Creatine phosphokinase release as a measure of tourniquet effect on skeletal muscle

Systemic glucose-insulin-potassium reduces skeletal muscle injury, kidney injury, and pain in a murine ischaemia-reperfusion model

Glucose-insulin-potassium (GIK) is protective following cardiac myocyte ischaemia-reperfusion (IR) injury, however the role of GIK in protecting skeletal muscle from IR injury has not been evaluated. Given the similar mechanisms by which cardiac and skeletal muscle sustain an IR injury, we hypothesized that GIK would similarly protect skeletal muscle viability. A total of 20 C57BL/6 male mice (10 control, 10 GIK) sustained a hindlimb IR injury using a 2.5-hour rubber band tourniquet. Immediately prior to tourniquet placement, a subcutaneous osmotic pump was placed which infused control mice with saline (0.9% sodium chloride) and treated mice with GIK (40% glucose, 50 U/l insulin, 80 mEq/L KCl, pH 4.5) at a rate of 16 µl/hr for 26.5 hours. At 24 hours following tourniquet removal, bilateral (tourniqueted and non-tourniqueted) gastrocnemius muscles were triphenyltetrazolium chloride (TTC)-stained to quantify percentage muscle viability. Bilateral peroneal muscles were used for gene expression analysis, serum creatinine and creatine kinase activity were measured, and a validated murine ethogram was used to quantify pain before euthanasia. GIK treatment resulted in a significant protection of skeletal muscle with increased viability (GIK 22.07% (SD 15.48%)) compared to saline control (control 3.14% (SD 3.29%)) (p = 0.005). Additionally, GIK led to a statistically significant reduction in gene expression markers of cell death (CASP3, p < 0.001) and inflammation (NOS2, p < 0.001; IGF1, p = 0.007; IL-1β, p = 0.002; TNFα, p = 0.012), and a significant reduction in serum creatine kinase (p = 0.004) and creatinine (p < 0.001). GIK led to a significant reduction in IR-related pain (p = 0.030). Systemic GIK infusion during and after limb ischaemia protects murine skeletal muscle from cell death, kidneys from reperfusion metabolites, and reduces pain by reducing post-ischaemic inflammation.

Systemic Review of Animal Models Used in the Study of Crush Syndrome

ABSTRACT

Crush syndrome (CS), also known as traumatic rhabdomyolysis, is the leading cause of death following extrication from structural collapse due to earthquakes. Due to the unfeasibility of human studies, animal models are used to study crush syndrome pathophysiology, including biochemistry and treatment regimes. The aim of this systematic literature review was to identify the differences and benefits of various animal models used in the study of CS and provide valuable information for design of future research. A systematic search was conducted in two methods: with the filters "(crush syndrome) AND (crush muscle injury)" and with the keywords "(crush syndrome) AND (animal model)" covering all articles in the PubMed databases. The search generated 378 articles. After screening abstracts, 91 articles were retrieved and read, then 11 repeated articles were removed and 2 reference papers were included. We finally reviewed 82 original articles. There appear to be two primary methods employed for inducing crush syndrome in animal models, which are chemically induced injury and physically induced injury. Chemical method mainly includes intramuscular (IM) injection of tissue extract solution and IM injection of 50% glycerine. Physical method can be classified into invasive and non-invasive physical compression by elasticated material, inflatable band and heavy load. Various species of animals have been used to study CS, including mice (13.4%), rats (68.3%), rabbits (11.0%), canines (4.9%), goats (1.2%), and pigs (1.2%). Small animals are suitable for researches exploring the mechanism of disease or drug efficacy while large animals can work better with clinical application-related researches. In regard to the choice of modeling method, compressing the certain muscle of animals by heavy things is superior to others to cause systemic trauma-related rhabdomyolysis signs. In addition, due to the significant burden of crush injuries on animals, further attention shall be paid to the selection of the most suitable anesthetics and appropriate analgesics.

A reproducible method for biochemical, histological and functional assessment of the effects of ischaemia-reperfusion syndrome in the lower limbs

Current methodology described to mimic lower limb ischaemia-reperfusion injury (LL-IRI) does not accurately define the procedures and pressures exerted to induce and maintain ischaemia. In this piece of work, we propose a well-defined and detailed rat model that simulates the conditions established in clinical practice guidelines for tourniquet application and allows us to test treatments that aim to prevent/reduce LL-IRI. Eighty-six male WAG/RijHsd rats were subjected to hind limb IRI (LL-IRI), using a mechanical system applying a 1 kg tension to induce and maintain ischemia for 2 or 3 h, and assessed the damage caused by reperfusion at biochemical and muscular levels at different time points. At the biochemical level, both 2 and 3 h of ischemia induced changes (except for electrolyte levels); 3 h of ischemia induced greater changes in specific markers of muscular damage: creatine kinase (CK) and lactate dehydrogenase (LDH). At the histopathological level, 3 h of ischemia and 24 h of reperfusion was associated with an increase in hind limb girth, cross-sectional area, and weight and presence of neutrophils, as well as histological damage in more than 60% of muscle fibres. Our model allows to reliably reproduce the damage associated with the use of a pneumatic tourniquet. CK and LDH, as well as measures of tissue damage, allow to define and characterize the response to LL-IRI-related damage. A period of 3 h of ischemia followed by 3 h of reperfusion caused only local damage but showed greater sensitivity to detect differences in future studies on prophylactic treatments against LL-IRI.

Tourniquet-induced ischemia and reperfusion in subcutaneous tissue, skeletal muscle, and calcaneal cancellous bone

This study aimed to evaluated ischemic metabolites in subcutaneous tissue, skeletal muscle, and calcaneal cancellous bone before, during, and after tourniquet application in a simultaneous paired comparison of tourniquet-exposed and non-tourniquet-exposed legs. Ten patients scheduled for hallux valgus or hallux rigidus surgery were included. Microdialysis catheters were placed to simultaneously and continuously sample the metabolites glucose, lactate, pyruvate, and glycerol bilaterally for 12 h in subcutaneous tissue, skeletal muscle, and calcaneal cancellous bone. A tourniquet was applied on the leg planned for surgery (inflation time: 15 min, mean tourniquet duration time (range): 65 (58;77) min). During tourniquet inflation, a 2- to 3-fold increase of the mean lactate/pyruvate ratio was found for all investigated tissues in the tourniquet-exposed leg compared with the non-tourniquet-exposed leg. The lactate/pyruvate ratio recovery time after tourniquet release was within 30 min for skeletal muscle, 60 min for subcutaneous tissue, and 130 min for calcaneal cancellous bone. Only the tourniquet-exposed skeletal muscles were found to be ischemic during tourniquet inflation, defined by a significant increase of the lactate/pyruvate ratio exceeding the ischemic cutoff level of 25; however, this level decreased below 25 immediately after tourniquet release. The glycerol ratio increased instantly after inflation in the tourniquet-exposed leg in skeletal muscle and subcutaneous tissue, and recovered within 60 (skeletal muscle) and 130 min (subcutaneous tissue) after tourniquet release. These findings suggest that applying tourniquet for approximately 1 h results in limited tissue ischemia and cell damage in subcutaneous tissue, skeletal muscle, and calcaneal cancellous bone.

The Role of Tourniquet Placement in Management of a Patient With Status Epilepticus

BACKGROUND

The global burden of seizure disorders is apparent and necessitates the effective management of patients with status epilepticus (SE). The goal of management is universally accepted as the prompt mitigation of seizure activity with appropriate supportive care. During management, patients may require intubation. In the process of endotracheal tube placement, patients are administered neuromuscular blockers and general anesthesia. Paralytic activity on the neuromuscular junction hinders the emergency physician's ability to effectively observe seizure activity. Moreover, little can be discerned about patient sedation levels for titration. Effective tourniquet placement may be used to separate a region of the body from general circulation, rendering distal tissues unaffected by neuromuscular blockade.

CASE REPORT

A 73-year-old white woman presented to the emergency department with a stroke, and her condition generalized into diffuse tonic-clonic seizures. Concern for airway integrity warranted intubation with appropriate induction of paralysis and sedation. A tourniquet was placed proximal to the right knee and tightened until a dorsalis pedis pulse was no longer palpable. Computed tomography and computed tomography angiography of the head revealed no cerebrovascular event. After imaging, purposeful movements were noted in the right lower extremity distal to the tourniquet despite the initiation of standard dose post-intubation sedation with fentanyl (0.5 μg/kg/h) and propofol (20 μg/kg/min). No tonic-clonic activity was observed. With necessary up-titration, movements ceased. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: The observations made support the use of temporally limited tourniquet placement during paralytic administration to assess patient seizure status and sedation levels. Mindful tourniquet use in this manner permits a more effective sedation and management protocol for SE patients coming into the ED and may outweigh the minor risks associated with short-term hypoperfusion.

Validation of digital tourniquet pressures: An experimental comparison of T-RingTM and conventional surgical glove in human volunteers

Digital tourniquets are widely used for the management of digital injuries in emergency departments or outpatient clinics. This study is focused on the pressure analysis of digital tourniquets on some points not covered in the existing literature.A total of thirty volunteers were enrolled in this study. Instantaneous surface pressure was measured at the thumbs, index fingers, and little fingers. We investigated the pressure according to the circumference of digits, tourniquet types, and measurement sites (dorsal and mid lateral volar sides) above the digital vessels. Continuous pressure was measured in artificial silicone models to determine the change of pressure over 2 hours.The average pressure measured on the mid lateral volar side of volunteers fingers were 154.3 ± 54.9 mm Hg by T-Ring and 162.6 ± 61.0 mm Hg by surgical glove. The pressure on the dorsal side were 224.7 ± 57.7 mm Hg by T-Ring and 228.8 ± 66.0 mm Hg by surgical glove, each significantly higher than the mid lateral volar side. The circumference of digits did not significantly affect the surface pressure. The pressure pattern did not change significantly over 2 hours in both tourniquet types.The surface pressure of the mid lateral volar side was significantly lower than that of the dorsal side. However, there was no significant pressure difference according to the circumference of digits. Time dependent pressure change were not significantly different between 2 tourniquets.

Tourniquet-induced tissue hypoxia characterized by near-infrared spectroscopy during ankle surgery: an observational study

BACKGROUND

Pneumatic tourniquet inflation during extremity surgery leads to profound and prolonged tissue ischemia. Its effect on tissue oxygenation is inadequately studied.

METHODS

Patients undergoing elective ankle surgery with tourniquet application participated in this observational cohort study. Somatic and cerebral tissue oxygen saturation (SstO₂ and SctO₂) were monitored using tissue near-infrared spectroscopy. Oxygenation was monitored distally (SstO₂-distal) and proximally to the tourniquet, on the contralateral leg, and the forehead (a total of 4 tissue beds). Tissue oxygenation at different time points was compared. The magnitude, duration, and load (product of magnitude and duration) of tissue desaturation during tourniquet inflation were correlated with tissue resaturation and hypersaturation after tourniquet deflation.

RESULTS

Data of 26 patients were analyzed. The tourniquet inflation time was 120 ± 31 mins. Following a rapid desaturation from 77 ± 8% pre-inflation to 38 ± 20% 10 mins post-inflation, SstO₂-distal slowly and continuously desaturated and reach the nadir (16 ± 11%) toward the end of inflation. After deflation, SstO₂-distal rapidly resaturated from 16 ± 11% to 91 ± 5% (i.e., hypersaturation); SstO₂ monitored proximally to the tourniquet and on contralateral leg had significant but small desaturation (~ 2-3%, p <  0.001); in contrast, SctO₂ remained stable. The desaturation load had a significant correlation with resaturation magnitude (p <  0.001); while the desaturation duration had a significant correlation with hypersaturation magnitude (p = 0.04).

CONCLUSIONS

Tissue dys-oxygenation following tourniquet application can be reliably monitored using tissue oximetry. Its outcome significance remains to be determined.

Changes in biomarker levels and myofiber constitution in rat soleus muscle at different exercise intensities

Although exercise affects the function and structure of skeletal muscle, our knowledge regarding the biomedical alterations induced by different intensities of exercise is incomplete. Here we report on the changes in biomarker levels and myofiber constitution in the rat soleus muscle induced by exercise intensity. Male adult rats at 7 weeks of age were divided into 3 groups by exercise intensity, which was set based on the accumulated lactate levels in the blood using a treadmill: stationary control (0 m/min), aerobic exercise (15 m/min), and anaerobic exercise (25 m/min). The rats underwent 30 min/day treadmill training at different exercise intensities for 14 days. Immediately after the last training session, the soleus muscle was dissected out in order to measure the muscle biomarker levels and evaluate the changes in the myofibers. The mRNA expression of citrate synthase, glucose-6-phosphate dehydrogenase, and Myo D increased with aerobic exercise, while the mRNA expression of myosin heavy-chain I and Myo D increased in anaerobic exercise. These results suggest that muscle biomarkers can be used as parameters for the muscle adaptation process in aerobic/anaerobic exercise. Interestingly, by 14 days after the anaerobic exercise, the number of type II (fast-twitch) myofibers had decreased by about 20%. Furthermore, many macrophages and regenerated fibers were observed in addition to the injured fibers 14 days after the anaerobic exercise. Constitutional changes in myofibers due to damage incurred during anaerobic exercise are necessary for at least about 2 weeks. These results indicate that the changes in the biomarker levels and myofiber constitution by exercise intensity are extremely important for understanding the metabolic adaptations of skeletal muscle during physical exercise.

Voluntary running protects against neuromuscular dysfunction following hindlimb ischemia-reperfusion in mice

Ischemia-reperfusion (IR) due to temporary restriction of blood flow causes tissue/organ damages under various disease conditions, including stroke, myocardial infarction, trauma, and orthopedic surgery. In the limbs, IR injury to motor nerves and muscle fibers causes reduced mobility and quality of life. Endurance exercise training has been shown to increase tissue resistance to numerous pathological insults. To elucidate the impact of endurance exercise training on IR injury in skeletal muscle, sedentary and exercise-trained mice (5 wk of voluntary running) were subjected to ischemia by unilateral application of a rubber band tourniquet above the femur for 1 h, followed by reperfusion. IR caused significant muscle injury and denervation at neuromuscular junction (NMJ) as early as 3 h after tourniquet release as well as depressed muscle strength and neuromuscular transmission in sedentary mice. Despite similar degrees of muscle atrophy and oxidative stress, exercise-trained mice had significantly reduced muscle injury and denervation at NMJ with improved regeneration and functional recovery following IR. Together, these data suggest that endurance exercise training preserves motor nerve and myofiber structure and function from IR injury and promote functional regeneration. NEW & NOTEWORTHY This work provides the first evidence that preemptive voluntary wheel running reduces neuromuscular dysfunction following ischemia-reperfusion injury in skeletal muscle. These findings may alter clinical practices in which a tourniquet is used to modulate blood flow.

Color-coded Digital Subtraction Angiography for Assessing Acute Skeletal Muscle Ischemia-Reperfusion Injury in a Rabbit Model

RATIONALE AND OBJECTIVES

This paper describes an ongoing investigation of imaging and characterization of ischemia-reperfusion (IR) and investigated the use of color-coded digital subtraction angiography (DSA) to assess reperfusion injury or potential injury.

METHODS

New Zealand white rabbits were subjected to right hindlimb ischemia (IR, n = 24) or sham operation (control, n = 6). After 3 hours, the IR rabbits underwent reperfusion and were assessed at 0, 6, 12, or 24 hours (n = 6 each). DSA of the bilateral vastus lateralis muscle of each animal was performed. The maximum contrast enhancement value of a consistent region of interest in the right and left hind limbs (peak enhancement-R/L) was determined. Associations between the relative ratio of the peak right limb to the peak left limb (peak-R/L) and the following blood indicators of IR injury were analyzed: lactic dehydrogenase (LDH), creatine kinase (CK), malondialdehyde (MDA), and superoxide dismutase (SOD).

RESULTS

Serum LDH, CK, and MDA values in each IR group were significantly higher than those of the control group and were positively associated with the IR interval, whereas SOD was significantly lower and negatively associated. The mean peak-R/L decreased linearly with the IR interval from 1.07 ± 0.01 in the control group, and 0.93 ± 0.06, 0.79 ± 0.05, 0.65 ± 0.04, and 0.47 ± 0.04 at 0, 6, 12, and 24 hours in the IR groups. The coefficients of correlation between the peak-R/L and LDH, CK, MDA, SOD serum levels were -0.885, -0.908, -0.541, and 0.832, respectively.

CONCLUSIONS

Color-coded DSA may be used for monitoring the dynamics of skeletal muscle IR injury.

The Long-term Clinical Effect of Minimal-Invasive TLIF Technique in 1-Segment Lumbar Disease

STUDY DESIGN

A prospective cohort double-center study.

OBJECTIVE

To assess the clinical effect of minimally invasive transforaminal lumbar interbody fusion (miTLIF) using the tunnel technique.

SUMMARY OF BACKGROUND DATA

A series of short-term studies have indicated that miTLIF could reduce blood loss and improve clinical results. However, long-term clinical study and magnetic resonance imaging research are still scare.

METHODS

From January 2008 to January 2009, 187 patients with 1-segment lumbar disease requiring intervertebral fusion were enrolled in this study. Patients were divided into 2 groups according to the operative methods. Postoperative low back pain (LBP), postoperative lumbar function, the fusion rate, lower extremity pain relief, variation of lumbar lordosis, and implant failure were assessed. At 48 months postoperation, the cross-sectional area of the paraspinal muscle was measured using magnetic resonance imaging.

RESULTS

The mean duration of follow-up was 54.4±5.9 months. The intermuscular pressure generated by the tunnel in the miTLIF group was lower than that generated in the oTLIF group. Patients in the miTLIF group reported a lower degree of LBP at all timepoints. The ODI scores were similar to the VAS scores. No significant differences were found in fusion rate, lower extremity pain relief, lumbar lordosis, or implant failure rate. A significant difference was found between the 2 groups in postoperative cross-sectional area.

CONCLUSIONS

This study confirmed the advantages of miTLIF in reducing postoperative LBP, improving postoperative quality of life and preventing paraspinal muscle atrophy compared with oTLIF, while achieving a similar therapeutic outcome. The lower intermuscular pressure generated by minimally invasive tunnel and subsequent moderate muscle atrophy were presumed to be possible reasons for its superiority.

A Comparison of Surgical Invasions for Spinal Nerve Ligation with or without Paraspinal Muscle Removal in a Rat Neuropathic Pain Model

L5 spinal nerve ligation (SNL) in rats is one of the most popular models for studying neuropathic pain because of its high reproducibility. During the surgery, a part of the L5 paraspinal muscle is usually removed, which produces extra trauma and may potentially affect the physiological processes involved in neuropathic pain. To reduce the surgical trauma, the paraspinal muscle retraction was developed for exposure of the spinal nerve. The current study was aimed at comparing the surgical invasions between the L5 SNL models with paraspinal muscle removal or retraction. The results showed that both methods induced similar neuropathic pain behavior. However, the paraspinal muscle retraction group exhibited an average of 2.7 mg less blood loss than the muscle removal group. This group also showed a significantly lower increase in serum myoglobin and creatine phosphokinase levels on postoperative days 1 and 2, as well as a lower increase in interleukin-1β and interleukin-6 levels on postoperative day 1. The paraspinal muscle maintained normal morphological features following paraspinal muscle retraction. Our results indicate that the SNL rat model with paraspinal muscle retraction is a reliable physiological model that is reproducible, readily available, and less invasive than the model with muscle removal.

Variability in local pressures under digital tourniquets

The UK National Patient Safety Agency issued a rapid response report in 2009 following reports of complications related to digital tourniquet use and inadvertent retention. In their guidance, they recommend the use of CE marked digital tourniquets and advise against the use of surgical gloves. There are a number of different commercially available non-pneumatic digital tourniquets, but little clear data relating to their comparable physical properties, clinical efficacy or safety. The aim of this study was to investigate the variability of pressures exerted by non-pneumatic digital tourniquets. A Tekscan FlexiForce(®) force sensor was used to measure applied force and to calculate the surface pressures under: the Toe-niquet™; T-Ring™ and surgical glove 'roll down' tourniquets in finger models. The lowest mean pressures were produced by the larger glove sizes (size 8) (25 mmHg), while the highest pressures were produced by the Toe-niquet (1560 mmHg). There was a significant overall difference in pressures exerted under tourniquets when comparing tourniquet type (p<0.001) and finger size (p<0.001) with these techniques. It is difficult to anticipate and regulate pressures generated by non-pneumatic tourniquets. Safe limits for application time and surface pressures are difficult to define. Further work is required to model the pressure effects of commercially available digital tourniquets and to identify which are most effective but safe.

Skeletal muscle hypertrophy and regeneration: interplay between the myogenic regulatory factors (MRFs) and insulin-like growth factors (IGFs) pathways

Adult skeletal muscle can regenerate in response to muscle damage. This ability is conferred by the presence of myogenic stem cells called satellite cells. In response to stimuli such as injury or exercise, these cells become activated and express myogenic regulatory factors (MRFs), i.e., transcription factors of the myogenic lineage including Myf5, MyoD, myogenin, and Mrf4 to proliferate and differentiate into myofibers. The MRF family of proteins controls the transcription of important muscle-specific proteins such as myosin heavy chain and muscle creatine kinase. Different growth factors are secreted during muscle repair among which insulin-like growth factors (IGFs) are the only ones that promote both muscle cell proliferation and differentiation and that play a key role in muscle regeneration and hypertrophy. Different isoforms of IGFs are expressed during muscle repair: IGF-IEa, IGF-IEb, or IGF-IEc (also known as mechano growth factor, MGF) and IGF-II. MGF is expressed first and is observed in satellite cells and in proliferating myoblasts whereas IGF-Ia and IGF-II expression occurs at the state of muscle fiber formation. Interestingly, several studies report the induction of MRFs in response to IGFs stimulation. Inversely, IGFs expression may also be regulated by MRFs. Various mechanisms are proposed to support these interactions. In this review, we describe the general process of muscle hypertrophy and regeneration and decipher the interactions between the two groups of factors involved in the process.

Alterations of biochemical marker levels and myonuclear numbers in rat skeletal muscle after ischemia-reperfusion

Prolonged ischemia-reperfusion results in various damages in skeletal muscle. Following reperfusion, although the damaged muscles undergo regeneration, the precise process and mechanism of regeneration have not yet been fully understood. Here, we show the altered levels of plasma biochemical markers of muscle damage, and the change in myonuclear numbers in adult rat skeletal muscle by ischemia-reperfusion. Male Wistar rats were subjected to unilateral hindlimb ischemia by clamping the anterior tibial artery for 2 h before reperfusion. Both plasma creatine kinase activity and C-reactive protein levels in plasma were increased significantly at 0.5 h of reperfusion and returned to the control level at 24 h. The transverse sectional area of muscle belly of the anterior tibial muscles in ischemic side was significantly decreased by 20 % compared with those in sham-ischemic (control) side at 2 days, and returned to the control level at 5 days of reperfusion. Moreover, the number of interstitial nuclei in the ischemic side were significantly increased at 5-14 days and returned to the control level at 21 days of reperfusion. Central nuclei that are specifically observed in regenerating muscle, appeared at 5 days, reached a peak at 14 days, and disappeared at 28 days of reperfusion. Furthermore, MyoD, a regulatory factor for myogenesis, showed a transient expression at 5 days of reperfusion. These results indicate that, although the size of muscle seems to be recovered by 5 days of reperfusion, the most active muscle regeneration occurs much later, as shown by the increase in central nuclei.

Hemodynamic and oxidative mechanisms of tourniquet-induced muscle injury: near-infrared spectroscopy for the orthopedics setting

During orthopedic procedures, the tourniquets used to maintain bloodless surgical fields cause ischemia and then reperfusion (I/R), leading to oxidative muscle injury. Established methods exist neither for monitoring orthopedic I/R nor for predicting the extent of tourniquet-associated oxidative injury. To develop a predictive model for tourniquet-associated oxidative muscle injury, this study combined real-time near-infrared spectroscopy (NIRS) monitoring of I/R with Western blotting (WB) for oxidized proteins. We hypothesized strong correlations between NIRS-derived I/R indices and muscle protein oxidation. In 17 patients undergoing ankle fracture repair, a thigh tourniquet was inflated on the injured limb (300 mmHg). Using a continuous-wave (CW) NIRS setup, oxygenated (O2Hb), deoxygenated (HHb), and total (tHb) hemoglobin were monitored bilaterally (tourniquet versus control) in leg muscles. Leg muscle biopsies were collected unilaterally (tourniquet side) immediately after tourniquet inflation (pre) and before deflation (post). Average ischemia duration was 43.2 ± 14.6 min. In post-compared to pre-biopsies, muscle protein oxidation (quantified using WB) increased 172.3%± 145.7% (P<0.0005). Changes in O2Hb and tHb were negatively correlated with protein oxidation (respectively: P=0.040, R2=0.25 and P=0.003, R2=0.58). Reoxygenation rate was positively correlated with protein oxidation (P=0.041, R2=0.25). These data indicate that using CW NIRS, it is possible to predict orthopedic tourniquet-associated muscle oxidative injury noninvasively.

Cuff width increases the serum biochemical markers of tourniquet-induced skeletal muscle ischemia in rabbits

Tourniquet application is a widely accepted adjuvant technique in extremity surgery. The purpose of this prospective, randomized trial was to evaluate the effect of cuff width on skeletal muscle ischemia-reperfusion injury. A 2- or 4-cm wide curved tourniquet cuff was applied around the midthigh of 36 New Zealand White rabbits and inflated to a pressure of 200 or 400 mm Hg for 2 hours: group A=2 cm to 200 mm Hg; group B=2 cm to 400 mm Hg; group C=4 cm to 200 mm Hg; group D=4 cm to 400 mm Hg. Blood levels of potassium, lactic acid, urea, lactic dehydrogenase, and creatinine phosphokinase MM isoenzyme (CPK-MM) were measured as basic indicators for limb ischemia before tourniquet inflation and 1, 5, and 30 minutes after cuff release.Potassium values did not differ among the 4 groups. Lactic acid and urea concentrations were always higher in the 400 mm Hg groups (B and D) (P<.001). However, cuff width did not affect their levels (P>.16). Lactic dehydrogenase and CPK-MM values were also greater in the 400 mm Hg groups at all times (P<.001). Further subgroup analysis of 200 mm Hg pressure groups showed higher lactic dehydrogenase (P<.02) but not CPK-MM (P>.9) concentrations in group C than in group A during the 30-minute period. At 400 mm Hg, lactic dehydrogenase and CPK-MM values were higher in group D compared with group B only 30 minutes after cuff deflation (P<.001). Broad tourniquets are associated with significantly greater and prolonged elevation of serum biochemical markers of inducible skeletal muscle ischemia-reperfusion injury compared with narrow ones. This difference is more prominent when a wide cuff is inflated to a high pressure.

Serum creatine phosphokinase activity and histological changes in the multifidus muscle: a prospective randomized controlled comparative study of discectomy with or without retraction

OBJECT

The aim of this study was to determine the extent of muscle injury caused by continuous or intermittent muscle retraction during macro- and microdiscectomy in lumbar disc surgery. Pain scores, serum creatine phosphokinase (CPK) levels, and histological findings obtained in muscle specimens were compared.

METHODS

Sixty patients who underwent surgery for a one-level disc herniation during a 1-year period (January 2004-January 2005) and who had similar demographic characteristics were randomly assigned to one of four groups, each consisting of 15 patients: Group A, microdiscectomy in which the retractor was never released; Group B, microdiscectomy in which the retractor was released every 15 minutes; Group C, macrodiscectomy in which the retractor was never released; and Group D, macrodiscectomy in which the retractor was released every 15 minutes. Muscle biopsy samples were acquired in each group, and biochemical studies were conducted to determine serum CPK levels. The duration of muscle retraction was 15 minutes followed by 3 minutes of relaxation in Groups B and D. In all groups, muscle degeneration and elevation in serum CPK levels were observed immediately after surgery. The overall results, however, were different. The decline of serum CPK levels started 1 week after surgery. The smallest degree of muscle injury (reflected by the lowest serum CPK level) was observed in Group B. When the pre- and postoperative CPK values were compared in all groups, the patients in Groups B and D reported the least amount of back pain (p < 0.001). No significant differences in serum CPK levels were observed between Groups A and C or between Groups B and D. The extent of back pain was evaluated using a visual analog scale, and the consumption of analgesics was also assessed. The groups exhibited significantly different responses: the lowest analgesic consumption and the lowest pain scores were demonstrated in Groups B and D.

CONCLUSIONS

In this prospective randomized clinical trial, the authors determined that muscle injury during lumbar disc surgery was closely related to muscle retraction and relaxation times whereas the size of the paravertebral skin incision had no effect on postoperative back pain and disability. There was no significant difference among the groups in terms of back pain during the long-term follow-up period (18-19 months).

A facile nonviral method for delivering genes and siRNAs to skeletal muscle of mammalian limbs

Delivery is increasingly being recognized as the critical hurdle holding back the tremendous promise of nucleic acid-based therapies that include gene therapy and more recently siRNA-based therapeutics. While numerous candidate genes (and siRNA sequences) with therapeutic potential have been identified, their utility has not yet been realized because of inefficient and/or unsafe delivery technologies. We now describe an intravascular, nonviral methodology that enables efficient and repeatable delivery of nucleic acids to muscle cells (myofibers) throughout the limb muscles of mammals. The procedure involves the injection of naked plasmid DNA or siRNA into a distal vein of a limb that is transiently isolated by a tourniquet or blood pressure cuff. Nucleic acid delivery to myofibers is facilitated by its rapid injection in sufficient volume to enable extravasation of the nucleic acid solution into muscle tissue. High levels of transgene expression in skeletal muscle were achieved in both small and large animals with minimal toxicity. Evidence of siRNA delivery to limb muscle was also obtained. The simplicity, effectiveness, and safety of the procedure make this methodology well suited to limb muscle gene therapy applications.

BACK PAIN AND DISABILITY AFTER LUMBAR LAMINECTOMY: IS THERE A RELATIONSHIP TO MUSCLE RETRACTION?

OBJECTIVE

Preliminary studies have suggested that prolonged retraction of the paraspinal muscle during spinal surgery may produce ischemic damage. We report the continuous measurement of intramuscular pressure (IMP) during decompressive lumbar laminectomy and its relationship to subsequent back pain and disability.

METHODS

Twenty patients undergoing two-level decompressive lumbar laminectomy for lumbar canal stenosis were recruited. Back pain and disability were assessed by use of the Visual Analog Score (VAS), Oswestry Disability Index (ODI), and Short-Form 36 (SF-36) Health Survey. During surgery, IMP was recorded continuously from the multifidus muscle by use of a pressure transducer. The intramuscular perfusion pressure (IPP) was estimated as the difference between the patient's mean arterial pressure and IMP.

RESULTS

Two muscle retractors were used: the Norfolk and Norwich (n = 10) and the McCulloch (n = 10). The mean duration of deep muscle retraction was 62.7 +/- 8 minutes (range, 19-133 min). On application of deep muscle retraction, there was a rapid and sustained increase in IMP (P < 0.001), and overall, the calculated mean IPP approached 0 mm Hg or less during this period (P < 0.001). On release of deep muscle retraction, there was a rapid decrease in IMP to preoperative levels. The IPP was greater with the Norfolk and Norwich than the McCulloch retractor (P < 0.001). Compared with preoperative values, there was a decrease in ODI (P < 0.001) and VAS for back pain (P < 0.001) at discharge and 4 to 6 weeks and 6 months after surgery. In addition, there was a decrease in SF-36 scores at 6 months compared with preoperative values (P < 0.001). Total duration of muscle retraction greater than 60 minutes was associated with worse VAS scores for back pain and ODI and SF-36 scores for disability at 6 months after surgery (P < 0.05). There was no relationship between the VAS, ODI, and SF-36 scores and other parameters measured, including the mean IPP, retractor type, operating surgeon, and wound length.

CONCLUSION

The McCulloch retractor generates a higher IMP than the Norfolk and Norwich retractor. However, postoperative improvement in VAS, ODI, and SF-36 scores in these patients was associated with a shorter duration of muscle retraction and not the degree of IMP or IPP generated. In this respect, periodic relaxation of the paraspinal muscle retractors during surgery to allow muscle perfusion may help to reduce postoperative back pain and disability.

Tourniquet-induced ischemia and reperfusion in human skeletal muscle

Microdialysis conceivably enables longitudinal and simultaneous investigation of several metabolites by repeated measurements in skeletal muscle. We used and evaluated microdialysis as an in vivo method to characterize the time-course and relative kinetics of pyruvate, glucose, lactate, glycerol, hypoxanthine, uric acid, and urea, in skeletal muscles, exposed to ischemia and reperfusion, in eight patients having arthroscopic-assisted anterior cruciate ligament reconstruction. A dialysis probe was implanted before surgery in the rectus femoris muscle. Dialysate samples were collected at 10-minute intervals at a flow rate of 1 microL/minute until 2 hours after tourniquet deflation. Ninety minutes of ischemia resulted in accumulation of lactate (234% +/- 38%), hypoxanthine (582% +/- 166%), and glycerol (146% +/- 46%), consumption of glucose (54% +/- 9%) and pyruvate (16% +/- 44%), and a slight decrease of urea (78% +/- 11%) compared with baseline (100%). Uric acid was unchanged (95% +/- 12%). Within 90 minutes after tourniquet deflation the concentrations were virtually normalized for all measured metabolites, suggesting that the duration of ischemia was well tolerated by the patients. The results indicate that the use of microdialysis for monitoring energy metabolic events during orthopaedic surgery that requires ischemia and reperfusion is feasible and safe.

Disaster nephrology: medical perspective

Disaster medicine is an extension of emergency medicine involving mass casualties and use of the best available techniques in search and rescue. To achieve the best results extensive predisaster preparedness is mandatory. Earthquakes have caused the loss of more than 1 million lives in the 20th century. Evidence-based medicine confirms that these deaths were mostly preventable based on experience in developed countries. The key to success is implementing building codes and structural reinforcement. In earthquakes as well as in collapse of buildings in bomb blasts, loss of life is either because of the direct effect of trauma or to the metabolic consequences of rhabdomyolysis and complications of its management. Hyperkalemia and infection are the commonest causes of death in victims who survive the direct effect of trauma. Acute renal failure, a grave complication of rhabdomyolysis, is mostly preventable by timely rehydration and bicarbonate therapy. Mannitol therapy can be very efficient in reducing the severity of muscle damage and its sequelae. Fasciotomy can be limb saving if it is done in the early hours, although a firm guideline is still lacking. Although each country is responsible for improving the structure of buildings and organizing an efficient disaster response, national and international organizations in developed countries should give high priority to communicating with developing countries to encourage their preparedness.

Compartment syndrome associated with the Lloyd Davies position. Three case reports and review of the literature

The Lloyd Davies position was developed to facilitate access to the pelvis for gynaecological, urological and colorectal procedures. Previous case reports have demonstrated that prolonged adoption (> 4 h) of this position has been associated with the development of bilateral compartment syndrome of the calves. All three patients reported here suffered severe bilateral calf pain despite the use of thoracic epidurals. All three cases required three-compartment fasciotomies and, 6 months after surgery, were all still severely disabled as a consequence of the compartment syndrome. These case reports stress the dangers of use of the Lloyd Davies position for prolonged procedures and demonstrate that some patients are at risk after relatively short periods (< 3 h). Previous case reports and clinical studies have focused on the effect of limb elevation in stirrups on the arterial pressure in the lower limb. We review the pathophysiology of compartment syndrome and consider factors other than a decrease in arterial pressure that may predispose to compartment syndrome during adoption of the Lloyd Davies position.

Pneumatic tourniquets in extremity surgery

Pneumatic tourniquets maintain a relatively bloodless field during extremity surgery, minimize blood loss, aid identification of vital structures, and expedite the procedure. However, they may induce an ischemia-reperfusion injury with potentially harmful local and systemic consequences. Modern pneumatic tourniquets are designed with mechanisms to regulate and maintain pressure. Routine maintenance helps ensure that these systems are working properly. The complications of tourniquet use include postoperative swelling, delay of recovery of muscle power, compression neurapraxia, wound hematoma with the potential for infection, vascular injury, tissue necrosis, and compartment syndrome. Systemic complications can also occur. The incidence of complications can be minimized by use of wider tourniquets, careful preoperative patient evaluation, and adherence to accepted principles of tourniquet use.

Postoperative changes in paraspinal muscle thickness after various lumbar back surgery procedures

Damage to the paraspinal muscle after various lumbar back surgery procedures was evaluated by measuring the paraspinal muscle thickness preoperatively and postoperatively in 89 patients, 61 males and 28 females. There were 42 single interlaminar level procedures (SL group), 13 multiple interlaminar level procedures (ML group), and 34 posterolateral fusion procedures (PLF group). Changes in paraspinal muscle thickness were evaluated at more than 10 months after surgery, because muscle swelling continued as long as 10 months after surgery, and then reduced as the edema subsided. Postoperative serum creatine phosphokinase (CPK) level on postoperative day 2 was also measured. The decrease of paraspinal muscle thickness was significantly larger in the PLF group than in the SL group (-12.9% and -2.7%, respectively, p < 0.02). There was no significant correlation between postoperative serum CPK level and decrease of paraspinal muscle thickness. However, the postoperative elevation of serum CPK level was significantly higher in the PLF group than in the SL and ML groups (979 +/- 114 vs. 292 +/- 45 and 410 +/- 44 IU/l, respectively, p < 0.001). In conclusion, posterolateral fusion is the most invasive procedure of the paraspinal muscles in various lumbar back surgery procedures. Paraspinal muscle damage during lumbar back surgery may be one of the most important factors that causes atrophy of the muscles.

Intermittent reperfusion fails to prevent posttourniquet neurapraxia

This study examined the effects of intermittent reperfusion on peripheral nerve function. Rabbits were randomized to undergo 4 hours of 350 mm Hg tourniquet compression to a hind limb either continuously, interrupted by a single 10-minute reperfusion interval after 2 hours, or interrupted by 10 minutes of reperfusion after each hour. A control group had the tourniquet applied for 4 hours but it was never inflated. The animals were examined clinically for neuromuscular dysfunction and the structure and function of the peripheral nerves were evaluated 1 week after tourniquet compression. Animals that underwent compression had a foot drop and decreased toe-spread reflex. There was greater intraneural edema and slower nerve conduction velocity in nerve segments that were directly compressed by the tourniquet but no apparent abnormalities in segments distal to the tourniquet. Intermittent reperfusion failed to diminish the clinical, structural, or functional consequence of the neurologic injury.

Back muscle injury after posterior lumbar spine surgery. A histologic and enzymatic analysis

STUDY DESIGN

Back muscle injury after posterior lumbar surgery was studied by muscle histology and serum creatine phosphokinase MM isoenzyme activity.

OBJECTIVES

To investigate intraoperative factors influencing the magnitude of back muscle injury after posterior lumbar surgery.

SUMMARY OF BACKGROUND DATA

The authors previously have reported iatrogenic back muscle injury in an animal model and in humans. Serious injury of the back muscle has been shown by short-term and long-term follow-up evaluation.

METHODS

The retraction pressure was monitored, and the retraction pressure-time products were calculated in 24 patients. Early histologic changes of multifidus muscle, which were taken at completion of surgery, and serum creatine phosphokinase MM isoenzyme activity changes were examined.

RESULTS

The magnitude of back muscle injury was significant as the pressure-time product increased. Creatine phosphokinase MM isoenzyme activity increased after surgery and reached a plateau 1 day after surgery, followed by recovery to the normal value 1 week after surgery. Creatine phosphokinase MM isoenzyme activity tended to be high in cases with multilevel exposure and with high pressure-time product.

CONCLUSIONS

Back muscle injury occurs in all patients who underwent posterior lumbar surgery, and these injuries are related to the retraction pressure, time, and extent of exposure.

Surgical hemostasis by pneumatic ankle tourniquet during 3027 podiatric operations

A retrospective study was performed at the Denver Doctors Hospitals in which 3818 surgical cases on the foot and/or ankle were reviewed over a 4-year period from July 1986 through May 1990. From the 3027 ankle tourniquet cases reviewed, it was determined that pneumatic ankle tourniquets are safe and effective in providing hemostasis during foot surgery. There were five postoperative complications noted with ankle cuffs, with post-tourniquet syndrome being the most common (three cases). Over the 4-year period, ankle tourniquets failed a total of 50 times, a 1.8% failure rate (0.25% failure rate in the last 17 months). The most common pressure setting used for ankle cuffs was 325 mm. Hg (400 mm. Hg for thigh cuffs). Tourniquet ischemia lasted from 4 to 139 min.; the most common duration of ischemia noted for ankle tourniquets was 30 to 60 min. (60 to 90 min. for thigh tourniquets). A review of the potential complications associated with tourniquets, as well as safeguards, recommendations, and contraindications are presented.

Effects of reperfusion intervals on skeletal muscle injury beneath and distal to a pneumatic tourniquet

To date there have been no experimental studies specifically directed at effects of reperfusion intervals on skeletal muscle injury beneath the tourniquet. 99mTechnetium pyrophosphate (Tc 99) incorporation and correlative histology were used to assess injury 2 days after tourniquet application in muscles beneath (thigh) and distal (leg) to the cuff. Tourniquets were applied to rabbit hindlimbs for a total of either 2 or 4 hours. In the 4-hour series, tourniquet compression (either 125 mm Hg or 350 mm Hg cuff inflation pressure) was either continuous or interrupted by 10-minute reperfusion intervals after 2 hours or after every hour of cuff inflation. In the 2-hour series, tourniquet compression (350 mm Hg) was either continuous or interrupted by 10-minute reperfusion intervals after 2 hours or after every hour of cuff inflation. In the 2-hour series, tourniquet compression (350 mm Hg) was either continuous or interrupted by a 10-minute reperfusion interval after 1 hour. Pyrophosphate incorporation (Tc 99 uptake) was significantly greater in the thigh region than in the leg region in all of the 4-hour tourniquet groups. Tc 99 uptake was significantly reduced by reperfusion after each hour of cuff inflation. With 350 mm Hg tourniquet pressure, a reperfusion interval after 2 hours of cuff inflation tended to exacerbate tourniquet compression injury. Reperfusion intervals did not significantly affect Tc 99 uptake in the leg region of these groups. With a 2-hour tourniquet time, Tc 99 uptake in the thigh was significantly decreased by reperfusion after 1 hour of cuff inflation. Previous clinical recommendations, based on serum creatine phosphokinase abnormalities after experimental tourniquet ischemia, probably reflected tourniquet compression injury. Hourly reperfusion limits skeletal muscle injury during extended periods of tourniquet use.

Skeletal muscle injury induced by a pneumatic tourniquet: an enzyme- and immunohistochemical study in rabbits

The pathophysiology of skeletal muscle injury induced by compression beneath pneumatic tourniquets is poorly understood. Tourniquet hemostasis was induced in rabbit hindlimbs for 2 hr with a cuff inflation pressure of either 125 mm Hg (n = 5) or 350 mm Hg (n = 5). Skeletal muscle biopsies, taken 2 days later from tissue beneath and distal to the tourniquet, were frozen and analyzed using enzyme- and immunohistochemical techniques. In the 350 mm Hg tourniquet group, four of 10 thigh muscle samples demonstrated significant regional necrosis (mean 37.3% of the total cross-sectional area). Regional necrosis was not observed in thigh muscles of the 125 mm Hg tourniquet group or in any of the ischemic leg muscles. A topographic pattern of necrosis consistent with the arterial distribution of skeletal muscle suggested pathogenic events during the reperfusion period, such as granulocyte-mediated superoxide radical formation. Extremely large and rounded fibers (histochemically identified as Type IIB fibers) were observed in compressed thigh muscles, indicating differential fiber sensitivity to tourniquet compression and ischemia. The present study demonstrated significant skeletal muscle necrosis after a 2 hr tourniquet applied at a clinically relevant cuff inflation pressure. Recent studies of systemic changes associated with limb "ischemia" should be reassessed in consideration of the confounding effects of tissue compression induced beneath pneumatic tourniquets.

Muscle injury induced beneath and distal to a pneumatic tourniquet: a quantitative animal study of effects of tourniquet pressure and duration

Previous recommendations regarding the "safe" period of tourniquet hemostasis were based largely on studies of ischemia distal to the tourniquet. This study quantitatively analyzed skeletal muscle injury induced beneath and distal to a pneumatic tourniquet applied to the hindlimbs of rabbits for 1, 2, or 4 hours with a cuff inflation pressure of 125, 200, or 350 mm Hg. Technetium Tc 99m pyrophosphate incorporation after systemic injection (Tc 99 uptake) and correlative histology were used to evaluate tissue damage 2 days after tourniquet application. Compared with the contralateral control limbs, compression and ischemia induced statistically significant increases in Tc 99 uptake in the thigh and leg regions of all groups. Pyrophosphate incorporation was significantly greater in the thigh region than in the leg region after 2 hours of compression in the 200 and 350 mm Hg pressure groups and following 4 hours of compression in all pressure groups. Focal and regional fiber necrosis and degeneration were observed in thigh muscles after 2 hours of tourniquet compression. Two hours of continuous tourniquet application at clinically relevant cuff inflation pressures induced significant skeletal muscle necrosis beneath the tourniquet. Use of the lowest possible inflation pressure for a limited duration should minimize the degree of tissue injury caused by tourniquet application.

An animal model for the study of neuromuscular injury induced beneath and distal to a pneumatic tourniquet

A well-controlled animal model is presented for the study of neuromuscular injury induced by a pneumatic tourniquet. This model comprises a curved tourniquet surrounded by a stiff exterior shell, both of which were specifically designed to fit the conical and oblong shape of the rabbit hindlimb. Computed tomographic imaging was used to assess transverse tissue displacement induced by tourniquet compression. The curved tourniquet/shell configuration occluded the distal arterial blood flow to the extremity at a significantly lower cuff inflation pressure than a straight tourniquet of equal width. The magnitude and distribution of tissue pressures in the subcutaneous and deep tissues beneath the tourniquet were similar to those recorded in previous human cadaver studies of tourniquet compression. This animal model will facilitate the quantitation and analysis of tissue injury induced beneath and distal to a pneumatic tourniquet. Such data can help define the critical pressure and time limits for the safe use of pneumatic tourniquets in extremity surgery.

Reversible changes of skeletal muscular capillaries after application of a tourniquet

Morphological studies of skeletal muscular capillaries after a 60-min tourniquet application were performed in the rat extensor hallucis proprius muscle. On the basis of the period of reflow, the rats were divided into three groups (15-min group, 24-hr group, and 7-day group). FITC-albumin was injected intravenously to detect open capillaries. The percentage of interstitial space of the muscle was high in the 24-hr group, but had recovered in the 7-day group. Capillary density, calculated under a fluorescence microscope, was low in both the 15-min and 24-hr groups, but in the 7-day group, it had recovered. Intramuscular pressure was high in the 15-min group, whereas it was almost normal in the 7-day group. Electron microscopic studies showed stenosis or collapse of the capillaries in the 15-min group, whereas it was almost normal in the 7-day group. We consider that the changes in the microcirculatory system in the rat extensor hallucis proprius muscle after a 60-min tourniquet application are reversible.

Myoglobin release after tourniquet ischemia

The concentration of myoglobin in plasma was assessed before and up to 68 hours after tourniquet release in 27 patients who underwent elective operations with no incision into skeletal muscle. The duration of ischemia was 1-3 hours. A control group underwent the same kind of surgery without the use of tourniquet. There was a minimal elevation in myoglobin values after 65 and 90 minutes of ischemia, and a marked elevation after more than 150 minutes of ischemia. Maximum values were reached 8 to 10 hours after tourniquet release, and preoperative values after 50 to 60 hours.

Local compression patterns beneath pneumatic tourniquets applied to arms and thighs of human cadavera

Distributions of tissue fluid pressure were examined beneath a standard pneumatic tourniquet in six upper extremities and six lower extremities of fresh human cadavera, disarticulated at the shoulder and hip, respectively. A standard 8-cm-wide tourniquet cuff was applied at mid-humerus or mid-femur position. Tissue fluid pressures were measured by 100-cm-long slit catheters inserted parallel to the bone at four tissue depths: subcutaneous, subfascial, mid-muscle, and adjacent to bone. All arms and thighs were studied at the following cuff pressures: 100, 150, 200, 250, 300, 400, and 500 mm Hg. Tissue fluid pressure was always maximal in subcutaneous tissue at mid-cuff. Transmission of cuff pressures to deeper tissues was significantly less (p less than 0.01) in the thighs with a girth of 40-52 cm than in the arms with a girth of 22-33 cm. At the four tissue depths studied, tissue fluid pressures fell steeply in a longitudinal direction near the cuff edge to levels near zero at points 1-2 cm outside each cuff edge. Our results suggest that wider cuffs are required on thighs than on arms to provide a bloodless field during limb surgery and to minimize underlying tissue injury associated with high cuff pressures. Our recommendation for wider tourniquet cuffs than those presently used during orthopaedic surgery is contrary to recent prevailing knowledge.

Extracellular potassium concentration and membrane potential in rabbit gastrocnemius muscle during tourniquet ischemia

The relationship between the extracellular potassium concentration (K+ e.c.) and the resting membrane potential (MP) of the gastrocnemius muscle was studied in the anesthetized rabbit during a 3-h period of hindleg ischemia and a subsequent 1.5-h period of resumed flow. The K+ e.c. was measured on the skeletal muscle surface, using a potassium selective electrode. The MP was recorded with conventional microelectrodes. Small biopsies were taken and analysed for content of ATP and lactate. The lactate content increased fourfold during the ischemic period, but returned to normal values after reflow. No significant changes occurred in the ATP content during the period of the experiment. K+ e.c. increased from 3.6 +/- 0.2 to 16.1 +/- 0.7 mmol/l, and the MP decreased from -90.2 +/- 0.6 to -58.5 +/- 1.9 mV during the 3-h period of ischemia. After release of the tourniquet there was an initial rapid decrease in K+ e.c. to 7.8 +/- 0.9 mmol/l during the first 15 min of resumed flow, followed by a slower decrease. The MP increased linearly during the first hour of resumed flow and both variables returned to near normal values 1.5 h after releasing the tourniquet.

Effect of tourniquet ischaemia on muscle energy metabolism in meniscectomy patients

The enzyme levels of muscle energy metabolism were studied in eight male meniscectomy patients before and 10 minutes after release of the tourniquet and on the third post-operative day. The average tourniquet time was 65.1 min. The muscle samples were taken from the vastus lateralis muscles; the healthy side served as the control. The greatest enzyme changes 10 min after release of the tourniquet were the falls in succinate dehydrogenase (SDH) and creatine phosphokinase (CPK) activities, (p less than 0.01 and p less than 0.025 respectively). On the 3rd day phosphofructokinase (FFK) and malate dehydrokinase (MDH) activities were also lowered in the tourniquet limb, but the lactate dehydrogenase (LDH) was not changed significantly. In the control extremity only SDH showed a lowered value on the 3rd post-operative day (p less than 0.05), perhaps due to hypokinesia in hospital. The results indicate that even one-hour tourniquet ischaemia causes an enzyme release from muscle and for at least three days after the tourniquet enzyme activities in muscle are lowered, perhaps because of the combined effect of the tourniquet ischaemia and hypokinesia after the operation.

Systemic reactions to tourniquet ischaemia

In 15 patients, mean age 60 years, undergoing knee arthroplasty under lumbar epidural analgesia, changes in ECG, blood pressure, blood gases, serum potassium, acid-base status and serum creatine-phosphokinase were studied following release of a tourniquet applied for 70-135 min. During and after the ischaemia, the skin temperature of the leg operated on was monitored. Although dextran-70 was rapidly infused following tourniquet release, the blood pressure decreased significantly, due to a reduction in peripheral resistance. There were no signs of myocardial or pulmonary disturbances. Serum potassium in arterial blood increased significantly and reached a peak 3 min after tourniquet release. There was a tendency to metabolic acidosis, most pronounced after 3 min and caused by local lactate production. The skin temperature of the ischaemic leg fell progressively, which, combined with muscular relaxation, indicates a low metabolic rate. There was no evidence of local ischaemic muscular injury. It is concluded that the systemic changes after interruption of up to 2 h of tourniquet ischaemia are moderate and reversible, even in the elderly.