function calculateABGInterpretation() {
var pH = parseFloat(document.getElementById("phValue").value);
var paco2 = parseFloat(document.getElementById("paco2Value").value);
var hco3 = parseFloat(document.getElementById("hco3Value").value);
var na = parseFloat(document.getElementById("naValue").value);
var cl = parseFloat(document.getElementById("clValue").value);
var primaryDisorder = "";
var compensationStatus = "";
var anionGapText = "";
var deltaGapText = "";
var overallSummary = "";
// Clear previous results
document.getElementById("primaryDisorder").innerHTML = "";
document.getElementById("compensationStatus").innerHTML = "";
document.getElementById("anionGapResult").innerHTML = "";
document.getElementById("deltaGapResult").innerHTML = "";
document.getElementById("overallSummary").innerHTML = "";
if (isNaN(pH) || isNaN(paco2) || isNaN(hco3)) {
document.getElementById("overallSummary").innerHTML = "Please enter valid numbers for pH, PaCO2, and HCO3.";
return;
}
// Normal Ranges
var normal_pH_low = 7.35;
var normal_pH_high = 7.45;
var normal_paco2_low = 35;
var normal_paco2_high = 45;
var normal_hco3_low = 22;
var normal_hco3_high = 26;
var normal_ag_low = 8;
var normal_ag_high = 12;
var normal_ag_mid = 10; // For delta gap calculation
var isAcidemic = pH normal_pH_high;
var isNormalpH = !isAcidemic && !isAlkalemic;
var isRespAcidosis = paco2 > normal_paco2_high;
var isRespAlkalosis = paco2 < normal_paco2_low;
var isMetAcidosis = hco3 normal_hco3_high;
var primaryProblem = [];
var secondaryProblem = [];
// Determine Primary Disorder
if (isAcidemic) {
if (isRespAcidosis && !isMetAcidosis) {
primaryProblem.push("Respiratory Acidosis");
} else if (isMetAcidosis && !isRespAcidosis) {
primaryProblem.push("Metabolic Acidosis");
} else if (isRespAcidosis && isMetAcidosis) {
primaryProblem.push("Mixed Respiratory and Metabolic Acidosis");
} else {
// pH is acidemic, but PaCO2 and HCO3 are not clearly primary
// This could be a compensated alkalosis or a complex mixed disorder
if (isRespAlkalosis) secondaryProblem.push("Respiratory Alkalosis");
if (isMetAlkalosis) secondaryProblem.push("Metabolic Alkalosis");
if (secondaryProblem.length > 0) {
primaryProblem.push("Complex Acid-Base Disorder (pH acidemic, but primary not clear)");
} else {
primaryProblem.push("Unclear Primary Acidosis");
}
}
} else if (isAlkalemic) {
if (isRespAlkalosis && !isMetAlkalosis) {
primaryProblem.push("Respiratory Alkalosis");
} else if (isMetAlkalosis && !isRespAlkalosis) {
primaryProblem.push("Metabolic Alkalosis");
} else if (isRespAlkalosis && isMetAlkalosis) {
primaryProblem.push("Mixed Respiratory and Metabolic Alkalosis");
} else {
// pH is alkalemic, but PaCO2 and HCO3 are not clearly primary
if (isRespAcidosis) secondaryProblem.push("Respiratory Acidosis");
if (isMetAcidosis) secondaryProblem.push("Metabolic Acidosis");
if (secondaryProblem.length > 0) {
primaryProblem.push("Complex Acid-Base Disorder (pH alkalemic, but primary not clear)");
} else {
primaryProblem.push("Unclear Primary Alkalosis");
}
}
} else { // pH is normal
if (isRespAcidosis && isMetAlkalosis) {
primaryProblem.push("Mixed Respiratory Acidosis and Metabolic Alkalosis (pH compensated)");
} else if (isRespAlkalosis && isMetAcidosis) {
primaryProblem.push("Mixed Respiratory Alkalosis and Metabolic Acidosis (pH compensated)");
} else if (isRespAcidosis && hco3 > normal_hco3_high) { // Compensated respiratory acidosis
primaryProblem.push("Compensated Respiratory Acidosis");
} else if (isRespAlkalosis && hco3 < normal_hco3_low) { // Compensated respiratory alkalosis
primaryProblem.push("Compensated Respiratory Alkalosis");
} else if (isMetAcidosis && paco2 normal_paco2_high) { // Compensated metabolic alkalosis
primaryProblem.push("Compensated Metabolic Alkalosis");
} else {
primaryProblem.push("Normal Acid-Base Status");
}
}
// Determine Compensation Status
var hasCompensation = false;
var compensationType = "";
if (primaryProblem.includes("Respiratory Acidosis") || primaryProblem.includes("Mixed Respiratory and Metabolic Acidosis")) {
if (hco3 > normal_hco3_high) {
hasCompensation = true;
compensationType = "Metabolic Compensation";
}
}
if (primaryProblem.includes("Respiratory Alkalosis") || primaryProblem.includes("Mixed Respiratory and Metabolic Alkalosis")) {
if (hco3 < normal_hco3_low) {
hasCompensation = true;
compensationType = "Metabolic Compensation";
}
}
if (primaryProblem.includes("Metabolic Acidosis") || primaryProblem.includes("Mixed Respiratory and Metabolic Acidosis")) {
if (paco2 normal_paco2_high) {
hasCompensation = true;
compensationType = "Respiratory Compensation";
}
}
if (hasCompensation) {
if (isNormalpH) {
compensationStatus = "Fully Compensated (" + compensationType + ")";
} else {
compensationStatus = "Partially Compensated (" + compensationType + ")";
}
} else if (!isNormalpH && primaryProblem[0] !== "Normal Acid-Base Status" && !primaryProblem[0].includes("Mixed")) {
compensationStatus = "Uncompensated";
} else if (isNormalpH && primaryProblem[0] === "Normal Acid-Base Status") {
compensationStatus = "No significant compensation needed.";
} else {
compensationStatus = "Compensation status not clearly determined for complex/mixed disorders.";
}
// Anion Gap Calculation
var anionGap = NaN;
if (!isNaN(na) && !isNaN(cl)) {
anionGap = na – (cl + hco3);
anionGapText = "Anion Gap: " + anionGap.toFixed(1) + " mEq/L (Normal: " + normal_ag_low + "-" + normal_ag_high + ")";
if (anionGap > normal_ag_high && (primaryProblem.includes("Metabolic Acidosis") || primaryProblem.includes("Mixed Respiratory and Metabolic Acidosis"))) {
anionGapText += " – High Anion Gap Metabolic Acidosis (HAGMA)";
// Delta Gap / Delta-Delta Calculation
var deltaAG = anionGap – normal_ag_mid;
var deltaHCO3 = normal_hco3_high – hco3; // Using 24 as normal HCO3 for calculation
var deltaGap = deltaAG + hco3; // Or (deltaAG – deltaHCO3) + 24
deltaGapText = "Delta Gap: " + deltaGap.toFixed(1) + " mEq/L";
if (deltaGap > 30) {
deltaGapText += " – Suggests concurrent Metabolic Alkalosis.";
} else if (deltaGap < 20) {
deltaGapText += " – Suggests concurrent Non-Anion Gap Metabolic Acidosis.";
} else {
deltaGapText += " – Consistent with isolated High Anion Gap Metabolic Acidosis.";
}
} else if (anionGap 0) {
overallSummary += primaryProblem.join(" and ");
} else {
overallSummary += "Normal Acid-Base Status";
}
if (compensationStatus && compensationStatus !== "No significant compensation needed.") {
overallSummary += ", " + compensationStatus;
}
document.getElementById("primaryDisorder").innerHTML = "
" + primaryProblem.join(" and ");
document.getElementById("compensationStatus").innerHTML = "
" + compensationStatus;
document.getElementById("anionGapResult").innerHTML = anionGapText;
document.getElementById("deltaGapResult").innerHTML = deltaGapText;
document.getElementById("overallSummary").innerHTML = overallSummary;
}
Understanding Arterial Blood Gas (ABG) Interpretation
Arterial Blood Gas (ABG) analysis is a critical diagnostic tool used in medicine to assess a patient's acid-base balance, ventilation, and oxygenation status. It involves measuring the pH, partial pressure of carbon dioxide (PaCO2), and bicarbonate (HCO3) in arterial blood. These values provide crucial insights into the body's physiological state and help identify various respiratory and metabolic disorders.
Key Parameters and Normal Ranges:
- pH: Measures the acidity or alkalinity of the blood.
- Normal Range: 7.35 – 7.45
- Acidemia: pH < 7.35
- Alkalemia: pH > 7.45
- PaCO2 (Partial Pressure of Carbon Dioxide): Represents the respiratory component of acid-base balance. CO2 is an acid.
- Normal Range: 35 – 45 mmHg
- > 45 mmHg: Respiratory Acidosis (hypoventilation)
- < 35 mmHg: Respiratory Alkalosis (hyperventilation)
- HCO3 (Bicarbonate): Represents the metabolic component of acid-base balance. HCO3 is a base.
- Normal Range: 22 – 26 mEq/L
- < 22 mEq/L: Metabolic Acidosis (bicarbonate loss or acid gain)
- > 26 mEq/L: Metabolic Alkalosis (bicarbonate gain or acid loss)
- Anion Gap (AG): An optional but important calculation, especially in metabolic acidosis. It helps differentiate causes of metabolic acidosis.
- Normal Range: 8 – 12 mEq/L
- Formula: Na – (Cl + HCO3)
Steps for ABG Interpretation:
- Assess pH: Determine if the patient is acidemic, alkalemic, or has a normal pH. This tells you the overall acid-base status.
- Assess PaCO2: Look at the PaCO2. If it's abnormal, it indicates a respiratory problem. If it moves in the same direction as the pH (e.g., low pH, high PaCO2), it suggests a primary respiratory disorder. If it moves in the opposite direction, it might be compensation.
- Assess HCO3: Look at the HCO3. If it's abnormal, it indicates a metabolic problem. Similar to PaCO2, its direction relative to pH helps identify a primary metabolic disorder or compensation.
- Match Primary Disorder: Identify which component (respiratory or metabolic) best explains the pH abnormality.
- If pH is low and PaCO2 is high: Primary Respiratory Acidosis.
- If pH is low and HCO3 is low: Primary Metabolic Acidosis.
- If pH is high and PaCO2 is low: Primary Respiratory Alkalosis.
- If pH is high and HCO3 is high: Primary Metabolic Alkalosis.
- Check for Compensation: The body tries to correct primary acid-base imbalances.
- If primary is respiratory, the kidneys compensate by adjusting HCO3.
- If primary is metabolic, the lungs compensate by adjusting PaCO2.
- Uncompensated: pH is abnormal, and the compensating component is normal.
- Partially Compensated: pH is abnormal, but the compensating component is moving in the correct direction to normalize pH.
- Fully Compensated: pH is within the normal range (7.35-7.45), but both PaCO2 and HCO3 are abnormal, indicating a successful compensation.
- Calculate Anion Gap (if metabolic acidosis): If metabolic acidosis is present (low HCO3), calculate the Anion Gap. A high anion gap (>12 mEq/L) suggests specific causes like lactic acidosis, ketoacidosis, renal failure, or toxic ingestions (MUDPILES). A normal anion gap metabolic acidosis is often due to bicarbonate loss (e.g., diarrhea) or chloride excess.
- Calculate Delta Gap / Delta-Delta (if High AG Metabolic Acidosis): This helps identify concurrent metabolic alkalosis or non-anion gap metabolic acidosis in the presence of a high anion gap metabolic acidosis.
Example Scenarios:
Example 1: Uncompensated Respiratory Acidosis
- pH: 7.25 (Acidemic)
- PaCO2: 60 mmHg (High – Respiratory Acidosis)
- HCO3: 24 mEq/L (Normal)
- Interpretation: Primary Respiratory Acidosis, Uncompensated. The high PaCO2 is causing the low pH, and the HCO3 has not yet risen to compensate.
Example 2: Partially Compensated Metabolic Acidosis
- pH: 7.30 (Acidemic)
- PaCO2: 30 mmHg (Low – Respiratory Alkalosis)
- HCO3: 15 mEq/L (Low – Metabolic Acidosis)
- Na: 140 mEq/L, Cl: 100 mEq/L
- Interpretation: Primary Metabolic Acidosis. The low HCO3 is causing the low pH. The low PaCO2 indicates respiratory compensation (hyperventilation) is occurring, but the pH is still acidemic, so it's partially compensated. Anion Gap = 140 – (100 + 15) = 25 mEq/L (High Anion Gap Metabolic Acidosis).
Example 3: Fully Compensated Respiratory Alkalosis
- pH: 7.42 (Normal)
- PaCO2: 25 mmHg (Low – Respiratory Alkalosis)
- HCO3: 18 mEq/L (Low – Metabolic Acidosis)
- Interpretation: Primary Respiratory Alkalosis. The low PaCO2 is the initial problem. The HCO3 has decreased (metabolic compensation) to bring the pH back into the normal range.