Carabini et al. authored an insightful article on caring for patients undergoing complex spine surgery.  Their discussion and referenced studies on the predictive ability of pulse pressure variation in prone-positioned patients during volume expansion merit attention. The referenced studies have limitations, particularly regarding their relevance to patients with higher BMI, poor pulmonary compliance, and abdominal obesity.

Reference 30 was a nonrandomized, crossover study with patients in the prone position experiencing increased blood pressure during volume expansion, with pulse pressure variationexceeding 15% predicting this response. The study’s population had an average body mass index of 22, and the ventilation settings, including a positive end-expiratory pressure (PEEP) range of 0 to 3 cm H2O, raise concerns about applicability. Moreover, the observed rise in plateau pressure during prone positioning raises questions about generalizing these findings to patients with abdominal obesity, where abdominal compression is common and increases in plateau pressure are higher and more common. 

Similarly, reference 31 investigated pulse pressure variation as a predictor of fluid responsiveness in patients with an average BMI of 23 prone on a Wilson frame. However, differences in patient positioning techniques and lack of detailed ventilation mode information complicate interpretation, particularly in patients with varying pulmonary dynamics. Furthermore, the observed low peak airway pressures may not have significantly affected venous return and right ventricular afterload, limiting extrapolation to scenarios with higher airway pressures, as encountered in patients with reduced pulmonary compliance. 

While Carabini et al. propose the predictive value of pulse pressure variation in prone-positioned patients, recent research casts doubt on the broad applicability of this assertion. Ali et al. compared the ability of pulse pressure variation to predict fluid responsiveness in prone and supine positions. They assessed the impact of body mass index, intraabdominal pressure, and static respiratory compliance on pulse pressure variation.

Involving 88 patients undergoing neurosurgery, this study found that pulse pressure variation in the prone position could predict fluid responsiveness as effectively as in the supine position, with caveats. Patients with a body mass index greater than 30 and a static respiratory compliance value less than 31 ml/cm H2O showed reduced predictive accuracy of pulse pressure variation in the prone position. Elevated intraabdominal pressure values also diminished pulse pressure variation’s predictive performance.

These findings underscore the importance of considering patient-specific factors like BMI, static respiratory compliance, and intraabdominal pressure when interpreting pulse pressure variation in prone-positioned patients. The applicability of earlier research to patients with higher BMI, poor pulmonary compliance, and abdominal obesity may be limited.

While the studies referenced by Carabini et al. offer valuable insights into the clinical utility of pulse pressure variation in prone-positioned patients during volume expansion, caution is necessary due to limitations in patient demographics, ventilation settings, and positioning techniques. Future research should aim to understand these factors better to help further refine the predictive value of pulse pressure variation in prone-positioned patients.