Differential Ventilation and Selective PEEP During Anaesthesia in the Lateral Decubitus Posture

The potential of differential ventilation (DV) with selective positive end-expiratory pressure (PEEP) has been tested versus conventional ventilation with and without general PEEP. Gas exchange and central haemodynamics were studied in 15 subjects with no clinical or radiological signs of pulmonary disease. The rationale of the method was to ensure ventilation of the well-perfused dependent lung and to counteract airway closure within that lung. The subjects were intubated with a double-lumen catheter prior to scheduled abdominal surgery. During general anaesthesia in the lateral posture, they were given DV. The mean inspired oxygen fraction was 0.32. Fifty per cent ("even" tidal volume (VT) distribution) or 70% ("inverted" VT distribution) of the inspired volume was administered to the dependent lung. Two synchronized ventilators were used. In eight subjects DV was also combined with PEEP applied solely to the dependent lung (selective PEEP). The major findings were that DV with even VT distribution reduced venous admixture by 26% ( P <0.05) and the alveolo-arterial oxygen tension gradient (P(A-a)o2) by 30% ( P <0.05) in comparison with conventional ventilation in the lateral position. The addition of selective PEEP further reduced the P(A-a)o2 by 13%. P(A-a)o2 was consequently 43% lower than during conventional ventilation without PEEP in the lateral posture ( P <0.01). Selective PEEP also had less impact on cardiac output than general PEEP (P<0.05). It is concluded that DV with even distribution of VT and selective PEEP can reduce the P(A-a)o2 in anaesthetized lung-healthy subjects in the lateral position.     

Distribution of Inspired Gas to Each Lung in Anesthetized Human Subjects

The distribution of ventilation in man during halothane anesthesia was studied in a two-compartment lung model in which each lung was ventilated separately by means of a double-lumen tracheal tube. Eight subjects were studied prior to scheduled surgery. Tidal volume distribution was even between the lungs in the supine position (horizontal distribution) as was distribution of dynamic lung compliance, resistance and dead space. The vertical distribution was assessed when the patient was in the left lateral position. Dependent dynamic lung compliance and dead space were lower and lung resistance was higher than in the non-dependent lung. These factors favoured a non-dependent lung ventilation and, moreover, caused a re-distribution from dependent to non-dependent lung during an end-inspiratory pause (EIP), thus increasing the inhomogeneity of ventilation. The application of a positive end-expiratory pressure (PEEP) of 10 cmH₂O improved dependent ventilation and abolished redistribution between the lungs. In conclusion, uneven distribution of dynamic lung compliance and lung resistance causes inhomogeneous ventilation distribution, favouring the non-dependent lung. An EIP enhances and a PEEP reduces the inhomogeneity of ventilation.     

Positive end-expiratory pressure applied to the dependent lung during one-lung ventilation improves oxygenation and respiratory mechanics in patients with high FEV1

BACKGROUND AND OBJECTIVE: The aim of this study was to test the efficacy of positive end-expiratory pressure (PEEP) to the dependent lung during one-lung ventilation, taking into consideration underlying lung function in order to select responders to PEEP. METHODS: Forty-six patients undergoing open-chest thoracic surgical procedures were studied in an operating room of a university hospital. Patients were randomized to receive zero end-expiratory pressure (ZEEP) or 10 cmH2O of PEEP to the dependent lung during one-lung ventilation in lateral decubitus. The patients were stratified according to preoperative forced expiratory volume in 1 s (FEV1) as an indicator of lung function (below or above 72%). Oxygenation was measured in the supine position, in the lateral decubitus with an open chest, and after 20 min of ZEEP or PEEP. The respiratory system pressure-volume curve of the dependent hemithorax was measured in supine and open-chest lateral decubitus positions with a super-syringe. RESULTS: Application of 10 cmH2O of PEEP resulted in a significant increase in PaO2 (P < 0.05). This did not occur in ZEEP group, considered as a time matched control. PEEP improved oxygenation only in patients with high FEV1 (from 11.6+/-4.8 to 15.3+/-7.1 kPa, P < 0.05). There was no significant change in the low FEV1 group. Dependent hemithorax compliance decreased in lateral decubitus, more in patients with high FEV1 (P < 0.05). PEEP improved compliance to a greater extent in patients with high FEV1 (from 33.6+/-3.6 to 48.4+/-3.9 mLcmH2O(-1), P < 0.05). CONCLUSIONS: During one-lung ventilation in lateral decubitus, PEEP applied to the dependent lung significantly improves oxygenation and respiratory mechanics in patients with rather normal lungs as assessed by high FEV1.     

Differential ventilation and selective positive end-expiratory pressure: effects on patients with acute bilateral lung disease

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.     

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)     

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.     

Regional Differences in Lung Function during Anaesthesia and Intensive Care: Clinical Implications

Anaesthesia and most frequently acute respiratory failure are accompanied by a lowered functional residual capacity (FRC). This lowering promotes airway closure in dependent lung units and forces ventilation to non-dependent regions. Perfusion, on the other hand, is forced towards dependent lung units. A ventilation-perfusion mismatch is created and hypoxaemia may develop. General PEEP counters airway closure, but impedes cardiac output and forces perfusion further to dependent regions. In addition, barotrauma may occur. Improved matching of ventilation and perfusion can be achieved by: (1) positioning the subject in the lateral posture; (2) ventilating each lung separately in proportion to its perfusion (differential ventilation); and (3) applying PEEP only to the dependent lung (selective PEEP). Because of less overall intrathoracic pressure and lung expansion, interference with the total lung blood flow and the danger of barotrauma should be less than with general PEEP. Improved gas exchange with a 50-100% increase in PaO2 has been observed in a limited number of patients with acute bilateral lung disease studied so far during differential ventilation and selective PEEP.     

Prospective,randomized, controlled evaluation of the preventive effects of positive end-expiratory pressure on patient oxygenation during one-lung ventilation

BACKGROUND AND OBJECTIVE: This prospective, randomized, controlled study evaluated the effects on oxygenation by applying a selective and patient-specific value of positive end-expiratory pressure (PEEP) to the dependent lung during one-lung ventilation. METHODS: Fifty patients undergoing thoracic surgery under combined epidural/general anaesthesia were randomly allocated to receive zero PEEP (Group ZEEP, n = 22), or the preventive application of PEEP, optimized on the best thoracopulmonary compliance (Group PEEP, n = 28). Patients' lungs were mechanically ventilated with the same setting during two- and one-lung ventilation (FiO2 = 0.5; VT = 9mL kg(-1), inspiratory :expiratory time = 1 : 1, inspiratory pause = 10%). RESULTS: Lung-chest wall compliance decreased in both groups during one-lung ventilation, but patients of Group PEEP had 10% higher values than patients with no end-expiratory pressure (ZEEP) applied--Group ZEEP (P < 0.05). During closed chest one-lung ventilation, the PaO2 : FiO2 ratio was lower in Group PEEP (232 +/- 88) than in Group ZEEP (339 +/- 97) (P < 0.05); but no further differences were reported throughout the study. No differences were reported between the two groups in the need for 100% oxygen ventilation (10 patients of Group ZEEP (45%) and 14 patients of Group PEEP (50%) (P = 0.78)) or re-inflation of the operated lung during surgery (two patients of Group ZEEP (9%) and three patients of Group PEEP (10%) (P = 0.78)). Postanaesthesia care unit discharge required 48 min (25th-75th percentiles: 32-58 min) in Group PEEP and 45 min (30-57 min) in Group ZEEP (P = 0.60). CONCLUSIONS: The selective application of PEEP to the dependent, non-operated lung increases the lung-chest wall compliance during one-lung ventilation, but does not improve patient oxygenation.     

The effect of PEEP-ventilation on gas exchange and airway closure in experimental pulmonary emphysema

The benefits of mechanical ventilation with positive end-expiratory pressure (PEEP) are well documented, especially for patients with acute respiratory failure. PEEP increases functional residual capacity (FRC) and reduces closing volume (CV) and ventilation-perfusion mismatching. Little is known about the effects of PEEP in patients with chronic obstructive pulmonary disease, where closing volume and ventilation-perfusion mismatching are increased. We investigated the effects of PEEP in a canine model of panlobular emphysema (PLE). METHODS. After completion of control-period measurements, PLE was induced in eight dogs by intratracheal application of 20 ml aerosolized 16% papain solution. Three weeks later the effects of continuous positive-pressure ventilation (CPPV, PEEP 10 cmH2O) on gas exchange, FRC, and CV were investigated. Conventional intermittent positive-pressure ventilation (IPPV) served as reference. Measurements of CV were done using both the foreign gas bolus method and the single-breath oxygen test. FRC was determined by the nitrogen dilution technique. RESULTS. The papain-induced emphysema produced a deteriation in oxygenation, enlargement of FRC and CV, and an increase in quasi-static lung compliance. CPPV led to a further increase of FRC, but gas exchange was not improved nor was CV reduced. In the PLE period, mean pulmonary arterial pressures (MPAP) were higher during both modes of ventilation. CPPV tended to increase MPAP and pulmonary capillary wedge pressure when compared with IPPV. Systemic hemodynamic conditions were stable throughout the experiment. CONCLUSIONS. The application of PEEP to emphysematous lungs seemed to enlarge FRC, predominantly in the nondependent rather than in the dependent lung regions, which are prone to airway closure. In patients with emphysema, ventilation with PEEP may further deteriorate the impaired distribution of ventilation and thus counteract any improvement of gas exchange.     

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.     

The effect of positive end expiratory pressure on the respiratory profile during one-lung ventilation for thoracotomy

Summary In this randomised controlled trial we examined the effects of four different levels of positive end expiratory pressure (PEEP at 0, 5, 8 or 10 cmH(2)O), added to the dependent lung, on respiratory profile and oxygenation during one lung ventilation. Forty-six patients were recruited to receive one of the randomised PEEP levels during one lung ventilation. We did not find significant differences in lung compliance, intra-operative or postoperative oxygenation amongst the four different groups. However, the physiological deadspace to tidal volume ventilation ratio was significantly lower in the 8 cmH(2)O PEEP group compared with the other levels of PEEP (p < 0.0001). We concluded that the use of PEEP (< or =10 cmH(2)O) during one lung ventilation does not clinically improve lung compliance, intra-operative or postoperative oxygenation despite a statistically significant reduction in the physiological deadspace to tidal volume ratio.     

Protective ventilation attenuates postoperative pulmonary dysfunction in patients undergoing cardiopulmonary bypass

OBJECTIVE: To ascertain if protective ventilation can attenuate the damaging postoperative pulmonary effects of cardiopulmonary bypass (increases in airway pressure, decreases in lung compliance, and increases in shunt). DESIGN: Prospective, randomized clinical trial. SETTING: Single university hospital. PARTICIPANTS: Twenty-five patients undergoing elective coronary artery bypass graft procedure and early extubation. INTERVENTIONS: Thirteen patients received conventional mechanical ventilation (CV; respiratory rate, 8 breaths/min; tidal volume, 12 mL/kg; fraction of inspired oxygen [FIO2], 1.0; positive end-expiratory pressure [PEEP], +5), and 12 patients received protective mechanical ventilation (PV; respiratory rate, 16 breaths/min; tidal volume, 6 mL/kg; FIO2, 1.0; PEEP, +5). Perioperative anesthetic and surgical management were standardized. Various pulmonary parameters were determined twice perioperatively: 10 minutes after intubation and 60 minutes after arrival in the intensive care unit. MEASUREMENTS AND MAIN RESULTS: The mean postoperative increase in peak airway pressure in group CV was significantly larger than the mean postoperative increase in peak airway pressure in group PV (7.1 v 2.4 cm H2O; p < 0.001). Group CV experienced significant postoperative increases in plateau airway pressure (p = 0.007), but group PV did not (p = 0.644). The mean postoperative decrease in dynamic lung compliance in group CV was significantly larger than the mean postoperative decrease in dynamic lung compliance in group PV (14.9 v 5.5 mL/cm H2O; p = 0.002). Group CV experienced significant postoperative decreases in static lung compliance (p = 0.014), but group PV did not (p = 0.645). Group CV experienced significant postoperative increases in shunt (15.5% to 21.4%; p = 0.021), but group PV did not (18.4% to 21.2%; p = 0.265). CONCLUSIONS: Data indicate that protective ventilation decreases pulmonary damage caused by mechanical ventilation in normal and abnormal lungs. The results of this investigation indicate that protective ventilation may also help attenuate the postoperative pulmonary dysfunction (increases in airway pressure, decreases in lung compliance, and increases in shunt) commonly seen in patients after exposure to cardiopulmonary bypass.     

The effect of induction of anesthesia and intubation on end-expiratory lung level and regional ventilation distribution in cardiac children

Background: During the induction of anesthesia, changes in functional residual capacity and ventilation distribution (VD) occur. Although these physiological changes are well investigated in adults, little data are available in infants and children. Aim: To describe continuous changes in lung physiology during the induction of anesthesia in infants and children using electrical impedance tomography (EIT). Methods: Lung mechanics and volume changes in 38 infants and children undergoing elective cardiac surgery were assessed using EIT before, during, and after the induction of anesthesia. End‐expiratory level (EEL as an equivalent to FRC) and VD were measured with EIT and referenced to a period of spontaneous breathing prior to induction. Results: EEL changed significantly during induction with the lowest during the intubation phase and normalized with the application of positive end‐expiratory pressures (PEEP) after induction. Ventilation prior to induction was preferentially distributed toward the dependent lung, whereas after induction, the nondependent lung was better ventilated. PEEP during mechanical ventilation did not improve ventilation inhomogeneity. Conclusion: Lung volume and mechanics deteriorate significantly during the induction of anesthesia and remain altered during mechanical ventilation.     

Airway Closure During Anaesthesia, and its Prevention by Positive End Expiratory Pressure

Airway closure, functional residual capacity (FRC) and the transpulmonary pressure volume relationship of each lung were studied in the anaesthetized subject in the supine and the left lateral positions. In the supine posture, FRC was of approximately the same size in each lung as was closing capacity (CC). CC exceeded FRC in either lung. In the left lateral position, FRC was increased by 0.91 in the non-dependent lung and was reduced by 0.2 1 in the dependent lung, while CC was unaltered in either lung. Consequently, FRC exceeded CC in the non-dependent lung and was further lowered beneath CC in the dependent lung. Airway closure did not occur in the non-dependent lung until an average of 0.51 of gas had been expelled after the dependent lung had ceased to empty. The addition of positive end-expiratory pressure (PEEP) in the range 0.5–2 kPa, increased FRC more in the non-dependent than the dependent lung. The findings suggest that airway closure is evenly distributed in the horizontal level, while it has a discontinuous distribution between the dependent and non-dependent lung. Moreover, the increase in lung volume caused by PEEP has a distribution that is by no means ideal for the purpose of countering airway closure.     

"Closing volume" during high–frequency ventilation in anesthetized dogs

Airway closure, mean airway pressure, gas exchange and different modes of artificial ventilation were investigated in anesthetized and paralyzed dogs with clinically healthy lungs. The animals were ventilated with either intermittent positive pressure ventilation (IPPV), continuous positive pressure ventilation (GPPV, positive end-expiratory pressure (PEEP) = 0.49 kPa) or high-frequency jet ventilation (HFJV, open system) of 2 and 30 Hz with an inspiratory to expiratory (I/E) - ratio of 30/70 and 60/40. Closing volume (CV) was determined by a modified technique, submitting the lung to constant subatmospheric pressure after an inspiratory vital capacity of oxygen. Two different tests for CV were used: the foreign gas bolus (FGB) with helium as nonresident gas and the single breath nitrogen dilution technique (SBO2). During conventional mechanical ventilation, CV decreased significantly (P less than 0.05) after establishing a PEEP of 0.49 kPa. During HFJV, CV increased significantly (P less than 0.01). This effect was predominantly dependent on I/E duration time ratio and to a lesser extent on ventilatory frequency. There were significant differences between CV obtained by the FGB-method (CV(helium] and CV derived from the SBO2-test (CV(SBO2], although both tests revealed the same proportional changes of CV during the different modes of ventilation. The elevated CV was associated with a decreasing Pao2 and increasing Aa-Do2 and Paco2, indicating substantial hypoventilation and mismatching of ventilation and perfusion. Mean airway pressure increased with both CPPV and HFJV, revealing a dissociation between airway pressure and regional FRC distribution during HFJV. It is concluded that certain modes of high-frequency ventilation lead to impaired distribution of inspired gas to dependent lung regions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Immediate effects of positive end-expiratory pressure and low and high tidal volume ventilation upon gas exchange and compliance in patients with acute lung injury.

BACKGROUND: Protective ventilation, in general, includes low tidal volume ventilation and maintaining end-inspiratory plateau pressures less than 35 cmH2O. Recent clinical studies have determined that such an approach results in improved survival in patients with moderate to severe acute lung injury and acute respiratory distress syndrome. However, experimental evidence suggests that repeated end-expiratory collapse and reexpansion contributes to ventilator-induced lung injury. We sought to determine the immediate effects of specific tidal volume-PEEP combinations upon oxygenation and static compliance in patients with moderate to severe acute lung injury. METHODS: Fourteen patients were prospectively studied and were treated with each of 10 tidal volume-PEEP combinations, applied in random order. After 5 minutes at each tidal volume-PEEP combination, PaO2/FIO2 and static compliance were recorded. Comparisons were made between low and high tidal volume ventilation as well as across five PEEP levels. RESULTS: At both low (6 mL/kg) and high (10 mL/kg) tidal volume ventilation, PaO2/FIO2 increased with increasing PEEP, up to 20 cmH2O. Similar changes in static compliance were not evident. Static compliance was highest at PEEP of 10 and 15 cmH2O, regardless of tidal volume. With PEEP set at 5 cmH2O, static compliance was significantly lower with 6 mL/kg than with 10 mL/kg tidal volumes. Overall, static compliance was lowest for both tidal volume conditions with PEEP set at 25 cmH2O. CONCLUSION: Low tidal volume ventilation with PEEP set at 5 cmH2O results in poor oxygenation and compliance in patients with moderate to severe acute lung injury. Similarly, PEEP set at 25 cmH2O did not improve oxygenation or compliance.     

Hemodynamic effects of positive end-expiratory pressure during partial liquid ventilation in newborn lambs

BACKGROUND/PURPOSE: The aim of this study was to compare the effect of positive end-expiratory pressure (PEEP) application on hemodynamics, lung mechanics, and oxygenation in the intact newborn lung during conventional ventilation (CV) and partial liquid ventilation (PLV) at functional residual capacity (FRC). CV or PLV modes of ventilation do not affect hemodynamics nor the optimum PEEP for oxygenation. METHODS: Seven newborn lambs (1 to 3 days old) were instrumented to measure pulmonary hemodynamics and airway mechanics. Each lamb was used as their own control to compare different modes of ventilation (CV followed by PLV) under graded variations of PEEP (4, 8, 12, and 16 cm H(2)O) on the influence on pulmonary blood flow and pulmonary vascular resistance. RESULTS: There was a significant drop in pulmonary blood flow (PBF) from baseline (PEEP of 4 cm H(2)O on CV, 1,229 +/- 377 mL/min) in both modes of ventilation on a PEEP of 16 cm H(2)O (CV, 750 +/- 318 mL/min v PLV, 926 +/- 396 mL/min, respectively; P <.05). Peak inspiratory pressure (PIP) was higher on PLV at PEEP states of 4 cm H(2)O (16.5 +/- 1.3 cm H(2)O to 10.6 +/- 2.1 cm H(2)O; P <.05) and 8 cm H(2)O (18.8 +/- 2.2 cm H(2)O to 15.1 +/- 2.6 cm H(2)O; P <.05) when compared with CV. Conversely, PIP required to maintain the pCO(2) was lower on PLV at PEEP states of 12 (22.5 +/- 3.6 cm H(2)O to 24.2 +/- 3.8 cm H(2)O; P <.05) and 16 cm H(2)O (27.0 +/- 1.6 cm H(2)O to 34.0 +/- 5.9 cm H(2)O; P <.05). CONCLUSIONS: Hemodynamically, CO is impaired at a PEEP above 12 cm H(2)O in intact lungs. PFC at FRC does provide an advantage in lung mechanics more than 10 to 12 cm H(2)O of PEEP by decreasing the amount PIP needed to achieve the similar levels of gas exchange and minute ventilation, implying a reduced risk for barotrauma with chronic ventilation. Thus, selection of the appropriate level of PEEP appears to be important if PLV is to be utilized at FRC. The best strategy for PLV, including the selection of PEEP, remains to be determined.     

Lateral Positioning With Differential Lung Ventilation and Unilateral PEEP Following Unilateral Acid Aspiration in the Dog

Body position can significantly alter the efficiency of gas exchange following unilateral lung injury. We systematically examined three positions during differential lung ventilation with unilateral positive end-expiratory pressure (PEEP) following unilateral hydrochloric acid aspiration in the dog. Twelve mongrel dogs were intubated with a double-lumen endobronchial tube and mechanically ventilated with a microcomputer-controlled pair of ventilators. A tidal volume of 7.5 ml/kg was delivered to each lung. The PaCO2 was maintained at 4.67 kPa. A unilateral injury was induced with an injection of 0.1 N hydrochloric acid (2.5 ml/kg) into one lumen of the endobronchial tube. 0.984 kPa PEEP was applied to the injured lung and the dogs were placed sequentially in one of three positions (supine, lateral decubitus with injured lung non-dependent, and lateral decubitus with injured lung dependent) for 1 h apiece. There was no significant difference between the three positions with regard to PaO2 (F (2, 10) = 1.60, P = 0.25) of venous admixture (F (2, 10) = 0.49, P = 0.63). Our data indicated that position did not alter oxygenation. This was probably due to the use of differential ventilation with unilateral PEEP which eliminated redistribution of ventilation between the two lungs and minimized position-dependent changes in pulmonary blood flow.     

Effect of PEEP and suction via chest drain on functional residual capacity and lung compliance after surgical repair of congenital diaphragmatic hernia: preliminary observations in 5 patients

BACKGROUND/PURPOSE: Congenital diaphragmatic hernia (CDH) is associated with pulmonary hypoplasia that limits survival. The authors' knowledge on lung mechanics and lung volumes in these patients with hypoplastic lungs is still limited. Therefore, the authors performed measurements of functional residual capacity (FRC), compliance of the respiratory system (CRS), and tidal volume in 5 full-term infants (gestational age, 38 to 40 weeks; birth weight, 2,800 to 3,530 g) before and after surgical repair of neonatal CDH. METHODS: The authors studied the influence of different levels of positive end-expiratory pressure (PEEP) and suction via inserted ipsilateral chest tube connected to a water seal on lung volume and lung mechanics. A computerized tracer gas (SF6) washout method was used for serial measurements of FRC. Compliance of the respiratory system was determined according to insufflatory method. RESULTS: The authors found a preoperative compliance between 1.5 and 3.9 mL/kPa/kg and a preoperative FRC between 9.1 and 12.9 mL/kg indicating severe hypoplasia of the lungs in all patients. Immediately after surgical repair of CDH, compliance decreased to 85% (78% to 91%) of preoperative value, and FRC increased to 132% (110% to 150%) of preoperative value under mechanical ventilation while at 4 cm of water of PEEP and at -10 cm of water of suction via chest drain with the need of high fraction of inspired oxygen. After reduction of PEEP from 4 to 2 or 1 cm of water and lowering suction from -10 cm of water to -2 or 0 cm of water FRC decreased to 103% (80% to 122%) of preoperative value and compliance, and tidal volume improved to 135% (110% to 147%) of preoperative value resulting in increased alveolar ventilation, correction of acidosis and improvement in oxygenation. During the first days after surgery inadequate high PEEP or strong suction via chest tube drainage resulted in increase in FRC paralleled by decrease in compliance indicating overdistension of these hypoplastic lungs. CONCLUSIONS: The data show that overdistension of hypoplastic lungs in infants with CDH can be detected and excluded by repeated measurements of FRC and compliance in these critical ill infants. These data might help setting appropriate ventilator parameters, adequate suction via chest drain, and thereby improve gas exchange and outcome.     

Evaluation of pressure/volume loops based on intratracheal pressure measurements during dynamic conditions

BACKGROUND: The aim of this study was to evaluate and compare information about lung mechanics obtained by dynamic pressure/volume loops based on Y-piece and intratracheal airway pressure. METHODS: Airway pressure was measured simultaneously at the Y-piece and trachea. Flow/tidal volume was measured by sidestream spirometry at the Y-piece. The effect of an intraluminal catheter in the tube was evaluated in a lung model. Ten adults with acute lung injury and mechanical ventilation were studied. Measurements were performed during volume-(VC) and pressure-controlled (PC) ventilation at different ventilator settings. RESULTS: Lung model: There was a statistically significant difference (P<0.001) between trachea and Y-piece pressure/volume loop areas during both VC and PC ventilation. The ratio trachea area/Y-piece area decreased with increased endotracheal tube resistance (r=0.96). Patients: The difference between trachea and Y-piece P/V-loops was statistically significant at all 21 ventilatory settings (P<0.05-0.001). The tracheal loop revealed clearly intrinsic PEEP and lowered compliance during overinflation, which was difficult or impossible to see in the Y-piece pressure/volume loop. CONCLUSION: By measuring airway pressure at the trachea the effect of endotracheal tube resistance during inspiration is excluded while it is included during expiration, yielding correct end-points of inspiration and expiration. This makes it possible to calculate accurately total compliance of the respiratory system during dynamic conditions. By monitoring of airway pressure in the trachea, respiratory mechanics can be assessed more accurately and ventilatory settings adjusted to attenuate ventilator induced lung injury.