40 - Coagulation part 6 of 7

KYJ40-Series on Coagulation part 6-  the role of calcium.

As a young ICU nurse in a big tertiary hospital more than 20 years ago, we had these blokes (4) who were burned in a caravan fire, all came into our unit.  It was  one of the most interesting (physiology) experiences of my life.  The daily grind of bathing these guys, drug paralysed, sedated and fully ventilated became monotonous and the relentless surgeries, skin harvests and grafts made one wing of our ICU look nothing short of a macabre scene from some horror movie.

Daily these blokes seemed to return from theatre, and the dressing of choice was a product called Kaltostat.  A calcium rich mesh that filled with blood oozing from graft sites, and became a clot.

Two points will be addressed in today's post. The first is the difference between a clot and a thrombus, the second is the role of calcium in this dressing and in the coagulation system in general.

First the Jargon.  Clot vs Thrombus.

When platelets stick to the damaged inside wall of a vessel. This is called Platelet Adhesion.

When platelets stick to each other like a snow flakes in a snow ball, this is called Platelet Aggregation.

When platelets release substances to signal new tissue to grow eg- (Platelet Derived Growth Factor (PDGF)), or to signal other platelets to come (Thromboxane A2, ADP), or to initiate the coagulation cascade (PGI and calcium, factor V and VIII).  This is all collectively called Platelet activation.

All these processes (adhesion, aggregation and activation) occur in the intravascular space. Ultimately this leads to a plug of solid matter at the site of vessel injury.  This is called a thrombus.

When a thrombus breaks away from its attachment on a vessel wall and travels in the blood stream, it is called an embolus or embolism.

A clot is a thrombus, but outside the  blood vessel.
A scab is a dehydrated or dried clot- usually over an external wound.  The active mushy slough at the base of the scab and the wound bed is often active platelets, releasing PDGF stimulating the growth of new granulation tissue .

Now let's focus on Calcium.
Fundamentally a positively charged ion (cation) abbreviated to Ca++ .

Calcium is present in plasma, and interstitial fluid, but also specialised granules inside platelets called Delta granules.  When a platelet is activated it releases the contents of its Delta granules which among other chemicals, includes Calcium onto its surface and into the surrounding plasma.

Factoid: sleeping (dormant) plasma coagulation factors like 7,9,10 and prothrombin(F2), are all negatively charged proteins. They therefore readily accept a positive charged particle to bind with. Calcium does this.
It is like the glue that makes factor 7 activate Factor 10.
It is the glue that activates 9 to 9a, and the glue that activates 10 to 10a, and the glue which converts (2) prothrombin into (2a) thrombin.

In a simplified way, think of calcium a positively electrically charged particle that "electrically" flicks a switch to start these protein chemical reactions.

Now back to my burns patient covered in calcium rich impregnated gauze mesh; do you appreciate Kaltostat and products like it a little more?