[Cardiopulmonary effects of CPPV (continuous positive pressure ventilation) and IRV (inverse ratio ventilation) in experimental myocardial ischemia]

Continuous positive pressure ventilation (CPPV) is an established therapy for treatment of acute respiratory failure (ARF). However, cardiac performance may be severely disturbed due to elevated intrathoracic pressure, inducing a decrease in cardiac output (CO) and oxygen delivery (DO2). Alternatively, mechanical ventilation with prolonged inspiratory to expiratory duration ratio (inversed ratio ventilation IRV) has been successfully used in ARF. No data are available about IRV in acute haemodynamic oedema. Thus, the cardiopulmonary effects of CPPV (positive end-expiratory pressure [PEEP] = 10 cm H2O) and IRV (inspiration to expiration duration ratio [I:E] = 3.0) were studied in nine dogs (body weight 29.9 +/- 4.3 kg) before and after induction of myocardial ischaemia. METHODS. Continuous intravenous anaesthesia and muscle paralysis were provided by 1.2 mg.kg-1 x h-1 piritramide and 0.08 mg.kg-1 x h-1 pancuronium, and the animals were ventilated with intermittent positive pressure ventilation (IPPV) as reference method. Cardiocirculatory performance was determined by means of heart rate (HR), mean arterial pressure (MAP), mean pulmonary arterial pressure (MPAP), central venous pressure (CVP), pulmonary artery occlusion pressure (PAOP) and left ventricular end-diastolic pressure (LVEDP). Cardiac output (CO) was determined by thermodilution method. Systemic vascular resistance (SVR) was calculated. Pulmonary function was assessed by arterial and mixed venous blood gas tension for oxygen (PaO2, PvO2) and carbon dioxide (PaCO2). Functional residual lung capacity (FRC) was measured by means of the foreign gas wash-in method using helium as inert gas, and determination of extravascular lung water (EVLW) using the thermal-dye indicator technique. CPPV and IRV were studied in random sequence in the control phase and 60 min after induction of acute left ventricular ischaemia, which was achieved by occlusion of the ramus interventricularis anterior. RESULTS. During the control phase CPPV induced an increase in MPAP (P < 0.05), CVP (P < 0.05) and PAOP (P < 0.05). HR and MAP remained unchanged, whereas CO decreased by 16% (P < 0.05). FRC was elevated by 25 ml.kg-1 (P < 0.01), but not EVLW (9.1 +/- 3.5 ml.kg-1). There was no improvement in oxygenation; instead, oxygen delivery (DO2) decreased (P < 0.05). During inversed ratio ventilation MPAP, CVP, PAOP increased, but less than during CPPV. FRC was elevated mu 7.0 ml.kg-1 (P < 0.05), which was significantly less than during CPPV (P < 0.05). EVLW revealed no differences. During IPPV in the ischaemia phase cardiopulmonary performance deteriorated significantly. CO decreased by 19% (P < 0.05), whereas HR, MPAP, CVP and PAOP increased (P < 0.05). PaO2 was lower (P < 0.05) and alveolo-arterial PO2 gradient (PAaO2) increased (P < 0.05). All animals revealed moderate pulmonary oedema (EVLW = 15.1 +/- 8.4 ml.kg-1) (P < 0.01) and a lower FRC. Mechanical ventilation with PEEP significantly improved oxygenation and FRC; however, DO2 was slightly lower than during IPPV (not significant). IRV elevated PaO2, FRC and DO2, since CO was not depressed when compared with IPPV. CONCLUSIONS. CPPV and IRV may induce a recruitment of collapsed or hypoventilated lung areas, which is more pronounced during CPPV. During both modes of ventilation, oxygenation was improved without apparent changes in EVLW. Haemodynamic performance was more impaired during CPPV, and no improvement of left ventricular function secondary to an elevated intrathoracic pressure was observed. Occlusion of the RIVA coronary artery typically induces an infarction of 35% of left ventricular muscle mass; however, non-ischaemic myocardium reveals an unchanged or increased contractility. Thus, a reduction of left ventricular preload secondary to CPPV mainly contributes to haemodynamic depression, which is less pronounced during IRV due to a lower peak inspiratory airway pressure and mean airway pressure. IRV may be useful for mechanical ventCntCo

Gas exchange impairment and pulmonary densities after cardiac surgery

In 11 patients with impaired respiratory function after coronary artery revascularization surgery, thoracic computed tomography (TCT) and cardiopulmonary profile were obtained. The patients were haemodynamically stable without clinical or radiological signs of lung oedema. Oxygenation was reduced in all patients (alveolo-arterial PO2-difference (PA-aO2) = 37.3 +/- 10.39 kPa, venous admixture (QVA/QT) = 26.4 +/- 4.4%) during mechanical ventilation with positive end-expiratory pressure (PEEP = 5 cmH2O) (0.5 kPa). TCT-scan analysis revealed considerable amounts of crest-shaped bilateral densities in dependent lung regions. There were no differences between the right and left hemithorax. Atelectatic lung tissues were defined as areas presenting with attenuation values of -200 to +20 Hounsfield Units. The magnitude of non-ventilated areas correlated with QVA/QT (r = 0.875, P < or = 0.01), but not with the duration of either extracorporeal circulation, surgical procedure or general anaesthesia. It is concluded that atelectasis in dependent lung areas contributes to impaired gas exchange after cardiac surgery.

Aortic annular enlargement with the use of a homograft valve

A technique of annular enlargement for use in homograft aortic valve surgery is described. Potential advantages of this technique, that allows convenient valve sizes in small aortic annuli, lie in the pediatric group of patients requiring aortic valve replacement.

Echinococcal cyst of the interventricular septum: a rare cause of myocardial ischemia

A 30-year-old woman developed ischemia-like chest pain due to myocardial compression by an intracardiac cyst. The cyst was located in the interventricular septum. Its etiology could not be ascertained despite several diagnostic measures but exstirpation was indicated by the clinical symptoms. Intraoperatively the diagnosis of echinococcosis was established. The cyst was extirpated in toto without perforation of the thinned interventricular septum. Postoperatively the patient was symptomfree.

[Initial clinical experiences with a transvenous-subcutaneous defibrillation system]

In 19 patients with an indication for an implantable defibrillator, it was tried to avoid thoracotomy by using two electrodes positioned via the subclavian vein in the right ventricle (for pacing, sensing, and defibrillation) and the superior vena cava or coronary sinus (for defibrillation), and one electrode positioned subcutaneously near the ventricular apex (for defibrillation). In 17 patients (89%) the transvenous-subcutaneous leads were implanted, whereas in the remaining two patients an epi-/pericardial lead system was subsequently used due to an insufficient defibrillation threshold. Perioperatively, no major complications were observed and patients were rapidly mobilized. Within a follow-up period of 7 +/- 4 months, no malfunction of the lead system became evident. Sixty-eight episodes of spontaneous ventricular tachyarrhythmias occurred, all of which were successfully terminated. In one patient an infection of the lead system developed after 2 months that proved refractory to antibiotics and required surgical removal. Thus, transvenous-subcutaneous placement of leads for implantable defibrillators yielded a sufficient defibrillation threshold in the majority of patients. Long-term efficacy was excellent and no malfunctions were observed. This approach seems to be feasible and advisable in patients with an increased risk for thoracotomy.

Cardiopulmonary effects of constant-flow ventilation in experimental myocardial ischaemia

The cardiopulmonary effects of constant-flow ventilation were investigated in dogs with normal heart function (control-phase, n = 14) and after development of acute myocardial ischaemia (ischaemia phase, n = 14). Heated, humidified and oxygen-enriched air was continuously delivered with an inspiratory flow rate of 1.21.kg-1.min-1 via two catheters positioned within each mainstem bronchus. Continuous positive pressure ventilation with a positive end-expiratory pressure of 0.5 kPa (5 cmH2O) was used as a reference. During control, neither continuous positive pressure ventilation nor constant-flow ventilation showed impairment of cardiopulmonary performance. Oxygenation and CO2 removal were more efficiently achieved by continuous positive pressure ventilation (P less than or equal to 0.05). Acute myocardial ischaemia was induced by occlusion of the left anterior descending (LAD) coronary artery; measurements during the ischaemia phase were performed 60 min following LAD occlusion. Myocardial ischaemia resulted in moderate changes of cardiac output, left ventricular end-diastolic pressure and dP/dtmax. Both modes of ventilation were well tolerated in the ischaemia phase, and cardiovascular performance revealed no significant differences between continuous positive pressure ventilation and constant-flow ventilation. Haemodynamic parameters could be more precisely assessed during constant-flow ventilation. Oxygenation deteriorated, but hypoxaemia did not occur in any animal and CO2 elimination remained unchanged. It is concluded that 'non-conventional' ventilation by continuous intrabronchial gas flow maintains adequate gas exchange with no adverse effects on haemodynamics in dogs with acute myocardial ischaemia. Constant-flow ventilation may be advantageous in the experimental setting to study cardiac function without cyclic heart-lung interaction due to airway pressure alterations.

Cardiopulmonary effects of internal cardioverter/defibrillator implantation

Cardiopulmonary effects of electrophysiological testing of internal cardioverter/defibrillator (ICD) devices were studied in ten patients undergoing general anaesthesia. In the control-phase, haemodynamic performance and oxygenation were slightly impaired. After completion of the electrophysiological procedures (ICD-phase), cardiopulmonary function had deteriorated significantly. Cardiac index declined by 16%, whereas left ventricular filling pressure and pulmonary vascular resistance increased (P less than or equal to 0.01). Oxygenation, but not CO2-elimination deteriorated (P less than or equal to 0.01) and venous admixture increased by 72% (P less than or equal to 0.01). Alveolo-arterial PO2-difference (PA-aO2) increased by 43% (P less than or equal to 0.01), indicating ventilation-perfusion (VA/Q) mismatching. Repeated inductions of ventricular tachycardia and/or fibrillation subject the myocardium to transient global ischaemia, leading to acute congestive heart failure, and positive inotropic intervention was necessary in 40% of the patients. Partial pulmonary insufficiency resulted possibly from interstitial oedema and VA/Q-inhomogeneities. ICD implantation has detrimental effects on haemodynamics and gas exchange in patients with impaired left ventricular function.

Effects of enflurane on inducibility of ventricular tachycardia

The effects of enflurane on cardiac electrophysiologic parameters and on inducibility of ventricular tachycardia (VT) by programmed stimulation were studied in 12 patients (11 men, 1 woman, mean age +/- standard deviation 55 +/- 8 years) with drug refractory sustained monomorphic VT who underwent transcatheter ablation with high-energy direct-current shocks. One catheter ablation procedure was performed in 10 patients, whereas 2 ablation sessions were necessary in 2 patients. Programmed ventricular stimulation was performed on 2 separate days (mean interval 19). There were 2 baseline studies, 1 several days before ("baseline study I") and the second at the beginning of the ablation procedure ("baseline study II") while the patient was awake and nonsedated. The third programmed stimulation study was done 15 to 30 minutes after administration of anesthesia with enflurane, oxygen and nitrous oxide ("enflurane study"). Rate of sinus rhythm, QRS duration, PQ interval and ventricular effective refractory period were unaltered, whereas QTc interval increased significantly after initiation of anesthesia. Before and after induction of general anesthesia, clinical VT was inducible in all patients. However, in 1 patient, induction of VT was only possible by pacing in the left ventricle after enflurane administration. Based on these data, it is concluded that general anesthesia with enflurane, oxygen and nitrous oxide has no marked influence on inducibility of clinical VTs. Therefore, this type of anesthesia may be useful for nonpharmacologic, ablative procedures requiring general anesthesia.

High frequency jet ventilation in experimental pulmonary emphysema

The effects of high frequency jet ventilation (HFJV, f = 2 Hz and 8 Hz, I:E = 0.43, FiO2 = 0.4) were studied and compared with intermittent positive pressure ventilation (IPPV, f = 10-14 breaths/min, VT = 15 ml/kg, I:E = 0.5, FiO2 = 0.4) in 8 dogs before and after induction of panlobular emphysema (PLE). PLE increased alveolar-arterial PO2 difference (PA-aO2) during all modes of ventilation, whereas PaCO2 did not change significantly. In both periods of the study, HFJV8 Hz was less effective in terms of CO2-elimination and oxygenation. In the control-period, functional residual capacity (FRC) was 937 +/- 212 ml. The increase during HFJV (HFJV2 Hz: 1156 +/- 508 ml, HFJV8 Hz: 1153 +/- 433 ml) did not reach significance (P = 0.09). Closing volume (CV) increased from 1.5 +/- 4.3% of vital capacity (%VC) (IPPV) to 6.3 +/- 7.1%VC (HFJV2 Hz) and 10.8 +/- 9.8% VC (HFJV8 Hz), respectively. In the PLE-period, FRC and CV increased significantly to 1107 +/- 207 ml and 14.1 +/- 7.0% VC respectively during IPPV (P less than 0.05). Application of HFJV neither increased FRC (HFJV2 Hz: 1153 +/- 433 ml, HFJV8 Hz: 1005 +/- 344 nor CV 14.8 +/- 6.0% VC and 13.9 +/- 8.1% VC, respectively). It is concluded that HFJV induces no alveolar overdistension in dogs with emphysematous lungs.

[Artificial respiration in the prone position in a case of acute respiratory distress syndrome]

A patient is presented in whom an acute respiratory distress syndrome (ARDS) developed after severe lung contusion. Exchange of gas was markedly restricted under aggressive respiration (FiO2 = 1.0, PEEP = 10 mmHg, breathing time quotient = 0.5, respiratory minute volume = 16 litres; gas exchange values: PaO2 = 67 mmHg, PaCO2 = 45 mmHg, PA-aO2 = 461 mmHg). After control of the computed tomogram of the lungs showed marked densifications in those parts of the lung that are lower most by gravitation according to the positioning of the patient at a particular time the patient was ventilated in ventricumbent (prone) position for 60 hours. After having remained in this position for 48 hours, there was a significant improvement in the gas exchange (PaO2 = 89 mmHg, PaCO2 = 36 mmHg, PA-aO2 = 77 mmHg at FiO2 = 0.3, PEEP = 6 mmHg, breathing time quotient = 0.5 and respiratory minute volume = 9 litres). The control CT in dorsal position showed that the dorsal densifications had disappeared completely. Five days later the patient could be extubated. Respiration in ventricumbent (prone) position may considerably improve oxygenation by perfusion of well-ventilated regions of the lung that are lower-most by gravitation according to the relative positioning of the patient. Besides regions not well ventilated or not ventilated at all (according to the patient's position) may be better ventilated or re-opened and made accessible to ventilation by this method.

[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.

Implantable cardioverter/defibrillators (ICD): a new lead-system using transvenous-subcutaneous approach in patients with prior cardiac surgery

The current approach in cardioverter-defibrillator implantation requires placement of epicardial leads which may lead to pericardial and/or pleural effusion and pneumonia during the perioperative period. Although ICD implantation is less invasive than other surgical techniques for the treatment of rhythm disturbances, the perioperative mortality must be considered. Minimizing the operative procedure could lead to a reduction in perioperative mortality. Therefore, we investigated an approach without the need for thoracotomy using a transvenous/subcutaneous lead system. In nine patients with prior cardiac surgery, defibrillator implantation was performed by a transvenous/subcutaneous approach. There was no perioperative mortality. In all patients, a sufficient defibrillation threshold was achieved. The defibrillation pulses were delivered as two sequential pulses between a right ventricular electrode (cathode) and a coronary sinus or superior caval vein electrode (anode 1) and a subcutaneous patch electrode (anode 2). Intubation of the coronary sinus was necessary in 4 patients in order to obtain satisfactory defibrillation thresholds. These data demonstrate that a transvenous/subcutaneous approach is feasible in patients with prior cardiac surgery obviating the need for thoracotomy. Sensing function of the RV-electrode, intubation of the coronary sinus and the intraoperative use of an epicutaneous patch electrode are current problems of this new technique.

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)

[Mixed venous versus central venous oxygen saturation in intensive medicine]

Mixed venous oxygen saturation (SvO2) has been established as a useful guide in observing whole body oxygenation. Since SvO2 provides limited information about adequate tissue oxygenation for a specific organ, the usefulness of central venous saturation (ScvO2) as a guide was analysed, which is a less invasive parameter. In 19 ICU patients 44 pairs of blood samples were drawn from a separate central venous catheter and from the tip of an SG-catheter. The correlation of oxygen partial pressures was 0.687 and the correlation of the saturation reached 0.779. The calculation of venous admixture showed a correlation of 0.901. It is concluded that ScvO2 yields adequate information on the oxygen saturation of venous return.

Constant-flow ventilation in canine experimental pulmonary emphysema

The efficacy of constant-flow ventilation (CFV) was investigated in eight mongrel dogs before (control-phase) and after development of papain-induced panlobular emphysema (PLE-phase). For CFV, heated, humidified and oxygen-enriched air was continuously delivered via two catheters positioned within each mainstem bronchus at flow rates (V) of 0.33, 0.5 and 0.66 l/s. Data obtained during intermittent positive pressure ventilation (IPPV) served as reference. In the control-phase, Pao2 was lower (P less than or equal to 0.05) and alveolo-arterial O2 difference (P(A-a)O2) was higher (P less than or equal to 0.01) during CFV at all flow rates when compared with IPPV. This may be due to inhomogeneities of intrapulmonary gas distribution and increased ventilation-perfusion (VA/Q) mismatching. Paco2 and V showed a hyperbolic relationship; constant normocapnia (5.3 kPa) was achieved at 0.48 +/- 0.21 l/s (V53). Development of PLE resulted in an increase of functional residual capacity (FRC), residual volume (RV) and static compliance (Cstat) (P less than or equal to 0.05). PaO2 had decreased and P(A-a)O2 had increased (P less than or equal to 0.05), indicating moderate pulmonary dysfunction. Oxygenation during CFV was not significantly different in the PLE-phase when compared with the control-phase. Paco2 and V showed a hyperbolic relationship and V5.3 was even lower than in the control-group (0.42 +/- 0.13 l/s). In dogs with emphysematous lungs CFV maintains sufficient gas exchange. This may be due to preferential ventilation of basal lung units, thereby counterbalancing the effects of impaired lung morphometry and increased airtrapping. Conventional mechanical ventilation is more effective in terms of oxygenation and CO2-elimination.

Single breath N2 washout in papain-induced pulmonary emphysema

Single breath nitrogen washout tests were analyzed in dogs (n = 8) with healthy lungs and after development of emphysema. The animals were in the supine position and studied during anaesthesia and mechanical ventilation (FiO2 = 0.4, FiN2 = 0.6). During controlled expiration with constant flow (VE = 0.15 l/s) onset of phase IV of the alveolar plateau was related to airway closure of dependent lung regions (closing volume CV). In the control state, CV accounted for 6.2 +/- 1.5% VC, and closing capacity (CC) was lower than functional residual capacity (FRC). Likewise, gas exchange was normal in all animals (PaO2 = 24.7 +/- 3.32 kPa, PaCO2 = 5.18 +/- 0.53 kPa, PA-aO2 = 2.6 +/- 0.3 kPa). Panlobular emphysema (PLE) was induced by inhalation of papain (100 mg/kg). After three weeks development of PLE was documented by measurements of lung volumes (functional residual capacity (FRC), expired vital capacity (EVC), total lung capacity (TLC), residual volume (RV], pulmonary mechanics (dynamic and static compliance (Cdyn, Cstat), mean airway resistance (Raw], gas exchange (PaO2, PaCO2, PA-aO2), and by radiomorphological analysis. In the PLE-group, FRC and RV (p less than or equal to 0.05), and Cstat (p less than or equal to 0.01) were significantly elevated. CV increased to 16.2 +/- 2.7% VC (p less than or equal to 0.01) and CC exceeded FRC by 80 ml, indicating that tidal volume breathing took place within the range of closing volume. Oxygenation was significantly impaired (PaO2 = 18.6 +/- 3.72 kPa, PA-aO2 = 6.5 +/- 1.1 kPa, p less than or equal to 0.05), but not CO2-elimination. Pathological analysis by radiomorphological means showed dissiminate parenchymal lesions compatible with emphysema of grade II severity located predominantly in subpleural areas. In dogs with papain-induced PLE, premature closure of dependent airways is enhanced, which is due to structural changes and a loss of elastic recoil in the lungs.

High-frequency jet ventilation during oleic-acid induced pulmonary oedema

In oleic acid-induced pulmonary oedema (OAPO) sequential intrapulmonary fluid accumulation occurs leading to different expiratory flow pattern in dependent lung regions. The potential effects on efficacy of high-frequency jet ventilation (HFJV, f = 3 Hz, I: E = 0.43, FiO2 = 0.4) were studied and compared with continuous positive pressure ventilation (CPPV, f = 12-18/min, I:E = 0.5, TV = 12 ml/kg, PEEP = 0.5 kPa, FiO2 = 0.4) in a dog model of OAPO. In the control state (lung-healthy dogs), 15 min after oleic acid lung injury (interstitial oedema, period I) and 60 min after onset of OAPO (alveolar oedema, period II), gas exchange, lung volumes, compliance, resistance and haemodynamics were measured. The course of lung oedema was determined indirectly by means of washout curves of helium (foreign gas bolus-test, FGB) and nitrogen (single breath-test for oxygen, SBO2). During control, there were no significant differences between the HFJV-group (n = 7) and the CPPV-group (n = 6) by virtue of gas exchange, lung volumes and haemodynamics. During period I, PaO2 decreased significantly both with HFJV (p less than 0.01) and CPPV (p less than 0.05), being lower in the HFJV-group (p less than 0.05). PaCO2, pulmonary and haemodynamic parameters were unchanged. Onset of phase IV of the alveolar plateau (closing volume CV) occurred significantly earlier (p less than 0.05) in all animals. Impaired ventilation of dependent lung regions, increased maldistribution of intrapulmonary gas and VA/Q-mismatching may be the underlying mechanisms for lower efficacy of HFJV during interstitial lung oedema. In period II, pulmonary and cardiocirculatory parameters had changed significantly in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential ventilation with low-flow CPAP and CPPV in the treatment of unilateral chest trauma

A case of severe unilateral chest trauma with bronchopleural fistula is presented. Ventilatory therapy consisted of asynchronous independent lung ventilation (AILV). The injured lung was ventilated with intermittent positive pressure ventilation (IPPV) [tidal volume (TV) = 200 ml, f = 25/min, I:E = 0.5, minute volume (MV) = 5.0 l/min, FiO2 = 0.4], and the unaffected lung was ventilated with continuous positive pressure ventilation (CPPV) (TV = 600 ml, f = 12/min, I:E = 0.5, MV = 7.2 l/min, PEEP = 0.5 kPa, FiO2 = 0.4). Adequate gas exchange was obtained (PaO2 = 14.5 +/- 2.3 kPa, PaCO2 = 5.5 +/- 0.7 kPa), but high air leakage volumes persisted. Thus, differential low-flow CPAP (V = 5.0-7.5 l/min, PEEP = 0.5 kPa, FiO2 = 0.4) of the injured lung and CPPV (TV = 600 ml, f = 12/min, MV = 7.2 l/min, I:E = 0.5, PEEP = 0.5 kPa, FiO2 = 0.4) of the unaffected lung was applied for 36 hours. Further deterioration of pulmonary function was prevented, and the bronchopleural fistula closed after several hours. After another period of AILV the patient was treated with conventional mechanical ventilation, and finally weaned with high-flow CPAP.