Respiratory muscle oxygen saturation during weaning

Introduction

Unnecessary prolongation of mechanical ventilation is related to increased morbidity. On the contrary, early discontinuation of mechanical ventilation with reintubation is also related to bad prognosis. High respiratory rate, cardiac load and neuromuscular dysfunction are known factors related to weaning failure. Oxygen tissue saturation (StO₂) obtained by near-infrared spectroscopy (NIRS) reflects the balance between oxygen delivery and consumption at the muscle level. StO₂ evolution during weaning may have a role in assessing respiratory muscle performance and help us to predict patient readiness to be weaned. The study objective is to describe respiratory muscle StO₂ during a T-tube test.

Methods

A patient with mild head injury and pulmonary contusion was submitted to a T-tube trial after obtaining stability on day 5. The NIRS signal from serratus anterior muscle was acquired by placing an Inspectra device probe on the skin surface of the muscle [1]. Simultaneously, the respiratory rate, heart rate, mean arterial pressure and arterial oxygen saturation were recorded.

Results

After 5 minutes the patient failed on his first T-tube trial, showing profuse sweating, accessory muscle recruitment and increasing respiratory rate and mean arterial pressure (Figure 1). The StO₂ signal decreased during ventilatory failure until the patient was on assistance again.

Figure 1

StO ₂ evolution during the T-tube trial. HR, heart rate; RR, respiratory rate; MAP, mean arterial pressure.

Conclusion

NIRS was sensitive to respiratory muscle fatigue but further research is in process to assess its predictive capability.