ABSTRACT
Objective@#To better understand the significance of the pressure-time curve and flow-time curve from the perspective of PB840 ventilator working principle.@*Methods@#① Mechanical principle: flow supply valves (air valve and oxygen valve) and exhalation valve in PB840 ventilator were controlled to achieve the ventilation target (volume or pressure) by the central processing unit according to the monitoring data from pressure sensors (P1 at the supply side, P2 at the exhalation side) and flow sensors (Q1 at the air side, Q2 at the oxygen side, Q3 at the exhalation side). ② The essence of curve: each point means a value of pressure or flow at a certain time measured by the sensors or calculated by the system. ③ The respiratory process could be divided into inspiratory part, expiratory part, and the connection part from expiratory to inspiratory. The air running state and the respiratory mechanics relationship at the three parts could be inferred according to the form of curves.@*Results@#① Inspiratory process: at volume-controlled and constant flow ventilation: there should be a relationship "Pc-Pa = XR" between alveolar pressure (Pa) and circuit pressure (Pc) according to Ohm law. So, the Pc curve (pressure-time curve) could indirectly reflect the Pa curve with the flow (X) and resistance (R) being constant. At pressure-set ventilation: it is the goal of ventilator to maintain the Pc at the target level. So, the stability of the target pressure line in pressure-time curve reflects the matching ability of the flow supply valves and the exhalation valve. ② Expiratory process: it could be divided into pre-expiratory [without basic flow (Ba) or bias flow (Bi)] and post-expiratory (with Ba or Bi), where Ba or Bi is equal to "Q1+Q2". So, the mathematical function are "X(t) = Q3t" in pre-part, and "X(t) = Q3t-(Q1t+Q2t)" in post-part. The relationship between pressure and flow at peak expiratory flow point: it could be found that there is an obvious time span and area formation under the curve from 0 to peak point (Fpeak) after stretching the abscissa axis of flow-time curve. It means that some gas have been discharged from the lung when it arrives at the peak point. So, the alveolar pressure should be lower than the platform pressure at the point (Pplat). The circuit pressure is significantly higher than positive end expiratory pressure (PEEP) at the point in the stretching axis diagram. So, it means that the formula "RE = (Pplat-PEEP)/Fpeak" to calculate the expiratory resistance (RE) is unreasonable in the angle of Ohm law. ③ The process from exhalation to inspiratory: according to the difference of the starting point of the conversion, it could be divided into two cases: one is that the inspiratory started from the ending of exhalation. Here, the inhaling starting point is lying in the abscissa axis. The other is that the inspiratory started before the ending of exhalation (with endogenous positive end expiratory pressure). Here, the starting point is lying below the abscissa axis, and the slope of the following curve is obviously larger than the slope of natural expiratory curve. According to the difference of results from the starting point to the end of the inhalation triggering effort, it could be divided into two cases: one is that it reach the trigger point. Here, the expiratory curve extends upward from or below the horizontal axis until an effective air supply is triggered. The other is that it could not reach the trigger point. Here, the expiratory curve extends upward from or below the horizontal axis, but then runs downward (meaning exhaling).@*Conclusion@#It is helpful to analyze the ventilation state, ventilation failure, and the causes of man-machine confrontation with understanding the ventilation principle and the air route map of the ventilator.
ABSTRACT
Objective To better understand the significance of the pressure-time curve and flow-time curve from the perspective of PB840 ventilator working principle. Methods ① Mechanical principle: flow supply valves (air valve and oxygen valve) and exhalation valve in PB840 ventilator were controlled to achieve the ventilation target (volume or pressure) by the central processing unit according to the monitoring data from pressure sensors (P1 at the supply side, P2 at the exhalation side) and flow sensors (Q1 at the air side, Q2 at the oxygen side, Q3 at the exhalation side). ② The essence of curve: each point means a value of pressure or flow at a certain time measured by the sensors or calculated by the system. ③ The respiratory process could be divided into inspiratory part, expiratory part, and the connection part from expiratory to inspiratory. The air running state and the respiratory mechanics relationship at the three parts could be inferred according to the form of curves. Results ① Inspiratory process: at volume-controlled and constant flow ventilation: there should be a relationship "Pc-Pa = XR" between alveolar pressure (Pa) and circuit pressure (Pc) according to Ohm law. So, the Pc curve (pressure-time curve) could indirectly reflect the Pa curve with the flow (X) and resistance (R) being constant. At pressure-set ventilation: it is the goal of ventilator to maintain the Pc at the target level. So, the stability of the target pressure line in pressure-time curve reflects the matching ability of the flow supply valves and the exhalation valve. ② Expiratory process: it could be divided into pre-expiratory [without basicflow (Ba) or bias flow (Bi)] and post-expiratory (with Ba or Bi), where Ba or Bi is equal to "Q1+Q2". So, the mathematical function are "X(t) = Q3t" in pre-part, and "X(t) = Q3t-(Q1t+Q2t)" in post-part. The relationship between pressure and flow at peak expiratory flow point: it could be found that there is an obvious time span and area formation under the curve from 0 to peak point (Fpeak) after stretching the abscissa axis of flow-time curve. It means that some gas have been discharged from the lung when it arrives at the peak point. So, the alveolar pressure should be lower than the platform pressure at the point (Pplat). The circuit pressure is significantly higher than positive end expiratory pressure (PEEP) at the point in the stretching axis diagram. So, it means that the formula "RE = (Pplat-PEEP)/Fpeak" to calculate the expiratory resistance (RE) is unreasonable in the angle of Ohm law. ③ The process from exhalation to inspiratory: according to the difference of the starting point of the conversion, it could be divided into two cases: one is that the inspiratory started from the ending of exhalation. Here, the inhaling starting point is lying in the abscissa axis. The other is that the inspiratory started before the ending of exhalation (with endogenous positive end expiratory pressure). Here, the starting point is lying below the abscissa axis, and the slope of the following curve is obviously larger than the slope of natural expiratory curve. According to the difference of results from the starting point to the end of the inhalation triggering effort, it could be divided into two cases: one is that it reach the trigger point. Here, the expiratory curve extends upward from or below the horizontal axis until an effective air supply is triggered. The other is that it could not reach the trigger point. Here, the expiratory curve extends upward from or below the horizontal axis, but then runs downward (meaning exhaling). Conclusion It is helpful to analyze the ventilation state, ventilation failure, and the causes of man-machine confrontation with understanding the ventilation principle and the air route map of the ventilator.
ABSTRACT
Objective To explore the variation and clinical value of the degradation of endothelial glycocalyx in the patients with septic shock. Methods A prospective case control study was conducted. Patients of 18 years or older diagnosed with septic shock and admitted to Department of Critical Care Medicine of Affiliated Hospital of Binzhou Medical University from June 2014 to May 2015 were enrolled. The levels of degradation products, including hyaluronic acid (HA) and heparin sulfate (HS), at 0, 6, 12, 24, 48 hours were determined, while 20 healthy people were enrolled and served as controls. The changes of HA and HS were analyzed in the patients with septic shock. The differences of HA and HS between survival group and death group after 28 days were also analyzed. The relationships between HA, HS and tumor necrosis factor-α (TNF-α), sequential organ failure assessment (SOFA) score, arterial blood lactate (Lac), platelet, albumin were analyzed by Pearson correlation analysis. The receiver-operating characteristic (ROC) curve was plotted to assess the prognostic value of HA and HS for patients with septic shock. Results Thirty-one patients diagnosed as septic shock were enrolled, among whom 17 patients died after 28 days, with a mortality of 54.8%. The levels of HA and HS in patients with septic shock were increased significantly as compared with those of health control group, peaked at 48 hours, and the levels of HA and HS at 48 hours were significantly higher than those at 0 hour [HA (μg/L): 119.47±32.44 vs. 94.84±23.63, HS (μg/L): 72.83±19.03 vs. 58.83±16.63, both P < 0.05]. The levels of HA and HS at 0 hour and 48 hours in death group were significantly higher than those of the survival group [HA (μg/L): 130.42±27.67 vs. 93.29±29.80, 105.14±19.18 vs. 70.82±13.24; HS (μg/L): 67.23±25.01 vs. 39.23±14.58, 79.74±19.84 vs. 56.17±14.53, all P < 0.05]. The levels of HA and HS in patients with septic shock were remarkably positively correlated with the levels of TNF-α, SOFA score, Lac, and platelet, but were remarkably negatively correlated with albumin levels (r value of HA was 0.595, 0.462, 0.545, 0.466, -0.534, respectively; r value of HS was 0.607, 0.468, 0.563, 0.547, -0.455, respectively; all P < 0.05). It was demonstrated by ROC curves that the areas under ROC curve (AUC) of HA and HS at 0 hour and 48 hours for predicting the prognosis of patients with septic shock were 0.881, 0.940 and 0.833, 0.821, respectively, the sensitivities of HA and HS were 87.5%, 100.0% and 83.3%, 81.3%, respectively, and the specificities of HA and HS were 82.6%, 78.3% and 91.3%, 78.3%, respectively. Conclusions The concentrations of degradation products generated by endothelial glycocalyx in the blood of the patients with septic shock are remarkably increased. The elevated levels of the degradation products are closely associated with the severity of septic shock, microcirculation disturbance, and the levels of inflammatory factors.