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Reabsorption of solutes and water from fluid-filled rabbit lungs
ABSTRACTS
Pressure
277
Support
to Endotracheal Airway Pressure.
93:499,
Compensation Tubes
Fiastro
and
for lnspiratory Demand
JE,
Habib
Work
Continuous
MP,
Quan
Due
Positive
SF. Chest
1988.
We evaluated the use of pressure support to compensate for the added inspiratory work of breathing due to the resistances of endotracheal tubes and a ventilator demandvalve system for continuous positive airway pressure (CPAP). A mechanical model was used to simulate spontaneous breathing at five respiratory rates through 7-mm, 8-mm, and 9-mm endotracheal tubes with and without a ventilator demand CPAP circuit. Added work was measured as the integral of the product of airway pressure and volume during inspiration. Additional work was a function of the tube’s size, and each l-mm decrease in the tube’s diameter resulted in a 67 to 100 percent increase in work. Adding the ventilator CPAP circuit further increased work and was responsible for 30 to 50 percent of the total work resulting from a tube and CPAP circuit together. Pressure support was added to a level at which net work on the airway was zero, and a relationship between mean inspiratory flow (VT/TI) and the optimal level of pressure support was established for each endotracheal tube. The inspiratory work of breathing was then measured in normal subjects breathing with and without each endotracheal tube plus the demand CPAP circuit. Work per liter of minute ventilation due to the endotracheal tube and CPAP circuit was increased from 54 to 240 percent over levels measured while breathing through an open airway. For each endotracheal tube and VT/TI, a level of pressure support (range, 2 to 20 cm H,O) was found which eliminated added work in the spontaneously breathing subject. This level correlated well with that predicted from the data derived using the mechanical model. We conclude that when adjusting for an endotracheal tube’s diameter and VT/TI, pressure support can be used to compensate for the added inspiratory work due to artificial airway resistances. (Reprinted with permission.) Improved
Efficacy
tory
Pressure
Am
Rev Respir
of Spontaneous
Breathing
Brochard L, Pluskwa Dis 136:411, 1987.
Support.
With
Inspira-
F. Lemaire
F.
During inspiratory pressure support (IPS) ventilation, first a negative airway pressure is produced by the patient to open a demand valve and then a constant positive airway pressure is maintained at a preset level while the patient inhales. The aim of this study was to assess the ability of 10 cm H,O IPS to improve the efficacy of spontaneous ventilation. We studied 8 intubated patients recovering from acute respiratory failure, all were breathing spontaneously via 3 different systems: (1) a Servo 900 C ventilator LSVC) without IPS, (2) a Servo 900 C ventilator with 10 cm HZ0 IPS, and (3) a continuous flow system (CFS). Compared with the CFS, breathing with the SVC without IPS resulted in an increased respiratory rate (RR), increased tidal Volume (VT), increased transdiaphragmatic pressure (Pdl), and no sign.ificant change in PA, or Pacol. Ventilation with IPS resulted in significant improvements in VT, Pao2, and Pacol with a decreased RR and Pdl when compared with both the other modes of spontaneous ventilation. A significant decrease in the pressure-time index
of the diaphragm (i.e., the product of the mean transdiaphragmatic pressure and the inspiratory duty cycle) occurred during IPS. In 2 patients, we recorded diaphragmatic electromyographic activity during both SVC and IPS. In both patients during IPS, an increased VT and a decreased Pdl coincided with a major reduction of electromyographic activity. We conclude that IPS at a level of 10 cm HZ0 markedly increases the efficacy of spontaneous breathing while reducing the activity of the inspiratory muscles. (Reprinted with permission.) Hemodynamic Effects of External Pressure Ventilation Compared With Positive Pressure Injury. Skaburskis
Dis 136:886,
Ventilation
M, He/al
Continuous Negative Those of Continuous
in Dogs
R. Zidulka
With
Acute
Lung
A. Am Rev Respir
1987.
Patients with noncardiogenic pulmonary edema requiring ventilatory assistance are usually supported with CPPV using positive end-expiratory pressure (PEEP), but CPPV requires endotracheal intubation and may decrease cardiac output (QT). The purpose of this study was to examine thoracoabdominal continuous negative pressure ventilation (CNPV) using external negative end-expiratory pressure (NEEP). The effects on gas exchange and hemodynamics were compared with those of CPPV with PEEP, with the premise that CNPV might sustain venous return and improve QT. In 6 supine, anesthetized and paralyzed dogs with oleic-acidinduced pulmonary edema, 30 min of CNPV was alternated twice with 30 min of CPPV. Positive and negative pressure ventilation were carefully matched for fractional inspired oxygen concentration (FioZ = 0.56), breathing frequency, and tidal volume. In addition, we matched the increase in AFRC obtained with the constant distending pressures produced by both modes of ventilation. An average of -9 cm H,O of NEEP produced the same AFRC as 10.8 cm H,O of PEEP. Gas exchange did not differ significantly between the 2 modes. However, QT was 15.8% higher during CNPV than during CPPV (p < 0.02). Mixed venous oxygen saturation also improved during CNPV compared with that during CPPV (58.3 versus 54.5%, p < 0.01). Negative pressure ventilation using NEEP may be a viable alternative to positive pressure ventilation with PEEP in the management of critically ill patients with noncardiogenic pulmonary edema. It offers comparable improvement in gas exchange with the advantages of less cardiac depression and the possible avoidance of endotracheal intubation. (Reprinted with permission.) Reabsorption Lungs. Eflros
of Solutes
and Water
From
RM, Mason GR, Hukkanen Am Rev Respir Dis 136:669, 1987.
Fluid-Filled
Rabbit
J, Silverman
P.
Uncertainty persists concerning the mechanisms responsible for fluid clearance from the lungs after the air spaces become flooded in severe pulmonary edema. In this study, solute and water fluxes were investigated in an isolated, fluid-filled, perfused rabbit lung preparation. These lungs were perfused with physiologic 1.0 or 5.0 g/d1 albumin solutions, and the air spaces were flushed and filled with the same solutions. Samples were obtained at intervals from the
278
ABSTRACTS
perfusate, and at the end of I or 2 h, fluid was pumped from the trachea into collection tubes. Concentrations of albumin (labeled with Evans blue) in the air space increased by 2.4 * 0.7% (SEM) at 1 h and by 7.0 + 0.8% at 2 h. Approximately half of the increase at 2 h could be attributed to dehydration (as judged by increases in perfusate and air-space Na+ concentration). Because previous studies have indicated that the movement of labeled protein between these compartments is very slow in this preparation, it can be concluded that fluid is being reabsorbed from the air spaces. However, reabsorption appears to be slower in rabbits than in rats and it is not stimulated by terbutaline, an effect observed in other species. Under control conditions, potassium concentrations in the air-space fluid fell from 4.01 + 0.05 (SEM) mEq/L to 3.37 + 0.14 mEq/L at 1 h. Concentrations of K’ in the perfusate rose during this interval from 3.95 i- 0.05 mEq/L to 4.39 + 0.08 mEq/L. A decrease in air-space K’ concentrations and an increase in perfusate K+ were also observed during a 2-h period when the lungs were perfused with the 5 g/d1 albumin solution. Addition of IO-’ M terbutaline to the airway and perfusion solutions resulted in an increase in the concentration of K+ in the air space from 3.97 i 0.05 mEq/L to 4.49 t 0.13 mEq/L. This action of terbutaline was largely blocked by lo-’ M propranolol. These studies suggest that fluid may be transported out of the air spaces of rabbit lungs by forces other than hydrostatic pressure or protein concentration differences. In addition, electrolyte transport across the pulmonary epithelium may differ between species. (Reprinted with permission.) A Prospective Study Patient Management
of Lung Water in an Intensive
PR. Hansbrough JR, Anderson Respir Dis 136:662, 1987.
Measurements Care Unit.
D, Schuster
Assessment of Lung Water Distribution by Nuclear Magnetic Resonance: A New Method for Quantifying and Monitoring
Ailion Akhtari
Lung injury. Cutillo AG, Morris AH, DC, Case TA, Durney CH. Ganesan K, Watanabe F. M. Am Rev Respir Dis 137:1371, 1988.
Experimental
We have developed a new analytical method that uses nuclear magnetic resonance (NMR) imaging data to quantify lung water content and distribution. This new method generates a distribution of lung water density in which the fraction of voxels corresponding to a given water density is plotted on the vertical axis as a function of water density on the horizontal axis, thereby complementing the spatial information provided by the NMR image. We obtained reproducible lung water distribution data at comparable lung volumes in normal excised lungs and in intact living rats. In normal excised unperfused rat lungs, the distribution varied with the degree of inflation, but the changes were small compared with those associated with lung edema. The lung water density distribution changed markedly after induction of lung edema by intrabronchial saline instillation, intravenous oleic acid injection, and rapid intravenous saline infusion. Lung water density distribution data were well correlated (correlation coefficient = 0.948 for the excised lungs and 0.823 for the intact living rats) with gravimetric lung water measurements. The new analytical method is noninvasive, provides easily repeatable measurements, and is as sensitive as the gravimetric technique to lung water changes. (Reprinted with permission.)
During
Eisenberg DP. Am Rev
We prospectively evaluated a protocol that included extravascular thermal volume (ETV) as a measure of extravascular lung water (EVLW) instead of pulmonary artery wedge pressure (Ppaw) measurements to guide the hemodynamic management of 48 critically ill patients. Patients were randomized to either a protocol management (PM), or to a routine management (RM) group. In the RM group, EVLW measurements were unknown to the primary care physicians. The 2 groups were similar with respect to age, gender, and severity of illness. In patients with initially high EVLW, EVLW fell to a greater extent in PM than in RM patients (18 f 5 versus 4 k 8% decrease, p < 0.05). This difference was even greater in patients with heart failure. No adverse effects on oxygenation or renal function occurred in following the protocol. Mortality for the groups as a whole was similar, but was significantly better (p < 0.05) for PM patients with initially high EVLW and normal Ppaw (predominantly patients with sepsis or the adult respiratory distress syndrome). For both groups, patients with an initial EVLW > 14 ml/kg had a significantly greater mortality than did those with a lesser amount of EVLW: 13 of 15 (87%) versus 13 of 32 (41%), p < 0.05. We conclude that management based on a protocol using EVLW measurements is safe, may hasten the resolution of pulmonary edema, and may lead to improved outcome in some critically ill patients. (Reprinted with permission.)
Minimal “Best
Positive Peep.”
WG. Wool 1988.
End-Expiratory
Carroll N, Goldin
Pressure
(PEEP)
GC, Tuman KJ, Braverman M, Ivankovich, AD. Chest
May
be
B, Logas 93:1020,
In the absence of clinical trials, positive end-expired pressure (PEEP) has been accepted as efficacious for treatment of postoperative decreases in arterial oxygen tension (PaO,) from a variety of causes including adult respiratory distress syndrome (ARDS). PEEP is thought to increase PaO, by alveolar recruitment, which in turn, has been hypothesized to play a decisive role in pulmonary recovery. One hundred and eighteen patients were followed prospectively, and after development of decreased PaO,, randomized to receive recruitive PEEP (determined by blood gas criteria) or supportive PEEP (the minimal PEEP required to maintain PaO, above 60 mm Hg on .5 inspired 0, fraction (FIo,). No prognostic factors were significantly different between the two groups. Recruitive PEEP application in 22 patients yielded a significantly increased incidence of hypotension (55 percent), pneumothorax (20 percent), and death during treatment (27 percent) when compared to the 28 supportive PEEP patients who had no hypotension or pneumothorax and only one death during treatment (4 percent). After PEEP treatment, deaths in each group were similar (19 percent and 15 percent, respectively). We find no evidence that PEEP treatment promotes beneficial outcomes and conclude that recruitment attempts may be harmful. (Reprinted with permission.)
Pressure
277
Support
to Endotracheal Airway Pressure.
93:499,
Compensation Tubes
Fiastro
and
for lnspiratory Demand
JE,
Habib
Work
Continuous
MP,
Quan
Due
Positive
SF. Chest
1988.
We evaluated the use of pressure support to compensate for the added inspiratory work of breathing due to the resistances of endotracheal tubes and a ventilator demandvalve system for continuous positive airway pressure (CPAP). A mechanical model was used to simulate spontaneous breathing at five respiratory rates through 7-mm, 8-mm, and 9-mm endotracheal tubes with and without a ventilator demand CPAP circuit. Added work was measured as the integral of the product of airway pressure and volume during inspiration. Additional work was a function of the tube’s size, and each l-mm decrease in the tube’s diameter resulted in a 67 to 100 percent increase in work. Adding the ventilator CPAP circuit further increased work and was responsible for 30 to 50 percent of the total work resulting from a tube and CPAP circuit together. Pressure support was added to a level at which net work on the airway was zero, and a relationship between mean inspiratory flow (VT/TI) and the optimal level of pressure support was established for each endotracheal tube. The inspiratory work of breathing was then measured in normal subjects breathing with and without each endotracheal tube plus the demand CPAP circuit. Work per liter of minute ventilation due to the endotracheal tube and CPAP circuit was increased from 54 to 240 percent over levels measured while breathing through an open airway. For each endotracheal tube and VT/TI, a level of pressure support (range, 2 to 20 cm H,O) was found which eliminated added work in the spontaneously breathing subject. This level correlated well with that predicted from the data derived using the mechanical model. We conclude that when adjusting for an endotracheal tube’s diameter and VT/TI, pressure support can be used to compensate for the added inspiratory work due to artificial airway resistances. (Reprinted with permission.) Improved
Efficacy
tory
Pressure
Am
Rev Respir
of Spontaneous
Breathing
Brochard L, Pluskwa Dis 136:411, 1987.
Support.
With
Inspira-
F. Lemaire
F.
During inspiratory pressure support (IPS) ventilation, first a negative airway pressure is produced by the patient to open a demand valve and then a constant positive airway pressure is maintained at a preset level while the patient inhales. The aim of this study was to assess the ability of 10 cm H,O IPS to improve the efficacy of spontaneous ventilation. We studied 8 intubated patients recovering from acute respiratory failure, all were breathing spontaneously via 3 different systems: (1) a Servo 900 C ventilator LSVC) without IPS, (2) a Servo 900 C ventilator with 10 cm HZ0 IPS, and (3) a continuous flow system (CFS). Compared with the CFS, breathing with the SVC without IPS resulted in an increased respiratory rate (RR), increased tidal Volume (VT), increased transdiaphragmatic pressure (Pdl), and no sign.ificant change in PA, or Pacol. Ventilation with IPS resulted in significant improvements in VT, Pao2, and Pacol with a decreased RR and Pdl when compared with both the other modes of spontaneous ventilation. A significant decrease in the pressure-time index
of the diaphragm (i.e., the product of the mean transdiaphragmatic pressure and the inspiratory duty cycle) occurred during IPS. In 2 patients, we recorded diaphragmatic electromyographic activity during both SVC and IPS. In both patients during IPS, an increased VT and a decreased Pdl coincided with a major reduction of electromyographic activity. We conclude that IPS at a level of 10 cm HZ0 markedly increases the efficacy of spontaneous breathing while reducing the activity of the inspiratory muscles. (Reprinted with permission.) Hemodynamic Effects of External Pressure Ventilation Compared With Positive Pressure Injury. Skaburskis
Dis 136:886,
Ventilation
M, He/al
Continuous Negative Those of Continuous
in Dogs
R. Zidulka
With
Acute
Lung
A. Am Rev Respir
1987.
Patients with noncardiogenic pulmonary edema requiring ventilatory assistance are usually supported with CPPV using positive end-expiratory pressure (PEEP), but CPPV requires endotracheal intubation and may decrease cardiac output (QT). The purpose of this study was to examine thoracoabdominal continuous negative pressure ventilation (CNPV) using external negative end-expiratory pressure (NEEP). The effects on gas exchange and hemodynamics were compared with those of CPPV with PEEP, with the premise that CNPV might sustain venous return and improve QT. In 6 supine, anesthetized and paralyzed dogs with oleic-acidinduced pulmonary edema, 30 min of CNPV was alternated twice with 30 min of CPPV. Positive and negative pressure ventilation were carefully matched for fractional inspired oxygen concentration (FioZ = 0.56), breathing frequency, and tidal volume. In addition, we matched the increase in AFRC obtained with the constant distending pressures produced by both modes of ventilation. An average of -9 cm H,O of NEEP produced the same AFRC as 10.8 cm H,O of PEEP. Gas exchange did not differ significantly between the 2 modes. However, QT was 15.8% higher during CNPV than during CPPV (p < 0.02). Mixed venous oxygen saturation also improved during CNPV compared with that during CPPV (58.3 versus 54.5%, p < 0.01). Negative pressure ventilation using NEEP may be a viable alternative to positive pressure ventilation with PEEP in the management of critically ill patients with noncardiogenic pulmonary edema. It offers comparable improvement in gas exchange with the advantages of less cardiac depression and the possible avoidance of endotracheal intubation. (Reprinted with permission.) Reabsorption Lungs. Eflros
of Solutes
and Water
From
RM, Mason GR, Hukkanen Am Rev Respir Dis 136:669, 1987.
Fluid-Filled
Rabbit
J, Silverman
P.
Uncertainty persists concerning the mechanisms responsible for fluid clearance from the lungs after the air spaces become flooded in severe pulmonary edema. In this study, solute and water fluxes were investigated in an isolated, fluid-filled, perfused rabbit lung preparation. These lungs were perfused with physiologic 1.0 or 5.0 g/d1 albumin solutions, and the air spaces were flushed and filled with the same solutions. Samples were obtained at intervals from the
278
ABSTRACTS
perfusate, and at the end of I or 2 h, fluid was pumped from the trachea into collection tubes. Concentrations of albumin (labeled with Evans blue) in the air space increased by 2.4 * 0.7% (SEM) at 1 h and by 7.0 + 0.8% at 2 h. Approximately half of the increase at 2 h could be attributed to dehydration (as judged by increases in perfusate and air-space Na+ concentration). Because previous studies have indicated that the movement of labeled protein between these compartments is very slow in this preparation, it can be concluded that fluid is being reabsorbed from the air spaces. However, reabsorption appears to be slower in rabbits than in rats and it is not stimulated by terbutaline, an effect observed in other species. Under control conditions, potassium concentrations in the air-space fluid fell from 4.01 + 0.05 (SEM) mEq/L to 3.37 + 0.14 mEq/L at 1 h. Concentrations of K’ in the perfusate rose during this interval from 3.95 i- 0.05 mEq/L to 4.39 + 0.08 mEq/L. A decrease in air-space K’ concentrations and an increase in perfusate K+ were also observed during a 2-h period when the lungs were perfused with the 5 g/d1 albumin solution. Addition of IO-’ M terbutaline to the airway and perfusion solutions resulted in an increase in the concentration of K+ in the air space from 3.97 i 0.05 mEq/L to 4.49 t 0.13 mEq/L. This action of terbutaline was largely blocked by lo-’ M propranolol. These studies suggest that fluid may be transported out of the air spaces of rabbit lungs by forces other than hydrostatic pressure or protein concentration differences. In addition, electrolyte transport across the pulmonary epithelium may differ between species. (Reprinted with permission.) A Prospective Study Patient Management
of Lung Water in an Intensive
PR. Hansbrough JR, Anderson Respir Dis 136:662, 1987.
Measurements Care Unit.
D, Schuster
Assessment of Lung Water Distribution by Nuclear Magnetic Resonance: A New Method for Quantifying and Monitoring
Ailion Akhtari
Lung injury. Cutillo AG, Morris AH, DC, Case TA, Durney CH. Ganesan K, Watanabe F. M. Am Rev Respir Dis 137:1371, 1988.
Experimental
We have developed a new analytical method that uses nuclear magnetic resonance (NMR) imaging data to quantify lung water content and distribution. This new method generates a distribution of lung water density in which the fraction of voxels corresponding to a given water density is plotted on the vertical axis as a function of water density on the horizontal axis, thereby complementing the spatial information provided by the NMR image. We obtained reproducible lung water distribution data at comparable lung volumes in normal excised lungs and in intact living rats. In normal excised unperfused rat lungs, the distribution varied with the degree of inflation, but the changes were small compared with those associated with lung edema. The lung water density distribution changed markedly after induction of lung edema by intrabronchial saline instillation, intravenous oleic acid injection, and rapid intravenous saline infusion. Lung water density distribution data were well correlated (correlation coefficient = 0.948 for the excised lungs and 0.823 for the intact living rats) with gravimetric lung water measurements. The new analytical method is noninvasive, provides easily repeatable measurements, and is as sensitive as the gravimetric technique to lung water changes. (Reprinted with permission.)
During
Eisenberg DP. Am Rev
We prospectively evaluated a protocol that included extravascular thermal volume (ETV) as a measure of extravascular lung water (EVLW) instead of pulmonary artery wedge pressure (Ppaw) measurements to guide the hemodynamic management of 48 critically ill patients. Patients were randomized to either a protocol management (PM), or to a routine management (RM) group. In the RM group, EVLW measurements were unknown to the primary care physicians. The 2 groups were similar with respect to age, gender, and severity of illness. In patients with initially high EVLW, EVLW fell to a greater extent in PM than in RM patients (18 f 5 versus 4 k 8% decrease, p < 0.05). This difference was even greater in patients with heart failure. No adverse effects on oxygenation or renal function occurred in following the protocol. Mortality for the groups as a whole was similar, but was significantly better (p < 0.05) for PM patients with initially high EVLW and normal Ppaw (predominantly patients with sepsis or the adult respiratory distress syndrome). For both groups, patients with an initial EVLW > 14 ml/kg had a significantly greater mortality than did those with a lesser amount of EVLW: 13 of 15 (87%) versus 13 of 32 (41%), p < 0.05. We conclude that management based on a protocol using EVLW measurements is safe, may hasten the resolution of pulmonary edema, and may lead to improved outcome in some critically ill patients. (Reprinted with permission.)
Minimal “Best
Positive Peep.”
WG. Wool 1988.
End-Expiratory
Carroll N, Goldin
Pressure
(PEEP)
GC, Tuman KJ, Braverman M, Ivankovich, AD. Chest
May
be
B, Logas 93:1020,
In the absence of clinical trials, positive end-expired pressure (PEEP) has been accepted as efficacious for treatment of postoperative decreases in arterial oxygen tension (PaO,) from a variety of causes including adult respiratory distress syndrome (ARDS). PEEP is thought to increase PaO, by alveolar recruitment, which in turn, has been hypothesized to play a decisive role in pulmonary recovery. One hundred and eighteen patients were followed prospectively, and after development of decreased PaO,, randomized to receive recruitive PEEP (determined by blood gas criteria) or supportive PEEP (the minimal PEEP required to maintain PaO, above 60 mm Hg on .5 inspired 0, fraction (FIo,). No prognostic factors were significantly different between the two groups. Recruitive PEEP application in 22 patients yielded a significantly increased incidence of hypotension (55 percent), pneumothorax (20 percent), and death during treatment (27 percent) when compared to the 28 supportive PEEP patients who had no hypotension or pneumothorax and only one death during treatment (4 percent). After PEEP treatment, deaths in each group were similar (19 percent and 15 percent, respectively). We find no evidence that PEEP treatment promotes beneficial outcomes and conclude that recruitment attempts may be harmful. (Reprinted with permission.)