Central Venous Pressure Referencing in the Lateral Position: Comparison With Direct Right Atrial Pressure in Mechanically Ventilated ICU Patients.

Abstract

Right atrial pressure (RAP) is a key determinant of venous return and reflects right-sided filling pressures in critically ill patients. Central venous pressure (CVP) is commonly used as a surrogate, but its accuracy depends on appropriate transducer levelling. While reference points have been evaluated in supine positions, evidence is lacking for the lateral position, despite its frequent use in intensive care. Furthermore, it remains unclear whether lateral positioning alters RAP itself. In this prospective observational study, 16 sedated, mechanically ventilated ICU patients with central venous catheters were included. RAP was measured using a solid-state catheter positioned in the mid-right atrium, confirmed by waveform analysis and echocardiography. Simultaneous CVP was recorded with the transducer levelled 5 cm below the mid-sternum. Measurements were obtained at end-expiration in supine, 45° left lateral, and 45° right lateral positions. Agreement between RAP and CVP was assessed using Bland-Altman analysis, intraclass correlation coefficients, and predefined clinical thresholds. Stepwise hydrostatic adjustments were applied to identify optimal reference levels. In the right lateral position, CVP referenced 5 cm below the sternum closely approximated RAP (bias -0.4 mmHg; limits of agreement -3.2 to +2.4; ICC 0.85). In the left lateral position, the same reference point systematically overestimated RAP (bias -2.2 mmHg; limits of agreement -5.0 to +0.7; ICC 0.58). Adjustment to approximately 2 cm below the sternum minimised bias (-0.1 mmHg) and improved agreement (ICC 0.82). RAP increased in the right lateral position compared with both supine (Δ +2.9 mmHg, p < 0.001) and left lateral (Δ +2.8 mmHg, p < 0.001) positions, while no difference was observed between supine and left lateral positions (p = 0.78). In mechanically ventilated ICU patients, central venous pressure accuracy was position-dependent, and optimal external reference levels differed between lateral positions. Right atrial pressure increased in the right lateral position, suggesting that lateral positioning influences cardiopulmonary physiology beyond hydrostatic measurement effects alone. https://clinicaltrials.gov/study/NCT06705374, registration date 30 April 2024 EDITORIAL COMMENT: The study showed that central venous pressure systematically overestimated right atrial pressure in mechanically ventilated patients placed in the left lateral position. This means that preload and venostasis can be misinterpreted in this position. The influence of increased right atrium pressure on venous return and cardiac output during left lateral positioning in mechanically ventilated patients requires further studies before the clinical relevance can be assessed.