Mechanical ventilation in the operating room frequently includes application of positive end expiratory pressure (PEEP). This is done to improve intraoperative oxygen delivery, as well as to improve lung mechanics postoperatively. PEEP increases intrathoracic pressure, decreasing venous return, and potentially raising venous pressure. This raises potential concern that PEEP may increase bleeding, particularly in operations such as sinus surgery that may open venous vascular beds.
Dr. Samuel DeMaria, Department of Anesthesiology, Icahn School of Medicine at Mount Sinai, New York, New York, and colleagues randomized 47 patients to receive either 5 cm H2O of PEEP or zero added PEEP during Functional Endoscopic Sinus Surgery to see whether PEEP influenced intraoperative bleeding. Their findings are published in this month’s issue of Anesthesia & Analgesia in the article “The Influence of Positive End-Expiratory Pressure on Surgical Field Conditions During Functional Endoscopic Sinus Surgery.”
Bleeding was no different between the study groups. Thus, PEEP per se did not degrade the surgical field through increased blood loss. However, peak inspiratory pressure was directly correlated with increased bleeding and a decreased quality of the surgical field. The punchline is that PEEP can be safely used, but ventilation strategy should minimize peak pressures to create the best possible surgical field. This might include using pressure rather than volume mode, increased I:E ratio (to permit full expansion with less pressure), the use of muscle relaxants, and elevation of the head of the bed.
Patients with a body mass index > 40 kg/m2 were excluded. The authors explain that in these patients “body habitus would be more likely to affect respiratory variables.” Unstated is the possibility that obese patients might require PEEP, and randomizing the obese subjects to the PEEP group might compromise their care.