Haemodynamic changes induced by two I:E ratios: a transoesophageal echocardiographic study

To assess the effects of controlled ventilation with two I:E ratios on haemodynamic and left ventricular function in mechanically ventilated patients with moderate to severe respiratory disease, using fluctuation of the arterial pressure waveform and the changes in left ventricular areas obtained by transoesophageal echocardiography.

Nine patients had their lungs ventilated using volume controlled ventilation with two I:E ratios 1:3 and 1:1). Respiratory rate was adjusted so that six cardiac beats occurred during a respiratory cycle. Systolic blood pressure variation (SBPV), left ventricular area variations measured by TEE and haemodynamic variables measured by PA catheter were compared.

When compared with I:E (1:3), I:E (1:1) decreased end diastolic area (EDA) throughout the respiratory cycle from 3% to 8% (P < 0.01) and increased SBPV from 6 +/- 1 to 11 +/- 1 mmHg (P < 0.01). In four patients, SBPV was > 12 mmHg with I:E 1:1. Conversely, SBPV was < 10 mmHg in all patients with I:E 1:3. With I:E (1:1), EDA decreased up to 7% during expiration (P < 0.01). The ejection fraction area remained stable for both ventilatory patterns and throughout the ventilatory cycle for a given I:E. The usual invasive haemodynamic variables were unchanged throughout the study, as was PaO2/FIO2.

In this setting, EDA and SBPV allow beat-to-beat evaluation of left ventricular preload during change of I:E ratio. Switch from I:E 1:3 to 1:1 may be used as a rapid, safe and reversible test to estimate intravascular volume status assessed by changes in SBPV or EDA.