Time schedule and assessments of the study
| Timepoints | Baseline T0 | MV T1 | SBT T2 | SBT T3 | SBT T4 | Day x T0+48 hours |
| Enrolment | ||||||
| Eligibility screen | · | |||||
| Informed consent | · | |||||
| Demographics—baseline characteristics | ||||||
| Age, years | · | |||||
| Gender, male/female | · | |||||
| Body mass index, kg/m2 | · | |||||
| Diagnosis | · | |||||
| Comorbidities | · | |||||
| Duration on MV before SBT, days | · | |||||
| Tissues blood flow and oxygenation parameters | ||||||
| Cerebral cortex BFI, nMol/s and TOI*, % | · | · | · | · | ||
| Scalene muscles BFI, nMol/s and TOI*, % | · | · | · | · | ||
| Abdominal muscle BFI, nMol/s and TOI*,% | · | · | · | · | ||
| Thenar muscle BFI, nMol/s and TOI*, % | · | · | · | · | ||
| Cerebral cortex DO2 index, arbitrary units | · | · | · | · | ||
| Scalene muscles DO2 index, arbitrary units | · | · | · | · | ||
| Abdominal muscle DO2 index, arbitrary units | · | · | · | · | ||
| Thenar muscle DO2 index, arbitrary units | · | · | · | · | ||
| Cerebral cortex VC index, arbitrary units | · | · | · | · | ||
| Scalene muscles VC index, arbitrary units | · | · | · | · | ||
| Abdominal muscle VC index, arbitrary units | · | · | · | · | ||
| Thenar muscle VC index, arbitrary units | · | · | · | · | ||
| Haemodynamic parameters | ||||||
| Heart rate*, beats/min | · | · | · | · | ||
| Mean arterial blood pressure*, mm Hg | · | · | · | · | ||
| Cardiac output*, L/min | · | · | · | · | ||
| Systemic vascular resistance*, dynes/s/cm–5 | · | · | · | · | ||
| Norepinephrine/epinephrine, yes/no and dose, μg/kg/min | · | · | · | · | ||
| Respiratory parameters and ventilatory settings | ||||||
| Respiratory rate*, breaths/min | · | · | · | · | ||
| Tidal volume*, mL/min | · | · | · | · | ||
| Minute ventilation*, L/min | · | · | · | · | ||
| FIO2, inspiratory oxygen fraction*, % | · | · | · | · | ||
| PS, pressure support*, cmH2O | · | · | · | · | ||
| PEEP, positive end-expiratory pressure*, cmH2O | · | · | · | · | ||
| Neuromuscular activation index of the respiratory system (P0.1), cmH2O | · | · | · | |||
| Blood gas values | ||||||
| PaO2, arterial O2 partial pressure, mm Hg | · | · | · | · | ||
| PaCO2, arterial CO2 partial pressure, mm Hg | · | · | · | · | ||
| SaO2, arterial O2 saturation, % | · | · | · | · | ||
| Systemic arterial O2 content, mL O2/L | · | · | · | · | ||
| Systemic DO2, L O2/min | · | · | · | · | ||
| pH | · | · | · | · | ||
| Hb, haemoglobin concentration, g/L | · | · | · | · | ||
| SpO2, stands for peripheral capillary O2 saturation*, % | · | · | · | · | ||
| Weaning outcomes | ||||||
| SBT outcomes, failure/success | · | · | · | |||
| SBT duration, minutes | · | · | · | |||
| Reason(s) for SBT failure | · | · | · | |||
| Weaning outcome (failure/success) | · | |||||
Measurements will be performed on the day clinicians will judge that the patient is ready to wean.
Systemic vascular resistance would be calculated using the following formula: [80 x (mean arterial blood pressure - central venous pressure/cardiac output)]. Systemic arterial O2 content will be calculated using the following formula: [(1.34 x Hb x SaO2) + (0.003 x PaO2)]. Systemic DO2 will be calculated by multiplying cardiac output to systemic arterial O2 content. Tissues DO2 index will be calculated by multiplying tissues BFI to systemic arterial O2 content and will be presented in arbitrary units. Conductance to flow for each tissue will be calculated by dividing BFI with mean arterial blood pressure and will be presented in arbitrary units. Measurement of P0.1 -the negative airway pressure generated during the first 100 ms of an occluded inspiration- will be measured by the ventilator as an index of the neuromuscular activation of the respiratory system.39 Development of stress and anxiety manifested by rapid and unexplained increase in physiological measures such as heart rate, blood pressure and respiratory rate will be evaluated during the transition from MV to SBT and throughout spontaneous breathing attempt will be evaluated in all patients.40
*Asterisk denotes the parameters that will be assessed continuously on MV and during SBT period.
BFI, blood flow index; DO2, oxygen delivery; MV, mechanical ventilation; pH, hydrogen ion concentration; SBT, spontaneous breathing trial; TOI, tissue oxygenation index; VC, vascular conductance.