Haemodynamic and Respiratory Effects of a Low Positive End Expiratory Pressure Associated With a Fluid Challenge in Knee-chest Position

Number of occurrences of a MAP

The genu pectoral position is a surgical position used for spine surgery. This surgical
 position will lead to physiological hemodynamic and respiratory changes during the procedure.
 
 The knee-pectoral position notably induces an increase in CRF and improves pulmonary
 ventilation/perfusion ratios. On the other hand, it has been shown that it is accompanied by
 a reduction in cardiac output of approximately 15% Protective perioperative ventilation
 including a tidal volume between 6 and 8 ml/kg of theoretical ideal weight, PEEP and alveolar
 recruitment maneuvers is applied in the operating room to reduce postoperative pulmonary
 complications. The application of high PEEP and the performance of recruitment maneuvers
 induce arterial hypotension through changes in intra- and transpulmonary pressures. However,
 investigators hypothesize that the deleterious hemodynamic effects of PEEP seem to
 counterbalance its beneficial respiratory effects in this particular position.
 
 The combination of the effects of the knee-pectoral position and protective ventilation could
 be potentiated and be the cause of the sometimes severe arterial hypotension observed in
 clinical practice. Since this position improves pulmonary ventilation perfusion ratios, the
 investigators hypothesized that a lower PEEP and the elimination of intraoperative
 recruitment maneuvers could be beneficial from a hemodynamic point of view without being
 deleterious in terms of perioperative pulmonary complications. An exploratory study was
 carried out at the CAEN University Hospital in 2021 under the name PEEP POSTURE (CLERS
 Agreement No. 2198 of February 17, 2021) on 90 patients aiming to collect hemodynamic and
 respiratory parameters in 3 surgical positions: supine decubitus, ventral decubitus ,
 pectoral genu. No difference was found in the evolution of respiratory compliance. On the
 other hand, a significant drop in SBP, DBP and MAP in the pectoral position was shown
 compared to the supine group as well as greater vascular filling.
 
 The investigators therefore hypothesize that a reduction in PEEP and optimization of vascular
 filling could help reduce the adverse effects on blood pressure linked to the surgical
 position.