Veterinary Surgery, 21, 6, 491-493, 1992
Measurement of Muscle Surface Capillary Blood Flow by Laser Doppler Flowmetry WENDY M. NORMAN, WSC, MICHAEL H. COURT, BvSc. Diplomate AWA, NICHOLAS H. DODMAN, BVMS, Diplomate ACVA, and FRANK s. PIPERS, DVM, PhD, Diplomate ACVfM Muscle surface capillary blood flow was measured in the biceps femoris and lateral head of the triceps brachii muscles in six horses before and during halothane anesthesia by using laser Doppler flowmetry. During 90 minutes of anesthesia, muscle surface capillary blood flow was reduced to 20% to 40% of preanesthetic values. Muscle surface capillary blood flow tended to be lower in dependent muscles than in nondependent muscles, and this disparity was greater in the forelimbs than in the hind limbs.
a well-recognized and P potentially disastrous complication of equine anesthesia.' Much effort has been devoted to identifying causOSTANESTHETIC MYOPATHY IS
ative factors and their relative ~ignificance.~-~ The roles of arterial hypotension and increased intracompartmental muscle pressure have received attention.'^^ It has been suggested, but not proven, that reduced muscle blood flow associated with anesthesia and recumbency results in ischemic muscle injury. Radioactive isotopes have been used to measure muscle blood flow in standing and anesthetized The methods require specialized equipment, permit only a limited number of measurements per experiment, and are expensive to perform. Laser Doppler flowmetry allows relatively noninvasive, continuous measurement of tissue perfusion. It cannot determine absolute values for tissue blood flow, but it does indicate changes in the perfusion of a particular tissue. Excellent correlation was shown between laser Doppler flowmetry and standard techniques for measurement of blood flow in skeletal muscle.8 Differences in muscle blood flow between dependent and nondependent muscles in horses during recumbency and general anesthesia measured with laser Doppler flowmetry have been reported, but no control (preanesthetic) values were given.' In the current study, laser Doppler flowmetry was used to measure muscle surface capillary blood flow in standing and laterally recumbent, halothane-anesthetized
horses to determine the effect of recumbency and general anesthesia on equine muscle blood flow. The study was approved by the animal welfare committee of Tufts University. Materials and Methods
Six horses, 2 to 22 years old (mean, 12 years) and weighing 353 to 484 kg (mean, 410 kg) were determined to be healthy by physical examination and serum biochemical evaluations. Less than 1 hour before induction of anesthesia, muscle surface capillary blood flow was determined by laser Doppler flowmetry in the right and left biceps femoris and the right and left lateral head of the triceps brachii muscles. After intradermal infiltration with 2% lidocaine, a 1 cm skin incision was made to expose the muscle surface. The probe of the laser Doppler unit,* which had been calibrated with a standard motility solution, was applied to the muscle surface. The output of the laser Doppler unit was transferred to a personal computer, digitized, displayed graphically, and stored for future analysis. Food was withheld for 12 hours before anesthesia. After premedication with xylazine (0.5 mg/kg intravenously [IV]), general anesthesia was induced with guaifenesin (50
* Medex Periflux PF3, Medex Inc., Hilliard, Ohio
From the Department of Surgery (Norman, Court, Dodman) and Medicine(Pipers),Tufts School of Veterinary Medicine, Grafton, Massachusetts. Presented as an abstract at the 1988 Veterinary Midwest Anesthesia Conference, Urbana, Illinois, June 1988, No reprints available.
491
492
MUSCLE CAPILLARY BLOOD FLOW TABLE 1. Muscle Surface Capil/ary Blood Flow * in Six Anesthetized Horses
Minutes after Induction
Mean Arterial Pressure (mm Hg)
Mean End-Tidal Halothane Conc. %
Nondependent Triceps Brachii
Dependent Triceps Brachii
Nondependent Biceps Femoris
Dependent Biceps Femoris
30 45 60 75 90
64 k 06 70 f 14 68 f 12 69 k 07 73f 1 1
0.84f 0.17 1.09f 0.06 1.06f 0.22 1.12f 0.13 1.11 -+ 0.14
37 f 14 33 .+ 107 38 f 15t 24f 16 26 f 20
22 f 07 13 k 04 17 f 07 14 f 06 15 f 08
28 k 06 30 f 10 35 f 19 29 & 1 1 28 f 09
23 -+ 10 25 -t 16 20 t 08 17 -+ 03 20 f 12
* Blood flow values are expressed as a percentage of preanesthetic values.
t Significantly higher than blood flow in the dependent triceps brachii muscles at the same time intervals All values are mean f SD.
to 70 mg/kg, IV) and thiamylal (4 to 5 mg/kg, IV). The trachea was intubated, and anesthesia was maintained with halothane in oxygen ( 5 to 10 L/min) and a large animal circle anesthesia system. The depth of anesthesia was adjusted to maintain a light surgical plane at which the mean arterial pressure was above 60 mm Hg. Intermittent positive pressure ventilation was administered after induction to maintain eucapnia (PaC02 35 to 45 mm Hg). Each horse was positioned in right lateral recumbency on an unpadded table. The dependent thoracic limb was pulled forward, and the nondependent thoracic and pelvic limbs were elevated so that all limbs were parallel to the ground. A 20-gauge catheter was inserted into the facial artery for direct arterial pressure measurement and collection of blood samples for blood gas analysis. The electrocardiogram was monitored continuously. Lactated Ringer’s solution was infused intravenously (3 to 5 mL/ kg per hour). No other drugs were administered. Vaporizer setting, oxygen flow rate, end-tidal halothane concentration, heart rate, mean arterial pressure, and respiratory rate were recorded every 5 minutes. Samples were collected for arterial blood gas analysis every 30 minutes. Muscle surface capillary blood flow was measured at each site every 15 minutes during anesthesia, starting 30 minutes after induction (except horse 1, in which measurements were made every 30 minutes). Access to dependent (right) muscles was gained through holes in the surgery table. Anesthesia was maintained for 90 minutes, after which the horses were allowed to recover in a padded recovery box. Stored laser Doppler output data for each muscle at each time interval were averaged over a 1-minute collection period to yield muscle surface capillary blood flow expressed in arbitrary perfusion units. The data collected during the anesthetic period were expressed as a percentage of values collected before anesthesia was induced. Statistical analysis included two-way analysis of variance with repeated measures of Fisher’s PLSD. Significance was accepted at p < .05.
Results Thirty minutes after induction of anesthesia, mean muscle surface capillary blood flow decreased to 37 f 14% and 22 k 07% of preanesthetic values in the nondependent and dependent triceps brachii muscles, respectively (Table 1). The reductions in flow persisted for the duration of anesthesia without significant change. Although the reduction in flow was consistently greater in the dependent than the nondependent muscles, the flow reduction differences were statistically significant only at the 45- and 60-minute intervals. Thirty minutes after induction of anesthesia, mean muscle surface capillary blood flow decreased to 28 k 06% and 23 -+ 10%ofpreanesthetic values in the nondependent and dependent biceps femoris muscles, respectively (Table 1). This reduction in flow persisted for the duration of anesthesia without significant change. The reduction in muscle surface capillary blood flow was consistently greater in the dependent muscles than in the nondependent muscles, but the differences were not statistically significant at any time interval.
Discussion In horses, halothane-induced anesthesia and recumbency have been associated with physiologic changes that could result in skeletal muscle ischemia and hypoxic myocyte damage.2%3.7.7*9-’ Quantification of the effects of general anesthesia and recumbency on equine muscle blood flow has been technically difficult and is sparsely documented. Results of this study demonstrate the occurrence of a substantial and persistent decrease in muscle surface capillary blood flow during halothane anesthesia. Although this suggests that oxygen delivery to myocytes is decreased during anesthesia, it does not necessarily indicate that myocytes subsequently suffer hypoxic damage because the myocytic metabolic rate may decrease in proportion to oxygen delivery. Measurement of the aerobic
’
493
NORMAN, COURT, DODMAN, AND PIPERS and anaerobic metabolic products are needed to evaluate the cellular metabolic status. The magnitude of reduction in muscle blood flow was similar to that reported in a radioactive isotope study of ponies anesthetized with isoflurane: in which isoflurane anesthesia and recumbency decreased muscle blood flow to approximately 36% and 32% of control values in the nondependent and dependent triceps muscles, respectively. Blood flow in the nondependent and dependent biceps femoris muscles decreased to approximately 19% and 2 1 % of conscious values. By radioactive xenon clearance, muscle blood flow was estimated to be 3 1% of awake values in horses anesthetized with h a l ~ t h a n e . ~ The pattern of muscle blood flow with increasing anesthetic duration was also similar to that found with radioactive isotope techniques. In general, increasing duration of anesthesia was not associated with fluctuations in muscle blood flow. This differs from results of the previous laser Doppler flowmetry study in halothane-anesthetized horses, in which microflow in the nondependent triceps brachii muscle significantly increased with time.’ The difference may have been caused by differences in arterial pressure. N o attempt was made to influence arterial pressure in either study. In general, there was no statistically significant difference in muscle surface capillary blood flow between dependent and nondependent muscle groups during anesthesia. This agrees with some findings6.’ but differs from others.’ Discrepancies in results may be attributed to differences in arterial pressure during anesthesia, table padding, body weight of subjects, or properties of anesthetic drugs used. Intradermal infiltration with lidocaine to perform skin incisions in standing horses was necessary for humane reasons, but the lidocaine may have affected results by causing vasodilation. If the lidocaine caused sig-
nificant vasodilation in adjacent tissues (muscle), our preanesthetic perfusion values and the changes during anesthesia would be overestimated. However, the muscle sheath probably isolated lidocaine from the underlying muscle tissue, and the similarity of our results and those of radioactive isotope studies causes us to believe that the effects of lidocaine were minimal.
References 1. White NA. Postanesthetic recumbency myopathy in horses. Com-
pend Cont Educ Pract Vet 1982;4:S44-S50. 2. Grandy JL, Steffey EP, Hodgson DS, Woliner MJ. Arterial hypotension and the development of postanesthetic myopathy in halothane-anesthetized horses. Am J Vet Res 1987;48:192-197. 3. Lindsay WA, McDonell W, Bingnell W. Equine postanesthetic forelimb lameness: Intracompartmental muscle pressure changes and biochemical patterns. Am J Vet Res 1980;41:1919-1924. 4. Waldron-Mease E. Correlation of post-operative and exercise-induced equine myopathy with the defect malignant hyperthermia. Proc Am Assoc Eq Pract 1978;24:95-99. 5. Lindsay WA, Robinson GM, Brunson DB, Majors W.Induction of equine postanesthetic myositis after halothane-induced hypotension. Am J Vet Res 1989;50:404-410. 6. Manohar M, Gustafson R, Nganwa D. Skeletal muscle perfusion during prolonged 2.03% end-tidal isoflurane-02 anesthesia in isocapnic ponies. Am J Vet Res 1987;48:946-95 1. 7. Weaver B, Lunn CEM, Staddon G. Muscle perfusion in the horse. Eq Vet J 1984; 16:66-68. 8. Smits GJ, Roman RJ. Lombard JH. Evaluation of laser-Doppler flowmetry asa measure oftissue blood flow. J Appl Physiol I986;2: 666-672. 9. Serteyn D, Mottart E, Michaux C, et al. Laser Doppler flowmetry: Muscular microcirculation in anesthetized horses. Eq Vet J 1986; 18:391-395. 10. Serteyn D, Coppens P, Mottart E, et al. Measurements of muscular microcirculation by laser Doppler flowmetry in isoflurane and halothane anesthetized horses. Vet Rec 1987: I2 1:324-326. 1 I . Trim C , Mason J. Post-anesthetic forelimb lameness in horses. Eq Vet J 1973;5:71-76.
Measurement of Muscle Surface Capillary Blood Flow by Laser Doppler Flowmetry WENDY M. NORMAN, WSC, MICHAEL H. COURT, BvSc. Diplomate AWA, NICHOLAS H. DODMAN, BVMS, Diplomate ACVA, and FRANK s. PIPERS, DVM, PhD, Diplomate ACVfM Muscle surface capillary blood flow was measured in the biceps femoris and lateral head of the triceps brachii muscles in six horses before and during halothane anesthesia by using laser Doppler flowmetry. During 90 minutes of anesthesia, muscle surface capillary blood flow was reduced to 20% to 40% of preanesthetic values. Muscle surface capillary blood flow tended to be lower in dependent muscles than in nondependent muscles, and this disparity was greater in the forelimbs than in the hind limbs.
a well-recognized and P potentially disastrous complication of equine anesthesia.' Much effort has been devoted to identifying causOSTANESTHETIC MYOPATHY IS
ative factors and their relative ~ignificance.~-~ The roles of arterial hypotension and increased intracompartmental muscle pressure have received attention.'^^ It has been suggested, but not proven, that reduced muscle blood flow associated with anesthesia and recumbency results in ischemic muscle injury. Radioactive isotopes have been used to measure muscle blood flow in standing and anesthetized The methods require specialized equipment, permit only a limited number of measurements per experiment, and are expensive to perform. Laser Doppler flowmetry allows relatively noninvasive, continuous measurement of tissue perfusion. It cannot determine absolute values for tissue blood flow, but it does indicate changes in the perfusion of a particular tissue. Excellent correlation was shown between laser Doppler flowmetry and standard techniques for measurement of blood flow in skeletal muscle.8 Differences in muscle blood flow between dependent and nondependent muscles in horses during recumbency and general anesthesia measured with laser Doppler flowmetry have been reported, but no control (preanesthetic) values were given.' In the current study, laser Doppler flowmetry was used to measure muscle surface capillary blood flow in standing and laterally recumbent, halothane-anesthetized
horses to determine the effect of recumbency and general anesthesia on equine muscle blood flow. The study was approved by the animal welfare committee of Tufts University. Materials and Methods
Six horses, 2 to 22 years old (mean, 12 years) and weighing 353 to 484 kg (mean, 410 kg) were determined to be healthy by physical examination and serum biochemical evaluations. Less than 1 hour before induction of anesthesia, muscle surface capillary blood flow was determined by laser Doppler flowmetry in the right and left biceps femoris and the right and left lateral head of the triceps brachii muscles. After intradermal infiltration with 2% lidocaine, a 1 cm skin incision was made to expose the muscle surface. The probe of the laser Doppler unit,* which had been calibrated with a standard motility solution, was applied to the muscle surface. The output of the laser Doppler unit was transferred to a personal computer, digitized, displayed graphically, and stored for future analysis. Food was withheld for 12 hours before anesthesia. After premedication with xylazine (0.5 mg/kg intravenously [IV]), general anesthesia was induced with guaifenesin (50
* Medex Periflux PF3, Medex Inc., Hilliard, Ohio
From the Department of Surgery (Norman, Court, Dodman) and Medicine(Pipers),Tufts School of Veterinary Medicine, Grafton, Massachusetts. Presented as an abstract at the 1988 Veterinary Midwest Anesthesia Conference, Urbana, Illinois, June 1988, No reprints available.
491
492
MUSCLE CAPILLARY BLOOD FLOW TABLE 1. Muscle Surface Capil/ary Blood Flow * in Six Anesthetized Horses
Minutes after Induction
Mean Arterial Pressure (mm Hg)
Mean End-Tidal Halothane Conc. %
Nondependent Triceps Brachii
Dependent Triceps Brachii
Nondependent Biceps Femoris
Dependent Biceps Femoris
30 45 60 75 90
64 k 06 70 f 14 68 f 12 69 k 07 73f 1 1
0.84f 0.17 1.09f 0.06 1.06f 0.22 1.12f 0.13 1.11 -+ 0.14
37 f 14 33 .+ 107 38 f 15t 24f 16 26 f 20
22 f 07 13 k 04 17 f 07 14 f 06 15 f 08
28 k 06 30 f 10 35 f 19 29 & 1 1 28 f 09
23 -+ 10 25 -t 16 20 t 08 17 -+ 03 20 f 12
* Blood flow values are expressed as a percentage of preanesthetic values.
t Significantly higher than blood flow in the dependent triceps brachii muscles at the same time intervals All values are mean f SD.
to 70 mg/kg, IV) and thiamylal (4 to 5 mg/kg, IV). The trachea was intubated, and anesthesia was maintained with halothane in oxygen ( 5 to 10 L/min) and a large animal circle anesthesia system. The depth of anesthesia was adjusted to maintain a light surgical plane at which the mean arterial pressure was above 60 mm Hg. Intermittent positive pressure ventilation was administered after induction to maintain eucapnia (PaC02 35 to 45 mm Hg). Each horse was positioned in right lateral recumbency on an unpadded table. The dependent thoracic limb was pulled forward, and the nondependent thoracic and pelvic limbs were elevated so that all limbs were parallel to the ground. A 20-gauge catheter was inserted into the facial artery for direct arterial pressure measurement and collection of blood samples for blood gas analysis. The electrocardiogram was monitored continuously. Lactated Ringer’s solution was infused intravenously (3 to 5 mL/ kg per hour). No other drugs were administered. Vaporizer setting, oxygen flow rate, end-tidal halothane concentration, heart rate, mean arterial pressure, and respiratory rate were recorded every 5 minutes. Samples were collected for arterial blood gas analysis every 30 minutes. Muscle surface capillary blood flow was measured at each site every 15 minutes during anesthesia, starting 30 minutes after induction (except horse 1, in which measurements were made every 30 minutes). Access to dependent (right) muscles was gained through holes in the surgery table. Anesthesia was maintained for 90 minutes, after which the horses were allowed to recover in a padded recovery box. Stored laser Doppler output data for each muscle at each time interval were averaged over a 1-minute collection period to yield muscle surface capillary blood flow expressed in arbitrary perfusion units. The data collected during the anesthetic period were expressed as a percentage of values collected before anesthesia was induced. Statistical analysis included two-way analysis of variance with repeated measures of Fisher’s PLSD. Significance was accepted at p < .05.
Results Thirty minutes after induction of anesthesia, mean muscle surface capillary blood flow decreased to 37 f 14% and 22 k 07% of preanesthetic values in the nondependent and dependent triceps brachii muscles, respectively (Table 1). The reductions in flow persisted for the duration of anesthesia without significant change. Although the reduction in flow was consistently greater in the dependent than the nondependent muscles, the flow reduction differences were statistically significant only at the 45- and 60-minute intervals. Thirty minutes after induction of anesthesia, mean muscle surface capillary blood flow decreased to 28 k 06% and 23 -+ 10%ofpreanesthetic values in the nondependent and dependent biceps femoris muscles, respectively (Table 1). This reduction in flow persisted for the duration of anesthesia without significant change. The reduction in muscle surface capillary blood flow was consistently greater in the dependent muscles than in the nondependent muscles, but the differences were not statistically significant at any time interval.
Discussion In horses, halothane-induced anesthesia and recumbency have been associated with physiologic changes that could result in skeletal muscle ischemia and hypoxic myocyte damage.2%3.7.7*9-’ Quantification of the effects of general anesthesia and recumbency on equine muscle blood flow has been technically difficult and is sparsely documented. Results of this study demonstrate the occurrence of a substantial and persistent decrease in muscle surface capillary blood flow during halothane anesthesia. Although this suggests that oxygen delivery to myocytes is decreased during anesthesia, it does not necessarily indicate that myocytes subsequently suffer hypoxic damage because the myocytic metabolic rate may decrease in proportion to oxygen delivery. Measurement of the aerobic
’
493
NORMAN, COURT, DODMAN, AND PIPERS and anaerobic metabolic products are needed to evaluate the cellular metabolic status. The magnitude of reduction in muscle blood flow was similar to that reported in a radioactive isotope study of ponies anesthetized with isoflurane: in which isoflurane anesthesia and recumbency decreased muscle blood flow to approximately 36% and 32% of control values in the nondependent and dependent triceps muscles, respectively. Blood flow in the nondependent and dependent biceps femoris muscles decreased to approximately 19% and 2 1 % of conscious values. By radioactive xenon clearance, muscle blood flow was estimated to be 3 1% of awake values in horses anesthetized with h a l ~ t h a n e . ~ The pattern of muscle blood flow with increasing anesthetic duration was also similar to that found with radioactive isotope techniques. In general, increasing duration of anesthesia was not associated with fluctuations in muscle blood flow. This differs from results of the previous laser Doppler flowmetry study in halothane-anesthetized horses, in which microflow in the nondependent triceps brachii muscle significantly increased with time.’ The difference may have been caused by differences in arterial pressure. N o attempt was made to influence arterial pressure in either study. In general, there was no statistically significant difference in muscle surface capillary blood flow between dependent and nondependent muscle groups during anesthesia. This agrees with some findings6.’ but differs from others.’ Discrepancies in results may be attributed to differences in arterial pressure during anesthesia, table padding, body weight of subjects, or properties of anesthetic drugs used. Intradermal infiltration with lidocaine to perform skin incisions in standing horses was necessary for humane reasons, but the lidocaine may have affected results by causing vasodilation. If the lidocaine caused sig-
nificant vasodilation in adjacent tissues (muscle), our preanesthetic perfusion values and the changes during anesthesia would be overestimated. However, the muscle sheath probably isolated lidocaine from the underlying muscle tissue, and the similarity of our results and those of radioactive isotope studies causes us to believe that the effects of lidocaine were minimal.
References 1. White NA. Postanesthetic recumbency myopathy in horses. Com-
pend Cont Educ Pract Vet 1982;4:S44-S50. 2. Grandy JL, Steffey EP, Hodgson DS, Woliner MJ. Arterial hypotension and the development of postanesthetic myopathy in halothane-anesthetized horses. Am J Vet Res 1987;48:192-197. 3. Lindsay WA, McDonell W, Bingnell W. Equine postanesthetic forelimb lameness: Intracompartmental muscle pressure changes and biochemical patterns. Am J Vet Res 1980;41:1919-1924. 4. Waldron-Mease E. Correlation of post-operative and exercise-induced equine myopathy with the defect malignant hyperthermia. Proc Am Assoc Eq Pract 1978;24:95-99. 5. Lindsay WA, Robinson GM, Brunson DB, Majors W.Induction of equine postanesthetic myositis after halothane-induced hypotension. Am J Vet Res 1989;50:404-410. 6. Manohar M, Gustafson R, Nganwa D. Skeletal muscle perfusion during prolonged 2.03% end-tidal isoflurane-02 anesthesia in isocapnic ponies. Am J Vet Res 1987;48:946-95 1. 7. Weaver B, Lunn CEM, Staddon G. Muscle perfusion in the horse. Eq Vet J 1984; 16:66-68. 8. Smits GJ, Roman RJ. Lombard JH. Evaluation of laser-Doppler flowmetry asa measure oftissue blood flow. J Appl Physiol I986;2: 666-672. 9. Serteyn D, Mottart E, Michaux C, et al. Laser Doppler flowmetry: Muscular microcirculation in anesthetized horses. Eq Vet J 1986; 18:391-395. 10. Serteyn D, Coppens P, Mottart E, et al. Measurements of muscular microcirculation by laser Doppler flowmetry in isoflurane and halothane anesthetized horses. Vet Rec 1987: I2 1:324-326. 1 I . Trim C , Mason J. Post-anesthetic forelimb lameness in horses. Eq Vet J 1973;5:71-76.
