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(Chest. 2000;117:191-198.)
© 2000 American College of Chest Physicians

The Relationship Between Gas Delivery Patterns and the Lower Inflection Point of the Pressure-Volume Curve During Partial Liquid Ventilation*

Gabriela Ferreyra, PT; Sven Goddon, MD; Yuji Fujino, MD and Robert M. Kacmarek, PhD, RRT, FCCP

* From the Department of Anaesthesia/Respiratory Care, Massachusetts General Hospital, Harvard Medical School, Boston, MA.

Correspondence to: Robert M. Kacmarek, PhD, FCCP, Respiratory Care, Ellison 401, Massachusetts General Hospital, Boston, MA 02114


   Abstract
TOP
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 Conclusion
 References
 
Study question: To determine whether a positive end-expiratory pressure (PEEP) level equivalent to the lower inflection point (LIP) could be identified by evaluation of the airway pressure, flow (), and volume vs time waveforms during partial liquid ventilation (PLV).

Design: Prospective application of PEEP during PLV in a healthy animal model.

Setting: University hospital animal laboratory.

Participants: Five healthy sheep weighing 30 kg each.

Interventions: The sequential application of 0 to 20 cm H2O PEEP in 2.5-cm H2O steps during PLV with both pressure and volume ventilation.

Measurements: Analysis of the pressure, volume, and waveforms as PEEP is sequentially increased.

Results: At 0 cm H2O PEEP, VT was markedly reduced compared with PEEP VT at >= 7.5 cm H2O (p < 0.05) in pressure control ventilation (PCV), and peak inspiratory pressure minus PEEP was markedly increased compared with PEEP at >= 5.0 cm H2O (p < 0.05) in volume control ventilation. At 10 cm H2O PEEP, all waveforms began to stabilize, and no significant differences in any variable assessed were measured at > 12.5 cm H2O PEEP.

Conclusions: The application of PEEP during PLV markedly alters airway waveforms. Low PEEP decreases VT in PCV and increases airway pressure in VCV. The PEEP level equal to the LIP during PLV can be grossly estimated from airway waveforms. PEEP at >= 10 cm H2O is needed to normalize gas delivery to functional residual capacity in the uninjured lung that is partially filled with perfluorocarbon.

Key Words: compliance • gas delivery pattern • lower inflection point • partial liquid ventilation • resistance


   Introduction
TOP
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 Conclusion
 References
 
Partial liquid ventilation (PLV) is the partial filling of the lung with a perfluorocarbon (PFC) and the provision of gas ventilation on top of the lung that is partially filled with PFC. Numerous animal studies1 2 3 and select patient studies4 5 6 7 have indicated that PLV improves lung mechanics and gas exchange during acute lung injury. However, since perflubron (LiquiVent; Alliance Pharmaceutical Corp; San Diego, CA), the PFC used in this study, has a high density (1.92 g/mL), there is a high initial impedance to gas ventilation, which can be overcome with the use of large tidal volumes (VTs).8 However, large VT ventilation during PLV induces further lung in-jury.9 10 Recently, it has been shown that impedance to gas ventilation can be reduced, lung mechanics can be improved, and gas exchange can be enhanced by the application of positive end-expiratory pressure (PEEP) above the lower inflection point (LIP) of the pressure-volume (P-V) curve of the total respiratory system in the lung partially filled with PFC.11 The setting of PEEP at this level allows the VT required to maintain gas exchange also to be reduced. Determination of the LIP, however, is not without problems; no commercially designed system is available, interruption of mechanical ventilation for 30 to 40 s is required, and careful performance of the procedure by two practitioners is necessary. Identification of the LIP on the P-V curve by a method that avoids the use of a super syringe would make the selection of PEEP levels (above LIP) during PLV easier and more precise. We questioned whether the level of PEEP consistent with the LIP during PLV could be estimated by changes in the gas delivery pattern and lung mechanics during incremental increases in PEEP. We studied the effects of 2.5-cm H2O increases in applied PEEP to a total PEEP of 20 cm H2O during both volume- and pressure-targeted ventilation in the noninjured lung that is partially filled with PFC.


   Materials and Methods
TOP
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 Conclusion
 References
 
The following protocol was approved by the Subcommittee on Research Animal Care of the Massachusetts General Hospital.

Preparation
Five fasted Hampshire sheep ([mean ± SD] body weight, 29.7 ± 3.9 kg) were anesthetized with halothane and were orally intubated using endotracheal tubes (HiLo Tube; Mallinckrodt Medical, Inc; St. Louis, MO) that had inner diameters of 9 mm. To ensure gastric drainage, a 14F orogastric tube (model 151–14; Mallinckrodt Laboratories Ltd; Athelone, Ireland) was inserted for each sheep. After cannulating the right jugular vein and administering a loading dose of fentanyl (0.3 mg) and diazepam (10 mg), anesthesia was maintained using fentanyl (3 µg/kg/h) and sodium pentobarbital (5 mg/kg/h), and paralysis was established with pancuronium bromide (2 mg/kg/h). Lactated Ringer’s solution was administered IV to maintain adequate intravascular volume. Body temperature was maintained at 39°C by the use of a heating blanket, and mechanical ventilation was provided (PB 7200 ae ventilator; Nellcor Puritan Bennett; Carlsbad, CA).

Experimental Protocol
Following the preparation of each animal and a stabilization period of 15 min, each animal was administered perflubron in the supine position until a meniscus could be observed at the incisors (PEEP, 0 cm H2O). A total dose of about 30 mL/kg was administered. Because of the short duration of the study period (< 2 h), no supplemental doses of PFC were given. Based on our prior experience with this model, we would expect <= 1 mL/kg of PFC to evaporate during the study. Each sheep was ventilated using both volume control ventilation (VCV) and pressure control ventilation (PCV) applied in random order. In the VCV mode, VT was 10 mL/kg, respiratory rate was 20 breaths/min, total inspiratory time was 1.5 s (with an inflation hold of 0.7 s), and the flow () pattern was square wave, set at 1 L/min/kg, yielding about 30 L/min on average. In the PCV mode, the inspiratory pressure was adjusted to deliver a VT of about 10 mL/kg at a set PEEP level of 10 cm H2O with a respiratory rate of 20 breaths/min and a total inspiratory time of 1.5 s. The fraction of inspired oxygen was 0.5 throughout the experiment in both PCV and VCV. In both modes of ventilation, the PEEP was increased sequentially in 2.5-cm H2O increments from 0 to 20 cm H2O. Following each increase, the animals were allowed to stabilize for 5 min before measurements were made. Based on prior experience with this model, ventilatory parameters were set to ensure that peak alveolar pressures (end-inspiratory plateau pressures [PPLATs]) were below the upper inflection point on the P-V curve of the total respiratory system throughout the spectrum of applied PEEP (Fig 1 ). Throughout this evaluation, the end-inspiratory PPLAT remained at < 35 cm H2O, and no auto-PEEP was measured in either PCV or VCV at any PEEP setting.



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  		Figure 1. P-V curve of the total respiratory system in a representative animal partially filled with PFC. Tangents drawn to the various slopes of the inspiratory curve were used to identify the LIP and UIP of the curve.

 
Measurements
Gas flow was monitored at the airway opening using a pneumotachometer (3700A; Hans Rudolph Inc; Kansas City, MO) with differential pressure transducer (model 45–32-871 ± 2; Validyne; Northridge, CA). Airway pressure was monitored using a pressure transducer (model 45–32-871 ± 100; Validyne) calibrated with a water manometer. VT was integrated using the signal and was reconfirmed with a 500-mL calibrated syringe. At each setting, we also measured total PEEP with an end-expiratory hold maneuver (for 5 s) using the auto-PEEP function of the mechanical ventilator. All signals were amplified (model 8805C; Hewlett Packard; Waltham, MA) and recorded at 100 Hz using an analog-to-digital conversion system (WINDAQ/200V1.36; Dataq Instruments; Hartfield, PA) and a personal computer. All devices were calibrated at the beginning of the experiment.

A P-V curve of the lung-thorax system was obtained using a calibrated 500-mL syringe to detect the LIP and a 2,000-mL syringe to detect the upper inflection point (UIP) after partial filling of the lung with PFC. After the establishment of a volume history to 50 cm H2O pressure, stepwise 50-mL inflations with a 500-mL syringe and 100-mL inflations with a 2,000-mL syringe were performed while recording the corresponding airway pressure before the stepwise sequential application of PEEP in 2.5-cm H2O increments. We stopped inflation when airway pressure exceeded 50 cm H2O. The total procedure lasted <= 30 s. The lung filled with liquid demonstrated a nonlinear P-V relationship. The pressures associated with changes in the slope of the P-V curve were identified as the LIP and UIP. LIP and UIP were determined from the crossing of tangents applied to the various slopes of the curve (Fig 1) .

In the VCV mode, peak , time from initiation of inspiration to peak , time from initiation of inspiration to 75% of peak , peak inspiratory pressure (PIP) minus PEEP, time from initiation of inspiration to PIP, and end-inspiratory PPLAT, were recorded at each level of PEEP. Inspiratory resistance was then calculated as peak pressure minus PPLAT divided by , and quasi-static compliance was calculated by dividing the PPLAT-PEEP by the VT. In the PCV mode, , peak pressure minus PEEP, time from initiation of inspiration to peak , time from initiation of inspiration to peak pressure, VT, and peak pressure minus PEEP at peak were recorded at each level of PEEP. In addition, quasi-static compliance was calculated by dividing the end-inspiratory pressure minus PEEP by the VT.

Statistical Analysis
Data were collected from three consecutive breaths at each PEEP level and were averaged in both PCV and VCV after a 5-min stabilization period. Overall, data are expressed as mean ± SD as obtained from the five sheep that were studied. A software package (STATISTICA 5.1; Statsoft Inc; Tulsa, OK) was used for statistical analysis. Analysis of variance (ANOVA) for repeated measures was applied to each variable evaluated in both PCV and VCV. When statistical significance was reached by ANOVA, a post hoc analysis was performed using the Schéffe F test. A p value <= 0.05 was considered statistically significant.


   Results
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 Conclusion
 References
 
LIP
The LIP after the instillation of about 30 mL/kg of PFC was 12.6 ± 1.1 cm H2O, with a range for the five animals studied of 11 to 14 cm H2O.

Waveforms
Figures 2 and 3 illustrate the changes in pressure and as PEEP increased during both PCV and VCV. As observed in Figure 2 , the greatest peak airway pressure above the set PEEP during volume ventilation occurred at 0 PEEP and decreased with each increment of PEEP added (p < 0.05; Table 1 ). In addition, the slope of the airway pressure increase was almost vertical at a PEEP of 0 cm H2O, decreasing as PEEP was applied and showing a more normal volume targeted (square wave ) airway pressure waveform at a PEEP >= 10 cm H2O. during VCV (Fig 2) changed in a similar manner (p < 0.05; Table 1 ), and peak exceeded set levels at low PEEP. With the application of >= 10 cm H2O PEEP, a more normal square wave pattern was observed. Both pressure and waveforms were consistent with typical gas ventilation with the application of >= 10 cm H2O PEEP.



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  		Figure 2. The effect of increasing PEEP on airway pressure above PEEP and with volume ventilation during partial liquid ventilation are illustrated. The panels depict variations of each parameter over time as PEEP increased from 0 to 20 cm H2O by increments of 5 cm H2O in a representative animal. ZEEP = 0 cm H2O PEEP.

 

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  		Table 1. VCV Ventilatory Mechanics With Different Levels of PEEP During PLV*

 
Airway pressure and waveforms during PCV are depicted in Figure 3 . At low or no PEEP, peak airway pressure exceeded the set level by 5 to 10 cm H2O during the onset of the inspiratory phase (p < 0.05; Table 2 ). However, as PEEP reached >= 10 cm H2O, a more normal airway pressure waveform was observed, with initial pressure nonsignificantly decreasing as PEEP was further increased from 12.5 to 20 cm H2O. The peak rate during PCV (Fig 3) was markedly decreased at 0 to 5 cm H2O PEEP (p < 0.05; Table 2 ), assuming a more normal waveform at >= 10 cm H2O PEEP but continuing to nonsignificantly increase as PEEP was increased from 12.5 to 20 cm H2O. Again, both pressure and waveforms were consistent with typical gas ventilation with the application of >= 10 cm H2O PEEP.



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  		Figure 3. The effect of increasing PEEP on airway pressure above PEEP and with pressure ventilation during partial liquid ventilation. The panels depict variations of each parameter over time as PEEP increased from 0 to 20 cm H2O by increments of 5 cm H2O in a representative animal. See Figure 2 for other abbreviations.

 

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  		Table 2. PCV Ventilatory Mechanics With Different Levels of PEEP During PLV*

 
VCV
Specific changes in measured and calculated variables during VCV are listed in Table 1 and Figure 4 . Time to 75% of peak decreased from a maximum of 0.35 ± 0.10 s at 0 cm H2O PEEP to 0.09 ± 0.02 s at 20 cm H2O PEEP (p < 0.05). Airways resistance was 26.8 ± 10.7 cm H2O/L/s at 0 cm H2O PEEP and decreased to 5.6 ± 1.0 cm H2O/L/s at 20 cm H2O PEEP (p < 0.05). The difference between PPLAT and PEEP continually decreased with each increment of PEEP from 20.6 ± 6.59 cm H2O at 0 cm H2O PEEP to 11.49 ± 3.66 cm H2O at 20 cm H2O PEEP (p < 0.05). The PIP minus PPLAT decreased dramatically from 0 cm H2O PEEP (25.9 ± 14.0 cm H2O) to 20 cm H2O PEEP (3.0 ± 0.4 cm H2O), as did PIP minus PEEP (46.5 ± 19.4 cm H2O to 14.1 ± 4.5 cm H2O), pressure at peak minus PEEP (35.2 ± 13.5 cm H2O to 9.5 ± 2.7 cm H2O), time to peak (0.45 ± 0.10 s to 0.30 ± 0.08 s), and peak (0.92 ± 0.21 L/s to 0.54 ± 0.09 L/s) (p < 0.05). The opposite change occurred with time to peak pressure, increasing from 0 cm H2O PEEP (0.29 ± 0.07 s) to 20 cm H2O PEEP (0.56 ± 0.01 s) (p < 0.05). Peak expiratory also decreased from 0 cm H2O PEEP (0.53 ± 0.13 L/s) to 20 cm H2O PEEP (0.40 ± 0.09 L/s) (p < 0.05). Finally, as shown in Figure 6 , as PEEP increased, the quasi-static compliance increased from 18.93 ± 4.77 to 31.57 ± 9.84 mL/cm H2O (p < 0.05). There were no significant differences in any variables as PEEP was increased from 12.5 to 20 cm H2O.



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  		Figure 4. Inspiratory resistance, time to 75% peak , and PPLAT minus PEEP during volume ventilation during partial liquid ventilation at incremental increases in PEEP are illustrated. {dagger} = vs 0 cm H2O PEEP, p < 0.05; {ddagger} = vs 12.5 cm H2O PEEP, p < 0.05.

 


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  		Figure 6. Change in quasi-static compliance during volume ventilation (top) and pressure ventilation (bottom) as PEEP was increased from 0 to 20 cm H2O. See Figure 4 for explanation of symbols.

 
PCV
The changes in gas delivery pattern during PCV are depicted in Figure 5 and Table 2 . The most striking change was in VT delivery. As PEEP increased from 0 to 20 cm H2O, VT increased from 0.13 ± 0.05 to 0.40 ± 0.07 L (p < 0.05). In addition, time to peak pressure increased from 0.21 ± 0.03 s to 1.27 ± 0.06 s as PEEP increased from 0 to 20 cm H2O (p < 0.05), whereas time to peak decreased from 0.65 ± 0.23 s at 0 cm H2O PEEP to 0.14 ± 0.07 s at 20 cm H2O PEEP (p < 0.05). Peak increased from 0.16 ± 0.04 to 0.62 ± 0.11 L/s as PEEP increased from 0 to 20 cm H2O (p < 0.05). Pressure at peak minus PEEP decreased from 13.6 ± 5.2 to 8.6 ± 5.5 cm H2O, and peak pressure minus PEEP decreased from 19.0 ± 8.2 to 15.3 ± 5.9 cm H2O as PEEP increased from 0 to 20 cm H2O (p < 0.05). Contrary to volume ventilation, peak expiratory decreased (p < 0.05) as PEEP was increased from 0 to 20 cm H2O (0.31 ± 0.10 to 0.42 ± 0.14 L/s). Finally, as shown in Figure 6 , as PEEP increased from 0 to 20 cm H2O the quasi-static compliance increased (9.61 ± 3.21 to 26.85 ± 9.54 mL/cm H2O) (p < 0.05). There were no significant differences in any variables as PEEP was increased from 12.5 to 20.0 cm H2O.



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  		Figure 5. Time to peak , time to peak pressure, and VT with pressure ventilation during PLV at various PEEP levels are illustrated. See Figure 4 for explanation of symbols.

 

   Discussion
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
Conclusion
 References
 
The major findings of this study can be summarized as follows: (1) at low PEEP levels (< 10 cm H2O), VT is markedly decreased during PCV and PIP is markedly increased during VCV; (2) during PLV, a PEEP level >= 10 cm H2O is needed to normalize airway pressure, , and volume waveforms; (3) the PEEP level equivalent to the LIP during PLV can be grossly estimated from the changes in airway pressure, , and volume waveforms; (4) with both volume- and pressure-targeted ventilation, no measured variables significantly changed at PEEP > 12.5 cm H2O; and (5) the mean LIP (12.6 ± 1.1 cm H2O) was approximately equivalent to the PEEP level (12.5 cm H2O) where no additional significant changes in measured variables occurred.

Effects of PEEP
It has been demonstrated by numerous groups that in the gas-filled lung of the ARDS patient, setting PEEP above the LIP of the P-V curve of the total respiratory system prevents lung derecruitment and improves oxygenation and lung mechanics.12 13 The partial filling of the ARDS lung with PFC has been shown to have similar effects.1 2 3 PLV demonstrates a dose-dependent improvement in oxygenation and a reduction in shunt fraction.14 Recently, we demonstrated that the application of PEEP 1 cm H2O above the LIP of the P-V curve in the lung partially filled with PFC further increases oxygenation, reduces physiologic dead space ventilation, and improves total respiratory system compliance when compared with 5 cm H2O PEEP.11 Similar data has been recorded by Kaisers et al15 when 3.8, 7.6, and 11.4 cm H2O PEEP were applied to a lung partially filled with PFC. The mechanism for this improvement with PEEP is unclear but may be a result of (1) the maintenance of PFC in the lung periphery at end exhalation reducing impedance to gas ventilation, and (2) the stabilization of the nondependent lung, preventing collapse.

Reduced Impedance: Perflubron has a density of 1.92 g/mL. This is coupled with the fact that at 0 cm H2O PEEP, PFC resides not just in the lung periphery but in nondistendable central airways, causing a high impedance to ventilation. At 0 cm H2O PEEP, the impedance to gas delivery results in distortion of the pressure and waveform (Figs 2 , 3) . During pressure ventilation, the pressure target is rapidly met with minimal delivery resulting in very small VT delivery. Because of the high impedance, the pressure target is exceeded in early inspiration. The ventilator cannot adjust delivery rapidly enough to prevent overshooting the set pressure target. With volume-targeted ventilation, dramatic increases in peak airway pressure (as compared with PEEP at LIP) are initially observed. The high PIP is necessary to ensure that the /VT targets are met. As observed in Figure 4 and noted in Figure 2 , the time to 75% of peak with 0 cm H2O PEEP is markedly increased over that at >= 7.5 cm H2O PEEP, and the actual peak is higher than the set peak (Table 1) . The high impedance of the PFC prevents the ventilator from achieving gas delivery in the early phase of inspiration. As a result, must increase above the set level as the ventilator attempts to overcome the impedance of the PFC and complete the VT delivery in the allocated time. As noted in Table 1 , VT was constant during volume ventilation regardless of the PEEP setting.
Nondependent Lung: In the gas-filled lung, while the animal is in the supine position both perfusion and ventilation predominate in the dependent regions. As recently demonstrated by Quintel et al,16 with PLV, the majority of the VT goes to the nondependent lung. In addition, a number of studies have shown that in the lung partially filled with PFC to functional residual capacity (FRC), there is a shifting of both intravascular and extravascular fluid from the dependent to the nondependent lung.17 18 This shift in intrapulmonary fluid volume reverses the alveolar inflation gradient. That is, in the lung partially filled with PFC the nondependent region acts like the dependent region in the gas-filled lung. In this setting, the alteration in the alveolar inflation gradient favors instability and collapse of the nondependent lung. PEEP stabilizes the nondependent lung, improving oxygenation. As would be expected, the more the lung is filled with PFC, the greater is the tendency for nondependent instability and the greater is the effect of the addition of PEEP on oxygenation and lung mechanics.11 Although other positions were not studied, one would expect a similar situation to occur regardless of position. That is, ventilation during PLV would always distribute to the nondependent lung since the PFB would distribute to gravity.

LIP
After filling the lung with PFC, the LIP was measured at 12.6 ± 1.1 cm H2O. From the evaluation of the changes in airway pressure and waveforms, only nonsignificant changes in all variables occurred with the application of a PEEP of > 12.5 cm H2O. Visual observation of the airway pressure and waveforms in all animals showed the establishment of waveforms equivalent to gas ventilation with PEEP set at >= 10 cm H2O. Previously, we have measured the LIP on 34 (healthy and injured) sheep whose lungs were filled to FRC with PFC.9 10 11 18 In all of these animals the LIP was between 10 and 15 cm H2O, averaging 11.9 ± 3.6 cm H2O. This is in the same range (>= 10 cm H2O) for which airway pressure and curves "normalized." These data imply that the minimal PEEP level during PLV with an FRC fill should be that PEEP associated with normalization of the airway pressure and waveforms during both pressure- and volume-targeted ventilation, but always >= 10 cm H2O. Since the actual measurement of a P-V curve is difficult and since all of our data point to a need for a PEEP of about 12.5 cm H2O during PLV, we would recommend that the initial setting of PEEP during PLV be at this level. The assessment of pressure, volume, and waveforms, and of oxygenation above and below this level, should then be performed to determine the final PEEP setting.

Pressure Ventilation
Of primary concern during pressure ventilation at low PEEP (< 10 cm H2O) was the low VT delivered. This is a result of the limited driving pressure during pressure ventilation (equal to the set pressure control level). With high impedance, regardless of the cause, VT decreases, and the application of PEEP more than or equal to the LIP reduces impedance in the lung partially filled with PFC, which maximizes VT delivery.18

Volume Ventilation
VT delivery was maintained during volume ventilation regardless of the PEEP level but at a cost of markedly elevated peak airway pressure. Since the PPLAT during low levels of PEEP was not excessive, it is unlikely that this high peak pressure induced lung injury.9 However, the use of low vs high PEEP with the same VT reduces oxygenation.11 15 18 Increasing VT has been shown to improve oxygenation at low PEEP, but it also increases PPLAT8 and the risk of induced lung injury.9 10

Compliance
Increasing PEEP from 0 to >= 10 cm H2O in both pressure and volume ventilation resulted in significantly increased compliance. This corresponded to a continual decrease in the difference between PPLAT and PEEP during volume ventilation and the continual increase in VT in pressure ventilation. Beyond 10 cm H2O, only minor nonsignificant changes in compliance, PIP, and VT occurred. We do not fully understand why. However, it may be primarily a result of inadequate time for either end-inspiratory or end-expiratory equilibration. As indicated, we measured quasi-static compliance. During volume ventilation, the end-inspiratory hold period was 0.7 s, and during pressure ventilation it was < 0.2 s. As a result, each compliance measurement may have underestimated actual compliance because of the failure to reach static conditions. In fact, compliance was always lower with PCV than with VCV (Fig 6) . The application of high levels of PEEP may have reduced the equilibration time and may have resulted in a more accurate calculation of compliance especially at PEEP levels of >= 10 cm H2O.

Limitations of the Study
There are several limitations of this study. As indicated above, the methodology used to calculate compliance may have underestimated compliance at all PEEP levels. No gas exchange or hemodynamic data are presented. However, our previous data do indicate a greater PaO2 and lower PCO2 when PEEP is 1 cm H2O above the LIP11 compared with PEEP at 5 cm H2O, and they indicate no greater hemodynamic compromise than when PEEP was set at 5 cm H2O.11 18 Other studies also have observed improved oxygenation without hemodynamic compromise at PEEP levels of 11.4 cm H2O when compared with a lower PEEP setting.15 Finally, this study was performed in a noninjured sheep model, which may not represent the actual changes that occur in patients with ARDS.


   Conclusion
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Conclusion
References
 
The application of PEEP during PLV in both VCV and PCV markedly alters pressure, , and volume waveforms. The use of low-level PEEP results in a marked decrease in VT in PCV and a marked increase in airway pressure in VCV. Observation of the airway pressure and waveforms in either pressure or volume ventilation are useful in grossly identifying the LIP on the P-V curve of the lung partially filled with PFC. In this animal model, normalization of the airway pressure and waveform was always associated with a PEEP level of >= 10 cm H2O.


   Footnotes
 
Abbreviations: ANOVA = analysis of variance; FRC = functional residual capacity; LIP = lower inflection point; PCV = pressure control ventilation; PEEP = positive end-expiratory pressure; PFC = perfluorocarbon; PIP = peak inspiratory pressure; PLV = partial liquid ventilation; PPLAT = plateau pressure; P-V = pressure-volume; UIP = upper inflection point; = flow; VCV = volume control ventilation; VT = tidal volume;

Supported in part by Alliance Pharmaceutical Corp. Dr. Fujino was supported by a grant from the Japanese Government. Dr. Goddon was supported by a grant from the Deutsche Forschungsgemeinschaft (GO 855/1–1).

Received for publication April 7, 1999. Accepted for publication August 10, 1999.


   References
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Conclusion
 References
 

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  9. Fujino, Y, Kirmse, M, Chiche, JD, et al (1998) Partial liquid ventilation (PLV) does not protect against high stretch lung injury in healthy sheep [abstract]. Am J Respir Crit Care Med 157,A461
  10. Chiche, JD, Fujino, Y, Kirmse, M, et al (1998) High stretch ventilatory strategies induce alveolar damage during partial liquid ventilation (PLV) [abstract]. Am J Respir Crit Care Med 157,A462
  11. Kirmse, M, Fujino, Y, Hess, D, et al (1998) Relationship between fill-volume during partial liquid ventilation (PLV) and the lower inflection point (LIP) on the static pressure-volume curve. Am J Respir Crit Care Med 158,1550-1556[Abstract/Free Full Text]
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