Transcapillary forces in patients with lower limb ischemia.

Starling pressures (interstitial fluid pressure, plasma and interstitial fluid colloid osmotic pressures) were measured in subcutaneous tissue at the ankle in 20 healthy controls and 27 patients with lower limb atherosclerosis. Subcutaneous interstitial fluid pressure (Pif) of the leg was also measured in seven patients with arterial emboli of the lower limb. Interstitial fluid was collected by implantation of nylon wicks and Pif was measured by the 'wick-in-needle', technique. The calculated reabsorption pressure (equal to capillary pressure if no net filtration occurs) was 18.3 mmHg in the group with atherosclerosis, which was higher than in controls (15.8 mmHg, P less than 0.05). Colloid osmotic pressure of interstitial fluid (COPif) was significantly lower in patients with atherosclerosis than in controls (5.9 v. 9.2 mmHg). This finding in itself could make those patients more susceptible to edema formation postoperatively. On the other hand, there was no correlation between COPif and ankle systolic blood pressure within the group of patients. There was a slight, but statistically significant positive correlation between ankle systolic blood pressure and Pif in patients with lower limb atherosclerosis although mean Pif was not different from controls (-1.0 v. -0.8 mmHg). In patients with arterial emboli, however, Pif was lower (mean -4.5 mmHg).