Table 3.
Physiological characteristics of the patients—prospective phase (N = 30 patients)
| Physiological characteristics | |
| Age (mean ± SD) | 61.4 ± 11.8 |
| Sex ratio (F/M) | 11/19 |
| BMI (kg/m2; mean ± SD) | 27.1 ± 7.0 |
| SAPS II (mean ± SD) | 41.8 ± 16.8 |
| Chronic respiratory disorder n-(%) | 10 (33.3) |
| Immunodepression n-(%) | 2 (6.7) |
| Admission diagnosis | |
| Respiratory failure n-(%) | 23 (76.7) |
| Cardiovascular failure n-(%) | 1 (3.3) |
| Neurological failure n-(%) | 3 (10.0) |
| Other n-(%) | 2 (6.6) |
| ICU length of stay (day; mean ± SD) | 16.3 ± 15.5 |
| Hospital length of stay (day; mean ± SD) | 27.9 ± 20.8 |
| Overall survival rate n-(%) | 22 (73.3) |
| Respiratory conditions | |
| Mechanical ventilation n-(%) | 10 (33.3) |
| Spontaneous ventilation n-(%) | 20 (66.6) |
| SpO2 (%; mean ± SD) | 93.1 ± 2.5 |
| PaO2/FIO2 or SpO2/FIO2 (mean ± SD) | 311 ± 79 |
| Sedation n-(%) | 6 (20) |
| Hemodynamic conditions | |
| Heart rate (b/min; mean ± SD) | 94.2 ± 18.9 |
| Mean arterial blood pressure (mmHg; mean ± SD) | 87.2 ± 19.2 |
| Atrial fibrillation | 0 (0) |
| Vasopressive agents n-(%) | 5 (16.7) |
| Hemodynamic instability n-(%) | 2 (6.7) |
| Number of patients with reference values | |
| RR-Manual (reference) n-(%) | 30/30 (100) |
| RR-ECG n-(%) | 28/30 (93.3) |
| RR-PPG n-(%) | 30/30 (100) |
| Measurements | |
| Reference RR (c/min) | 22 ± 4 |
| Estimated RR-PPG (c/min) | 22 ± 5 |
| Estimated RR-ECG (c/min) | 23 ± 6 |
Values are provided as n-(%) or mean ± SD, unless specified otherwise
Reference RR values are provided as the chronometric measurement measured over 30 s under spontaneous ventilation or as the ventilatory rate for patients under ventilatory assistance
Chronic respiratory disorders are considered for a previous medical history of COPD, OSA and chronic respiratory insufficiency
Oxygenation parameters are provided as PaO2/FIO2 for patients under mechanical ventilation or as SpO2/FIO2 for patients under spontaneous ventilation
Hemodynamic instability was defined as a need for fluid challenge (≥ 500 mL) and/or vasopressive agent increase during the past 2 h of care
BMI, body mass index; SAPS II, Simplified Acute Physiology Score version 2; ICU, intensive care unit; SpO2, pulse oximetry saturation; PaO2, partial pressure of oxygen in arterial blood; FIO2, inspiratory fraction of oxygen; IV, intravenous; PEEP, positive end-expiratory pressure; RR-Manual, chronometric measurement of the respiratory rate; RR-PPG, estimated respiratory rate using the plethysmographic curve analysis; RR-ECG, evaluation of the respiratory rate on the electrocardiogram, using electrical impedance