Positive And Expiratory Pressure Research Articles

Biomarkers as predictors of mortality in critically ill obese patients with COVID-19 at high altitude

BackgroundObesity is a common chronic comorbidity of patients with COVID-19, that has been associated with disease severity and mortality. COVID-19 at high altitude seems to be associated with increased rate of ICU discharge and hospital survival than at sea-level, despite higher immune levels and inflammation. The primary aim of this study was to investigate the survival rate of critically ill obese patients with COVID-19 at altitude in comparison with overweight and normal patients. Secondary aims were to assess the predictive factors for mortality, characteristics of mechanical ventilation setting, extubation rates, and analytical parameters.MethodsThis is a retrospective cohort study in critically ill patients with COVID-19 admitted to a hospital in Quito-Ecuador (2,850 m) from Apr 1, 2020, to Nov 1, 2021. Patients were cathegorized as normal weight, overweight, and obese, according to body mass index [BMI]).ResultsIn the final analysis 340 patients were included, of whom 154 (45%) were obese, of these 35 (22.7%) were hypertensive and 25 (16.2%) were diabetic. Mortality in obese patients (31%) was lower than in the normal weight (48%) and overweight (40%) groups, but not statistically significant (p = 0.076). At multivariable analysis, in the overall population, older age (> 50 years) was independent risk factor for mortality (B = 0.93, Wald = 14.94, OR = 2.54 95%CI = 1.58–4.07, p < 0.001). Ferritin and the neutrophil/lymphocyte ratio were independent predictors of mortality in obese patients. Overweight and obese patients required more positive and-expiratory pressure compared to normal-weight patients. In obese patients, plateau pressure and mechanical power were significantly higher, whereas extubation failure was lower as compared to overweight and normal weight.ConclusionsThis preliminary study suggests that BMI was not associated with mortality in critically ill patients at high altitude. Age was associated with an increase in mortality independent of the BMI. Biomarkers such as ferritin and neutrophils/lymphocytes ratio were independent predictors of mortality in obese patients with COVID-19 at high altitude.

Effect of early mechanical ventilation with continuous vacuum suction in treatment of serious pulmonary contusion

Objective To summarize the value of early mechanical ventilation plus continuous vacuum suction in treatment of serious pulmonary contusion. Methods Forty-eight cases of severe pulmonary contusion were assigned to mechanical ventilation plus continuous vacuum suction (observation group, n=20) and mechanical ventilation plus discontinuous vacuum suction (control group, n=28) according to the random number table. Modes of mechanical ventilation were synchronized intermittent mandatory ventilation (SIMV), pressure support ventilation (PSV), and positive and expiratory pressure (PEEP). Changes in blood gas analysis, mechanical ventilation time, and associated complications were compared between groups. Results At ventilation time of 6 and 24 hours, PaO2 in observation group was (100.36±5.90)mmHg and (105.34±7.40)mmHg respectively, with significant differences from (75.36±8.95)mmHg and (76.36±8.35)mmHg in control group (P 0.05). Conclusion Early mechanical ventilation with sustained vacuum suction is effective to keep airway clear, improve oxygenation index, decrease PEEP level, and control the duration of mechanical ventilation, but may not lower the risks of ventilator-associated pneumonia and pulmonary atelectasis. Key words: Lung injury; Ventilators, negative-pressure; Treatment outcome

Early noncardiogenic pulmonary edema and the use of PEEP and prone ventilation after emergency liver transplantation

Noncardiogenic pulmonary edema in liver transplant recipients is usually secondary to TRALI (transfusion related acute lung injury) or liver ischemic-reperfusion injury. If persistent, the resultant hypoxemia is associated with increased ventilator days, prolonged length of stay (intensive care and hospital) and increased 28-day mortality. Ventilation strategies for the management of hypoxemia in acute lung injury include moderate to high levels of PEEP (positive and expiratory pressure) and prone ventilation (PV). Such strategies have theoretical adverse effects on graft perfusion. Evidence does however exist to demonstrate that maintenance of cardiac output and correct positioning of the prone patient to allow abdominal excursion can negate the deleterious effects of PEEP and PV. A liver transplant recipient became profoundly hypoxemic on our intensive care unit following the onset of noncardiogenic pulmonary edema. A risk-benefit assessment performed at the time deemed that the potential adverse effects of PEEP and PV were outweighed by the life-threatening nature of hypoxemia. The patient's condition improved following prone positioning and application of PEEP (10-15 cm H(2)O). We conclude that such ventilation strategies are appropriate in hypoxemic liver transplant recipients if an appropriate risk-benefit assessment is performed.

Positive end-expiratory pressure increases pulmonary venous vascular resistance in patients after coronary artery surgery.

To investigate the effect of positive and-expiratory pressure (PEEP) on the longitudinal distribution of pulmonary vascular resistance in patients immediately after coronary artery bypass grafting. Prospective, intervention study. Postcardiac surgery intensive care unit in a teaching institution. Twenty patients after elective coronary artery bypass grafting. The effect of PEEP on pulmonary circulation, at four different levels (0, 5, 10, and 15 cm H2O), was analyzed in 20 patients. Mean pulmonary arterial pressure, left atrial pressure, pulmonary artery occlusion pressure, and pulmonary capillary pressure were measured at each PEEP level. A model consisting of two resistances in series was used to analyze the effect of PEEP on the pulmonary circulation. The pulmonary vascular resistance for each area (arterial and venous) of the circulation was calculated. Pulmonary vascular resistance increased from 216 +/- 70 dyne.sec/cm5 at a PEEP of 0 cm H2O to 308 +/- 125 dyne.sec/cm5 at a PEEP of 15 cm H2O (p < .001). This increase, however, resulted solely from an increase in the resistance of the venous part of the pulmonary circulation from 66 +/- 29 to 134 +/- 69 dyne.sec/cm5 (p < .001), without any change in pulmonary arterial resistance. PEEP increases pulmonary vascular resistance solely by increasing pulmonary venous resistance. When applying PEEP, changes in pulmonary vascular resistance may impede the resorption of pulmonary edema fluid.

Positive end expiratory pressure reduces intracranial compliance in the rabbit.

Acute respiratory distress syndrome is commonly encountered in head-injured patients. Positive and expiratory pressure (PEEP) is useful in improving oxygenation. However, PEEP, by increasing intrathoracic pressure, decreases venous return, mean arterial pressure, and cardiac output and increases jugular vein pressure. There is conflicting evidence in the literature as to the potential effect of PEEP on intracranial pressure (ICP). The present study was undertaken to examine the effect of PEEP on ICP and intracranial compliance. Twelve male rabbits weighing 3.5-4.5 kg were used. The following parameters were monitored: arterial blood pressure, ICP (intraparenchymal Camino device), PaCO2, and PaO2. A space-occupying lesion was produced by inflation of a double lumen pediatric Swan-Ganz catheter placed over the right parietal dura. The amount of fluid required to reach the point of exponential increase of ICP was recorded at PEEP of 0 and 10 cm H2O. The mean volume needed to reach the deflection point of ICP was significantly lower when PEEP was 10 cm H2O compared to the value when PEEP was 0 cm H2O (685 +/- 48 vs. 883.3 +/- 46 microliters, respectively; p < 0.01). The results of the present study indicated that PEEP of 10 cm H2O decreases intracranial compensatory reserves for maintaining ICP at normal levels in the presence of an expanding intracranial mass.

Intensive care management of varicella pneumonia

To determine the clinical features, treatment and outcome of severe varicella pneumonia with hypoxic respiratory failure requiring intensive care management, a prospective survey of consecutive cases was undertaken. Fifteen consecutive adult cases of varicella pneumonia with respiratory failure admitted to a 10-bed respiratory intensive care unit over a period of 10 y from 1984–1993 were studied. All patients were given acyclovir immediately on admission. The level of ventilatory support needed was determined by the severity of gas exchange abnormality, and varied from face mask oxygen (three patients), through continuous positive airway pressure (CPAP) by face mask (eight patients), to continuous positive pressure ventilation (CPPV) (four patients). The majority of patients were young females, only one of whom was pregnant. All patients had been in close contact with a known case of chickenpox. All patients responded well to acyclovir and ventilatory support with improved oxygenation. Monitoring with pulse oximetry was important to detect episodes of desaturation on inadvertent discontinuation of positive and expiratory pressure (PEEP). Two patients were admitted with bacterial superinfection, and one patient, who had required intubation and CPPV, developed nosocomial respiratory tract infection. There were no deaths. This experience suggests that intensive care admission, with the early administration of intravenous acyclovir and recognition of the severity of the hypoxaemia resulting from varicella pneumonia (which can be reversed with PEEP), should reduce the mortality of severe varicella pneumonia in adults.

Comparison of Pulmonary Vascular Pressures Based on Blood Volume and Ventilator Status

Pulmonary artery pressures (PAP), hemodynamic and oxygen transport variables, arterial blood gases (ABG), and blood volume (BV) were measured in 30 hypervolemic, normovolemic, and hypovolemic critically ill adults receiving physiologic levels of positive and expiratory pressure (PEEP). The measurements were taken while patients remained on the ventilator and during brief discontinuance of mechanical ventilation. The purposes of the study were to determine whether BV status could affect PAP and to quantify the effect of temporary discontinuance of ventilation on ABG. No differences were seen in PAP, mean arterial pressure, cardiac index, oxygen delivery, oxygen extraction, or oxygen consumption regardless of ventilator or BV status. Arterial oxygen tension dropped significantly, p less than .001, in less than 1 minute off ventilation and the decrease persisted for 1 hour after mechanical ventilation was resumed. These results suggest that recording PAP off the ventilator should be abandoned, as this technique contributes little to increased validity of PAP and may result in persistent hypoxemia.

Controversial Aspects of PEEP Ventilation in Emergency Medicine

Controlled mechanical ventilation using positive and expiratory pressure (PEEP) is a well-established therapeutic measure in intensive care. Its early application has been shown to markedly decrease morbidity and mortality, especially in polytraumatized patients with an acute respiratory distresss syndrome. It therefore seems reasonable to use positive end expiratory pressure as early as possible in the clinical treatment of emergency patients before extensive pulmonary changes have had time to develop completely.

1690 DIRECT MEASUREMENT OF LOCAL CEREBRAL BLOOD FLOW (ICBF) IN THE GREYHOUND: Possible Relationship to Intraventricular Hemorrhage in the Newborn

The pathogenesis of neonatal periventricular-intraventricular hemorrhage (PVH-IVH) remains unclear, although an aberration in cerebral hemodynamics imposed upon prematurity appears fundamental. Microthermistors were implanted in the cerebral cortex of 17 adult greyhounds. An analog-digital hybrid system developed using the IBM PC computer to provide simultaneous continuous 1CBF data at four discrete sites. Variables of peak inspiratory pressure (PIP), positive and expiratory pressure (PEEP), total minute ventilation and pulse pressure were investigated through a 1 mm burr hole as well as 2 cm craniotomy to compare cranial compliance effects. Positive pressure ventilation induces a fluctuating pattern of 1CBF with blood flow lowest during peak inspiration. A large craniotomy defect (simulating the open fontanel), high PIP or high PEEP accentuate this effect. The use of a small burr hole to simulate a closed fontanel results in the obliteration of the fluctuating pattern and the enhancement of beat-to-beat changes in 1CBF that were directly proportional to pulse pressure. These data suggest that hemodynamic changes produce fluctuations in local tissue perfusion which are dependent upon cranial compliance. The exact relation of such changes to the pathogenesis of PVH-IVH requires continuous 1CBF measurement in the subependymal zone in the human newborn or an animal model.

Cerebral and Cardiopulmonary Responses to High-Frequency Jet Ventilation and Conventional Mechanical Ventilation in a Model of Brain and Lung Injury

The cardiopulmonary and intracranial effects of high-frequency jet ventilation (HFJV) were evaluated in four groups of 10 mongrel dogs and compared to conventional mechanical ventilation with and without positive and expiratory pressure (PEEP). Each group of animals was studied with various combinations of normal and abnormal brain and lung function. Experimental brain injury (abnormal cerebral elastance) was produced by infusion of saline into the subarachnoid space to increase intracranial pressure (ICP), while lung injury resulted from intratracheal instillation of 0.1N HCl. Animals responded similarly to HFJV and conventional ventilation except for those with abnormal lungs, in whom peak airway pressures were significantly lower with HFJV (P less than 0.05). The application of PEEP (10 and 20 cm H2O) produced significant increases in mean airway pressure compared to HFJV (P less than 0.05). Animals with abnormal lungs demonstrated significantly improved mean PaO2 (194 vs 104 mm Hg) and shunt fraction (0.20 vs 0.45) with 20 cm H2O PEEP compared to HFJV. In all dogs subjected to 20 cm H2O PEEP, cardiac index and mean arterial pressure were decreased significantly (P less than 0.05) below values with HFJV. ICP responses did not vary significantly with the different modes of ventilation and were not influenced by the status of lung or brain function. However, significant reductions in cerebral perfusion pressure were noted with 20 cm H2O PEEP compared to HFJV. We conclude that unless high levels of PEEP (15-20 cm H2O) are required for adequate oxygenation, the cardiovascular and cerebral effects of HFJV do not differ significantly from those of conventional mechanical ventilation.

Cardiovascular effects of ventilation with positive expiratory airway pressure.

The broad clinical application of positive and expiratory pressure (PEEP) in the treatment of a variety of respiratory disorders has led to the observation that positive airway pressure can result in cardiac dysfunction. Recent attempts to integrate and extend the results of past research have led to diverse explanations of the overall cardiopulmonary effects of PEEP. This review summarizes previous work in the field and attempts to explain the basis of the divergent conclusions of previous investigators. Data are presented from several experimental models, as well as studies in postoperative patients to formulate an overall analysis of the influence of airway pressure on the central circulation. It appears that the effects of PEEP are primarily mechanical and are mediated through a combination of right ventricular preload limitation and outflow obstruction. Both effects are additive in limiting left ventricular preload and can be ameliorated by volume loading in the absence of significant right ventricular or pulmonary vascular disease. Neural, humoral and ventricular interactive forces appear to be insignificant under most circumstances. The clinical implications of these advances in the current understanding of PEEP are reviewed.

Radiographic Findings and Effect of PEEP in Dogs with Oleic Acid Induced ARDS

The sensitivity of standard radiography for the study of oleic acid (OA) induced canine acute respiratory distress syndrome (ARDS) and the effect of positive and expiratory pressure (PEEP) on the radiographic appearance was investigated. Comparison was made with similar study done with computerized gamma camera following intravenous injection of 99mTC-human serum albumin (HSA) in canine oleic acid induced pulmonary capillary protein leak and pulmonary edema. Three dogs were studied at each of the following doses of OA: 0.06, 0.10, and 0.20 ml/kg. Ten cm PEEP was applied for 1/2 hour, 1/2 hours after OA. A-P chest radiographs were obtained at 1/2 hour intervals and 5 min. after PEEP was applied and discontinued. Standard radiography was able to detect OA induced ARDS within 1/2 hour in each animal given 0.2 ml/kg OA. In only 1 of 3 dogs given 0.05 ml/kg could any changes be detected over the 90 min. of study. Immediately following the application of PEEP, a marked reduction in the apparent severity of ARDS was seen in each animal which was reversed shortly after PEEP was released. Blood gasses did not deteriorate until a dose of 1.10 ml/kg was reached. Gamma scintigraphy was able to detect a marked protein leakage at 0.05 ml/kg OA. In conclusion, standard radiography can detect ARDS but is less sensitive than gamma scintigraphy and can be markedly altered with PEEP.

The relationship between peak inspiratory pressure and positive end expiratory pressure on the volume of air lost through a bronchopleural fistula

A bronchopleural fistula (BPF) may complicate the management of patients with major pulmonary disease or thoracic surgery. Neonates with idiopathic respiratory distress syndrome and requiring ventilation are especially susceptible to pulmonary barotrauma, which may result in a BPF. Morbidity and mortality are consistently high. In ventilating patients with BPF, the effects of peak inspiratory pressure (PIP) and positive and expiratory pressure (PEEP) on air leak have not been documented. These relationships were studied in rabbits prepared by thoracotomy and creation of a standardized BPF. Randomized trials of various levels of PIP and PEEP were applied, and the percent of inspired tidal volume lost through the BPF calculated. The percent of inspired volume lost does not increase significantly from 10 to 30 cm H2O PIP (p greater than 0.05). Percent leak does increase significantly when increasing PEEP frm 0 to 16 cm H2O (p less than 0.001). Any PEEP greater than 6 cm H2O results in more air loss through the BPF than any level of PIP (p less than 0.01). Linear regressions through a common origin were calculated to illustrate the relationship of PIP versus leak and PEEP versus leak. The slopes of these lines (0.572 and 3.97, respectively) are significantly different (p less than 0.001). When using equal increments of PIP and PEEP, PEEP will have over a sixfold greater effect on air leak than doses PIP. These data suggests that PIP should be increased preferentially when ventilating patients with BPF in order to minimize air leak. PEEP less than 6 cm H2O can be used without any significant increase in the volume of air lost.

The Association of Lung Distention, PEEP and Biventricular Failure

Although positive and expiratory pressure (PEEP) is known to depress the cardiac output, the mechanism remains debated. Two series of experiments were designed to explore this mechanism. In the first study, the application of 15 cm H(2)O of PEEP to nine anesthetized, ventilated dogs led to a reduction of cardiac index from (mean +/- one standard error of the mean) 2.71 L/min .m (2) +/- 0.35 to 2.19 L/min m(2) +/- 0.22 (p < .05) and a drop in mean arterial pressure (MAP) from 117 mm Hg +/- 8 to 91 mm Hg +/- 11 (p < .01). The mean net (vascular minus pleural pressure) pulmonary artery pressure (MPAP) rose from 15.3 mm Hg +/- 1.2 to 20.6 mm Hg +/- 1.8 (p < .02). The mean net central venous pressure (CVP) rose from 5.2 mm Hg +/- 0.9 to 8.4 mm Hg +/- 0.9 (p < .05) and the net pulmonary arterial wedge pressure (PAWP) rose from 6.7 mm Hg +/- 0.7 to 9.5 mm Hg +/- 0.9 (p < .01). There was a nonsignificant rise in the mean net left atrial pressure (LAP). As PEEP was raised in increments from 0 to 20 cm H(2)O, both LAP and PAWP increased. The rise in PAWP was always greater than the increase in LAP. The difference between PAWP and LAP was strongly correlated with the increase in MPAP (r = 0.98). This relationship was useful in correcting the PAWP during PEEP. The problem of cardiac depression was evaluated in a second series of eight dogs. These animals underwent complete chest wall excision to eliminate any possible direct effects of increased pleural pressure on the heart and great vessels. The absence of the chest wall permitted hyperexpansion of the lungs, particularly with positive end expiratory pressure. At 15 cm H(2)O of PEEP, the mean cardiac index fell in these animals from 2.36 L/min. m(2) +/- 0.26 to 1.47 L/min.m(2) +/- 0.18 (p < .01) and the MAP fell from 105 mm Hg +/- 16.2 to 68 mm Hg +/- 4.8 (p < .001). The CVP rose from a mean of 5.5 mm Hg +/- 0.4 to 8.3 mm Hg +/- 0.6 (p < .01) and the LAP rose from 6.3 mm Hg +/- 0.8 to 8.0 mm Hg +/- 1.1 (p < .05). The MPAP rose from 18.0 mm Hg +/- 0.6 to 23.3 mm Hg +/- 1.6 (p < .01). Comparison of Group I and II showed a significantly greater depression of the cardiac output and MAP in the open-chested animals. At the same time LAP was significantly higher. These data strongly suggest that PEEP and particularly pulmonary hyperinflation induce biventricular failure.

The effects of PEEP on arterial oxygenation

The effect of positive and expiratory pressure (PEEP) on arterial oxygenation depends on many factors. Two of the most important are the "quality" and the "quantity" of the physiological shunt. The "quality" depends on the mixed venous oxygen tension, and the "quantity" on the shunt fraction. Each of these factors may rise or fall with PEEP, depending on the pulmonary and circulatory state of the patient. Their ultimate balance influences the change in arterial oxygen tension.

REDUCED INSPIRATORY EFFORT DURING INTERMITTENT MANDATORY VENTILATION WITH PEEP

The use of intermittent mandatory ventilation (IMV) and positive and expiratory pressure (PEEP) may demand the patient mount an inspiratory pressure equivalent to the pressure level of the PEEP for spontaneous breathing. During respiratory failure, ineffective inspiratory muscles may be unable to consistently meet such demands, especially if high levels of PEEP are used. A technique which reduces the required inspiratory effort was devised for use in patients being treated with IMV and PEEP. Using this technique, isovolume inspiratory time was dramatically reduced and less inspiratory effort was required. This maneuver may assist spontaneous breathing in patients with respiratory failure on high levels of PEEP.

PEEP: radiographic features and associated complications

Positive and expiratory pressure (PEEP) has been used for several years in the treatment of acute respiratory failure. Dramatic improvement in the chest radiograph may occur with institution of PEEP; the degree of change parallels the levels of positive and expiratory pressure used. Conversely, weaning from mechanical ventilation may be associated with deterioration in the radiographic picture despite improvement in arterial blood gases and lung compliance. Serial chest films of representative patients with adult respiratory distress syndrome are reviewed and changes in the radiographic pattern are correlated with the amount of PEEP. The efficacy of PEEP in reducing intrapulmonary shunting and improving arterial oxygenation is related to increasing functional residual capacity, with improvement of diffuse atelectasis and associated shift of pulmonary water from the alveoli to the interstitial space and pulmonary capillaries. The changing radiologic manifestations reflect these physiologic phenomena. Pulmonary barotrauma is a frequent complication of PEEP therapy. Pneumothorax, pneumomediastinum, and interstitial emphysema may lead to rapid deterioration of a patient maintained on mechanical ventilation with an already compromised respiratory status.