The Importance of Oxygen During Hemodialysis

By Anne Diroll, RN, CNN
 
While dialysis patients know that their treatment sessions can be annoying, painful, scary, and draining, they are also aware that they are a lifesaving necessity. Dialysis is work, and work requires energy. Energy requires fuel.

A large amount of energy is necessary for excess water and poisons to move out of our body’s cells and into the tissue fluid, blood, and dialyzer. Each cell in the body has a "powerhouse" called the mitochondria which needs "fuel" to run. Oxygen is the fuel for the "powerhouse" of the cell. (Oxygen isn't everything, but it's right up there with money!)

What is the Problem?

Dialysis causes lowered blood oxygen levels. It is known that oxygen levels in the arterial blood can drop 5%-23% during dialysis. This may go unnoticed. For patients with heart or lung problems, however, it can cause unpleasant symptoms.

It is not OK for staff to ignore patient pain and discomfort. Problems like low blood pressure (BP) and cramping interfere with fluid removal. Inadequate fluid removal leads to heart problems.

Hemoglobin Levels
Hemoglobin (Hgb) levels are checked regularly, because Hgb's job is to carry oxygen. Without enough Hgb, your cells don't get enough oxygen delivered for them to properly do their work. There are more red blood cells in the body than any other cell, which tells you how important it is for all the other cells to have enough of these oxygen carriers. The life of any living thing depends on oxygen. Without it, cells die.

Dialysis patients know how obsessed everyone is with BP, which reflects the pumping strength of your heart and the ability of your blood vessels to dilate or constrict. Your heart needs oxygen to contract, and your blood vessels need oxygen for tone.

Tissue Hypoxia
An inadequate supply of oxygen to the body's cells and organs is called tissue hypoxia, which results in the release of lactic acid. This can worsen the chronic acidosis (increased acidity of the blood) experienced by dialysis patients.

Tissue hypoxia also causes the release of a substance called adenosine, which in turn blocks another substance called norepinephrine. This then causes the blood vessels to dilate. What happens to BP when blood vessels dilate? It goes down! This is commonly when your staff-person turns off the ultrafiltration (UF) and/or gives you saline "for your blood pressure."

"Watch Your Fluids"
This may also be the time when you get the lecture to "watch your fluids." If your BP is low because of hypoxia, this is your opportunity to tell your staff-person: "No, you need to watch my fluids!"

Hypoxia can also cause problems in the muscles, digestive system, eyes, and brain, including muscle cramping, nausea, blurred vision, dizziness, and confusion. So, how will you know if your symptoms need to be treated with oxygen or saline? You measure the oxygen level in your blood.

Measuring Oxygen Levels
There are three possible methods by which oxygen levels (called “O2 sat”) can be measured:
•    Pulse oximetry. This involves a non-invasive probe being attached to your ear or finger.
•    Blood gas analysis. This involves a needlestick into an artery and an onsite lab.
•    Blood volume monitor. This non-invasive, continuous procedure uses an infrared optical sensor attached to a blood chamber at the arterial end of the dialyzer. This technology is patented by HemaMetrics®, maker of the Crit-Line™ monitor, which, as well as measuring hematocrit (the percentage of red blood cells in your blood) and actual blood volume changes, also measures continuous O2 sat.

What is Normal?
If you have a graft or fistula as your vascular access, the monitor will be measuring arterial blood. A normal O2 sat in an artery is 97%. It is clinically significant if your arterial O2 sat drops below 90%. If it does, it is standard clinical practice to give oxygen via a cannula with two prongs in the nostrils. An arterial O2 sat tells you how your lungs are doing.

If you have a catheter as your vascular access, the monitor will be measuring venous blood. This is because the catheter is placed in a vein. A normal venous O2 sat is 75%, with a range of 60%-80%. A venous O2 sat tells you how your heart is doing, and a reading below 60% shows heart problems. A venous O2 sat below 30% indicates severe heart problems. If your heart doesn't pump strongly, it affects your BP. (Actually, heart failure is defined as the inability of the heart to meet the tissue needs for oxygen at the cellular level.)

Oxygen delivered via a cannula is definitely recommended during dialysis treatments if you have a history of heart problems or a venous O2 sat below 60%. It is important to note that, since catheters are placed in veins, the O2 sat reading is a venous level, even though the monitor sensor is placed at the arterial end of the dialyzer. This confuses many staff people, and they think the reading is inaccurate. It is important that they know the difference between normal levels for arterial and venous readings. We are all a team, and the patient has a role in educating the staff!

How Does Your Body Transport and Use Oxygen?

Many factors affect the ability of the body to transport and use oxygen. For the body to be an efficient, working machine--picking up “the goods” and delivering them in a timely manner to the end-user--we need to have all our ducks in a row. This is especially important for someone on dialysis because, as you remember, dialysis is serious work. You cannot do serious work without a steady, reliable source of fuel.

The Lungs. First, "the goods" (oxygen) get delivered to the lungs when you breathe. In the lungs, the oxygen crosses a membrane, traveling from the many tiny air sacs in your lungs into your blood.

A low amount of oxygen in the blood can be due to any lung condition that interferes with you receiving a good, deep breath and getting enough oxygen traveling from the air sacs into the blood. These include asthma, cancer, emphysema, fluid overload, and osteoporosis.

Hemoglobin. Next, "the carrier" picks up "the goods." A good Hgb level is important because Hgb is the primary oxygen carrier. Remember that energy expenditure is increased during dialysis, and that oxygen is the fuel that the powerhouse of the cell uses for energy.

If energy expenditure goes up while you’re on dialysis, then oxygen consumption also rises. This may be compared to using more gas when your car goes faster. Therefore, if you are anemic (have a decreased number of red bloods cells to carry the Hgb), there is a chance that you should be given oxygen during dialysis. Ask you doctor.

The Heart. The heart is "the engine" that pushes "the carrier" that picks up "the goods." In order to do its work, the heart consumes oxygen. Remember that oxygen is "fuel," and the heart is a heavy user of this "fuel." Measured in milliliters per minute (mpm), the kidneys consume 4.6 mpm while the heart consumes 7.7 mpm. This gives you an idea what a heavy user of oxygen the heart is.

Heart problems affect oxygen delivery to all of the body’s cells. On top of this, research shows that the heart oxygen balance is down after 20 minutes on dialysis, and that this supply/demand ratio is at its lowest level after 60 minutes on dialysis. This means that the heart's demand for oxygen is exceeding its available oxygen supply. If the heart muscle is not getting enough oxygen, its ability to contract goes down. And what happens when the heart doesn't contract properly? BP goes down!

Releasing the Oxygen Molecule. At the "delivery dock," "the carrier" has to unload "the goods" that "the engine" helped push to its final destination--the body’s cells and organs. Oxygen forms an easily reversible relationship with Hgb. In the lung, the Hgb says to the oxygen, "Hop on board. Let's go on a trip!" When the blood reaches the cells and organs, the Hgb says to the oxygen, "It's been nice knowing you. You can get off now!"

Research suggests that oxygen delivery is decreased in dialysis patients because uremia increases the Hgb's affinity for oxygen. In other words, the Hgb doesn't want to let loose of the oxygen at the "delivery dock" (your body’s cells and organs).

The Cell. The cell--the "end user"--has to be able to use "the goods" dropped off at the "delivery dock." Some toxins, such as those produced by infections, interfere with the ability of cells and tissues to use the available oxygen.

Why Do Oxygen Levels Go Down?
Sleep Apnea. If your arterial O2 sat (oxygen level) goes down after you go on dialysis, it’s possible that you might have a disorder known as sleep apnea or sleep-disorder breathing, in which you have trouble breathing while asleep. (The staff at your unit might notice this if you doze off during treatment.)

The incidence of sleep disorders is higher in the dialysis patient population than in the general population. Nearly one-third of hemodialysis patients show evidence of sleep-disordered breathing, and half of those meet the diagnostic criteria for sleep apnea syndrome.

Sleep apnea promotes high BP. Additionally, hypoxia (decreased delivery of oxygen to tissues) at night is a risk factor for heart disease in renal patients. And, of course, if you aren't getting enough good quality sleep, your quality of life can be affected. The good news is that treatment is available. Anyone on dialysis with decreasing arterial O2 sat while dozing or asleep should be referred to a sleep specialist for evaluation.

Decreased Oxygen Supply. If you have pain or a change in sensation change in the arm in which your fistula is located, it could be related to oxygen, not fluid removal. There could be a decrease in oxygen supply to your fistula arm during dialysis.

Vascular Disease. Patients with vascular disease can also have complicated dialysis treatments due to oxygen-related issues. The blood supply carrying nutrients (oxygen is a nutrient) is impaired during dialysis. This can complicate dialysis for patients with arteriosclerosis (hardening of the arteries) or peripheral vascular disease (found in those with diabetes), and is more pronounced in patients with peripheral arterial occlusive disease (those with past or present nicotine use).

Declining Heart Function. A declining venous O2 sat corresponds with more oxygen consumption by your cells and tissues, which extract more oxygen when heart function has declined. A decline in heart function will result in a drop in BP.

Signs and Symptoms of Hypoxia
Following are some of the signs and symptoms of hypoxia:
•    angina
•    anxiety
•    blurred vision
•    confusion
•    dizziness
•    fast breathing rate
•    fast heart rate
•    low blood pressure
•    muscle cramps
•    nausea
•    pale or blue skin
•    restlessness
•    shortness of breath

If you experience any of these problems, you may benefit from supplemental oxygen. Request that your provider "Hook me up with some O-s." After all, when you are on dialysis, it is all about you and your successful clinical outcomes!

What Does the Dialysis Staff Need to Know?
Oxygen supplementation is medically justified in the following circumstances:
•    arterial O2 sat below 90%
•    venous O2 sat below 60%
•    systolic blood pressure (the upper number) below 100
•    pulse rate below 60 or above 100 beats per minute
•    breathing rate above 24 breaths per minute
•    Hgb below 10 or hematocrit below 33%
•    history of heart, lung, or blood vessel disease
•    a diagnosis of sleep apnea or sleep-disordered breathing

Conclusion
Knowledge is power! The more you know about how oxygen works in your body, the more successful your dialysis experience will be.

Oxygen has also been shown to help transfer fluid from the tissues into the blood vessels. This means more fluid off, less saline in. Imagine how much better the rest of your day will go if you leave your facility feeling better!

Remember that, while oxygen may not be everything, it's still at the top of the list with the most desirable and necessary things in life. If it "protects the pump," it's good, and you deserve what is good. Keep saying "no!" to phosphorous and potassium. Start saying "yes!" to oxygen.

About the Author:
Anne Diroll, RN, CNN, is Clinical Support Specialist for HemaMetrics, Kaysville, UT, and is President-Elect of the American Nephrology Nurses' Association Chapter #509, Sacramento, CA. She calls lungs and circulatory physiology her first love because "where there's breath, there's life." Anne lives in Rocklin, CA.