Propofol/Remifentanil Anesthesia Might Not Alter the Middle Cerebral Artery Diameter by Digital Subtraction Angiography.

INTRODUCTION: Transcranial Doppler (TCD) of the middle cerebral artery (MCA) enables the measurement of the mean blood velocity (MCAVm) and the estimation of the cerebral blood flow (CBF), provided that no significant changes occur in the MCA diameter (MCADiam). Previous studies described a decrease in the MCAVm associated with the induction of total intravenous anesthesia (TIVA) by propofol and remifentanil. This decrease in blood velocity might be interpreted as a decrease in the CBF only where the MCADiam is not modified across TCD examinations. METHODS: In this observational study, we measured the MCADiam of 24 subjects (almost exclusively females) on digital subtraction angiography under awake and TIVA conditions. RESULTS: Across the two phases, we observed a decrease in the mean arterial blood pressure (from 84 ± 9 to 71 ± 6 mmHg; p < 0.001) and heart rate (76 ± 10 vs. 65 ± 8 beats/min; p < 0.001), and a concomitant decrease in the MCAVm (61 vs. 42 cm/s; p < 0.001). In contrast, the MCADiam did not vary in association with TIVA (2.3 ± 0.2 vs. 2.3 ± 0.2 mm; p = 0.52). CONCLUSIONS: Those results suggested that in this population, no significant changes in the MCADiam are associated with TIVA.

Measurement of Diaphragmatic Electrical Activity by Surface Electromyography in Intubated Subjects and Its Relationship With Inspiratory Effort.

BACKGROUND: Quantification of patient effort during spontaneous breathing is important to tailor ventilatory assistance. Because a correlation between inspiratory muscle pressure (Pmus) and electrical activity of the diaphragm (EAdi) has been described, we aimed to assess the reliability of surface electromyography (EMG) of the respiratory muscles for monitoring diaphragm electrical activity and subject effort during assisted ventilation. METHODS: At a general ICU of a single university-affiliated hospital, we enrolled subjects who were intubated and on pressure support ventilation (PSV) and were on mechanical ventilation for > 48 h. The subjects were studied at 3 levels of pressure support. Airway flow and pressure; esophageal pressure; EAdi; and surface EMG of the diaphragm (surface EAdi), intercostal, and sternocleidomastoid muscles were recorded. Respiratory cycles were sampled for off-line analysis. The Pmus/EAdi index (PEI) was calculated by relying on EAdi and surface EAdi (surface PEI) from an airway pressure drop during end-expiratory occlusions performed every minute. RESULTS: surface EAdi well correlated with EAdi and Pmus, in particular, after averaging breaths into deciles (R = 0.92 and R = 0.84). When surface PEI was used with surface EAdi, it provided a reliable estimation of Pmus (R = 0.94 in comparison with measured Pmus). CONCLUSIONS: During assisted mechanical ventilation, EAdi can be reliably monitored by both EAdi and surface EMG. The measurement of Pmus based on the calibration of EAdi was also feasible by the use of surface EMG.

Clinical assessment of auto-positive end-expiratory pressure by diaphragmatic electrical activity during pressure support and neurally adjusted ventilatory assist.

BACKGROUND: Auto-positive end-expiratory pressure (auto-PEEP) may substantially increase the inspiratory effort during assisted mechanical ventilation. Purpose of this study was to assess whether the electrical activity of the diaphragm (EAdi) signal can be reliably used to estimate auto-PEEP in patients undergoing pressure support ventilation and neurally adjusted ventilatory assist (NAVA) and whether NAVA was beneficial in comparison with pressure support ventilation in patients affected by auto-PEEP. METHODS: In 10 patients with a clinical suspicion of auto-PEEP, the authors simultaneously recorded EAdi, airway, esophageal pressure, and flow during pressure support and NAVA, whereas external PEEP was increased from 2 to 14 cm H2O. Tracings were analyzed to measure apparent "dynamic" auto-PEEP (decrease in esophageal pressure to generate inspiratory flow), auto-EAdi (EAdi value at the onset of inspiratory flow), and IDEAdi (inspiratory delay between the onset of EAdi and the inspiratory flow). RESULTS: The pressure necessary to overcome auto-PEEP, auto-EAdi, and IDEAdi was significantly lower in NAVA as compared with pressure support ventilation, decreased with increase in external PEEP, although the effect of external PEEP was less pronounced in NAVA. Both auto-EAdi and IDEAdi were tightly correlated with auto-PEEP (r = 0.94 and r = 0.75, respectively). In the presence of auto-PEEP at lower external PEEP levels, NAVA was characterized by a characteristic shape of the airway pressure. CONCLUSIONS: In patients with auto-PEEP, NAVA, compared with pressure support ventilation, led to a decrease in the pressure necessary to overcome auto-PEEP, which could be reliably monitored by the electrical activity of the diaphragm before inspiratory flow onset (auto-EAdi).