- Email: [email protected]
COMPARATIVE INVESTIGATIONS ON ULTRASHORT ANAESTHETIC METHODS IN DOGS
Proceedings of the 4th International Congress of Veterinary Anaesthesia
COMPARATIVE INVESTIGATIONS ON ULTRASHORT ANAESTHETIC METHODS IN DOGS J. Henke, C. Moll, S. Winkler, B. Giissregen, H. Bockeliihr, L. Ruprecht, M. Niissl, W.Erhardt. Institut fiir Experimentelle Chirurgie der Technischen Universitat Miinchen und Gesellschaft fiir Strah-
len- und Umweltforschung, Neuherberg of fentanyl (Fentanyl? + climazolam antagonized with naloxone (Narcanti? + sarmazenil, and methadone (Polamivet9 + xylazine (Rompun? antagonized with naloxone (Narcanti9 + tolazoline (~riscol9. Climazolam and sarmazenil are substances undergoing clinical trial. Antagonization took place u) min after induction.
Introduction
For diagnostic and therapeutic purposes as well as for anaesthetic induction we investigated different types of ultrashort anaesthesias. A method without any sideeffect on vital functions and with a short recovery-time is desired. Materials and methods
For o u investigations 39 beagle dogs of both sexes with a mean body weight of 19.4 kg and
an age of 2-5 years are used. The dogs were divided in 6 groups, two prernedicated with a very low dose of acepromazine, two without any premedication and two with antagonization.
Table 2. Effective doses suitable for ultrashort anaesthesias
Ipremedication Ianaesthesia acepromazine + thiamylal
Table 1. Anaesthetic method and number of dogs used
0.02
8.8 16.8
thiamylal acepromazine premedication:
1. thiamvlal
n=7
2. propofol
n=7
without Dremedication: 3. thiamylal
n=7
4. propofol
n=7
acepromazine + propofol
I
propofol
antagonization:
5. fentanyl/climazolam
n=7
6. methadone/xylazine
n=4
We compared thiamylal (Surital? and propofol (Propof019 with and without intramuscular acepromazine-prernedication (Vetranquil? and two antagonizable anaesthesias: the combination 205
0.02
4.4
6.2
Proceedinis of the 4th International Conmas of Veterinarv Anaesthesia
Table 3. Effective doses suitable for antagonizable anaesthesias
anaesthesia
m d k g Iv
antagonization
m i 3 k Iv
fentanyl
0.02
naloxone
0.003
ClimazOlaIll
2.0
sarmazenil
0.03
methadone
0.8
naloxone
0.003
xylazine
1.0
tolazoline
5.0
Each method was investigated using the following parameters: intubation tolerance (time until coughing reflex returns) time of recovery (until all reflexes have been fully restored) pulse-rate bloodpressure (measured by a sphygmomanometer cuff) respiratory-frequency oxygen-saturation (measured by the non-invasive pulse-oximetry) behaviour during anaesthesia and waking-time Results Premedicated thiamylal anaesthesia showed a reduction in intubation-tolerance (nearly 25%) as well as in time of recovery (more than 30%). In propofol we saw no change in recovery-time after premedication, but intubation-tolerance was prolonged by 25%. Duration time was shorter with propofol than thiamylal. When antagonized 20 min after induction, coughing reflex returned at once in both methods. All reflexes were fully restored in methadone/xylazine 1 min later, in fentanyl/climazolam not before 16 mh. But it is remarkable, that nearly all reflexes disappear again for many hours in the methadone/xylazine anaesthesia.
Table 4.
anaesthesia
intub. tolerance (mi.)
recovery time
aceprom. + thiamylal
19
30
thiamylal
25
41
aceprom. + propofol
10
15
propofol
8
15
fentanyl+ climaz.
20
36
methadone+xylazine
u)
21
~~
U
Intubation tolerance and time of recovery
~
rebounds for 9 hours!
The premedicated anaesthesias caused only minimal changes in bloodpressure and the pulse-rates remained always within control level. Without premedication we initially had high values of bloodpressure (thiamylal: 166/110, propofol: 150/90) and a remarkable drop at the end of anaesthesia (thiamylal: 110/80, propofol: 120/70). The pulse-rate shows a parallel decrease in propofol (from 164 beats/min to 116/min), but not in thiamylal anaesthesia. There is always a slight increase in the waking time. Both antagonizable anaesthesias caused drops in bloodpressure immediately at induction (down to 100/80), which normalized after antagonizing.
Proceedings of the 4th International Congress of Veterinary Anaesthesia
Respiratory frequencies remained on the same physiological level in the thiamylal and the propofol anaesthesias. Oxygen-saturation however, dropped without acepromazine premedication. Under fentanyl/climazolam anaesthesia dogs breathed less often, but they had good oxygenation. Both respiratory parameters were unsatisfactory for the combination methadone/xylazine. Because of the bad experiences with this method in 4 dogs, we decided to stop this procedure. We noticed calm sleeping in both thiamylal groups, but sometimes cramps of different intensity appear during waking-time. Contrasting to this, propofol anaesthesia produced calm awaking after a short initial respiratory depression. Fentanyl/climazolam shows calm anaesthesia without any excitation. During our investigations with methadone/xylazine, artificial respiration was often necessary. Rebound effects combined with dangerous hypothermia were seen for many hours in all animals.
Table 6.
Table 5.
Mean respiratory frequency and mean oxygen saturation
anaesthesia
breaths (mi4
SaO,
(%I
Behaviour during anaesthesia and waking time
aceprom. + thiamylal
calm sleeping
mild cramps
thiamylal
calm sleeping
tonic-clonic cramps (n=4) with opisthotonos (n=2)
aceprom. + propofol
sometimes coughing
propofol
apnoea for 1 min (n=3)
calm awaking calm awaking
fentanyl+ climaz.
strong perspiration (n= 3)
calm awaking
methadone +xylazine
calm sleeping
rebound effects for 9 h
apnoea artXcial
hypothermia for many hours
resp. necessary (n=2)
(drop to 35.2 C) pilierection (n =4) lidedemas for 2 days (n= 1) prolapsus of the tongue (n=2)
Proceedin= of the 4th International Conmess of Veterinarv Anaesthesia
Conclusion There is no doubt that premedication with azepromazine in this very low dose (0.02 mg/kg IM) causes deep sedation (Horner-syndrome, prolapsus of the nicitating-membrane). With this kind of anaesthesia we have the possibility to avoid cramps, to reduce the initial dose to effect to 2/3 (thiamylal and propofol) as well as sleep ing and recovery time (thiamylal). The investigated respiratory and cardiac parameters showed the positive effect of this premedication in an impressive way. Because of these results we prefer propofol for diagnostic treatments after premedication with acepromazine. To manage more invasive operations, fentanyl combined with climazolam is a suitable method when using antagonization. The very common method of anaesthesia with methadone/xylazine seems to be not practicable even when antagonized.
COMPARATIVE INVESTIGATIONS ON ULTRASHORT ANAESTHETIC METHODS IN DOGS J. Henke, C. Moll, S. Winkler, B. Giissregen, H. Bockeliihr, L. Ruprecht, M. Niissl, W.Erhardt. Institut fiir Experimentelle Chirurgie der Technischen Universitat Miinchen und Gesellschaft fiir Strah-
len- und Umweltforschung, Neuherberg of fentanyl (Fentanyl? + climazolam antagonized with naloxone (Narcanti? + sarmazenil, and methadone (Polamivet9 + xylazine (Rompun? antagonized with naloxone (Narcanti9 + tolazoline (~riscol9. Climazolam and sarmazenil are substances undergoing clinical trial. Antagonization took place u) min after induction.
Introduction
For diagnostic and therapeutic purposes as well as for anaesthetic induction we investigated different types of ultrashort anaesthesias. A method without any sideeffect on vital functions and with a short recovery-time is desired. Materials and methods
For o u investigations 39 beagle dogs of both sexes with a mean body weight of 19.4 kg and
an age of 2-5 years are used. The dogs were divided in 6 groups, two prernedicated with a very low dose of acepromazine, two without any premedication and two with antagonization.
Table 2. Effective doses suitable for ultrashort anaesthesias
Ipremedication Ianaesthesia acepromazine + thiamylal
Table 1. Anaesthetic method and number of dogs used
0.02
8.8 16.8
thiamylal acepromazine premedication:
1. thiamvlal
n=7
2. propofol
n=7
without Dremedication: 3. thiamylal
n=7
4. propofol
n=7
acepromazine + propofol
I
propofol
antagonization:
5. fentanyl/climazolam
n=7
6. methadone/xylazine
n=4
We compared thiamylal (Surital? and propofol (Propof019 with and without intramuscular acepromazine-prernedication (Vetranquil? and two antagonizable anaesthesias: the combination 205
0.02
4.4
6.2
Proceedinis of the 4th International Conmas of Veterinarv Anaesthesia
Table 3. Effective doses suitable for antagonizable anaesthesias
anaesthesia
m d k g Iv
antagonization
m i 3 k Iv
fentanyl
0.02
naloxone
0.003
ClimazOlaIll
2.0
sarmazenil
0.03
methadone
0.8
naloxone
0.003
xylazine
1.0
tolazoline
5.0
Each method was investigated using the following parameters: intubation tolerance (time until coughing reflex returns) time of recovery (until all reflexes have been fully restored) pulse-rate bloodpressure (measured by a sphygmomanometer cuff) respiratory-frequency oxygen-saturation (measured by the non-invasive pulse-oximetry) behaviour during anaesthesia and waking-time Results Premedicated thiamylal anaesthesia showed a reduction in intubation-tolerance (nearly 25%) as well as in time of recovery (more than 30%). In propofol we saw no change in recovery-time after premedication, but intubation-tolerance was prolonged by 25%. Duration time was shorter with propofol than thiamylal. When antagonized 20 min after induction, coughing reflex returned at once in both methods. All reflexes were fully restored in methadone/xylazine 1 min later, in fentanyl/climazolam not before 16 mh. But it is remarkable, that nearly all reflexes disappear again for many hours in the methadone/xylazine anaesthesia.
Table 4.
anaesthesia
intub. tolerance (mi.)
recovery time
aceprom. + thiamylal
19
30
thiamylal
25
41
aceprom. + propofol
10
15
propofol
8
15
fentanyl+ climaz.
20
36
methadone+xylazine
u)
21
~~
U
Intubation tolerance and time of recovery
~
rebounds for 9 hours!
The premedicated anaesthesias caused only minimal changes in bloodpressure and the pulse-rates remained always within control level. Without premedication we initially had high values of bloodpressure (thiamylal: 166/110, propofol: 150/90) and a remarkable drop at the end of anaesthesia (thiamylal: 110/80, propofol: 120/70). The pulse-rate shows a parallel decrease in propofol (from 164 beats/min to 116/min), but not in thiamylal anaesthesia. There is always a slight increase in the waking time. Both antagonizable anaesthesias caused drops in bloodpressure immediately at induction (down to 100/80), which normalized after antagonizing.
Proceedings of the 4th International Congress of Veterinary Anaesthesia
Respiratory frequencies remained on the same physiological level in the thiamylal and the propofol anaesthesias. Oxygen-saturation however, dropped without acepromazine premedication. Under fentanyl/climazolam anaesthesia dogs breathed less often, but they had good oxygenation. Both respiratory parameters were unsatisfactory for the combination methadone/xylazine. Because of the bad experiences with this method in 4 dogs, we decided to stop this procedure. We noticed calm sleeping in both thiamylal groups, but sometimes cramps of different intensity appear during waking-time. Contrasting to this, propofol anaesthesia produced calm awaking after a short initial respiratory depression. Fentanyl/climazolam shows calm anaesthesia without any excitation. During our investigations with methadone/xylazine, artificial respiration was often necessary. Rebound effects combined with dangerous hypothermia were seen for many hours in all animals.
Table 6.
Table 5.
Mean respiratory frequency and mean oxygen saturation
anaesthesia
breaths (mi4
SaO,
(%I
Behaviour during anaesthesia and waking time
aceprom. + thiamylal
calm sleeping
mild cramps
thiamylal
calm sleeping
tonic-clonic cramps (n=4) with opisthotonos (n=2)
aceprom. + propofol
sometimes coughing
propofol
apnoea for 1 min (n=3)
calm awaking calm awaking
fentanyl+ climaz.
strong perspiration (n= 3)
calm awaking
methadone +xylazine
calm sleeping
rebound effects for 9 h
apnoea artXcial
hypothermia for many hours
resp. necessary (n=2)
(drop to 35.2 C) pilierection (n =4) lidedemas for 2 days (n= 1) prolapsus of the tongue (n=2)
Proceedin= of the 4th International Conmess of Veterinarv Anaesthesia
Conclusion There is no doubt that premedication with azepromazine in this very low dose (0.02 mg/kg IM) causes deep sedation (Horner-syndrome, prolapsus of the nicitating-membrane). With this kind of anaesthesia we have the possibility to avoid cramps, to reduce the initial dose to effect to 2/3 (thiamylal and propofol) as well as sleep ing and recovery time (thiamylal). The investigated respiratory and cardiac parameters showed the positive effect of this premedication in an impressive way. Because of these results we prefer propofol for diagnostic treatments after premedication with acepromazine. To manage more invasive operations, fentanyl combined with climazolam is a suitable method when using antagonization. The very common method of anaesthesia with methadone/xylazine seems to be not practicable even when antagonized.