Acid-Base Balance Notes

Homeostatic Challenge: Maintaining hydrogen ion concentration (pH) is crucial for cellular function. Deviations from the normal pH range can disrupt enzymatic activities and metabolic processes, leading to compromised cellular integrity and potential organ dysfunction.

Normal pH Range for Blood: 7.35 to 7.45.

Impact of pH: Affects protein structure and function, which in turn influences various biological processes including oxygen transport, metabolic reactions, and overall homeostasis. Even slight changes in pH can significantly affect the physiological state of the body.

Regulatory Mechanisms for pH Maintenance

2. Chemical Buffer Systems

Types of Buffers:

• Protein Buffers: (e.g., albumin, hemoglobin) play a vital role in maintaining pH within the bloodstream as they can bind to excess hydrogen ions, thus minimizing fluctuations.

• Carbonic Acid-Bicarbonate Buffer System: This system regulates pH through a reversible reaction-dependent pair of carbonic acid (H₂CO₃) and bicarbonate (HCO₃⁻) ions. It plays a pivotal role in physiological responses to respiratory changes and metabolic activities.

• Phosphate Buffers: Mainly operate in the intracellular fluid, involving monohydrogen phosphate (HPO₄²⁻) and dihydrogen phosphate (H₂PO₄⁻) which help in acutely responding to pH changes within cells.

1. Respiratory System

Function: The respiratory system maintains blood pH by adjusting the exhalation rate of carbon dioxide (CO₂). Carbon dioxide reacts with water to form carbonic acid, which in turn dissociates to release hydrogen ions, affecting overall pH.

Volatile Acid: Carbonic acid can be eliminated through respiration; thus, an increased breathing rate can reduce CO₂ levels, effectively raising blood pH (becoming more alkaline).

6. Kidneys

Function: The renal system plays a crucial role in long-term pH balance by excreting hydrogen ions and reabsorbing bicarbonate ions, which helps to counteract acidemia or alkalemia. The kidneys’ ability to adjust for non-volatile acids, especially during prolonged disturbances, is paramount.

Speed: The slowest among the three regulatory mechanisms; crucial for recovery from chronic conditions resulting in acid-base disturbances.

Chemical Buffer Systems in Detail

Protein Buffers:

• Proteins serve as weak acids or bases, effectively minimizing pH changes when excess hydrogen ions are present.

• Hemoglobin plays a significant role as it buffers hydrogen ions released from carbonic acid and transports oxygen, thereby linking respiratory function to acid-base balance.

Carbonic Acid-Bicarbonate Buffer:

• Excess hydrogen ions result in increased carbonic acid levels which dissociate, releasing bicarbonate and counteracting acidosis.

• Relies heavily on the availability of CO₂; increased metabolism or hypoventilation can lead to respiratory acidosis, while hyperventilation can lead to respiratory alkalosis.

Phosphate Buffer System:

• Predominantly regulating intracellular fluid pH, the phosphate buffer system utilizes monohydrogen and dihydrogen phosphate to either accept or release hydrogen ions, thus maintaining physiological pH levels effectively within cells.

Acid-Base Imbalances

Acidosis: pH < 7.35 leading to decreased cellular function and may result in potential respiratory failure.

Alkalosis: pH > 7.45 leading to increased neuronal excitability and may provoke muscle spasms or seizures.

Types of Acidosis/Alkalosis:

• Respiratory: Caused by CO₂ retention or loss, affecting central nervous system control of respiration.

  • Respiratory Acidosis: Results from hypoventilation (e.g., emphysema, pneumonia) where CO₂ accumulates in the bloodstream.

  • Respiratory Alkalosis: Results from hyperventilation (e.g., anxiety, high altitude) leading to excessive CO₂ exhalation.

• Metabolic: Caused by loss or gain of bicarbonate.

  • Metabolic Acidosis: Caused by a significant loss of bicarbonate (e.g., severe diarrhea, kidney failure).

  • Metabolic Alkalosis: Caused by the gain of bicarbonate (e.g., vomiting, diuretic use).

Compensation Mechanisms

Respiratory Compensation:

• A quick response mechanism to acid-base disturbances through adjustments in respiration rate, either increasing ventilation to blow off CO₂ (reduces acidity) or decreasing ventilation to retain CO₂ (increases acidity).

Renal Compensation:

• A slower response mechanism that adjusts blood pH over hours to days through the secretion of hydrogen ions and reabsorption of bicarbonate, essential for chronic acid-base disturbance management.

Diagnostic Approach for Acid-Base Imbalance

1. Assess pH Level: Establish whether acidosis or alkalosis is present through blood gas analysis.

2. Identify Abnormal Values:

   • Bicarbonate: Indicates metabolic issues, assessed to understand the buffer status of the plasma.

   • Partial Pressure of CO₂: Indicates respiratory issues, showing the adequacy of gas exchange in lungs.

3. Compensation Evaluation: Analyze whether compensation is complete, partial, or absent to inform appropriate treatment interventions.

Differences in Acid-Base Balance: Infants vs. Adults

• Total Body Water: Infants have a higher percentage of body water (approximately 75% compared to adults at 55-60%), affecting fluid balance and distribution.

• Kidney Function: Infants’ kidneys are less effective in managing electrolytes and acid-base status until roughly one month of age, impacting their ability to maintain homeostasis.

• Metabolic Rates: Higher metabolic rates in infants (double that of adults) impact CO₂ production and elimination efficiency, heightening risk for imbalances.

• Body Composition: The higher surface area-to-volume ratio in infants leads to greater fluid losses, making them more susceptible to dehydration and electrolyte imbalances.

• Ion Concentrations: Newborns exhibit elevated potassium and chloride levels resulting from rapid growth and development processes, influencing overall acid-base balance.

Key Takeaways

• Maintaining pH: Critical for enzymatic reactions and cellular processes, indicating the necessity of sophisticated regulatory mechanisms.

• Homeostasis: Achieved through the dynamic interaction of buffering systems, respiration, and renal functions, sustaining vital physiological functions.

• Clinical Implications: Understanding these mechanisms is imperative for accurate diagnosis and effective treatment of acid-base disorders, enhancing patient outcomes in critical care environments.