About Oxygen Equipments, Part 2 Print E-mail



The Initial Continuous Flow Device: The most common connection between you and your oxygen source delivers it continuously though your nose. (First came the mask, fitting over mouth and nose. This is infrequently used now because it is cumbersome and makes speaking difficult.) The nasal cannula is a piece of plastic tubing connected to the oxygen container that ends in two small prongs which rest in your nostrils. The tubing leading to your nostrils rests on your ears. It does away with the mask's difficulties, but some patients find it irritates their ears and/or nose.

But delivering oxygen continuously throughout the respiratory cycle is wasteful. You are paying for a substantial amount of oxygen you never get to use. During exhalation, the extra oxygen joins the stale air leaving your lungs. Oxygen delivered during the second half of inspiration never goes beyond the dead space. Only oxygen taken in during the start of inspiration actually reaches the alveoli to participate in gas exchange. Recognition of this problem has led to alternative solutions. Laboratory studies indicate that these newer, more efficient techniques achieve the same oxygenation while using substantially less oxygen, and work well for the majority of patients.

Transtracheal Oxygen Delivery: This techniquethe most innovative and perhaps most important refinement in oxygen therapymaintains continuous flow but moves the delivery site below the dead-space area. Permanently inserting a catheter (a thin plastic tube) into the patient's trachea to bypass dead space was the brainchild of Dr. Henry Heimlichthe same person who developed the "Heimlich maneuver" for choking victims. Much more of the supplemental oxygen reaches the alveoli because little is wasted in dead space, oxygen is lost only at the start of expiration, and the oxygen accumulating in the trachea during the rest of expiration can go right to the air sacs when inspiration starts. Patients switching to this technique drop their oxygen consumption by one-half to two-thirds.

Patients switching from a nasal cannula also spontaneously lower their ventilation (the amount of air they breathe in each minute), which reduces the effort they put into their breathing. This means less stress on their respiratory system, and frees for other muscles the additional oxygen the respiratory muscles would otherwise be using. There are also indications that switching results in less dyspnea. There are other advantages. The tracheal catheter is less noticeable (in fact, it can be completely covered) and more comfortable than tubing that crisscrosses the middle of your face. And it is less likely to become disconnected during sleep.

Reservoir Cannulas: Oxygen flows continuously from the container, but enters the nasal cannula only during inhalation. A tiny oxygen reservoireither coupled to the nasal prongs or worn as a neck pendantstores the oxygen during exhalation. Then it joins the start of inhalation. Patients adding such a reservoir to the standard nasal cannula drop their oxygen consumption by one-half to three-fourths.

Electronic Demand Devices: Also called conserving devices, these electronic devices can sense the start of inspiration, and rapidly deliver a short burst of oxygen during that phase of the breathing cycle. Avoiding dead space and exhalation means it should all go to the alveoli. So far these devices have been used with a nasal cannula rather than a tracheal catheter. In general, oxygen consumption with these electronic devices is one-half to one-fifth what it would be on continuous flow oxygen. Because a relatively small amount of gas can be stretched over a relatively long time period, this setup is much less costly than liquid oxygen.

The caution is that these electronic conserving devices are not appropriate or safe for all patients. Not all patients can use them safely during activity requiring an effort. Patients with severe disease, patients with end-stage diseaseeven patients who do not have good breathing techniquewill not maintain a high enough level of oxygen in their blood when they exercise or carry out an activity thatfor themis relatively strenuous. The DMEs favor conserving devices along with gas canisters because this increases their profit. The problem is that any supply company considering a conserving device along with a gas canister for a particular patient is supposed to make sure that his oxygen level remains safeyet too many them do not do this. Rehabilitation personnel estimate that roughly one-third of patients do not oxygenate adequately with conserving devices and need to be on continuous flow. (The few small studies confirming this observation need to be supported by a definitive study involving a large number of patients in different pulmonary rehabilitation programs.) It is very important not to let your DME insist that you use a conserving device unless you have been properly evaluated and know that this gives you enough oxygen regardless of what you are doing. If the DME persists in providing you with a conserving device despite it being wrong for you, ask your doctor and your rehabilitation professionals to put their weight behind you.


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