Usually, ICP elevation more than 30 mm Hg is an indication for fasciotomy.

However, 3 or more degree circumferential burns may need longitudinal escharotomy of affected limb (or chest) before the reaching of the ICP pressure. In this cases, escharotomy is a prophylactic of the circular strangulation and release of pressure as well. It's may be fasciotomy needed if ICP pressure dynamically elevated to 30 mm Hg.

Most Reliable and available device is " hand made" (manometer, arterial line transducer and Venflon). Modern  system as Stryker Intracompartmental Pressure Monitor Systemin may be used. 

For practical purposes, examination findings are more relevant than direct pressure testing and timing is also vitally important.  Deep, circumferential burns would usually mandate escharotomy (we use 2 longitudinal, bi-vlving incisions).  However, if you see the patient early, before significant IV resus fluid volumes have been administered, then the part may feel soft and not at risk.  The problem comes after a few hours of resus fluids, when that fluid floods out of the capilliaries into the interstitium.  If you are going to measure compartment pressures, then continuous, or repeat measurements would be necessary, as an initial normal reading doesn't tell you how the limb will be in a few hours' time.  If the pressure increases over 15mmHg (capilliary pressure), then capillary blood flow in the compartment will stop.  Values over 30-35mmHg indicate probable venous occlusion.

With the help of YOUR clinical expertise and experience, if you think "compartment syndrome" is the case; perform FASCIOTOMY/FASCIOTOMIES" without delay. Measuring intra-compartmental pressure is only academic and im-practical.

The stryker system is reasonably reliable, but should not preclude clinical evaluation.  As indicated, if there is any concern with regard to perfusion a fasciotomy is indicated.  The threshold for an escharotomy should be even lower.  Releasing the tight, necrotic burn tissue has relatively little risk.  That tissue will be excised and grafted in the future.  There are potential risks with regard to fasciotomy, but the risk of limb loss is greater than those.  In many burn patients escharotomy will be sufficient to improve perfusion and at least in my experience fasciotomies are not frequently needed in burn patients unless there is a concomitant crush injury or prolonged ischemia secondary to unreleased circumferential eschar.

if the value of the difference between diastolic blood pressure and actual compartment pressure is less than 30 it becomes critical. Clinically the  early sign  for critical tissue oxygenation is loss of tactile sensation

AS mentioned by others,the diagnosis of acute compartmental syndrome is based on high index of suspicion & clinical signs ( 6 Ps: Pain,Puffiness,Pallor,Parasthesia,Pulselessness & Paralysis ).Recording the compartmental pressure is an adjunct,but not a substitute to history & clinical examination.However,it may be useful in unconscious patients or where the diagnosis becomes doubtful with equivocal clinical findings.The cut off value of the pressure for diagnosis is well stated by Kornelia Bohler.

Very good points made by our colleagues, so far. I'd emphasize the importance of serial examinations, if in doubt and, particularly, when there is strong consideration for prophylactic intervention. 

Also, remember that 'the 6 Ps' have varying degrees of clinical significance; for example, pulselessness is a very late sign, by which time, a lot of ischaemic injury may have resulted. 'Pain on passive movements' and impaired sensation are one of the earlier signs, however. 

I advise colleagues to, where possible, clearly consent patients (and document) with regard to aesthetic implications consequential to the procedure.

in burn the decision should be taken wether to perform escheratomy ,is clinical.

sometimes 2nd degree burn need escheratomy , due to pressure overload, sever edema.

Sometimes, unburned anatomical sites may need fasciotomies, generally IV fluid overload.

well a device to measure intra-compartment pressure is not always within convenient reach and you can't always fashion a Whitesides device whenever you suspect a compartment syndrome. You can call it a gut feeling but as a physician, I really have a short fuse on ordering a fasciotomy; if I take a moment to think to myself "Should I do a fasciotomy on this one?", then I just go ahead and do it; especially if the limb is painful in passive motion of the joints. 

Escharotomies in children with circumfrential burns are a clinical judgement call in my practice, and there is no substitute for experience in this situation. In my experience fasciotomies are rarely required outside high voltage electrical burns, crush injuries and fluid overload.

There is some evidence from Germany that the early use of circumfrential negative pressure wound therapy may limit oedema and decrease the need for escharotomies, however this needs to be studied further.

Thanks to all those who share their experience. From this discussion I conclude that what we are doing is being done in other parts of the world. Instead to rely upon clinical feature (sign/symptom), pressure monitoring device;  we solely rely upon clinical assessment and judgement. Once a thought arise "Fasiotomy Needed" , we always do it accepting morbidity of the procedure over limb loss. 

or ischemic contracture... saving the limb is not much to be bragged about if you end up with an ischemic contracture which renders it practically useless!...

In addition to the excellent comments above I would like to add that the TBSA size of the burn injury which drives the amount of fluid used for resuscitation should be a variable in the decision making process. A circumferential burn with a small overall injury and lower volume resuscitation will not have the same effect as the same burn in a patient with a large TBSA burn. Usually burns less than 15% TBSA do not require significant IV fluid administration and with limb elevation and observation the patient may not need and escharotomy. I would have a lower threshold for action in a crush injury or electrical injury...