Influence of positive end-expiratory pressure on extravascular lung water during the formation of experimental hydrostatic pulmonary oedema

The influence of positive end-expiratory pressure (PEEP) on extravascular lung water measured with the double-indicator dilution technique (EVLWi) has been studied during formation of hydrostatic pulmonary oedema in a canine model. The oedema was created by elevating the mean pulmonary artery pressure (PAP) to 30 mmHg (4.0 kPa) by inflation of a left atrial balloon, and a simultaneous intravenous saline infusion of 15 ml.kg-1.h-1. All dogs were ventilated with zero end-expiratory pressure (ZEEP) until the initial EVLWi had increased by 50%. In one group (n = 5) a PEEP of 10 cmH2O (1.0 kPa) was applied and the dogs were studied for a further 4 h and in the other group (n = 5) ZEEP was maintained throughout the study. During the first 2 h after ZEEP/PEEP application EVLWi increased from 13.7 +/- 2.1 to 20.2 +/- 1.2 ml.kg-1 with ZEEP ventilation and from 13.6 +/- 1.2 to 18.6 +/- 1.9 ml.kg-1 with PEEP ventilation. EVLWi remained unchanged during the last 2 h in both groups. The gas exchange improved with PEEP, arterial oxygen tension increased from 30.4 +/- 8.9 kPa to 38.6 +/- 2.5 kPa (P less than 0.01), and the shunt fraction decreased from 6.0 +/- 3.8% to 1.2 +/- 0.8% (P less than 0.001). There were significant differences (P less than 0.01) in both PaO2 and shunt fraction between the ZEEP and PEEP groups throughout the study. In conclusion, positive end-expiratory pressure improves gas exchange but does not protect against increasing extravascular lung water during the creation of hydrostatic pulmonary oedema.     

Lung fluid balance evaluated by the rate of change of extravascular lung water content

Lung fluid balance was studied in 27 mongrel dogs by measuring changes in extravascular lung water content (EVLW). The expression delta EVLWi, which is the difference in EVLWi per kilo bodyweight per hour between two measurement occasions, was used as an estimate of the rate of change of EVLW. EVLW was measured by a double-indicator dilution technique (EVLWi) using iced glucose and indocyanine green. In addition, EVLW was determined at the end of each experiment with gravimetric technique (EVLWg), which enabled the calculation of a regression equation between EVLWi and EVLWg. Delta EVLWi was calculated repeatedly during an 8-h period of mechanical ventilation (MV) with no application of a positive end-expiratory pressure (n = 5), during an 8-h period with a positive end-expiratory pressure (PEEP) of 10 cmH2O (1.0 kPa) (n = 5), during the development of oleic acid (OA)-induced pulmonary oedema (n = 7), and hydrostatic pulmonary oedema (left atrial balloon inflation) (n = 9). An increase of EVLW was seen during PEEP 8 h (mean 35%) and after induction of OA and hydrostatic oedema (mean 300%), but no change was found during MV without PEEP. The regression equation was EVLWi = 5.5 + 0.97 x EVLWg (P = 0.001, r = 0.90). OA-induced oedema caused a mean maximum delta EVLWi of 5.1 ml/kg/h, indicating capillary leakage which, however, was self-limiting within 2 h after OA injection. In hydrostatic oedema there was a maximum delta EVLWi of 16.0 ml/kg/h. Delta EVLWi was negative after deflation of the left atrial balloon, indicating reabsorption of oedema.     

Measurement of dynamic lung fluid balance in the mechanically ventilated dog. Theory and results

An expression (LN) is presented for the net fluid leakage from the intravascular to the extravascular space in the lung. It is based on a new dog model and is the sum of rate of change in extravascular lung water content (EVLW), thoracic lymph flow, and pleural fluid formation. The rate of change of EVLW (delta EVLW) in ml/kg/h was calculated from repeated measurements of EVLW with a double-indicator dilution technique (dye/cold) and corrected according to the relation between EVLW measured by this technique and gravimetry. LN was studied in lung-healthy mechanically ventilated dogs during a prolonged period of mechanical ventilation with and without the application of a positive end-expiratory pressure of 10 cmH2O (1.0 kPa). During mechanical ventilation, LN was found to be 0.3 ml/kg/h in the basal condition, increasing to 0.5 ml/kg/h (P less than 0.01) after a mean period of 7 h. After the application of a positive end-expiratory pressure (PEEP) of 10 cmH2O (1 kPa) for 0.5-2 h, LN was found to increase significantly, from a mean of 0.3 ml/kg/h to 0.9 ml/kg/h (P less than 0.01). We conclude that LN is a useful quantitative expression in experimental studies on lung fluid balance.     

Effects of pleural fluid and positive end-expiratory pressure on the measurement of extravascular lung water by the double-indicator dilution technique

The reliability of the double-indicator dilution technique (dye/cold) for measuring extravascular lung water (EVLW) has been studied in lung-healthy dogs after pleural fluid injection of saline (up to 20 ml/kg) during mechanical ventilation at zero and 10 cmH2O (1.0 kPa) end-expiratory pressure (ZEEP and PEEP, respectively). Pleural fluid injection had no effect on EVLW at either ZEEP or PEEP. PEEP induced changes in cardiac output, and reduced both the intravascular (dye) and the thermal indicator volumes, but with no effect on the calculated EVLW. It is concluded that pleural fluid up to 20 ml/kg and ventilation with PEEP of 10 cmH2O (1.0 kPa) do not affect the reliability of the double-indicator dilution technique for measuring extravascular lung water in the dog.     

Effects of prolonged surgical trauma on the extravascular lung water and central blood volume in the dog

Extravascular lung water (EVLW) and central blood volume (CBV) were measured in 13 dogs with a double-indicator dilution technique (dye-cold), the indicators being detected intravascularly. Animals in a control group (n = 5) were mechanically ventilated for 8-15 h after baseline measurements. Another group of animals (n = 8) were subjected to extensive lymph duct cannulations, including a thoracoabdominal incision, and the dogs were followed for 8 to 18 h postoperatively. All dogs (n = 13) then received a dose of oleic acid intravenously in order to create lung damage. A positive fluid balance was maintained throughout the experiment. Basal EVLW was 8.8 ml/kg (n = 13) (similar in both groups), and did not change significantly in either group before oleic acid. Basal CBV was 18.5 ml/kg (n = 13); it increased (P less than 0.05) in the control group and decreased (P less than 0.05) in the surgery group during a 8-15-h period. EVLW was doubled (P less than 0.001) and CBV decreased slightly 2 h after oleic acid administration. The lung damage was similar in both groups, and was accompanied by increased pulmonary vascular pressures and marked reductions in arterial oxygen tension and thoracic compliance. The findings suggest that an earlier proposed dog model for the simultaneous measurement of EVLW and lymph flow can be used in long-term studies on lung fluid balance.     

Alveolar recruitment improves ventilatory efficiency of the lungs during anesthesia

PURPOSE: The goal of this study was to analyze the effect of positive end-expiratory pressure (PEEP), with and without a lung recruitment maneuver, on dead space. METHODS: 16 anesthetized patients were sequentially studied in three steps: 1) without PEEP (ZEEP), 2) with 5 cm H(2)O of PEEP and 3) with 5 cm H(2)O of PEEP after an alveolar recruitment strategy (ARS). Ventilation was maintained constant. The single breath test of CO(2) (SBT-CO(2)), arterial oxygenation, end-expiratory lung volume (EELV) and respiratory compliance were recorded every 30 min. RESULTS: Physiological dead space to tidal volume decreased after ARS (0.45 +/- 0.01) compared with ZEEP (0.50 +/- 0.07, P < 0.05) and PEEP (0.51 +/- 0.06, P < 0.05). The elimination of CO(2) per breath increased during PEEP (25 +/- 3.3 mL.min(-1)) and ARS (27 +/- 3.2 mL.min(-1)) compared to ZEEP (23 +/- 2.6 mL.min(-1), P < 0.05), although ARS showed larger values than PEEP (P < 0.05). Pa-etCO(2) difference was lower after recruitment (0.9 +/- 0.5 kPa, P < 0.05) compared to ZEEP (1.1 +/- 0.5 kPa) and PEEP (1.2 +/- 0.5 kPa). Slope II increased after ARS (63 +/- 11%/L, P < 0.05) compared with ZEEP (46 +/- 7.7%/L) and PEEP (56 +/- 10%/L). Slope III decreased significantly after recruitment (0.13 +/- 0.07 1/L) compared with ZEEP (0.21 +/- 0.11 1/L) and PEEP (0.18 +/- 0.10 1/L). The angle between slope II and III decreased only after ARS. After lung recruitment, PaO(2), EELV, and compliance increased significantly compared with ZEEP and PEEP. CONCLUSION: Lung recruitment improved the efficiency of ventilation in anesthetized patients.     

Positive end-expiratory pressure ventilation increases extravascular lung water due to a decrease in lung lymph flow

Positive end-expiratory pressure (PEEP) is used to improve gas exchange, increase functional residual capacity, recruit air spaces, and decrease pulmonary shunt in patients suffering from respiratory failure. The effect of PEEP on extravascular lung water (EVLW), however, is still not fully understood. This study was designed as a prospective laboratory experiment to evaluate the effects of PEEP on EVLW and pulmonary lymph flow (QL) under physiologic conditions. Twelve adult sheep were operatively prepared to measure haemodynamics of the systemic and pulmonary circulation, and to assess EVLW In addition, the lung lymphatic duct was cannulated and a tracheostomy performed. The animals were then mechanically ventilated in the awake-state without end-expiratory pressure (PEEP 0). After a two-hour baseline period, PEEP was increased to 10 cmH2O for the duration of two hours, and then reduced back to 0 cmH2O. Cardiopulmonary variables, QL, and arterial blood gases were recorded intermittently; EVLW was determined two hours after each change in PEEP. The increase in PEEP resulted in a decrease in QL (7 +/- 1 vs 5 +/- 1 ml/h) and an increase in EVLW (498 +/- 40 vs 630 +/- 58 ml; P<0.05 each) without affecting cardiac output. As PEEP was decreased back to baseline, QL increased significantly (5 +/- 1 vs 10 +/- 2 ml/h), whereas EVLW returned back to baseline. This study suggests that institution of PEEP produces a reversible increase in EVLW that is linked to a decrease in QL.     

Effects of lung recruitment maneuver and positive end-expiratory pressure on lung volume,respiratory mechanics and alveolar gas mixing in patients ventilated after cardiac surgery

BACKGROUND: It is unclear whether positive end-expiratory pressure (PEEP) is needed to maintain the improved oxygenation and lung volume achieved after a lung recruitment maneuver in patients ventilated after cardiac surgery performed in the cardiopulmonary bypass (CPB). METHODS: A prospective, randomized, controlled study in a university hospital intensive care unit. Sixteen patients who had undergone cardiac surgery in CPB were studied during the recovery phase while still being mechanically ventilated with an inspired fraction of oxygen (FiO2) 1.0. Eight patients were randomized to lung recruitment (two 20-s inflations to 45 cmH2O), after which PEEP was set and kept for 2.5 h at 1 cmH2O above the pressure at the lower inflexion point (14+/-3 cmH2O, mean +/-SD) obtained from a static pressure-volume (PV) curve (PEEP group). The remaining eight patients were randomized to a recruitment maneuver only (ZEEP group). End-expiratory lung volume (EELV), series dead space, ventilation homogeneity, hemodynamics and PaO2 (oxygenation) were measured every 30 min during a 3-h period. PV curves were obtained at baseline, after 2.5 h, and in the PEEP group at 3 h. RESULTS: In the ZEEP group all measures were unchanged. In the PEEP group the EELV increased with 1220+/-254 ml (P<0.001) and PaO2 with 16+/-16 kPa (P<0.05) after lung recruitment. When PEEP was discontinued EELV decreased but PaO2 was maintained. The PV curve at 2.5 h coincided with the curve obtained at 3 h, and both curves were both steeper than and located above the baseline curve. CONCLUSIONS: Positive end-expiratory pressure is required after a lung recruitment maneuver in patients ventilated with high FiO2 after cardiac surgery to maintain lung volumes and the improved oxygenation.     

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.     

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)     

Optimizing peroperative compliance with PEEP during upper abdominal surgery: effects on perioperative oxygenation and complications in patients without preoperative cardiopulmonary dysfunction.

BACKGROUND AND OBJECTIVE: Late postoperative hypoxaemia after upper abdominal surgery is common even among cardiopulmonary healthy patients. Atelectasis may develop after intubation and persist into or reveal a disposition for atelectasis in the postoperative period. Positive end-expiratory pressure (PEEP) eliminates peroperative atelectasis but the effect on perioperative oxygenation is controversial. This study evaluated the effect of peroperative PEEP optimized pulmonary compliance on perioperative oxygenation and complications. METHODS: Forty patients assessed by electrocardiography, spirometry, functional residual capacity and diffusion capacity were randomly assigned to receive positive end-expiratory pressure (PEEP) or zero end-expiratory pressure (ZEEP) during surgery. PaO2, SPO2 and complications in the postoperative period were evaluated without knowledge of peroperative PEEP or ZEEP application. RESULTS: Peroperative arterial oxygenation improved for all patients receiving PEEP, mean 2.1 kPa (0.7-3.5 kPa). There was no difference in postoperative median PaO2 between the groups. The differences in the incidence of late prolonged postoperative hypoxaemia and complications were 25% (-5% to 55%) and -1% (-31% to 29%) between the ZEEP and the PEEP group, but were not statistically significant.     

'Alveolar recruitment strategy' improves arterial oxygenation during general anaesthesia

Abnormalities in gas exchange during general anaesthesia are caused partly by atelectasis. Inspiratory pressures of approximately 40 cm H2O are required to fully re-expand healthy but collapsed alveoli. However, without PEEP these re-expanded alveoli tend to collapse again. We hypothesized that an initial increase in pressure would open collapsed alveoli; if this inspiratory recruitment is combined with sufficient end-expiratory pressure, alveoli will remain open during general anaesthesia. We tested the effect of an 'alveolar recruitment strategy' on arterial oxygenation and lung mechanics in a prospective, controlled study of 30 ASA II or III patients aged more than 60 yr allocated to one of three groups. Group ZEEP received no PEEP. The second group received an initial control period without PEEP, and then PEEP 5 cm H2O was applied. The third group received an increase in PEEP and tidal volumes until a PEEP of 15 cm H2O and a tidal volume of 18 ml kg-1 or a peak inspiratory pressure of 40 cm H2O was reached. PEEP 5 cm H2O was then maintained. There was a significant increase in median PaO2 values obtained at baseline (20.4 kPa) and those obtained after the recruitment manoeuvre (24.4 kPa) at 40 min. This latter value was also significantly higher than PaO2 measured in the PEEP (16.2 kPa) and ZEEP (18.7 kPa) groups. Application of PEEP also had a significant effect on oxygenation; no such intra-group difference was observed in the ZEEP group. No complications occurred. We conclude that during general anaesthesia, the alveolar recruitment strategy was an efficient way to improve arterial oxygenation.      

Constant-flow ventilation during experimental left ventricular failure

The efficacy of constant-flow ventilation (CFV) was investigated in dogs with normal heart function (control phase, n = 8) and after development of left ventricular failure (LVF phase, n = 8). Heated, humidified and oxygen-enriched air (inspired oxygen fraction (Fio2) = 0.4) was continuously delivered via two catheters positioned within each mainstem bronchus at two flow rates (1.2 and 1.6 l/kg/min). Conventional mechanical ventilation (CMV) with positive end-expiratory pressure (PEEP) of 0.5 kPa was used as reference ventilation. During control, neither CMV with PEEP nor CFV revealed severe impairment of cardiopulmonary performance. Alveolo-arterial PO2 difference (P(A-a)O2) increased significantly during CFV1.2 and CFV1.6, indicating a higher degree of ventilation-perfusion (VA/Q) inhomogeneity. Acute left ventricular failure (LVF) was induced by proximal occlusion of the left anterior descending (LAD) coronary artery. Cardiac output (CO), maximum velocity of pressure development (dP/dtmax) and mixed venous PO2 decreased (P less than or equal to 0.05), whereas left ventricular end-diastolic pressure (LVEDP) and pulmonary capillary wedge pressure (PCWP) increased (P less than or equal to 0.05). Extravascular lung water (EVLW), as determined by thermal-dye technique, increased from 10.1 ml/kg to 20.9 ml/kg (P less than or equal to 0.01). Oxygenation, but not CO2 elimination, deteriorated in the LVF phase. There were no haemodynamic differences between CMV with PEEP and CFV1.2, but cardiopulmonary performance deteriorated with CFV1.6. Gas exchange was significantly more impaired during CFV1.2 and CFV1.6 due to increased VA/Q mismatching. However, there were no significant differences for P(A-a)O2 values between CFVControl and CFVLVF.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of Positive End-expiratory Pressure and Different Tidal Volumes on Alveolar Recruitment and Hyperinflation

Background: The morphologic effect of positive end-expiratory pressure (PEEP) and of two tidal volumes were studied by computed tomography to determine whether setting the tidal volume (Vt) at the upper inflection point (UIP) of the pressure-volume (P-V) curve of the respiratory system or 10 ml/kg have different effects on hyperinflation and alveolar recruitment.

Methods: Alveolar recruitment and hyperinflation were quantified by computed tomography in nine patients with the acute respiratory distress syndrome (ARDS). First, end expiration was compared without PEEP and with PEEP set at the lower inflection point of the P-V curve; second, at end inspiration above PEEP, a reduced Vt set at the UIP (rVt) and a standard 10 ml/kg Vt (Vt) ending above the UIP were compared. Three lung zones were defined from computed tomographic densities: hyperdense, normal, and hyperinflated zones.

Results: Positive end-expiratory pressure induced a significant decrease in hyperdensities (from 46.8 +/- 18% to 38 +/- 15.1% of zero end-expiratory pressure (ZEEP) area; P < 0.02) with a concomitant increase in normal zones (from 47.3 +/- 20.9% to 56.5 +/- 13.2% of the ZEEP area; P < 0.05), and a significant increase in hyperinflation (from 8.1 +/- 5.9% to 17.8 +/- 12.7% of ZEEP area; P < 0.01). At end inspiration, a significant increase in hyperinflated areas was observed with Vt compared with rVt (33.4 +/- 17.8 vs. 26.8 +/- 17.3% of ZEEP area; P < 0.05), whereas no significant difference was observed for both normal and hyperdense zones.     

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.     

Furosemide, when used in combination with positive end-expiratory pressure, facilitates the resorption of extravascular lung water in experimental hydrostatic pulmonary oedema

The study aimed to establish whether furosemide given intravenously improved resorption of hydrostatic pulmonary oedema in 14 dogs mechanically ventilated with positive end-expiratory pressure (PEEP). Hydrostatic pulmonary oedema was created by simultaneous inflation of a left atrial balloon and rapid intravenous infusion of isotonic saline. The hydrostatic process was terminated by deflating the balloon and reducing the infusion rate. A PEEP of 10 cmH2O (1.0 kPa) was applied in all animals; in seven, furosemide was administered (diuretic group), 1 mg/kg intravenously as a bolus followed by an infusion of 0.5 mg/kg per hour, while the remaining seven dogs served as a control group. All dogs were studied for a period of 4 h. The extravascular lung water measured with the double indicator dilution technique was 28.3 +/- 3.8 (diuretic group) and 28.2 +/- 6.8 ml/kg (control group) during maximum oedema. It was reduced to 16.4 +/- 2.2 (diuretic group) vs 19.8 +/- 3.7 ml/kg (control group) after 4 h of resorption, P less than 0.05. Postmortem gravimetric values of extravascular lung water were 9.1 +/- 3.4 (diuretic group) vs 12.6 +/- 5.0 g/kg (control group). In the diuretic group the urinary output increased threefold, and haemoglobin and serum protein concentrations were higher than in the control group. There was a significantly greater decrease in cardiac output and central blood volume in the diuretic group. In conclusion, furosemide given intravenously improved lung fluid resorption in hydrostatic pulmonary oedema, probably by increasing the plasma colloid osmotic pressure.     

Effects of negative extra-thoracic pressure ventilation on extravascular lung water volume and central blood volume in normal dogs

In negative extra-thoracic pressure ventilation (NETPV), lung water volume and central blood volume (CBV) could increase because of increased venous return and intensified negative interstitial pressure. The effects of NETPV on the extravascular lung water and CBV were examined in ten normal dogs by the double-indicator method using Na and cold water. The lung water volume measured by the method (EVTV) was compared with the lung water volume measured by the gravimetric method (EVLW) in 17 dogs. EVTV did not show any significant change in any ventilation modes compared with IPPV. CBV decreased from 21.9 ml.kg-1 to 19.2 ml.kg-1 in CPPV compared with IPPV (P less than 0.05). EVTV correlated well (r = 0.91, P less than 0.001) with EVLW. In normal dogs, NETPV did not change the lung water volume and CBV. NETPV dogs do not seem to have any disadvantage in respect of lung water volume compared with conventional positive pressure ventilations.     

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.     

"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)     

HIGH PEEP DECREASES HYALINE MEMBRANE FORMATION IN SURFACTANT DEFICIENT LUNGS

Lung lav age was performed in 16 anaesthetized rabbits to producesurfactant-deficient lungs. This resulted in alveolar collapse,an arterial Po₂ of less than 15kPa on 100% oxygen and an inflectionpoint on the inspirator/ limb of the pressure-volume curve atan airway pressure of 8–10 mm Hg. One group of eight animalswas then ventilated with a positive end-expiratory pressure(PEEP) equal to the pressure at the inflection point, whilstthe second group of eight was ventilated with a PEEP 5 mm Hgless than the inflection point. Animals in the high PEEP grouphad a significantly greater arterial P02 than those in the lowPEEP group, but the mean survival time for each group was similar.However, there was a significantly greater incidence of hyalinemembranes in the low PEEP group. Various mechanisms to explainthese findings are discussed.