Bronchial blood flow reduction with positive end-expiratory pressure after acute lung injury in sheep

Smoke inhalation increases bronchial blood flow (Qbr) and produces edema of the airway system. This study investigates whether the increased Qbr seen 24 h after inhalation injury can be affected by mechanical ventilation with PEEP (5, 10, 15 cm H2O). Sheep (n = 8) previously prepared with cardiopulmonary catheters and ultrasonic transit time flow probes mounted around their bronchial arteries were insufflated with four sets of 12 breaths each of cotton smoke. Different levels of PEEP were added to the mechanical ventilation 24 h after injury; each PEEP level was applied for 45 min. There were significant increases in Qbr and lung lymph flow (QL) associated with a marked decrease in bronchial vascular resistance (BVR) 24 h after injury. However, no change was observed in mean arterial pressure (MAP) or cardiac index (CI). There was a substantial reduction in PaO2/FIO2 (P/F), which indicated a deterioration in arterial oxygenation. The application of varying levels of PEEP decreased Qbr (p less than .05) while BVR increased (p less than .05), but QL and P/F did not. CI and MAP were recorded. After removal of PEEP, none of the cardiopulmonary variables were significantly different from their postsmoke control values. These findings suggest that mechanical ventilation with PEEP markedly decreases the smoke-induced hyperemia edema frequently seen after inhalation injury without any significant alterations in MAP or CI.     

Effect of positive end-expiratory pressure on splanchnic perfusion in acute lung injury

Objective: To evaluate the acute effects of an increased positive end-expiratory pressure (PEEP) on splanchnic tissue perfusion.¶Design: Clinical prospective study.¶Setting: Intensive care unit in a university clinic.¶Patients: Six patients with severe acute lung injury (ALI) requiring mechanical ventilation. All patients had bilateral infiltrates in chest X-ray, PaO₂/FiO₂ < 200 mmHg and stable hemodynamics without vasoactive drugs.¶Interventions: PEEP was increased by 5 cmH₂O from a clinically selected PEEP level (8/6–11 cmH₂O) up to (13/10–14 cmH₂O) followed by a return to baseline.¶Measurements and main results: Splanchnic blood flow was measured using primed continuous infusion of indocyanine green dye with hepatic venous sampling and systemic hemodynamics by routine monitoring. In addition, we estimated gastric mucosal-arterial PCO₂ difference and splanchnic lactate/pyruvate exchange. After a baseline measurement, PEEP was increased. After 60 min all measurements were repeated. PEEP was returned to the baseline level and a third measurement followed. PEEP had no effect on cardiac index (baseline I: 3.2/6.1–2.5 l/min/m²; PEEP: 3.3/5.7–¶2.3 l/min/m²; baseline II: 3.4/6.0–2.5 l/min/m²); neither did PEEP have any effect on splanchnic blood flow (baseline I: 0.91/1.39–0.62 l/min/m²; PEEP: 1.04/1.75–0.54 l/min/m²; baseline II:1.07/1.42–0.68 l/min/m², respectively) or perfusion (gastric mucosal-arterial PCO₂ difference baseline I: 2.1/12.8–0.6 kPa; PEEP: 1.7/14.5–0.7 kPa; baseline II: 1.7/8.8–0.1 kPa; lactate uptake baseline I: 0.5/1.1–0.3 mmol/min/m²; PEEP: 0.4/1.0–0.3 mmol/min/m²; baseline II: 0.5/0.9–0.3 mmol/min/m²; hepatic venous lactate/pyruvate baseline I: 9.7/10.6–5.7; PEEP: 9.7/14.2–6.4; baseline II: 8.4/12.4–7.3; respectively).¶Conclusion: PEEP by itself does not have a consistent effect on splanchnic blood flow and metabolism when cardiac index is stable and patients are ventilated within the linear part of the pv curve.     

呼吸末正压通气治疗急性肺损伤的临床研究

目的 :对急性肺损伤 (ALI)病人进行呼吸机辅助呼吸比较不同值的呼气末正压(PEEP)对ALI氧供及氧耗的影响及其副作用。方法 :14例确诊为ALI病人在同一呼吸机参数下(不同PEEP)选择PEEP 0、 5、 10、 15、 2 0cmH2 O条件下监测其血流动力学、肺力学以及氧供氧耗的变化。结果 :(1)随着PEEP的增加气道峰值压 (pip)随之增加 ,肺顺应性在PEEP 0～15cmH2 O时逐渐增加 ,当PEEP大于 15cmH2 O反而下降 ;(2 )PEEP在 0～ 15cmH2 O时心输出量(CO)变化不大 ,差异无显著性 (P >0 0 5 ) ,在PEEP大于 15cmH2 O时CO明显下降 ,差异有显著性 ,P <0 0 5 ;(3)PEEP在一定范围内增加 ,氧供及氧耗也随之增加 ,当PEEP大于 15cmH2 O时氧供及氧耗反而下降。结论 :ALI的呼吸机治疗过程中 ,PEEP在 10～ 15cmH2 O时可获得最大的氧供最小的副作用     

Effects of positive end-expiratory pressure on the sigmoid equation in experimental acute lung injury

Objectives To describe inflation and deflation volume-pressure (V-P) curves of the respiratory system by the sigmoidal equation at different levels of positive end-expiratory pressure (PEEP) in acute lung injury.Design Experimental study.Setting Physiological laboratory in a university setting.Subjects Six pigs of 25 kg each.Interventions Acute lung injury was induced by oleic acid. PEEP was applied from 0 to 15 cmH₂O and from 15 to 0 cmH₂O for 10 min in steps of 5 cmH₂O.Measurements and results Inflation and deflation V-P curves were constructed from an automated super-syringe that delivers a constant flow of 7 l/min in both inspiratory and expiratory directions. V-P curves were obtained at each level of PEEP without disconnecting the animal from the ventilator. The experimental data were fitted to the sigmoid equation which provided the true inflection point (c), the point of maximal compliance increase (Pmci) reflecting opening/closure and the point of maximal compliance decrease (Pmcd) reflecting end of recruitment/onset of de-recruitment. The sigmoid equation provided an excellent fit. The values of the coefficients of determination were greater than 0.970 (median 0.996, IQR 0.994–0.997 for the 84 determinations). Negative values of Pmci in the deflation limb of the V-P curve were recorded in five pigs, suggesting closure below the volume range studied.Conclusions Inflation and deflation V-P curves at different PEEPs can be fitted by the sigmoid equation. However, further work is needed to investigate the meaning of negative values for Pmci.     

Effect of positive end-expiratory pressure on extravascular lung water in porcine acute respiratory failure

Recent studies of acute respiratory failure suggest that PEEP causes increased pulmonary interstitial fluid collection and therefore increased extravascular lung water (EVLW). We examined the effect of increasing levels of PEEP on EVLW in 20 to 25-kg pigs with acute respiratory failure induced by continuous infusion of live Pseudomonas aeruginosa (2 X 10(8) organisms/20 kg.min). Animals were intubated, paralyzed, and ventilated at 15 ml/kg tidal volume and an FIO2 of 0.4. Pigs in group 1 were given 4 ml/kg.h of iv fluid (lactated Ringer's solution) with no PEEP administered. Animals in groups 2 through 5 were given 0, 4, 17, and 44 ml/kg.h of lactated Ringer's solution, respectively, and PEEP was added at 5-cm H2O increments per half-hour, starting one hour after beginning P. aeruginosa infusion. EVLW in PEEP animals was less than or equal to that in controls despite variation in the administration of lactated Ringer's solution. This suggests that PEEP may slow EVLW accumulation over time and provide a protective effect that allows increased amounts of crystalloid fluids to be administered.     

Inspiratory vs. expiratory pressure-volume curves to set end-expiratory pressure in acute lung injury

Objective To study the effects of two levels of positive end-expiratory pressure (PEEP), 2 cmH₂O above the lower inflection point of the inspiratory limb and equal to the point of maximum curvature on the expiratory limb of the pressure-volume curve, in gas exchange, respiratory mechanics, and lung aeration.Design and setting Prospective clinical study in the intensive care unit and computed tomography ward of a university hospital.Patients Eight patients with early acute lung injury.Interventions Both limbs of the static pressure-volume curve were traced and inflection points calculated using a sigmoid model. During ventilation with a tidal volume of 6 ml/kg we sequentially applied a PEEP 2 cmH₂O above the inspiratory lower inflection point (15.5±3.1 cmH₂O) and a PEEP equal to the expiratory point of maximum curvature (23.5±4.1 cmH₂O).Measurements and results Arterial blood gases, respiratory system compliance and resistance and changes in lung aeration (measured on three computed tomography slices during end-expiratory and end-inspiratory pauses) were measured at each PEEP level. PEEP according to the expiratory point of maximum curvature was related to an improvement in oxygenation, increase in normally aerated, decrease in nonaerated lung volumes, and greater alveolar stability. There was also an increase in PaCO₂, airway pressures, and hyperaerated lung volume.Conclusions High PEEP levels according to the point of maximum curvature of the deflation limb of the pressure-volume curve have both benefits and drawbacks.This work was supported by a grant from Fondo de Investigación Sanitaria (PI03/0833) and Red GIRA (G03/063)     

Effects of recruitment maneuvers in patients with acute lung injury and acute respiratory distress syndrome ventilated with high positive end-expiratory pressure

Objective: Positive end-expiratory pressure (PEEP) and recruitment maneuvers (RMs) may partially reverse atelectasis and reduce ventilation-associated lung injury. The purposes of this study were to assess a) magnitude and duration of RM effects on arterial oxygenation and on requirements for oxygenation support (Fio2/PEEP) in patients with acute lung injury and acute respiratory distress syndrome (ALI/ARDS) receiving ventilation with low tidal volumes and high levels of PEEP; and b) frequency of adverse respiratory and circulatory events attributable to RMs. Design: Prospective, randomized, crossover study. Setting: Thirty-four intensive care units at 19 hospitals. Patients: Seventy-two patients with early ALI/ARDS. Baseline PEEP and Fio2 were 13.8 +/- 3.0 cm H2O and 0.39 +/- 0.10, respectively (mean +/- sd). Interventions: We conducted RMs by applying continuous positive airway pressure of 35-40 cm H2O for 30 secs. We conducted sham RMs on alternate days. We monitored oxyhemoglobin saturation by pulse oximetry (SpO2), Fio2/PEEP, blood pressure, and heart rate for 8 hrs after RMs and sham RMs. We examined chest radiographs for barotrauma. Measurements and Main Results: Responses to RMs were variable. Greatest increments from baseline SpO2 within 10 mins after RMs were larger than after sham RMs (1.7 +/- 0.2 vs. 0.6 +/- 0.3 %, mean +/- SEM, p < .01). Systolic blood pressure decreased more +/- 1.1 mm Hg, p < .01). Changes in Fio2/PEEP requirements were not significantly different at any time after RMs vs. sham RMs. Barotrauma was apparent on first radiographs after one RM and one sham RM.Conclusions: In ALI/ARDS patients receiving mechanical ventilation with low tidal volumes and high PEEP, short-term effects of RMs as conducted in this study are variable. Beneficial effects on gas exchange in responders appear to be of brief duration. More information is needed to determine the role of recruitment maneuvers in the management of ALI/ARDS.     

Effects of positive end-expiratory pressure on dead space and its partitions in acute lung injury

OBJECTIVE: A large tidal volume (VT) and lung collapse and re-expansion may cause ventilator-induced lung injury (VILI) in acute lung injury (ALI). A low VT and a positive end-expiratory pressure (PEEP) can prevent VILI, but the more VT is reduced, the more dead space (VD) compromises gas exchange. We investigated how physiological, airway and alveolar VD varied with PEEP and analysed possible links to respiratory mechanics. SETTING: Medical and surgical intensive care unit (ICU) in a university hospital. DESIGN: Prospective, non-randomised comparative trial. PATIENTS. Ten consecutive ALI patients. INTERVENTION: Stepwise increases in PEEP from zero to 15 cm H2O. MEASUREMENTS AND RESULTS: Lung mechanics and VD were measured at each PEEP level. Physiological VD was 41-64% of VT at zero PEEP and increased slightly with PEEP due to a rise in airway VD. Alveolar VD was 11-38% of VT and did not vary systematically with PEEP. However, in individual patients a decrease and increase of alveolar VD paralleled a positive or negative response to PEEP with respect to oxygenation (shunt), respectively. VD fractions were independent of respiratory resistance and compliance. CONCLUSIONS: Alveolar VD is large and does not vary systematically with PEEP in patients with various degrees of ALI. Individual measurements show a diverse response to PEEP. Respiratory mechanics were of no help in optimising PEEP with regard to gas exchange.     

呼气末正压对急性呼吸窘迫综合征肺复张容积及氧合影响的临床研究

目的　评价呼气末正压 (PEEP)对急性呼吸窘迫综合征 (ARDS)肺复张容积的影响 ,探讨ARDS患者 PEEP的选择方法。方法　以 11例血流动力学稳定、接受机械通气的 ARDS患者为研究对象 ,采用压力容积曲线法分别测定 PEEP为 5、10、15 cm H2 O(1cm H2 O=0 .0 98k Pa)时的肺复张容积 ,观察患者动脉血气、肺机械力学和血流动力学变化。结果　 PEEP分别 5、10和 15 cm H2 O时肺复张容积分别为 (4 0 .2±15 .3) ml、 (12 3.8± 4 3.1) ml和 (178.9± 4 3.5 ) m l,随着 PEEP水平的增加 ,肺复张容积亦明显增加 (P均 <0 .0 5 )。动脉氧合指数也随着 PEEP水平增加而增加 ,且其变化与肺复张容积呈正相关 (r=0 .4 83,P<0 .0 1)。不同 PEEP条件下 ,患者的肺静态顺应性无明显变化 (P>0 .0 5 )。将患者按有无低位转折点 (L IP)分为有 L IP组与无 L IP组 ,两组患者的肺复张容积都随着 PEEP水平的增加而增加 ,其中 PEEP15 cm H2 O时 L IP组患者的肺复张容积大于无 L IP组 (P<0 .0 5 )。结论　 PEEP水平越高 ,肺复张容积越大 ,肺复张容积增加与动脉氧合指数的变化呈正相关     

Influence of neurally adjusted ventilatory assist and positive end-expiratory pressure on breathing pattern in rabbits with acute lung injury

OBJECTIVE: To evaluate the influence of neurally adjusted ventilatory assist (NAVA) and positive end-expiratory pressure (PEEP) on the control of breathing in rabbits with acute lung injury. DESIGN: Prospective animal study. SETTING: Experimental laboratory in a university hospital. SUBJECTS: Male White New Zealand rabbits (n = 18). INTERVENTION: Spontaneously breathing rabbits with hydrochloric acid-induced lung injury were ventilated with NAVA and underwent changes in NAVA gain and PEEP (six nonvagotomized and five vagotomized). Seven other nonvagotomized rabbits underwent 4 hrs of ventilation with hourly titration of PEEP, Fio2, and NAVA gain. MEASUREMENTS AND MAIN RESULTS: We studied diaphragm electrical activity, respiratory pressures, and breathing pattern. After lung injury, 0 cm H2O of PEEP resulted in high tonic and no discernible phasic diaphragm electrical activity in the nonvagotomized rabbits; stepwise increases in PEEP (up to 11.7 +/- 2.6 cm H2O) reduced tonic but increased phasic diaphragm electrical activity. Increasing the NAVA gain reduced phasic diaphragm electrical activity to almost half and abolished esophageal pressure swings. Tidal volume remained at 4-5 mL/kg, and respiratory rate did not change. In the vagotomized group, lung injury did not induce tonic activity, and phasic activity and tidal volume were several times higher than in the nonvagotomized rabbits. Four hours of breathing with NAVA restored breathing pattern and neural and mechanical breathing efforts to pre-lung injury levels. CONCLUSIONS: Acute lung injury can cause a vagally mediated atypical diaphragm activation pattern in spontaneously breathing rabbits. Modulation of PEEP facilitates development of phasic diaphragm electrical activity, whereupon implementation of NAVA can efficiently maintain unloading of the respiratory muscles without delivering excessive tidal volume in rabbits with intact vagal function.     

Respiratory and haemodynamic changes during decremental open lung positive end-expiratory pressure titration in patients with acute respiratory distress syndrome

Introduction  

To investigate haemodynamic and respiratory changes during lung recruitment and decremental positive end-expiratory pressure (PEEP) titration for open lung ventilation in patients with acute respiratory distress syndrome (ARDS) a prospective, clinical trial was performed involving 12 adult patients with ARDS treated in the surgical intensive care unit in a university hospital.     

Positive end-expiratory pressure individualization guided by continuous end-expiratory lung volume monitoring during laparoscopic surgery

To determine whether end-expiratory lung volume measured with volumetric capnography (EELV_CO2) can individualize positive end-expiratory pressure (PEEP) setting during laparoscopic surgery. We studied patients undergoing laparoscopic surgery subjected to Fowler (F-group; n?=?20) or Trendelenburg (T-group; n?=?20) positions. EELV_CO2 was measured at 0° supine (baseline), during capnoperitoneum (CP) at 0° supine, during CP with Fowler (head up?+?20°) or Trendelenburg (head down ??30°) positions and after CP back to 0° supine. PEEP was adjusted to preserve baseline EELV_CO2 during and after CP. Baseline EELV_CO2 was statistically similar to predicted FRC in both groups. At supine and CP, EELV_CO2 decreased from baseline values in F-group [median and IQR 2079 (768) to 1545 (725) mL; p?=?0.0001] and in T-group [2164 (789) to 1870 (940) mL; p?=?0.0001]. Change in body position maintained EELV_CO2 unchanged in both groups. PEEP adjustments from 5.6 (1.1) to 10.0 (2.5) cmH₂O in the F-group (p?=?0.0001) and from 5.6 (0.9) to 10.0 (2.6) cmH₂O in T-group (p?=?0.0001) were necessary to reach baseline EELV_CO2 values. EELV_CO2 increased close to baseline with PEEP in the F-group [1984 (600) mL; p?=?0.073] and in the T-group [2175 (703) mL; p?=?0.167]. After capnoperitoneum and back to 0° supine, PEEP needed to maintain EELV_CO2 was similar to baseline PEEP in F-group [5.9 (1.8) cmH₂O; p?=?0.179] but slightly higher in the T-group [6.5 (2.2) cmH₂O; p?=?0.006]. Those new PEEP values gave EELV_CO2 similar to baseline in the F-group [2039 (980) mL; p?=?0.370] and in the T-group [2150 (715) mL; p?=?0.881]. Breath-by-breath noninvasive EELV_CO2 detected changes in lung volume induced by capnoperitoneum and body position and was useful to individualize the level of PEEP during laparoscopy.

Trial registry: Clinicaltrials.gov NCT03693352. Protocol started 1st October 2018.

     

Ventilation with biphasic positive airway pressure in experimental lung injury

Objective We investigated whether improvement in ventilation perfusion (_A/) distribution during mechanical ventilation using biphasic positive airway pressure (BIPAP) with spontaneous breathing may be attributed to an effectively increased transpulmonary pressure (P_TP) and can also be achieved by increasing P_TP during controlled ventilation.Design In 12 pigs with saline lavage-induced lung injury we compared the effects of BIPAP to pressure-controlled ventilation with equal airway pressure (PCV_AW) or equal transpulmonary pressure (PCV_TP) on _A/ distribution assessed by the multiple inert gas elimination technique (MIGET).Setting Animal laboratory study.Measurements and results Intrapulmonary shunt was 33±11% during BIPAP, 36±10% during PCV_AW and 33±15% during PCV_TP (p= n.s.). BIPAP resulted in higher PaO₂ than PCV_AW (188±83 versus 147±82 mmHg, p<0.05), but not than PCV_TP (187±139 mmHg). Oxygen delivery was significantly higher during BIPAP (530±109 ml/min) versus 374±113 ml/min during PCV_AW and 353±93 ml/min during PCV_TP (p<0.005). Tidal volume with PCV_TP increased to 11.9±2.3 ml/kg, compared to 8.5±0.8 with BIPAP and 7.6±1.4 with PCV_AW (p<0.001) and cardiac output decreased to 3.5±0.6 l/min (BIPAP 4.9±0.8 and PCV_AW 3.9±0.8, p<0.006).Conclusions In experimental lung injury, BIPAP with preserved spontaneous breathing was effective in increasing regional P_TP, since pressure-controlled ventilation with the same P_TP resulted in similar gas exchange effects. However, PCV_TP caused increased airway pressures and tidal volumes, whereby, with BIPAP, less depression of oxygen delivery and cardiac output were observed. BIPAP could be useful in maintaining pulmonary gas exchange and slightly improving oxygenation without interfering with circulation as strongly as PCV does.An editorial regarding this article can be found in the same issue ()     

The effect of positive end-expiratory pressure during partial liquid ventilation in acute lung injury in piglets.

OBJECTIVES: To investigate the effects of positive end-expiratory pressure (PEEP) application during partial liquid ventilation (PLV) on gas exchange, lung mechanics, and hemodynamics in acute lung injury. DESIGN: Prospective, randomized, experimental study. SETTING: University research laboratory. SUBJECTS: Six piglets weighing 7 to 12 kg. INTERVENTIONS: After induction of anesthesia, tracheostomy, and controlled mechanical ventilation, animals were instrumented with two central venous catheters, a pulmonary artery catheter and two arterial catheters, and an ultrasonic flow probe around the pulmonary artery. Acute lung injury was induced by the infusion of oleic acid (0.08 mL/kg) and repeated lung lavage procedures with 0.9% sodium chloride (20 mL/kg). The protocol consisted of four different PEEP levels (0, 5, 10, and 15 cm H2O) randomly applied during PLV. The oxygenated and warmed perfluorocarbon liquid (30 mL/kg) was instilled into the trachea over 5 mins without changing the ventilator settings. MEASUREMENTS AND MAIN RESULTS: Airway pressures, tidal volumes, dynamic and static pulmonary compliance, mean and expiratory airway resistances, and arterial blood gases were measured. In addition, dynamic pressure/volume loops were recorded. Hemodynamic monitoring included right atrial, mean pulmonary artery, pulmonary capillary wedge, and mean systemic arterial pressures and continuous flow recording at the pulmonary artery. The infusion of oleic acid combined with two to five lung lavage procedures induced a significant reduction in PaO2/FI(O2) from 485 +/- 28 torr (64 +/- 3.6 kPa) to 68 +/- 3.2 torr (9.0 +/- 0.4 kPa) (p < .01) and in static pulmonary compliance from 1.3 +/- 0.06 to 0.67 +/- 0.04 mL/cm H2O/kg (p < .01). During PLV, PaO2/FI(O2) increased significantly from 68 +/- 3.2 torr (8.9 +/- 0.4 kPa) to >200 torr (>26 kPa) (p < .01). The highest PaO2 values were observed during PLV with PEEP of 15 cm H2O. Deadspace ventilation was lower during PLV when PEEP levels of 10 to 15 cm H2O were applied. There were no differences in hemodynamic data during PLV with PEEP levels up to 10 cm H2O. However, PEEP levels of 15 cm H2O resulted in a significant decrease in cardiac output. Dynamic pressure/volume loops showed early inspiratory pressure spikes during PLV with PEEP levels of 0 and 5 cm H2O. CONCLUSIONS: Partial liquid ventilation is a useful technique to improve oxygenation in severe acute lung injury. The application of PEEP during PLV further improves oxygenation and lung mechanics. PEEP levels of 10 cm H2O seem to be optimal to improve oxygenation and lung mechanics.     

Positive end-expiratory pressure affects the value of intra-abdominal pressure in acute lung injury/acute respiratory distress syndrome patients: a pilot study

Introduction  

To examine the effects of positive end-expiratory pressure (PEEP) on intra-abdominal pressure (IAP) in patients with acute lung injury (ALI).     

Optimisation of positive end-expiratory pressure by forced oscillation technique in a lavage model of acute lung injury

Purpose  

We evaluated whether oscillatory compliance (C_X5) measured by forced oscillation technique (FOT) at 5 Hz may be useful for positive end-expiratory pressure (PEEP) optimisation.