NICOM

 

What is Fluid Responsiveness (FR) and why is it important?

• Definition: FR is defined by a 10-15% increase in cardiac output (CO) following fluid administration. FR does not mean fluid is required; it only indicates that CO will increase with volume.
• Clinical Relevance: Assessing FR can prevent fluid overload, minimizing risks like renal failure and prolonged vasopressor use. In septic patients, only 50% may be fluid responsive, highlighting the need for precise assessment.

How is Fluid Responsiveness measured?

• Static vs. Dynamic Tests:
  • Static: Central Venous Pressure (CVP), Pulmonary Capillary Wedge Pressure (PCWP)
  • Dynamic: Pulse Pressure Variation (PPV), Passive Leg Raise (PLR)
• Challenge Methods: Some methods (like PPV or LVOT VTI) predict FR independently, while others require a challenge maneuver (e.g., PLR or mini-bolus).

What are the different types of Fluid Responsiveness tests?

• Measurement-Based: Respiratory variation in PPV or LVOT VTI can predict FR.
• Challenge Maneuver: PLR or mini-bolus used with bio-reactance (NICOM) or End-Tidal CO₂ (ETCO₂) changes. A ≥5% increase in ETCO₂ with PLR suggests FR.

What is Fluid Tolerance (FT)?

• Definition: FT indicates the absence of harm, such as pulmonary edema, upon fluid administration. It is assessed to avoid fluid overload and related complications.

Which clinical parameters may not reliably predict FR?

• Limitations: Parameters such as hourly urine output (UOP) and mean arterial pressure (MAP) tend to lag and do not consistently predict FR. Dynamic assessments are generally more reliable.

How can bio-reactance (NICOM) be used to assess FR?

• Principle: Measures blood flow by applying an electric field to the chest.
• Protocol: Combine with PLR or mini-bolus; a ≥10% increase in stroke volume (SV) indicates FR.
• Effectiveness: Works well even in prone patients, with an AUROC (Area Under the Receiver Operating Characteristic) of 0.75-0.88.

How does Passive Leg Raise (PLR) predict Fluid Responsiveness?

• Mechanism: Elevating legs to 45° from flat position mimics a 300ml bolus. An increase in CO during this maneuver suggests FR.
• Effectiveness: Non-invasive and effective in various settings. Generally requires continuous monitoring for CO changes.

What is the role of the arterial line in assessing FR?

• Pulse Pressure Variation (PPV): A >12% increase in PPV with mechanical ventilation suggests FR.
• Requirements: Reliable with tidal volume >6 mL/kg, sinus rhythm, and without spontaneous breaths. Not ideal for patients in the prone position.

What alternative tests are available for FR assessment?

• End-Tidal CO₂ (ETCO₂): Increase of ≥5% with PLR predicts FR.
• End Expiratory Occlusion (EEO): Performed on mechanically ventilated patients; a 5% increase in CO during a 15-second hold suggests FR.
• High PEEP Challenge: Used with mechanically ventilated patients, increasing PEEP from 10 to 20 cm H₂O. A 10% decrease in CO or an 8% drop in MAP suggests FR.

Are there any ultrasound-based methods for assessing FR?

• IVC Size & Distensibility: Measures IVC variation with respiration; >15% suggests FR. However, performance is lower overall.
• Carotid VTI: A simpler alternative to LVOT VTI, useful in repeat assessments.

What are the challenges associated with static FR assessments?

• Limitations of CVP: While widely used, CVP has poor predictive ability for FR and is affected by various factors, including right ventricular function.