Invasive PPV in Severe Systolic Heart Failure
Although there is near-universal use of non-invasive PPV in patients with acute pulmonary oedema, there is more concern in employing invasive PPV with PEEP in this clinical scenario owing to its potentially significant haemodynamic impact. However, a number of reports in patients with severe LV dysfunction and cardiogenic shock suggest that the haemodynamic effects of PEEP may work in favour of the patient with severe left heart failure (see Table 2).
In a study of 21 mechanically ventilated patients with LV dysfunction of diverse aetiologies (7 had acute MI with CHF, 8 had acute MI with cardiogenic shock and 6 had CHF without acute MI), initiation of PEEP led to decreased CO in patients with normal pulmonary capillary wedge pressure (PCWP). However, 4 of 6 patients with a PCWP of 14–18 mm Hg and 12 out of 13 patients with a PCWP ≥19 mm Hg experienced improvement in their CO with the addition of 3–8 cm H2O of PEEP. Similarly, in 12 patients with baseline LV dysfunction who were mechanically ventilated after coronary artery bypass graft surgery, the initiation of 5 cm H2O of PEEP (in either controlled or intermittent mechanical ventilation) was associated with a significant improvement in the PCWP, cardiac index and stroke index compared with spontaneous or intermittent ventilation without PEEP. The authors' conclusion was that PEEP should be used in all the cases of severe LV dysfunction. These results are consistent with the finding that, in mechanically ventilated patients with cardiogenic shock after coronary artery bypass graft surgery, the usage of 10 cm H2O of PEEP can decrease intrapulmonary shunting and improve the lung compliance, and that alveolar recruitment manoeuvres with high levels of PEEP are successful in improving oxygenation and atelectasis without any concomitant detrimental changes in haemodynamics.
Mechanical ventilation with PEEP has not only been associated with improved haemodynamic measurements, but also with superior clinical end points as well. A small study of 18 patients with cardiogenic shock necessitating intra-aortic balloon pump placement found that the patients randomised to receive elective mechanical ventilation with 10 cm H2O of PEEP were more likely to be weaned off the intra-aortic balloon pump and survive to discharge than patients who received oxygen supplementation alone. In addition, several clinical variables were improved in the mechanically ventilated patients as well, such as urine output, PCWP, cardiac index, ratio of partial pressure of arterial oxygen to the fraction of inspired oxygen (PaO2/FIO2) and usage of vasopressors and inotropes. Of note, this is the only study to measure patient survival, rather than surrogate clinical or haemodynamic end points, in evaluating this query.
While these results are promising and suggest potential benefit for PEEP beyond respiratory support, other studies have not shown haemodynamic improvement with the use of PEEP. Of note, these authors found that PEEP was not associated with a functional decline in LV function at high levels of PEEP, and it was therefore considered safe in these group of patients.