Thursday, June 19, 2008

The basics of oxygen therapy: part 2

(This is part 2 of an ongoing series, to view the rest click here)

There are a few exceptions to this rule I'm about to state, but for the most part, no patient admitted to the hospital should ever be ordered on a specific oxygen device at a specific FiO2 or a specific liter flow.

Personally, with the exception of the exceptions I will list in a moment, the amount of oxygen a patient receives should be based on the patients sat, otherwise known as the SpO2.

This is why I love it when doctors order oxygen per protocol, because both our oxygen and ventilator protocols call to maintain an SpO2 of 92% unless otherwise specified.

We must realize that as a patient ages, or a chronic illness progresses, his or her normal resting SpO2 drops. This is especially true as an aging person sleeps. If I had a dollar for every time I was called to an elderly person's bedside because his or her sat was 88-89% while the patient was sleeping, I'd be rich.

To me, that's an exception to my rule. I see no reason to provide supplemental oxygen to these patients, unless they show complications. The same thing is true with a chronic CO2 retainer. If he or she is maintaining an SpO2 of 88-90% and shows no complications, then leave that patient alone.

Three more exceptions: the anemic patient, carbon monoxide toxicity, and the cardiac patient. For these patients, you probably want to maintain an SpO2 of 98%. Otherwise, 92% should be the target SpO2.

That should be plenty of oxygen to maintain a PO2 of greater than 60, and thus prevent hypoxemia, or too low oxygen level to the blood supply which causes the heart to be overworked in normal patients.

So, basically, if a doctor orders a 40% ventimask because the patient's sat was 88% on 3LPM, you should question the order. What if the sat is 100% on 40%. Then why can't you decrease the oxygen to 30%, or even 28%, or even lower if that maintains the required SpO2?

Why keep someone on a nonrebreather for two days with a sat of 100%, when you could just as easily get by with a 50% ventimask to maintain the sat.

See what I mean. The RT should always have the opportunity to lower the oxygen to maintain that sat.

He should also have the opportunity to increase the oxygen should that be required. Now, if I had to increase oxygen from 2LPM to 4LPM no big deal. But if the oxygen now required is 50% instead of the 2LPM the patient was on, then I'd sure be calling the doctor so he knows that something is changing with this patient.

However, as it stands where I work, we can go down on oxygen without an order, but we cannot go up over the original order. But, if I had my way, I'd add the above paragraph into our protocol.

A ventimask should be ordered in only two situations: 1) if the nasal cannula just isn't quite cutting it, but a partial rebreather isn't needed 2) the patient has a normal SpO2, but has an irregular respiratory rate. A ventimask will guarantee that FiO2 of 24-50% regardless of the patients minute ventilation.

One rule of thumb for a ventimask: to maintain the desired FiO2, you have to dial in the recommended liter flow. It usually goes something like this: 24% and 26% = 3LPM, 28% and 30% = 6LPM, 35% = 9LPM, 40% = 12LPM, and 50% = 15LPM.

If you set the mask to 50% and you do not at least set the flow at 15, the patient will not be getting 50% FiO2, and he may be retaining CO2. We don't want that. However, it is okay to go over the recommended liter flow.

If a patient is so bad off that a ventimask isn't working, then order a non-rebreather (NRB). However, don't assume a NRB delivers 100% Fio2, because it doesn't. It only provides about 75% FiO2. So don't call it a 100% NRB. With both flaps on it would deliver 100%, but since by law one of the flaps has to be removed, it only delivers 75%.

If a patient still needs more oxygen on an NRB, then turn that flowmeter to flush. If that still don't work (and perhaps even if it does work) you may want to consider CPAP, BiPAP or the more invasive ventilator.

If that sat on 75%FiO2 is 96%, then take off the other flap and turn the NRB into a partial rebreather (PRB). Now you are giving the patient about 60% FiO2. But certainly don't keep it there if a 50% ventimask would suffice to maintain that 92% sat.

Why all this complicity about oxygen? Because oxygen is a drug, and it can cause complications. Not only that, but it costs money to have patients on oxygen when they don't need it.

And this includes post-operative patients. Let's not be putting patients on 2LPM just because they had surgery. If the sat is 92%, lets cut them off.

So, technically speaking, and with the exception of the exceptions stated above, liter flow and FiO2 really don't matter so long as you are maintaining the recommended SpO2.

Regardless, doctors often have exceptions of their own, and we RTs do what we are ordered to do. But that doesn't mean we can't question an order, or push for changes that might benefit the patient.

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