system
Given the following post, respond as if you're commenting on Reddit:
human
Why major human body organs like kidneys and heart weaken or stop functioning in COVID patients?

I heard that when the virus enters the body it causes septicemia(bloodstream infection) which damages the organs.
gpt
Nurse here, spent the past 12 months working in Covid ICUs.

The primary mechanism of organ damage is NOT direct viral damage from virus being spread through the blood as you mention in your post, but a lack of oxygen to the organs from a terrible combination of several different things that all cause a lack of oxygen by themselves, and when combined cause a severe enough lack of oxygen to the major organs to damage them beyond repair.

  
The first and most obvious mechanism is lack of oxygenation from the lungs. What laypeople might not understand is that we don't only put people on ventilators because their lungs are full of fluid, mucus, etc. We often put people on ventilators because their respiratory muscles are literally too tired to keep breathing. The ventilator does the breathing for them, so those muscles can get some rest. Ventilators are pretty effective for this.

  
With Covid though, you can have a situation where someone is on the ventilator, but their lung tissue is literally too damaged by the virus itself to be working properly. So despite being ventilated, they are still not getting enough oxygen. Clearly, this low oxygen can damage other organs and is a major problem. (We can try to mitigate this problem with things like turning the person over to lay on their stomach, which exposes a great surface area on the backs of the lungs to the oxygen being pumped in by the ventilator or by putting the person on a full heart-lung bypass machine called Extra-Corporeal Membrane Oxygenation or ECMO, but these things come with their own set of complications and are not easy, guaranteed solutions.)

The second thing related to damaged lung tissue is the failure to remove CO2 from the blood. Dissolved CO2 in the blood causes the blood to become acidic (called "respiratory acidosis"). Acidic blood and acidic body tissues do not function very well. Body proteins (enzymes, etc.) don't work in a high-acid environment.

Adding to the acid problem is the fact that in the absence of sufficient oxygen, your body cells resort to an alternative method of producing energy called lactic acid fermentation. Obviously the buildup of lactic acid further exacerbates the problems caused by bad pH levels. This acidosis itself can cause organ damage and organ failure on top of the organ damage from lack of oxygen.

Acidosis can also contribute to low blood pressure, although primarily the cause of the severely low blood pressure that we see in Covid is a medical condition known as sepsis. Sepsis is not quite the same as septicemia as you mentioned in your post. Sepsis is a medical condition of wildly out-of-whack immune responses, the precise mechanisms of which are very complicated and not 100% understood. The results of sepsis are tachycardia, tachypnea, both of which can just tire a person's body, but the real killer in sepsis is profoundly low blood pressure.

Low blood pressure *again* exacerbates the problem of lack of oxygen to the major organs. Not enough blood flow means that even if the blood had enough oxygen in the first place, that oxygen isn't flowing into the organs like it should, so that oxygen isn't getting to where it's needed.

All of the above mechanisms *are not unique to Covid.* These processes can occur in any situation where a person's lungs are not working properly (things like Acute Respiratory Distress Syndrome or ARDS), although they are much much worse in severe Covid just due to the sheer amount of damage to the lungs. And the sepsis reaction in Covid is profoundly worse than what we see in other infections for reasons we don't understand yet - complete speculation might be because this virus is completely new to our entire species? maybe because Covid has direct effects on the immune system? We don't know for sure yet.

But we do know that if we treat people with immune suppressants (steroids specifically) about a week into a Covid infection, they are less likely to develop the severe kind of sepsis that causes people with Covid to die. It's possible that this immune system dysregulation itself is causing some damage to major organs in ways we don't fully understand yet.

Additionally, ON TOP OF the above problems, Covid also directly causes blood clotting through mechanisms that we don't entirely understand. Kidneys in particular are extraordinarily sensitive to even microscopic blood clots, and this is thought to be one way that Covid causes kidney damage. Again, blood clots block blood flow, which prevents delivery of oxygen to the organs even if there is enough oxygen in the blood.