Physical Examination

Metabolic Acidosis. Inspect the patient's skin, noting if it feels warm. Note a flushed appearance. Assess the patient's breathing pattern for Kussmaul's respirations, a compensatory mechanism that the body uses to attempt to balance the pH by blowing off carbon dioxide. Check for an increased heart rate caused by stimulation of the sympathetic nervous system. To detect changes in cardiac performance, use a cardiac monitor for patients with a pH less than 7 and a potassium level greater than 5 mEq/L. Assess for changes in heart rate, ventricular ectopics, T-wave configuration, QRS, and P-R intervals. Include neurological status checks at least every 4 hours, or more frequently if the patient is confused or lethargic.

Metabolic Alkalosis. The patient with metabolic alkalosis demonstrates signs associated with the accompanying electrolyte imbalances. If hypocalcemia is present, the patient may demonstrate positive Chvostek's and Trousseau's signs (see Hypocalcemia, p. 473). Hypocalcemia and hypokalemia affect muscle strength and irritability. Assess the strength of the patient's hand grasps. Observe the patient's gait for unsteadiness, and note the presence of any hyperactive reflexes such as spasms and seizures. Observe the patient's breathing patterns for a compensatory decrease in the rate and depth of breathing. Use continuous cardiac monitoring, and check for an increased heart rate or ventricular dysrhythmias. Assess the patient for atrial tachycardias, ventricular dysrhythmias, and a prolonged Q-T interval.

Respiratory Acidosis. Assess the patient for an increased heart rate. As PaO2 decreases and PaCO2 increases, the sympathetic nervous system is stimulated, resulting in a release of catecholamines, epinephrine, and norepinephrine, which causes an increase in heart rate and cardiac output. Note cardiovascular abnormalities, such as tachycardia, hypertension, and atrial and ventricular dys-rhythmias. During periods of acute respiratory acidosis, monitor the cardiac rhythm continuously. Take the patient's pulse, noting a bounding quality characteristic of hypercapnia. If the cause of the respiratory acidosis is respiratory center depression or respiratory muscle paralysis, respirations are slow and shallow. As respiratory acidosis worsens and respiratory muscles fail, the rate of respirations decreases.

Respiratory Alkalosis. The hallmark sign of respiratory alkalosis is hyperventilation; the patient may be taking 40 or more respirations per minute and may manifest a breathing pattern that is reminiscent of Kussmaul's breathing caused by diabetic acidosis. Check the patient for an increased heart rate, caused by hypoxemia. Test the patient's hand grasps for signs of weakness. Observe the patient's gait for unsteadiness, and note any indications of hyperactive reflexes such as spasms, tetany, and seizures. The presence of a positive Chvostek's or Trousseau's sign may indicate hypocalcemia (see Hypocalcemia, p. 473), which may occur from lower amounts of ionized calcium during periods of alkalosis.

PSYCHOSOCIAL. Acid-base imbalances frequently affect patients with both acute and chronic illnesses. Their response to yet another problem is at best unpredictable. Neurological changes such as confusion, agitation, or psychosis are upsetting if they occur, as are electrolyte disturbances. Anticipate the patient's feeling powerless, and plan care to support all psychological needs.

Diagnostic Highlights


Normal Result

Abnormality with Condition


Arterial blood gases

Anion gap

pH 7.35-7.45; Pa02 80-100 mm Hg; PaC02 35-45 mm Hg; Sa02 > 95%; HC03 22-26 mEq/L

12-16 mEq/L

Metabolic acidosis: pH < 7.35; HCO3 < 22 mEq/L; metabolic alkalosis: pH > 7.45; HCO3 > 26 mEq/L; respiratory acidosis: pH < 7.35; Paco2 > 45 mm Hg; respiratory alkalosis: pH > 7.45; Paco2 < 35 mm Hg

Metabolic acidosis: increased; Metabolic alkalosis: decreased

All values are prior to compensation

Calculation of difference between major cations and anions in blood

Other Tests: Electrocardiogram; serum electrolyte levels (sodium, chloride, calcium, potassium, magnesium); glucose; lactate; total protein; blood urea nitrogen; creatinine; urine pH

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