Hemodynamics and tissue oxygenation effects after increased in positive end-expiratory pressure in coronary artery bypass surgery.
Vanessa Marques Ferreira Méndez, Mayron F Oliveira, Adriana do Nascimento Baião and 4 others
PMID 29340197WHAT IT FOUND
After coronary bypass, patients on mechanical ventilation with oxygen support had lung oxygen levels rise but central venous oxygen saturation fall and lactate rise when PEEP was increased.
Blood pressure and central venous pressure did not change. The study had no control group.
Key findings
01While all patients remained on volume-controlled mechanical ventilation with oxygen support at FiO2 0.4, raising PEEP from 5 to 12 cmH2O for 30 min increased arterial oxygen pressure and the PaO2/FiO2 ratio.
02The same PEEP increase lowered central venous oxygen saturation and raised blood lactate.
03Mean arterial pressure and central venous pressure did not change, but heart rate decreased from 97 to 92 bpm.
STILL TO COME
How it was doneWhat they found
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What it does not show
There was no control group without PEEP increase, so changes during the 30 min period cannot be separated from the concurrent mechanical ventilation and oxygen support. Cardiac output was not measured directly, and central venous oxygen saturation was used as an indirect marker of tissue oxygen delivery and utilization. All patients had positive water balance during the protocol, and the study did not use additional measurements such as a Swan-Ganz catheter. Venous blood samples were taken from a catheter in the right atrium, not from a Swan-Ganz catheter. The study included only patients with hypoxemia defined by a PaO2/FiO2 ratio under 200 after coronary bypass.
The easy way to misread this
Do not read the higher arterial oxygen values as proof that raising PEEP is beneficial overall. Patients remained on mechanical ventilation with oxygen support, central venous oxygen saturation fell and blood lactate rose during the same period, and the study had no control group.