Rebreathing of Inert Gas for Measurement of Cardiac Output and Validation of Intra-Cardiac Shunt
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This policy addresses use of inert (foreign) gas rebreathing techniques to measure cardiac output and to validate intra-cardiac shunts, and states Aetna's coverage stance for these procedures and related indications.
No material clinical or coverage changes in this revision.
Coverage Criteria
Experimental and Investigational
The policy lists the following procedures as experimental and investigational because effectiveness has not been established:
These three specific uses are designated experimental/investigational in the policy.
This policy addresses the use of inert gas rebreathing (IGR) techniques for noninvasive measurement of cardiac output and for validation of intra-cardiac shunt. Aetna considers the following procedures experimental and investigational because their effectiveness has not been established: (1) rebreathing of inert gas for the measurement of cardiac output; (2) rebreathing of inert gas for prediction of survival in persons with pulmonary hypertension; and (3) rebreathing of inert gas for validation of intra-cardiac shunt.
Accuracy of IGR can be limited in certain pulmonary conditions. Incomplete alveolar gas mixing and intrapulmonary shunting can cause underestimation of pulmonary blood flow, reducing the reliability of IGR measurements in patients with significant lung disease. Comparisons to reference methods are also affected by limitations of those methods (for example, thermodilution is less reliable with tricuspid regurgitation or low cardiac output, and indirect Fick depends on estimated oxygen consumption). These factors should be considered when interpreting IGR results and when selecting alternative or confirmatory CO measurement techniques.
The policy explicitly classifies the listed inert gas rebreathing applications as experimental and investigational because current evidence does not establish their effectiveness. As a result, these procedures are not supported for routine clinical use for cardiac output measurement, prognostication in pulmonary hypertension, or intra-cardiac shunt validation.
Clinical use considerations
Evidence considerations and contextual guidance from cited studies
Supported by studies including postural stress, PH cohorts, and device validations.
Authors suggest potential utility but emphasize need for multicenter validation and serial measurements.
Explicit limitations described in PH and comparative studies.
Mixed findings reported across studies; multicenter and serial-measure studies recommended.
Coding and Device Authorization
| I27.0 | Pulmonary hypertension |
| I27.20 | Pulmonary hypertension, unspecified |
| I27.21 | |
| I27.22 | |
| I27.23 | |
| I27.24 | |
| I27.29 | |
| Q21.0 | Congenital malformations of cardiac septa [intra cardiac shunt] |
| Q21.1 | |
| Q21.2 |
| No codes listed |
| K051907 | FDA 510(k) summary for Innocor Noninvasive Cardiac Output Monitor |
| K041450 | FDA 510(k) summary for NICO with MARS, Model 7300 |
Provider Actions and Authorization Guidance
Coding / Authorization
Coding/Authorization note: No specific CPT or HCPCS codes are assigned to inert gas rebreathing (IGR) procedures in this policy. When billing, verify applicable procedure and diagnosis codes; note that ICD‑10 codes for pulmonary hypertension (I27.0, I27.20‑I27.29) and congenital cardiac septal defects (Q21.0‑Q21.9) are listed as related indications and may affect claim adjudication. Because IGR is classified as experimental/investigational for measurement of cardiac output and validation of intra‑cardiac shunt under this policy, payers may deny reimbursement for these procedures.
- No specific CPT/HCPCS codes designated in this policy.
- Related ICD‑10 codes called out: I27.0, I27.20‑I27.29 (pulmonary hypertension); Q21.0‑Q21.9 (congenital cardiac septa).
- Procedures deemed experimental/investigational may be denied as not medically necessary.
Device Clearance and Authorization
Device clearance/authorization: Some IGR devices have received FDA 510(k) clearance (for example, the Innocor system and the NICO systems noted in device summaries). Clearance of a device does not, by itself, establish clinical utility for the indications in this policy. Providers should include device 510(k) documentation and model identifiers when submitting requests or appeals, and check payer-specific prior authorization requirements, as prior authorization may still be required despite device clearance.
- FDA 510(k) summaries referenced: Innocor (K051907) and NICO with MARS, Model 7300 (K041450).
- Include device model and 510(k) summary or equivalent documentation with authorization or appeal requests.
- Confirm and obtain any payer prior authorization before performing IGR when coverage is uncertain.
Denial Risk — Experimental/Investigational Classification
Experimental/Investigational denial risk: IGR for measurement of cardiac output, prediction of survival in pulmonary hypertension, and validation of intra‑cardiac shunt is classified as experimental and investigational in this policy. As such, claims for these indications are at risk for medical necessity denial. Anticipate denials and prepare clinical justification and supporting evidence if pursuing coverage or appeal.
- IGR for CO measurement, prognostication in pulmonary hypertension, and shunt validation is considered experimental/investigational.
- Claims for these indications may be denied as not medically necessary.
- When pursuing coverage, supply robust clinical evidence and rationale in prior authorization/appeal submissions.
Accuracy Limitations and Interpretation
Accuracy limitations that may affect interpretation: IGR may underestimate pulmonary blood flow and cardiac output in patients with pulmonary disease because of incomplete alveolar gas mixing and intrapulmonary shunting. Thermodilution and indirect Fick methods also have known limitations (e.g., tricuspid regurgitation, low output states, and assumptions about oxygen consumption). Be aware of these modality-specific limitations when interpreting results and documenting clinical decisions.
- IGR underestimation risk in the presence of lung disease (incomplete gas mixing, intrapulmonary shunt).
- Thermodilution and indirect Fick have limitations that can affect comparative accuracy (tricuspid regurgitation, low CO, O2 consumption estimation).
- Document clinical context and known limitations when using CO measurements to guide care.
Documentation for Shunt Validation Studies
Documentation for shunt validation studies: For cases where IGR (often combined with thoracic bioimpedance) is used to estimate Qp/Qs, submit a clear comparison plan and supporting data. Provide the reference standard used (direct Fick, Doppler echocardiography, or catheterization), timing of measurements (pre/post intervention), device identifiers, and the method of simultaneous measurements. Include institutional review/ethics approval or trial registration when applicable.
- State the reference standard for Qp/Qs (direct Fick, Doppler echo, or catheterization) and provide comparative protocol details.
- Include device model, calibration/validation records, and timing of paired measurements (before/after closure or intervention).
- Attach trial registration or institutional review documentation for prospective studies.
Consider Alternative Methods in Lung Disease
Consider alternative methods in lung disease: In patients with coexisting pulmonary disease or when intrapulmonary shunt is suspected, consider confirmatory or alternative cardiac output measurement methods (e.g., thermodilution via right heart catheterization, direct or indirect Fick method, Doppler echocardiography, or cardiac MRI) and document the rationale for method selection. When IGR is used in this context, document any measures taken to mitigate known accuracy issues and the clinical reason for choosing IGR.
- Prefer alternative or confirmatory CO measurement methods when lung disease or intrapulmonary shunt may bias IGR results.
- Document rationale for using IGR despite pulmonary disease and any mitigation steps taken.
- When available, corroborate IGR findings with an accepted reference method.
Definitions
Background
Measurement of cardiac output is an important component of cardiovascular assessment and management. Invasive thermodilution using a pulmonary artery catheter (PAC) has been the established reference method in many clinical settings. Noninvasive techniques such as inert gas rebreathing aim to estimate pulmonary blood flow and cardiac output by analyzing gas uptake or washout during a closed rebreathing maneuver; however, despite device clearances and published studies, IGR remains differentiated from the established thermodilution approach and, per this policy, is designated as experimental/investigational for the listed indications.
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