COVID takes our breath away
Most of what I've seen in the popular press about a severe COVID infection is about how we deal with this as a respiratory disease. Indeed, the name SARS-CoV-2 means severe acute respiratory syndrome coronavirus 2 (SARS-CoV-1 is what we think of as the genetically similar SARS from the 2003 outbreak). COVID-19 just means coronavirus disease from 2019.
The most worrisome pulmonary manifestation of COVID is something called acute respiratory distress syndrome, or ARDS. ARDS is a medical term that basically refers to fluid buildup in the lungs that isn't caused by congestive heart failure. Because ARDS fills the lung with fluids instead of gas, this causes difficulty in gas exchange, the process by which oxygen from the air gets swapped in the lungs for carbon dioxide, allowing oxygen to get to your body's tissues and for carbon dioxide to be exhaled.
But before you develop full-blown ARDS, most people have disease manifestations that come on much earlier. There's a typical pattern that many patients with the disease will have (at least those who are sick enough to come into contact with the medical system) - cough, fever, anosmia (loss of sense of smell, which Michael Lewis wrote about in Bloomberg), along with some GI symptoms, and general weakness/malaise. The exact order that these come on is variable, and there's a big proportion of people who don't seem to have any major symptoms at all.
The current thought is that around 10-20% of COVID patients develop any kind of pneumonia, and only a small proportion of these patients develop true ARDS. The prevalence seems to be vary with geography as well as someone's comorbidities (read: other non-COVID medical problems), but the data are spotty and I'm not sure that we can draw true conclusions about these numbers yet, especially given our difficulties in testing.
After you test positive for COVID, the major criteria to admit you to the hospital is the need for extra oxygen because your blood oxygen levels are low.
We measure two different types of blood oxygen levels, the percent of hemoglobin (your body's major oxygen carrying protein) that is bound to oxygen - this is the oxygen saturation - and the amount of free floating oxygen dissolved in the blood. Since hemoglobin carries about 1000-fold more oxygen than is dissolved in blood, we generally just care about your oxygen saturation (the number on a pulse oximeter, or pulse ox), which is a percentage from 0-100%. The free floating oxygen is really only considered when someone is on a ventilator or supplemental oxygen and you're thinking about making adjustments to their oxygen treatment. Most people live at a level of 98-100%, and we don't start oxygen treatment on most patients with chronic lung or heart disease until their level drop below 90%.
So if your oxygen saturation is below 90% or so, you're going to get supplemental oxygen. The need for supplemental oxygen is what keeps people in the hospital. If someone can maintain an oxygen level over 90% without extra oxygen, they're going to be stable to be discharged home with a plan to come back to the hospital if symptoms worsen.
After you're admitted to the hospital with low oxygen levels (medical term: hypoxia), the experience is basically "hurry up and wait." For the majority of patients admitted, you stay in a hospital room and have your oxygen levels monitored while you're getting a small amount of oxygen through a nasal cannula. You get vitals signs (temperature, blood pressure, heart rate, oxygen levels) checked every few hours and bloodwork checked daily, but not much else happens. You're likely not feeling particularly well, but it's otherwise boring and uneventful. Your doctors don't feel like they're able to do very much to make a difference in your course. Most people improve over a few days and are able to be discharged home.
One of the scary things about COVID is that patients can stay in this state of stable sickness for days and days before they decompensate. Pulmonary decompensation occurs when oxygen levels drop and increasing the amount of extra oxygen through a nasal cannula is inadequate to keep their saturation over 88-90%. Normally, we have a couple of other noninvasive tools to use such as a high flow nasal cannula and a noninvasive mask - both of which provide air with pressure to push into your lungs as an extra support tool before getting a breathing tube placed - but in COVID, we're worried about aerosolizing the virus and so we don't generally use these options because it puts providers at higher risk of contacting the disease.
When someone starts decompensating, we try to postpone putting them on a ventilator by having them prone, or lie on their stomach. Here's a picture of a CT scan of the chest that helps visualize why this works. The pictures on top are normal CT images. The ones on the bottom are a patient lying on his/her stomach. The black stuff in the chest is the amount of lung that's able to participate in normal lung function and the darker it is the more available lung there is. You can see how much more is available when someone flips onto the stomach (left side is after expiration, right side after inspiration).
But if you're not able to get oxygen levels up with a nasal cannula and proning, you're going to end up on a ventilator. I'll save my two cents on the ventilator experience for another email, as I think this one is starting to get a bit long.
The ARDS in COVID patients can take weeks to resolve, which means that the time on the ventilator can last for weeks. There are quite a few different parameters we are looking at to evaluate how someone is doing and a whole bunch of other treatments that we're considering during this time. While you're on a ventilator, I almost consider it a race against the clock to see if we can improve your breathing to the point of removing the tube before any other organs fail. What other organ systems can get screwed up in this horrid disease is probably a topic for a different email as well.
Have a great weekend everyone! Probably nothing more from me until next week as I'll be in the ICU again tomorrow