Effects of extrinsic positive end-expiratory pressure on mechanically ventilated patients with chronic obstructive pulmonary disease and dynamic hyperinflation

Objective To examine the circulatory and respiratory effects of extrinsic positive end-expiratory pressure (PEEPe) in patients with chronic obstructive pulmonary disease (COPD) and dynamic hyperinflation during controlled mechanical ventilation.Design Different levels of PEEPe were applied randomly in mechanically ventilated patients with COPD and dynamic hyperinflation.Setting Respiratory Intensive Care Unit of a University Hospital.Patients 9 patients with acute respiratory failure and dynamic hyperinflation due to acute exacerbation of COPD.Interventions PEEPe 35%, 58% and 86% of intrinsic PEEP (PEEPi) were applied.Measurements and results Using flow-directed pulmonary artery catheters hemodynamic measurements were obtained, while simultaneously lung volumes, airflows and airway pressures were recorded. In order to estimate alveolar pressures (P_alv), rapid airway occlusions during passive expiration were also performed. At no level of PEEPe were significant changes in cardiac output, gas exchange variables, dead space, airways inflation resistances and respiratory system static end-inspiratory compliance observed. At high level of PEEPe central venous, mean pulmonary arterial and pulmonary capillary wedge pressures were increased significantly. All but one patient were flow-limited during passive expiration. PEEPe 86% of PEEPi caused a significant increase in end-expiratory lung volume and total PEEP. Iso-volume pressure-flow curves showed volume-dependence expiratory flow limitation in 2 patients, while in 8 patients volume-dependence of critical driving pressure (P_alv-mouth pressure) that decreased flows was also observed.Conclusions The effects of PEEPe on iso-volume flow and hence on lung mechanics and hemodynamics, depend on many factors, such as airways resistances, lung volumes and airway characteristics, making the patient response to PEEPe unpredictable.     

Effects of helium-oxygen on intrinsic positive end-expiratory pressure in intubated and mechanically ventilated patients with severe chronic obstructive pulmonary disease

OBJECTIVE: To test the hypothesis that replacing 70:30 nitrogen: oxygen (Air-O2) with 70:30 helium:oxygen (He-O2) can decrease dynamic hyperinflation ("intrinsic" positive end-expiratory pressure) in mechanically ventilated patients with chronic obstructive pulmonary disease (COPD), and to document the consequences of such an effect on arterial blood gases and hemodynamics. DESIGN: Prospective, interventional study. SETTING: Medical intensive care unit, university tertiary care center. PATIENTS: Twenty-three intubated, sedated, paralyzed, and mechanically ventilated patients with COPD enrolled within 36 hrs after intubation. INTERVENTIONS: Measurements were taken at the following time points, all with the same ventilator settings: a) baseline; b) after 45 mins with He-O2; c) 45 mins after return to Air-O2. The results were then compared to those obtained in a test lung model using the same ventilator settings. MAIN RESULTS (MEAN + SD): Trapped lung volume and intrinsic positive end-expiratory pressure decreased during He-O2 ventilation (215+/-125 mL vs. 99+/-15 mL and 9+/-2.5 cm H2O vs. 5+/-2.7 cm H2O, respectively; p < .05). Likewise, peak and mean airway pressures declined with He-O2 (30+/-5 cm H2O vs. 25+/-6 cm H2O and 8+/-2 cm H2O vs. 7+/-2 cm H2O, respectively; p < .05). These parameters all rose to their baseline values on return to Air-O2 (p < .05 vs. values during He-O2). These results were in accordance with those obtained in the test lung model. There was no modification of arterial blood gases, heart rate, or mean systemic arterial blood pressure. In 12/23 patients, a pulmonary artery catheter was in place, allowing hemodynamic measurements and venous admixture calculations. Switching to He-O2 and back to Air-O2 had no effect on pulmonary artery pressures, right and left ventricular filling pressures, cardiac output, pulmonary and systemic vascular resistance, or venous admixture. CONCLUSION: In mechanically ventilated COPD patients with intrinsic positive end-expiratory pressure, the use of He-O2 can markedly reduce trapped lung volume, intrinsic positive end-expiratory pressure, and peak and mean airway pressures. No effect was noted on hemodynamics or arterial blood gases. He-O2 might prove beneficial in this setting to reduce the risk of barotrauma, as well as to improve hemodynamics and gas exchange in patients with very high levels of intrinsic positive end-expiratory pressure.     

Estimating cardiac filling pressure in mechanically ventilated patients with hyperinflation

OBJECTIVE: When positive end-expiratory pressure (PEEP) is applied, the intracavitary left ventricular end-diastolic pressure (LVEDP) exceeds the LV filling pressure because pericardial pressure exceeds 0 at end-expiration. Under those conditions, the LV filling pressure is itself better reflected by the transmural LVEDP (tLVEDP) (LVEDP minus pericardial pressure). By extension, end-expiratory pulmonary artery occlusion pressure (eePAOP), as an estimate of end-expiratory LVEDP, overestimates LV filling pressure when pericardial pressure is >0, because it occurs when PEEP is present. We hypothesized that LV filling pressure could be measured from eePAOP by also knowing the proportional transmission of alveolar pressure to pulmonary vessels calculated as index of transmission = (end-inspiratory PAOP--eePAOP)/(plateau pressure--total PEEP). We calculated transmural pulmonary artery occlusion pressure (tPAOP) with this equation: tPAOP = eePAOP--(index of transmission x total PEEP). We compared tPAOP with airway disconnection nadir PAOP measured during rapid airway disconnection in subjects undergoing PEEP with and without evidence of dynamic pulmonary hyperinflation. DESIGN: Prospective study. SETTING: Medical intensive care unit of a university hospital. PATIENTS: We studied 107 patients mechanically ventilated with PEEP for acute respiratory failure. Patients without dynamic pulmonary hyperinflation (group A; n = 58) were analyzed separately from patients with dynamic pulmonary hyperinflation (group B; n = 49). INTERVENTION: Transient airway disconnection. MEASUREMENTS AND MAIN RESULTS: In group A, tPAOP (8.5+/-6.0 mm Hg) and nadir PAOP (8.6+/-6.0 mm Hg) did not differ from each other but were lower than eePAOP (12.4+/-5.6 mm Hg; p < .05). The agreement between tPAOP and nadir PAOP was good (bias, 0.15 mm Hg; limits of agreement, -1.5-1.8 mm Hg). In group B, tPAOP (9.7+/-5.4 mm Hg) was lower than both nadir PAOP and eePAOP (12.1+/-5.4 and 13.9+/-5.2 mm Hg, respectively; p < .05 for both comparisons). The agreement between tPAOP and nadir PAOP was poor (bias, 2.3 mm Hg; limits of agreement, -0.2-4.8 mm Hg). CONCLUSIONS: Indexing the transmission of proportional alveolar pressure to PAOP in the estimation of LV filling pressure is equivalent to the nadir method in patients without dynamic pulmonary hyperinflation and may be more reliable than the nadir PAOP method in patients with dynamic pulmonary hyperinflation.     

Relationship between respiratory impedance and positive end-expiratory pressure in mechanically ventilated neonates

Purpose

To evaluate the feasibility of forced oscillation technique (FOT) measurements at the bedside and to describe the relationship between positive end-expiration pressure (PEEP) and lung mechanics in different groups of ventilated infants.

Methods

Twenty-eight infants were studied: 5 controls, 16 newborns with respiratory distress syndrome (RDS) and 7 chronically ventilated newborns that developed bronchopulmonary dysplasia. An incremental/decremental PEEP trial was performed by changing PEEP in 1-min steps of 1 cmH₂O between 2 and 10 cmH₂O. Forced oscillations at 5 Hz were superimposed on the ventilator waveform. Pressure and flow, measured at the inlet of the ETT, were used to compute resistance (Rrs) and reactance (Xrs).

Results

In controls Rrs and Xrs were on average 41 ± 21 and ?22 ± 6 cmH₂O s/l respectively and were almost unaffected by PEEP. RDS infants presented similar Rrs (48 ± 25 cmH₂O s/l) and reduced Xrs (?71 ± 19 cmH₂O s/l) at the beginning of the trial. Two behaviours were observed as PEEP was increased: in extremely low birth weight infants Xrs decreased with PEEP with marked hysteresis; in very low and low birth weight infants Xrs and Rrs were less PEEP dependent. Chronically ventilated infants had very high Rrs and very negative Xrs values at very low PEEPs (121 ± 41 and ?95 ± 13 cmH₂O s/l at PEEP = 2 cmH₂O) that markedly changed as PEEP exceeded 3–4 cmH₂O.

Conclusions

Rrs and Xrs measurement in preterm newborns is feasible, and data are representative of the lung mechanics and very sensitive to its changes with PEEP, making FOT a promising technique for the non-invasive bedside titration of mechanical ventilation in preterm newborns.     

呼气末正压对机械通气患者中心静脉压及髂总静脉压的影响

目的 观察不同呼气末正压(PEEP)水平对机械通气患者中心静脉压(CVP)和髂总静脉压(CIVP)及两者相关关系的影响.方法 将2007年2-8月收住重症加强治疗病房(ICU),无心肺疾患、循环稳定、无腹胀、无凝血功能异常,需机械通气的20例成年患者列为观察对象,采用自身对照,随机加用0、5和10 cm HzO(1 am H2O=0.098 kPa)PEEP,评估在此条件下,CVP、CIVP和两者压力阶差变化及其与机械通气压力变化间的相关关系.结果 CVP及CIVP随PEEP增加而增高,差异有统计学意义(P0.05);CVP及CIVP与机械通气各压力值变化呈正相关,但CVP及CIVP仅与平均气道压(Pmean)及PEEP有统计学意义(CVP与PEEP r=0.751,CIVP与PEEP r=0.685,CVP与Pmean r=0.634,CIVP与Pmena r=0.603,P均相似文献   

Intrinsic positive end-expiratory pressure in mechanically ventilated patients with and without tidal expiratory flow limitation

OBJECTIVE: To assess static intrinsic positive end-expiratory pressure (PEEPi,st) and expiratory flow limitation (FL) in 32 consecutive mechanically ventilated patients with acute respiratory failure (ARF), using a commercial ventilator with an incorporated device that allows the application of a negative expiratory pressure (NEP). DESIGN: Prospective clinical study. SETTING: Multidisciplinary intensive care unit of a university hospital. PATIENTS: Thirty-two consecutive ventilated patients with ARF of various etiologies. INTERVENTIONS: Evaluation of respiratory mechanics, PEEPi,st, and FL from pressure, flow, and volume traces provided by the ventilator. MEASUREMENTS: Peak airway pressure, PEEPi,st, dynamic elastance, and interrupter resistance were measured in relaxed patients in a supine position. Comparison of tidal flow-volume curves before and during the application of an NEP of 5 cm H2O was used to assess tidal expiratory FL. RESULTS: Twelve of 32 patients studied exhibited tidal expiratory FL, which was detected by the absence of increase in expiratory flow despite application of an NEP over the entire or part of the baseline expiratory flow-volume curve. All patients exhibited PEEPi,st, which amounted to 1.2 +/- 0.9 cm H2O (mean +/- SD) in the 20 non-FL patients and 7.1 +/- 2.8 cm H2O in the 12 FL patients (p < 0.00001). The majority of patients with ARF resulting from underlying lung disease (11 of 13) had FL and a PEEPi,st > 4 cm H2O, whereas in patients with ARF of extrapulmonary origin, PEEPi,st was always < 4 cm H2O and only one grossly obese patient exhibited FL. Based on multiple regression analysis, in non-FL patients, PEEPi,st correlated significantly only with minute ventilation, whereas in FL patients PEEPi,st correlated significantly with peak airway pressure. CONCLUSIONS: Because all the patients exhibited PEEPi,st and 12 of 32 patients (38%) also had FL, the authors conclude that the assessment of these variables at the bedside could provide useful information concerning respiratory mechanics in mechanically ventilated patients.     

Acoustic effects of positive end-expiratory pressure on normal lung sounds in mechanically ventilated pigs

Computerized lung sounds analysis offers a new technique to monitor regional ventilation during spontaneous breathing. The purpose of the present study was to assess the acoustic behaviour of the respiratory system in healthy pigs during mechanical ventilation when a positive end-expiratory pressure (PEEP) is applied. Lung sounds were recorded during mechanical ventilation and different PEEP levels of 0, 5, 10, 15 and 20 cm H(2)O were applied. The increase in end-expiratory lung volume (EELV) related to the PEEP application was also measured and the correlation between changes in EELV (DeltaEELV) and sound amplitude (DeltaA) was examined. The amplitude of normal lung sounds was reduced by application of PEEP >or=10 cm H(2)O (P<0.05). The increase in PEEP from 0 to 20 cm H(2)O reduced the acoustic energy of lung sounds recorded at ZEEP by 0.3 dB (PEEP 5), 2 dB (PEEP 10), 5 dB (PEEP 15) and 7 dB (PEEP 20), which corresponds to 1%, 6%, 14% and 21% in acoustic attenuation, respectively. The variations in DeltaA correlated with changes in lung volume (P<0.05) and with changes in compliance of the respiratory system (P<0.05), but were not correlated with changes of the resistance of respiratory system. The frequency analysis showed a downward shifting of the spectra at frequencies between 150 and 600 Hz for PEEP levels >or=10 cm H(2)O and frequencies between 75 and 600 Hz for PEEP levels >or=15 cm H(2)O. The application of increasing levels of PEEP reduced the amplitude and changed the spectral characteristics of normal lung sounds.     

Effects of the heat-moisture exchangers on dynamic hyperinflation of mechanically ventilated COPD patients

In recent years the use of devices called Heat and Moisture Exchangers (HME) has become widespread as gas conditioners for ICU patients requiring mechanical ventilation. As an important variation of the resistive properties of the HME, related to flow and duration of use, has recently been pointed out during in vitro studies, the use of these devices in COPD patients could increase the levels of auto PEEP and dynamic hyperinflation. In this study we have compared the levels of auto PEEP and difference in functional residual capacity ( FRC) in a group of COPD patients, requiring controlled mechanical ventilation (CMV), at basal conditions and after the insertion into the circuit of three HMEs (Dar Hygrobac, Pall Ultipor, Engstrom Edith) at random: the results obtained excluded a significant increase of auto PEEP and (FRC) both with new HMEs and after 12 h of continuous use.     

Therapeutic use of intrinsic positive end-expiratory pressure

A patient with acute hypoxemic respiratory failure undergoing mechanical ventilation with PEEP developed significant obstructive airway disease. We found that intrinsic PEEP, substituted for externally applied PEEP, could maintain oxygenation. The increased inspiratory/expiratory time ratio, which resulted in the development of intrinsic PEEP, beneficially reduced airway pressures.     

Effective correction of lung hyperinflation in pneumonia using positive end-expiratory pressure

AIM: Study of PEEP effects on breathing biomechanics in patients with pneumonia. MATERIALS AND METHODS: In 37 patients with pneumonia breathing biomechanics was studied using Masterlab (Jaeger). PEEP (3-10 cm H2O) was employed during 20 min. RESULTS: Sputum expectoration, expiration and inspiration were improved, lung hyperventilation observed in pneumonia reduced after PEEP. CONCLUSION: There is early expiration obstruction of the airways in pneumonia. PEEP removes this obstruction through control of lung hyperinflation. Thus, PEEP can be applied in the treatment of pneumonia.     

Effects of breathing patterns on mechanically ventilated patients with chronic obstructive pulmonary disease and dynamic hyperinflation

Objective To examine the circulatory and respiratory effects of breathing pattern in patients with chronic obstructive pulmonary disease (COPD) and dynamic hyperinflation (DH) during controlled mechanical ventilation.Design Prospective, controlled, randomized, non-blinded study.Setting Respiratory intensive care unit of a university hospital.Patients Nine patients with acute respiratory failure and DH due to acute exacerbations of COPD.Interventions Keeping tidal volume and total breath duration (T_TOT) constant, patients were ventilated at six different values of expiratory time (T_E). T_E changes were randomly induced by alterations of constant inspiratory flow and/or end-inspiratory pause (EIP). Patients were studied at three levels of (0.93±0.08, 0.72±0.06 and 0.55±0.04 l/s, mean ±SE), with and without EIP (10% of T_TOT).Measurements and results Lung volumes, airflows, airways pressures, oxygenation indices and dead space were measured. Alveolar pressure and airway resistance (Rmin), as well as the additional resistance (R) due to viscoelastic pressure dissipation and time-constant inequalities, were estimated by rapid airway occlusion during inflation. In seven out of nine patients, right-heart catheterization was performed and hemodynamic parameters were obtained at each value of T_E. A significant decrease of intrinsic positive end-expiratory pressure (PEEPi), end-inspiratory static and mean (mPaw) airway pressures, end-expiratory lung volume above passive FRC (Vtrap), R and venous admixture and a significant increase of peak airway pressure, Rmin, stroke volume index and mixed venous PO₂ were observed when increased. At each , the addition of EIP significantly decreased iso-volume expiratory flows and and increased Vtrap and mPaw.Conclusions We conclude that in mechanically ventilated patients with COPD, the pattern of lung inflation and T_E alteration have a significant impact on respiratory system mechanics, gas exchange and hemodynamics. Addition of EIP in patients with COPD may be detrimental.     

Effect of intrinsic positive end-expiratory pressure on respiratory compliance

We evaluated the influence of intrinsic positive end-expiratory pressure (PEEPi) on the measurement of static respiratory compliance in 15 adult patients with acute respiratory failure under mechanical ventilation. Modifying the inspiratory/expiratory ratio from 1:2 to 2:1, and the respiratory frequency from 15 to 20 and 25 breath/min significantly changed compliance values. Because PEEPi can increase the work of breathing, we suggest adjusting ventilatory variables to minimize PEEPi.     

Comparative evaluation of the haemodynamic effects of continuous negative external pressure (CNEP) and positive end-expiratory pressure (PEEP) in mechanically ventilated trauma patients

Objective To compare the haemodynamic effects of identical values of continuous negative external pressure (CNEP) and positive end-expiratory pressure (PEEP) in a group of mechanically ventilated patients. Setting General ICU, Vicenza Hospital, Italy. Patients 15 consecutive patients, admitted after road accident trauma. Methods We compared the haemodynamic effects of ZEEP, 10 cmH₂O of PEEP, and 10 cmH₂O CNEP, applied in random order, in 15 head trauma patients under going controlled mechanical ventilation; 9 had associated thoracic trauma, while 6 did not have lung involvement. CNEP was obtained with a “poncho”. Results We observed a significant increase in CI during CNEP, compared with both ZEEP and PEEP 10 cmH₂O. Accordingly the oxygen delivery index significantly increased during CNEP, compared with PEEP 10 cmH₂O. Conversely, decreased with CNEP, if compared with PEEP, both in patients with and without lung damage. Conclusion CNEP can significantly increase CI in mechanically ventilated patients in patients with and without associated lung damage.     

Comparative effects of helium-oxygen and external positive end-expiratory pressure on respiratory mechanics,gas exchange,and ventilation-perfusion relationships in mechanically ventilated patients with chronic obstructive pulmonary disease

Objective To compare the effects of He/O₂ and external PEEP (PEEPe) on intrinsic PEEP (PEEPi), respiratory mechanics, gas exchange, and ventilation/perfusion (_A/) in mechanically ventilated COPD patients.Design and setting Prospective, interventional study in the intensive care unit of a university hospital.Interventions Ten intubated, sedated, paralyzed, mechanically ventilated COPD patients studied in the following conditions: (a) baseline settings made by clinician in charge, air/O₂, ZEEP; (b) He/O₂, ZEEP; (c) air/O₂, ZEEP; (d) air/O₂, PEEPe 80% of PEEPi. Measurements at each condition included _A/ by the multiple inert gas elimination technique (MIGET).Results PEEPi and trapped gas volume were comparably reduced by He/O₂ (4.2±4 vs. 7.7±4 cmH₂O and 98±82 vs. 217±124 ml, respectively) and PEEPe (4.4±1.3 vs. 7.8±3.6 cmH₂O and 120±107 vs. 216±115 ml, respectively). He/O₂ reduced inspiratory and expiratory respiratory system resistance (15.5±4.4 vs. 20.7±6.9 and 19±9 vs. 28.8±15 cmH₂O l^–1s^–1, respectively) and plateau pressure (13±4 vs. 17±6 cmH₂O). PEEPe increased airway pressures, including total PEEP, and elastance. PaO₂/FIO₂ was slightly reduced by He/O₂ (225±83 vs. 245±82) without significant _A/ change.Conclusions He/O₂ and PEEPe comparably reduced PEEPi and trapped gas volume. However, He/O₂ decreased airway resistance and intrathoracic pressures, at a small cost in arterial oxygenation. He/O₂ could offer an attractive option in COPD patients with PEEPi/dynamic hyperinflation.     

Safety of percutaneous dilational tracheostomy in patients ventilated with high positive end-expiratory pressure (PEEP)

OBJECTIVE: To assess the impact of bronchoscopically guided percutaneous dilational tracheostomy (PDT) on oxygenation in patients with severe respiratory failure ventilated with high positive end-expiratory pressure (PEEP). DESIGN: Prospective clinical study. SETTING: Anaesthesiological ICU, referral centre for acute respiratory distress syndrome (ARDS) therapy, university hospital. PATIENTS: Mechanically ventilated patients with indication for PDT. Two hundred three consecutive PDTs were performed in 198 patients on either high (>10 mbar, n=88) or low (相似文献   

Effects of manual hyperinflation and suctioning in respiratory mechanics in mechanically ventilated patients with ventilator-associated pneumonia

Ventilator-associated pneumonia results from bacterial colonisation of the aerodigestive tract or aspiration of contaminated secretions into the lower airways. As a consequence of infection of the lung parenchyma and alveolitis, accumulation of inflammatory exudates and infiltration of airway mucosa can lead to unfavourable respiratory mechanics in ventilator-associated pneumonia. Tracheal suction is often employed by nursing staff in the management of mechanically ventilated patients with ventilator-associated pneumonia but this technique has the potential to increase respiratory resistance. Manual hyperinflation is used by physiotherapists to improve lung volume and mobilise secretions and has been shown to increase lung compliance. The effect of manual hyperinflation on airway resistance has not been studied. This study aims to demonstrate an additional mechanical benefit to the respiratory system when manual hyperinflation and suction techniques are combined, by comparing the application of manual hyperinflation and suction with suction alone on static lung compliance (C(L)) and inspiratory resistance (R(AW)) in mechanically ventilated patients with ventilator-associated pneumonia. Fifteen adult patients with ventilator-associated pneumonia were recruited and acted as their own controls. Manual hyperinflation followed by suction (manual hyperinflation plus suction) and suction alone were applied consecutively, in random order, on two occasions, four hours apart. Respiratory variables, C(L) and R(AW), were measured five times and the averaged value documented. Data were recorded before, immediately after, and 30 minutes after each intervention protocol. C(L) increased by 22% and R(AW) decreased by 21%, up to 30 minutes after manual hyperinflation plus suction, but not after suction alone. This study suggests that manual hyperinflation in conjunction with suction induces beneficial changes in respiratory mechanics in mechanically ventilated patients with ventilator-associated pneumonia.     

Measurement of alveolar gas mixing in mechanically ventilated patients.

OBJECTIVE: To evaluate a computer-based, real-time, multibreath nitrogen washout technique in mechanically ventilated patients, incorporating an in-line flow measurement device to measure functional residual capacity and two indices of gas mixing, ventilatory efficiency, and alveolar mixing efficiency. SETTING: ICU, Charing Cross Hospital, London. DESIGN: Within-patient reproducibility of a multibreath nitrogen washout technique. PATIENTS: Seven intubated patients requiring mechanical ventilation. One patient completed two sets of readings. INTERVENTIONS: Patients were connected to a pneumatically driven ventilator fitted with a switching device to be operated either by an appropriate oxygen-nitrogen mixture or equivalently blended oxygen-argon mixture. An inspiratory-expiratory, two-way valve was attached to the delivery port of the ventilator, with a pneumotachograph for flow measurement and a gas sampling probe for gas concentration measurement in line with the patient's endotracheal tube. The analog signals were digitized and handled by a microcomputer. MEASUREMENTS AND MAIN RESULTS: No significant differences were found for any index, with coefficients of variation of 1.5%, 2.9%, and 2.1% for functional residual capacity, ventilatory efficiency, and alveolar mixing efficiency, respectively. CONCLUSIONS: This method gives excellent reproducibility for biological measurements in a clinical setting and shows that these measurements can readily be made on mechanically ventilated patients.