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Why it’s important to recognize for early prevention the deterioration of electrolyte imbalances for your patient during your EMS call?

Interplaying Relationship between Sodium, ETCO2, Bicarb (Hco3-), and Potassium

For the every day EMS provider:

Understanding the Interplay between Sodium, Bicarbonate, End-Tidal CO2, and

pH: Key Concepts in Physiology

When discussing the balance of bodily fluids and their impact on our role as EMS

providers, it is essential to understand the relationships between sodium, potassium,

bicarbonate, end-tidal CO2 (EtCO2), and pH. These components play critical roles in

maintaining our body’s s homeostasis, in Injury patterns, and signs and symptoms that our

patients exhibit that we often times MISS OUT ON COMPLETELY! It also is important in

regulating blood pH through respiratory and metabolic processes to either speed up, or slow

down the compensating time period, and can be fatal if not corrected during the golden hour.

The Role of Sodium and Bicarbonate in Blood pH

Sodium (Na+) is one of the primary EXTRACELLULAR electrolytes in the body, crucial

for maintaining fluid balance, nerve transmission, and muscle function. While sodium itself does

not directly alter pH, its interactions with other ions, such as bicarbonate, influence the body’s

pH balance. The levels of Sodium in the body are 135-145. This is one of the big 3 cardiac

action potential electrolytes needed to create an action potential in the heart. (technically there

is a 4 th ..Magnesium, but we will discuss this later on not in today’s blog)

Bicarbonate (HCO3-), a predominant buffer in the blood, directly impacts the pH by

neutralizing excess acids in the blood. The kidneys regulate the concentration of bicarbonate,

excreting it or retaining it based on pH requirements. When acid levels in the body are high,

bicarbonate binds with hydrogen ions to form carbonic acid (H2CO3), which is then converted to carbon dioxide (CO2) and water, a reaction facilitated by the enzyme carbonic anhydrase. This conversion is reversible and central to the body's ability to regulate pH. FORMULA: if pH is ,7.20, 0.1 x (-BE) x kg = Amount of Bicard Needed.

The Next Formula that we are going to discuss is: for every change of 10mmhg of

ETCO2, the pH will change 0.08 in the opposite direction. For example, if you have a pH of

7.20, and your ETCO2 is 50mmhg, then your ETCO2 will drop by 20, and your pH will raise to 7.36 (two times 0.08 = 0.16).

Also, for every change of 0.15 in pH, BiCarb will change by 10 mmol/L in the SAME

direction. So if your pH is 7.20 and your Bicarb is 16, and your pH jumps to 7.35 then your


The Role of End-Tidal CO2

End-Tidal CO2 (EtCO2) is the maximum concentration of carbon dioxide at the end of

an exhaled breath and is a key indicator of ventilation efficiency. It reflects how well CO2 is

being eliminated from the body, and indirectly, how well the body is maintaining the acid-base

balance. Normal EtCO2 levels indicate effective alveolar ventilation and appropriate metabolic

function impacting acid-base balance.

A change in EtCO2 is often the first sign that either the respiratory system is adjusting to

correct a metabolic pH imbalance or that a respiratory issue is causing a pH imbalance. For

instance, hyperventilation can decrease EtCO2, reflecting a respiratory compensation for a

metabolic acidosis (like in diabetic ketoacidosis). Conversely, hypoventilation can increase

EtCO2, possibly indicating respiratory acidosis.

The Interactions and Balance

The body's pH is tightly regulated within a range of 7.35 to 7.45. Both the respiratory

system and the kidneys play crucial roles in maintaining this balance. The lungs adjust the

levels of CO2 (and thus carbonic acid) via breathing rate and depth, while the kidneys manage

bicarbonate levels. This dual system allows the body to quickly respond to pH changes through

respiratory adjustments (fast but short-term) and more gradually through metabolic changes via

renal adjustments (slow but long-lasting).

For example, in metabolic acidosis, the body compensates by increasing breathing to

expel more CO2, thereby reducing the concentration of carbonic acid and raising blood pH

towards normal. Similarly, in respiratory alkalosis, the kidneys may excrete more bicarbonate to

lower the body's pH by reducing its base concentration.

Potassium is a significant electrolyte in the body, playing essential roles in cellular

function, including nerve transmission, muscle contraction, and overall cellular health. Like

sodium and bicarbonate, potassium also interacts with the body's acid-base balance,

influencing blood pH. Here’s how potassium affects pH:

For Every change in 0.10 in pH, then K+ will change 0.6 mEq’s in the OPPOSITE

direction. So, for an increase in 0.10 in pH, you will have a DECREASE in 0.6 in K+! If

your pH is 7.20 and your K+ is 4.0 and your pH increases to 7.40 then your K+


1. Interaction with Hydrogen Ions

Potassium and hydrogen ions often exchange places across cell membranes. This

exchange is crucial in maintaining cellular function and also impacts the acid-base balance. In

states where there is an excess of hydrogen ions in the blood (acidemia), potassium moves

from the extracellular fluid into cells in exchange for hydrogen ions moving out of the cells. This

movement can help mitigate increases in blood acidity by temporarily sequestering hydrogen

ions within cells.

Conversely, during alkalemia (when the blood is too alkaline), hydrogen ions may move

into cells in exchange for potassium moving out, which can exacerbate the alkaline state of the


2. Role in Kidney Function

The kidneys help regulate both potassium levels and the body’s acid-base balance.

They adjust the excretion or retention of potassium and hydrogen ions based on the body’s needs. When blood pH decreases (becomes more acidic), the kidneys may excrete more

hydrogen ions and retain potassium, helping to normalize the pH. On the other hand, if the

blood is too alkaline, the kidneys might retain hydrogen ions and excrete more potassium to

help correct the pH imbalance.

3. Impact on Urinary pH

Potassium also affects the pH of urine. Potassium is excreted in urine, and its excretion

can be accompanied by the loss of accompanying anions like bicarbonate. When bicarbonate is lost with potassium, this can reduce the buffering capacity of blood against acid, potentially

leading to a more acidic environment.

4. Relation to Other Electrolytes

The balance of potassium with other electrolytes, like sodium and bicarbonate, is

essential for the overall electrolyte and acid-base balance. Disorders of potassium metabolism

(like hypokalemia or hyperkalemia) can indirectly influence pH by altering cellular functions and

the kidney’s ability to manage hydrogen and bicarbonate ions.


In summary, potassium indirectly influences blood pH mainly through its interactions with

hydrogen ions and its role in renal function. The body's ability to regulate potassium levels

alongside other ions is crucial in maintaining the delicate balance required for optimal

physiological functioning and acid-base homeostasis. This intricate balance highlights the

interconnectedness of electrolytes and the body's constant regulation to maintain stability.

The relationships between sodium, bicarbonate, EtCO2, and pH are foundational in

understanding physiological responses to various conditions and treatments. These parameters

are often monitored in critical care settings to assess and manage patients effectively. By

appreciating how these factors interact, healthcare providers can better predict the body’s

responses to disturbances and intervene appropriately, ensuring patient stability and health.

This interplay also highlights the incredible capacity of the human body to maintain equilibrium,

constantly adjusting to internal and external changes.

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