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Small dose of exogenous surfactant combined with partial liquid ventilation in experimental acute lung injury: effects on gas exchange, haemodynamics, lung mechanics, and lung pathology
British Journal of Anaesthesia 87 (4): 593±601 (2001)
LABORATORY INVESTIGATIONS Small dose of exogenous surfactant combined with partial liquid ventilation in experimental acute lung injury: effects on gas exchange, haemodynamics, lung mechanics, and lung pathology S. Wolf1, H. Lohbrunner1, T. Busch1, A. Sterner-Kock4, M. Deja1, A. Sarrafzadeh2, U. Neumann3 and U. Kaisers1 1
Klinik fuÈr Anaesthesiologie und Operative Intensivmedizin, ChariteÂ, Campus Virchow Klinikum, Medizinische Fakultaet der Humboldt-Universitaet, Augustenburger Platz 1, D-13353 Berlin, Germany, 2 Abteilung fuÈr Neurochirurgie, ChariteÂ, Campus Virchow Klinikum, Medizinische Fakultaet der HumboldtUniversitaet, Augustenburger Platz 1, D-13353 Berlin, Germany, 3Chirurgische Klinik und Poliklinik, ChariteÂ, Campus Virchow Klinikum, Medizinische Fakultaet der Humboldt-Universitaet, Augustenburger Platz 1, D-13353 Berlin, Germany and 4Molekulare Haematologie, Klinikum der Johann Wolfgang von Goethe Universitaet, Theodor-Stern-Kai 7, D-60590 Frankfurt Main, Germany A combination of exogenous surfactant and partial liquid ventilation (PLV) with per¯uorocarbons should enhance gas exchange, improve respiratory mechanics and reduce tissue damage of the lung in acute lung injury (ALI). We used a small dose of exogenous surfactant with and without PLV in an experimental model of ALI and studied the effects on gas exchange, haemodynamics, lung mechanics, and lung pathology. ALI was induced by repeated lavages (PaO2/FIO2 less than 13 kPa) in 24 anaesthesized, tracheotomized and mechanically ventilated (FIO2 1.0) juvenile pigs. They were treated randomly with either a single intratracheal dose of surfactant (50 mg kg±1, Curosurfâ, Serono AG, MuÈnchen, Germany) (SURF-group, n=8), a single intratracheal dose of surfactant (50 mg kg±1, Curosurfâ) followed by PLV with 30 ml kg±1 of per¯uorocarbon (PF 5080, 3M, Germany) (SURF-PLV-group, n=8) or no further intervention (controls, n=8). Pulmonary gas exchange, respiratory mechanics, and haemodynamics were measured hourly for a 6 h period. In the SURF-group, the intrapulmonary right-to-left shunt (QÇS/QÇT) decreased signi®cantly from mean 51 (SEM 5)% after lavage to 12 (2)%, and PaO2 increased signi®cantly from 8.1 (0.7) to 61.2 (4.7) kPa compared with controls and compared with the SURF-PLV-group (P<0.05). In the SURF-PLV-group, QÇS/QÇT decreased signi®cantly from 54 (3)% after induction of ALI to 26 (3)% and PaO2 increased signi®cantly from 7.2 (0.5) to 30.8 (5.0) kPa compared with controls (P<0.05). Static compliance of the respiratory system (CRS), signi®cantly improved in the SURF-PLV-group compared with controls (P<0.05). Upon histological examination, the SURF-group revealed the lowest total injury score compared with controls and the SURF-PLV-group (P<0.05). We conclude that in this experimental model of ALI, treatment with a small dose of exogenous surfactant improves pulmonary gas exchange and reduces the lung injury more effectively than the combined treatment of a small dose of exogenous surfactant and PLV. Br J Anaesth 2001; 87: 593±601 Keywords: lung, acute injury; ventilation, partial liquid; lung, surfactant; lung, gas exchange; blood, haemodynamics; model, animal Accepted for publication: May 10, 2001
De®ciency of alveolar surfactant, pulmonary hypertension, intrapulmonary right-to-left shunting, and poor arterial oxygenation are features of both experimental acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS).1 Loss of surfactant increases
surface tension, end-expiratory alveolar collapse, and atelectasis. Mechanical ventilation can further damage the alveolocapillary unit by overdistension, and cyclic collapse and reopening of terminal airways.2±5 Mechanical ventilation with
Ó The Board of Management and Trustees of the British Journal of Anaesthesia 2001
Wolf et al.
tidal volumes of 6 ml kg±1, a positive end-expiratory pressure (PEEP) level above the lower in¯ection point, and a peak inspiratory pressure below the upper in¯ection point may protect against this effect.2 6 Other treatments to reduce the mechanical shear stress of the lung include surfactant replacement,7±11 partial liquid ventilation (PLV),12±17 and extracorporal membrane oxygenation (ECMO).18 Giving surfactant may reduce surface tension, improve gas exchange and lung mechanics.7±11 In PLV the lung is partially ®lled with a per¯uorocarbon and conventional mechanical ventilation is resumed. PLV can improve gas exchange and lung mechanics without signi®cantly affecting systemic circulation.12±17 Exogenous surfactant and PLV have been investigated using different doses and different experimental models of ALI.19±29 The effects on gas exchange, haemodynamics, lung mechanics, and lung damage were variable. A combination of 100 mg kg±1 of surfactant with PLV, restored pulmonary gas exchange more ef®ciently in an experimental model of neonatal ALI than surfactant therapy alone. However, a combination of PLV with only 5 mg kg±1 of surfactant failed to give additional bene®t compared with PLV alone.27 29 We compared a single dose of 50 mg kg±1 surfactant alone vs 50 mg kg±1 surfactant combined with PLV in a pig model of ALI, with measurements of gas exchange, haemodynamics, respiratory mechanics, and progression of lung injury.
Methods This study was approved by the Berlin Animal Protection Committee in accordance with German Animal Protection Law, and conforms with the Guide for the Care and Use of Laboratory Animals (DHHS, PHS, NIH Publication No. 8523).
General experimental procedures We studied 24 piglets (weight 23±27 kg), aged between 6 and 8 weeks. Anesthesia was induced with thiopental (10 mg kg±1 i.v.) and fentanyl (10 mg kg±1 i.v. followed by an infusion of 0.05±0.08 mg kg±1 min±1). Muscle relaxation was obtained with pancuronium bromide (0.15 mg kg±1 i.v. bolus, followed by a continuous infusion of 2.5 mg kg±1 min±1). Immediately after induction, the pigs were tracheotomized and intubated with a 9.0 mm outer diameter tracheal tube, ®tted with a heat and moisture exchanger. The animals were placed supine and ventilated in a volume controlled mode (tidal volume 10±12 ml kg±1, respiratory rate 16 min±1, FIO2 1.0, I:E ratio 1:1, PEEP 5 cm H2O) with an EVITA 2 model 76 ventilator (DraÈger, LuÈbeck, Germany). Core temperature was maintained within 60.5°C of the pre-study value using a heating pad. No drugs were used to support the circulation.
We placed a pulmonary artery catheter (model 93A-4317.5 Fr, Baxter Healthcare Corporation, Irvine, CA, USA) percutaneously via the femoral vein, and an arterial cannula (18 G; Vygon, Ecouen, France) into the femoral artery, for blood sampling and haemodynamic measurements. Heart rate (HR), central venous pressure (CVP), mean arterial pressure (MAP), mean pulmonary artery pressure (MPAP), and pulmonary artery wedge pressure (PCWP) were recorded using a Hewlett-Packard monitoring system (Model 66 S, BoÈblingen, Germany). Measurements were taken with pigs in the supine position with zero at the level of the midaxilla. Vascular pressures were the average taken at end-expiration of three successive respiratory cycles. Cardiac output (CO) was determined by thermodilution using the mean of four measurements (10 ml saline at 1±5°C) arbitrarily performed during different phases of the Ç T), systemic Ç S/Q respiratory cycle. Intrapulmonary shunt (Q vascular resistance (SVR), and pulmonary vascular resistance (PVR) were calculated using standard formulae. All blood samples (arterial and mixed venous) were collected anaerobically, and analysed within 5 min (ABL 520, Radiometer, Copenhagen, Denmark). Arterial oxygen saturation (SaO2) and mixed venous oxygen saturation (SvO2) were measured by spectrophotometry with the analyser calibrated with pig blood (OSM 3 Hemoximeter, Radiometer). Static compliance of the respiratory system (CRS) was determined using automated inspiratory, repetitive occlusions (1 s) at single volume steps (SCASS).30 Measurements started with 10 ml Vt up to a maximum Vt of 10±12 ml kg±1, using volume steps of 10 ml each. CRS was calculated as mean of all generated pressure±volume curves from the inspiratory limb. Lung tissue from all animals was examined histologically. After killing the animals, the tracheal tube was clamped at end-expiration (PEEP 5 cm H2O) and the lungs were removed. Per¯uorocarbon was left in situ in animals treated with PLV. Tissues were ®xed in 5% formalin. Specimens from the cranial ventral (non-dependent) and caudal dorsal (dependent) lobes were stained with haematoxylin and eosin and then scored using a semiquantitative scoring system by an experienced veterinary pathologist (A. S-K.), blinded to treatment, for interstitial in®ltration, interstitial oedema, emphysema, and atelectasis. Each variable was scored using a 0±4-point scale, with no injury scored 0, injury in 25% of the ®eld scored 1, injury in 50% of the ®eld scored 2, injury in 75% of the ®eld scored 3, and injury throughout the ®eld scored 4. The total score maximum was 16.
Induction of ALI Repeated lavage with warmed isotonic saline (37°C) was done to produce lung surfactant depletion as reported by Lachmann and co-workers, and described in detail elsewhere.31 32 Induction of ALI was assumed when the PaO2/ FIO2 ratio was persistently less than 13 kPa for 1 h.
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Exogenous surfactant and PLV Table 1 Time course of HR, MABP, MPAP, CO, SVR, and PVR during baseline (pre-lavage), after induction of ALI (post-lavage), and for 6 h thereafter, in controls (n=8 at ALI; four pigs died before 6 h after ALI), in pigs treated with a single intratracheal dose of 50 mg kg±1 of surfactant (Curosurfâ) after induction of ALI (SURF-group) (n=8 pigs, none died), and in pigs treated with a single intratracheal dose of 50 mg kg±1 of surfactant (Curosurfâ) followed by PLV with 30 ml kg±1 of per¯uorocarbon (PF 5080) after induction of ALI (SURF-PLV-group) (n=8 pigs, none died). Data are mean (SEM). Intergroup comparison: controls vs SURF-PLV-group and controls vs SURF-group: *P<0.05, and SURF-PLV-group vs SURF-group: ²P<0.05 (Kruskal±Wallis ANOVA and post hoc Dunn's test). Intragroup comparison: data measured after induction of ALI vs data obtained at hourly intervals thereafter: ³P<0.05 (Friedman test and post hoc Dunn's test) Group
Baseline ALI 1h 2h 3h 4h 5h 6h
SURF SURF-PLV Controls SURF SURF-PLV Controls SURF SURF-PLV Controls SURF SURF-PLV Controls SURF SURF-PLV Controls SURF SURF-PLV Controls SURF SURF-PLV Controls SURF SURF-PLV Controls
HR (beats min±1)
MABP (mm Hg)
MPAP (mm Hg)
CO (litre min±1)
SVR (dyn s cm±5)
PVR (dyn s cm±5)
Mean
SEM
Mean
SEM
Mean
SEM
Mean
SEM
Mean
SEM
Mean
SEM
77 95 95 102 102 93 92 100 93 88 89 93 86 88 100 77 90 97 79 93 102 80 95 109
4 5 9 11 6 6 10 6 5 9 5 7 9 6 10 5 5 10 8 11 9 8 8 7
102 99 88 94 94 89 91 92 87 92 94 83 98 93 87 99 91 89 99 88 81 97 82 74³
5 5 5 4 5 6 4 6 7 6 5 7 6 2 8 5 4 9 5 6 9 5 7 11
20 23 20 25 28 28 27 32 30 28 34³ 35 30 36³ 36 30* 38²³ 39³ 29* 39²³ 41³ 30* 40²³ 41³
1 1 1 1 2 2 2 2 2 2 2 2 2 1 2 2 1 2 2 1 3 3 1 3
3.6 3.8 3.6 4.4 4.4 3.8 3.7 4.0 3.9 3.4 3.5 3.4 2.8³ 3.1³ 3.8 2.6³ 2.9³ 3.7 2.6³ 3.2³ 3.5 2.6³ 3.1³ 3.5
0.2 0.5 0.3 0.6 0.4 0.2 03 03 04 0.3 0.3 0.2 0.3 0.3 0.4 0.2 0.3 0.3 0.3 0.4 0.4 0.2 0.3 0.5
2081 2026 1827 1650 1593 1718 1769 1614 1688 1930 1944 1697 2573 2145 1767 2723 2278 1845 2831 2009 1742 2662 1857 1601
119 285 201 210 191 227 150 160 243 163 229 194 186 192 279 176 258 326 207 290 323 188 337 427
149 241 165 266 268 301 335 366 329 392 466 466 525³ 578³ 486 592³ 667³ 563 581³ 663³ 596³ 560³ 659³ 627
30 52 25 49 28 53 63 38 49 60 76 33 73 79 50 79 69 70 98 104 100 83 82 110
Experimental procedure After induction of ALI, the animals were randomly assigned to receive a single intratracheal dose of surfactant alone (50 mg kg±1, Curosurfâ) (SURF-group, n=8), or a single intratracheal dose of surfactant (50 mg kg±1), followed after 30 min by 30 ml kg±1 of per¯uorocarbon (PF 5080, 3M, Germany) (SURF-PLV-group, n=8), or no further intervention (controls, n=8). Evaporative losses of PF 5080 were replaced at a dose of 4 (3) ml kg±1 every hour as previously found by our group.33 PF 5080 (C8F18) is a non-ozone-depleting PFC with boiling point 102°C, density (at 25°C) 1.76 g ml±1, viscosity (at 25°C) 1.4 cp, vapour pressure (at 37°C) 6.8 kPa, solubility of oxygen (at 37°C) 49 ml 100 ml±1, solubility of carbon dioxide (at 37°C) 176 ml 100 ml±1, and surface tension (at 25°C) of 15 dyn s cm±1 (information taken from 3M data sheet). Curosurfâ is isolated from minced pig lungs and contains 99% lipids, mainly phospholipids, and 1% low molecular weight hydrophobic apoproteins SP-B and SP-C.16
Statistical analysis Results are expressed as mean (SEM). The data were obtained at baseline (pre-lavage), immediately after the
induction of ALI (post-lavage) and at hourly intervals for 6 h thereafter. Statistical analysis was performed using SPSS for Windows 8.0 and Sigmastat (SPSS Inc., Chicago, IL, USA). Differences between groups were evaluated using Kruskal±Wallis ANOVA followed by post hoc comparisons with Dunn's test (intergroup comparison). The Friedman test was used to compare the data after induction of ALI with the data measured during the subsequent 6 h (intragroup comparison). For post hoc testing, Dunn's test also was applied. Statistical signi®cance was assumed at P<0.05.
Results All animals were comparable with regard to body weight and pre-study conditions. Pre-lavage data of pulmonary gas exchange, lung compliance, and haemodynamics did not differ signi®cantly between groups (Tables 1 and 2). ÇT Ç S/Q In all animals, induction of ALI increased Q concomitant with a decrease in PaO2. Cardiac output (CO), mean pulmonary artery pressure (MPAP), and pulmonary vascular pressure (PVR) increased while mean arterial blood pressure (MABP), and systemic vascular resistance (SVR) decreased (Tables 1 and 2).
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Wolf et al. Ç S/Q Ç T), arterial oxygen tension (PaO ), arterial carbon dioxide tension (PaCO ), arterial pH (pHa), oxygen Table 2 Time course of intrapulmonary shunting (Q 2 2 delivery (DO2), oxygen consumption (VÇO2), static compliance of the respiratory system (CRS), and survivors during baseline (pre-lavage), after induction of ALI (post-lavage), and for 6 h thereafter, in controls (n=8 at ALI; four pigs died before 6 h after ALI), in pigs treated with a single intratracheal dose of 50 mg kg±1 of surfactant (Curosurfâ) after induction of ALI (SURF-group) (n=8 pigs, none died), and in pigs treated with a single intratracheal dose of 50 mg kg±1 of surfactant (Curosurfâ) followed by PLV with 30 ml kg±1 of per¯uorocarbon (PF 5080) after induction of ALI (SURF-PLV-group) (n=8 pigs, none died). Data are mean (SEM). Intergroup comparison: controls vs SURF-PLV-group and controls vs SURF-group: *P<0.05, and SURF-PLV-group vs SURFgroup: ²P<0.05 (Kruskal±Wallis ANOVA and post hoc Dunn's test). Intragroup comparison: data measured after induction of ALI vs data obtained at hourly intervals thereafter: ³P<0.05 (Friedman test and post hoc Dunn's test) Group
Baseline SURF SURF-PLV Controls ALI SURF SURF-PLV Controls 1h SURF SURF-PLV Controls 2h SURF SURF-PLV Controls 3h SURF SURF-PLV Controls 4h SURF SURF-PLV Controls 5h SURF SURF-PLV Controls 6h SURF SURF-PLV Controls
Ç T (%) Ç S/Q Q
PaO2 (kPa)
PaCO2 (kPa)
pHa
Mean
SEM
Mean
SEM
Mean
SEM
Mean
12 16 16 51 54 56 38* 44³ 57 25*³ 28³ 52 20*³ 24*³ 53 13*³ 22*³ 52 12*³ 24³ 56 12*³ 26³ 56
1 3 3 5 3 4 4 4 3 3 2 4 2 2 5 1 2 3 2 3 6 2 3 4
75.7 68.0 72.7 8.1 7.2 7.6 19.2* 11.0 7.3 36.8* 23.5* 8.0 48.3*³ 31.6*³ 8.1 64.5*³ 34.0³ 7.7 64.9*³ 35.1³ 7.2 61.2*³ 30.8²³ 7.0
3.2 3.8 3.6 0.7 0.5 0.7 4.8 3.1 0.4 6.7 3.6 0.5 6.6 3.3 0.6 2.6 3.4 0.5 3.7 4.6 0.7 4.7 5.0 0.4
4.7 5.5 6.1 6.1 7.3 7.5 6.6 7.6 7.1 5.7* 8.4² 8.0 5.7* 8.4² 8.5 5.7* 8.5² 8.2 5.9* 9.2² 9.1 7.0 10.0³ 9.9³
0.5 0.4 0.7 0.6 0.6 0.5 0.4 0.7 0.6 0.3 0.3 0.8 0.4 0.4 0.8 0.3 0.6 0.4 0.5 0.8 0.8 1.0 1.0 0.7
7.56 7.48 7.43 7.42 7.37 7.33 7.41 7.37 7.36 7.46 7.32 7.33 7.48 7.34 7.30 7.47 7.34 7.32 7.46 7.31 7.29 7.45 7.29 7.27
Gas exchange Surfactant alone improved PaO2 from 8.1 (0.7) kPa after onset of ALI to 61.2 (4.7) kPa after 6 h of treatment (P<0.05 vs controls; Fig. 1, Table 2). The increase of PaO2 in the SURF-group was greater than the increase in the SURFPLV-group after 6 h of treatment (P<0.05 vs SURF-PLV; Fig. 1, Table 2). In the PLV-SURF-group the increase of PaO2 from 7.2 (0.5) kPa after onset of ALI to 30.8 (5.0) kPa after 6 h of treatment was greater than in controls (P<0.05 vs controls; Fig. 1, Table 2). Ç T decreased signi®cantly comÇ S/Q In the SURF group Q pared with controls (51 (5)% at onset of ALI to 12 (2)% 6 h after treatment, P<0.05 vs controls; Fig. 2, Table 2). In the Ç T was signi®cantly decreased comÇ S/Q SURF-PLV-group Q pared with controls (54 (4)% at onset of ALI to 26 (3)% after 6 h of treatment, P<0.05 vs controls; Fig. 2, Table 2).
Haemodynamics There were no signi®cant changes between groups in HR, MABP, and SVR. In the SURF-group the MPAP increased from 25 (1) mm Hg at onset of ALI to 30 (3) mm Hg after 6 h of treatment, and was signi®cantly less than in controls and in the SURF-PLV-group (P<0.05 vs controls and vs SURFPLV; Fig. 3, Table 1). In the SURF-group, PVR increased
DO2 (ml min±1)
VÇO2 (ml min±1)
CRS (ml mbar±1)
SEM
Mean
SEM
Mean
SEM
Mean
SEM
0.03 0.02 0.04 0.04 0.02 0.03 0.03 0.02 0.04 0.03 0.02 0.04 0.04 0.01 0.04 0.04 0.02 0.03 0.04 0.03 0.03 0.04 0.03 0.03
423 418 396 361 338 257 363 349 277 365* 362 249 324 331 282 321 308 296 312 348 278 326 338 291
28 50 26 34 33 20 27 29 25 31 38 17 31 25 32 28 27 25 28 39 46 23 38 57
142 143 110 134 150 122 130 152 118 136 152 111 128 139 126 132 136 131 125 146 121 133 139 137
14 21 10 16 14 14 15 10 11 11 15 10 16 12 19 13 16 11 12 14 3 14 13 19
22 21 23 9 9 9 9 12* 8 9 14* 9 10 13* 8 9 13* 6 9 14 6 9 15* 7
1.0 1.8 1.0 0.6 1.0 1.0 0.3 0.9 0.4 0.3 1.7 1.0 0.3 1.3 0.5 0.2 0.4 0.9 0.1 1.2 0.4 0.2 0.4 0.5
Survivors (n)
8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 7 8 8 5 8 8 4
signi®cantly from 266 (49) dyn s cm±5 at onset of ALI to 560 (83) dyn s cm±5 at 6 h of treatment (P<0.05 vs ALIvalues; Table 1). In the SURF-PLV-group, PVR increased signi®cantly from 268 (28) to 659 (82) dyn s cm±5 (P<0.05 vs ALI-values, Table 1). In the SURF-group and in the SURF-PLV-group, CO decreased signi®cantly during the treatment period compared with ALI-values (P<0.05 vs ALI-values; Table 1). In controls there were no signi®cant changes in PVR and CO.
Lung mechanics After induction of ALI, static compliance of the respiratory system decreased from 22 (2) ml cm H2O±1 in all groups to 9 (1) ml cm H2O±1. No further changes of CRS occurred in the SURF-group. In the SURF-PLV-group, CRS improved signi®cantly compared with controls from 9 (1) to 15 (0.4) ml cm H2O±1 at 6 h of treatment (P<0.05 vs controls; Fig. 4, Table 2).
Lung injury The non-dependent lobes in the SURF-group had a signi®cantly smaller injury score for interstitial oedema and emphysema compared with controls and the SURF-PLV-
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Exogenous surfactant and PLV
Ç S/Q Ç T) during baseline Fig 2 Time course of intrapulmonary shunting (Q (pre-lavage), after induction of ALI (post-lavage), and for 6 h thereafter, in controls (n=8 at ALI; four pigs died before 6 h after ALI), in pigs treated with surfactant (Curosurfâ) after induction of ALI (SURF-group) (n=8 pigs, none died), and in pigs treated with a single surfactant (Curosurfâ) followed by PLV with 30 ml kg±1 of per¯uorocarbon (PF 5080) after induction of ALI (SURF-PLV-group) (n=8 pigs, none died). Data are mean (SEM). Intergroup comparison: controls vs SURF-PLV-group and controls vs SURF-group: *P<0.05, and SURF-PLV-group vs SURF-group: ²P<0.05 (Kruskal±Wallis ANOVA and post hoc Dunn's test). Intragroup comparison: data measured after induction of ALI vs data obtained at hourly intervals thereafter: ³P<0.05 (Friedman test and post hoc Dunn's test).
Fig 1 Time course of arterial oxygen tension (PaO2) during baseline (prelavage), after induction of ALI (post-lavage), and for 6 h thereafter, in controls (n=8 at ALI; four pigs died before 6 h after ALI), in pigs treated with surfactant (Curosurfâ) after induction of ALI (SURF-group) (n=8 pigs, none died), and in pigs treated with surfactant (Curosurfâ) followed by PLV with 30 ml kg±1 of per¯uorocarbon (PF 5080) after induction of ALI (SURF-PLV-group) (n=8 pigs, none died). Data are mean (SEM). Intergroup comparison: controls vs SURF-PLV-group and controls vs SURF-group: *P<0.05, and SURF-PLV-group vs SURF-group: ²P<0.05 (Kruskal±Wallis ANOVA and post hoc Dunn's test). Intragroup comparison: data measured after induction of ALI vs data obtained at hourly intervals thereafter: ³P<0.05 (Friedman test and post hoc Dunn's test).
group (P<0.05, Table 3). In the SURF-PLV-group, scores for interstitial oedema were signi®cantly greater compared with controls in the non-dependent lobes (P<0.05, Table 3). Comparing tissue damage in dependent lobes, the SURFgroup had signi®cantly less atelectasis and emphysema than controls (P<0.05) and less interstitial oedema and emphysema than the SURF-PLV-group (P<0.05, Table 3). In the SURF-PLV-group, interstitial in®ltration and atelectasis of the dependent lobes was less than in controls and the SURFgroup (P<0.05 vs controls and vs SURF), while interstitial oedema and emphysema in the dependent lobes in the SURF-PLV-group was greater than in controls and the SURF-group (P<0.05, Table 3). The overall lung injury score of the SURF-group was less in the non-dependent lobes, compared with the SURF-PLVgroup and controls (P<0.05, Table 3).
Survival All animals in both treatment groups survived to the end of the study. In the control-group, four animals died of irreversible hypoxaemia during the study, one after 3 h, two after 4 h, and one 5 h after induction of ALI (Table 2).
Discussion In this study, we compared the effects of a single, small dose of surfactant alone and combined with a full dose of PLV on oxygenation, haemodynamics, respiratory mechanics, and lung injury in an animal model of ALI. A small dose of
surfactant was better than a combined treatment with a small dose of surfactant and PLV to restore gas exchange. Respiratory mechanics were only improved in the group treated with the combination of surfactant and PLV. Atelectasis, interstitial oedema, and emphysema were signi®cantly less in the surfactant group than in controls. Compared with the group receiving surfactant and PLV, the surfactant group had a signi®cant smaller total lung injury score. Surfactant therapy combined with PLV has been studied in different types of ALI.19 29 Studies have been done in surfactant de®cient pre-term animals,19 24 26 29 isolated lungs of pre-term animals,23 27 newborn animals with ALI induced by surfactant wash-out,21 25 27 and experimental ALI in adult animals.20 22 Criteria for onset of ALI after surfactant wash-out was a PaO2/FIO2 ratio below 8 kPa (60 mm Hg), with the exception of the studies by Hartog and co-workers and Kelly and co-workers, who used a value below 13 kPa (100 mm Hg) to indicate ALI.20 22 The duration of PaO2/FIO2 less than 8 kPa of 30 min to indicate the induction of ALI was speci®ed only in one study.21 Our lavage procedure caused a stable PaO2/FIO2 ratio of 7.6 (0.6) kPa (57 (5) mm Hg) for at least 1 h after the last lavage. The severity of the lung injury in our animals resembles surfactant de®cient pre-term animals, shown by the high shunt fraction, which was 54 (4)% after lung injury. Mrozek and co-workers compared four different treatments in newborn piglets, after induction of ALI. One group received 100 mg kg±1 surfactant, one group received PFC in a dose equivalent to the functional residual capacity, one group received PFC 30 min after surfactant replacement, and one group received surfactant 30 min after instillation of
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Fig 3 Time course of MPAP during baseline (pre-lavage), after induction of ALI (post-lavage), and for 6 h thereafter, in controls (n=8 at ALI; four pigs died before 6 h after ALI), in pigs treated with surfactant (Curosurfâ) after induction of ALI (SURF-group) (n=8 pigs, none died), and in pigs treated with surfactant (Curosurfâ) followed by PLV with 30 ml kg±1 of per¯uorocarbon (PF 5080) after induction of ALI (SURFPLV-group) (n=8 pigs, none died). Data are mean (SEM). Intergroup comparison: controls vs SURF-PLV-group and controls vs SURF-group: *P<0.05, and SURF-PLV-group vs SURF-group: ²P<0.05 (Kruskal±Wallis ANOVA and post hoc Dunn's test). Intragroup comparison: data measured after induction of ALI vs data obtained at hourly intervals thereafter: ³P<0.05 (Friedman test and post hoc Dunn's test).
PFC.27 In contrast to our ®nding that a single dose of surfactant caused the greatest improvement in PaO2, Mrozek and colleagues found that a combination of surfactant and PLV was better than the effect of surfactant alone on gas exchange, lung mechanics, and lung pathology. They make no comment on the decrease in PaO2 after instillation of PFC in the group treated with PLV after surfactant replacement. These differences could be attributed to the following: (1) different timepoints of measurement, (2) the use of a bovine surfactant (Survanta), (3) a higher dose of surfactant (100 mg kg±1), (4) newborn piglets as study subjects, and (5) the use of pre-oxygenated per¯ubron (LiquiVent). Another difference was positioning the animals while ®lling the lungs with PFC, which might have allowed greater per¯uorocarbon dose and a more homogenous distribution of PFC throughout the lungs, although this technique appears to be impractical under clinical circumstances. In a study of ALI induced in premature lambs, Leach and coworkers compared either surfactant replacement, a combination of surfactant replacement and PLV, or PLV alone.29 In this study, a very small dose (5 mg kg±1) of an arti®cial surfactant (Exosurf) did not improve oxygenation and respiratory mechanics when compared with conventional ventilation. The combination of surfactant and PLV was not better than PLV alone. Leach and co-workers attributed the lack of surfactant ef®cacy to the small dose used and to the modest physiologic activity of synthetic surfactant, which gives a greater surface tension than natural surfactant.29 In our study, improvements in oxygenation and intrapulmonary right-to-left shunt were delayed in the SURF-PLV-
Fig 4 Time course of static compliance of the respiratory system (CRS) during baseline (pre-lavage), after induction of ALI (post-lavage), and for 6 h thereafter, in controls (n=8 at ALI; four pigs died before 6 h after ALI), in pigs treated with surfactant (Curosurfâ) after induction of ALI (SURF-group) (n=8 pigs, none died), and in pigs treated with surfactant (Curosurfâ) followed by PLV with 30 ml kg±1 of per¯uorocarbons (PF 5080) after induction of ALI (SURF-PLV-group) (n=8 pigs, none died). Data are mean (SEM). Intergroup comparison: controls vs SURF-PLVgroup: *P<0.05 (Kruskal±Wallis ANOVA and post hoc Dunn's test).
group. This could have been because: (1) PLV was started 30 min after surfactant was instilled, to avoid wash-out of exogenous surfactant; (2) inhomogeneous surfactant distribution could have caused PFC to only enter some regions and, thereby, limit alveolar recruitment. Leach and coworkers describe a transient increase in the expiratory resistance of their surfactant-PLV group and suggested that the distal movement of per¯uorocarbons could have been delayed, as surfactant will remain in small airways and alveolar ducts.27 In a study from GoÈthberg and co-workers using a model of premature ALI, the treatment of PLV combined with conventional ventilation or combined with high-frequency oscillatory ventilation (HFOV) 2 h after giving 100 mg kg±1 of surfactant (Infasurf) improved oxygenation compared with treatment with surfactant and conventional ventilation alone.17 HFOV after surfactant replacement improved PaO2 to a similar extent than HFOV combined with PLV and was signi®cantly more effective than PLV and conventional ventilation. The different results of a treatment with PLV and conventional ventilation after surfactant replacement, compared with our data, might be because of different models, a different PFC, a later application of PFC, and different doses of surfactant. Improvement in oxygenation with HFOV, with and without PLV, could be explained by changes in airway pressures and the development of a high intrinsic PEEP from the ventilatory pattern. Previous studies showed that combining PFC and high levels of PEEP enhances the effects of PLV on pulmonary gas exchange. 15±17 The improvement in CRS in our piglets treated with the combination of surfactant and PLV supports the ®ndings of other investigators, and appears to be dose dependent.9 13 20 We measured the static compliance of the respiratory system, with an inspiratory shutter technique, to exclude
598
Exogenous surfactant and PLV Table 3 Lung injury score of the non-dependent and the dependent lobes for atelectasis, interstitial in®ltration, interstitial oedema, emphysema, and total lung injury score in controls (n=8 at ALI; four pigs died before 6 h after ALI), in pigs treated with a single intratracheal dose of 50 mg kg±1 of surfactant (Curosurfâ) after induction of ALI (SURF-group) (n=8 pigs, none died), and in pigs treated with a single intratracheal dose of 50 mg kg±1 of surfactant (Curosurfâ) followed by PLV with 30 ml kg±1 of per¯uorocarbon (PF 5080) after induction of ALI (SURF-PLV-group) (n=8 pigs, none died). Data are mean (SEM). Intergroup comparison: controls vs SURF-PLV-group and controls vs SURF-group: *P<0.05, and SURF-PLV-group vs SURF-group: ²P<0.05 (Kruskal±Wallis ANOVA and post hoc Dunn's test). Intragroup comparison: non-dependent vs dependent lobes: §P<0.05 (Friedman test and post hoc Dunn's test) Non-dependent lobes SURF
Atelectasis Interstitial in®ltration Interstitial oedema Emphysema Total injury score
Dependent lobes PFC-SURF
Controls
SURF
PFC-SURF
Controls
Mean
SEM
Mean
SEM
Mean
SEM
Mean
SEM
Mean
SEM
Mean
SEM
0.68* 1.38 0.1*§ 0.11* 2.27*§
0.09 0.1 0.04 0.03
0.94*§ 0.31*² 1.32*²§ 1.76²§ 4.33²
0.1 0.08 0.09 0.15
0.3§ 1.46§ 0.5§ 1.9§ 3.86
0.04 0.02 0.05 0.04
0.78* 1.65 1.11 0.19* 4.02
0.07 0.04 0.05 0.03
0.08*² 0.34*² 2.13*² 1.47*² 3.73
0.03 0.04 0.05 0.05
1.41 1.76 1.2 0.4 3.77
0.07 0.04 0.05 0.5
effects of PFC vapour-pressure on expiratory volumes. We used 30 ml kg±1 of per¯uorocarbon, approximately the functional residual capacity of healthy lungs and added further liquid according to our past observations.33 TuÈtuÈncuÈ and co-workers compared the effects of PLV with 18 ml kg±1 PFC with PLV using 18 ml kg±1 saline, in a similar model of ALI in rabbits, and found that compliance of the respiratory system increased in the PFC group.13 Studying adult rabbits with induced ALI, Kelly and colleagues compared the effects of different treatments.20 The treatments were PLV with 20 ml kg±1 PFC, nebulized PFC, 100 mg kg±1 arti®cial surfactant (ALEC), 100 mg kg±1 porcine surfactant (Curosurfâ), the combination of PLV and ALEC, the combination of PLV and Curosurfâ, and a control group. Our observations support their ®ndings for arterial oxygenation. Regarding lung mechanics, 100 mg kg±1 of Curosurfâ improved compliance as effectively as the combination of PLV and Curosurfâ. In our study, the smaller dose of exogenous surfactant, was not suf®cient to improve lung mechanics. Kelly and co-workers point out that surfactant from animals contains surfactant apoproteins, which prevent inhibition of surfactant by protein-rich ¯uid in lungs after induction of ALI, and that this effect is dose-dependent.20 In studies in humans, lung compliance decreases after surfactant treatment, despite increases in functional residual capacity and improvements in oxygenation. This could be because of slow recruitment of atelectatic lung areas, with stabilization of the initially opened lung units.34 35 Lack of improvement in lung compliance after surfactant administration in experimental ALI was also found by Mrozek and co-workers.27 We consider that the small dose of surfactant used in our study did not entirely overcome surfactant inhibition, and that the amount of lung tissue opened up in the SURF-group, although suf®cient to improve gas exchange, was not suf®cient to produce effects on CRS.
Treatment with surfactant alone caused less histological injury, for interstitial oedema, atelectasis, and emphysema compared with controls and compared with the SURF-PLVgroup. Comparing the overall lung injury scores between groups, treatment with surfactant alone caused less damage in non-dependent lobes compared with controls and the SURF-PLV-group. A small dose of surfactant reduces the in¯ammatory response in ALI, prevents further atelectasis, and improves gas exchange. The effects on in¯ammation could be attributed to the apoproteins of natural surfactant, which might prevent in¯ammation. The greater lung injury scores in the SURF-PLV-group contrasts with previous results of Mrozek and co-workers, who found least injury with the combined treatment.27 They suggest that the lower inspiratory pressures needed for effective alveolar ventilation could be the reason for less lung injury in this group. The different PFC used for PLV and a higher dose of surfactant could account for these differences. In rats with lavage-induced ALI, Hartog and colleagues compared lung injury after treatment with surfactant, PLV, and high values of PEEP vs healthy controls and injured controls.22 Surfactant prevented progression of lung injury, when compared with healthy controls, and PLV increased lung tissue injury compared with healthy controls. In our study, we found that cardiac output decreased signi®cantly during the study in both treatment groups, which has not been reported previously in short term studies of lavage-induced lung injury.26 36 37 However, DO2 and VÇO2 remained unchanged in both groups, indicating maintenance of a suf®cient oxygen delivery. A possible explanation for the lower values of CO might be reduced sympathic activity in both treatment groups because of better oxygenation. This view is supported by poorer survival in control animals. As suggested by Dantzker and co-workers, a reduction in CO could reduce the intrapulmonary right-toleft shunt.38 The magnitude of this mechanism of shunt
599
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reduction with a CO reduction of 40% in the SURF-group and 30% in the SURF-PLV-group, suggests that this would only partly account for the reduction found, and indicate other mechanisms, such as alveolar recruitment, could be involved. The increase in MPAP in animals treated with the combination of surfactant and PLV could be caused by the PFC. In a study from Morris and co-workers healthy pigs had their lungs ®lled with 40 ml kg±1 of per¯uorocarbons and were conventionally ventilated.35 Pulmonary blood ¯ow was diverted from the dependent regions of the lung, associated with an increase in MPAP. The authors suggested that a greater hydrostatic pressure gradient in PFC-®lled alveoli, compared with the gradient in the blood vessels, could cause this effect.37 In conclusion, using an experimental model of ALI in piglets, we found that treatment with a single small dose of surfactant improved oxygenation, decreased intrapulmonary right-to-left shunt, and reduced lung tissue damage more effectively than a combination of surfactant with PLV. However, only the combined treatment of exogenous surfactant and PLV improved lung mechanics. Taken with other evidence, these ®ndings show that further research is needed to ®nd the least dose of surfactant that is effective.
11 12 13
14
15
16
17 18
Acknowledgements Supported by a grant from Deutsche Forschungsgemeinschaft (KA 1212/ 3±1). Curosurfâ was generously provided by Serono AG, MuÈnchen, Germany.
References 1 Lewis JF, Jobe AH. Surfactant and the adult respiratory distress syndrome. Am Rev Respir Dis 1993; 147: 218±33 2 Lee WL, Detsky AS, Stewart TE. Lung-protective mechanical ventilation strategies in ARDS. Intensive Care Med 2000; 26: 1151±5 3 Green®eld LJ, Ebert PA, Benson DW. Effect of positive pressure ventilation on surface tension properties of lung extracts. Anesthesiology 1964; 25: 312±6 4 McClenahan JB, Urtnowski A. Effect of ventilation on surfactant and its turn over rate. J Appl Physiol 1967; 23: 215±20 5 Hickling KG. Ventilatory management of ARDS: can it affect the outcome? Intensive Care Med 1990; 16: 219±26 6 Amato MB, Barbas CS, Medeiros DM, et al. Effect of a protectiveventilation strategy on mortality in the acute respiratory distress syndrome. N Engl J Med 1998; 338: 347±54 7 Goldsmith LS, Greenspan JS, Rubenstein DS, Wolson MR, Shaffer TH. Immediate improvement in lung volume after exogenous surfactant: alveolar recruitment versus increased distension. J Pediatr 1991; 119: 424±8 8 Lewis JF, Gof®n J, Yue P, McCaig LA, Bjarneson D, Veldhuizen RA. Evaluation of exogenous surfactant treatment strategies in an adult model of acute lung injury. J Appl Physiol 1996; 80: 1156±64 9 Gregory TJ, Steinberg P, Spragg R, et al. Bovine surfactant therapy for patients with acute respiratory distress syndrome. Am J Respir Crit Care Med 1997; 155: 1309±15 10 Walmrath D, GuÈnther A, Ghofrani HA, et al. Bronchoscopic
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surfactant administration in patients with severe adult respiratory distress syndrome and sepsis. Am J Respir Crit Care Med 1996; 154: 57±62 Gladstone IM, Ray AO, Sala®a CM, Perez-Fontan J, Mercurio MR, Jacobs HC. Effect of arti®cial surfactant on pulmonary function in preterm and full-term lambs. J Appl Physiol 1990; 69: 465±72 Fuhrmann BP, Paczan PR, DeFrancisis M. Per¯uorocarbon associated gas exchange. Crit Care Med 1991; 19: 712±22 TuÈtuÈncuÈ AS, Faithfull NS, Lachmann B. Comparison of ventilatory support with intratracheal per¯uorocarbon administration and conventional mechanical ventilation in animals with acute respiratory failure. Am Rev Respir Dis 1993; 148: 785±92 Papo MC, Paczan PR, Fuhrmann BP, et al. Per¯uorocarbonassociated gas exchange improves oxygenation, lung mechanics, and survival in a model of adult respiratory distress syndrome. Crit Care Med 1996; 24: 466±74 Zobel G, Rodl S, Urlesberger B, Dacar D, Trafojer U, Trantina A. The effect of positive end-expiratory pressure during partial liquid ventilation in acute lung injury in piglets. Crit Care Med 1999; 27: 1934±9 Kirmse M, Fujino Y, Hess D, Kacmarek RM. Positive endexpiratory pressure improves gas exchange and pulmonary mechanics during partial liquid ventilation Am J Respir Crit Care Med 1998; 158: 1550±6 Kaisers U, Kuhlen R, Keske U, et al. Superimposing positive endexpiratory pressure during partial liquid ventilation in experimental lung injury. Eur Respir J 1998; 11: 1035±42 Lewandowski K, Rossaint R, Pappert D, et al. High survival rate in 122 ARDS patients managed according to a clinical algorithm including extracorporeal membrane oxygenation. Intensive Care Med 1997; 23: 819±35 GoÈthberg S, Parker TA, Abman SH, Kinsella JP. High-frequency oscillatory ventilation and partial liquid ventilation after acute lung injury in premature lambs with respiratory distress syndrome. Crit Care Med 2000; 28: 2450±6 Kelly KP, Stenson BJ, Drummond GB. Randomised comparison of partial liquid ventilation, nebulised per¯uorocarbon, porcine surfactant, and combined treatments on oxygenation, lung mechanics, and survival in rabbits after saline lung lavage. Intensive Care Med 2000; 26: 1523±30 Merz U, Kellinghaus M, HaÈusler M, Pakrawan N, Klosterhalfen B, HoÈrnchen H. Partial liquid ventilation with surfactant: effects on gas exchange and lung pathology in surfactant-depleted piglets. Intensive Care Med 2000; 26: 109±16 Hartog A, Vazquez de Anda GF, Gommers D, et al. Comparison of exogenous surfactant therapy, mechanical ventilation, with high end-expiratory pressure and partial liquid ventilation in a model of acute lung injury. Br J Anaesth 1999; 82: 81±6 Tarczy-Hornoch P, Hildebrandt J, Standaert TA, Jackon JC. Surfactant replacement increases compliance in premature lamb lungs during partial liquid ventilation in situ. J Appl Physiol 1998; 84: 1316±22 Wolfson MR, Kechner NE, Roache RF, et al. Per¯uorochemical rescue after surfactant treatment: effect of per¯ubron dose and ventilatory frequency. J Appl Physiol 1998; 84: 624±40 Mrozek JD, Bing DR., Meyers PA, Connett JE, Mammel MC. High-frequency oscillation versus conventional ventilation following surfactant administration and partial liquid ventilation. Pediatr Pulmonol 1998; 26: 21±9 Davidson A, Heckmann JL, Donner RM, Miller TF, Shaffer TH, Wolfson MR. Cardiopulmonary interaction during partial liquid ventilation in surfactant-treated preterm lambs. Eur J Pediatr 1998; 157: 138±45
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27 Mrozek JD, Smith KM, Bing DR, et al. Exogenous surfactant and partial liquid ventilation: physiologic and pathologic effects. Am J Respir Crit Care Med 1997; 156: 1058±65 28 Tarczy-Hornoch P, Hildebrandt J, Mates EA, et al. Effects of exogenous surfactant on lung pressure-volume characteristics during liquid ventilation. J Appl Physiol 1996; 80: 1764±71 29 Leach CL, Holm B, Morin FC, et al. Partial liquid ventilation in premature lambs with respiratory distress syndrome: ef®cacy and compatibility with exogenous surfactant. J Pediatr 1995; 126: 412±20 30 Sydow M, Burchardi H, Zinserling J, Ische H, Crozier TA, Weyland W. Improved determination of static compliance by automated single volume steps in ventilated patients. Intensive Care Med 1991; 17: 108±14 31 Kaisers U, Max M, Walter J, et al. Partial liquid ventilation with small volumes of FC 3280 increases survival time in experimental ARDS. Eur Respir J 1997; 10: 1955±61 32 Lachmann B, Robertson B, Vogel J. In-vivo lavage as an experimental model of the respiratory distress syndrome. Acta Anaesthesiol Scand 1980; 24: 231±6 33 Kaisers U, Max M, Schnabel R, et al. Partial liquid ventilation with
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FC 3280 in experimental lung injury: dose-dependent improvement of gas exchange and lung mechanics. Appl Cardiopulm Pathophysiol 1996; 6: 163±70 Cotton RB, Olsson T, Law AB, et al. The physiologic effects of surfactant treatment on gas exchange in newborn premature infants with hyaline membrane disease. Pediatr Res 1993; 34: 495±501 Goldsmith LS, Greenspan JS, Rubenstein SD, Wolfson MR, Shaffer TH. Immediate improvement in lung volume after exogenous surfactant: alveolar recruitment versus increased distention. J Pediatr 1991; 119: 424±8 Moen A, Yu XQ, Almaas R, Curstedt T, Saugstad OD. Acute effects on systemic circulation after intratracheal instillation of Curosurf or Survanta in surfactant-depleted newborn piglets. Acta Paediatr 1998; 87: 297±303 Morris KP, Cox PN, Mazer CD, Frndova H, McKerlie C, Wolfe R. Distribution of pulmonary blood ¯ow in the per¯uorocarbon®lled lung. Intensive Care Med 2000; 26: 756±63 Dantzker DR, Lynch JP, Weg JG. Depression of cardiac output is a mechanism of shunt reduction in the therapy of acute respiratory failure. Chest 1980; 77: 636±42
LABORATORY INVESTIGATIONS Small dose of exogenous surfactant combined with partial liquid ventilation in experimental acute lung injury: effects on gas exchange, haemodynamics, lung mechanics, and lung pathology S. Wolf1, H. Lohbrunner1, T. Busch1, A. Sterner-Kock4, M. Deja1, A. Sarrafzadeh2, U. Neumann3 and U. Kaisers1 1
Klinik fuÈr Anaesthesiologie und Operative Intensivmedizin, ChariteÂ, Campus Virchow Klinikum, Medizinische Fakultaet der Humboldt-Universitaet, Augustenburger Platz 1, D-13353 Berlin, Germany, 2 Abteilung fuÈr Neurochirurgie, ChariteÂ, Campus Virchow Klinikum, Medizinische Fakultaet der HumboldtUniversitaet, Augustenburger Platz 1, D-13353 Berlin, Germany, 3Chirurgische Klinik und Poliklinik, ChariteÂ, Campus Virchow Klinikum, Medizinische Fakultaet der Humboldt-Universitaet, Augustenburger Platz 1, D-13353 Berlin, Germany and 4Molekulare Haematologie, Klinikum der Johann Wolfgang von Goethe Universitaet, Theodor-Stern-Kai 7, D-60590 Frankfurt Main, Germany A combination of exogenous surfactant and partial liquid ventilation (PLV) with per¯uorocarbons should enhance gas exchange, improve respiratory mechanics and reduce tissue damage of the lung in acute lung injury (ALI). We used a small dose of exogenous surfactant with and without PLV in an experimental model of ALI and studied the effects on gas exchange, haemodynamics, lung mechanics, and lung pathology. ALI was induced by repeated lavages (PaO2/FIO2 less than 13 kPa) in 24 anaesthesized, tracheotomized and mechanically ventilated (FIO2 1.0) juvenile pigs. They were treated randomly with either a single intratracheal dose of surfactant (50 mg kg±1, Curosurfâ, Serono AG, MuÈnchen, Germany) (SURF-group, n=8), a single intratracheal dose of surfactant (50 mg kg±1, Curosurfâ) followed by PLV with 30 ml kg±1 of per¯uorocarbon (PF 5080, 3M, Germany) (SURF-PLV-group, n=8) or no further intervention (controls, n=8). Pulmonary gas exchange, respiratory mechanics, and haemodynamics were measured hourly for a 6 h period. In the SURF-group, the intrapulmonary right-to-left shunt (QÇS/QÇT) decreased signi®cantly from mean 51 (SEM 5)% after lavage to 12 (2)%, and PaO2 increased signi®cantly from 8.1 (0.7) to 61.2 (4.7) kPa compared with controls and compared with the SURF-PLV-group (P<0.05). In the SURF-PLV-group, QÇS/QÇT decreased signi®cantly from 54 (3)% after induction of ALI to 26 (3)% and PaO2 increased signi®cantly from 7.2 (0.5) to 30.8 (5.0) kPa compared with controls (P<0.05). Static compliance of the respiratory system (CRS), signi®cantly improved in the SURF-PLV-group compared with controls (P<0.05). Upon histological examination, the SURF-group revealed the lowest total injury score compared with controls and the SURF-PLV-group (P<0.05). We conclude that in this experimental model of ALI, treatment with a small dose of exogenous surfactant improves pulmonary gas exchange and reduces the lung injury more effectively than the combined treatment of a small dose of exogenous surfactant and PLV. Br J Anaesth 2001; 87: 593±601 Keywords: lung, acute injury; ventilation, partial liquid; lung, surfactant; lung, gas exchange; blood, haemodynamics; model, animal Accepted for publication: May 10, 2001
De®ciency of alveolar surfactant, pulmonary hypertension, intrapulmonary right-to-left shunting, and poor arterial oxygenation are features of both experimental acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS).1 Loss of surfactant increases
surface tension, end-expiratory alveolar collapse, and atelectasis. Mechanical ventilation can further damage the alveolocapillary unit by overdistension, and cyclic collapse and reopening of terminal airways.2±5 Mechanical ventilation with
Ó The Board of Management and Trustees of the British Journal of Anaesthesia 2001
Wolf et al.
tidal volumes of 6 ml kg±1, a positive end-expiratory pressure (PEEP) level above the lower in¯ection point, and a peak inspiratory pressure below the upper in¯ection point may protect against this effect.2 6 Other treatments to reduce the mechanical shear stress of the lung include surfactant replacement,7±11 partial liquid ventilation (PLV),12±17 and extracorporal membrane oxygenation (ECMO).18 Giving surfactant may reduce surface tension, improve gas exchange and lung mechanics.7±11 In PLV the lung is partially ®lled with a per¯uorocarbon and conventional mechanical ventilation is resumed. PLV can improve gas exchange and lung mechanics without signi®cantly affecting systemic circulation.12±17 Exogenous surfactant and PLV have been investigated using different doses and different experimental models of ALI.19±29 The effects on gas exchange, haemodynamics, lung mechanics, and lung damage were variable. A combination of 100 mg kg±1 of surfactant with PLV, restored pulmonary gas exchange more ef®ciently in an experimental model of neonatal ALI than surfactant therapy alone. However, a combination of PLV with only 5 mg kg±1 of surfactant failed to give additional bene®t compared with PLV alone.27 29 We compared a single dose of 50 mg kg±1 surfactant alone vs 50 mg kg±1 surfactant combined with PLV in a pig model of ALI, with measurements of gas exchange, haemodynamics, respiratory mechanics, and progression of lung injury.
Methods This study was approved by the Berlin Animal Protection Committee in accordance with German Animal Protection Law, and conforms with the Guide for the Care and Use of Laboratory Animals (DHHS, PHS, NIH Publication No. 8523).
General experimental procedures We studied 24 piglets (weight 23±27 kg), aged between 6 and 8 weeks. Anesthesia was induced with thiopental (10 mg kg±1 i.v.) and fentanyl (10 mg kg±1 i.v. followed by an infusion of 0.05±0.08 mg kg±1 min±1). Muscle relaxation was obtained with pancuronium bromide (0.15 mg kg±1 i.v. bolus, followed by a continuous infusion of 2.5 mg kg±1 min±1). Immediately after induction, the pigs were tracheotomized and intubated with a 9.0 mm outer diameter tracheal tube, ®tted with a heat and moisture exchanger. The animals were placed supine and ventilated in a volume controlled mode (tidal volume 10±12 ml kg±1, respiratory rate 16 min±1, FIO2 1.0, I:E ratio 1:1, PEEP 5 cm H2O) with an EVITA 2 model 76 ventilator (DraÈger, LuÈbeck, Germany). Core temperature was maintained within 60.5°C of the pre-study value using a heating pad. No drugs were used to support the circulation.
We placed a pulmonary artery catheter (model 93A-4317.5 Fr, Baxter Healthcare Corporation, Irvine, CA, USA) percutaneously via the femoral vein, and an arterial cannula (18 G; Vygon, Ecouen, France) into the femoral artery, for blood sampling and haemodynamic measurements. Heart rate (HR), central venous pressure (CVP), mean arterial pressure (MAP), mean pulmonary artery pressure (MPAP), and pulmonary artery wedge pressure (PCWP) were recorded using a Hewlett-Packard monitoring system (Model 66 S, BoÈblingen, Germany). Measurements were taken with pigs in the supine position with zero at the level of the midaxilla. Vascular pressures were the average taken at end-expiration of three successive respiratory cycles. Cardiac output (CO) was determined by thermodilution using the mean of four measurements (10 ml saline at 1±5°C) arbitrarily performed during different phases of the Ç T), systemic Ç S/Q respiratory cycle. Intrapulmonary shunt (Q vascular resistance (SVR), and pulmonary vascular resistance (PVR) were calculated using standard formulae. All blood samples (arterial and mixed venous) were collected anaerobically, and analysed within 5 min (ABL 520, Radiometer, Copenhagen, Denmark). Arterial oxygen saturation (SaO2) and mixed venous oxygen saturation (SvO2) were measured by spectrophotometry with the analyser calibrated with pig blood (OSM 3 Hemoximeter, Radiometer). Static compliance of the respiratory system (CRS) was determined using automated inspiratory, repetitive occlusions (1 s) at single volume steps (SCASS).30 Measurements started with 10 ml Vt up to a maximum Vt of 10±12 ml kg±1, using volume steps of 10 ml each. CRS was calculated as mean of all generated pressure±volume curves from the inspiratory limb. Lung tissue from all animals was examined histologically. After killing the animals, the tracheal tube was clamped at end-expiration (PEEP 5 cm H2O) and the lungs were removed. Per¯uorocarbon was left in situ in animals treated with PLV. Tissues were ®xed in 5% formalin. Specimens from the cranial ventral (non-dependent) and caudal dorsal (dependent) lobes were stained with haematoxylin and eosin and then scored using a semiquantitative scoring system by an experienced veterinary pathologist (A. S-K.), blinded to treatment, for interstitial in®ltration, interstitial oedema, emphysema, and atelectasis. Each variable was scored using a 0±4-point scale, with no injury scored 0, injury in 25% of the ®eld scored 1, injury in 50% of the ®eld scored 2, injury in 75% of the ®eld scored 3, and injury throughout the ®eld scored 4. The total score maximum was 16.
Induction of ALI Repeated lavage with warmed isotonic saline (37°C) was done to produce lung surfactant depletion as reported by Lachmann and co-workers, and described in detail elsewhere.31 32 Induction of ALI was assumed when the PaO2/ FIO2 ratio was persistently less than 13 kPa for 1 h.
594
Exogenous surfactant and PLV Table 1 Time course of HR, MABP, MPAP, CO, SVR, and PVR during baseline (pre-lavage), after induction of ALI (post-lavage), and for 6 h thereafter, in controls (n=8 at ALI; four pigs died before 6 h after ALI), in pigs treated with a single intratracheal dose of 50 mg kg±1 of surfactant (Curosurfâ) after induction of ALI (SURF-group) (n=8 pigs, none died), and in pigs treated with a single intratracheal dose of 50 mg kg±1 of surfactant (Curosurfâ) followed by PLV with 30 ml kg±1 of per¯uorocarbon (PF 5080) after induction of ALI (SURF-PLV-group) (n=8 pigs, none died). Data are mean (SEM). Intergroup comparison: controls vs SURF-PLV-group and controls vs SURF-group: *P<0.05, and SURF-PLV-group vs SURF-group: ²P<0.05 (Kruskal±Wallis ANOVA and post hoc Dunn's test). Intragroup comparison: data measured after induction of ALI vs data obtained at hourly intervals thereafter: ³P<0.05 (Friedman test and post hoc Dunn's test) Group
Baseline ALI 1h 2h 3h 4h 5h 6h
SURF SURF-PLV Controls SURF SURF-PLV Controls SURF SURF-PLV Controls SURF SURF-PLV Controls SURF SURF-PLV Controls SURF SURF-PLV Controls SURF SURF-PLV Controls SURF SURF-PLV Controls
HR (beats min±1)
MABP (mm Hg)
MPAP (mm Hg)
CO (litre min±1)
SVR (dyn s cm±5)
PVR (dyn s cm±5)
Mean
SEM
Mean
SEM
Mean
SEM
Mean
SEM
Mean
SEM
Mean
SEM
77 95 95 102 102 93 92 100 93 88 89 93 86 88 100 77 90 97 79 93 102 80 95 109
4 5 9 11 6 6 10 6 5 9 5 7 9 6 10 5 5 10 8 11 9 8 8 7
102 99 88 94 94 89 91 92 87 92 94 83 98 93 87 99 91 89 99 88 81 97 82 74³
5 5 5 4 5 6 4 6 7 6 5 7 6 2 8 5 4 9 5 6 9 5 7 11
20 23 20 25 28 28 27 32 30 28 34³ 35 30 36³ 36 30* 38²³ 39³ 29* 39²³ 41³ 30* 40²³ 41³
1 1 1 1 2 2 2 2 2 2 2 2 2 1 2 2 1 2 2 1 3 3 1 3
3.6 3.8 3.6 4.4 4.4 3.8 3.7 4.0 3.9 3.4 3.5 3.4 2.8³ 3.1³ 3.8 2.6³ 2.9³ 3.7 2.6³ 3.2³ 3.5 2.6³ 3.1³ 3.5
0.2 0.5 0.3 0.6 0.4 0.2 03 03 04 0.3 0.3 0.2 0.3 0.3 0.4 0.2 0.3 0.3 0.3 0.4 0.4 0.2 0.3 0.5
2081 2026 1827 1650 1593 1718 1769 1614 1688 1930 1944 1697 2573 2145 1767 2723 2278 1845 2831 2009 1742 2662 1857 1601
119 285 201 210 191 227 150 160 243 163 229 194 186 192 279 176 258 326 207 290 323 188 337 427
149 241 165 266 268 301 335 366 329 392 466 466 525³ 578³ 486 592³ 667³ 563 581³ 663³ 596³ 560³ 659³ 627
30 52 25 49 28 53 63 38 49 60 76 33 73 79 50 79 69 70 98 104 100 83 82 110
Experimental procedure After induction of ALI, the animals were randomly assigned to receive a single intratracheal dose of surfactant alone (50 mg kg±1, Curosurfâ) (SURF-group, n=8), or a single intratracheal dose of surfactant (50 mg kg±1), followed after 30 min by 30 ml kg±1 of per¯uorocarbon (PF 5080, 3M, Germany) (SURF-PLV-group, n=8), or no further intervention (controls, n=8). Evaporative losses of PF 5080 were replaced at a dose of 4 (3) ml kg±1 every hour as previously found by our group.33 PF 5080 (C8F18) is a non-ozone-depleting PFC with boiling point 102°C, density (at 25°C) 1.76 g ml±1, viscosity (at 25°C) 1.4 cp, vapour pressure (at 37°C) 6.8 kPa, solubility of oxygen (at 37°C) 49 ml 100 ml±1, solubility of carbon dioxide (at 37°C) 176 ml 100 ml±1, and surface tension (at 25°C) of 15 dyn s cm±1 (information taken from 3M data sheet). Curosurfâ is isolated from minced pig lungs and contains 99% lipids, mainly phospholipids, and 1% low molecular weight hydrophobic apoproteins SP-B and SP-C.16
Statistical analysis Results are expressed as mean (SEM). The data were obtained at baseline (pre-lavage), immediately after the
induction of ALI (post-lavage) and at hourly intervals for 6 h thereafter. Statistical analysis was performed using SPSS for Windows 8.0 and Sigmastat (SPSS Inc., Chicago, IL, USA). Differences between groups were evaluated using Kruskal±Wallis ANOVA followed by post hoc comparisons with Dunn's test (intergroup comparison). The Friedman test was used to compare the data after induction of ALI with the data measured during the subsequent 6 h (intragroup comparison). For post hoc testing, Dunn's test also was applied. Statistical signi®cance was assumed at P<0.05.
Results All animals were comparable with regard to body weight and pre-study conditions. Pre-lavage data of pulmonary gas exchange, lung compliance, and haemodynamics did not differ signi®cantly between groups (Tables 1 and 2). ÇT Ç S/Q In all animals, induction of ALI increased Q concomitant with a decrease in PaO2. Cardiac output (CO), mean pulmonary artery pressure (MPAP), and pulmonary vascular pressure (PVR) increased while mean arterial blood pressure (MABP), and systemic vascular resistance (SVR) decreased (Tables 1 and 2).
595
Wolf et al. Ç S/Q Ç T), arterial oxygen tension (PaO ), arterial carbon dioxide tension (PaCO ), arterial pH (pHa), oxygen Table 2 Time course of intrapulmonary shunting (Q 2 2 delivery (DO2), oxygen consumption (VÇO2), static compliance of the respiratory system (CRS), and survivors during baseline (pre-lavage), after induction of ALI (post-lavage), and for 6 h thereafter, in controls (n=8 at ALI; four pigs died before 6 h after ALI), in pigs treated with a single intratracheal dose of 50 mg kg±1 of surfactant (Curosurfâ) after induction of ALI (SURF-group) (n=8 pigs, none died), and in pigs treated with a single intratracheal dose of 50 mg kg±1 of surfactant (Curosurfâ) followed by PLV with 30 ml kg±1 of per¯uorocarbon (PF 5080) after induction of ALI (SURF-PLV-group) (n=8 pigs, none died). Data are mean (SEM). Intergroup comparison: controls vs SURF-PLV-group and controls vs SURF-group: *P<0.05, and SURF-PLV-group vs SURFgroup: ²P<0.05 (Kruskal±Wallis ANOVA and post hoc Dunn's test). Intragroup comparison: data measured after induction of ALI vs data obtained at hourly intervals thereafter: ³P<0.05 (Friedman test and post hoc Dunn's test) Group
Baseline SURF SURF-PLV Controls ALI SURF SURF-PLV Controls 1h SURF SURF-PLV Controls 2h SURF SURF-PLV Controls 3h SURF SURF-PLV Controls 4h SURF SURF-PLV Controls 5h SURF SURF-PLV Controls 6h SURF SURF-PLV Controls
Ç T (%) Ç S/Q Q
PaO2 (kPa)
PaCO2 (kPa)
pHa
Mean
SEM
Mean
SEM
Mean
SEM
Mean
12 16 16 51 54 56 38* 44³ 57 25*³ 28³ 52 20*³ 24*³ 53 13*³ 22*³ 52 12*³ 24³ 56 12*³ 26³ 56
1 3 3 5 3 4 4 4 3 3 2 4 2 2 5 1 2 3 2 3 6 2 3 4
75.7 68.0 72.7 8.1 7.2 7.6 19.2* 11.0 7.3 36.8* 23.5* 8.0 48.3*³ 31.6*³ 8.1 64.5*³ 34.0³ 7.7 64.9*³ 35.1³ 7.2 61.2*³ 30.8²³ 7.0
3.2 3.8 3.6 0.7 0.5 0.7 4.8 3.1 0.4 6.7 3.6 0.5 6.6 3.3 0.6 2.6 3.4 0.5 3.7 4.6 0.7 4.7 5.0 0.4
4.7 5.5 6.1 6.1 7.3 7.5 6.6 7.6 7.1 5.7* 8.4² 8.0 5.7* 8.4² 8.5 5.7* 8.5² 8.2 5.9* 9.2² 9.1 7.0 10.0³ 9.9³
0.5 0.4 0.7 0.6 0.6 0.5 0.4 0.7 0.6 0.3 0.3 0.8 0.4 0.4 0.8 0.3 0.6 0.4 0.5 0.8 0.8 1.0 1.0 0.7
7.56 7.48 7.43 7.42 7.37 7.33 7.41 7.37 7.36 7.46 7.32 7.33 7.48 7.34 7.30 7.47 7.34 7.32 7.46 7.31 7.29 7.45 7.29 7.27
Gas exchange Surfactant alone improved PaO2 from 8.1 (0.7) kPa after onset of ALI to 61.2 (4.7) kPa after 6 h of treatment (P<0.05 vs controls; Fig. 1, Table 2). The increase of PaO2 in the SURF-group was greater than the increase in the SURFPLV-group after 6 h of treatment (P<0.05 vs SURF-PLV; Fig. 1, Table 2). In the PLV-SURF-group the increase of PaO2 from 7.2 (0.5) kPa after onset of ALI to 30.8 (5.0) kPa after 6 h of treatment was greater than in controls (P<0.05 vs controls; Fig. 1, Table 2). Ç T decreased signi®cantly comÇ S/Q In the SURF group Q pared with controls (51 (5)% at onset of ALI to 12 (2)% 6 h after treatment, P<0.05 vs controls; Fig. 2, Table 2). In the Ç T was signi®cantly decreased comÇ S/Q SURF-PLV-group Q pared with controls (54 (4)% at onset of ALI to 26 (3)% after 6 h of treatment, P<0.05 vs controls; Fig. 2, Table 2).
Haemodynamics There were no signi®cant changes between groups in HR, MABP, and SVR. In the SURF-group the MPAP increased from 25 (1) mm Hg at onset of ALI to 30 (3) mm Hg after 6 h of treatment, and was signi®cantly less than in controls and in the SURF-PLV-group (P<0.05 vs controls and vs SURFPLV; Fig. 3, Table 1). In the SURF-group, PVR increased
DO2 (ml min±1)
VÇO2 (ml min±1)
CRS (ml mbar±1)
SEM
Mean
SEM
Mean
SEM
Mean
SEM
0.03 0.02 0.04 0.04 0.02 0.03 0.03 0.02 0.04 0.03 0.02 0.04 0.04 0.01 0.04 0.04 0.02 0.03 0.04 0.03 0.03 0.04 0.03 0.03
423 418 396 361 338 257 363 349 277 365* 362 249 324 331 282 321 308 296 312 348 278 326 338 291
28 50 26 34 33 20 27 29 25 31 38 17 31 25 32 28 27 25 28 39 46 23 38 57
142 143 110 134 150 122 130 152 118 136 152 111 128 139 126 132 136 131 125 146 121 133 139 137
14 21 10 16 14 14 15 10 11 11 15 10 16 12 19 13 16 11 12 14 3 14 13 19
22 21 23 9 9 9 9 12* 8 9 14* 9 10 13* 8 9 13* 6 9 14 6 9 15* 7
1.0 1.8 1.0 0.6 1.0 1.0 0.3 0.9 0.4 0.3 1.7 1.0 0.3 1.3 0.5 0.2 0.4 0.9 0.1 1.2 0.4 0.2 0.4 0.5
Survivors (n)
8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 7 8 8 5 8 8 4
signi®cantly from 266 (49) dyn s cm±5 at onset of ALI to 560 (83) dyn s cm±5 at 6 h of treatment (P<0.05 vs ALIvalues; Table 1). In the SURF-PLV-group, PVR increased signi®cantly from 268 (28) to 659 (82) dyn s cm±5 (P<0.05 vs ALI-values, Table 1). In the SURF-group and in the SURF-PLV-group, CO decreased signi®cantly during the treatment period compared with ALI-values (P<0.05 vs ALI-values; Table 1). In controls there were no signi®cant changes in PVR and CO.
Lung mechanics After induction of ALI, static compliance of the respiratory system decreased from 22 (2) ml cm H2O±1 in all groups to 9 (1) ml cm H2O±1. No further changes of CRS occurred in the SURF-group. In the SURF-PLV-group, CRS improved signi®cantly compared with controls from 9 (1) to 15 (0.4) ml cm H2O±1 at 6 h of treatment (P<0.05 vs controls; Fig. 4, Table 2).
Lung injury The non-dependent lobes in the SURF-group had a signi®cantly smaller injury score for interstitial oedema and emphysema compared with controls and the SURF-PLV-
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Exogenous surfactant and PLV
Ç S/Q Ç T) during baseline Fig 2 Time course of intrapulmonary shunting (Q (pre-lavage), after induction of ALI (post-lavage), and for 6 h thereafter, in controls (n=8 at ALI; four pigs died before 6 h after ALI), in pigs treated with surfactant (Curosurfâ) after induction of ALI (SURF-group) (n=8 pigs, none died), and in pigs treated with a single surfactant (Curosurfâ) followed by PLV with 30 ml kg±1 of per¯uorocarbon (PF 5080) after induction of ALI (SURF-PLV-group) (n=8 pigs, none died). Data are mean (SEM). Intergroup comparison: controls vs SURF-PLV-group and controls vs SURF-group: *P<0.05, and SURF-PLV-group vs SURF-group: ²P<0.05 (Kruskal±Wallis ANOVA and post hoc Dunn's test). Intragroup comparison: data measured after induction of ALI vs data obtained at hourly intervals thereafter: ³P<0.05 (Friedman test and post hoc Dunn's test).
Fig 1 Time course of arterial oxygen tension (PaO2) during baseline (prelavage), after induction of ALI (post-lavage), and for 6 h thereafter, in controls (n=8 at ALI; four pigs died before 6 h after ALI), in pigs treated with surfactant (Curosurfâ) after induction of ALI (SURF-group) (n=8 pigs, none died), and in pigs treated with surfactant (Curosurfâ) followed by PLV with 30 ml kg±1 of per¯uorocarbon (PF 5080) after induction of ALI (SURF-PLV-group) (n=8 pigs, none died). Data are mean (SEM). Intergroup comparison: controls vs SURF-PLV-group and controls vs SURF-group: *P<0.05, and SURF-PLV-group vs SURF-group: ²P<0.05 (Kruskal±Wallis ANOVA and post hoc Dunn's test). Intragroup comparison: data measured after induction of ALI vs data obtained at hourly intervals thereafter: ³P<0.05 (Friedman test and post hoc Dunn's test).
group (P<0.05, Table 3). In the SURF-PLV-group, scores for interstitial oedema were signi®cantly greater compared with controls in the non-dependent lobes (P<0.05, Table 3). Comparing tissue damage in dependent lobes, the SURFgroup had signi®cantly less atelectasis and emphysema than controls (P<0.05) and less interstitial oedema and emphysema than the SURF-PLV-group (P<0.05, Table 3). In the SURF-PLV-group, interstitial in®ltration and atelectasis of the dependent lobes was less than in controls and the SURFgroup (P<0.05 vs controls and vs SURF), while interstitial oedema and emphysema in the dependent lobes in the SURF-PLV-group was greater than in controls and the SURF-group (P<0.05, Table 3). The overall lung injury score of the SURF-group was less in the non-dependent lobes, compared with the SURF-PLVgroup and controls (P<0.05, Table 3).
Survival All animals in both treatment groups survived to the end of the study. In the control-group, four animals died of irreversible hypoxaemia during the study, one after 3 h, two after 4 h, and one 5 h after induction of ALI (Table 2).
Discussion In this study, we compared the effects of a single, small dose of surfactant alone and combined with a full dose of PLV on oxygenation, haemodynamics, respiratory mechanics, and lung injury in an animal model of ALI. A small dose of
surfactant was better than a combined treatment with a small dose of surfactant and PLV to restore gas exchange. Respiratory mechanics were only improved in the group treated with the combination of surfactant and PLV. Atelectasis, interstitial oedema, and emphysema were signi®cantly less in the surfactant group than in controls. Compared with the group receiving surfactant and PLV, the surfactant group had a signi®cant smaller total lung injury score. Surfactant therapy combined with PLV has been studied in different types of ALI.19 29 Studies have been done in surfactant de®cient pre-term animals,19 24 26 29 isolated lungs of pre-term animals,23 27 newborn animals with ALI induced by surfactant wash-out,21 25 27 and experimental ALI in adult animals.20 22 Criteria for onset of ALI after surfactant wash-out was a PaO2/FIO2 ratio below 8 kPa (60 mm Hg), with the exception of the studies by Hartog and co-workers and Kelly and co-workers, who used a value below 13 kPa (100 mm Hg) to indicate ALI.20 22 The duration of PaO2/FIO2 less than 8 kPa of 30 min to indicate the induction of ALI was speci®ed only in one study.21 Our lavage procedure caused a stable PaO2/FIO2 ratio of 7.6 (0.6) kPa (57 (5) mm Hg) for at least 1 h after the last lavage. The severity of the lung injury in our animals resembles surfactant de®cient pre-term animals, shown by the high shunt fraction, which was 54 (4)% after lung injury. Mrozek and co-workers compared four different treatments in newborn piglets, after induction of ALI. One group received 100 mg kg±1 surfactant, one group received PFC in a dose equivalent to the functional residual capacity, one group received PFC 30 min after surfactant replacement, and one group received surfactant 30 min after instillation of
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Fig 3 Time course of MPAP during baseline (pre-lavage), after induction of ALI (post-lavage), and for 6 h thereafter, in controls (n=8 at ALI; four pigs died before 6 h after ALI), in pigs treated with surfactant (Curosurfâ) after induction of ALI (SURF-group) (n=8 pigs, none died), and in pigs treated with surfactant (Curosurfâ) followed by PLV with 30 ml kg±1 of per¯uorocarbon (PF 5080) after induction of ALI (SURFPLV-group) (n=8 pigs, none died). Data are mean (SEM). Intergroup comparison: controls vs SURF-PLV-group and controls vs SURF-group: *P<0.05, and SURF-PLV-group vs SURF-group: ²P<0.05 (Kruskal±Wallis ANOVA and post hoc Dunn's test). Intragroup comparison: data measured after induction of ALI vs data obtained at hourly intervals thereafter: ³P<0.05 (Friedman test and post hoc Dunn's test).
PFC.27 In contrast to our ®nding that a single dose of surfactant caused the greatest improvement in PaO2, Mrozek and colleagues found that a combination of surfactant and PLV was better than the effect of surfactant alone on gas exchange, lung mechanics, and lung pathology. They make no comment on the decrease in PaO2 after instillation of PFC in the group treated with PLV after surfactant replacement. These differences could be attributed to the following: (1) different timepoints of measurement, (2) the use of a bovine surfactant (Survanta), (3) a higher dose of surfactant (100 mg kg±1), (4) newborn piglets as study subjects, and (5) the use of pre-oxygenated per¯ubron (LiquiVent). Another difference was positioning the animals while ®lling the lungs with PFC, which might have allowed greater per¯uorocarbon dose and a more homogenous distribution of PFC throughout the lungs, although this technique appears to be impractical under clinical circumstances. In a study of ALI induced in premature lambs, Leach and coworkers compared either surfactant replacement, a combination of surfactant replacement and PLV, or PLV alone.29 In this study, a very small dose (5 mg kg±1) of an arti®cial surfactant (Exosurf) did not improve oxygenation and respiratory mechanics when compared with conventional ventilation. The combination of surfactant and PLV was not better than PLV alone. Leach and co-workers attributed the lack of surfactant ef®cacy to the small dose used and to the modest physiologic activity of synthetic surfactant, which gives a greater surface tension than natural surfactant.29 In our study, improvements in oxygenation and intrapulmonary right-to-left shunt were delayed in the SURF-PLV-
Fig 4 Time course of static compliance of the respiratory system (CRS) during baseline (pre-lavage), after induction of ALI (post-lavage), and for 6 h thereafter, in controls (n=8 at ALI; four pigs died before 6 h after ALI), in pigs treated with surfactant (Curosurfâ) after induction of ALI (SURF-group) (n=8 pigs, none died), and in pigs treated with surfactant (Curosurfâ) followed by PLV with 30 ml kg±1 of per¯uorocarbons (PF 5080) after induction of ALI (SURF-PLV-group) (n=8 pigs, none died). Data are mean (SEM). Intergroup comparison: controls vs SURF-PLVgroup: *P<0.05 (Kruskal±Wallis ANOVA and post hoc Dunn's test).
group. This could have been because: (1) PLV was started 30 min after surfactant was instilled, to avoid wash-out of exogenous surfactant; (2) inhomogeneous surfactant distribution could have caused PFC to only enter some regions and, thereby, limit alveolar recruitment. Leach and coworkers describe a transient increase in the expiratory resistance of their surfactant-PLV group and suggested that the distal movement of per¯uorocarbons could have been delayed, as surfactant will remain in small airways and alveolar ducts.27 In a study from GoÈthberg and co-workers using a model of premature ALI, the treatment of PLV combined with conventional ventilation or combined with high-frequency oscillatory ventilation (HFOV) 2 h after giving 100 mg kg±1 of surfactant (Infasurf) improved oxygenation compared with treatment with surfactant and conventional ventilation alone.17 HFOV after surfactant replacement improved PaO2 to a similar extent than HFOV combined with PLV and was signi®cantly more effective than PLV and conventional ventilation. The different results of a treatment with PLV and conventional ventilation after surfactant replacement, compared with our data, might be because of different models, a different PFC, a later application of PFC, and different doses of surfactant. Improvement in oxygenation with HFOV, with and without PLV, could be explained by changes in airway pressures and the development of a high intrinsic PEEP from the ventilatory pattern. Previous studies showed that combining PFC and high levels of PEEP enhances the effects of PLV on pulmonary gas exchange. 15±17 The improvement in CRS in our piglets treated with the combination of surfactant and PLV supports the ®ndings of other investigators, and appears to be dose dependent.9 13 20 We measured the static compliance of the respiratory system, with an inspiratory shutter technique, to exclude
598
Exogenous surfactant and PLV Table 3 Lung injury score of the non-dependent and the dependent lobes for atelectasis, interstitial in®ltration, interstitial oedema, emphysema, and total lung injury score in controls (n=8 at ALI; four pigs died before 6 h after ALI), in pigs treated with a single intratracheal dose of 50 mg kg±1 of surfactant (Curosurfâ) after induction of ALI (SURF-group) (n=8 pigs, none died), and in pigs treated with a single intratracheal dose of 50 mg kg±1 of surfactant (Curosurfâ) followed by PLV with 30 ml kg±1 of per¯uorocarbon (PF 5080) after induction of ALI (SURF-PLV-group) (n=8 pigs, none died). Data are mean (SEM). Intergroup comparison: controls vs SURF-PLV-group and controls vs SURF-group: *P<0.05, and SURF-PLV-group vs SURF-group: ²P<0.05 (Kruskal±Wallis ANOVA and post hoc Dunn's test). Intragroup comparison: non-dependent vs dependent lobes: §P<0.05 (Friedman test and post hoc Dunn's test) Non-dependent lobes SURF
Atelectasis Interstitial in®ltration Interstitial oedema Emphysema Total injury score
Dependent lobes PFC-SURF
Controls
SURF
PFC-SURF
Controls
Mean
SEM
Mean
SEM
Mean
SEM
Mean
SEM
Mean
SEM
Mean
SEM
0.68* 1.38 0.1*§ 0.11* 2.27*§
0.09 0.1 0.04 0.03
0.94*§ 0.31*² 1.32*²§ 1.76²§ 4.33²
0.1 0.08 0.09 0.15
0.3§ 1.46§ 0.5§ 1.9§ 3.86
0.04 0.02 0.05 0.04
0.78* 1.65 1.11 0.19* 4.02
0.07 0.04 0.05 0.03
0.08*² 0.34*² 2.13*² 1.47*² 3.73
0.03 0.04 0.05 0.05
1.41 1.76 1.2 0.4 3.77
0.07 0.04 0.05 0.5
effects of PFC vapour-pressure on expiratory volumes. We used 30 ml kg±1 of per¯uorocarbon, approximately the functional residual capacity of healthy lungs and added further liquid according to our past observations.33 TuÈtuÈncuÈ and co-workers compared the effects of PLV with 18 ml kg±1 PFC with PLV using 18 ml kg±1 saline, in a similar model of ALI in rabbits, and found that compliance of the respiratory system increased in the PFC group.13 Studying adult rabbits with induced ALI, Kelly and colleagues compared the effects of different treatments.20 The treatments were PLV with 20 ml kg±1 PFC, nebulized PFC, 100 mg kg±1 arti®cial surfactant (ALEC), 100 mg kg±1 porcine surfactant (Curosurfâ), the combination of PLV and ALEC, the combination of PLV and Curosurfâ, and a control group. Our observations support their ®ndings for arterial oxygenation. Regarding lung mechanics, 100 mg kg±1 of Curosurfâ improved compliance as effectively as the combination of PLV and Curosurfâ. In our study, the smaller dose of exogenous surfactant, was not suf®cient to improve lung mechanics. Kelly and co-workers point out that surfactant from animals contains surfactant apoproteins, which prevent inhibition of surfactant by protein-rich ¯uid in lungs after induction of ALI, and that this effect is dose-dependent.20 In studies in humans, lung compliance decreases after surfactant treatment, despite increases in functional residual capacity and improvements in oxygenation. This could be because of slow recruitment of atelectatic lung areas, with stabilization of the initially opened lung units.34 35 Lack of improvement in lung compliance after surfactant administration in experimental ALI was also found by Mrozek and co-workers.27 We consider that the small dose of surfactant used in our study did not entirely overcome surfactant inhibition, and that the amount of lung tissue opened up in the SURF-group, although suf®cient to improve gas exchange, was not suf®cient to produce effects on CRS.
Treatment with surfactant alone caused less histological injury, for interstitial oedema, atelectasis, and emphysema compared with controls and compared with the SURF-PLVgroup. Comparing the overall lung injury scores between groups, treatment with surfactant alone caused less damage in non-dependent lobes compared with controls and the SURF-PLV-group. A small dose of surfactant reduces the in¯ammatory response in ALI, prevents further atelectasis, and improves gas exchange. The effects on in¯ammation could be attributed to the apoproteins of natural surfactant, which might prevent in¯ammation. The greater lung injury scores in the SURF-PLV-group contrasts with previous results of Mrozek and co-workers, who found least injury with the combined treatment.27 They suggest that the lower inspiratory pressures needed for effective alveolar ventilation could be the reason for less lung injury in this group. The different PFC used for PLV and a higher dose of surfactant could account for these differences. In rats with lavage-induced ALI, Hartog and colleagues compared lung injury after treatment with surfactant, PLV, and high values of PEEP vs healthy controls and injured controls.22 Surfactant prevented progression of lung injury, when compared with healthy controls, and PLV increased lung tissue injury compared with healthy controls. In our study, we found that cardiac output decreased signi®cantly during the study in both treatment groups, which has not been reported previously in short term studies of lavage-induced lung injury.26 36 37 However, DO2 and VÇO2 remained unchanged in both groups, indicating maintenance of a suf®cient oxygen delivery. A possible explanation for the lower values of CO might be reduced sympathic activity in both treatment groups because of better oxygenation. This view is supported by poorer survival in control animals. As suggested by Dantzker and co-workers, a reduction in CO could reduce the intrapulmonary right-toleft shunt.38 The magnitude of this mechanism of shunt
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reduction with a CO reduction of 40% in the SURF-group and 30% in the SURF-PLV-group, suggests that this would only partly account for the reduction found, and indicate other mechanisms, such as alveolar recruitment, could be involved. The increase in MPAP in animals treated with the combination of surfactant and PLV could be caused by the PFC. In a study from Morris and co-workers healthy pigs had their lungs ®lled with 40 ml kg±1 of per¯uorocarbons and were conventionally ventilated.35 Pulmonary blood ¯ow was diverted from the dependent regions of the lung, associated with an increase in MPAP. The authors suggested that a greater hydrostatic pressure gradient in PFC-®lled alveoli, compared with the gradient in the blood vessels, could cause this effect.37 In conclusion, using an experimental model of ALI in piglets, we found that treatment with a single small dose of surfactant improved oxygenation, decreased intrapulmonary right-to-left shunt, and reduced lung tissue damage more effectively than a combination of surfactant with PLV. However, only the combined treatment of exogenous surfactant and PLV improved lung mechanics. Taken with other evidence, these ®ndings show that further research is needed to ®nd the least dose of surfactant that is effective.
11 12 13
14
15
16
17 18
Acknowledgements Supported by a grant from Deutsche Forschungsgemeinschaft (KA 1212/ 3±1). Curosurfâ was generously provided by Serono AG, MuÈnchen, Germany.
References 1 Lewis JF, Jobe AH. Surfactant and the adult respiratory distress syndrome. Am Rev Respir Dis 1993; 147: 218±33 2 Lee WL, Detsky AS, Stewart TE. Lung-protective mechanical ventilation strategies in ARDS. Intensive Care Med 2000; 26: 1151±5 3 Green®eld LJ, Ebert PA, Benson DW. Effect of positive pressure ventilation on surface tension properties of lung extracts. Anesthesiology 1964; 25: 312±6 4 McClenahan JB, Urtnowski A. Effect of ventilation on surfactant and its turn over rate. J Appl Physiol 1967; 23: 215±20 5 Hickling KG. Ventilatory management of ARDS: can it affect the outcome? Intensive Care Med 1990; 16: 219±26 6 Amato MB, Barbas CS, Medeiros DM, et al. Effect of a protectiveventilation strategy on mortality in the acute respiratory distress syndrome. N Engl J Med 1998; 338: 347±54 7 Goldsmith LS, Greenspan JS, Rubenstein DS, Wolson MR, Shaffer TH. Immediate improvement in lung volume after exogenous surfactant: alveolar recruitment versus increased distension. J Pediatr 1991; 119: 424±8 8 Lewis JF, Gof®n J, Yue P, McCaig LA, Bjarneson D, Veldhuizen RA. Evaluation of exogenous surfactant treatment strategies in an adult model of acute lung injury. J Appl Physiol 1996; 80: 1156±64 9 Gregory TJ, Steinberg P, Spragg R, et al. Bovine surfactant therapy for patients with acute respiratory distress syndrome. Am J Respir Crit Care Med 1997; 155: 1309±15 10 Walmrath D, GuÈnther A, Ghofrani HA, et al. Bronchoscopic
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