OBJECTIVE: To find out the circuit pressure and flow at the trigger point by observing the characteristics of the inspiratory trigger waveform of the ventilator, confirm the intra-alveolar pressure as the index to reflect the effort of the trigger according to the working principle of the ventilator combined with the laws of respiratory mechanics, establish the related mathematical formula, and analyze its influencing factors and logical relationship. METHODS: A test-lung was connected to the circuit in a PB840 ventilator and a SV600 ventilator set in pressure-support mode. The positive end-expiratory pressure (PEEP) was set at 5 cmH₂O (1 cmH₂O ≈ 0.098 kPa), and the wall of test-lung was pulled outwards till an inspiratory was effectively triggered separately in slow, medium, fast power, and separately in flow-trigger mode (sensitivity V_Trig 3 L/min, 5 L/min) and pressure-trigger mode (sensitivity P_Trig 2 cmH₂O, 4 cmH₂O). By adjusting the scale of the curve in the ventilator display, the loop pressure and flow corresponding to the trigger point under different triggering conditions were observed. Taking intraalveolar pressure (Pa) as the research object, the Pa (called P_a-T) needed to reach the effective trigger time (T_T) was analyzed in the method of respiratory mechanics, and the amplitude of pressure change (ΔP) and the time span (ΔT) of Pa during triggering were also analyzed. RESULTS: (1) Corresponding relationship between pressure and flow rate at TT time: in flow-trigger mode, in slow, medium and fast trigger, the inhalation flow rate was V_Trig, and the circuit pressure was separately PEEP, PEEP-Pn, and PEEP-Pn' (Pn, Pn', being the decline range, and Pn' > Pn). In pressure-trigger mode, the inhalation flow rate was 1 L/min (PB840 ventilator) or 2 L/min (SV600 ventilator), and the circuit pressure was PEEP-P_Trig. (2) Calculation of P_a-T: in flow-trigger mode, in slow trigger: P_a-T = PEEP-V_TrigR (R represented airway resistance). In medium trigger: P_a-T = PEEP-Pn-V_TrigR. In fast trigger: P_a-T = PEEP-Pn'-V_TrigR. In pressure-trigger mode: P_a-T = PEEP-P_Trig-1R. (3) Calculation of ΔP: in flow trigger mode, in flow trigger: without intrinsic PEEP (PEEPi), ΔP = V_TrigR; with PEEPi, ΔP = PEEPi-PEEP+V_TrigR. In medium trigger: without PEEPi, ΔP = Pn+V_TrigR; with PEEPi, ΔP = PEEPi-PEEP+Pn+V_TrigR. In fast trigger: without PEEPi, ΔP = Pn'+V_TrigR; with PEEPi, ΔP = PEEPi-PEEP+Pn'+V_TrigR. In pressure-trigger mode, without PEEPi, ΔP = P_Trig+1R; with PEEPi, ΔP = PEEPi-PEEP+P_Trig+1R. (4) Pressure time change rate of Pa (F_P): F_P = ΔP/ΔT. In the same ΔP, the shorter the ΔT, the greater the triggering ability. Similarly, in the same ΔT, the bigger the ΔP, the greater the triggering ability. The FP could better reflect the patient's triggering ability. CONCLUSIONS The patient's inspiratory effort is reflected by three indicators: the minimum intrapulmonary pressure required for triggering, the pressure span of intrapulmonary pressure, and the pressure time change rate of intrapulmonary pressure, and formula is established, which can intuitively present the logical relationship between inspiratory trigger related factors and facilitate clinical analysis.
Humans ; Respiration, Artificial/methods* ; Positive-Pressure Respiration ; Lung ; Ventilators, Mechanical ; Respiratory Mechanics

Without artificial airway though oral, nasal or airway incision, the bi-level positive airway pressure (Bi-PAP) has been widely employed for respiratory patients. In an effort to investigate the therapeutic effects and measures for the respiratory patients under the noninvasive Bi-PAP ventilation, a therapy system model was designed for virtual ventilation experiments. In this system model, it includes a sub-model of noninvasive Bi-PAP respirator, a sub-model of respiratory patient, and a sub-model of the breath circuit and mask. And based on the Matlab Simulink, a simulation platform for the noninvasive Bi-PAP therapy system was developed to conduct the virtual experiments in simulated respiratory patient with no spontaneous breathing (NSB), chronic obstructive pulmonary disease (COPD) and acute respiratory distress syndrome (ARDS). The simulated outputs such as the respiratory flows, pressures, volumes, etc, were collected and compared to the outputs which were obtained in the physical experiments with the active servo lung. By statistically analyzed with SPSS, the results demonstrated that there was no significant difference ( P > 0.1) and was in high similarity ( R > 0.7) between the data collected in simulations and physical experiments. The therapy system model of noninvasive Bi-PAP is probably applied for simulating the practical clinical experiment, and maybe conveniently applied to study the technology of noninvasive Bi-PAP for clinicians.
Humans ; Respiration, Artificial/methods* ; Positive-Pressure Respiration/methods* ; Respiration ; Ventilators, Mechanical ; Lung

Neurocritical care (NCC) is not only generally guided by principles of general intensive care, but also directed by specific goals and methods. This review summarizes the common pulmonary diseases and pathophysiology affecting NCC patients and the progress made in strategies of respiratory support in NCC. This review highlights the possible interactions and pathways that have been revealed between neurological injuries and respiratory diseases, including the catecholamine pathway, systemic inflammatory reactions, adrenergic hypersensitivity, and dopaminergic signaling. Pulmonary complications of neurocritical patients include pneumonia, neurological pulmonary edema, and respiratory distress. Specific aspects of respiratory management include prioritizing the protection of the brain, and the goal of respiratory management is to avoid inappropriate blood gas composition levels and intracranial hypertension. Compared with the traditional mode of protective mechanical ventilation with low tidal volume (Vt), high positive end-expiratory pressure (PEEP), and recruitment maneuvers, low PEEP might yield a potential benefit in closing and protecting the lung tissue. Multimodal neuromonitoring can ensure the safety of respiratory maneuvers in clinical and scientific practice. Future studies are required to develop guidelines for respiratory management in NCC.
Humans ; Lung ; Lung Diseases/etiology* ; Positive-Pressure Respiration/methods* ; Respiration, Artificial/adverse effects* ; Tidal Volume

To date, preterm infants with respiratory distress syndrome (RDS) after birth have been managed with a combination of endotracheal intubation, surfactant instillation, and mechanical ventilation. It is now recognized that noninvasive ventilation (NIV) such as nasal continuous positive airway pressure (CPAP) in preterm infants is a reasonable alternative to elective intubation after birth. Recently, a meta-analysis of large controlled trials comparing conventional methods and nasal CPAP suggested that CPAP decreased the risk of the combined outcome of bronchopulmonary dysplasia or death. Since then, the use of NIV as primary therapy for preterm infants has increased, but when and how to give exogenous surfactant remains unclear. Overcoming this problem, minimally invasive surfactant therapy (MIST) allows spontaneously breathing neonates to remain on CPAP in the first week after birth. MIST has included administration of exogenous surfactant by intrapharyngeal instillation, nebulization, a laryngeal mask, and a thin catheter. In recent clinical trials, surfactant delivery via a thin catheter was found to reduce the need for subsequent endotracheal intubation and mechanical ventilation, and improves short-term respiratory outcomes. There is also growing evidence for MIST as an alternative to the INSURE (intubation-surfactant-extubation) procedure in spontaneously breathing preterm infants with RDS. In conclusion, MIST is gentle, safe, feasible, and effective in preterm infants, and is widely used for surfactant administration with noninvasive respiratory support by neonatologists. However, further studies are needed to resolve uncertainties in the MIST method, including infant selection, optimal surfactant dosage and administration method, and need for sedation.
Bronchopulmonary Dysplasia ; Catheters ; Continuous Positive Airway Pressure ; Humans ; Infant ; Infant, Newborn ; Infant, Premature ; Intubation ; Intubation, Intratracheal ; Laryngeal Masks ; Methods ; Noninvasive Ventilation ; Parturition ; Respiration ; Respiration, Artificial

BACKGROUNDPropofol is increasingly used during partial support mechanical ventilation such as pressure support ventilation (PSV) in postoperative patients. However, breathing pattern, respiratory drive, and patient-ventilator synchrony are affected by the sedative used and the sedation depth. The present study aimed to evaluate the physiologic effects of varying depths of propofol sedation on respiratory drive and patient-ventilator synchrony during PSV in postoperative patients.

METHODSEight postoperative patients receiving PSV for <24 h were enrolled. Propofol was administered to achieve and maintain a Ramsay score of 4, and the inspiratory pressure support was titrated to obtain a tidal volume (VT) of 6-8 ml/kg. Then, the propofol dose was reduced to achieve and maintain a Ramsay score of 3 and then 2. At each Ramsay level, the patient underwent 30-min trials of PSV. We measured the electrical activity of the diaphragm, flow, airway pressure, neuro-ventilatory efficiency (NVE), and patient-ventilator synchrony.

RESULTSIncreasing the depth of sedation reduced the peak and mean electrical activity of the diaphragm, which suggested a decrease in respiratory drive, while VT remained unchanged. The NVE increased with an increase in the depth of sedation. Minute ventilation and inspiratory duty cycle decreased with an increase in the depth of sedation, but this only achieved statistical significance between Ramsay 2 and both Ramsay 4 and 3 (P < 0.05). The ineffective triggering index increased with increasing sedation depth (9.5 ± 4.0%, 6.7 ± 2.0%, and 4.2 ± 2.1% for Ramsay 4, 3, and 2, respectively) and achieved statistical significance between each pair of depth of sedation (P < 0.05). The depth of sedation did not affect gas exchange.

CONCLUSIONSPropofol inhibits respiratory drive and deteriorates patient-ventilator synchrony to the extent that varies with the depth of sedation. Propofol has less effect on breathing pattern and has no effect on VT and gas exchange in postoperative patients with PSV.

Adolescent ; Adult ; Aged ; Aged, 80 and over ; Blood Pressure ; drug effects ; physiology ; Female ; Hemodynamics ; drug effects ; physiology ; Humans ; Intensive Care Units ; Male ; Middle Aged ; Positive-Pressure Respiration ; methods ; Propofol ; therapeutic use ; Prospective Studies ; Respiration, Artificial ; methods ; Tidal Volume ; drug effects ; physiology ; Young Adult

PURPOSE: Hypoxemia during one-lung ventilation (OLV) remains a serious problem, particularly in the supine position. We investigated the effects of alveolar recruitment (AR) and positive end-expiratory pressure (PEEP) on oxygenation during OLV in the supine position. MATERIALS AND METHODS: Ninety-nine patients were randomly allocated to one of the following three groups: a control group (ventilation with a tidal volume of 8 mL/kg), a PEEP group (the same ventilatory pattern with a PEEP of 8 cm H2O), or an AR group (an AR maneuver immediately before OLV followed by a PEEP of 8 cm H2O). The tidal volume was reduced to 6 mL/kg during OLV in all groups. Blood gas analyses, respiratory variables, and hemodynamic variables were recorded 15 min into TLV (TLVbaseline), 15 and 30 min after OLV (OLV15 and OLV30), and 10 min after re-establishing TLV (TLVend). RESULTS: Ultimately, 92 patients were analyzed. In the AR group, the arterial oxygen tension was higher at TLVend, and the physiologic dead space was lower at OLV15 and TLVend than in the control group. The mean airway pressure and dynamic lung compliance were higher in the PEEP and AR groups than in the control group at OLV15, OLV30, and TLVend. No significant differences in hemodynamic variables were found among the three groups throughout the study period. CONCLUSION: Recruitment of both lungs with subsequent PEEP before OLV improved arterial oxygenation and ventilatory efficiency during video-assisted thoracic surgery requiring OLV in the supine position.
Adult ; Aged ; Anoxia ; Female ; Humans ; Lung/physiopathology ; Lung Compliance/physiology ; Male ; Middle Aged ; One-Lung Ventilation/*methods ; Oxygen/*blood ; Positive-Pressure Respiration/*methods ; Pulmonary Alveoli/*physiology ; Pulmonary Gas Exchange ; Respiratory Mechanics/*physiology ; *Supine Position ; Thoracic Surgery, Video-Assisted ; Tidal Volume

BACKGROUNDElectrical impedance tomography (EIT) is a real-time bedside monitoring tool, which can reflect dynamic regional lung ventilation. The aim of the present study was to monitor regional gas distribution in patients with acute respiratory distress syndrome (ARDS) during positive-end-expiratory pressure (PEEP) titration using EIT.

METHODSEighteen ARDS patients under mechanical ventilation in Department of Critical Care Medicine of Peking Union Medical College Hospital from January to April in 2014 were included in this prospective observational study. After recruitment maneuvers (RMs), decremental PEEP titration was performed from 20 cmH 2 O to 5 cmH 2 O in steps of 3 cmH 2 O every 5-10 min. Regional over-distension and recruitment were monitored with EIT.

RESULTSAfter RMs, patient with arterial blood oxygen partial pressure (PaO 2) + carbon dioxide partial pressure (PaCO 2 ) >400 mmHg with 100% of fractional inspired oxygen concentration were defined as RM responders. Thirteen ARDS patients was diagnosed as responders whose PaO 2 + PaCO 2 were higher than nonresponders (419 ± 44 mmHg vs. 170 ± 73 mmHg, P < 0.0001). In responders, PEEP mainly increased recruited pixels in dependent regions and over-distended pixels in nondependent regions. PEEP alleviated global inhomogeneity of tidal volume and end-expiratory lung volume. PEEP levels without significant alveolar derecruitment and over-distension were identified individually.

CONCLUSIONSAfter RMs, PEEP titration significantly affected regional gas distribution in lung, which could be monitored with EIT. EIT has the potential to optimize PEEP titration.

Aged ; Electric Impedance ; Female ; Humans ; Male ; Middle Aged ; Positive-Pressure Respiration ; Respiratory Distress Syndrome, Adult ; diagnosis ; Tomography ; methods

BACKGROUNDHigh-frequency oscillatory ventilation (HFOV) allows for small tidal volumes at mean airway pressures (mPaw) above that of conventional mechanical ventilation (CMV), but the effect of HFOV on hemodynamics, oxygen metabolism, and tissue perfusion in acute respiratory distress syndrome (ARDS) remains unclear. We investigated the effects of HFOV and CMV in sheep models with ARDS.

METHODSAfter inducing ARDS by repeated lavage, twelve adult sheep were randomly divided into a HFOV or CMV group. After stabilization, standard lung recruitments (40 cmH2O × 40 seconds) were performed. The optimal mPaw or positive end-expiratory pressure was obtained by lung recruitment and decremental positive end-expiratory pressure titration. The animals were then ventilated for 4 hours. The hemodynamics, tissue perfusion (superior mesenteric artery blood flow, pHi, and Pg-aCO2), oxygen metabolism and respiratory mechanics were examined at baseline before saline lavage, in the ARDS model, after model stabilization, and during hourly mechanical ventilation for up to 4 hours. A two-way repeated measures analysis of variance was applied to evaluate differences between the groups.

RESULTSThe titrated mPaw was higher and the tidal volumes lower in the HFOV group than the positive end-expiratory pressure in the CMV group. There was no significant difference in hemodynamic parameters between the HFOV and CMV groups. There was no difference in the mean alveolar pressure between the two groups. After lung recruitment, both groups showed an improvement in the oxygenation, oxygen delivery, and DO2. Lactate levels increased in both groups after inducing the ARDS model. Compared with the CMV group, the superior mesenteric artery blood flow and pHi were significantly higher in the HFOV group, but the Pg-aCO2 decreased in the HFOV group.

CONCLUSIONCompared with CMV, HFOV with optimal mPaw has no significant side effect on hemodynamics or oxygen metabolism, and increases gastric tissue blood perfusion.

Animals ; Disease Models, Animal ; Hemodynamics ; physiology ; High-Frequency Ventilation ; methods ; Male ; Oxygen ; metabolism ; Positive-Pressure Respiration ; methods ; Respiration, Artificial ; methods ; Respiratory Distress Syndrome, Adult ; metabolism ; therapy ; Sheep

Cardiac Surgical Procedures ; adverse effects ; Humans ; Positive-Pressure Respiration ; methods ; Respiratory Insufficiency ; therapy

OBJECTIVETo analyze the clinical characteristics of negative pressure pulmonary edema (NPPE).

METHODA retrospective investigation of the clinical manifestation, imageology, clinical course and outcome of 4 children with NPPE seen between June 2012 and July 2013 in a children's hospital. The causation of the airway obstruction was also explored.

RESULTAll the 4 cases were boys, the range of age was 40 days to 9 years. They had no history of respiratory and circulatory system disease. In 3 cases the disease had a sudden onset after the obstruction of airway, and in one the onset occurred 1.5 hours after removing the airway foreign body. All these cases presented with tachypnea, dyspnea, and cyanosis, none had fever. Three cases had coarse rales. Chest radiography was performed in 3 cases and CT scan was performed in 1 case, in all of them both lungs displayed diffuse ground-glass-like change and patchy consolidative infiltrates. Three cases were admitted to the ICU, duration of mechanical ventilation was less than 24 hours in 2 cases and 39 hours in one. Oxygen was given by mask to the remaining one in emergency department, whose symptoms were obviously improved in 10 hours. None was treated with diuretics, glucocorticoids or inotropic agents. Chest radiographs were taken within 24 hours of treatment in 2 cases and 24-48 hours in the other 2; almost all the pulmonary infiltrates were resolved. All the 4 cases were cured. The causes of airway obstruction were airway foreign bodies in two cases, laryngospasm in one and laryngomalacia in the other.

CONCLUSIONNPPE is a life-threatening emergency, which is manifested by rapid onset of respiratory distress rapidly (usually in several minutes, but might be hours later) after relief of the airway obstruction, with findings of pulmonary edema in chest radiograph. The symptoms resolve rapidly by oxygen therapy timely with or without mechanical ventilation. In children with airway obstruction, NPPE should be considered.

Acute Disease ; Airway Obstruction ; complications ; Child ; Child, Preschool ; Foreign Bodies ; complications ; Humans ; Infant ; Intensive Care Units ; Intubation, Intratracheal ; methods ; Laryngismus ; complications ; Larynx ; Lung ; diagnostic imaging ; pathology ; Male ; Oxygen Inhalation Therapy ; Positive-Pressure Respiration ; methods ; Pulmonary Edema ; diagnosis ; etiology ; therapy ; Radiography, Thoracic ; Retrospective Studies ; Tomography, X-Ray Computed