Purpose: Several variables related to tourniquet (TQ) inflation contribute to ischemic muscle injury. Among these the duration of ischemia has been identified as a primary factor. The purposes of this study were to investigate the following during and after TQ-induced ischemia during orthopedic trauma surgery:

muscle oxygenation changes measured by near infrared spectroscopy (NIRS);

Method: Consented patients aged 19–69 yrs (n=18) with unilateral ankle fracture requiring surgery at our institution were recruited. A pair of NIRS probes was fixed over the midpoint of the tibialis anterior muscle (TA) on both the injured and healthy legs. A thigh TQ was applied to the injured leg and inflated to 300 mmHg. Using the NIRS apparatus coupled to a laptop with data acquisition software, changes in oxygenated (O2Hb), deoxygenated (HHb), and total hemoglobin (tHb) levels in the TA of both legs were measured before and during TQ inflation, and after release until values returned to baseline. PRE surgical biopsies were collected from the peroneus tertius muscle (PT) immediately after TQ inflation and incision. POST biopsies were collected from the same PT immediately before TQ deflation. Oxidation of PT myosin, actin, and total protein was quantified using Western blot analysis of 4-hydroxynonenal (4-HNE) modified proteins. Data are reported as mean±SD.

Results: In PRE biopsies compared to POST biopsies there were large and statistically significant increases in the PT content of 4-NE modified myosin (174.4±128%; P< 1×10-6), actin (223.7±182%; P< 5×10-9), and total protein (567.5±378%; P< 5×10-7). There was a greater increase in PT protein oxidation in male subjects than in female subjects (50.8% difference; P< 0.05). In the TA of the fractured side, there were moderate to strong linear correlations between total protein oxidation and: the relative change in tHb (r=−0.704) and O2Hb (r=−0.415) during the period of TQ inflation and the rate at which the muscle became reoxygenated following TQ release (r=0.502). There was no relationship between muscle protein oxidation and TQ time, nor between muscle protein oxidation and age of patients.

Conclusion: TQ-induced muscle ischemia for 21 to 74 min during lower extremity surgery leads to oxidative muscle injury as measured according to myofibrillar contractile protein oxidation. Importantly, we observed that when the TQ was “leaky,” local increases in muscle tHb were associated with a lower magnitude of protein oxidation, however, when local decreases in muscle O2Hb were observed, perhaps due to local blood loss below the TQ, more oxidative changes resulted. Intriguingly, gender appeared to influence the extent of muscle oxidative injury, but age did not. Surprisingly, there was no significant correlation between muscle oxidative injury and the TQ-induced ischemia interval.

FUNDING: MSFHR, COF, BCLA.

Purpose: Near-infrared spectroscopy (NIRS) detects changes in chromophore concentrations of oxygenated (O2Hb) and deoxygenated hemoglobin (HHb) in target tissues approximately 2 to 3 cm below the skin. The main purpose of this study was to non-invasively measure skeletal muscle oxygenation in the leg during and after tourniquet (TQ)-induced ischemia using continuous wave NIRS. Secondarily, we aimed to assess the sensitivity, specificity, and reliability of this optical technique for detection and continuous monitoring of changes in muscle oxygenation and hemodynamics during TQ-induced ischemia throughout orthopedic surgery.

Method: Consented patients aged 19–69 (n=21) with unilateral ankle fracture requiring emergency or elective surgery at our institution were recruited. All patients underwent standard general anesthetic. A pair of NIRS probes was fixed over the midpoint of the tibialis anterior muscle (TA) of both the fractured and healthy legs. A thigh TQ was applied to the injured leg and inflated to 300 mmHg. Using the NIRS apparatus coupled to a laptop with data acquisition software, changes in O2Hb, HHb, and total hemoglobin (tHb) levels in the TAs of both legs were measured at 10 Hz before and during TQ inflation, and after release until values returned to baseline. In each surgery the TQ was released when arterial obstruction was no longer required by the clinical team. Data are reported as mean±SD.

Results: Changes in O2Hb, HHb, and tHb were successfully collected, stored and transmitted for graphic display in all subjects. TQ time (ischemia interval) varied among subjects, from 1245 s to 4431 s (2753±854). NIRS measured a progressive increase in HHb (2.6±2 μmol/L) during the first minute of TQ inflation and a sharp increase in O2Hb (23.3±12 μmol/L) during the first minute of leg muscle reperfusion (after deflation). Following TQ inflation a progressive increase in HHb (24.2±10.3 μmol/L) with a concomitant decrease in O2Hb (mean – 24.4±8 μmol/L) in the under-TQ TA were consistent across subjects. These changes in ΔHHb and ΔO2Hb began to reverse immediately after TQ deflation. Significant correlations were observed between ischemia interval and, respectively, oxygenation recovery time (r2=0.84) and changes of deoxygenated hemoglobin (r2=0.57).

Conclusion: We demonstrated that, following TQ inflation and deflation respectively, NIRS can sensitively monitor muscle deoxygenation and reoxygenation. Consistent patterns of ΔHHb and ΔO2Hb occurred during TQ-induced ischemia in all subjects. These data confirm that near infrared spectroscopy is useful for the non-invasive detection and monitoring of muscle ischemia. These results indicate that it may be useful to investigate the efficacy of NIRS in the early detection of muscle ischemia or hypoxemia in conditions such as compartment syndrome.

FUNDING: MSFHR, COF, BC Lung.

Purpose: It is well established that skeletal muscle ischemia followed by reperfusion induces oxidative damage, metabolic stress, and an inflammatory response. This ischemia-reperfusion injury has been studied extensively in experimental models and, importantly, in the clinical setting where it is associated with tourniquet (TQ) inflation during orthopedic trauma surgery. Of particular clinical concern is the notion that reperfusion upon TQ release is central to oxidative injury, since release necessarily follows surgery. Consequently, the effects of ischemia alone, without reperfusion, is poorly documented. That is, it remains unknown what are the effects of muscle ischemia, per se, on muscle properties that could influence functional recovery postoperatively or what preventative measures might be taken to minimize the potentially deleterious effects of the ischemic period alone. Hence the purpose of this study was to investigate changes in myofibrillar contractile protein oxidation over the course of TQ-induced leg muscle ischemia during orthopedic trauma surgery.

Method: Among patients with unilateral ankle fractures requiring surgery at our institution, 24 subjects gave informed consent to participate. All subjects underwent standard general anesthesia. PRE surgical biopsies were collected from the peroneus tertius muscle (PT) immediately after TQ inflation and incision of the skin and underlying connective tissue. POST surgical biopsies were collected from the same muscle immediately before TQ release. Oxidation of PT myosin, actin, and total protein was quantified using Western blot analysis for 4-hydroxynonenal (4-HNE) modified proteins. Results are reported as mean ± standard deviation.

Results: Total TQ time ranged from about 21 to 84 min (50.5±16). As anticipated, in PRE biopsies compared to POST biopsies there were large increases in the PT content of 4-NE modified myosin (174.4±128%; P< 1×10-6), actin (223.7±182%; P< 5×10-9), and total protein (567.5±378%; P< 5×10-7). Intriguingly, there was a much greater increase in PT protein oxidation in males than in females (43.3% difference; P< 0.05), although there was no relationship observed between PT protein oxidation and subject age. Surprisingly, there was no significant relationship between muscle protein oxidation and duration of the TQ-induced ischemia.

Conclusion: TQ-induced skeletal muscle ischemia for 21 to 84 min during orthopedic trauma surgery leads to considerable oxidative muscle injury as measured by muscle protein oxidation, including of the functionally relevant contractile proteins myosin and actin. This injury occurs even without reperfusion. Interestingly, the extent of oxidative muscle injury appears to be influenced by gender, but is not dependent upon the duration of ischemia.

FUNDING: MSFHR, COF, BCLA.