer measurements revealed nonlinear relationships for sevoflurane, desflurane, and N2O. Desflurane measurements were notably affected; bias ± limits of agreement (2 SD) were small (0.1 ± 0.22 volume percent) at < 12 volume percent, but both bias and limits of agreement increased at higher concentrations. Because IAGM measurements did not but refractometer measurements did agree with the desflurane vaporizer dial settings, infrared measurement technology was a suspected cause of the nonlinear relationships.
Conclusions and Clinical Relevance—Given that the assumption of linearity is a cornerstone of anesthetic monitor calibration, this assumption should be confirmed before anesthetic monitors are used in experiments.
Objective—To examine stress-related neurohormonal
and metabolic effects of butorphanol, fentanyl, and
ketamine administration alone and in combination
with medetomidine in dogs.
Procedure—5 dogs received either butorphanol (0.1
mg/kg), fentanyl (0.01 mg/kg), or ketamine (10 mg/kg)
IM in a crossover design. Another 5 dogs received
either medetomidine (0.02 mg/kg) and butorphanol
(0.1 mg/kg), medetomidine and fentanyl (0.01 mg/kg),
medetomidine and ketamine (10 mg/kg), or medetomidine
and saline (0.9% NaCl) solution (0.1 mL/kg) in
a similar design. Blood samples were obtained for 6
hours following the treatments. Norepinephrine, epinephrine,
cortisol, glucose, insulin, and nonesterified
fatty acid concentrations were determined in plasma.
Results—Administration of butorphanol, fentanyl, and
ketamine caused neurohormonal and metabolic
changes similar to stress, including increased plasma
epinephrine, cortisol, and glucose concentrations. The
hyperglycemic effect of butorphanol was not significant.
Ketamine caused increased norepinephrine concentration.
Epinephrine concentration was correlated
with glucose concentration in the butorphanol and fentanyl
groups but not in the ketamine groups, suggesting
an important difference between the mechanisms
of the hyperglycemic effects of these drugs.
Medetomidine prevented most of these effects
except for hyperglycemia. Plasma glucose concentrations
were lower in the combined sedation groups
than in the medetomidine-saline solution group.
Conclusions and Clinical Relevance—Opioids or
ketamine used alone may cause changes in stressrelated
biochemical variables in plasma.
Medetomidine prevented or blunted these changes.
Combined sedation provided better hormonal and
metabolic stability than either component alone. We
recommend using medetomidine-butorphanol or
medetomidine-ketamine combinations for sedation or
anesthesia of systemically healthy dogs. (Am J Vet Res 2005;66:406–412)
To evaluate the repeatability and accuracy of fingertip pulse oximeters (FPO) for measurement of hemoglobin oxygen saturation in arterial blood and pulse rate (PR) in anesthetized dogs breathing 100% O2.
29 healthy client-owned anesthetized dogs undergoing various surgical procedures.
In randomized order, each of 7 FPOs or a reference pulse oximeter (PO) was applied to the tongue of each intubated anesthetized dog breathing 100% O2. Duplicate measurements of oxygen saturation (Spo2) and PR were obtained within 60 seconds of applying an FPO or PO. A nonparametric version of Bland-Altman analysis was used. Coefficient of repeatability was the interval between the 5th and 95th percentiles of the differences between duplicate measurements. Bias was the median difference, and the limits of agreement were the 5th and 95th percentiles of the differences between each FPO and the PO. Acceptable values for the coefficient of repeatability of Spo2 were ≤ 6%. Agreements were accepted if the limits of agreement had an absolute difference of ≤ ± 3% in Spo2 and relative difference of ≤ ± 10% in PR.
Coefficient of repeatability for Spo2 was acceptable for 5 FPOs, but the limits of agreement for Spo2 were unacceptable for all FPOs. The limits of agreement for PR were acceptable for 2 FPOs.
CONCLUSIONS AND CLINICAL RELEVANCE
Results suggested that some FPOs may be suitable for accurately monitoring PRs of healthy anesthetized dogs breathing 100% O2, but mild underestimation of Spo2 was common.