Selective Positive End-expiratory Pressure Research Articles

Improving the survival and growth of African catfish (Clarias gariepinus) fingerlings by using Nile tilapi

General anaesthesia and many types of acute respiratory failure are accompanied by a decrease in functional residual capacity (FRC). This reduction promotes closure of dependent airways and alveolar collapse, thus impeding ventilation of these regions. Perfusion, on the other hand, is forced towards dependent regions by lowered pulmonary vascular pressure and increased alveolar pressure. Ventilation-perfusion (V/Q) inequality develops, impairing gas exchange and arterial oxygenation. Application of general positive end-expiratory pressure (PEEP) increases FRC and may improve gas exchange but cannot restore V/Q to normal. Differential ventilation, with equal distribution of ventilation between the lungs, and the application of PEEP solely to the dependent lung (selective PEEP) with the patient in the lateral position, improve V/Q matching and gas exchange with less impedance of cardiac output and less danger of barotrauma. This ventilation technique has proved successful in short-term experiments and in a small number of patients treated over several days.

Unilateral lung injury.

Mechanical ventilation is a supportive lifesaving therapy that can potentially cause lung injury if periodic alveolar overdistension, or cyclic collapse, and reopening occur. The use of a low tidal volume with moderate to high positive end-expiratory pressure improves the survival of patients with acute lung injury and acute respiratory distress syndrome. Positioning the patient with the "good lung down" and using differential ventilation with selective positive end-expiratory pressure are the two currently accepted ventilatory strategies to be applied in patients with severe unilateral lung injury. However, both have serious limitations in clinical practice. Lung injury may be rather inhomogeneous-confined to one lung or preferentially distributed toward the dependent lung areas. In unilateral lung injury, ventilatory strategies that allow recruitment of injured lung and that avoid overdistension of uninjured lung parenchyma should be applied. Experimental studies have shown that the use of selective tracheal gas insufflation and partial liquid ventilation facilitates low tidal volume with appropriate gas exchange while reducing cyclic lung stretch and shear stresses. Further studies are needed to determine future applications of these therapies in humans.

Selective positive end–expiratory pressure and right ventricular function in dogs

Differential ventilation with selective positive end-expiratory pressure (PEEP) has been shown to reduce cardiac output less than general PEEP. In previous studies we have demonstrated that during selective PEEP left ventricular preload is better maintained than during general PEEP. The present study was designed to determine whether the different haemodynamic responses to selective and general PEEP also might be due to different effects on RV preload. The study was performed on nine acutely instrumented dogs, in which extraventricular pressure was measured by pericardial balloon transducers. Measures of RV preload were obtained by the use of ultrasonic segment length transducers as well as end-diastolic transmural pressure (RVEDP). The study showed reductions in RVEDP during general and selective right (R) PEEP, accompanied by moderate reductions in RV inflow tract segment lengths. These changes were most marked with general PEEP. Selective LPEEP did not change RV preload significantly. Therefore, better maintained cardiac output with selective PEEP than with general PEEP is partly due to less impairment of right ventricular filling.

Selective positive end-expiratory pressure and intracardiac dimensions in dogs.

Effects of differential ventilation with general vs. selective right (R) and left (L) positive end-expiratory pressure (PEEP) on left (LV) and right ventricular (RV) end-diastolic dimensions were compared in seven pentobarbital-anesthetized dogs. All three modes of PEEP reduced LV cross-sectional area: general PEEP more than RPEEP and RPEEP more than LPEEP. General PEEP and, to a lesser degree, RPEEP decreased both the LV anteroposterior diameter and LV septum-free wall diameter, whereas LPEEP reduced the LV septum-free wall diameter only. Cardiac output was unaffected by LPEEP, whereas general PEEP (20 cmH2O) reduced cardiac output by 48%, and RPEEP (20 cmH2O) reduced it by 23%. RV septum-free wall diameter was not changed by any mode of PEEP. In conclusion, cardiac output was better maintained with selective PEEP than with general PEEP because LV filling was less impeded with selective PEEP. During LPEEP LV assumed a different configuration than during RPEEP and general PEEP, probably reflecting a different pattern of heart-lung interaction.

Haemodynamic effects of selective positive end-expiratory pressure after unilateral pulmonary hydrochloric acid-aspiration in dogs

We investigated 1) the effects of HCl-mediated acute left lung injury on regional juxtacardiac pressures and 2) the haemodynamic effects of different modes of ventilation before and after induction of left lung injury. The study was done in 7 mechanically ventilated, anaesthetized dogs. Juxtacardiac pressures and haemodynamic variables were recorded during 1) differential ventilation (DV) with zero positive end-expiratory pressure (PEEP = 0) and 2) DV with general (G) PEEP and selective right (R) and left (L) lung PEEP. Left lung injury increased left, but not right pleural pressure of pericardial pressure. Pulmonary vascular resistance (PVR) and pulmonary artery pressure (PAP) were increased moderately. Cardiac output (CO) did not change. GPEEP reduced LV filling and cardiac output markedly and by approximately the same degree before and after lung injury. The haemodynamic effects of LPEEP were minor before as well as after the induction of lung injury. RPEEP, which had only moderate haemodynamic effects during control, caused a marked reduction in cardiac function after the induction of left lung injury. The transmission of airway pressure to the pleura was reduced in the diseased lung. These results suggest that serious haemodynamic side effects may be avoided by applying PEEP selectively to the diseased lung.

A comparison of changes in esophageal pressure and regional juxtacardiac pressures

The relationship between esophageal pressure and juxtacardiac pressures was studied during positive end-expiratory pressure (PEEP) ventilation applied to both lungs or selectively to one lung. The experiments were performed in eight anesthetized dogs with balloon catheters in the esophagus and in the left and right pericardial and overlying pleural cavities and with an open-ended liquid-filled catheter in the pleural cavity. Bilateral PEEP (10, 20, and 30 cmH2O) caused progressive and similar increments in left and right pleural pressure. Selective PEEP, however, increased ipsilateral pleural balloon pressure more than contralateral pressure. The increase in ipsilateral pleural balloon pressure markedly exceeded the increase in esophageal pressure. There was a small increase in pleural open-ended catheter pressure that approximated the increase in esophageal pressure. During selective PEEP, pericardial balloon pressure remained uniform because of a decrease in ipsilateral pericardial transmural pressure. In conclusion, selective PEEP caused nonuniform increments in regional pleural balloon pressure. Left and right pericardial balloon pressure, however, increased uniformly with selective PEEP because of reduced ipsilateral pericardial transmural pressure. The esophageal balloon did not reflect the marked regional increments in pleural balloon pressure with selective PEEP and consistently underestimated the changes in pleural balloon pressure with general PEEP.

Ventilation‐perfusion relationships and atelectasis formation in the supine and lateral positions during conventional mechanical and differential ventilation

Patients without respiratory symptoms were studied awake and during general anesthesia with mechanical ventilation prior to elective surgery. Ventilation-perfusion (VA/Q) relationships, gas exchange and atelectasis formation were studied during five different conditions: 1) supine, awake; 2) supine during anesthesia with conventional mechanical ventilation (CV); 3) in the left lateral position during CV; 4) as 3) but with 10 cm of positive end-expiratory pressure (PEEP) and 5) as 3) but using differential ventilation with selective PEEP (DV + SPEEP) to the dependent lung. Atelectatic areas and increases of shunt blood flow and blood flow to regions with low VA/Q ratios appeared after induction of anesthesia and CV. With the patients in the lateral position, further VA/Q mismatch with a fall in PaO2 and increased dead space ventilation was observed. Atelectatic lung areas were still present, although the total atelectatic area was slightly decreased. Some of the effects caused by the lateral position could be counteracted by adding PEEP. Perfusion of regions with low VA/Q ratios and venous admixture were then diminished, while PaO2 was slightly increased; shunt blood flow and dead space ventilation were essentially unchanged. During CV + PEEP, there was a decrease in cardiac output, compared to CV in the lateral position. DV + SPEEP was more effective than CV + PEEP in decreasing shunt flow and increasing PaO2 in the lateral position; in addition to this, cardiac output was not affected.

Selective positive end-expiratory pressure and cardiac function in dogs

Effects of general (G) versus selective (S) right (R) and left (L) positive end-expiratory pressure (PEEP) were compared during differential lung ventilation in 11 anaesthetized dogs in the supine position. GPEEP 20 cmH2O decreased cardiac output (1 min-1) from 2.9 +/- 0.2 (mean +/- SE) to 1.7 +/- 0.5 (p less than 0.05), RPEEP from 2.8 +/- 0.2 to 2.2 +/- 0.2 (p less than 0.05) while LPEEP caused no significant change in cardiac output. GPEEP increased pleural pressure more than SPEEP. Pleural pressure was asymmetric during SPEEP. Both SPEEP and GPEEP increased pericardial pressure uniformly, but the increase was less marked with SPEEP. During GPEEP 20 cmH2O transmural left ventricular end-diastolic pressure (LVEDP) decreased markedly. SPEEP caused less marked reductions in transmural LVEDP. Qualitatively similar, but less marked changes were observed with PEEP 10 cmH2O. In conclusion, cardiac output decreased less with selective PEEP than with general PEEP. This was explained by less increase in pleural and pericardial pressure, and accordingly less decrease in LV transmural filling pressure.

The influence of body position and differential ventilation on lung dimensions and atelectasis formation in anaesthetized man

The effects of body position and anaesthesia with mechanical ventilation on thoracic dimensions and atelectasis formation were studied by means of computerized tomography in 14 patients. Induction of anaesthesia in the supine position reduced the cross-sectional area for both lungs and caused atelectasis formation in dependent lung regions in 4/5 patients. Conventional ventilation with positive end-expiratory pressure (PEEP) increased thoracic dimensions and reduced, but did not eliminate, the atelectatic areas. The vertical diameters of both lungs were smaller in the lateral position as compared to the supine position (16.7 vs 10.4 cm in the left lung and 17.3 vs 12.8 cm in the right lung). The lateral positioning also caused a large reduction of the atelectatic area in the non-dependent lung. Differential ventilation with selective PEEP to the dependent lung eliminated (3/8 patients) or reduced (5/8 patients) dependent lung atelectasis. It can be concluded that lung geometry is altered in the lateral position: the shape of the lung makes the vertical diameter of each lung less in the lateral position, compared to the supine position. The atelectatic areas are mainly located in the dependent lung in the lateral position, and these atelectatic areas could be further reduced by selective PEEP to this lung.

SELECTIVE MECHANICAL VENTILATION OF DEPENDENT LUNG REGIONS IN THE ANAESTHETIZED HORSE IN DORSAL RECUMBENCY

The effect of selective mechanical ventilation of dependent lung regions were studied in anaesthetized horses (mean weight 486 kg) in dorsal recumbency. Blood-gas measurements were performed with the horse in the lateral position during spontaneous breathing (before selective intubation) and in dorsal recumbency during spontaneous breathing, general mechanical ventilation, and spontaneous breathing + selective mechanical ventilation. Arterial oxygen tension (PaO2) was 32.3 kPa in the lateral position during spontaneous breathing with a high inspired oxygen fraction (FlO2 greater than 92%). In dorsal recumbency PaO2 decreased to 10.9 kPa during spontaneous breathing and was not significantly affected by general mechanical ventilation (PaO2 12.6 kPa). The institution of selective mechanical ventilation with a selective positive end-expiratory pressure (PEEP) of 20 cm H2O caused a marked increase in PaO2 to an average of 35.3 kPa. It is concluded that selective intubation of dependent regions in the diaphragmatic lobes is a feasible procedure and that selective mechanical ventilation with PEEP markedly improves arterial oxygenation in the anaesthetized horse in dorsal recumbency.

Lung and chest wall mechanics during differential ventilation with selective PEEP.

Eight patients free from cardio-pulmonary disease and with a mean age of 46 years were studied during general anaesthesia in the lateral position. Measurements of hemithoracic mechanics were made during four different modes of ventilation: 1. Conventional ventilation (free distribution of ventilation) with no positive end-expiratory pressure (PEEP) (CV), 2. differential ventilation (50% of ventilation to each lung) with no PEEP (DV:0), and 3 and 4. DV with selective PEEP of 0.8 and 1.6 kPa, respectively, to the dependent lung only (DV:8, DV:16). During CV, 60% of ventilation was distributed to the non-dependent lung. Non-dependent hemithoracic compliance was 64% greater and inspiratory resistance 39% lower than those of the dependent hemithorax. No significant differences between the two hemithoraces were noted during DV:0, but on application of selective PEEP the compliance of the dependent hemithorax increased and its resistance decreased. With DV:16, the compliances of the two hemithoraces were essentially equal, as were their resistances. Selective PEEP caused a larger volume increase in the dependent lung than general PEEP. Selective PEEP reduced the volume of the non-dependent lung but only by 1/3 of the simultaneous increase in that of the dependent lung. Oesophageal pressure increased only slightly on selective inflation of the dependent lung, and remained negative within the 21 volume range studied. It is suggested that the altered mechanics of the dependent lung during selective PEEP result in a more even distribution of the inspired gas within that lung.

Effect of Selective PEEP on Pulmonary Blood Flow following Unilateral Hydrochloric Acid Aspiration in the Dog

We investigated the effect of unilateral or bilateral positive end-expiratory pressure (PEEP) on pulmonary perfusion in 12 dogs with a hydrochloric acid aspiration injury of the left lung. The lungs were ventilated separately and PEEP was applied to the left lung at 10 cmH2O (1.0 kPa) in six and at 15 cmH2O (1.5 kPa) in six others. Measurements of the right and left pulmonary arterial blood flows (QR and QL) and venous admixture were made before, during and after PEEP. After this study, 5 and 10 cmH2O (0.5 and 1.0 kPa) PEEP were applied to both lungs in six dogs and measurements were repeated. Following the application of PEEP to the left lung, a significant decrease in QL and increase in QR were observed. However, the application of PEEP to both lungs was followed by significant decreases in both QL and QR. The cardiac output decreased slightly during unilateral PEEP and markedly during bilateral PEEP. The venous admixture decreased significantly during PEEP in all the groups. These findings indicate that selective PEEP causes a transfer of pulmonary blood flow from the injured lung to the normal lung, improving ventilation-perfusion inequality, and improves gas exchange without impeding oxygen delivery.

Development and evaluation of a flow-dividing unit for differential ventilation and selective PEEP.

Differential ventilation with selective positive end-expiratory pressure (PEEP) was studied in a two-compartment lung model, using one ventilator and a flow-dividing unit consisting of inspiratory flow resistors and an inspiratory threshold valve. The compliance of each lung compartment was varied between 0.15 and 0.23 1 X kPa-1 and the resistance was varied from 0 to 3.5 kPa X 1(-1) X s. The minute volume was 12 1 and the respiratory frequency 12/min, with an inspiratory:expiratory ratio of 1:2. An even distribution of ventilation to the two lung compartments was obtained with the inspiratory flow resistors or the threshold valve under all conditions studied. However, a stepwise increase in the inspiratory resistance of one lung compartment from 1.0 to 2.5 or from 2.5 to 3.5 kPa X 1(-1) X s required readjustment of the inspiratory flow resistor to achieve an even distribution of ventilation, whereas the inspiratory threshold valve needed no readjustment. Large differences in the inspiratory impedance of the two lung compartments caused asynchronous gas delivery when the ventilation distribution was adjusted by means of the flow resistors. Use of the threshold valve resulted in synchronous gas delivery. The flow-dividing unit consists of non-active elements and can thus be connected to any ventilator.

Differential Ventilation and Selective Positive End-expiratory Pressure

Eleven patients with acute respiratory failure due to diffuse, bilateral lung disease were treated according to a new ventilation concept. The patients were intubated with a double-lumen catheter and positioned in the lateral decubital posture. With two synchronized ventilators, each lung received half of the tidal volume (VT), in accordance with its presumed perfusion (differential ventilation--DV), and the end-expiratory pressure was increased locally in the dependent lung (selective PEEP). DV with and without selective PEEP was compared with conventional ventilation with free distribution of VT, with and without PEEP applied to both lungs. The major findings were that DV with a selective PEEP of 12 cmH2O to the dependent lung decreased venous admixture by 38% (P less than 0.01) in comparison with conventional ventilation with no PEEP. Furthermore, it was found that selective PEEP, in contrast to general PEEP, had no deleterious effect on cardiac output. Consequently, DV with selective PEEP increased arterial oxygen tension by 23% (P less than 0.05) compared with general PEEP and by 46% (P less than 0.001) in comparison with conventional ventilation with no PEEP.

Ventilation and perfusion of each lung during differential ventilation with selective PEEP.

Lung perfusion was studied in 10 patients (mean age 58 yr) in the lateral position during enflurane anesthesia. They were ventilated through a double-lumen endotracheal catheter: 1) by one ventilator with free distribution of ventilation between the lungs, with no (zero) end-respiratory pressure (ZEEP); 2) as above but with a general positive end-expiratory pressure (PEEP) of 9 cmH2O; or 3) by two ventilators with equal distribution of ventilation between the lungs and with a selective PEEP of 8 cmH2O to the dependent lung only. Total ventilation was on average 8 l/min (BTPS) throughout the study. During the first method, 34% of ventilation was distributed to the dependent and 66% to the nondependent lung. Cardiac output (thermodilution) was 4.5 l/min, 57% being distributed to the dependent lung as assessed by iv boli of Xenon 133. During the second method, ventilation was assumed to be distributed equally between the lungs. Cardiac output was decreased to 3.8 l/min, and the dependent lung received 81% of lung blood flow. During the third method, cardiac output was significantly greater than during the second method (4.1 l/min), 51% passing to the dependent lung. Peak and end-inspiratory airway pressures were 5-18 cm H2O lower during selective than during general PEEP. Arterial oxygen tension was significantly greater during the third method than during either of the other ventilator settings and the alveolar-arterial oxygen tension difference was almost halved compared with the first method. It is concluded that differential ventilation with selective PEEP improves ventilation-perfusion matching and thus oxygenation.

Differential lung ventilation with unilateral PEEP following unilateral hydrochloric acid aspiration in the dog.

Differential lung ventilation with positive end expiratory pressure (PEEP) improves pulmonary gas exchange when used in the supportive care of patients with severe unilateral or asymmetrical lung disease. Once the provision of selective PEEP to the two lungs is accomplished, the best method of partitioning the tidal volume between the two lungs is unknown. Twelve mongrel dogs were given a unilateral hydrochloric acid (HCl) aspiration injury. A computer controlled differential lung ventilation system was used to ventilate four dogs with equal volumes to each lung, four dogs with equal driving pressure (end inspiratory pressure-PEEP) to each lung, and four dogs with equal end-tidal CO2 fraction from each lung. The respiratory rate was feedback controlled to maintain PaCO2 at 4.67 kPa. The dogs were kept supine and ventilated with 30% O2. Following injury, the PEEP was set at 0 kPa for 1 h. The dogs were then given 1.36 kPa and 2.72 kPa PEEP to the injured lung for 2 h in a cross-over fashion. The assignment of the tidal volume controller, the side of injury, and the PEEP sequence was random. Oxygen tension fell and pulmonary venous admixture increased after giving the HCl injury. In all three groups considered simultaneously, unilateral PEEP improved PaO2 and venous admixture. The equal tidal volume distribution was the only group to show a significant improvement in PaO2 at both PEEP increments (0 to 1.36 kPa and 2.72 kPa). There was a significant difference in tidal volume allocation between the three groups with the equal end-tidal and equal pause pressure groups only minimally ventilating the injured lung.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective PEEP in acute bilateral lung disease. Effect on patients in the lateral posture.

Seven patients with acute respiratory failure due to diffuse and fairly uniform lung disease were studied during mechanical ventilation in the lateral decubital position with: (a) zero end-expiratory pressure (ZEEP) through a double-lumen oro-bronchial tube to permit a recording of the ventilation to each lung; (b) bilateral positive end-expiratory pressure (PEEP) of 1.2 kPa, with maintenance of ventilation distribution between lungs as observed during ZEEP; (c) selective PEEP of 1.2 kPa, applied to the dependent lung only, with ventilation as during ZEEP; and (d) conventional PEEP of 1.2 kPa applied to both lungs through a single-lumen tube, with free distribution of ventilation between the lungs. During ZEEP, 69% of ventilation was distributed to the non-dependent and 31% to the dependent lung; cardiac output was 6.51 X min-1, venous admixture (QS/QT) 40% and arterial oxygen tension (PaO2) 8.3 kPa. With bilateral PEEP, functional residual capacity (FRC) increased by 0.331, cardiac output was reduced to 5.11 X min-1 and venous admixture to 32%. PaO2 increased to 10.1 kPa. With selective PEEP the dependent lung FRC increased by 0.211 and the FRC of the non-dependent lung decreased by 0.081. Cardiac output increased to 6.11 X min-1, which was no longer significantly different from that during ZEEP. Venous admixture remained at the same level as with bilateral PEEP.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Improved Oxygenation During Thoracotomy with Selective PEEP to the Dependent Lung

In 22 patients during thoracotomy in the lateral position, the effects of selective positive end-expiratory pressure (PEEP) to the dependent lung while simultaneously ventilating the non-dependent lung at zero end-expiratory pressure (ZEEP) on (1) inspired O2 concentration required to maintain adequate Pao2 during thoractomy and 2) alveolar-arterial oxygen difference (AaO2D) while breathing 100 percent O2 at the end of thoractomy were examined and compared to ventilation of both lungs at ZEEP, Selective PEEP to the dependent lung resulted in adequate PaO2 with a lower inspired O2 concentration (44 +/- SD 6% versus 70 +/- SD 21%), and a smaller AsO2D while breathing 100 percent O2 189 +/- SD 31 versus 342 +/- SD 69 torr) at the end of thoracotomy.