‘Blood is the argument’: The Pathophysiology of Shock
Shock is the general response of the body to inadequate tissue perfusion and oxygenation. This simple statement encompasses a complex pathophysiological process. If progressive and uncorrected, this process will lead to cell death, organ failure and the death of the casualty.1
IN ORDER TO STAY ALIVE, a person needs to breathe every few seconds. Oxygen gives every cell in our bodies the ability to generate energy necessary for life to be sustained. Breathing carries oxygen down into the lungs, where it is infused through the finest membranes in the human body into red blood cells that then circulate from head to toes. This is oxygenated blood, and when a person is wounded, its loss will determine whether they start to heal or, in the case of such extreme forces as blast, start to die. Everyone knows that a human being will die if they lose too much blood. This is why.
Blast blows holes in the body that bleed profusely, catastrophically, oxygenated blood draining out and around them, or inside the body’s own cavities without a drop spilling on the floor – going everywhere except where blood needs to be. One of the simplest ways to see if this is happening after injury is by compressing a fingernail. If the colour fails to return after two seconds (the length of time it takes to say ‘capillary refill’), then circulation is compromised. However, the test may not be effective if it takes place in freezing darkness or blinding sunshine, where the fingernail may be caked in dirt and gore because its owner may have clutched their hand to their wound in an effort to stem the tide of blood, because they are shocked beyond rational action, because they cannot see, because they are shivering uncontrollably from hypothermia as their body temperature falls rapidly as its warm energy from oxygenated blood drains away. Shock is the condition a body finds itself in when it can no longer draw on the oxygen in its blood, when it is entering the state that will lead to absolute physiological abnormality.
Initially the body tries automatically to reseal itself after blood loss by clotting. If this doesn’t work, because it is not possible to clot on the scale required to remedy the damage from blast injury, then the body prioritises its remaining blood and oxygen resources. It shunts what blood it can to the brain and the heart, effectively abandoning other organs, such as the liver and kidneys. Once the body has lost a third of its oxygenated blood, the signs of shock can be clearly seen, but once it can be seen – grey, pale, chilly, cold skin, flattened veins – it is already approaching too late, so in Afghanistan its presence was always assumed in a wounded soldier. In the meantime, the heart races to keep what blood remains moving: human systems are designed to cling on to diminishing fragments of life, obstinately refusing to let go, except that the mechanisms that have evolved to do this can only do so much, and life starts to slip away anyway. Not slipping now, a cascade, surging through the body, smashing anything in its way. Acid from failing organs floods into the system, breaking down the finest capillary walls, so even more blood bursts out. Less blood, less clotting, less oxygen, less energy to breathe in oxygen, more cold, less clotting, less blood – the cascade stronger, faster, deadlier. Other mechanisms designed to save life begin to collapse. Inflammatory mechanisms and the entire immune system go into free fall. Respiratory distress (no more breathing), no more oxygen, almost nothing left to hold on to, life drawing closer to point zero.