4 Clinical Manifestations and Treatment Priorities

Prioritize clinical stability

Treat clinical instability before treating an ABG value. Begin with airway, breathing, circulation, and mental status; assess vital signs, oxygen saturation, work of breathing, and perfusion. Obtain an ECG and electrolytes when indicated.

Confusion, drowsiness, exhaustion, hypotension, dysrhythmia, or worsening hypoxemia calls for urgent escalation and close monitoring.

Interpret the ABG in context

Read an ABG by first identifying the direction of the pH, then determining whether carbon dioxide or bicarbonate best explains that direction. Check whether compensation is appropriate: it helps identify the primary disorder, but does not mean the underlying illness is harmless. A near-normal pH can conceal a mixed disorder.

Assess oxygenation separately. The pH alone does not show whether oxygen delivery or ventilation is adequate, so interpret the blood gas alongside the patient's breathing, oxygenation, circulation, mental status, and likely cause.

Severe metabolic acidosis with suspected DKA

The patient is vomiting, tachycardic, dehydrated, weak, and breathing deeply and rapidly. The results are $\mathrm{pH}=7.12$, $\mathrm{PaCO_2}=18\ \mathrm{mmHg}$, $\mathrm{HCO_3^-}=6\ \mathrm{mEq/L}$, and potassium $5.6\ \mathrm{mEq/L}$. This is severe metabolic acidosis, likely from diabetic ketoacidosis (DKA); the deep breathing is compensatory.

For $\mathrm{HCO_3^-}=6\ \mathrm{mEq/L}$, Winter’s formula predicts $\mathrm{PaCO_2}$ of about $17\pm2\ \mathrm{mmHg}$. The measured $\mathrm{PaCO_2}$ of $18\ \mathrm{mmHg}$ is appropriate compensation. A high serum potassium does not rule out total-body potassium depletion.

Assess airway, breathing, circulation, mental status, volume status, glucose, ketones, electrolytes, and ECG promptly. Identify and treat the precipitating cause. Initiate fluids, insulin, and potassium management according to the clinical protocol, paying particular attention to potassium before and during insulin therapy. Follow glucose frequently and repeat electrolytes and acid–base testing as directed.

Bicarbonate is not routine DKA treatment; the current adult consensus generally reserves consideration for extreme acidemia, with $\mathrm{pH}<7.0$.

Acute worsening of respiratory acidosis

A patient with COPD becomes drowsy and uses accessory muscles to breathe. The ABG shows $\mathrm{pH}=7.25$, $\mathrm{PaCO_2}=72\ \mathrm{mmHg}$, and $\mathrm{HCO_3^-}=31\ \mathrm{mEq/L}$; a previous ABG had a higher pH and $\mathrm{PaCO_2}$ near $60\ \mathrm{mmHg}$. This indicates acute worsening of respiratory acidosis on chronic carbon dioxide retention.

Drowsiness and increased work of breathing raise concern for ventilatory failure. Do not dismiss these signs because bicarbonate is elevated or the patient has chronic hypercapnia. Urgently assess airway protection, breathing, oxygenation, and the cause of deterioration; obtain respiratory support and senior review.

For a patient at risk of hypercapnic respiratory failure, titrate oxygen to the prescribed target—commonly $88\text{–}92\%$ while blood gases are being assessed—rather than giving uncontrolled high-concentration oxygen. Assess suitability for noninvasive ventilation and escalate if the patient deteriorates or cannot protect the airway.

Reassess consciousness, work of breathing, respiratory rate, saturation, and repeat blood gases as clinically directed. When oxygen is adjusted in this risk group, the BTS guideline advises rechecking gases after $30\text{–}60$ minutes.

Metabolic alkalosis and dysrhythmia risk

After several days of vomiting, the patient has weakness and palpitations. Results are $\mathrm{pH}=7.55$, $\mathrm{PaCO_2}=48\ \mathrm{mmHg}$, $\mathrm{HCO_3^-}=41\ \mathrm{mEq/L}$, and potassium $2.7\ \mathrm{mEq/L}$. This is metabolic alkalosis with respiratory compensation.

Severe hypokalemia, palpitations, and an abnormal ECG make dysrhythmia an immediate concern. Prioritize cardiac monitoring and assessment of volume status; evaluate potassium, chloride, and magnesium. Treat vomiting or another cause and replace deficits safely under clinical supervision. Chloride-responsive alkalosis associated with volume depletion may require chloride-containing fluid when appropriate.

Reassess symptoms, ECG, electrolytes, and acid–base status.

Sudden postoperative respiratory alkalosis

A postoperative patient develops sudden rapid breathing, pleuritic chest pain, and low oxygen saturation. The ABG shows $\mathrm{pH}=7.50$, $\mathrm{PaCO_2}=28\ \mathrm{mmHg}$, and $\mathrm{HCO_3^-}=21\ \mathrm{mEq/L}$, a likely acute respiratory alkalosis pattern.

The ABG describes the acid–base disturbance but does not establish its cause. Sudden postoperative symptoms with hypoxemia require urgent assessment for serious cardiopulmonary causes, including pulmonary embolism, as well as other possible causes such as pain or infection. Do not automatically attribute the rapid breathing to anxiety.

Support oxygenation if the patient is hypoxemic, escalate for urgent evaluation, and monitor vital signs, oxygenation, mental status, and clinical trajectory. Do not use paper-bag rebreathing or suppress compensatory breathing without identifying the cause.

Reassess for complications and improvement

Prioritize clinical instability over the ABG label. Use the ABG to recognize the primary disorder and assess compensation, then connect the pattern to breathing, oxygenation, circulation, mental status, and the likely cause.

Treat the underlying problem and monitor for complications, especially altered ventilation, electrolyte-related dysrhythmia, and worsening perfusion. Repeat assessments to determine whether the patient is improving.