Variation in the Stress Index Due to Changes in the Head of the Bed in Patients with Mechanical Respiratory Assistance

Abstract

Introduction: patients admitted to intensive care units require, with some frequency, mechanical respiratory assistance. The implementation of positive pressure ventilation can cause lung injury. Parameters such as the stress index (SI) are important to know the behavior of the system when a volume of gas is admitted and to avoid the collapse or overdistention of the respiratory units.
Objective: to study the variation of the stress index in patients with mechanical ventilation in different angulations of the supine decubitus.
Material and methods: interventional, physiological, cohort study with patients older than 18 years and mechanical ventilation ≤ 48 hs, without pulmonary pathology. Stress index was recorded at 0°, 10°, 20°, 30°, 40°, 50° and 60°; then to 50°, 40°, 30°, 20°, 10° and 0°. The variables were computed without modification of the ventilatory parameters.
Results: 11 patients were studied. The mean age was 56.64±25.57 (median, 55). Men 54.54%, women 45.45%. Size: 167.2±8.36 cm. PBW: 61.25±9.46 kg (60.6 kg). RBW: 73.63±12.86 kg (80 kg). The SI were: 0°: 0.947±0.098 (0.968), 10°: 0.966±0.082 (0.980), 20°: 0.986±0.097 (0.990), 30°: 0.994±0.095 (0.995), 40°: 1.013±0.110 (1.018), 50°: 1.017±0.083 (1.012), 60°: 1.014±0.087 (1.004), 50°: 1.024±0.078 (1.025), 40°: 1.027±0.080 (1.050), 30°: 1.020±0.083 (1.024), 20°: 1.001±0.066 (1.010), 10°: 0.991±0.083 (1.022), 0°: 0.976±0.076 (0.998).
Conclusion: the SI showed a graphical behavior similar to the hysteresis curve. Values close to 1 were found at 30 ° for the ascent phase and at 20 ° for the descent phase.