What is the significance of a respiratory variation of greater than 50% in Inferior Vena Cava (IVC) calibre, measuring 1.3 cm, with a right atrial (RA) pressure of 3 mmHg, indicating hypotension?

From the Guidelines

The patient's IVC diameter of 1.3 cm with respiratory variation greater than 50% and low RA pressure of approximately 3 mmHg suggests adequate volume status and normal cardiac filling pressures, and therefore, no fluid expansion is recommended at this time. The findings are consistent with euvolemia, and the collapsibility of the IVC with respiration is a normal physiologic response, reflecting the negative intrathoracic pressure during inspiration which increases venous return to the right heart 1. According to the experts' opinion on management of hemodynamics in ARDS patients, focus should be on the effects of mechanical ventilation, and respiratory settings adaptation, such as driving pressure, Pplateau, and PEEP, should be considered to minimize lung injury and optimize cardiac output 1. Additionally, limiting hypercapnia and considering prone position may also be beneficial in managing the patient's condition 1. It is essential to monitor the patient's hemodynamic status closely and adjust the management strategy as needed to optimize outcomes and minimize morbidity and mortality. The use of echocardiography, such as transthoracic echocardiography (TTE) or transesophageal echocardiography (TEE), can provide valuable information on ventricular dimensions and function, and help guide fluid management and other therapeutic interventions 1. In patients with severe ARDS or sepsis-associated disorders, advanced hemodynamic monitoring, such as pulmonary artery catheter (PAC) or transpulmonary thermodilution systems, may be considered to optimize cardiac output and minimize fluid overload 1. However, the most recent and highest quality study, which is the 2019 perioperative quality initiative consensus statement on postoperative blood pressure, risk and outcomes for elective surgery, suggests that a passive leg raise (PLR) test can be useful in detecting whether inadequate preload is contributing to hypotension, and that fluid bolus may not be appropriate in all cases of postoperative hypotension 1. Therefore, a careful assessment of the patient's volume status and cardiac function is necessary to determine the best course of management. Key considerations in managing the patient's condition include:

• Monitoring of IVC diameter and respiratory variation to assess volume status
• Assessment of cardiac function using echocardiography
• Optimization of respiratory settings to minimize lung injury and optimize cardiac output
• Consideration of prone position and limitation of hypercapnia
• Close monitoring of hemodynamic status and adjustment of management strategy as needed.

From the Research

Respiratory Variation in Inferior Vena Cava Diameter

• The respiratory variation in inferior vena cava diameter (DeltaD(IVC)) is a parameter that has been studied as a guide to fluid therapy in mechanically ventilated patients 2.
• A study published in 2004 found that DeltaD(IVC) was closely correlated with the increase in cardiac output (r=0.82, P<0.001) and a 12% DeltaD(IVC) cut-off value allowed identification of responders with positive and negative predictive values of 93% and 92%, respectively 2.
• However, another study published in 2012 found that in spontaneously breathing patients with acute circulatory failure, high cIVC values (>40%) are usually associated with fluid responsiveness while low values (< 40%) do not exclude fluid responsiveness 3.

Prediction of Fluid Responsiveness

• A systematic review and meta-analysis published in 2017 found that respiratory variation in inferior vena cava diameter has limited ability to predict fluid responsiveness, particularly in spontaneously ventilating patients 4.
• The pooled sensitivity and specificity for a positive IVC ultrasound as a predictor of fluid responsiveness were 0.63 (95% confidence interval [CI]: 0.56-0.69) and 0.73 (95% CI: 0.67-0.78), respectively, with a pooled area under the receiver operating characteristic curve of 0.79 (standard error 0.05) 4.
• A commentary published in 2012 noted that there is still confusion about the meaning of IVC respiratory variations, whether the patient is spontaneously breathing or mechanically ventilated 5.

Clinical Application

• The studies suggest that respiratory variation in inferior vena cava diameter can be a useful parameter in predicting fluid responsiveness in mechanically ventilated patients, but its use in spontaneously breathing patients should be cautious 2, 3, 4.
• Clinical context should be taken into account when using IVC ultrasound to help make treatment decisions 4.
• Other factors such as central venous pressure and cardiac output should also be considered when assessing fluid responsiveness 5.