A delta P (diastolic blood pressure minus compartment pressure measurement)of < 30 mmHg is an indication for fasciotomies with the caveat that the diastolic pressure is measured either pre- or postoperatively.
Given the poor outcomes associated with missed compartment syndromes, it is important to obtain both clinical and objective data when determining if a patient needs fasciotomies. Determining if a patient needs fasciotomies in the operating room while a patient is under anesthesia is complicated by the fact that obtaining a clinical exam is impossible, and that the diastolic blood pressure may be falsely decreased compared to normal pre- or postoperative measurements. Currently, it is recommended that intraoperative compartment pressures be compared to preoperative diastolic blood pressures, with delta p < 30 indicating the need for fasciotomies.
Kakar et al. review the preoperative, intraoperative, and postoperative diastolic blood pressure (DBP) in 242 patients with a tibia fracture treated operatively. They found the mean DBP was 18 points lower in the operating room compared to the preoperative measurement. In addition, they found the difference between preoperative and postoperative diastolic blood pressures to be within 2 points, indicating the decrease seen intraoperatively is likely a spurious value induced by anesthetic.
McQueen and Court-Brown prospectively review 116 patients with tibia fractures that had continuous monitoring of their anterior compartment for 24 hours. They found that using an absolute pressure of 30 mmHg would have resulted in 50 patients (43%) treated with unnecessary fasciotomies. They conclude using a differential pressure of 30 mmHg is a more reliable indicator of compartment syndrome.
Answer 2: a delta p of 35 is not an indication for fasciotomies in the setting of a benign clinical exam.
Answer 3: a delta p of 25 when calculated with the intraoperative diastolic blood pressure is not an indication for fasciotomies. This value should be obtained from preoperative diastolic blood pressure measurements.
Answer 4: a delta p of 44 is not an indication for fasciotomies.
Answer 5: mean arterial pressure is not used for calculation of delta p.
Kakar S, Firoozabadi R, McKean J, Tornetta P III. Diastolic blood pressure in patients with tibia fractures under anaesthesia: implications for the diagnosis of compartment syndrome. J Orthop Trauma. 2007 Feb;21(2):99-103.
PMID:17304064 (Link to Abstract)
McQueen MM, Court-Brown CM. Compartment monitoring in tibial fractures. The pressure threshold for decompression. J Bone Joint Surg Br. 1996 Jan;78(1):99-104.
PMID:8898137 (Link to Abstract)