Heartrate Variability During Conventional and Variable Pressure Support Mechanical Ventilation: a Cross-over Study

Spontaneous-continuous positive airway pressure support (SPN-CPAP/PS) is the routine ventilator mode used in critically ill patients submitted to an intensive care unit (ICU). It guarantees a positive end expiratory pressure, which prevents atelectasis and minimizes weaning time, by supporting the patient's respiratory drive.

A few years ago, this very established ventilation technique was modified by simply altering the rhythm and volume of gas application: instead of administering same tidal volumes in equal time intervals a variation of applied volume as well as altering frequency in ventilation is introduced. This ventilation method is termed noisy pressure support ventilation (noisy PSV) or variable pressure support ventilation (variable PSV). The variation of pressure support will be within a range around a mean support-pressure (Psupp) and won't exceed a maximum pressure (Pmax), which are both adjusted before starting noisy PSV.

Any variation of breathing is physiological and may occur during speaking, moving and many other factors. As novel concept, the investigator proposes that such variation of ventilation rhythm and volume may have an important impact on heart rate variability (HRV), which is known as to be an indicator of a healthy heart. Since it has been observed that HRV is an important predictor of mortality in coronary care units, investigation of HRV became more important. Recently it was found that low HRV is associated with an increasing mortality and proposed low HRV to be a marker for critical illness.

The analysis and further investigation of HRV has therefore become an important issue in modern medicine. Mechanical ventilation plays a pivotal role in ICUs and should be further improved. Mechanical ventilation per se is stressful for the cardiovascular system. Cardiovascular homeostasis is of major importance and the investigator hypothesises that noisy PSV will decrease the stress applied to the human heart measured via heart rate variability.

In this interventional clinical study, the investigator will apply, in a randomized fashion, conventional PSV and variable PSV each for a duration of one hour. During ventilation the investigator will record all data of the patients monitor, including the electrocardiogram (ECG), which is routinely monitored in patients, and respiratory data, to determine HRV parameters retrospectively. All other ventilatory, hemodynamic and pharmacological treatment will be part of the clinical routine. As two modes of ventilation will be compared, this study is an interventional clinical trial.