**6.3 Testing the proposals for rational mechanical prophylaxis**

Preferably, these proposals would require further animal testing before clinical deployment. Perhaps the original experimental design created and used by Hamer & Malone (1984) would suffice as a basis.

Three matched groups of anaesthetised animals would be required initially, each to be subjected to prolonged non-pulsatile blood flow in the leg veins, with brief alternating pulsatile episodes: (a) controls, untreated; (b) given standard anticoagulant prophylaxis; (c) given mechanical prophylaxis by one or other of the methods proposed in section 6.2. At the end of the experiment, valves from deep limb veins would be examined microscopically. The VCH prediction would be that group (a) will show the formation of quasiautochthonous thrombi; group (b) might show incipient thrombi on the parietalis endothelia; and group (c) will show normal endothelia with no incipient thrombi.

Positive results might suggest that a randomised controlled clinical trial of one or both of the approaches outlined in section 6.2 should be undertaken. At the same time, this experimental set-up could provide a means for testing the efficacy of anticoagulants in absolute terms; for the past 50 years, anticoagulant prophylaxis has been evaluated only by statistical evidence, without the use of such a 'measuring rod'.

Pathophysiology and Clinical Aspects of 150 Venous Thromboembolism in Neonates, Renal Disease and Cancer Patients

anticoagulants 'in case' he/she develops DVT might be seen as akin to dosing such patient

That is an extreme view. Nevertheless, the balance between the anticoagulant and mechanical approaches to prophylaxis needs to be re-evaluated in the light of the VCH thesis, since they seem likely in time to perfect a more impartial 'cross-party' view of the

The simple objective of mechanical prophylaxis is to ensure that blood in the valve pockets is exchanged at regular intervals (Malone & Agutter, 2008). Modern surgical prophylaxis could readily be improved if the VCH principle were added to the classical objective: 'regular' (i.e. regular intermittent) pulsation need not necessarily mean '*as frequent as is current practice*'. In chapter 9 of our monograph we calculated that valve pocket hypoxaemia does not become dangerous (i.e. potentially injurious) until non-pulsatile flow has persisted for 1.5-3 hours, an estimate consistent with the empirical data (Hamer *et al.*, 1981). Less frequent, i.e. *relatively infrequent*, artificial pulses (perhaps once per hour, though that would need experiential confirmation) would preclude thrombogenesis, and would be more comfortable for patients than what must seem incessant limb compression at short intervals,

For patients confined to prolonged bed-rest, insensible, automatic alternate end-to-end Trendelenberg/ anti-Trendelenberg tilting of the bed, through a 5-10 degree angle, every hour or so, should be prophylactic by emptying the valve pockets in the upper and lower parts of the body by gravity, allowing them to refill passively with fresh venous blood at relatively short intervals (as above) and preventing unsuspected but potentially fatal

Preferably, these proposals would require further animal testing before clinical deployment. Perhaps the original experimental design created and used by Hamer & Malone (1984)

Three matched groups of anaesthetised animals would be required initially, each to be subjected to prolonged non-pulsatile blood flow in the leg veins, with brief alternating pulsatile episodes: (a) controls, untreated; (b) given standard anticoagulant prophylaxis; (c) given mechanical prophylaxis by one or other of the methods proposed in section 6.2. At the end of the experiment, valves from deep limb veins would be examined microscopically. The VCH prediction would be that group (a) will show the formation of quasiautochthonous thrombi; group (b) might show incipient thrombi on the parietalis

Positive results might suggest that a randomised controlled clinical trial of one or both of the approaches outlined in section 6.2 should be undertaken. At the same time, this experimental set-up could provide a means for testing the efficacy of anticoagulants in absolute terms; for the past 50 years, anticoagulant prophylaxis has been evaluated only by

endothelia; and group (c) will show normal endothelia with no incipient thrombi.

with chemotherapeutic drugs 'in case' he/she develops a cancer.

**6.3 Testing the proposals for rational mechanical prophylaxis** 

statistical evidence, without the use of such a 'measuring rod'.

aetiology of DVT and of patient management.

day and night.

hypoxaemia in unmoved pockets.

would suffice as a basis.

**6.2 Mechanical prophylaxis: a rational approach** 
