Transcapillary forces in subcutaneous tissue of patients following operation for lower limb atherosclerosis

Colloid osmotic pressure in plasma (COPpl) and in interstitial fluid (COPif) was measured in 18 healthy controls and 38 patients with leg oedema following femoropopliteal arterial reconstruction. Interstitial fluid was collected from nylon wicks which had been implanted subcutaneously for 1 h. Interstitial fluid pressure was measured with the 'wick-in-needle' technique. The patients were examined once in the period 1-16 days after surgery. Twenty-three had oedema at the time of examination. Nearly all recordings of patients with oedema were performed 4-16 days postoperatively. Mean increase in leg volume in patients with oedema was 20%. Mean COPif of the operated extremity were 5.4, 6.8 and 7.5 mmHg in the periods 1-3, 4-7 and 8-16 days after surgery, respectively. These values were lower than in controls (9.3 mmHg, P less than 0.05). Mean COPif in the operated leg was 1.2 mmHg lower than in the contralateral leg of patients without oedema. In patients with moderate oedema (less than 15% leg volume increase) this difference was approximately three times higher. For more extensive oedema the difference declined, and above 20% leg volume increase, COPif of nearly all legs operated on was higher than the contralateral. This probably reflects an increased transcapillary fluid filtration in patients with moderate oedema whereas lymphatic obstruction due to the surgical procedure is the main causative factor in patients with extensive oedema. Compared to the contralateral leg, mean increases in Pif of the leg operated on were 0.6, 2.3 and 3.6 mmHg in the three investigation periods respectively. Pif in operated legs in the two last periods was also higher than in controls (-0.7 mmHg, P less than 0.005). Increased Pif may thus contribute towards limiting oedema formation postoperatively.