Lungs, Kidneys, Oxygen: an orchestrated response

Receiving all circulating blood

Lungs and Kidneys work in an orchestrated manner to maintain an appropriate level of oxygen in blood. Both organs receive all blood flow at one point. Lungs receive blood to facilitate gas exchange: CO2 released and oxygen caught from air. Kidneys filtrate the blood to clear from many residues of metabolism. Given these circumstances, these organs are perfect to carry on with all the blood during its circulation.

Filtering but controlling what’s being filtered

However, what about if lungs fail to catch oxygen and this gas is reduced in blood. Which organ should control the signal? If this task is deferred to the brain the consequences may be deleterious for the entire body. Then, the best option is to give this duty to kidneys.

The kidney’s erithropoyetin

When kidneys sense that the blood being filtered is lacking oxygen, they cooperate recommending the creation of more red cells with enough Hemoglobin (Hb) to catch up oxygen from lungs. The renal cooperation is provided with an hormone called erithropoyetin which works at the bone marrow to induce the formation of red blood cells (RBC) that may be able to take oxygen and bring it to the tissues.

Erithocytosis: increased red blood cells

This situation may take some time (when kidneys consider that the lack of oxygen seems to be serious). The resultant condition is an increased level of RBC with high levels of Hb. This effect is called erithrocytosis, erithremia, polyglobulia, secondary polycytemia, and so forth. Blood turns into thick and slow during its circulation leading to some dizziness and headaches.

Cardiovascular effect of erithrocytosis

With this type of blood, the heart needs to work harder: how to push this heavy luggage? The condition may generate a bigger heart in terms of walls with less space to fill.

Lung diseases as responsible of erithrocytosis

Many lung illnesses are signaled by the presence of secondary erithrocytosis due to difficulties in allowing the access of oxygen to the blood. Advanced stages of COPD are presented with high levels of Hb and RBC and this indicates distant complications from the lungs. The Chronic Bronchitis phenotype (constant cough and sputum production) is classically accompanied with erithrocytosis and increased Hb.

Not a healthy feature

The key fact is that secondary erithrocytosis with high Hb is not a healthy feature when they are seen in an adequate context. COPD and its eventual lung decrease in oxygen catch leads to kidney to send signals that create a huge confusion in the body with a consequence as the one described.

Final point

It’s good to assess oxygen levels and blood samples to evaluate further the lung and kidney cooperation in many pulmonary diseases. And this is just one of several joined efforts of lungs and kidneys preserving our corporal functions.

Oxygen as indicator of lung disease

Importance of energy

Making our organs to work implies the transformation of energy from different instances. Each organ require a provition of nutrients to accomplish its functions. The most visible function is seen in muscles. Muscular actions are designed to help in life with almost every activity. Our muscles take a big part of nutrients and transform them into energy and subsequent physical actions.

Oxygen: a combustible

For the transformation of nutrients at celular muscular level, the combustible “gas” is Oxygen. It is brought to that level bound to Iron in Hemoglobin (Hb) of the red blood cells. Oxygen binds to iron in Hb at lungs where blood is exposed to oxygen. In the lungs, the thin barrier between blood and air is amazingly wide to allow this fuction.

Lung illness and oxygen change

Respiratory diseases affecting the surface for exchange will have an eventual impact in the take over of oxygen from atmospheric air. Acute and chronic conditions will (depending on their severity) reduce the healthy surface for exchange. The good news is that most of acute conditions will reverse or let minimal sequelae. Chronic conditions like extensive scaring, wide destruction of alveolar walls will manifest oxygen reduction in blood at some point of the course of the disease.

Reduced oxygen

Preserving the surface available for a healthy gas exchange provides with an adequate field for physical activities. Exercise requires, not only a healthy lung but also some physical (progressive training). Curiously, lung reserve for gas exchange is big and delay clinical manifestations of reduced blood oxygen (also called hypoxemia). When hypoxemia occurs something severe and serious may be happening and physical activities will be affected.

COPD and reduced oxygen

COPD is characterized by progressive destruction of alveolar walls as well as persistent bronchoconstriction that impedes air of leaving the alveoli. Under these circumstances oxygenated air can not reach the surface that allow access to blood and the surface that can be reached it’s already reduced.

What we can expect from COPD effects at some point of the disease development is hypoxemia. COPD patients with advanced disease will have their physical activities impacted due to hypoxemia especially when the energy requirements are increased (exercise).

Oxygen reduction in other lung diseases: a few examples

These effects may be seen during some asthma crisis. In a set of pulmonary disease called interstitial lung diseases the gas exchange surface is severely affected. In some cases of pneumonia the infectio may lead to pus accumulation in air spaces limiting air access into the lungs.

From Oxygen to where?

Oxygen measurement may be required in many respiratory symptoms assessments. If oxygen is reduced it may be necessary to consider levels of other gases like CO2 as well as levels of acidity. This is for having a more complete profile of the gas exchange and the responses of the body due to this effect.

Oxygen as a drug in some respiratory diseases

Oxygen is a key element for our body to work properly. All the effort of breathing is made to keep the levels of this gas in the appropriate range. The healthy human being does not realize of the physical breathing process as a routine when the entire body is working in the positive balance of oxygen taking. However a challenge to the environment is accompanied by an increase need in oxygen so our muscles can work for running away, jumping, cycling, climbing stairs quickly, making strides, etc.

Oxygen as a excess requirement

Respiratory ill patients like those with pulmonary fibrosis, chronic obstructive disease and asthma, pneumonia, rib fractures, etc. have a diminished surface to exchange oxygen and CO2 with the atmosphere. Although the surface for exchange may be big enough to favor CO2 release, some times oxygen will not find sufficient permeable tissue to get into the blood. That’s the reason why some patients must need supplemental oxygen and others may have a delayed requirement.

Lower level of activities acting as indicators

The respiratory imposed condition may not wait for for typical exhausting tasks to add symptoms or make the reduced level of oxygen more diminished. These diseases may make the oxygen need more apparent when getting up, walking, carrying a bag with groceries, or taking a shower. For some patients, just lying on bed may reduce the surface for exchange due to obesity, diafragm weakness, occlusive upper airway (as in sleep apnea/hypopnea) or enlarged heart (just some examples).

Basement of Oxygen prescription

To indicate oxygen therapy, physicians base their decision on objective oxygen measurement that may be non-invasive or invasive. The non-invasive procedure is the Pulse Oxymetry that assesses only oxygen through the skin. The invasive procedure implies a blood sample taken from an peripheral artery (with blood coming from the heart after taking oxygen from the lungs). With the measurement of Gases of Arterial Blood it comes also the levels of CO2, as well as HCO3, and pH (among other values).

Once the reduced arterial blood oxygen level is confirmed low (hypoxemia), the election is made. Of course the supplemental oxygen is not administered to correct hypoxemia only. The oxygen therapy is started to decrease the intensity of symptoms and to reduce the workload imposed to the cardiopulmonary system when it is trying to get its best for maintaining oxygen in the best range.

Oxygen Therapy Precautions 

The oxygen therapy has potential complications although it is clearly indicated. It needs to be re-assessed on a regular basis to avoid the complications. When the right level is reached re-assessments are less frequent.

One of the most feared complications of oxygen therapy is depression of ventilatory centers (chemically confused due to the new excessive amount of oxygen supplied). Unfortunately it may appear in patients with more requirement of oxygen like those with elevated CO2 levels. This tends to appear in the most serious cases of hypoxemia: advanced stages of COPD, severe persistent asthma, obstructive sleep apnea.

When the inspired fraction of oxygen is increased over the normal atmospherical level, there’s a described risk of atelectasis (colapse of lung units where the oxygen is taken). Other risk is oxygen toxicity.

Oxygen Toxicity: special chapter

Oxygen toxicity occurs due to its chemical effect on a cellular level. This excessive oxidation leads to death of cells where the impact occurs. Actually, this effect is correlated with time of exposure and what happens is an inflammatory reaction. First with the irritating action may appear the inflammation of the trachea and bronchi with middle chest pain. Then it may be followed by reduced lung space for exchange, rigidity of local tissues, altered balance of oxygen between air and blood, hypoxemia during exercise, and reduced diffusing capacity of gases that leads to CO2 retention and no oxygen is taken.

All this occurs while the injure is being established with lession of capillaries, swelling of the lungs, and cellular destruction.

Amount and Time

As the levels and time of continuous exposure represent a risky situation, the prescription of oxygen is regulated in terms of Liters of Oxygen and hours of exposure. This needs to be clearly communicated to patients with oxygen therapy and care givers to avoid toxicity and imbalance in blood gases that may lead to confusion at respiratory centers, for instance in the Central Nervous System, with CO2 retention and worsening hypoxemia.

Oxygen may be considered a drug as it has been described with biological effects and benefits as well as potential adverse effects and events that imply warnings and precautions.

Long term Oxygen Therapy in COPD

Patients with COPD have necessary long term supplemental oxygen indicated when they have severe COPD and arterial oxygen levels less than 7.3 kPa (55 mm Hg) with or without CO2 retention or if they have arterial oxygen levels in the range of 7.3 kPa to 8 kPa (60 mm Hg) with evidence of pulmonary arterial hypertension or peripheral edema (swelling) and increased red blood cells (also called erithrocytosis, erithrocythemia more appropriately, or polycithemia) as an exaggerated response to chronic reduced arterial oxygen.

A summary

In summary, respiratory conditions may reduce the oxygen in the circulating blood. This implies that some patients may require supplemental oxygen administration. In those patients, oxygen may be required for better performance of a wide range of physical tasks. Oxygen may be injuring if given in high amounts and for extended periods of time. The administration may be required for short or long periods of time and is based on body levels of oxygen.

Previous steps?

This may be a reason to think more about Pulmonary Rehabilitation when considering to adapt to some chronic respiratory conditions.