3 Nursing Care for Acid–Base Imbalances

Prioritize the patient and recognize urgency

Acid–base imbalances may signal respiratory failure, shock, kidney dysfunction, uncontrolled diabetes, or another urgent problem. Treat the patient, not just the blood gas: first assess airway, breathing, circulation, mental status, and vital signs. Escalate promptly for worsening work of breathing, falling oxygen saturation, new confusion or reduced consciousness, hypotension, dysrhythmia, or rapidly changing results.

An acidosis or alkalosis is a process that tends to lower or raise pH, respectively. Acidemia and alkalemia describe a measured blood pH below or above the reference range. Typical adult reference values are:

Use the laboratory's ranges. PaO₂ and oxygen saturation help assess oxygenation, which is related to but distinct from acid–base status.

Interpret an arterial blood gas systematically

Use a consistent sequence to interpret an arterial blood gas (ABG):

1. Check pH. A value below $7.35$ indicates acidemia; a value above $7.45$ indicates alkalemia. A pH within range does not rule out a compensated or mixed disorder.

2. Check PaCO₂. It reflects the respiratory component. Higher CO₂ lowers pH, while lower CO₂ raises pH.

3. Check HCO₃⁻. It reflects the metabolic component. Lower bicarbonate lowers pH, while higher bicarbonate raises pH.

4. Identify the primary process. In a primary respiratory disorder, the PaCO₂ change points opposite the pH. In a primary metabolic disorder, the HCO₃⁻ change points in the same direction as the pH. The memory aid ROME means Respiratory Opposite, Metabolic Equal.

5. Assess compensation and context. The lungs respond to metabolic changes relatively quickly; renal compensation for respiratory changes takes longer. Compensation moves pH toward normal but does not, by itself, explain an abnormal result. If values do not fit expected compensation, consider a mixed disorder and notify the provider.

For metabolic acidosis, clinicians may calculate the anion gap:

Interpret it using the laboratory's reference range and the clinical picture. An elevated gap can prompt evaluation for causes such as lactate, ketones, kidney failure, or toxins.

Assess beyond the blood gas

Review symptom onset and trends; respiratory rate, depth, effort, breath sounds, oxygenation, circulation, mental status, pain, temperature, and fluid balance. Check medication and treatment history, including opioids or sedatives, diuretics, bicarbonate, oxygen and ventilator support, vomiting, and gastric suction.

Review relevant electrolytes, glucose, renal function, lactate, and ketones as ordered. When an ABG is collected, document oxygen delivery and ventilator settings at the time of sampling. After arterial puncture, follow local procedure for pressure and site assessment.

Recognize respiratory disorders

A primary respiratory acidosis has low pH and high PaCO₂. Hypoventilation may result from airway obstruction, COPD exacerbation, sedation or opioids, or neuromuscular weakness. Headache, confusion, drowsiness, or reduced consciousness may occur.

Prioritize airway and ventilation. Assess respiratory effort and breath sounds; support positioning, prescribed oxygen, airway clearance, and prescribed ventilatory support. Promptly report declining consciousness or ventilation and review possible medication-related hypoventilation. Treat the cause; oxygen alone does not correct inadequate ventilation.

A primary respiratory alkalosis has high pH and low PaCO₂. Hyperventilation may be associated with pain, fever, anxiety, hypoxemia, infection, pulmonary embolism, or other illness. Dizziness, tingling, palpitations, or muscle cramps may occur.

Assess oxygenation and look for a serious cause rather than assuming anxiety. Treat the cause and provide calm coaching or prescribed pain or anxiety care as appropriate. Do not use paper-bag rebreathing because it can worsen hypoxemia and is not recommended.

Recognize metabolic disorders

A primary metabolic acidosis has low pH and low HCO₃⁻. Possible causes include ketoacidosis, lactic acidosis, kidney dysfunction, toxins, or bicarbonate loss, such as severe diarrhea. Deep, rapid compensatory breathing, nausea, weakness, hypotension, or altered consciousness may occur.

Promptly report suspected or worsening acidosis. Monitor breathing, perfusion, mental status, glucose, electrolytes, renal function, and ordered tests. Treatment targets the cause—for example, prescribed fluids and glucose management in an appropriate clinical context, or treatment of shock, renal dysfunction, or toxic exposure. Bicarbonate is not a routine fix; it may be considered for selected severe cases under provider direction.

A primary metabolic alkalosis has high pH and high HCO₃⁻. It is often associated with vomiting, gastric suction, diuretics, volume or chloride depletion, or excess alkali. Weakness, cramps, confusion, or dysrhythmias may occur, especially with potassium or magnesium abnormalities.

Track intake and output, volume status, ECG when indicated, and potassium, chloride, and magnesium. Report ongoing gastric losses and review prescribed suction, diuretics, or alkali with the care team. Treatment depends on the cause and volume status; prescribed fluid, chloride, potassium, or magnesium replacement may be appropriate but must be individualized.

Monitor and evaluate the response

After an intervention, reassess relevant bedside findings, not just the next laboratory value. Compare respiratory effort, oxygenation, mental status, hemodynamics, urine output, fluid balance, and ECG or electrolyte findings with baseline. Repeat ABG or other tests as ordered and according to clinical status.

A favorable response means the underlying problem and clinical condition are improving, with pH and gas values trending toward the expected range and no deterioration in oxygenation, ventilation, perfusion, or electrolytes. Report worsening trends, unexpected compensation, or lack of response so the plan can be reassessed. A more normal pH alone does not establish that the patient is safe or that treatment is complete.

Apply interpretation to clinical situations

Opioid-associated hypoventilation

A postoperative patient is difficult to arouse, breathing slowly, and has an ABG of $\mathrm{pH}=7.28$, $\mathrm{PaCO_2}=58\,\mathrm{mm\,Hg}$, and $\mathrm{HCO_3^-}=26\,\mathrm{mEq/L}$. This is acute respiratory acidosis. Prioritize airway and breathing, summon appropriate help, support ventilation and oxygenation per protocol, and promptly report a possible opioid effect. Reassess consciousness, respiratory status, and response to prescribed treatment.

Vomiting and weakness

A patient with persistent vomiting has $\mathrm{pH}=7.49$, $\mathrm{PaCO_2}=47\,\mathrm{mm\,Hg}$, and $\mathrm{HCO_3^-}=35\,\mathrm{mEq/L}$. This is metabolic alkalosis with respiratory compensation. Assess volume status and ECG, review potassium and chloride, track ongoing losses, and notify the provider. Replacement or changes to gastric suction or medications require an individualized order and plan.

Diarrhea with low bicarbonate

A patient with diarrhea has $\mathrm{pH}=7.30$, $\mathrm{PaCO_2}=32\,\mathrm{mm\,Hg}$, and $\mathrm{HCO_3^-}=16\,\mathrm{mEq/L}$. The primary disorder is metabolic acidosis; the low PaCO₂ is consistent with compensatory increased ventilation. Assess severity, perfusion, fluid losses, electrolytes, and the cause, and report deterioration. In a primary metabolic disorder, pH and HCO₃⁻ move in the same direction. Do not mistake compensation for a separate primary respiratory disorder unless the values or clinical context suggest a mixed process.

Rapid breathing with hypoxemia

A patient is breathing rapidly, reports tingling fingers, and has an SpO₂ of $88\%$ on room air. Assess and address oxygenation promptly while evaluating the cause of rapid breathing and escalating care as indicated. Hypoxemia can cause hyperventilation and requires assessment; paper-bag breathing is not recommended because it may worsen hypoxemia. Do not assume anxiety until dangerous causes are considered.

Near-normal pH with abnormal gases

A patient with chronic respiratory disease has $\mathrm{pH}=7.37$, $\mathrm{PaCO_2}=58\,\mathrm{mm\,Hg}$, and $\mathrm{HCO_3^-}=33\,\mathrm{mEq/L}$. The ABG is not necessarily normal. The near-normal pH with elevated PaCO₂ and HCO₃⁻ may reflect compensated respiratory acidosis, but interpretation depends on history, baseline values, oxygenation, and whether the changes fit expected compensation. Assess the patient and compare with prior results.

Improved pH with new symptoms

A patient being treated for metabolic alkalosis has a better pH on repeat testing but develops new weakness and an irregular pulse. Promptly assess and escalate the new clinical changes; review the ECG and ordered electrolyte results, especially potassium and magnesium, and evaluate treatment response with the care team. Clinical deterioration and electrolyte-related dysrhythmia risk require prompt attention.