BiPAP refers to Bilevel or two-level Positive Airway Pressure

TUBING AND VENTILATING

CPAP and BiPAP

In our last blog we talked about ventilators, how they work and why they are needed. We already know that we do not have enough ventilators to support patients with serious symptoms. But you may have heard of other machines in the news called CPAP and BiPAP. Hospitals are using them for COVID patients, companies are acquiring and donating them at a time when ventilators are worth their weight in gold. Will they do the same job? Lets find out.

TUBING AND VENTILATING

In the previous blog we discussed the basics of ventilation. We explained that sometimes patients require a tube to be placed into the unconscious patients windpipe through their mouth by an experienced anaesthetist. This tube is then attached to a ventilator that pushes air into the patients lungs and does the effort of breathing for them. This procedure is known as intubation and ventilation and it is invasive.

Patients require intubation if they are unconscious, if they cannot breathe by themselves or if their lung function is so severely affected they cannot oxygenate their blood enough. If the patient is conscious they will need to be anesthetised and put to sleep to tolerate having a tube in their windpipe. Anaesthetising a patient is a specialist procedure with its own risks, and requires monitoring and support only available in intensive care facilities. Due to these risks not all patients who are intubated can be successfully woken up — this is especially true for the very sickest of patients. This is why intensive care phsyicians are very selective in deciding who receives invasive ventilation.

CPAP AND BIPAP

Sometimes patients will have respiratory problems that affect their airway and breathing, but is not serious enough to require them to be put to sleep. This includes Obstructive Sleep Apnoea, a condition where the squishy tube like airways collapse when sleeping, reducing airflow so much that it can cause the patient to gasp and wake up. This leads to very poor sleep and a constant feeling of tiredness and poor cognitive function. It is very common in overweight and obese patients.

In these cases additional breathing support can be provided by a CPAP (continuous positive airway pressure) machine. Without going too much into complicated respiratory physiology, a CPAP machine keeps the patients airway open by continuously forcing air into the lungs. This is done at a pressure that’s low enough to let the patient breathe in and out by themselves. To do this a tight mask is required to create a seal and prevent air leak.

In severe respiratory disease when a patient cannot breathe in enough air a BiPAP machine may be required. The principles are similar to CPAP, with air continuously forced in to provide support to the airway and prevent collapse. However when the patient breathes in, the machine helps push more air into their lungs. In this way it is similar to a ventilator, but the patient remains awake, breathes for themselves and does not have a tube inserted in their windpipe. BiPAP is also referred to as NON INVASIVE VENTILATION (NIV), and it is an option that far more patients can receive.

REPLACEMENT FOR VENTILATORS?

Having suffered through that lesson in respiratory physiology, why do we care about CPAP and BIPAP? The key is in the name — NON INVASIVE VENTILATION. In moderate to severe cases COVID can severely affect a patients ability to breathe (discussed in the previous blog). Hospitals around the world are running short of ventilators. So can we use NIV to ventilate the patients instead? They don’t require a tube, they don’t need to be put to sleep, so they can be taken care of on a regular ward by medical specialists. It sounds like the perfect solution to the problem.

If you have been reading these blogs you should know by now there is never a perfect solution. This is no exception.

1. AEROSOLS

The first problem with CPAP and BiPAP is that it is an aerosol generating procedure, whereas intubation and ventilation is not.

Coronavirus spreads by attaching to tiny droplets of water and moisture (called aerosols) generated by coughing and sneezing. Aerosols can be blocked by sneezing into a handkerchief, and masks can prevent a person from breathing in aerosols with coronavirus. Putting a COVID patient on BIPAP converts them into a coronavirus factory that can spread COVID to the other patients and medical staff on the ward. If adequate measures are not taken to isolate the patient and to give staff protective gear, it can increase the patient load for the hospital and make a bad situation worse.

2. PLUMBING

Another problem is that CPAP and BiPAP draw huge amounts of high-pressure oxygen for their use, usually from outlets in the wall. A simple analogy is comparing the piping and outlets to water taps. If only one person is using a tap in a house, the water pressure remains strong. However if everyone starts using every single tap, shower, toilet flush, dishwasher and washing machine at the same time, the plumbing cannot cope and water pressure drops. This will lead to poor shower, unwashed clothes etc.

Usually in a hospital very few patients need high pressure oxygen or ventilation, and the plumbing is not designed to support every single patient on high pressure oxygen. There are fears placing large number of patients on CPAP and BiPAP will deplete the hospitals oxygen supply. Some hospitals have already reported such issues, and are planning to ration the high flow oxygen for patients who need it most.

3. DO THEY EVEN WORK?

Finally we don’t know if CPAP and BiPAP will have a beneficial effect to patients, or whether the increased pressure in the lungs leads to more problems or worsens the symptoms of COVID. This is an issue that can only be solved with more data, so it is not worth speculating.

DOES ANYTHING WORK?

Why have I written this blog, if CPAP and BiPAP have so many problems? Despite the issues we have discussed, the Faculty of Intensive Care Medicine have written an open letter that states “it is now clearer that CPAP may be of benefit to patients earlier on in the disease process than first thought and may prevent deterioration of some patients to the extent of them not going on to need invasive ventilation.”

Beyond this there very little published evidence on CPAP and BiPAP. Anecdotal evidence from doctors is not particularly helpful (read our blog on hydroxychloroquine for more info). So it seems we will have to wait until more evidence is available.

So what should you take away from this? Yes we do have a shortage of ventilators. Yes lots of patients are going to need ventilation. Will NIV help? Possibly. Despite its shortcomings, BiPAP might be helpful in patients that need support but cannot be intubated, thereby ensuring the survival of more COVID patients. We will have to wait and see.

Dr Rajan Choudhary, UK, Chief Product Officer, Second Medic Inc

www.secondmedic.com