Transcapillary forces in muscle compartments of lower limbs with deep venous thrombosis

Abstract

Interstitial fluid pressure (P_if), plasma- and interstitial fluid colloid osmotic pressures (COP_pl, COP_it) were measured in muscle compartments of the calf in lower limbs of patients with deep venous thrombosis (DVT) and in contralateral limbs.

P_if was measured with the ‘wick-in-needle’ technique in the anterior and deep posterior compartments in three periods of time following start of treatment for DVT. The first period was from 0-24 h, the second from 24-48 h and the third later than 48 h.

We found a significant increase in both muscular compartments in legs with DVT compared to the contralateral in the three periods except for P_if in the anterior compartment in the third period. A significant reduction of P_it in both muscular compartments of limbs with DVT was found when comparing the first and second periods but not from the second to the third period. No difference was found in P_if in the muscular compartments of the contralateral limbs between the three periods.

Interstitial fluid for COP_if measurements was obtained by inserting intravenous cannulas in the deep posterior muscle compartment of the calf of limbs with DVT and contralateral limbs. In oedematous tissue it was possible to collect some fluid, but this was almost impossible in the non-oedematous tissues of the contralateral limbs. COP_it was 4.2(2.4) mmHg (mean(SD)) in the deep posterior compartment of limbs with DVT, which is probably significantly reduced.

Increased P_it and reduced COP_if indicate increased transcapillary fluid filtration and reduced reabsorption as the main cause of oedema in muscular compartments in DVT of the lower limbs. The increase in P_if was greater than the fall in COP_it leaving P_if as the more important factor in limiting further development of oedema. However, P_if increase may be partly caused by vascular distention secondary to raised venous pressure (P_v) and/or swelling of muscle rather than increase in interstitial fluid volume (IFV).

The use of elastic stockings increases P_if and will probably help to reduce oedema in limbs with DVT. Caution must be taken that P_if is not dangerously elevated (>30 mmHg), as compartment syndromes may result and cause ischaemic tissue damage. Elevation of the limb with DVT will lower capillary hydrostatic pressure (P_c) and reduce transcapillary filtration and oedema formation.

Key Words:

• transcapillary filtration
• colloid osmotic pressure
• interstitial fluid pressure
• wick-in-needle technique