Deep sedation contributes to high release of hypoxic pulmonary vasoconstriction in mechanically ventilated acute respiratory distress syndrome patients

Background: We report the cases of 2 patients with severe pneumonia who exhibited increased changes in hypoxic pulmonary vasoconstriction (HPV) during temporary increases in stroke volume and decreased stroke volume variation caused by in­creasing positive end-expiratory pressure (PEEP) under different sedation.

Cases: The first case was observed in a 79-year-old man with acute respiratory distress syndrome (ARDS) followed by pneumonia. The second case was observed in a 73-year-old woman on mechani­cal ventilation who suffered from ARDS following interstitial pneumonia.

The first patient was treated with 2 kinds of sedatives to improve oxygenation and protect the lungs. The second patient was treated with 3 kinds of sedatives. The first patient had a low P/F ratio (53.9/0.7=77) on mechanical ventilation. According to the recruit­ment maneuvers, an increasing PEEP leads to a slight temporary increase in stroke volume of about 2 mL. The patient died 3 days later due to multiple organ failure and disseminated intravascular co­agulation. The second patient had a low P/F ratio (38.5/0.7=55). As the PEEP increased, her stroke volume temporarily increased dramatically by about 8 mL. The patient recovered 56 days later.

Conclusions: HPV is an obstacle to oxygenation, prompting recruitment maneuvers for treating me­chanically ventilated ARDS patients; it is considered to be caused by physiological changes in the intracel­lular Ca2+ concentration in the pulmonary artery smooth muscle cells according to the sedation levels. The sedation level may contribute to decreased HPV in lung recruitment maneuvers.