M Singer1, D Bennett. 1. Department of Medicine 1, St George's Hospital Medical School, London.
Abstract
OBJECTIVE: To assess oesophageal Doppler ultrasonography as a convenient means of optimising positive end expiratory pressure for maximal delivery of oxygen to tissues. DESIGN: Measurements of blood flow, arterial oxygen saturation, and cardiac output by thermodilution (when available) at baseline and at 20-30 minutes after each incremental increase (2.5-5.0 cm H2O) in positive and expiratory pressure to a maximum of 20.0 cm H2O. If the cardiac output fell by more than 15% measurements were repeated after stepwise decreases in positive end expiratory pressure. No other manoeuvre such as endotracheal suction or changing ventilator settings, drug or fluid dosage, or the patient's position was performed for at least one hour before the start of the study or during it. SETTING: Intensive care unit. PARTICIPANTS: 10 Patients being mechanically ventilated for acute respiratory failure who had stable haemodynamic and blood gas values and required a fractional inspired oxygen concentration of greater than or equal to 0.45. They were assessed on a total of 11 occasions. INTERVENTIONS: Incremental increases in positive end expiratory pressure followed when indicated by stepwise decreases. END POINT: The positive end expiratory pressure providing maximal delivery of oxygen to tissues. MEASUREMENTS AND MAIN RESULTS: Arterial oxygen saturation increased with positive end expiratory pressure in all patients by an average of 6.1%. In nine of the 11 studies, however, cardiac output fell by 15% to 30% after the second increment. On the two other occasions cardiac output and oxygen delivery rose by up to 54%. Positive end expiratory pressure was decreased on seven occasions; there was considerable individual variation in the time taken for cardiac output to rise and arterial oxygen saturation to fall. In six patients good agreement was seen between the results from Doppler ultrasonography and thermodilution, the mean of the differences being -0.3% with narrow limits of agreement (-14.4% to 13.9%). CONCLUSIONS: Oesophageal Doppler ultrasonography is a rapid, safe, and reliable technique for optimising positive end expiratory pressure to obtain maximal delivery of oxygen to tissues. The results show the need to consider haemodynamic consequences when altering positive end expiratory pressure.
OBJECTIVE: To assess oesophageal Doppler ultrasonography as a convenient means of optimising positive end expiratory pressure for maximal delivery of oxygen to tissues. DESIGN: Measurements of blood flow, arterial oxygen saturation, and cardiac output by thermodilution (when available) at baseline and at 20-30 minutes after each incremental increase (2.5-5.0 cm H2O) in positive and expiratory pressure to a maximum of 20.0 cm H2O. If the cardiac output fell by more than 15% measurements were repeated after stepwise decreases in positive end expiratory pressure. No other manoeuvre such as endotracheal suction or changing ventilator settings, drug or fluid dosage, or the patient's position was performed for at least one hour before the start of the study or during it. SETTING: Intensive care unit. PARTICIPANTS: 10 Patients being mechanically ventilated for acute respiratory failure who had stable haemodynamic and blood gas values and required a fractional inspired oxygen concentration of greater than or equal to 0.45. They were assessed on a total of 11 occasions. INTERVENTIONS: Incremental increases in positive end expiratory pressure followed when indicated by stepwise decreases. END POINT: The positive end expiratory pressure providing maximal delivery of oxygen to tissues. MEASUREMENTS AND MAIN RESULTS: Arterial oxygen saturation increased with positive end expiratory pressure in all patients by an average of 6.1%. In nine of the 11 studies, however, cardiac output fell by 15% to 30% after the second increment. On the two other occasions cardiac output and oxygen delivery rose by up to 54%. Positive end expiratory pressure was decreased on seven occasions; there was considerable individual variation in the time taken for cardiac output to rise and arterial oxygen saturation to fall. In six patients good agreement was seen between the results from Doppler ultrasonography and thermodilution, the mean of the differences being -0.3% with narrow limits of agreement (-14.4% to 13.9%). CONCLUSIONS: Oesophageal Doppler ultrasonography is a rapid, safe, and reliable technique for optimising positive end expiratory pressure to obtain maximal delivery of oxygen to tissues. The results show the need to consider haemodynamic consequences when altering positive end expiratory pressure.