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Efficient inspired concentration of sevoflurane for vital capacity rapid inhalation induction (VCRII) technique
Efficient Inspired Concentration of Sevoflurane for Vital Capacity Rapid Inhalation Induction (VCRII) Technique Masaki Yurino,
MD, PhD,* Hitomi
Kimura,
MDT
Department of Anesthesiology and Resuscitology, Asahikawa Medical College, Hokkaido, Japan.
*Assistant Professor tStaff Anesthesiologist Address reprint requests to Dr. Yurino at the Department of Anesthesiology and Resuscitology, Asahikawa Medical College, 4-5-3-l 1, Nishikagura, Asahikawa City, Hokkaido 078, Japan. Received for publication January 6, 1994; revised manuscript accepted for publication June 28, 1994.
Study Objectives: To evaluate the efficient inspired concentration of sevoflurane for a vital capacity rapid inhalation induction (VCZUZ) technique with respectto induction time, characteristics, and accepability. Design: Prospective study. Setting: Medical college hospital. Patients: 68 unpremeditated healthy adult volunteers were assigned to one of four groups in order of sequential entry of informed consent. Interventions: 3%, 4.5%, 6%, or 7.5% concentrations of sevoflurane were administeredfor 5 minutes (3% and 4.5%) or 3 minutes (6% and 7.5%) using a single breath technique. Measurements and Main Results: The mean induction time required with 3%, 4.5%, 6%, or 7.5% sevoflurane was 120 2 26 set, 79 + 18 set, 52 + 15 set, or 47 + 17 seconds,respectively. Each induction time was significantly different from the others (p < 0.05) exceptfor that between6% and 7.5% There appeared to be a direct inverse relationship between the mean induction time and the logarithm of inspired concentration of sevoflurane, but thzLs relationship did not extend beyondconcentrations above 6%. Blood pressure decreasedby approximately 18% from baseline at the end of inhalation of the drug, and heart rate remained constant in all groups. Except of one subject in the 7.5% group, no coughing was observed and laryngospasm, breathholding, and secretions were not seen in any subjects. Slight limb movement was observed in a few subjectsin each group. All subjectsexcept one in the 3% group would accept undergoing a similar procedure again. Conclusion: Seuoflurane 6% can be recommendedfor VCRZZ, but increasing the concentration higher than this doesnot markedly shorten the induction time and thus seemsto add little benefit. Administration, sevoflurane; vital capacity.
Keywords:
inhalation;
anesthesia, induction
of;
Introduction A high concentration rapid induction.
Journal of Clinical Anesthesia 7:228-23 1, 1995 Q 1995 by Elsevier Science Inc. 655 Avenue of the Americas, New York, NY 10010
of volatile anesthetic for inhalation
Rapid induction
induction
can obviate the subsequent
excitatory
results in move-
0952-8180/95/$10,00 SSDI 0952-8180(95)00006-4
SevofZurane concentration for VCRIII:
ments in light stages of induction. We demonstrated that sevofhrrane 3% or 4.5% allows a moderately rapid induction with only slight problems of induction using a vital capacity rapid inhalation induction (VCRII) technique. ‘~3 However, concentrations higher than 5% have not yet been tested, and an efficient inspired concentration of sevoflurane for the VCR11 technique is still being investigated. In the current study, we investigated the high inspired concentration of sevoflurane over a concentration range from 5% to 7.5% compared with low concentration for the VCR11 technique with respect to induction time, characteristics, and acceptability.
Materials and Methods This study was approved by the Asahikawa Medical College Clinical Human Research Committee. All volunteers with ASA physical status I gave informed consent and were assigned to one of four groups of 17 subjects in sequential order of entry. The first group received a 3% concentration of sevoflurane in oxygen (0,), and the second, third and fourth groups received 4.5%, S%, or 7.5% concentrations, respectively. The 3%, 4.5%, 6%, and 7.5% concentrations of sevoflurane in Oz represented approximately 1.36,2.0,2.73, and 3.41 minimum alveolar concentration (MAC; 2.05%),4 respectively. Subjects were blinded to the inhalation anesthetic used, as well as its concentration of anesthetic vapor. The 3% group consisted of 11 male and 6 female subjects ranging in age from 23 to 36 years, weight from 48 to 74 kg, and height from 158 to 181 cm. The 4.5% group included 12 males and 5 females ranging from 23 to 32 years, weighing from 47 to 71 kg, and measuring from 155 to 178 cm. In the 6% group there were 13 males and 4 females aged 23 to 30 years, weighing 45 to 83 kg, and measuring from 155 to 178 cm in height. The 7.5% group included 12 males and 5 females aged 23 to 30 years, weighing from 46 to 84 kg, and measuring from 157 to 174 cm (Table I). None of the subjects was premedicated. Mixtures of each concentration of sevoflurane and Oz were delivered at 8 Wmin by a calibrated Penlon PPVX vaporizer (Penlon Ltd., Abingdon, UK) into the circle system of an anesthesia machine. After replacing the face mask with a model lung, we set the vaporizer to a concentration slightly higher than each desired concentration of sevoflurane and circulated the respiratory gas
3.0 4.5 6.0 7.5
in the circuit. We controlled the vaporizer setting by monitoring the circulated gas concentration and then primed the circle according to the desired concentration of sevoflurane. The subjects, who were breathing room air, were instructed to breathe out to a residual volume. We then applied the anesthetic system and face mask, instructing subjects to breathe in deeply and hold their breath for as long as was comfortable. Following the vital capacity breath, the subjects were allowed to resume spontaneous respiration of the same concentration of sevoflurane for up to 5 minutes (3% and 4.5% groups) or 3 minutes (6% and 7.5% groups) from the end of their vital capacity breath. These periods of inhalation were to be adequate for the subjects to fall asleep. After that, the subjects continued to breathe 0, until they regained consciousness. Loss of consciousness was defined as absence of response to the verbal command “open eyes.” Verbal commands were repeated at 10 second intervals until subjects failed to respond. Induction time and excitatory phenomena, such as limb movements, breath-holding, and secretions, were recorded. Induction time was defined as the interval between the time at which the subject’s lung volume reached total lung capacity (the end of the vital capacity inspiration) and loss of consciousness. We defined an anesthetic induction as “complicated’ if one or more problems occurred. We grouped problems into the five categories established by Lamberty and Wilson.5 A single cough, laryngospasm, breathholding, movement of a limb, or excessive salivation (defined as enough secretions to wet our hands) were recorded. We monitored respiration using the display of a multi-gas monitor and the continuous movement of a rebreathing bag. We distinguished between breathholding and laryngospasm according to whether respiration could be restored by forced manual ventilation. Immediately after emergence from anesthesia, an independent observer, who was blinded to the concentra(sec)(
60
Table 1. Demographic Data of Subjects Sevoflurane (%)
40
Age W 25.6 25.6 24.6 24.9
f 2 f f
3.9 2.8 2.0 1.9
Note: Data are means k SD.
Weight (kg) 59.4 59.4 63.3 63.9
Ifr 9.0 f 6.5 k 11.9 -+ 10.4
Yurino and Kimura
168.2 166.0 167.1 167.7
* 7.5 + 7.9 +- 7.0 f 5.6
1
I
2
Height (cm)
3 5 7 CONCENTRATION OF SEVOFLURANE (log
10 %)
1. Relationship between induction time and sevoflurane concentration. The mean induction time is inversely proportional to the logarithm of concentration given but this relationship did not extend beyond concentration above 6%. Figure
J. Clin. Anesth., vol. 7, May 1995
229
Original C0ntribut~n.s Table 2. Cardiovascular Changes with Sevoflurane Group and Parameter
3.0% sevoflurane SBP (mmHg) DBP (mmHg)
Baseline Omin
3 min
5min
125 + 20
112 -c 15*
104 k 12*
702 11 80-c 15
59 2 14* 792 13
55 f 13* 75 + 13
117 -e 13 692 12
100 k 10*
96 * 8*
55 2 10* 735 15
52 + 9* 70+ 11
HR @pm) 4.5% sevoflurane
SBP (mmHg) DBP (mmHg)
70+ 12
HR @pm)
6.0% sevoflurane SBP (mmHg) DBP (mmHg)
115 2 10
96 2 ll*
65 -I- 6 682 10
49 k t3* 76 2 20
HR @pm) 7.5% sevoflurane
SBP (mmHg) DBP (mmHg)
Time after Induction
115 2 15 632 10
HR (bpm)
72 rf: 14
94 k 13* 48 -I- 12* 73 2 14
Note: Data are means+ SD. SBP = systolic blood pressure; DBP = diastolic blood pressure; HR = heart rate. p < 0.05 versus baseline.
tion used, asked the subjects to characterize the smell of the anesthetic (pleasant = subjects liked to did not mind the smell; unpleasant = very pungent or not tolerable; no comment = others), and asked whether they would have any objection to undergoing the VCR11 technique again, Monitoring included an automatic noninvasive blood pressure recorder with an ECG oscilloscope and pulse oximeter (Nippon Colin, Komaki, Japan) and multi-gas monitor (Capnomac Ultima, Datex Instrumentarium, Helsinki, Finland). The gas monitor was calibrated every day before the experiment using a calibration gas (Quick Cal, Datex). Three or four subjects were sequentially studied in a day. Respiratory gases were sampled from the elbow connector with the face mask at a rate of 150 ml/min to monitor end-tidal and inspired concentrations of anesthetic gases continuously. Statistical analysis consisted of one-way analysis of variance (ANOVA) for repeated measures and chi-
square test with Fisher’s exact probability test. Differences among the four groups were compared using the Kruskal-Wallis one-way ANOVA. All results are expressed as means ? SD. A p-value of less than 0.05 was considered to be statistically significant.
Results The groups were demographically similar with no significant differences in age, gender, weight, or height (Table I). Anesthesia was successfully induced in all groups. The mean induction time required with S%, 4.5%, S%, or 7.5% sevoflurane was 120 + 26 seconds, 79 k 18 seconds, 52 + 15 seconds, or 47 -I- 17 seconds, respectively. Each induction time was significantly different from the others V, < 0.05) except for time between 6% and 7.5%. There appeared to be a direct inverse relationship between the mean induction time and the logarithm of inspired concentration of sevoflurane in the range 3% to 6% but this relationship did not extend beyond concentrations above 6% (Figure I). After the anesthetic face mask was applied, 0, saturations increased slightly from baseline in the 3%, 4.5%, 6%, and 7.5% groups (baseline: 97.2 ? 0.4 mmHg, 97.4 + 0.5 mmHg, 97.1 2 0.2 mmHg, and 97.2 k 0.4 mmHg, respectively; during induction: 99.4 f 0.6 mmHg, 99.4 + 0.8 mmHg, 99.5 2 0.5 mmHg, and 99.5 + 0.6 mmHg, respectively). In each group, systolic and diastolic blood pressure decreased significantly by 16% to 18% and 2 1% to 25%, respectively, from baseline at the end of inhalation of drug (Table 2). Heart rate did not change significantly from baseline in any groups. The incidence of problems of inhalation anesthesia induction was very low (Table 3). Slight involuntary movement was observed in a few subjects in each group. Subjects in the 3%, 4.5%, and 6% groups found the smell more pleasant than those in the 7.5% group. However, all subjects in the 7.5% group indicated that they would be willing to undergo similar induction again, as did almost all subjects in the other groups (Table 4).
Discussion To achieve more rapid induction and reduce the anesthetist’s frustration during induction, higher concentra-
Table 3. Incidence of Complications during Induction of Anesthesia Sevoflurane Concentration Type of Induction Uncomplicated
Complicated Coughing Laryngospasm Breath holding Movements Secretions
430
3.0%
4.5%
6.0%
7.5%
15 (88.2%)
14 (82.4%)
15 (88.2%)
15 (88.2%)
-
-
-
1 (5.9%) -
2 (11.8%) -
J. Clin. Anesth., vol. 7, May 1995
3 (17.6%) -
2 (11.8%) -
1(5<%) -
Sevojlurane concentrationfor VCRIII: Yurino and Kimura Table 4. Acceptability and Smell of Anesthesia Sevoflurane Reaction of Subjects after Emergence
Sameinduction again? Yes No comment No Smell Pleasant No comment Unpleasant
Concentration
3.0%
4.5%
6.0%
7.5%
14 (82.3%) 1 (5.9%) 2 (11.8%)
17 (100%) -
17 (100%) -
17 (100%) -
9 (52.9%) 3 (17.7%) 5 (29.4%)
10 (58.8%) 6 (35.3%) 1 (5.9%)
9 (52.9%) 8 (47.1%) 0 (0.0%)
5 (29.4%)* 9 (52.9%) 3 (17.7%)
*p < 0.05. dons of sevoflurane were tested in this study. Buffington6 reported that with isoflurane, the incidence of Iaryngospasm, coughing, and breath-holding was directly related to the concentration of anesthetic. Induction characteristics with enflurane are similar to those with isoflurane.5 Desflurane causes a high incidence of airway problems, and it appears unlikely that this drug will be used extensively for either conventional or VCR11 in children and adults.’ In contrast to these anesthetics, the current results demonstrate that sevoflurane had a lower incidence of induction-related problems regardless of the sevoflurane concentration. Slight involuntary movement, such as finger motions, was observed in a few subjects in each group but this action did not influence the course of induction and smooth induction was achieved in much the same way as in the other subjects. However, one subject who received 7.5% sevoflurane coughed during induction, which never occurred with lower concentrations. Moreover, only 30% of subjects in the 7.5% sevoflurane group described the smell of the anesthetic as “pleasant,” as opposed to 50% to 60% of volunteers in the other groups. With regard to induction speed, we have found that the induction time is inversely proportional to the sevoflurane concentration given on a logarithmic concentration scale. This relationship has not yet been proved with other drugs since an accurate measurement of real induction time might be difficult. We could measure precise induction times because a standardized vital capacity breath technique was applied, low irritation of airways did not produce the varieties of performance, and an anesthetic face mask could be kept completely tight during a shorter induction time. This relationship, however, did not extend beyond concentrations above 6%. We also showed that either 6% or 7.5% sevoflurane had a significantly shorter induction time than with 3% or 4.5%, but there was no significant difference between the induction times with 6% and 7.5% seroflurane (52
versw 47 seconds, respectively.) Although concentrations above 7.5% sevoflurane were not tested, it would seem, from our findings, that sevoflurane concentrations above 6.0% are not more efficient in achieving a higher speed of induction in VCRII. In view of the high cost of this anesthetic, the use of concentration above 6.0% is not cost effective. In summary, high concentrations of sevoflurane (either 6% or 7.5%) have a low incidence of complications without premeditation and/or use of supplementary drugs with more rapid induction. However, sevoflurane 7.5% is not any better than that of 6%. We therefore recommend 6% concentration of sevoflurane for the VCR11 technique.
References 1. Yurino M, Kimura H: Vital capacitybreath technique for rapid anaestheticinduction: comparison of sevoflurane and isoflurane. Am&h&a 1992;47:946-9. 2. Yurino M, Kimura H: Induction of anesthesiawith sevoflurane, nitrous oxide, and oxygen: a comparison of spontaneousventilation and vital capacity rapid inhalation induction (VCRII) techniques.An&h An&g 1993;76:598-601. 3. Yurino M, Kimura H: Vital capacity rapid inhalation induction technique: comparison of sevoflurane and halothane. Can J Am&h 1993;40(5Pt 1):440-T 4. Scheller MS, SaidmanLJ, Partridge BL: MAC of sevoflurane in humans and New Zealandwhite rabbit. CanAm&h Sot J 1988; 35:153-6. 5. LambertyJM, Wilson IH: Single breath induction of anesthesia with isoflurane. Br J Anuesth 1987;59:1214-8. 6. Buffington CW: Clinical evaluation of isoflurane: reflex actions during isoflurane anaesthesia.Can Anaesth Sot J 1982;29suppl:S3543. 7. Smiley RM: An overview of induction and emergencecharacteristicsof desflurane in pediatric, adult, and geriatric patients. Anesth Andg 1992;75(4Suppl):S38-46.
J. Clin. Anesth., vol. 7, May 1995
231
MD, PhD,* Hitomi
Kimura,
MDT
Department of Anesthesiology and Resuscitology, Asahikawa Medical College, Hokkaido, Japan.
*Assistant Professor tStaff Anesthesiologist Address reprint requests to Dr. Yurino at the Department of Anesthesiology and Resuscitology, Asahikawa Medical College, 4-5-3-l 1, Nishikagura, Asahikawa City, Hokkaido 078, Japan. Received for publication January 6, 1994; revised manuscript accepted for publication June 28, 1994.
Study Objectives: To evaluate the efficient inspired concentration of sevoflurane for a vital capacity rapid inhalation induction (VCZUZ) technique with respectto induction time, characteristics, and accepability. Design: Prospective study. Setting: Medical college hospital. Patients: 68 unpremeditated healthy adult volunteers were assigned to one of four groups in order of sequential entry of informed consent. Interventions: 3%, 4.5%, 6%, or 7.5% concentrations of sevoflurane were administeredfor 5 minutes (3% and 4.5%) or 3 minutes (6% and 7.5%) using a single breath technique. Measurements and Main Results: The mean induction time required with 3%, 4.5%, 6%, or 7.5% sevoflurane was 120 2 26 set, 79 + 18 set, 52 + 15 set, or 47 + 17 seconds,respectively. Each induction time was significantly different from the others (p < 0.05) exceptfor that between6% and 7.5% There appeared to be a direct inverse relationship between the mean induction time and the logarithm of inspired concentration of sevoflurane, but thzLs relationship did not extend beyondconcentrations above 6%. Blood pressure decreasedby approximately 18% from baseline at the end of inhalation of the drug, and heart rate remained constant in all groups. Except of one subject in the 7.5% group, no coughing was observed and laryngospasm, breathholding, and secretions were not seen in any subjects. Slight limb movement was observed in a few subjectsin each group. All subjectsexcept one in the 3% group would accept undergoing a similar procedure again. Conclusion: Seuoflurane 6% can be recommendedfor VCRZZ, but increasing the concentration higher than this doesnot markedly shorten the induction time and thus seemsto add little benefit. Administration, sevoflurane; vital capacity.
Keywords:
inhalation;
anesthesia, induction
of;
Introduction A high concentration rapid induction.
Journal of Clinical Anesthesia 7:228-23 1, 1995 Q 1995 by Elsevier Science Inc. 655 Avenue of the Americas, New York, NY 10010
of volatile anesthetic for inhalation
Rapid induction
induction
can obviate the subsequent
excitatory
results in move-
0952-8180/95/$10,00 SSDI 0952-8180(95)00006-4
SevofZurane concentration for VCRIII:
ments in light stages of induction. We demonstrated that sevofhrrane 3% or 4.5% allows a moderately rapid induction with only slight problems of induction using a vital capacity rapid inhalation induction (VCRII) technique. ‘~3 However, concentrations higher than 5% have not yet been tested, and an efficient inspired concentration of sevoflurane for the VCR11 technique is still being investigated. In the current study, we investigated the high inspired concentration of sevoflurane over a concentration range from 5% to 7.5% compared with low concentration for the VCR11 technique with respect to induction time, characteristics, and acceptability.
Materials and Methods This study was approved by the Asahikawa Medical College Clinical Human Research Committee. All volunteers with ASA physical status I gave informed consent and were assigned to one of four groups of 17 subjects in sequential order of entry. The first group received a 3% concentration of sevoflurane in oxygen (0,), and the second, third and fourth groups received 4.5%, S%, or 7.5% concentrations, respectively. The 3%, 4.5%, 6%, and 7.5% concentrations of sevoflurane in Oz represented approximately 1.36,2.0,2.73, and 3.41 minimum alveolar concentration (MAC; 2.05%),4 respectively. Subjects were blinded to the inhalation anesthetic used, as well as its concentration of anesthetic vapor. The 3% group consisted of 11 male and 6 female subjects ranging in age from 23 to 36 years, weight from 48 to 74 kg, and height from 158 to 181 cm. The 4.5% group included 12 males and 5 females ranging from 23 to 32 years, weighing from 47 to 71 kg, and measuring from 155 to 178 cm. In the 6% group there were 13 males and 4 females aged 23 to 30 years, weighing 45 to 83 kg, and measuring from 155 to 178 cm in height. The 7.5% group included 12 males and 5 females aged 23 to 30 years, weighing from 46 to 84 kg, and measuring from 157 to 174 cm (Table I). None of the subjects was premedicated. Mixtures of each concentration of sevoflurane and Oz were delivered at 8 Wmin by a calibrated Penlon PPVX vaporizer (Penlon Ltd., Abingdon, UK) into the circle system of an anesthesia machine. After replacing the face mask with a model lung, we set the vaporizer to a concentration slightly higher than each desired concentration of sevoflurane and circulated the respiratory gas
3.0 4.5 6.0 7.5
in the circuit. We controlled the vaporizer setting by monitoring the circulated gas concentration and then primed the circle according to the desired concentration of sevoflurane. The subjects, who were breathing room air, were instructed to breathe out to a residual volume. We then applied the anesthetic system and face mask, instructing subjects to breathe in deeply and hold their breath for as long as was comfortable. Following the vital capacity breath, the subjects were allowed to resume spontaneous respiration of the same concentration of sevoflurane for up to 5 minutes (3% and 4.5% groups) or 3 minutes (6% and 7.5% groups) from the end of their vital capacity breath. These periods of inhalation were to be adequate for the subjects to fall asleep. After that, the subjects continued to breathe 0, until they regained consciousness. Loss of consciousness was defined as absence of response to the verbal command “open eyes.” Verbal commands were repeated at 10 second intervals until subjects failed to respond. Induction time and excitatory phenomena, such as limb movements, breath-holding, and secretions, were recorded. Induction time was defined as the interval between the time at which the subject’s lung volume reached total lung capacity (the end of the vital capacity inspiration) and loss of consciousness. We defined an anesthetic induction as “complicated’ if one or more problems occurred. We grouped problems into the five categories established by Lamberty and Wilson.5 A single cough, laryngospasm, breathholding, movement of a limb, or excessive salivation (defined as enough secretions to wet our hands) were recorded. We monitored respiration using the display of a multi-gas monitor and the continuous movement of a rebreathing bag. We distinguished between breathholding and laryngospasm according to whether respiration could be restored by forced manual ventilation. Immediately after emergence from anesthesia, an independent observer, who was blinded to the concentra(sec)(
60
Table 1. Demographic Data of Subjects Sevoflurane (%)
40
Age W 25.6 25.6 24.6 24.9
f 2 f f
3.9 2.8 2.0 1.9
Note: Data are means k SD.
Weight (kg) 59.4 59.4 63.3 63.9
Ifr 9.0 f 6.5 k 11.9 -+ 10.4
Yurino and Kimura
168.2 166.0 167.1 167.7
* 7.5 + 7.9 +- 7.0 f 5.6
1
I
2
Height (cm)
3 5 7 CONCENTRATION OF SEVOFLURANE (log
10 %)
1. Relationship between induction time and sevoflurane concentration. The mean induction time is inversely proportional to the logarithm of concentration given but this relationship did not extend beyond concentration above 6%. Figure
J. Clin. Anesth., vol. 7, May 1995
229
Original C0ntribut~n.s Table 2. Cardiovascular Changes with Sevoflurane Group and Parameter
3.0% sevoflurane SBP (mmHg) DBP (mmHg)
Baseline Omin
3 min
5min
125 + 20
112 -c 15*
104 k 12*
702 11 80-c 15
59 2 14* 792 13
55 f 13* 75 + 13
117 -e 13 692 12
100 k 10*
96 * 8*
55 2 10* 735 15
52 + 9* 70+ 11
HR @pm) 4.5% sevoflurane
SBP (mmHg) DBP (mmHg)
70+ 12
HR @pm)
6.0% sevoflurane SBP (mmHg) DBP (mmHg)
115 2 10
96 2 ll*
65 -I- 6 682 10
49 k t3* 76 2 20
HR @pm) 7.5% sevoflurane
SBP (mmHg) DBP (mmHg)
Time after Induction
115 2 15 632 10
HR (bpm)
72 rf: 14
94 k 13* 48 -I- 12* 73 2 14
Note: Data are means+ SD. SBP = systolic blood pressure; DBP = diastolic blood pressure; HR = heart rate. p < 0.05 versus baseline.
tion used, asked the subjects to characterize the smell of the anesthetic (pleasant = subjects liked to did not mind the smell; unpleasant = very pungent or not tolerable; no comment = others), and asked whether they would have any objection to undergoing the VCR11 technique again, Monitoring included an automatic noninvasive blood pressure recorder with an ECG oscilloscope and pulse oximeter (Nippon Colin, Komaki, Japan) and multi-gas monitor (Capnomac Ultima, Datex Instrumentarium, Helsinki, Finland). The gas monitor was calibrated every day before the experiment using a calibration gas (Quick Cal, Datex). Three or four subjects were sequentially studied in a day. Respiratory gases were sampled from the elbow connector with the face mask at a rate of 150 ml/min to monitor end-tidal and inspired concentrations of anesthetic gases continuously. Statistical analysis consisted of one-way analysis of variance (ANOVA) for repeated measures and chi-
square test with Fisher’s exact probability test. Differences among the four groups were compared using the Kruskal-Wallis one-way ANOVA. All results are expressed as means ? SD. A p-value of less than 0.05 was considered to be statistically significant.
Results The groups were demographically similar with no significant differences in age, gender, weight, or height (Table I). Anesthesia was successfully induced in all groups. The mean induction time required with S%, 4.5%, S%, or 7.5% sevoflurane was 120 + 26 seconds, 79 k 18 seconds, 52 + 15 seconds, or 47 -I- 17 seconds, respectively. Each induction time was significantly different from the others V, < 0.05) except for time between 6% and 7.5%. There appeared to be a direct inverse relationship between the mean induction time and the logarithm of inspired concentration of sevoflurane in the range 3% to 6% but this relationship did not extend beyond concentrations above 6% (Figure I). After the anesthetic face mask was applied, 0, saturations increased slightly from baseline in the 3%, 4.5%, 6%, and 7.5% groups (baseline: 97.2 ? 0.4 mmHg, 97.4 + 0.5 mmHg, 97.1 2 0.2 mmHg, and 97.2 k 0.4 mmHg, respectively; during induction: 99.4 f 0.6 mmHg, 99.4 + 0.8 mmHg, 99.5 2 0.5 mmHg, and 99.5 + 0.6 mmHg, respectively). In each group, systolic and diastolic blood pressure decreased significantly by 16% to 18% and 2 1% to 25%, respectively, from baseline at the end of inhalation of drug (Table 2). Heart rate did not change significantly from baseline in any groups. The incidence of problems of inhalation anesthesia induction was very low (Table 3). Slight involuntary movement was observed in a few subjects in each group. Subjects in the 3%, 4.5%, and 6% groups found the smell more pleasant than those in the 7.5% group. However, all subjects in the 7.5% group indicated that they would be willing to undergo similar induction again, as did almost all subjects in the other groups (Table 4).
Discussion To achieve more rapid induction and reduce the anesthetist’s frustration during induction, higher concentra-
Table 3. Incidence of Complications during Induction of Anesthesia Sevoflurane Concentration Type of Induction Uncomplicated
Complicated Coughing Laryngospasm Breath holding Movements Secretions
430
3.0%
4.5%
6.0%
7.5%
15 (88.2%)
14 (82.4%)
15 (88.2%)
15 (88.2%)
-
-
-
1 (5.9%) -
2 (11.8%) -
J. Clin. Anesth., vol. 7, May 1995
3 (17.6%) -
2 (11.8%) -
1(5<%) -
Sevojlurane concentrationfor VCRIII: Yurino and Kimura Table 4. Acceptability and Smell of Anesthesia Sevoflurane Reaction of Subjects after Emergence
Sameinduction again? Yes No comment No Smell Pleasant No comment Unpleasant
Concentration
3.0%
4.5%
6.0%
7.5%
14 (82.3%) 1 (5.9%) 2 (11.8%)
17 (100%) -
17 (100%) -
17 (100%) -
9 (52.9%) 3 (17.7%) 5 (29.4%)
10 (58.8%) 6 (35.3%) 1 (5.9%)
9 (52.9%) 8 (47.1%) 0 (0.0%)
5 (29.4%)* 9 (52.9%) 3 (17.7%)
*p < 0.05. dons of sevoflurane were tested in this study. Buffington6 reported that with isoflurane, the incidence of Iaryngospasm, coughing, and breath-holding was directly related to the concentration of anesthetic. Induction characteristics with enflurane are similar to those with isoflurane.5 Desflurane causes a high incidence of airway problems, and it appears unlikely that this drug will be used extensively for either conventional or VCR11 in children and adults.’ In contrast to these anesthetics, the current results demonstrate that sevoflurane had a lower incidence of induction-related problems regardless of the sevoflurane concentration. Slight involuntary movement, such as finger motions, was observed in a few subjects in each group but this action did not influence the course of induction and smooth induction was achieved in much the same way as in the other subjects. However, one subject who received 7.5% sevoflurane coughed during induction, which never occurred with lower concentrations. Moreover, only 30% of subjects in the 7.5% sevoflurane group described the smell of the anesthetic as “pleasant,” as opposed to 50% to 60% of volunteers in the other groups. With regard to induction speed, we have found that the induction time is inversely proportional to the sevoflurane concentration given on a logarithmic concentration scale. This relationship has not yet been proved with other drugs since an accurate measurement of real induction time might be difficult. We could measure precise induction times because a standardized vital capacity breath technique was applied, low irritation of airways did not produce the varieties of performance, and an anesthetic face mask could be kept completely tight during a shorter induction time. This relationship, however, did not extend beyond concentrations above 6%. We also showed that either 6% or 7.5% sevoflurane had a significantly shorter induction time than with 3% or 4.5%, but there was no significant difference between the induction times with 6% and 7.5% seroflurane (52
versw 47 seconds, respectively.) Although concentrations above 7.5% sevoflurane were not tested, it would seem, from our findings, that sevoflurane concentrations above 6.0% are not more efficient in achieving a higher speed of induction in VCRII. In view of the high cost of this anesthetic, the use of concentration above 6.0% is not cost effective. In summary, high concentrations of sevoflurane (either 6% or 7.5%) have a low incidence of complications without premeditation and/or use of supplementary drugs with more rapid induction. However, sevoflurane 7.5% is not any better than that of 6%. We therefore recommend 6% concentration of sevoflurane for the VCR11 technique.
References 1. Yurino M, Kimura H: Vital capacitybreath technique for rapid anaestheticinduction: comparison of sevoflurane and isoflurane. Am&h&a 1992;47:946-9. 2. Yurino M, Kimura H: Induction of anesthesiawith sevoflurane, nitrous oxide, and oxygen: a comparison of spontaneousventilation and vital capacity rapid inhalation induction (VCRII) techniques.An&h An&g 1993;76:598-601. 3. Yurino M, Kimura H: Vital capacity rapid inhalation induction technique: comparison of sevoflurane and halothane. Can J Am&h 1993;40(5Pt 1):440-T 4. Scheller MS, SaidmanLJ, Partridge BL: MAC of sevoflurane in humans and New Zealandwhite rabbit. CanAm&h Sot J 1988; 35:153-6. 5. LambertyJM, Wilson IH: Single breath induction of anesthesia with isoflurane. Br J Anuesth 1987;59:1214-8. 6. Buffington CW: Clinical evaluation of isoflurane: reflex actions during isoflurane anaesthesia.Can Anaesth Sot J 1982;29suppl:S3543. 7. Smiley RM: An overview of induction and emergencecharacteristicsof desflurane in pediatric, adult, and geriatric patients. Anesth Andg 1992;75(4Suppl):S38-46.
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