Timely prediction of impending respiratory failure is vital, yet relies on subjective clinical assessment of the patient's respiratory status. Pulse oximetry plethysmographic signal analysis is indicative of the effort to breathe and may provide an objective measurement of respiratory loading.

Initiating invasive mechanical ventilation is a vital and delay-critical decision. Precise and timely prediction of impending respiratory failure would be highly consequential. Subjective evaluation of respiratory loading conditions is inconsistent, imprecise and may result in erroneous management. Photoplethysmographic (POP) waveform analysis provides a non-invasive, readily available tool to estimate breathing effort in a semiquantitative fashion.

It is the aim of this study to examine:

1. if the degree of dyspnoea, when clinically assessed by means of the respiratory rate and SpO2 values, correlates with the SpO2 wave variations (ΔPOP) in ICU spontaneously breathing COVID-19 and non-COVID-19 patients.
2. if a ΔPOP threshold could be identified to adequately predict further need of orotracheal intubation and invasive mechanical ventilation.

This study consists of three main steps:

1. Clinical evaluation of dyspnoea based on:

   1.1. Respiratory rate

   1.2. Oxygen saturation (SpO2)

2. Storage of SpO2 curve for ΔPOP computation according to a proprietary algorithm after offline POP analysis .

3. Within a time frame of 10 days from when the first two steps are met, monitor for need of invasive ventilatory support.

Inclusion Criteria:

• Informed consent from patient or next-of-kin according to local administrative decision
• Spontaneous breathing, including during prone position
• Sinus rhythm
• Minimum standards for ICU monitoring: ECG, blood pressure (invasive or non-invasive), respiratory rate (by ECG signal), SpO2 and temperature

Exclusion Criteria:

• Suspected pregnancy
• Weight > 120 Kg or < 60 kg
• Emergency or urgency
• Intubated ( and mechanically ventilated) patient
• Non- sinus rhythm
• Left ventricular ejection fraction (LVEF) ≤ 30%
• Right ventricular (RV) dysfunction ( RVEF ≤ 30% at transthoracic echocardiography (TTE))
• Significant pulmonary hypertension (PHT) (TTE: mean pulmonary arterial pressure (mPAP) ≥ 35 mm.Hg)

Spontaneously breathing ICU (COVID and non-COVID-19) adult patients with sinus rhythm, under any form of non-invasive respiratory support.