Continuous assessment of neuro-ventilatory drive during 12 h of pressure support ventilation in critically ill patients

Abstract

Introduction Pressure support ventilation (PSV) should allow spontaneous breathing with a “normal” neuro-ventilatory drive. Low neuro-ventilatory drive puts the patient at risk of diaphragmatic atrophy while high neuro-ventilatory drive may causes dyspnea and patient self-inflicted lung injury. We continuously assessed for 12 h the electrical activity of the diaphragm (EAdi), a close surrogate of neuro-ventilatory drive, during PSV. Our aim was to document the EAdi trend and the occurrence of periods of “Low” and/or “High” neuro-ventilatory drive during clinical application of PSV. Method In 16 critically ill patients ventilated in the PSV mode for clinical reasons, inspiratory peak EAdi peak (EAdiPEAK), pressure time product of the trans-diaphragmatic pressure per breath and per minute (PTPDI/b and PTPDI/min, respectively), breathing pattern and major asynchronies were continuously monitored for 12 h (from 8 a.m. to 8 p.m.). We identified breaths with “Normal” (EAdiPEAK 5–15 μV), “Low” (EAdiPEAK < 5 μV) and “High” (EAdiPEAK > 15 μV) neuro-ventilatory drive. Results Within all the analyzed breaths (177.117), the neuro-ventilatory drive, as expressed by the EAdiPEAK, was “Low” in 50.116 breath (28%), “Normal” in 88.419 breaths (50%) and “High” in 38.582 breaths (22%). The average times spent in “Low”, “Normal” and “High” class were 1.37, 3.67 and 0.55 h, respectively (p < 0.0001), with wide variations among patients. Eleven patients remained in the “Low” neuro-ventilatory drive class for more than 1 h, median 6.1 [3.9–8.5] h and 6 in the “High” neuro-ventilatory drive class, median 3.4 [2.2–7.8] h. The asynchrony index was significantly higher in the “Low” neuro-ventilatory class, mainly because of a higher number of missed efforts. Conclusions We observed wide variations in EAdi amplitude and unevenly distributed “Low” and “High” neuro ventilatory drive periods during 12 h of PSV in critically ill patients. Further studies are needed to assess the possible clinical implications of our physiological findings.

Flow Index: a novel, non-invasive, continuous, quantitative method to evaluate patient inspiratory effort during pressure support ventilation

“…This is a remarkable result since in clinical practice the inspiratory effort is seldom measured, and RR and V T are deemed as useful surrogates for setting the PSV level [ 29 ]. Indeed, PSV level is usually titrated to obtain a VT between 5 and 8 ml/kg predicted body weight (PBW) and a RR between 20 and 30 breaths/min [ 6 , 10 ]. The RSBI [ 13 ], which, by expressing an imbalance between load and effort, could be deemed as a sign of inadequate inspiratory support was not taken into account in the primary analysis since our model included both RR and V T .…”

“…Though this method is of interest, a manual occlusion is needed and P occl could not provide continuous monitoring of patient inspiratory effort [ 11 ]. The assessment of diaphragmatic electrical activity (E di ) is an accurate measure of neuro-ventilatory drive, and P musc may be estimated through the calculation of neuromuscular efficiency, obtained by comparing E di and P occl during an end-expiratory airway occlusion, or through the calculation of neuro-ventilatory efficiency, obtained by comparing E di and V T [ 10 , 33 , 34 ]. However, measuring E di is costly, requires the insertion of a patent-protected nasogastric catheter which functions only with specific mechanical ventilators and, finally, a manual occlusion is required to calculate neuromuscular efficiency [ 33 ].…”

“…Over-assistance, on the other hand, may lead to pulmonary hyperinflation and diaphragmatic atrophy and dysfunction, thus impairing weaning and prolonging the dependency from mechanical ventilation [ 1 , 2 , 8 , 9 ]. Independently from the appropriateness of inspiratory assistance, the patient's neuro-ventilatory drive and hence the breathing effort may unpredictably vary over time due to pain, anxiety, delirium, sepsis, sedation or other pathological conditions [ 10 ].…”

Estimated ECG Subtraction method for removing ECG artifacts in esophageal recordings of diaphragm EMG

“…The diaphragm is the most important respiratory muscle. Monitoring diaphragm activity in mechanically ventilated intensive care unit (ICU) patients is performed to facilitate diaphragm-protective ventilation, to assess patient-ventilator interaction and work of breathing, as well as to identify neuromuscular dysfunctions [1][2][3][4]. Bedside monitoring of diaphragm electrical activity (EAdi) is available on a specific ventilator (Getinge, Sweden) via a dedicated nasogastric (feeding) tube embedded with multiple ring-shaped electrodes positioned at the level of the diaphragm [5,6].…”

Can Abdominal Muscle Ultrasonography During Spontaneous Breathing and Cough Predict Reintubation in Mechanically Ventilated Patients?

“…Moreover, respiratory muscle function is usually explored mainly through the inspiratory muscles and the role of expiratory muscles, during an acute respiratory failure, has been largely neglected. [1][2][3] The function of expiratory muscles should be considered carefully: as an example, their recruitment may have beneficial effects in reducing the transpulmonary pressure, in clearing secretions through an effective cough and in supporting the ensuing inspiration by reducing functional residual capacity. This strategy, based on the elastic recoil pressure of the chest wall during the first part of inspiration, can help the inspiratory muscles to reduce their effort in the presence of increased work of breathing.…”