The acute effects of tourniquet ischemia on tissue and blood gas tensions in the primate limb Tourniquet ischemia results in tissue hypoxia which has been measured indirectly by blood gas analysis. The Medspect mass spectrometer allows direct measurement of gas tension in different tissues and may provide more useful information regarding safe tourniquet times. Calibrated Teflon catheters were inserted into the subcutaneous tissue (11 animals), tibial medullary cavities (bone) (nine animals), and tibialis anterior muscles (10 animals) in both lower extremities of anesthetized stumptail monkeys. Tourniquet ischemia was maintainedfor 1 hour at400 mm Hg. Tissue and venous blood gas tensions were recordedfrom both limbs for 1J /2 hours. Comparisons between gas tensions in each tissue group were made on the basis of their percentage change from control values . In the ischemic limb within 5 minutes muscle Podell 42 ± 4% (p < 0.001), whereas bone and subcutaneous P02 dropped 25 ± 4% (p < 0.05). Blood Podell 29 ± 3% and differed only from that of muscle (p < 0.01). One hour after tourniquet inflation, blood P02 levels hasfallen 90 ± 5% (p < 0.001 ) from their control. Changes in tissue Pco 2 were less dramatic and did not vary significantly from those recorded in venous blood. After deflation, blood P02 exceeded its control by 20 ± 6% (p < 0.005) in 5 minutes, but tissue tensions remained 50 ± 6% below their control values. These studies indicate that tissue gas tensions are a more sensitive indicator of tourniquet hypoxia than are blood gases within the ischemic extremity.
Stephen H. Miller, M.D., Richard J. Lung, M.D., William P. Graham, III, M.D., Thomas S. Davis, M.D., and Irena Rusenas, B.S., Hershey, Pa.
T
he pneumatic tourniquet has been accepted as a necessary adjunct for the performance of precise hand surgery despite the potential hazards associated with its use. Damage to local tissue by compression 1 ' 3 and to distant tissue because of ischemia and hypoxia3-6 have been reported. Many factors have been implicated in the development of post-tourniquet complications, but the duration of ischemia is probably the most important. 4 , 6·S Maintenance of ischemia to the upper limb of a healthy adult for less than 2 hours generally is considered to be "safe. "9, 10 If it is necessary to exceed this time limit, deflation of the tourniquet for 10 to 15 minutes after each hour of ischemia has been recommended. 3 , 9 Experimental evidence to document the veracity of these clinical aphorisms is sparse. Measurements of physiologic and metabolic alterSupported in part by the Irvin Zubar Memorial Cancer Fund. From the Department of Surgery, The Division of Plastic and Reconstructive Surgery, The Milton S. Hershey Medical Center of The Pennsylvania State University, Hershey, Pa. Received for publication Dec. 13, 1976. Reprint requests: Stephen H. Miller, M.D., Division of Plastic and Reconstructive Surgery, The Milton S. Hershey Medical Center of The Pennsylvania State University, 500 University Dr., Hershey, Pa. 17033.
Vol. 3, No. I, pp. 11-20
ations in human venous blood have been performed during and after use of a pneumatic tourniquet to establish guidelines for safe ischemia time. 6 -s These studies were based on the premise that metabolic alterations in venous blood accurately reflect changes which occur in capillary blood. This study tests this hypothesis by comparing tissue gas tensions to simultaneously measured blood gas tensions from within a primate limb kept ischemic for 1 hour by an inflated pneumatic tourniquet. P0 2 and Pco 2 in subcutaneous tissue, anterior tibial muscle, and tibial medullary canal were measured in vivo by mass spectrometry to determine if the degree of hypoxia produced by tourniquet ischemia varied with the type of tissue being measured. The Medspect is a mobile mass spectrometer capable of direct continuous measurements of respiratory, blood, or tissue gas tensions in vivo. l l In the tissue mode, gas is sampled through a Teflon diffusion membrane, % to 1 inch in length, and at a slow rate, 5 X 10-6 ml/second, to avoid depletion of tissue gases. The diffusion membrane is incorporated into a Tefloncovered, stainless steel cannula which transmits gases to the mass spectrometer aided by a vacuum system within the console of the instrument. Gases are analyzed quantitatively according to their January, 1978
THE JOURNAL OF HAND SURGERY 11
The Journal of 12
Miller et al.
molecular weights and actual partial pressures are displayed digitally on the face of the console. The values obtained represent the average tissue gas tension along the length of the diffusion membrane. The area or volume of tissue sampled by this technique is unknown. The response time of this system is slower than that of polarographic electrodes but faster than tissue tonometers.12 After an initial delay of 0.6 minutes for oxygen and 0.9 minutes for carbon dioxide, the machine responds to changes in tissue gas levels exponentially. Response time for the system to reflect a 99% changes in tissue gas tensions is 5 minutes for oxygen and 10 minutes for carbon dioxide .13 Materials and methods
Teflon diffusion membranes are flow dependent, and calibration adjustments are necessary to obtain accurate measurements of tissue gases in static interstitial fluid. All catheters were calibrated on the day of insertion and following removal from the tissue, with a known dry gas mixture, 5% CO2 and 95% air, heated to 37° C. Oxygen readings were set 22% higher and carbon dioxide 1% higher than their true values in the known gas in order to calibrate them for accurate interstitial tissue readings .12 Calibration drifts were less than 3 % per day in our laboratory. Adult female stumptail monkeys (M. arctoides) were anesthetized with intravenous sodium pentobarbital and endotracheal tubes were inserted. Maintenance doses of pentobarbital were administered approximately every IV2 hours. Rectal temperatures were monitored with a Gaymer Accra-Temp electric thermometer fitted with a YSI probe and subcutaneous limb temperatures monitored in both lower limbs with a YSI thermistor probe and a single channel Thermistep during each experiment. Twenty-one gauge butterfly needles were inserted into peripheral veins in each lower extremity. Calibrated Teflon catheters were inserted into the subcutaneous tissue of the midcalf (11 animals), beneath the fascia of the anterior tibial muscle (10 animals) , and into the superior half of the medullary cavity of the tibia (10 animals) in both lower extremities. Subcutaneous catheters were inserted through 1 mm incisions and the catheters were advanced into the tissue with the blunt end used as an obturator. Muscle catheters were placed through 1 cm skin and 1 mm fascial incisions in a similar fashion. A Hall Air Drill was used to perforate the cortex of the midshaft of the tibia through 1 cm skin incision. Catheters were advanced into the cavity in a superior direction for 3 to 4 cm. All skin wounds were sutured with No. 4-0 silk and each
HAND SURGERY
catheter secured to the skin with No. 4-0 silk pursestring sutures. Tissue gas tension recording was begun after P02 and Pco2 levels remained stable for at least 25 minutes. Known concentrations of oxygen were administered in each case to verify that the catheters were functioning, and pre tourniquet baseline gas tensions were rerorded after the animals breathed room air for 30 minutes. Three layers of 3 inch wide cotton bandage were wrapped circumferentially around the midthigh of one lower extremity and a Kidde pediatric tourniquet cuff was applied over the bandage. The pneumatic tourniquet gauge was adjusted three times weekly by calibration against a manometer. Baseline P02 and Pco 2 were recorded from like tissues in each limb and 0.9 cc of blood was withdrawn from each butterfly needle for blood gas and pH analysis. The latter was performed with an International Laboratory 313 pH Blood Gas Analyzer. The experimental limb then was exsanguinated with an elastic bandage and the tourniquet inflated to 400 mm Hg pressure for 1 hour. Tissue gas tensions were recorded at 5, 10, 15, 30, 45, and 60 minutes during ischemia and 5, 15, and 30 minutes after the tourniquet was deflated. Blood was sampled for pH and gas analysis at 5 and 60 minutes during ischemia and 5 minutes after tourniquet deflation. Statistical significance was determined by Student's t test. Results
Baseline P02 and Pco2 levels varied from day to day and in each type of tissue. The values are reported with their standard deviations to indicate the range of observed measurements. Mean PTo2 * in the anterior tibial muscle (N = 20) was 33 ± 12 mm Hg 49 ± 13 mm Hg in subcutaneous tissue (N = 29), and 56 ± 11 mm Hg in the medullary cavity of the tibia (N = 18). Mean PTco2 was 52 ± 6 mm Hg in muscle, 41 ± 7 mm Hg in subcutaneous tissue, and 54 ± 10 mm Hg in the medullary canal. Thirty minutes after breathing 100% oxygen, PTo2 and PTC02 returned to baseline levels in all tissues except muscle. PMo. in the latter remained elevated, 42.3 ± 13 mm Hg (SD) and continued at this level in the control limb for the duration of the experiment. PMco' *Pr0, = partial pressure, of oxygen in tissue; Pr co, = partial pressure of carbon dioxide in tissue; £>M o" PMco, = gas tensions in anterior tibial muscle; PsQo" PsQco, = gas tensions in subcutaneous tissue; PBo., PBco, = gas tensions in medullary cavity of tibia; Pv o" PVco, = gas tensions in venous blood.
Vol. 3 No.1
January, 1978
Acute effects of tourniquet ischemia
13
Table I. Anterior tibial muscle P02 and Pco2 during one hour of tourniquet ischemia Oxygen partial pressure Tourniquet (min)
Ischemic mean ± SEM (n = /0)
On: 0 5 10 15 30 60
41 ± 24 ± 14 ± 10 ± 5 ± 4 ±
Off: 5 15 30
20 ± 3 31 ± 5 38 ± 6
4 3 2 I I .5
Control mean ± SEM (n = /0)
43 44 44 42 43 38
± ± ± ± ± ±
4 5 5 5 5 5
38 ± 5 43 ± 4 44 ± 3
Carbon dioxide partial pressure
p
Stephen H. Miller, M.D., Richard J. Lung, M.D., William P. Graham, III, M.D., Thomas S. Davis, M.D., and Irena Rusenas, B.S., Hershey, Pa.
T
he pneumatic tourniquet has been accepted as a necessary adjunct for the performance of precise hand surgery despite the potential hazards associated with its use. Damage to local tissue by compression 1 ' 3 and to distant tissue because of ischemia and hypoxia3-6 have been reported. Many factors have been implicated in the development of post-tourniquet complications, but the duration of ischemia is probably the most important. 4 , 6·S Maintenance of ischemia to the upper limb of a healthy adult for less than 2 hours generally is considered to be "safe. "9, 10 If it is necessary to exceed this time limit, deflation of the tourniquet for 10 to 15 minutes after each hour of ischemia has been recommended. 3 , 9 Experimental evidence to document the veracity of these clinical aphorisms is sparse. Measurements of physiologic and metabolic alterSupported in part by the Irvin Zubar Memorial Cancer Fund. From the Department of Surgery, The Division of Plastic and Reconstructive Surgery, The Milton S. Hershey Medical Center of The Pennsylvania State University, Hershey, Pa. Received for publication Dec. 13, 1976. Reprint requests: Stephen H. Miller, M.D., Division of Plastic and Reconstructive Surgery, The Milton S. Hershey Medical Center of The Pennsylvania State University, 500 University Dr., Hershey, Pa. 17033.
Vol. 3, No. I, pp. 11-20
ations in human venous blood have been performed during and after use of a pneumatic tourniquet to establish guidelines for safe ischemia time. 6 -s These studies were based on the premise that metabolic alterations in venous blood accurately reflect changes which occur in capillary blood. This study tests this hypothesis by comparing tissue gas tensions to simultaneously measured blood gas tensions from within a primate limb kept ischemic for 1 hour by an inflated pneumatic tourniquet. P0 2 and Pco 2 in subcutaneous tissue, anterior tibial muscle, and tibial medullary canal were measured in vivo by mass spectrometry to determine if the degree of hypoxia produced by tourniquet ischemia varied with the type of tissue being measured. The Medspect is a mobile mass spectrometer capable of direct continuous measurements of respiratory, blood, or tissue gas tensions in vivo. l l In the tissue mode, gas is sampled through a Teflon diffusion membrane, % to 1 inch in length, and at a slow rate, 5 X 10-6 ml/second, to avoid depletion of tissue gases. The diffusion membrane is incorporated into a Tefloncovered, stainless steel cannula which transmits gases to the mass spectrometer aided by a vacuum system within the console of the instrument. Gases are analyzed quantitatively according to their January, 1978
THE JOURNAL OF HAND SURGERY 11
The Journal of 12
Miller et al.
molecular weights and actual partial pressures are displayed digitally on the face of the console. The values obtained represent the average tissue gas tension along the length of the diffusion membrane. The area or volume of tissue sampled by this technique is unknown. The response time of this system is slower than that of polarographic electrodes but faster than tissue tonometers.12 After an initial delay of 0.6 minutes for oxygen and 0.9 minutes for carbon dioxide, the machine responds to changes in tissue gas levels exponentially. Response time for the system to reflect a 99% changes in tissue gas tensions is 5 minutes for oxygen and 10 minutes for carbon dioxide .13 Materials and methods
Teflon diffusion membranes are flow dependent, and calibration adjustments are necessary to obtain accurate measurements of tissue gases in static interstitial fluid. All catheters were calibrated on the day of insertion and following removal from the tissue, with a known dry gas mixture, 5% CO2 and 95% air, heated to 37° C. Oxygen readings were set 22% higher and carbon dioxide 1% higher than their true values in the known gas in order to calibrate them for accurate interstitial tissue readings .12 Calibration drifts were less than 3 % per day in our laboratory. Adult female stumptail monkeys (M. arctoides) were anesthetized with intravenous sodium pentobarbital and endotracheal tubes were inserted. Maintenance doses of pentobarbital were administered approximately every IV2 hours. Rectal temperatures were monitored with a Gaymer Accra-Temp electric thermometer fitted with a YSI probe and subcutaneous limb temperatures monitored in both lower limbs with a YSI thermistor probe and a single channel Thermistep during each experiment. Twenty-one gauge butterfly needles were inserted into peripheral veins in each lower extremity. Calibrated Teflon catheters were inserted into the subcutaneous tissue of the midcalf (11 animals), beneath the fascia of the anterior tibial muscle (10 animals) , and into the superior half of the medullary cavity of the tibia (10 animals) in both lower extremities. Subcutaneous catheters were inserted through 1 mm incisions and the catheters were advanced into the tissue with the blunt end used as an obturator. Muscle catheters were placed through 1 cm skin and 1 mm fascial incisions in a similar fashion. A Hall Air Drill was used to perforate the cortex of the midshaft of the tibia through 1 cm skin incision. Catheters were advanced into the cavity in a superior direction for 3 to 4 cm. All skin wounds were sutured with No. 4-0 silk and each
HAND SURGERY
catheter secured to the skin with No. 4-0 silk pursestring sutures. Tissue gas tension recording was begun after P02 and Pco2 levels remained stable for at least 25 minutes. Known concentrations of oxygen were administered in each case to verify that the catheters were functioning, and pre tourniquet baseline gas tensions were rerorded after the animals breathed room air for 30 minutes. Three layers of 3 inch wide cotton bandage were wrapped circumferentially around the midthigh of one lower extremity and a Kidde pediatric tourniquet cuff was applied over the bandage. The pneumatic tourniquet gauge was adjusted three times weekly by calibration against a manometer. Baseline P02 and Pco 2 were recorded from like tissues in each limb and 0.9 cc of blood was withdrawn from each butterfly needle for blood gas and pH analysis. The latter was performed with an International Laboratory 313 pH Blood Gas Analyzer. The experimental limb then was exsanguinated with an elastic bandage and the tourniquet inflated to 400 mm Hg pressure for 1 hour. Tissue gas tensions were recorded at 5, 10, 15, 30, 45, and 60 minutes during ischemia and 5, 15, and 30 minutes after the tourniquet was deflated. Blood was sampled for pH and gas analysis at 5 and 60 minutes during ischemia and 5 minutes after tourniquet deflation. Statistical significance was determined by Student's t test. Results
Baseline P02 and Pco2 levels varied from day to day and in each type of tissue. The values are reported with their standard deviations to indicate the range of observed measurements. Mean PTo2 * in the anterior tibial muscle (N = 20) was 33 ± 12 mm Hg 49 ± 13 mm Hg in subcutaneous tissue (N = 29), and 56 ± 11 mm Hg in the medullary cavity of the tibia (N = 18). Mean PTco2 was 52 ± 6 mm Hg in muscle, 41 ± 7 mm Hg in subcutaneous tissue, and 54 ± 10 mm Hg in the medullary canal. Thirty minutes after breathing 100% oxygen, PTo2 and PTC02 returned to baseline levels in all tissues except muscle. PMo. in the latter remained elevated, 42.3 ± 13 mm Hg (SD) and continued at this level in the control limb for the duration of the experiment. PMco' *Pr0, = partial pressure, of oxygen in tissue; Pr co, = partial pressure of carbon dioxide in tissue; £>M o" PMco, = gas tensions in anterior tibial muscle; PsQo" PsQco, = gas tensions in subcutaneous tissue; PBo., PBco, = gas tensions in medullary cavity of tibia; Pv o" PVco, = gas tensions in venous blood.
Vol. 3 No.1
January, 1978
Acute effects of tourniquet ischemia
13
Table I. Anterior tibial muscle P02 and Pco2 during one hour of tourniquet ischemia Oxygen partial pressure Tourniquet (min)
Ischemic mean ± SEM (n = /0)
On: 0 5 10 15 30 60
41 ± 24 ± 14 ± 10 ± 5 ± 4 ±
Off: 5 15 30
20 ± 3 31 ± 5 38 ± 6
4 3 2 I I .5
Control mean ± SEM (n = /0)
43 44 44 42 43 38
± ± ± ± ± ±
4 5 5 5 5 5
38 ± 5 43 ± 4 44 ± 3
Carbon dioxide partial pressure
p
