Sven Jakobson

Influence of Plasma Oncotic Pressure on Lung Water Accumulation and Gas Exchange After Experimental Lung Injury in the Pig

In 18 anaesthetized and artificially ventilated pigs, oleic acid was infused intravenously in order to induce a lung injury characterized by increased lung water content, decreased compliance and a ventilation/perfusion disturbance. After a stabilizing period, half of the animals (group P) underwent repeated plasmapheresis, which halved their plasma oncotic pressure (POP). The rest of the animals were bled and re‐transfused with the shed blood, thus serving as a control group. In both groups, care was taken to keep the mean left atrial pressure as constant as possible. During plasmapheresis and “shamapheresis”, there was no significant increase in venous admixture (Fio2 0.21 and 0.6) in either of the groups. At the end of the study, end‐inspiratory pressure, dead space/tidal volume ratio and wet/dry lung weight ratio (WW/DW) were significantly higher in group P. Venous admixture and WW/DW correlated significantly with pulmonary arterial pressure and calculated pulmonary capillary pressure, but not with POP or POP minus pulmonary arterial occlusion pressure. It is concluded that reduction of plasma oncotic pressure may increase the lung water content in previously injured lungs, but this extra water accumulation does not necessarily impair oxygenation in the lungs.

Effects of Positive End-Expiratory Pressure on Cardiac Output Distribution in the Pig

Cardiac output (CO) and the blood flow to the heart, cerebellum, kidney, pancreas, spleen and skeletal muscle were studied in 20 pigs during spontaneous breathing (SB) and intermittent positive pressure ventilation (Ippv) with a positive end‐expiratory pressure (Peep) of 0, 8, 16 or 24 cmH2O. Microspheres (15 μm) labelled with either 85‐Sr or 141‐Ce were used. Injection of microspheres labelled with one of the isotopes was given during SB (all pigs) and with the other isotope during Ippv with Peep of 0, 8, 16 or 24 cmH2O (five pigs at each level). CO decreased by 11% during Ippv with Peep of 0 and 31%, 53% and 66% during Peep of 8, 16 or 24 cmH2O, respectively. Mean arterial blood pressure was fairly well maintained in all groups except the group with Peep of 24 cmH2O. The perfusion of the six organs deteriorated, but when taken as fractions of CO measured at the same time, the blood flow to the heart, cerebellum and kidney increased with increasing airway pressure, while that to the pancreas, spleen and skeletal muscle decreased. The vascular resistance of the three former organs did not change, while in the latter it increased markedly. It is concluded that when CO decreases as a result of positive pressure ventilation, a redistribution takes place, mainly due to vascular constriction in skeletal muscle, which acts to preserve the blood flow to vital organs.

The use of 125I-labelled fibrinogen for determination of fibrin trapping in the lungs in patients developing the microembolism syndrome.

The microembolism syndrome occurred in four patients out of a series of 15 patients with multiple injuries who were considered to run a risk of developing this syndrome. These four patients showed signs of fibrin trapping in the lungs, as demonstrated by the use of 125I‐labelled fibrinogen and external detection over the lungs. It is, therefore, considered that this method can be used for diagnosing the microembolism syndrome. The fibrin trapping occurred at the onset of the progressive respiratory insufficiency. The time relation between the uptake of fibrin and the onset of the progressive respiratory insufficiency supports the theory of a causal connection between fibrin and pulmonary damage. Measurements of different coagulation and fibrinolysis factors in the blood were not able to discriminate between patients who developed the microembolism syndrome and those who did not.

Effects of Intercostal Nerve Blocks (Bupivacaine 0.25% and Etidocaine 0.5%) on Chest Wall Mechanics in Healthy Men

Bilateral blockade of the 5th to 11th intercostal nerves, inclusive, was produced in 14 healthy subjects. In seven, bupivacaine 0.25% was used, and in the other seven, etidocaine 0.5%. The latter has been found to have a stronger motor‐blocking action than the former. Before and after the blockade, the vital capacity (VC), peak expiratory flow rate (PEF), tidal volumes, respiratory variations in rib cage and abdominal circumferences and in oesophageal and intragastric pressures were recorded. By transthoracic electrical impedance pneumography, measures indicating changes in the functional residual capacity (FRC) were obtained. Although it was considered that changes in the parameters investigated mainly demonstrated changes in motor function, no differences were found between the drugs. With this form of blockade they seem to have equivalent effects in this respect. Thus, VC decreased by an average of 7% and PEF by 6%. Signs of a reduction of FRC after the blockade were also observed. The blockade had no effect on the partitioning of costal and abdominal breathing at rest. Analysis of the relations between the fractions of costal and abdominal breathing and the corresponding variations in intragastric pressure gave support to the view that in normal individuals both intercostal and abdominal muscles remain passive during respiration at rest. This is thus achieved by the diaphragm alone.

The Effect of Positive End‐Expiratory Pressure on Central Haemodynamics in the Pig

The effect on central haemodynamics of a stepwise increase in airway pressure from spontaneous breathing (SB) to intermittent positive pressure ventilation with a positive end‐expiratory pressure (PEEP) of 0, 8, 16 and 24 cmH2O was studied in eight pigs under ketamine anaesthesia. Compared with SB, cardiac output (CO) was reduced by 12, 36, 50 and 64% at the respective ventilator settings. The transmural pressures of the right and left atrium, measured as the difference between atrial and pleural pressure, both decreased with increments in airway pressure. At a PEEP level of 24, there was a threefold increase in pulmonary vascular resistance. This increase was secondary to the decrease in CO and no signs of CO deterioration due to increased right ventricular afterload were found. When 250 ml of dextran 70 was administered at a PEEP level of 24 and the airway pressure was then released stepwise, the left ventricular function curve improved, disclosing a relative myocardial failure at the highest PEEP levels. It is concluded that the principal causative mechanism in CO reduction due to increased intrathoracic pressure is a decrease in preload to the right ventricle. At high PEEP levels there are also signs of myocardial depression.

Effects of intercostal nerve blocks (etidocaine 0.5%) on chest wall mechanics in cholecystectomized patients.

In 20 patients who had undergone cholecystectomy through a right oblique incision, an intercostal nerve block with etidocaine 0.5% was performed on the day after operation — in 10 patients on the right side only and in the other 10 bilaterally. The block was applied to the 5th‐11th intercostal nerves, inclusive.

The Effect of Peep-ventilation on Cardiac Function in Closed Chest Pigs

OBJECTIVE Does ventilation with positive end-expiratory pressure (PEEP) depress myocardial contractility? DESIGN Ten piglets were anaesthetized and prepared for the measurement of cardiac output (SV) and right (MRAPtm) and left (MLAPtm) mean transmural atrial pressure, the latter serving as indices of preload. 500 ml of autologous blood was re-transfused during intermittent positive pressure ventilation without PEEP (IPPV) and continuous positive pressure ventilation with 15 cm H2O PEEP (CPPV). MEASUREMENTS AND RESULTS Right and left ventricular function curves were drawn by plotting MRAPtm and MLAPtm respectively versus the corresponding strokevolumes before and after re-transfusion. Similar inclinations were obtained during IPPV and CPPV on either side of the heart. CONCLUSIONS Although the ventricular function curves during IPPV and CPPV covered partially different preload levels, the results suggest that CPPV i.e. PEEP does not affect myocardial contractility.

Assessment of lung water content by roentgen videodensitometry

In 17 anesthetized and mechanically ventilated pigs, different degrees of lung injury were induced by iv infusion of oleic acid (mean dose 0.1 ml/kg). The change in radiologic density of the chest was measured by a videodensitometer before and 4 h after oleic acid infusion. The lungs were then removed for determination of the wet/dry weight ratio (WW/DW). The change in radiologic density was significantly correlated to WW/DW (r = .87) and to the changes in end-inspiratory pressure (r = .80), mean pulmonary arterial pressure (r = .77) and venous admixture (r = .79), but not to changes in the oncotic-hydrostatic pressure gradient of the lungs (r = .46). Roentgen videodensitometry appears to be a useful method for assessing changes in extra-vascular lung water content.

Thoraco-abdominal perimetry for partitioning of the tidal volume into fractions due to rib cage expansion and diaphragmatic descent.

In 10 healthy males, respiratory variations in rib cage and abdominal circumferences were detected with mercury-in-rubber transducers. The volumes of respired air were measured by pneumotachography. The purpose was to divide quantitatively the tidal volume into fractions referable to rib cage expansion and to diaphragmatic descent (costal and abdominal breathing respectively). The main practical problem is to get the transducers properly scaled, the method of perimetry otherwise being easy to apply. For this purpose a manoeuvre producing deliberate variations in the partitioning of costal and abdominal breathing at different tidal volume levels proved satisfactory (the manoeuvre of variably combined costal and abdominal breathing). By calibrating the transducers in this way it was also possible to make fairly good estimates of the tidal volumes from the perimetric variations. The relation between changes in lung volumes and in circumferences was found to be approximately linear within a considerable range of tidal volumes. In the group investigated-under the condition of quiet respiration in the semirecumbent position-the fraction of abdominal breathing was found to be 0.64, on average.

Maintained cardiac output during positive end-expiratory pressure ventilation in open-chest pigs

Background:Does ventilation with positive end‐expiratory pressure (PEEP) act to reduce cardiac output (CO) not only by impeding venous return but also by inducing myocardial depression? The present study was aimed to demonstrate the possible existence of this latter mechanism.