What is the normal range for blood pH levels and how are deviations from this range treated?

Normal Blood pH Range and Management of Deviations

The normal range for blood pH is between 7.35 and 7.45, with deviations outside this range requiring prompt intervention based on the type and severity of the acid-base disorder.

Normal Blood pH Range

The normal blood pH is maintained within a narrow physiological range:

• Normal arterial pH: 7.35-7.45 1
• Corresponding hydrogen ion concentration: 35-45 nmol/L 1

This tight regulation is crucial as even small deviations can significantly impact cellular function, enzyme activity, and overall physiological processes.

Classification of pH Deviations

Acidosis (pH < 7.35)

• Respiratory acidosis: Caused by alveolar hypoventilation leading to CO₂ retention and elevated PaCO₂ > 6.1 kPa (46 mmHg) 1
• Metabolic acidosis: Characterized by decreased bicarbonate levels or increased acid production 1

Alkalosis (pH > 7.45)

• Respiratory alkalosis: Results from hyperventilation causing decreased PaCO₂
• Metabolic alkalosis: Occurs with increased bicarbonate levels or loss of acid

Severity Classification of Acidosis

Metabolic Acidosis Severity

Severity	pH Range
Mild	7.25-7.35
Moderate	7.00-7.24
Severe	< 7.00

Diabetic Ketoacidosis Classification 2

Parameter	Mild	Moderate	Severe
Arterial pH	7.25-7.30	7.00-7.24	<7.00
Bicarbonate (mEq/L)	15-18	10-14	<10
Mental Status	Alert	Alert/drowsy	Stupor/coma

Treatment of Acidosis

Respiratory Acidosis

1. Address underlying cause: Treat respiratory depression, airway obstruction, or neuromuscular disorders
2. Ventilatory support:
   • Non-invasive ventilation for mild-moderate cases
   • Mechanical ventilation for severe cases
3. Oxygen therapy: Titrate to maintain SpO₂ 94-98% in patients without risk of hypercapnic respiratory failure 1
   • For patients at risk of hypercapnic failure (COPD, severe chest wall disease), target SpO₂ 88-92% 1

Metabolic Acidosis

1. Treat underlying cause: Diabetic ketoacidosis, lactic acidosis, renal failure, etc.
2. Fluid resuscitation: Isotonic saline (0.9% NaCl) at 1-1.5 L in first hour for adults with DKA 2
3. Bicarbonate therapy:
   • Only recommended for severe acidosis (pH < 6.9) 1, 2
   • Administer 50 mmol sodium bicarbonate in 200 mL sterile water over 1 hour 1, 3
   • For less urgent forms, 2-5 mEq/kg over 4-8 hours depending on severity 3
4. Insulin therapy for DKA:
   • Continuous IV infusion of regular insulin at 0.1 U/kg/hour without bolus 2
   • Add dextrose when blood glucose reaches 250 mg/dL while continuing insulin to clear ketones 2
5. Potassium replacement:
   • Begin when serum K⁺ < 5.3 mEq/L with adequate urine output 2
   • Hold insulin if K⁺ < 3.3 mEq/L until corrected 2

Treatment of Alkalosis

Respiratory Alkalosis

1. Address underlying cause: Anxiety, pain, fever, hypoxemia, etc.
2. Breathing techniques: For hyperventilation due to anxiety
3. Sedation: May be required in severe cases

Metabolic Alkalosis

1. Correct volume depletion: With isotonic saline if present
2. Address potassium deficiency: Replace if hypokalemic
3. Discontinue causative medications: Diuretics, steroids, etc.
4. Acetazolamide: For selected cases to increase renal bicarbonate excretion

Monitoring Parameters

1. Arterial blood gases: To assess pH, PaCO₂, PaO₂, bicarbonate
2. Electrolytes: Particularly potassium, sodium, chloride
3. Blood glucose: Every 1-2 hours until stable in DKA 2
4. Ketones: Every 2-4 hours until resolving in DKA (β-hydroxybutyrate measurement preferred) 2
5. Vital signs: Including respiratory rate, heart rate, blood pressure
6. Mental status: Changes may indicate worsening acidosis or cerebral edema

Resolution Criteria for DKA

DKA is considered resolved when all of the following are met 2:

• Glucose < 200 mg/dL
• Serum bicarbonate ≥ 18 mEq/L
• Venous pH > 7.3

Important Considerations

• Avoid rapid correction: Stepwise correction is preferred as the degree of response from a given dose is not precisely predictable 3
• Monitor for complications: Cerebral edema can occur with rapid correction of osmolality, especially in DKA 2
• Continuous assessment: Use flow sheets to monitor recovery parameters and treatment interventions 1
• Caution with bicarbonate: Overzealous correction can lead to metabolic alkalosis and other complications 3

Extreme Cases

While the normal pH range is 7.35-7.45, survival has been documented in cases with pH as low as 6.7 in specific circumstances such as toxic alcohol ingestion 4. However, these are exceptional cases requiring intensive intervention including hemodialysis, respiratory support, and aggressive pharmacological treatment.