Role of Hydrogen Ions in the Body
Hydrogen ion concentration is not merely a laboratory marker, but a key factor in maintaining homeostasis (or homeokinesis) within cells and biological fluids. The correct functioning of the entire body depends on the stability of this parameter. Hydrogen ions directly interfere with the kinetics of enzymatic reactions, accelerating or slowing them down. They determine the physicochemical and structural state of cell membranes and influence macromolecule conformation, which is critical for protein structures.
Additionally, proton levels regulate hemoglobin oxygen affinity, determining the efficiency of tissue respiration. They also control the intensity of processes involving reactive oxygen species and lipid peroxidation. Finally, excitability and conduction in neural structures depend on the hydrogen index. Any deviations from the norm inevitably lead to metabolic disturbances, severe dysfunction, and ultimately the death of cells, tissues, and the entire organism.
Clinical Significance of pH Shifts
In clinical practice, the acid-base balance is always assessed by the pH value. The human body has an extremely narrow corridor of acceptable values for this parameter, and exceeding these limits is accompanied by a predictable and very severe clinical picture.
- Shift by ±0.1: Triggers initial pathological processes manifesting as respiratory and circulatory disorders.
- Shift by ±0.3: Transitions the patient's condition to critical. Loss of consciousness occurs, accompanied by profound hemodynamic and pulmonary ventilation disorders.
- Shift by ±0.4 and more: Considered fatal. Such changes are incompatible with the normal course of biochemical reactions and lead to the death of the organism.
Core Acid-Base Parameters
For accurate diagnosis of disorders in clinical practice, a complex of core parameters is used. They allow the physician to assess the degree of compensation and the nature of the shift. Normal values depend on the type of blood tested and the units of measurement used.
| Parameter | Description | Normal Range (SI) | Traditional Units |
|---|---|---|---|
| Arterial blood pH | Hydrogen ion exponent | 7.37–7.45 | — |
| Venous blood pH | Hydrogen ion exponent | 7.34–7.43 | — |
| Capillary blood pH | Hydrogen ion exponent | 7.35–7.45 | — |
| pCO₂ | Partial pressure of carbon dioxide | 4.3–6.0 kPa | 33–46 mmHg |
| SB | Standard Bicarbonate (plasma standard bicarbonate) | 22–26 mmol/L | — |
| BB | Buffer Base (capillary blood buffer bases) | 44–53 mmol/L | — |
| BE | Base Excess (capillary blood base excess) | –3.4 to +2.5 mmol/L | — |
These parameters form the baseline profile upon which the physician relies when making a diagnosis. Evaluation is performed strictly taking into account the normal range of each listed marker.
Additional Parameters
In addition to the baseline profile, there are additional parameters. Their primary clinical task is to assist in identifying the specific cause and detailed mechanism of non-respiratory (metabolic) forms of acid-base balance disorders. For this purpose, two types of biological fluids are examined: blood and 24-hour urine.
Blood Analysis: Blood tests determine the concentration of specific metabolites. The normal level of ketone bodies (KB) should range from 0.5 to 2.5 mg% (in traditional units). Lactic acid (LA) content in a healthy body is maintained within the range of 6–16 mg%.
24-Hour Urine Analysis: Renal compensation is assessed by two key parameters. The first is titratable acidity (TA), the normal value of which in SI units is 20–40 mmol/L. The second important marker is ammonia. Its normal excretion is 10–107 mmol/day, which translates to a concentration of 20–50 mmol/L.