Sat., 10/6/12 Femur/Tibial Fx/Knee Injuries, PAPER #76, 8:58 am OTA-2012
NIRS Versus Direct Pressure Monitoring of Acute Compartment Syndrome in a Porcine Model
Curtis J. Cathcart, DVM; Michael S. Shuler, MD; Lt Col Brett A. Freedman, MD;
Lisa R. Reynolds, BS, RVT; Ashley L. Cole, MPH; Thomas E. Whitesides, Jr., MD;
Emily K. Smith, MPH; Steven C. Budsberg, DVM, DAVCS;
University of Georgia, Athens, Georgia, USA
Purpose: Acute compartment syndrome (ACS) can have devastating sequelae if missed or if treatment is delayed. Near-infrared spectroscopy (NIRS) has been proposed for continual, noninvasive monitoring of traumatized extremities. This study sought to correlate NIRS and the tibial intracompartmental perfusion pressure (TIPP) in a porcine model of ACS.
Methods: The study consisted of Landrace swine divided into two groups: control (N = 16) and acute trauma (N = 15). All pigs were maintained on isoflurane with positive pressure ventilation, and supportive care. Pigs were positioned in dorsal recumbency. A median saphenous artery was catheterized for direct arterial pressure management. Each tibia was surgically scrubbed and an NIRS sensor (Nonin) placed over the craniolateral muscle compartment. On the test leg of all pigs, 2 18-gauge needles were centered on each side of the sensor, angled 20° toward the center. Proximal and distal needles were used for 5% albumin infusion to manually elevate tibial intracompartmental pressures (TICP). Cranial and caudal needles were used for direct pressure transducer measurement of TICP by averaging the values. An 18-gauge needle on the lateral aspect of the control leg sensor measured TICP via direct pressure transducer. Continual time synchronized measures of systolic (SAP), diastolic, and mean arterial pressures (MAP); pulse rate; respiratory rate; systemic pulse oximetry; body temperature; TICP; and NIRS from each leg were collected. For the control group, transducers were zeroed and TIPP of the test leg was incrementally increased by albumin infusion. Measurements were taken at baseline for 10 minutes, TIPP = 40, 30, 20, and 10 mmHg for 5 minutes each, TIPP = 0 mmHg for 10 minutes, TIPP equal to MAP for 10 minuntes, SAP for 10 minutes, and SAP + 10 mmHg for 10 minutes. Fasciotomies were then performed and measurements taken for 10 additional minutes. All pigs were euthanized at the end of the experiment. For the acute trauma group, instrumentation was marked and removed from the test leg after the 10-min baseline period. The limb was stabilized and trauma induced by dropping a 2-kg weight 30 times down a 100-cm high cylindrical tube on the craniolateral compartment. Instrumentation was replaced and a 45-min equilibration period observed before the infusion protocol was performed as described above. The contralateral (nontraumatized) leg was used as an internal control. For each group, a repeated-measures analysis of variance model, including factors for group, time, and group by time interaction, tested for differences in TICP, TIPP, and NIRS values. All tests were two-sided with α <0.05 considered significant. Pearson’s correlations were calculated between TICP and NIRS, and TIPP and NIRS.
Results: Both models created consistent, reproducible increases in TICP and decreases in TIPP. Significant increases in TICP between test and control limbs were found at all time points except TIPP = 40 mmHg and 5 and 10 minutes following fasciotomies. NIRS was able to detect significant changes in tissue oxygenation at all the same time points. All TICP of the test leg increased significantly from baseline except for 10 minutes following fasciotomy. Once TIPP reached 20 mmHg, NIRS decreased significantly from baseline and did not return to baseline levels until 5 and 10 minutes after fasciotomies. NIRS was able to detect decreased oxygenation at every TIPP decrease and subsequent increase following fasciotomies. TIPP was significantly different than baseline at all time points until 5 minutes after fasciotomies. Similar TIPP and TICP were observed among nontraumatized and traumatized test limbs, with the exception that traumatized test limb NIRS were significantly lower immediately after the trauma event. Significant negative correlations of TICP and NIRS (trauma: r = 0.70, P <0.0001; controls: r = 0.79, P <0.0001) and positive correlations of TIPP and NIRS (trauma: r = 0.70, P <0.0001; controls: r = 0.80, P <0.0001) were observed.
Conclusion: NIRS provided a reliable, sensitive measure correlating to both an increase and decrease in TICP and TIPP, respectively, in this model. The addition of acute trauma to the model did not alter the correlations of NIRS values with TICP and TIPP. Despite 70 minutes of TIPP that were significantly below baseline, oxygenation returned to normal after fasciotomy, suggesting no permanent muscle damage. Further research is needed to determine at what NIRS reading a fasciotomy may be indicated to prevent permanent tissue damage.
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• The FDA has not cleared this drug and/or medical device for the use described in this presentation (i.e., the drug or medical device is being discussed for an “off label” use). ◆FDA information not available at time of printing. Δ OTA Grant.