Interpretation for Medical Auditors & Health Insurance Claim Processors

Abstract:

Arterial Blood Gas Analysis (ABG) is commonly used diagnostic tool to evaluate the partial pressures of gas in blood and acid base content. It is integral to assessing emergency department patients with acute respiratory or metabolic disease. This medical test is done to measure the levels of oxygen and carbon dioxide in the blood of patient. It equally checks the balance of acids and bases known as the pH balance, in the blood. Understanding and using ABG analysis guides medical professionals to interpret respiratory, circulatory and metabolic disorders in any patient. It helps in interpreting

conditions that affect respiratory system, circulatory system and metabolic processes (how body transforms the food one eats into energy), especially in emergency situations.

Understanding ABG reports help medical auditors and health claim processors to determine the medical necessity of the treatment. This report is important clinical tool as well as it is very important document for health insurance professionals who process claims or medical auditors who investigate a case to determine its medical necessity.

A blood gas analysis may be performed on blood obtained from anywhere in the circulatory system say artery, vein or capillary. A medical auditor and claim processor should know that differences in measured blood gas values between arterial and venous blood are most pronounced for PO2 as PO2 is the only clinical reason for obtaining arterial collections. When blood is taken from an artery the report is known as ABG. Peripheral Venus blood gas (VBG) is a valuable alternate as it is less painful and easy to collect.

Interpreting an arterial blood gas (ABG) is a crucial skill for physicians, nurses, respiratory therapists, and other health care personnel. ABG interpretation is especially important in critically ill patients. ABG analysis assesses the patient’s partial pressures of oxygen (PaO₂) and carbon dioxide (PaCO₂) PaCO2 provides information on the oxygenation status & PaCO2 provides information on ventilation status i.e. chronic or acute respiratory failure. Though oxygenation and ventilation can be assessed non-invasively via pulse oximetry and end-tidal carbon di oxide monitoring respectively but where ABG being a standard is prescribed as mandatory investigation it must remain available to consider a pre-authorization of any specific treatment or to consider the final settlement of such treatment. If not mandatory the pulse oximetry readings and end-tidal carbon dioxide monitoring report are generally considered with evaluation of other medical documents.

For a reliable ABG report an ABG specimen should be collected in a heparinised blood gas syringe anaerobically and analysed within 30 minutes otherwise they should be placed on ice. Prior to an arterial puncture the Allen test should be performed to check for the ability of radial and ulnar arteries to return blood to the hand. Medical Auditors who find ABG report not that supportive of other medical documents do analyse this process during their medical audit to have fair idea of treatment.

For Health Insurance Claim Processors and Medical Auditors interpreting this report is equally important to understand the necessity of treatment provided. In Government Health Insurance Schemes the Standard Treatment Guidelines (STGs) prescribe the necessity of this report in specific procedures before pre-authorization of that procedure and necessity of serial ABG reports, as mandatory investigation, at the time of settlement of claim. For example, in case of neo-natal care packages for mild encephalopathy, care requiring mechanical ventilation or non-invasive respiratory support (CPAP, HFFNC) ABG is a mandatory medical investigation to consider the necessity of the treatment. Similarly, at the time of pre-authorization to consider admissibility of a claim for congestive cardiac failure, pneumonia, lower respiratory tract infection, bronchiolitis, asthma, COPD ( chronic lung condition), ARDS, severe sepsis, septic shock &poisoning etc ABG is prescribed as mandatory investigation report for emergency medicine, anaesthesiology, pulmonology, diabetes related ketoacidosis, renal tubular acidosis etc. Thus this medical test is very common in many of the disorders requiring in-patient treatment and care. This makes this medical document very important in its nature and professionals handling health insurance claims should know the basics of this medical test. It is expected from pre-authorization claim processor or final claim settling doctor/officer to diligently review the mandatory documents. Understanding ABG is very important to such professionals.

The following six-step process helps ensure a complete interpretation of every ABG component.

1. Is pH normal? It is measured acid-base balance of the blood.

2. Is CO₂ normal? Partial pressure of carbon di oxide in arterial blood.

3. Is HCO₃ normal? Calculated concentration of bicarbonate in arterial blood

4. Match CO₂ & HCO₃ with pH.

5. Does CO₂ or HCO₃ go the opposite direction of pH?

6. Are pO₂ & O₂ saturation normal?

Normal Arterial Value Range:

An acceptable normal range of ABG values of ABG components is the following. However the medical auditors and health claim processors may know that the range of normal values may vary among laboratories and in different age groups from neonates to geriatrics.

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Parameter                         Reference Range

pH                                           7.35-7.45

PaCO2                                   35-45 mmHg

PaO2                                      80-100 mmHg ( millimetres of mercury)

SaO2 (saturation)                95-100%

HCO3                                     22-26 mEq/L ( mill equivalents per litre)

Base excess/deficit              -4 to +2

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Interpretation of ABG systematically leads to understand the degree of severity of abnormalities and to assess whether the abnormalities are acute or chronic and whether the primary disorder is metabolic or respiratory in origin. This along with other medical documents helps to determine whether line of treatment claimed is in order or needs further investigation or assessment to ensure it is a genuinely claimed procedure.

In addition, you will find tables that list commonly encountered acid-base disorders.

Many methods exist to guide the interpretation of the ABG. This discussion does not include some methods, such as analysis of base excess or Stewart’s strong ion difference. A summary of these techniques can be found in some of the suggested articles. It is unclear whether these alternate methods offer clinically important advantages over the presented approach, which is based on the “anion gap.”

6-step approach:

Step 1:  Assess the internal consistency of the values using the Henderson-Hasselbalch equation:

[H+] = 24(PaCO₂)
[HCO₃-]

If the pH and the [H+] are inconsistent, the ABG is probably not valid.

Step 2:  Is there alkalemia or acidemia present?

pH < 7.35  acidemia
pH > 7.45  alkalemia

• This is usually the primary disorder
• Remember: an acidosis or alkalosis may be present even if the pH is in the normal range (7.35 – 7.45)
• You will need to check the PaCO₂, HCO₃– and anion gap

Step 3:  Is the disturbance respiratory or metabolic?  What is the relationship between the direction of change in the pH and the direction of change in the PaCO₂? In primary respiratory disorders, the pH and PaCO2 change in opposite directions; in metabolic disorders the pH and PaCO₂ change in the same direction.

Step 4:  Is there appropriate compensation for the primary disturbance?  Usually, compensation does not return the pH to normal (7.35 – 7.45).

If the observed compensation is not the expected compensation, it is likely that more than one acid-base disorder is present.

Step 5:  Calculate the anion gap (if a metabolic acidosis exists): AG= [Na+]-( [Cl-] + [HCO₃-] )-12 ± 2

• A normal anion gap is approximately 12 meq/L.
• In patients with hypoalbuminemia, the normal anion gap is lower than 12 meq/L; the “normal” anion gap in patients with hypoalbuminemia is about 2.5 meq/L lower for each 1 gm/dL decrease in the plasma albumin concentration (for example, a patient with a plasma albumin of 2.0 gm/dL would be approximately 7 meq/L.)
• If the anion gap is elevated, consider calculating the osmolal gap in compatible clinical situations.
  • Elevation in AG is not explained by an obvious case (DKA, lactic acidosis, renal failure
  • Toxic ingestion is suspected
• OSM gap =  measured OSM – (2[Na+] – glucose/18 – BUN/2.8
  • The OSM gap should be < 10

Step 6:  If an increased anion gap is present, assess the relationship between the increase in the anion gap and the decrease in [HCO₃-].

Assess the ratio of the change in the anion gap (∆AG ) to the change in  [HCO3-] (∆[HCO₃-]): ∆AG/∆[HCO₃-]

This ratio should be between 1.0 and 2.0 if an uncomplicated anion gap metabolic acidosis is present.

If this ratio falls outside of this range, then another metabolic disorder is present:

• If  ∆AG/∆[HCO₃-] < 1.0, then a concurrent non-anion gap metabolic acidosis is likely to be present.

• If  ∆AG/∆[HCO₃-] > 2.0, then a concurrent metabolic alkalosis is likely to be present.

It is important to remember what the expected “normal” anion gap for your patient should be, by adjusting for hypoalbuminemia (see Step 5, above.)

Table 1:  Characteristics of acid-base disturbances

Table 2:  Selected etiologies of respiratory acidosis

• Airway obstruction
  – Upper- Lower

• COPD

• asthma
• other obstructive lung disease
• CNS depression

• Sleep disordered breathing  (OSA or OHS)

• Neuromuscular impairment

• Ventilatory restriction

• Increased CO2  production: shivering, rigors, seizures, malignant hyperthermia, hypermetabolism, increased intake of carbohydrates

• Incorrect mechanical ventilation settings

Table 3:  Selected etiologies of respiratory alkalosis

• CNS stimulation: fever, pain, fear, anxiety, CVA, cerebral edema, brain trauma, brain tumor, CNS infection

• Hypoxemia or hypoxia: lung disease, profound anemia, low FiO2

• Stimulation of chest receptors: pulmonary edema, pleural effusion, pneumonia, pneumothorax, pulmonary embolus

• Drugs, hormones: salicylates, catecholamines, medroxyprogesterone, progestins

• Pregnancy, liver disease, sepsis, hyperthyroidism

• Incorrect mechanical ventilation settings

Table 4:  Selected causes of metabolic alkalosis

• Hypovolemia with Cl- depletion
  • GI loss of H+
    • Vomiting, gastric suction, villous adenoma, diarrhea with chloride-rich fluid
  • Renal loss H+
    • Loop and thiazide diuretics, post-hypercapnia (especially after institution of mechanical ventilation)
• Hypervolemia, Cl- expansion
  • Renal loss of H+:  edematous states (heart failure, cirrhosis, nephrotic syndrome), hyperaldosteronism, hypercortisolism, excess ACTH, exogenous steroids, hyperreninemia, severe hypokalemia, renal artery stenosis, bicarbonate administration

Table 5:  Selected etiologies of metabolic acidosis

• Elevated anion gap:
  • Methanol intoxication
  • Uremia
  • Diabetic ketoacidosis^a, alcoholic ketoacidosis, starvation ketoacidosis
  • Paraldehyde toxicity
  • Isoniazid
  • Lactic acidosis^a
    • Type A:  tissue ischemia
    • Type B:  Altered cellular metabolism
  • Ethanol^b or ethylene glycol^b intoxication
  • Salicylate intoxication

^a Most common causes of metabolic acidosis with an elevated anion gap
^b Frequently associated with an osmolal gap

• Normal anion gap: will have increase in [Cl-]
  • GI loss of HCO₃–
    • Diarrhea, ileostomy, proximal colostomy, ureteral diversion
  • Renal loss of HCO₃–
    • proximal RTA
    • carbonic anhydrase inhibitor (acetazolamide)
  • Renal tubular disease
    • ATN
    • Chronic renal disease
    • Distal RTA
    • Aldosterone inhibitors or absence
    • NaCl infusion, TPN, NH₄+ administration

Table 6:  Selected mixed and complex acid-base disturbances

ABG is an important diagnostic report and fair knowledge of its interpretation and knowledge of normal values of ABG test may help the claim processors to take prompt decisions in allowing or disallowing the hospitalization at pre-authorization level as well as in settlement of claim. It gives comprehensive view of condition and along with other mandatory documents of treatment including other diagnostic reports it helps professionals to process health insurance claims efficiently.

About Authors:

Vinay Verma is Mentor, Trainer, Educationist and Expert Health Insurance Professional Advisor. He retired as Deputy General Manager from the Oriental Insurance Company Limited. He was member of FICCI & CII’s Health Insurance Forums. He was member of IRDAI-National Health Authority’s joint working group on Fraud Control. He has vast experience as team leader in promoting retail, corporate and Government Schemes in health insurance at corporate level. He was member of Central Committee of PPN of public sector insurance companies and has serviced multiple health insurance programmes of various state governments in different capacities.

Dr Vaishali Pradhan is a medico-insurance expert with exposure & experience in servicing patients at Hospitals especially during Covid-19 period. She has equally good experience in servicing one of the largest Health Insurance Programme of Government of Rajasthan.