Suspension trauma
Synonyms and keywords: Harness Hang Syndrome (HHS)

# Overview
Suspension trauma, also known as Harness Hang Syndrome (HHS) occurs when the human body is held upright without any movement for a period of time. If the person is strapped into a harness or tied to an upright object they amy eventually sustain the Central Ischaemic Response (commonly known as Fainting).  If one faints but remains vertical, one risks death due to one's brain not receiving the oxygen it requires.

# Risk factors
People at risk of suspension trauma include people using industrial harnesses (fall arrest systems, abseiling systems, confined space systems), people using harnesses for sporting purposes (caving, climbing, parachuting, etc), stunt performers, circus performers, and so on.
In normal life, this problem does not occur because when we walk our veins naturally move blood back out of our legs, but when movement is restricted and we are stuck standing still we naturally faint to recover. Ordinarily, falling to the ground after fainting, would have the effect of raising the legs relative to the heart, and consciousness would soon return.
Averting Suspension Trauma is a major part of Cave rescue, Rope rescue and similar fields.  Tests have shown that healthy, rested individuals sitting immobile in standard harnesses will usually lose consciousness after around 6 minutes, and in no more than 10 minutes, and sometimes even as rapidly as 3.5 minutes.  Individuals who are starting out unhealthy, due to exhaustion, injury, hypothermia, and so on, are at a greater risk.  Because of this, if a person is found to be stranded in their harness, immediate action is required.
Symptoms begin with an overall feeling of illness, similar to influenza, excessive sweating, nausea, dizziness and hot flashes. Observers will notice brain function impairment that deteriorates rapidly. As the situation develops, the patient will have difficulty breathing, an elevated heart rate, cardiac arrhythmias, an abrupt increase in blood pressure, followed by unconsciousness, death.
Prevention of Suspension Trauma is preferable to dealing with its consequences. Specific recommendations for individuals doing technical ropework are to avoid exhausting themselves so much that they end up without the energy to keep moving, and making sure everyone in a group is trained in single rope rescue techniques, especially the single rope pickoff, a rather difficult technical maneuver that must be practiced frequently for smooth performance. If someone is stranded in a harness, but is not unconscious or injured, and has something to kick against or stand on (such as a rock ledge or caving leg-loops) it is helpful for them to use their leg muscles by pushing against it every so often, to keep the blood pumping back to the torso. If the person is stranded in midair or is exhausted, then keeping the legs moving can be both beneficial and rather dangerous. On the one hand, exercising the leg muscles will keep the blood returning to the torso, but on the other hand, as the movements become weaker the leg muscles will continue to demand blood yet they will become much less effective at returning it to the body, and the moment the victim ceases moving their legs, the blood will immediately start to pool. "Pedalling an imaginary bicycle" should only be used as a last-ditch effort to prolong consciousness, because as soon as the "pedalling" stops, fainting will shortly follow. If it is impossible to rescue someone immediately, then it is necessary to raise their legs to a sitting position, which can be done with a loop of rigging tape behind the knees or specialized equipment from a rescue kit.
During and after the rescue, it is important not to allow the subject to lie on the ground, as this can cause heart attack and multiple organ failurethey must be kept sitting upright for at least 30 minutes after the rescue, and these instructions must be forced upon any ambulance crew attending the scene. It is imperative to get the patient to a hospital as soon as possible, to avoid life-threatening complications due to reflow syndrome, compartment syndrome, reperfusion injury. These complications may not become obvious for hours or even days after the event, by which time irreparable damage may have occurred.