From the Guidelines
Yes, an IVC caliber of 1.3 cm with a respiratory variation greater than 50% and a right atrial pressure of 3 mmHg is considered normal. The inferior vena cava (IVC) diameter typically ranges from 1.0 to 2.0 cm in normal adults, with 1.3 cm falling well within this normal range, as an IVC diameter < 2.1 cm is considered normal 1. The significant respiratory variation (>50% collapse during inspiration) indicates normal volume status and cardiac function. This respiratory variation occurs because during inspiration, negative intrathoracic pressure increases venous return to the right heart, causing the compliant IVC to collapse partially. The right atrial pressure of 3 mmHg is also within the normal range of 0-5 mmHg, confirming normal central venous pressure. These findings together suggest adequate intravascular volume status without evidence of right heart failure, tamponade, or other conditions that would impair venous return. Some key points to consider in this assessment include:
- IVC diameter:
- Normal: < 2.1 cm 1
- Respiratory variation:
- Normal: >50% collapse during inspiration
- Right atrial pressure:
- Normal: 0-5 mmHg This assessment is commonly used in clinical settings to evaluate a patient's volume status and right heart function, as described in the European Heart Journal 1.
From the Research
IVC Calibre and Respiratory Variation
- An IVC calibre of 1.3 cm with a respiratory variation (resp.) >50% is generally considered to indicate a low volume status or high fluid responsiveness 2.
- However, the relationship between IVC calibre, respiratory variation, and volume status is complex and can be influenced by various factors, including cardiac function, venous return, and ventilator settings 3, 2.
Right Atrial Pressure
- A right atrial (RA) pressure of 3 mmHg is within the normal range, as central venous pressure (CVP) is typically measured between 0-8 mmHg 3.
- CVP is an estimate of right atrial pressure and is used to assess cardiac preload and volume status in critically ill patients 3.
Ultrasound Assessment of IVC
- Ultrasound assessment of IVC collapsibility is not a valid measure of preload changes during triggered positive pressure ventilation 2.
- The use of point-of-care ultrasound to assess IVC in the context of resuscitation is a controversial topic, with results being equivocal 4.
- Different acquisition techniques for IVC measurement by point-of-care ultrasonography (POCUS) have been compared, with sub-xiphoid transabdominal long axis (LA) view showing the highest intra-class correlation coefficient (ICC) for B-mode measurements 5.