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Acute Metabolic Acidosis

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In one line

·Blood pH drops below 7.35 because the body either makes too much acid or loses too much bicarbonate—the main buffer that neutralizes acid.

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Normal physiology

·Three systems work together every second to keep blood pH between 7.35 and 7.45: bicarbonate buffer (instant response), lungs blowing off CO₂ (acts within minutes), and kidneys dumping acid into urine (takes hours to days). Bicarbonate is the largest and fastest-acting buffer in the blood.

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What goes wrong

·Metabolic acidosis (acid building up in the blood) happens when the body either makes or absorbs too much acid, or loses too much bicarbonate. To figure out which, you calculate the anion gap—a simple formula that sorts the causes into two buckets.

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Hallmark signs

·Kussmaul respirations (deep, rapid breathing)
·Nausea and vomiting
·Belly pain
·Confusion, sleepiness, or trouble thinking
·Low blood pressure or shock
·Weakness and feeling exhausted
·Heart racing or skipping beats
·Peeing a lot and feeling very thirsty (in diabetic ketoacidosis (the acid crisis of missing insulin))

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Red flags · escalate now

·Blood pH below 7.1 or bicarbonate below 10 mEq/L (heart can stop or shock may not respond to treatment)
·Potassium above 6.5 mEq/L or EKG showing peaked T waves, wide QRS, or sine wave (heart rhythm about to become lethal)
·Confusion, unresponsiveness, or coma (brain swelling risk in diabetic ketoacidosis (the acid crisis of missing insulin) or severe acid affecting brain function)
·Blood pressure staying low despite IV fluids or strong medicines (acidic blood blocks adrenaline from working on heart and vessels)
·Lactic acid above 4 mmol/L (signals shock, sepsis, or organs not getting oxygen—find and fix the cause now)
·Suspected poison ingestion—methanol, antifreeze, or aspirin—with vision changes, kidney failure, or ringing in ears

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Workup

·Arterial blood gas (ABG)
·Basic metabolic panel (BMP) with anion gap calculation
·Serum lactate
·Serum and urine ketones
·Serum glucose
·Serum osmolality and osmolal gap
·Urinalysis with urine pH
·Serum creatinine and blood urea nitrogen (BUN)

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Treatment

·Identify and treat the root cause (shock causing lactic acidosis (acid from oxygen-starved tissues), insulin deficiency causing ketoacidosis, kidney failure causing uremic too much acid in the blood (acidosis), diarrhea causing bicarbonate loss, or toxin ingestion such as methanol, ethylene glycol, or aspirin)
·Give intravenous fluids (0.9% normal saline, typically 10–20 mL/kg bolus over 1 hour, then ongoing replacement at 250–500 mL/hour, adjusted to patient size and response)
·Give intravenous regular insulin (0.1 units/kg/hour continuous infusion; some protocols use an initial 0.1 units/kg bolus) with dextrose-containing fluids (add 5% dextrose to IV fluids) once glucose drops below 200–250 mg/dL (for diabetic ketoacidosis (the acid crisis of missing insulin) only)
·Treat dangerous high potassium (above 6.5 mEq/L or with ECG changes: tall peaked T waves, wide QRS, or sine wave) with IV calcium gluconate (1 g over 2–3 minutes) or calcium chloride to protect the heart; insulin (10 units IV) with dextrose (25 g, or 50 mL of 50% dextrose) and/or inhaled albuterol (10–20 mg nebulized) to move potassium into cells; and dialysis if kidneys are not working
·Give intravenous sodium bicarbonate (50–100 mEq mixed in 0.45% saline or dextrose solution, infused over 30–60 minutes) ONLY if pH is below 7.0–7.1 AND the patient has severe shock, life-threatening high potassium not responding to other treatments, or specific toxin ingestion (aspirin, tricyclic antidepressant, or toxic alcohol like methanol or ethylene glycol)
·Support breathing with supplemental oxygen (nasal cannula or mask to keep oxygen saturation ≥94%) and monitor for fluid in the lungs; prepare for mechanical ventilation if the patient's breathing muscles tire or too much acid in the blood (acidosis) is so severe the lungs cannot compensate
·Initiate urgent hemodialysis for refractory too much acid in the blood (acidosis) (pH remains below 7.1 despite treatment), severe severe waste buildup in the blood (uremia) (advanced kidney failure with BUN above 100 mg/dL or symptoms of uremic encephalopathy), refractory high potassium (hyperkalemia) (potassium above 6.5 mEq/L not responding to medical therapy), fluid overload with pulmonary edema (fluid flooding the lungs), or confirmed toxic alcohol ingestion (methanol, ethylene glycol) with end-organ damage

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NCLEX trap

·Sodium bicarbonate is used only when pH drops below 7.1 AND the patient has severe heart failure (the heart pump is too weak to do its job), life-threatening high potassium (hyperkalemia) (potassium dangerously high in the blood), or respiratory failure needing a breathing machine. First, treat the underlying cause—the disease that is making the acid pile up. Bicarbonate is a temporary bridge, not the real fix for acute metabolic acidosis (acid building up in the blood).
·Deep, rapid breathing (called Kussmaul respirations) in acute metabolic acidosis (acid building up in the blood) is the body's smart, built-in response. The lungs are blowing off carbon dioxide to raise the blood pH back up (compensatory respiratory alkalosis (blowing off too much carbon dioxide)). This breathing pattern is not the problem—the acid buildup is. The lungs are doing exactly what they should.
·High potassium (Hyperkalemia) in acute metabolic acidosis (acid building up in the blood) can cause sudden cardiac arrest (the heart stops) without any warning on the ECG. Keep the patient on continuous heart rhythm monitoring (telemetry) and treat high potassium early with calcium, insulin plus sugar (dextrose), and by fixing the too much acid in the blood (acidosis) itself. Do not wait for peaked T-waves or widened QRS complexes to appear on the monitor.
·IV fluids help keep blood flowing to the organs (perfusion), but they do not fix the main metabolic problem. If the cause is diabetic ketoacidosis (the acid crisis of missing insulin) (DKA), you need insulin to stop the body from making more ketones. If it is acute kidney injury, you may need emergency dialysis (a machine that filters the blood). If it is toxic alcohol poisoning, you need the antidote fomepizole or ethanol. Identify the specific acid piling up: lactate (from shock or sepsis), ketones (from DKA, alcoholic ketoacidosis, or starvation), uremic acids (from kidney failure), toxic alcohols (methanol or ethylene glycol), or salicylates (aspirin overdose)—then treat that specific cause.
·Confusion and widespread weakness in acute metabolic acidosis (acid building up in the blood) are reversible when you quickly correct the pH. The brain, spinal cord, and heart function recover once the blood pH (acidemia) goes back to normal. Immediate treatment can prevent permanent damage.
·Non-anion gap metabolic acidosis (acid building up in the blood) (from losing bicarbonate through diarrhea or from renal tubular too much acid in the blood (acidosis) where the kidneys fail to reclaim bicarbonate) is just as dangerous and carries equal risk of death. Use the anion gap to identify the acid source, not to decide how serious the situation is. The arterial pH value tells you the immediate danger.

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