Positive end expiratory pressure (2)

Adjusting PEEP

1 Measure blood gases and monitor haemodynamic variables.

2 If indicated, alter level of PEEP by 3–5cmH2O increments.

3 Re-measure gases and haemodynamic variables after 15–20min.

4 Consider further changes as necessary (including additional changes in PEEP, fluid challenge, or vasoactive drugs)

A number of clinical trials have adjusted PEEP levels according to FIO2 requirements (see table below). Although unlikely to constitute ‘optimal PEEP’ for an individual patient, this provides a useful approximation and starting point for further titration of therapy.

FIO2            0.3 0.4 0.4 0.5 0.5 0.6 0.7 0.7 0.7 0.8 0.9 0.9 0.9 1.0

PEEP           5      5     8    8    10 10  10  12  14  14  14  16 18  ≥18

(cmH2O)

Indications

• Hypoxaemia requiring high FIO2.

• Optimising the pressure–volume curve in severe respiratory failure.

• Hypoxaemia secondary to left heart failure.

• Improvement of cardiac output in left heart failure.

• Reduced work of breathing while weaning patients with high PEEPi.

• Neurogenic pulmonary oedema (i.e. non-cardiogenic pulmonary oedema following relief of upper airway obstruction).

Complications

• Reduced cardiac output. May need additional fluid loading or even inotropes. This should generally be avoided unless higher PEEP is necessary to maintain adequate arterial oxygenation. Caution should be exercised in patients with myocardial ischaemia.

• Increased airway pressure (and potential risk of ventilator trauma).

• Overinflation leading to air trapping and raised PaCO2. Use with caution in patients with chronic airflow limitation or asthma. In

pressure-controlled ventilation, over-distension is suggested when an increase in PEEP produces a significant fall in tidal volume.

• High levels will decrease venous return, raise intracranial pressure, and

increase hepatic congestion.

• PEEP may change the area of lung in which a pulmonary artery catheter tip is positioned from West zone III to non-zone III. This is suggested by a rise in wedge pressure of at least half the increase in PEEP and requires re-siting of the catheter.