Intensive Care Med (1992) 18:299-303
IntensiveCare Medicine 9 Springer-Verlag1992
A comparison of continuous positive pressure ventilation, combined high frequency ventilation and airway pressure release ventilation on experimental lung injury* I. Jousela, K. Linko and A. M~ikel~iinen Department of Anaesthesia, Helsinki University Central Hospital, Helsinki, Finland Received: 23 February 1992; accepted: 7 April 1992
Abstract In pigs with oleic induced lung injury, the effectiveness of combined high frequency ventilation (CHFV, with VDR-Phasitron) and airway pressure release ventilation (APRV) were compared to continuous positive pressure ventilation (CPPV) in a randomized study. The respiratory rate was 15/min, CPAP 8 m m H g and FiO2 0.25. PaCO2 was maintained at 5 kPa. PaO2 was significantly lower with APRV (12.5 + 3.9 kPa, CPPV: 15.8 • 3.9 kPa, and CHFV: 15.5_ 3.2 kPa). This was in accordance with the lowest peak airway pressure during APRV ( 2 0 . 9 + 4 . S m m H g , CPPV: 26.3 +_4.4 m m H g and CHFV: 28.2_+ 3.7 mmHg). There was no difference in the pericardiac pressure between the 3 ventilation modes. The pressure related depressive effects on the cardiovascular function during C H F V and APRV were similar to those during CPPV. Adequate oxygenation and ventilation could be achieved with both C H F V and APRV, but these methods were not superior to CPPV. Key words: High frequency ventilation - Airway pressure release ventilation - Mechanical ventilation CPAP - Pig
Airway pressure release ventilation (APRV) is a techniques of continuous positive airway pressure (CPAP) with an intermittent release o f pressure to a lower airway pressure level [1]. The cyclic decrease in airway pressure allows gas to passively leave the lungs, thus eliminating COz. Then airway pressure rapidly returns to the original higher level, thus increasing lung volume [1]. R~ts~inen et al. have shown that the peak airway pressure in dogs is lower during APRV than with CPPV with less cardiovascular depression [7]. The C H F V used here is a combination of diffusive and conventional ventilation thus producing periods of larger and smaller tidal volumes at high frequency so that in gross shape it resembles APRV, with its high and lower (release) pressure phases. The aim of the present study was to compare three techniques of mechanical ventilation i.e. CPPV, C H F V and APRV as regards gas exchange and cardiovascular function in acute experimentally induced lung injury in pigs.
Material and methods
Animals and anaesthesia Newer methods of ventilation therapy have been developed in order to achieve more effective gas exchange and to minimize the deleterious effects of high airway pressures on the pulmonary and cardiovascular systems in patients with lung injury [ 1 - 6 ] . Combined high frequency ventilation (CHFV) is a combination of large tidal volume mechanical breaths along with high frequency ventilation. The high frequency waves are claimed to improve carbon dioxide (COz) washout [61. Although high frequency ventilation is an effective mode of ventilation in pigs [4], it is unknown whether C H F V provides any advantages over continuous positive pressure ventilation (CPPV).
Eleven healthy pigs weighing 15-20kg (mean 16.7kg) were sedated with intramuscular ketamine20 mg/kg and azaperone 4 mg/kg. The ear vein was cannulated through which diazeparn 5 mg was injected. The pigs were intubated and ventilated with a Servo 900 B ventilator using intermittent positive pressure delivered at 15/rain with a FiO2 of 0.25. The pigs were placed supine on a heated mattress and coveredwith the body temperature kept at 37 ~ Anaesthesia was maintained with a continuous intravenous infusion of diazeparn (0.5 mg/kg/h), azaperone (4 mg/kg/h) and ketamine (4 mg/kg/h) through a physiological saline solution (15 ml/kg/h) and when needed, increments of diazeparn (2-2.5 rng) were given. During the instrumentation halothane (up to 0.5~ and tubocurarine (2 mg) were administered. Whole blood and hydroxyethyl starch solution (HES 120, Plasmafusin, Orion, Finland), both 15 ml/kg were infused during the preparation and, additionally if needed for circulatory support when the lung injury was developing.
Cathetrization and monitoring * The study was supported by Instrumentariumin Tiedes~i~tti6
A catheter (Leadercath, Vygon) was inserted into the femoral artery, and a fiberoptic pulmonary artery catheter (Opticath U440, Oximetrix
300 Inc, Mountain View, USA) was placed into the pulmonary artery via the femoral vein under pressure control and a fluidfilled 16 G Teflon catheter was inserted into the pericardium. The mid-thoracic line was taken as zero reference for the vascular and pericardiac pressures. The arterial oxygen saturation (SpO2) was continuously monitored from the nose of the animal as was the end tidal carbon dioxide (ETCO2) and FiO2 from the endotracheal tube (Cardiocap, Datex Oy, Helsinki, Finland). Airway pressure (Paw) from the tracheal end of the endotracheal tube was recorded, as were all the other pressures. Thermodilution cardiac output values were calculated from three injections of 5 ml of physiological saline solution at room temperature at a random moment in the respiratory cycle. Mixed venous oxygen saturation was continuously monitored with the fiberoptic pulmonary catheter (Oximetrix 3 System, SvO2/CO computer, Abbott Critical Care Systems, North Chicago, IL, USA). Arterial and pulmonary artery samples were drawn for prompt determination of blood gases (ABL2, Radiometer, Denmark) and oxygen saturation of haemoglobin (SaO2) (CO-Oximeter 282, Instrumentation Laboratory Inc, USA). The continuous SvO2 measurement was controlled by blood samples after insertion of the catheters and after the lung injury.
Protocol
CPAP of 8 mmHg was added after the measurements following the lung injury were made. ETCO z was kept to 5.0 kPa by adjusting the respirator tidal volume during CPPV and APRV. During CHFV blood samples were used instead of ETCO 2 for technical reasons. The measurements were made before (CON), and after the lung injury (ALI), and following each of the three ventilation modes (CPPV, CHFV, APRV). Vascular, pericardiac and airway pressures obtained from the pressure tracings were averaged for one complete respiratory cycle during each ventilation mode. Cardiac index (CI) and stroke volume index (SI) were calculated per body weight. LVSW, RVSW and oxygen delivery and consumption were calculated using standard formulae with CI and oxygen content difference.
Statistics The results are expressed as mean and standard deviation (SD). Differences between each ventilation mode were analyzed using the GLM procedure (analysis of variance) and Tuckey's studentized range test in SAS programme package. Statistical significance was taken at p < 0.05.
Results
Lung injury
The study was approved by the Committee on Ethics of the Department of Anaesthesia and the Animal Experiment Committee at Helsinki University Central Hospital. After a 30 min stabilization period following the insertion of the catheters, the lung injury was induced by injecting oleic acid within 5 rain through the central venous port of the pulmonary catheter (0.08 ml/kg, diluted with physiological saline solution to a volume of 5 ml). After 90 rain of stabilization with intermittent positive pressure ventilation, the pigs were ventilated in a random order for 30 rain each with the 3 ventilation modes: CPPV (Servo 900 B, Siemens-Elema, Solna, Sweden), CHFV (VDR with phasitorn, Bird corporation, USA) and APRV (Downs adjustable flow generator, Vital Signs, East Rutherford, N J, USA and pressure driven APRV timer prototype, Medith Oy, Espoo, Finland). FiO 2 was maintained at 0.25 throughout the study and ventilation frequency at 15/rain. The oscillating frequency of CHFV was maintained at 360/rain and I/E-ratio of high frequency at 1:1 during the low and high pressure phases with a driving pressure of 35 psi. A combination of diffusive and conventional ventilation produced here CHFV where the variation of the periods of larger and smaller tidal volume with high and lower peak airway pressure phases formed a combination which resembled APRV in gross shape. The release time for APRV and the low pressure time (with small tidal volume breaths) for CHFV was 1.5 s. On the contrary, the inspiratory time for CPPV was 1.5 s which produced an inspiration to expiration ratio of 0.6.
OA
SvO 2
I
I
I
I
I
Oleic acid administration resulted in a fall in PaO2 from 15.3+2.3 kPa to 7.5_+2.0 kPa (/7
IntensiveCare Medicine 9 Springer-Verlag1992
A comparison of continuous positive pressure ventilation, combined high frequency ventilation and airway pressure release ventilation on experimental lung injury* I. Jousela, K. Linko and A. M~ikel~iinen Department of Anaesthesia, Helsinki University Central Hospital, Helsinki, Finland Received: 23 February 1992; accepted: 7 April 1992
Abstract In pigs with oleic induced lung injury, the effectiveness of combined high frequency ventilation (CHFV, with VDR-Phasitron) and airway pressure release ventilation (APRV) were compared to continuous positive pressure ventilation (CPPV) in a randomized study. The respiratory rate was 15/min, CPAP 8 m m H g and FiO2 0.25. PaCO2 was maintained at 5 kPa. PaO2 was significantly lower with APRV (12.5 + 3.9 kPa, CPPV: 15.8 • 3.9 kPa, and CHFV: 15.5_ 3.2 kPa). This was in accordance with the lowest peak airway pressure during APRV ( 2 0 . 9 + 4 . S m m H g , CPPV: 26.3 +_4.4 m m H g and CHFV: 28.2_+ 3.7 mmHg). There was no difference in the pericardiac pressure between the 3 ventilation modes. The pressure related depressive effects on the cardiovascular function during C H F V and APRV were similar to those during CPPV. Adequate oxygenation and ventilation could be achieved with both C H F V and APRV, but these methods were not superior to CPPV. Key words: High frequency ventilation - Airway pressure release ventilation - Mechanical ventilation CPAP - Pig
Airway pressure release ventilation (APRV) is a techniques of continuous positive airway pressure (CPAP) with an intermittent release o f pressure to a lower airway pressure level [1]. The cyclic decrease in airway pressure allows gas to passively leave the lungs, thus eliminating COz. Then airway pressure rapidly returns to the original higher level, thus increasing lung volume [1]. R~ts~inen et al. have shown that the peak airway pressure in dogs is lower during APRV than with CPPV with less cardiovascular depression [7]. The C H F V used here is a combination of diffusive and conventional ventilation thus producing periods of larger and smaller tidal volumes at high frequency so that in gross shape it resembles APRV, with its high and lower (release) pressure phases. The aim of the present study was to compare three techniques of mechanical ventilation i.e. CPPV, C H F V and APRV as regards gas exchange and cardiovascular function in acute experimentally induced lung injury in pigs.
Material and methods
Animals and anaesthesia Newer methods of ventilation therapy have been developed in order to achieve more effective gas exchange and to minimize the deleterious effects of high airway pressures on the pulmonary and cardiovascular systems in patients with lung injury [ 1 - 6 ] . Combined high frequency ventilation (CHFV) is a combination of large tidal volume mechanical breaths along with high frequency ventilation. The high frequency waves are claimed to improve carbon dioxide (COz) washout [61. Although high frequency ventilation is an effective mode of ventilation in pigs [4], it is unknown whether C H F V provides any advantages over continuous positive pressure ventilation (CPPV).
Eleven healthy pigs weighing 15-20kg (mean 16.7kg) were sedated with intramuscular ketamine20 mg/kg and azaperone 4 mg/kg. The ear vein was cannulated through which diazeparn 5 mg was injected. The pigs were intubated and ventilated with a Servo 900 B ventilator using intermittent positive pressure delivered at 15/rain with a FiO2 of 0.25. The pigs were placed supine on a heated mattress and coveredwith the body temperature kept at 37 ~ Anaesthesia was maintained with a continuous intravenous infusion of diazeparn (0.5 mg/kg/h), azaperone (4 mg/kg/h) and ketamine (4 mg/kg/h) through a physiological saline solution (15 ml/kg/h) and when needed, increments of diazeparn (2-2.5 rng) were given. During the instrumentation halothane (up to 0.5~ and tubocurarine (2 mg) were administered. Whole blood and hydroxyethyl starch solution (HES 120, Plasmafusin, Orion, Finland), both 15 ml/kg were infused during the preparation and, additionally if needed for circulatory support when the lung injury was developing.
Cathetrization and monitoring * The study was supported by Instrumentariumin Tiedes~i~tti6
A catheter (Leadercath, Vygon) was inserted into the femoral artery, and a fiberoptic pulmonary artery catheter (Opticath U440, Oximetrix
300 Inc, Mountain View, USA) was placed into the pulmonary artery via the femoral vein under pressure control and a fluidfilled 16 G Teflon catheter was inserted into the pericardium. The mid-thoracic line was taken as zero reference for the vascular and pericardiac pressures. The arterial oxygen saturation (SpO2) was continuously monitored from the nose of the animal as was the end tidal carbon dioxide (ETCO2) and FiO2 from the endotracheal tube (Cardiocap, Datex Oy, Helsinki, Finland). Airway pressure (Paw) from the tracheal end of the endotracheal tube was recorded, as were all the other pressures. Thermodilution cardiac output values were calculated from three injections of 5 ml of physiological saline solution at room temperature at a random moment in the respiratory cycle. Mixed venous oxygen saturation was continuously monitored with the fiberoptic pulmonary catheter (Oximetrix 3 System, SvO2/CO computer, Abbott Critical Care Systems, North Chicago, IL, USA). Arterial and pulmonary artery samples were drawn for prompt determination of blood gases (ABL2, Radiometer, Denmark) and oxygen saturation of haemoglobin (SaO2) (CO-Oximeter 282, Instrumentation Laboratory Inc, USA). The continuous SvO2 measurement was controlled by blood samples after insertion of the catheters and after the lung injury.
Protocol
CPAP of 8 mmHg was added after the measurements following the lung injury were made. ETCO z was kept to 5.0 kPa by adjusting the respirator tidal volume during CPPV and APRV. During CHFV blood samples were used instead of ETCO 2 for technical reasons. The measurements were made before (CON), and after the lung injury (ALI), and following each of the three ventilation modes (CPPV, CHFV, APRV). Vascular, pericardiac and airway pressures obtained from the pressure tracings were averaged for one complete respiratory cycle during each ventilation mode. Cardiac index (CI) and stroke volume index (SI) were calculated per body weight. LVSW, RVSW and oxygen delivery and consumption were calculated using standard formulae with CI and oxygen content difference.
Statistics The results are expressed as mean and standard deviation (SD). Differences between each ventilation mode were analyzed using the GLM procedure (analysis of variance) and Tuckey's studentized range test in SAS programme package. Statistical significance was taken at p < 0.05.
Results
Lung injury
The study was approved by the Committee on Ethics of the Department of Anaesthesia and the Animal Experiment Committee at Helsinki University Central Hospital. After a 30 min stabilization period following the insertion of the catheters, the lung injury was induced by injecting oleic acid within 5 rain through the central venous port of the pulmonary catheter (0.08 ml/kg, diluted with physiological saline solution to a volume of 5 ml). After 90 rain of stabilization with intermittent positive pressure ventilation, the pigs were ventilated in a random order for 30 rain each with the 3 ventilation modes: CPPV (Servo 900 B, Siemens-Elema, Solna, Sweden), CHFV (VDR with phasitorn, Bird corporation, USA) and APRV (Downs adjustable flow generator, Vital Signs, East Rutherford, N J, USA and pressure driven APRV timer prototype, Medith Oy, Espoo, Finland). FiO 2 was maintained at 0.25 throughout the study and ventilation frequency at 15/rain. The oscillating frequency of CHFV was maintained at 360/rain and I/E-ratio of high frequency at 1:1 during the low and high pressure phases with a driving pressure of 35 psi. A combination of diffusive and conventional ventilation produced here CHFV where the variation of the periods of larger and smaller tidal volume with high and lower peak airway pressure phases formed a combination which resembled APRV in gross shape. The release time for APRV and the low pressure time (with small tidal volume breaths) for CHFV was 1.5 s. On the contrary, the inspiratory time for CPPV was 1.5 s which produced an inspiration to expiration ratio of 0.6.
OA
SvO 2
I
I
I
I
I
Oleic acid administration resulted in a fall in PaO2 from 15.3+2.3 kPa to 7.5_+2.0 kPa (/7
