Table 1.

Haemodynamic effects of positive pressure ventilation on cardiac output

Haemodynamic effect of positive pressure ventilation	Likely effect on cardiac output
	Preload dependent	Afterload dependent
RV preload ↓	↓	↑
RV afterload ↑	↓	↓
LV preload ↓	↓	↑
LV afterload ↓	↑	↑

The most prominent haemodynamic effects of invasive positive pressure mechanical ventilation include a decrease in right ventricular (RV) preload, an increase in RV afterload, a decrease in left ventricular (LV) preload and a decrease in LV afterload. The theoretical impact of the aforementioned haemodynamic changes on the overall cardiac output (CO) depends on the aetiology of the patient’s underlying physiology. In patients who are ‘preload dependent’, the decrease in RV and LV preload and increase in RV afterload would decrease the CO; the decrease in LV afterload would increase the CO. Overall, the patient would likely experience a net decrease in CO. In patients who are ‘afterload dependent’, the decreased RV and LV preload and decreased LV afterload would increase the CO, whereas the increase in RV afterload would decrease the CO. The patient would likely have an overall improvement in CO.