The effects of ventilation with positive end-expiratory pressure on the bronchial circulation

We studied the effects of ventilation with 10 cm H2O PEEP for 2 h in dogs with temporary unilateral pulmonary arterial occlusion (TUPAO) on bronchial blood flow to the occluded lung using the microsphere dispersion technique. We found that blood flow to the occluded left lung in dogs was 9.9 ml/min (0.122 ml X min-1 X g-1). Within 30 min following the addition of 10 cm H2O PEEP blood flow fell by 70-80% (to 2.3 ml/min) caused both by a 3-fold decrease in vascular conductance and a 25% fall in systemic blood pressure. The reduction in left bronchial blood flow persisted for at least 2 h. We conclude from these data that ventilation with PEEP in the presence of pulmonary artery occlusion has a severe, persistent adverse effect on bronchial blood flow. This reduction in bronchial blood flow is beyond what can be explained by the changes in airway pressure. The additional increase in bronchial vascular resistance may be caused by the increase in lung volume, by reflex bronchial vasoconstriction, or by release of mediators locally.     

Successful treatment of a critically ill patient with acute respiratory distress syndrome from COVID-19 using mechanical ventilation strategy with low levels of positive end-expiratory pressure: A CARE-compliant case report

Introduction:Acute respiratory distress syndrome (ARDS) secondary to COVID-19 is different from the ARDS caused by other infections. Conventional mechanical ventilation strategies using high levels of PEEP may not be beneficial and can even be harmful to patient with ARDS from COVID-19. So the ventilation strategies should be adjusted in order to improve the pulmonary ventilation function and oxygenation status, and outcomes of the patient.Patient concerns:Herein, we present a 76-year-old male patient with ARDS secondary to COVID-19. We describe our experience with mechanical ventilation strategy and the changes in respiratory mechanics in the patient during treatment.Diagnosis:The patient had tested positive for coronavirus (COVID-19) in nucleic acid test. Chest CT showed multiple ground glass shadows in both lungs.Interventions:The patient received mechanical ventilation with low tidal volume and low PEEP.Outcomes:After treatment, the patients condition, as well as oxygenation status was improved, and he tested negative for the coronavirus several times.Conclusion:This case demonstrated that the low tidal volume with low levels of PEEP ventilation strategy may be more suitable for ARDS from COVID-19.     

Instantaneous blood flow responses to positive end-expiratory pressure with spontaneous ventilation.

Variable hemodynamic responses to positive end-expiratory pressure (PEEP) with spontaneous ventilation have been reported. To clarify these responses, 15 awake patients were studied using a catheter-tip velocity transducer to record phasic aortic root blood flow continuously before, during and after PEEP (10 cm H2O) applied with a face mask. Central blood volume and effective ventricular filling pressures were measured. Phasic pulmonary artery blood flow was also simultaneously recorded in three of these patients. PEEP produced an acute aortic blood flow reduction, detected within one respiratory cycle. Stroke volume decreased 12%, and since heart rate was unchanged, cardiac output also declined (p less than 0.05). Inspiratory-to-expiratory aortic flow changes were less during PEEP. In contrast, inspiratory-to-expiratory pulmonary artery flow alterations were exaggerated due to a marked flow decline during expiration. Central blood volume and effective left ventricular filling pressure decreased 9% and 19%, respectively (p less than 0.05 in all patients). The decrease in pulmonary artery flow was associated with a decrease in central blood volume in the three patients in whom pulmonary flow was measured. PEEP promptly reduces cardiac output during spontaneous ventilation, related to a decrease in pulmonary flow in expiration.     

Ventilator-assisted patient vocalization with positive end-expiratory pressure and tracheostomy cuff leak: a brief report.

OBJECTIVE: To enable vocalization in a tracheostomized ventilator-assisted patient without compromising pulmonary status. DESIGN: Case report. SETTING: University-affiliated nonprofit hospital. PATIENT: A 62-year-old man with a medical history of metastatic lung cancer and chronic obstructive pulmonary disease received mechanical ventilation for 24 days. On the twenty-first day of ventilation the patient requested in writing the desire to vocalize with his family. INTERVENTION: Flow-generated positive end-expiratory pressure of +3 cm of water (PEEP of 3 cm H2O) was applied to the patient's airway and the tracheostomy cuff was slowly deflated to create a cuff leak. The patient was instructed to phonate the letter /a/ until the sound became audible. Lack of voice intensity necessitated PEEP titration of 1 cm H2O increments until 8 cm H2O of PEEP intensified the voice. CONCLUSION: During each session, the patient was able to vocalize clearly, without complications, as measured by the physiologic parameters: heart rate, respiratory rate, blood pressure, and oxygen saturation determined by oximetry.     

Malarial lung: report of a case from Africa successfully treated with intermittent positive pressure ventilation.

We describe the first recorded case from Africa of malarial lung, acute pulmonary insufficiency in Plasmodium falciparum malaria. The patient was successfully treated with intermittent positive pressure ventilation (IPPV). There was heavy parasitemia, preceding cerebral complications and rapid onset of pulmonary edema in the absence of fluid overload or cardiac failure. A further complication of polyuria from tubular dysfunction developed whilst the patient was being ventilated. IPPV may have an important place in the management of this rare and usually fatal complication of falciparum malaria.     

Effects of positive end-expiratory pressure ventilation and extracorporeal ultrafiltration method in patients with refractory heart failure

We studied the effects of positive end-expiratory pressure (PEEP) ventilation in ten patients with acute myocardial infarction (nine in Killip class III, one in Killip class IV; pulmonary capillary wedge pressure greater than 24 mmHg) and of extracorporeal ultrafiltration method (ECUM) in seven patients with refractory heart failure due to acute myocardial infarction and others. Application of PEEP resulted in significant increases in PaO2 and SaO2 and decrease in PaCO2. Significant reduction in mean pulmonary arterial and pulmonary capillary wedge pressures and heart rate was observed, while stroke work index increased significantly. There was a significant correlation between changes in stroke work index and PaO2 after the application of PEEP. The use of ECUM removed fluid of 1416 +/- 662 ml (680-2800 ml) with the ultrafiltration flux rate being 478 +/- 223 ml/hour. Significant decreases in mean pulmonary arterial, pulmonary capillary wedge and central venous pressures were observed, while PaO2 increased significantly. BUN and serum creatinine levels increased significantly, and total protein and serum albumin tended to increase. There was a significant correlation between fluid removed and change in PaO2 after the use of ECUM. Thus, PEEP and ECUM are beneficial for patients with refractory heart failure. The mechanism(s) are: reduction in preload due to an increased intrathoracic pressure and a decreased systemic venous return with PEEP, or due to removal of excess fluid with ECUM, and improvement of the oxygenation of the blood.     

Influence of lung injury on pulmonary wedge-left atrial pressure correlation during positive end-expiratory pressure ventilation

The correlation between pulmonary artery wedge pressure (Pw) and left atrial pressure (Pla) requires a continuous fluid column between the catheter tip and the left atrium. We hypothesized that lung injury may protect the fluid column from the collapsing effects of increased airway pressure. Correlation between Pw and Pla would then depend on catheter tip location in injured versus normal lung regions. In 7 anesthetized dogs with unilateral acid pneumonitis, we compared Pla and simultaneous Pw measurements from pulmonary artery catheters located in injured and normal lungs at different levels of positive end-expiratory pressure (PEEP). Studies were repeated in 10 dogs with normal lungs and 5 dogs with bilateral acid pneumonitis. In supine dogs with unilateral lung injury, Pw from the injured lung more accurately reflected Pla than did Pw obtained from the normal lung at PEEP levels of 7 mmHg or higher, in contrast to data from dogs with normal lungs or equally injured lungs. Discrepancies between Pw and Pla at PEEP levels of 7 and 11 mmHg from the normal lung were corrected when that lung was placed in the dependent position to increase venous pressure at the catheter tip. A good Pw-Pla correlation was not guaranteed by catheter tip location below the level of the left atrium during PEEP ventilation. We conclude that the continuity of the fluid column was protected by lung injury. Although Pw-Pla differences from the normal lung were modest at the levels of PEEP that are usually optimal for gas exchange in uneven lung injury, it is recommended that the injured lung should not be avoided during insertion of the balloon-tipped catheter.     

Esophageal pressure monitoring: a practical adjuvant to hemodynamic monitoring with positive end-expiratory pressure

With positive end-expiratory pressure (PEEP)-induced reduction in cardiac output, measurement of ventricular filling pressure assists in proper therapeutic decision-making. Because PEEP may increase pleural and juxtacardiac pressure, central venous pressure (CVP) and left atrial pressure (LAP) measurements during PEEP may not simply reflect ventricular filling, but rather reflect the sum of intracardiac and extracardiac forces. Monitoring devices placed within the central circulation use saline solution-filled lumens and transducer systems for pressure monitoring. Therefore, any device designed to estimate the extracardiac influence of PEEP on intraluminal monitoring devices would be expected to reflect such changes best when the device is also filled with saline solution. In the present study, esophageal pressure (Pes) was measured with a saline solution-filled balloon-equipped nasogastric tube to estimate the extracardiac influence of PEEP on CVP and LAP. Pes, CVP, LAP, and cardiac index (CI) were measured in 17 patients subjected to 0, 5, 10, 15, 20 cm H2O PEEP. Comparing 0 with 20 cm H2O PEEP, CVP (7 +/- 1.0 mm Hg to 13.4 +/- 1.3 mm Hg), LAP (6.3 +/- 1.1 mm Hg to 11.7 +/- 1.4 mm Hg), and Pes (6.1 +/- 1.4 mm Hg to 12.1 +/- 1.5 mm Hg) all increased significantly as CI fell (2.72 +/- 0.14 L/min/m2 to 2.20 +/- 0.15 L/min/m2).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of tidal volume and positive end-expiratory pressure on compliance during mechanical ventilation.

In 12 patients requiring therapy with mechanical ventilation for acute respiratory failure, total static compliance (Cst) increased from 29 +/- 4 ml/cm H2O at a tidal volume (TV) of 5 ml/kg to 42 +/- 7 ml/cm H2O at a TV of 15 ml/kg. Similarly, Cst increased from 42 +/- 7 ml/cm H2O to 52 +/- 8 ml/cm H2O between 0 and 6 cm H2O of positive end-expiratory pressure (PEEP). At high levels of pulmonary inflation (ie, high PEEP and large TV) compliance decreased. The changes of total respiratory compliance with TV were mainly due to changes in pulmonary compliance. With PEEP, the functional residual capacity increased, and specific compliance did not change. Two mechanisms may be responsible for the changes in compliance. First, varying TV or PEEP will alter the position of tidal ventilation on the pressure-volume curve, resulting in an increase in compliance with increasing TV and PEEP up to a point, where overdistention occurs and compliance decreases. Secondly, the function of the surface-lowering substance may be altered in acute pulmonary parenchymal disease, thus disturbing the regulation of surface tension over the range of pulmonary inflation studied.     

Effects of inverse ratio ventilation and positive end-expiratory pressure in oleic acid-induced lung injury

Continuous as well as cyclic (with each expiration) lung collapse in acute respiratory failure can be reduced by positive end-expiratory pressure (PEEP) or short expiration times, as in inverse ratio ventilation (IRV). In 20 pigs with oleic acid-induced lung edema, we compared the effects of a PEEP of 20 cm H(2)O with IRV, using an inspiratory-to-expiratory ratio of 3:1 without external PEEP. During IRV, expiration times of 0.5 or 1.0 s were obtained with respiratory rates of 30 breaths/min or 15 breaths/min, respectively. In 15 animals, ventilation-perfusion relationships were studied through the multiple inert gas elimination technique, and lung morphology was studied with computed tomography. In another five pigs, blood flow distribution was studied with perfusion scintigraphy. All three ventilatory modes had similar effects on mean arterial blood pressure, cardiac output, oxygen delivery, and mean airway pressure. PEEP reduced shunt and improved oxygenation to a greater extent than the two modes of IRV, although there was a large variation within each group. The improvement, irrespective of which ventilatory mode was superior in a particular pig, was caused by greater and more even aeration of the lung, whereas the perfusion distribution with PEEP was the same as with IRV. Thus, the strategy of stabilizing the lungs through short expiration times, as in IRV, did not offer any advantages in our lung injury model.     

Criteria for selective positive end-expiratory pressure and independent synchronized ventilation of each lung.

Respiratory failure of different origins often requires therapy with mechanical ventilation and positive end-expiratory pressure (PEEP). These supports are occasionally inadequate if the damage to one lung is significantly more pronounced than that to the other lung. Technical means exist to ventilate each lung independently or to provide a different PEEP to each lung. The findings from nine patients in whom one of these techniques was applied are presented, and advantages and disadvantages are discussed.     

Flow resistance of exhalation valves and positive end-expiratory pressure devices used in mechanical ventilation

We studied the flow-impeding characteristics of the exhalation valves and PEEP attachments commonly used in mechanical ventilation. To characterize these devices, the pressure difference across each mechanism was measured at a series of constant flows (5 to 160 L/min), and resistance-related energy dissipation was measured using mechanical models of passive and active exhalation. At ambient end-expiratory pressure, an inflatable diaphragm (mushroom) design commonly used to valve exhalation presented resistance comparable to that of an endotracheal tube with an internal diameter of 5 mm. The valve's energy dissipation increased further as PEEP was applied. By comparison, the servo-actuated scissor valve we tested presented less resistance during the passive deflation experiment but impeded the early phase of active exhalation. Spring-loaded PEEP attachments were prohibitively resistive in comparison with alternative methods using an underwater tube, a water column, a weighted spirometer, or an inflatable diaphragm to raise end-expiratory pressure. We conclude that the exhalation valves and PEEP attachments currently available for clinical use present significant impedance to air flow. Such resistance within the exhalation pathway may be clinically important for patients supported by mechanical ventilation during the hyperpneic or weaning phases of their illness.     

Modifications of plasma concentrations of hormonal and tissue factors during mechanical ventilation with positive end-expiratory pressure.

AIM: The aim of this study is to analyse if the decrease of cardiac performance due to positive end-expiratory pressure (PEEP) application, within low values applied in clinical practice (5 cm H(2)O) is able to trigger a response of the main endogenous factors which control and maintain the mean arterial pressure (MAP). METHODS: This study was applied to 18 patients, admitted to the Intensive Care Unit (ICU) of the University Hospital of Modena, who underwent oro-tracheal intubation and mechanical ventilation. On admission, patients did not suffer from cardiac or lung disease. This study analyses plasma concentrations of epinephrine, norepinephrine, ET-1, NO metabolites, renin, aldosterone at 4 different times: before PEEP application, 60 minutes after the beginning of mechanical ventilation with PEEP, and respectively 30 and 60 minutes after withdrawal of PEEP. At the same time, MAP values and heart rate (HR) have been observed. RESULTS: Results show an increase of epinephrine and norepinephrine after PEEP application and a decrease to basal values at PEEP withdrawal. All variations are statistically significant. After PEEP introduction, ET-1 showed an increased concentration, although it was not statistically significant, while a significant decreasing trend was observed after PEEP withdrawal. A significant increase of NO metabolite values has been observed together with the increase of ET-1, followed by a decrease to basal values after the withdrawal of PEEP. Concentrations of renin increased when PEEP was applied even though they were not significant and decreased significantly when PEEP was withdrawn. A similar trend was revealed by aldosterone even though it underwent constant significant variations. CONCLUSION: The administration of PEEP produces an effective response of endogenous substances whose function is to maintain a proper tissue perfusion.     

Expiratory flow limitation and intrinsic positive end-expiratory pressure at zero positive end-expiratory pressure in patients with adult respiratory distress syndrome

It has been suggested that in patients with adult respiratory distress syndrome (ARDS), intrinsic positive end-expiratory pressure (PEEPi) is generated by a disproportionate increase in expiratory flow resistance. Using the negative expiratory pressure (NEP) technique, we assessed whether expiratory flow limitation (EFL) and PEEPi were present at zero PEEP in 10 semirecumbent, mechanically ventilated ARDS patients. Because bronchodilators may decrease airway resistance, we also investigated the effect of nebulized salbutamol on EFL, PEEPi, and respiratory mechanics in these patients, and in seven patients we measured the latter variables in the supine position as well. In the semirecumbent position, eight of the 10 ARDS patients exhibited tidal EFL, ranging from 5 to 37% of the control tidal volume (VT), whereas PEEPi was present in all 10 subjects, ranging from 0.4 cm H(2)O to 7.7 cm H(2)O. The onset of EFL was heralded by a distinct inflection point on the expiratory flow-volume curve, which probably reflected small-airway closure. Administration of salbutamol had no statistically significant effect on PEEPi, EFL (as %VT), or respiratory mechanics. EFL (%VT) and PEEPi were significantly higher in the supine position than in the semirecumbent position, whereas the other respiratory variables did not change. Our results suggest that in the absence of externally applied PEEP, most ARDS patients exhibit EFL associated with small-airway closure and a concomitant PEEPi.     

呼气末正压的临床应用

呼气末正压是指在机械通气时,人为的使呼气末气道及肺泡内压力高于大气压.临床常用于治疗急性呼吸窘迫综合征、慢性阻塞性肺疾病、急性左心衰竭等,通过设置不同水平的呼气末正压,减轻肺渗出,改善氧合;改善患者与呼吸机的协调性以降低呼吸功;固定胸壁等.但针对不同疾病呼气末正压的作用机制有所不同,本文将逐一介绍.