Using the Heart-Lung Interaction Index (HLI)

• HLI cannot be used in patients with significant cardiac arrhythmias (e.g., arterial fibrillation, frequent premature beats, and ventricular fibrillation). Due to the irregular time between heart beats in these patients, HLI does not reflect the effect of mechanical ventilation on the stroke volume of the heart.
• HLI cannot be used in open-chest patients.

• Tidal volume is < 6 ml/kg
• Patient’s breathing activity is spontaneous
• Driving pressure is < 10 cmH2O
• Cardiac dysfunction is present

The likelihood of incorrect values may increase if you are using ASV® 1.1.

In active, spontaneously breathing patients, the value shown for the calculated HLI may be negative.

The formula for calculating HLI is as follows:

HLI = 100*(POPmax – POPmin)/((POPmax + POPmin)/2)

POPmax is the maximum amplitude of the plethysmogram within the same breath and POPmin is the minimum. In a spontaneously breathing patient, the POPmax and POPmin (one measured during inspiration and one during expiration) may be inverted, resulting in a negative HLI value. In general, patient values may range anywhere between approx. -10% and +30%.

When using the INTELLiVENT-ASV PEEP Controller with HLI activated, and in particular with ASV 1.1, the alarm Check INTELLiVENT PEEP limit setting may be triggered if the following criteria are met:

• HLI ≤ 10
• VT/kg ≤ 6 ml (or driving pressure ≤ 10 cmH2O)
• PEEP ≥ 10 cmH2O

The problem should be solved by turning off the alarm and deactivating the HLI checkbox, which will cause the alarm to reset.
Please see your device’s Operator’s Manual for information on causes for this alarm and the appropriate action. 

HLI sensitivity is decreased when:

• Transthoracic pressure is low
• HR/RR < 3 to 4

Relevant devices: HAMILTON-G5/S1 (sw v2.6x)