1. ACUTE RESPIRATORY DISTRESS SYNDROME
UNDERSTANDING PATHOPHYSIOLOGY AND MANAGEMENT
a historical review
Ubaidur Rahaman
Senior Resident, CCM, SGPGIMS
Lucknow, India

2. A Treatise on Diseases of the Chest Laennec, 1821
idiopathic anasarca of the lungs;
pulmonary edema without heart failure
PROBABLY FIRST PUBLISHED SCINTIFIC DISCRIPTION
Ubaidur Rahaman, S.R., CCM, SGPGIMS, Lucknow
Rahaman,

3. What's in a name? That which we call a rose by any other name
would smell as sweet.
-William Shakespeare
•Double pneumonia - till mid 1900’s
•Post-traumatic massive pulmonary collapse- WW I
•Traumatic wet lung- WW II
•Shock lung - Korea – early 1950’s
•Da Nang lung / ventilator lung- Vietnam war – late 1960’s
•Capillary leak syndrome
•Acute alveolar syndrome
•Post perfusion lung
•Congestive atelectasis
•Adult hyaline membrane disease
Ubaidur Rahaman, S.R., CCM, SGPGIMS, Lucknow
Rahaman,

4. Acute respiratory distress in adults.
Ashbaugh DG, Bigelow DB, Petty TL, Levine BE. 1967, Lancet 2:319-323
Case series of 12 patients presenting with
acute respiratory distress, cyanosis refractory to oxygen therapy,
decreased lung compliance and diffuse pulmonary infiltrates on chest x-ray.
AUTOPSY
lungs were heavy (average 2110 g),
microscopic examination Revealed
areas of alveolar atelectasis, interstitial and alveolar hemorrhage and edema,
dilated and congested capillaries
ACUTE RESPIRATORY DISTRESS SYNDROME
The adult respiratory distress syndrome: clinical
features, factors influencing prognosis and principles of management.
Petty TL, Ashbaugh DG, Chest 1971;60:233–239.

5. An expanded definition of the adult respiratory distress syndrome.
Murray JF, Matthay MA, Luce JM, Flick MR. Am Rev Respir Dis 1988; 138:720–723.
lung injury scoring system (LIS)
•Oxygenation,
•Positive end-expiratory pressure
•Respiratory system compliance
•Chest radiograph
•NO LUNG INJURY-------------0
•MILD TO MODERATE INJURY------0.1-2.5
•SEVERE LUNG INJURY (ARDS)---- >22.5
Addition of objective criteria- PEEP and Compliance

6. The American European consensus conference on ARDS: definitions mechanisms, relevant
outcomes and clinical trial coordination.
Bernard GR, Artigas A, Brigham KL, Carlet J, Falke K, Hudson L, Lamy M, Legall JR, Morris A, Spragg R.
Am J Respir Crit Care Med.1994;149:818–824.
Acute lung injury ( ALI)
ARDS – subset of ALI with severe hypoxaemia
•Acute onset
•CXR- bilateral infiltrates consistent with pulmonary oedema
•Ppaw ≤18 mmHg or absence of clinical evidence of left atrial hypertension,
•ALI - PaO2/FIO2 ≤300 ; ARDS PaO2/FIO2 ≤ 200.
Definition was made broad intentionally to encompass different types of AHRF occurring
in variety of settings
Problem
•CXR interpretation subjective
•P/F affected by level of PEEP
•Requirement of PAC- interpretation- Ppao may be higher in
absence of CHF

7. Development of a clinical definition for acute respiratory distress syndrome using the
delphi technique.
Ferguson ND, Davis AM, Slutsky AS, Stewart TE. J Crit Care. 2005;20:147-154
Delphi criteria
1
Hypoxaemia
PaO2/ FiO2 ≥ 200 mmHg with PEEP ≥10
2
Acute onset
Rapid onset ≤72 hours
3
CXR
Bilateral airspace disease ≥2 quadrants on
frontal CXR
4
Non cardiogenic
origin
No clinical e/o CHF
including use of PAC and/or echo
5
Decreased lung
compliance
Cs res syst <50 ml/cmH2O
( with patient sedated, VT= 8 ml/kg IBW, PEEP
≥10
6
Predisposition
Direct and or indirect factor associated with
lung injury
ARDS- presence of criteria 1-4 + one of 5 or 6

8. Development of a clinical definition for acute respiratory distress syndrome using the
delphi technique.
Ferguson ND, Davis AM, Slutsky AS, Stewart TE. J Crit Care. 2005;20:147-154
Airspace disease- presence of one or more of following1.
Air bronchogram
2.
Acinar shadows- nodular opacities 4-10 mm diam with poor margination
3.
Coalescence of acinar shadows
4.
Silhouette sign- loss of def of heart border or hemidiaphragm, excluding that caused by lobar
collapse
Ubaidur Rahaman, Senior Resident, CCM, SGPGIMS, Lucknow, India
Rahaman,
Lucknow,

9. 1970 to mid 1980s

10. Acute respiratory distress in adults.
Ashbaugh DG, Bigelow DB, Petty TL, Levine BE. 1967, Lancet 2:319-323
Case series of 12 patients presenting with
acute respiratory distress, cyanosis refractory to oxygen therapy,
decreased lung compliance and diffuse pulmonary infiltrates on chest x-ray.
AUTOPSY
lungs were heavy (average 2110 g),
microscopic examination revealed
areas of alveolar atelectasis, interstitial and alveolar hemorrhage and edema,
dilated and congested capillaries
ARDS LUNG IS HOMOGENOUSLY HEAVY AND STIFF
requiring high inflation pressure to ventilate
?
How to treat
Ubaidur Rahaman, S.R., CCM, SGPGIMS, Lucknow
Rahaman,

11. This Week’s Citation Classic OCTOBER 29, 1979
Ashbaugh D G, Petty T L, Bigelow D B & Harris T M. Continuous positive-pressure breathing
(CPPB) in adult respiratory distress syndrome. J. Thorac. Cardiovas. Surg. 57:31-41, 1969
The first patient in which we observed acute respiratory distress was a 29-year-oldman involved in
an automobile accident who, despite being placed on a respirator, went on to develop severe and
progressive respiratory failure and died within 48 hours.
Our failure, in what we felt should have been a salvageable case, stimulated us to look for
additional cases.
A few weeks after our first case,
a 12-year-old boy was admitted with a severe crushing chest injury. He too, began to follow a
similar downhill course despite a tracheotomy and being placed on our only volume respirator, an
Engstrom. Even with large volumes of air and 100% oxygen he was doing poorly.
In desperation it was decided to try adding
end expiratory pressure,
which happened to be a feature of that model of Engstrom respirator
Dramatic improvement occurred in the patient’s condition and
he eventually went on to make a very good recovery.
Several additional patients were then seen and treated with varying results
Ubaidur Rahaman, S.R., CCM, SGPGIMS, Lucknow
Rahaman,

12. The first ENLIGHTENMENT
Positive End Expiratory Pressure

13. Acute respiratory distress in adults.
Ashbaugh DG, Bigelow DB, Petty TL, Levine BE. 1967, Lancet 2:319-323
Mile stone paper- initially rejected by 3 major US journals
12 patients with ARDS of pulmonary and extra- pulmonary origin,
some with fluid overload and shock.
PEEP was applied in five of them (three survived)
ZEEP was applied in seven (two survived).
PEEP was described as a “buying time maneuver,” preventing alveolar collapse
at end-expiration.

14. The adult respiratory distress syndrome:
Clinical features, factors influencing prognosis and principles of management.
Petty TL, Ashbaugh DG, Chest 1971;60:233–239.
ETIOLOGY
•diffuse pulmonary injuries, direct or indirect, of lung parenchyma
•exudation of fluid and loss of surfactant activity
•impaired gas exchange and reduced pulmonary compliance
Outcome dependent on
1. Degree of original injury
2. Effectiveness of respiratory support
3. Prevention of further pulmonary injury
MANAGEMENT PRINCIPLE
Prevent alveolar collapse and
maintain oxygenation
•
Volume respirator
•
Oxygen control
•
PEEP
Prevent further injury
•
•
Oxygen control
•
Fluid restriction
Antibiotics for specific infections
•
Corticosteroid drugs

15. HOW PEEP HELPS IN IMPROVING OXYGENATION?
Ventilation with end expiratory pressure in acute lung disease.
Falke KJ, Pontoppidan H, Kumar A, Leith DE, Geffin B, Laver MB. J Clin Invest, 1972, 51:2315-2323
effects of PEEP in 10 patients with severe acute respiratory failure
when IPPV with Fio2 up to 0.5 failed to maintain PaO2 ≥ 70 torr.
PEEP of 0, 5, 10 and 15 cm H20 were applied for 30-min
Gas exchange, lung volumes, compliance, and hemodynamics- studied at each level of PEEP
FRC and PaO2 rose linearly with level of PEEP; Pao2 and FRC showed a close correlation.
Lung compliance
increased with lower PEEP- RECRUITMENT,
decreased with higher PEEP– OVERDISTENSION
Surprisingly increase in PaO2 may go along with fall in compliance*
C.I. fell in some patients and rose in others and there was no correlation with level of PEEP.
The most probable explanation for the effect of PEEP on PaO2 and compliance is
recruitment of gas exchange airspaces and prevention of terminal airway closure.
*recruitment and overdistension of alveoli may take place simultaneously.

16. WHAT LEVEL OF PEEP? is their any OPTIMUM PEEP
Optimum end-expiratory airway pressure in patients with acute pulmonary failure.
Suter PM, Fairley B, Isenberg. N Engl J Med, 1975; 292:284–289
ventilation within the range of pulmonary pressure/ volume range associated with
maximum compliance
negative effect of PEEP on CO is minimum.
•Optimum PEEP- best PaO2 with best oxygen transport ( C.O.)
•Associated with highest compliance of respiratory system compliance
•Recruitment prevails over overdistension.

17. WHAT LEVEL OF PEEP? is their any OPTIMUM PEEP
High level positive end expiratory pressure (PEEP) in acute respiratory insufficiency
Kirby RR, Downs JB, Civetta. Chest;1975; 67:156–163
SUPER PEEP concept- pressure that maximally reduces the shunt ( ≤20% at PaO2 20 torr)
Gas exchange, static pressure volume curve and positive-pressure ventilation at the
end of expiration. Study of 16 cases of acute respiratory insufficiency in adults.
Lemaire F, Harf A, Simonneau G. Ann Anesthesiol, 1981, Fr 22:435–441
Minimal PEEP- 2 cmH2O above the LIP on inflation limb of PV curve

18. SUMMARY
• ARDS lung is homogenously heavy and stiff
• Treat with high tidal volume and pressure to tackle high PaCO2
• Apply high PEEP- ?optimum PEEP to improve oxygenation
• Recognize side effects is barotrauma,
• Beware of hemodynamic impairment due to PEEP
Ubaidur Rahaman, S.R., CCM, SGPGIMS, Lucknow
Rahaman,

19. Mid 1980s
era of computed tomography
Concept of baby lung

20. Preservation of Normal Lung Regions in the Adult Respiratory Distress Syndrome
Analysis by Computed Tomography
Richard J. Maunder, W P. Shuman, et sl. JAMA 1986;255:2463-2465)
Despite appearance of diffuse, symmetric involvement by standard CXR
CT images demonstrate
sparing of substantial portion of lung parenchyma, lack of homogeneity and tendency
toward posterior involvement on CT images

21. L Gattinoni, A Presenti et al
•22 patients with acute respiratory failure
•Lung CT and physiological measurement at 5, 10 and 15 cmH2O PEEP
•Investigated for relationship between morphology and physiology
•Lung densities were concentrated in dependent regions
•Average lung weight was increased twofold above normal
•Excess lung weight correlated with mean Pulmonary artery pressure
•Venous admixture correlated with non-inflated tissue mass
Increasing PEEP
•Progressive clearing of densities and increased mass of normally aerated tissue
(Recruitment)
•Reduction of venous admixture

22. L Gattinoni, A Presenti et al

23. ARDS: the non-homogeneous lung; facts and hypothesis
Gattinoni L, Pesenti A,Intensive Crit Care Dig. 1987;6:1–4
ARDS lung is non homogenous with densities concentrated in most dependent regions
Amount of normally aerated tissue at end expiration was about
200-500 gm in severe ARDS: dimension of the lung of a 5-6 years old child
ARDS LUNG IS A BABY LUNG not STIFF LUNG
This baby lung is a healthy anatomical structure, located in the non dependent regions.
Respiratory compliance well correlated with the amount of the normally aerated tissue only

24. The second ENLIGHTENMENT
ARDS lung
non homogenous and BABY
not STIFF
Elasticity of this baby lung is nearly normal
Ubaidur Rahaman, S.R., CCM, SGPGIMS, Lucknow
Rahaman,

25. •We were ventilating the lung of a healthy child with about 1000ml of VT
• causing more damage then benefit
CAN IT BE PREVENTED
&
HOW
Ubaidur Rahaman, S.R., CCM, SGPGIMS, Lucknow
Rahaman,

26. Small healthy aerated tissue in non dependent
region with poor perfusion
can making it dependent help?
PRONE Ventilation
Ubaidur Rahaman, S.R., CCM, SGPGIMS, Lucknow
Rahaman,

27. The prone position in ARDS patients. A clinical study.
Langer M, Mascheroni D, Marcolin R, Gattinoni L. Chest, 1988; 94:103–107
•
•
13 moderate-severe ARDS patients proned for 2 hours.
The gas exchange and hemodynamics were evaluated before, during, and after proning
•
CT was obtained in both the supine and prone positions in two of these patients
•
Responder- Pa02 increase ≥ 10 mm Hg after 30 minutes of proning
CT in prone position
disappearance of posterobasal densities
and
appearance of new densities in the anterior regions
…..continued

28. The prone position in ARDS patients. A clinical study.
Redistribution of densities after proning
Langer M, Mascheroni D, Marcolin R, Gattinoni L. Chest, 1988; 94:103–107
Baby lung in not healthy anatomical structure but functional concept

29. Early 90s
Concept of sponge lung

30. Vertical gradient of regional lung inflation in adult respiratory distress syndrome.
Pelosi P, D’Andrea L, Vitale G. Am J Respir, 1994; Crit Care Med 149:8–13
Superimposed pressure
•edema fluid is evenly distributed from sternum to vertebra
•Increased lung weight due to accumulated edema raises hydrostatic pressure through out the
lung
•Gas in dependent lung regions is squeezed out by heavy lung parenchyma above
Generalized, not regional involvement
Densities are in fact due to loss of alveolar gases, not due to increase edema

31. ARDS LUNG IS SPONGE LUNG
The ARDS Lung. New insights from compute tomography,
Bone; JAMA, 1993, 269 (16): 2134-2135
Sponge lung explains
Redistribution of densities in prone position
Mechanism of PEEP
ARDS lung is both baby and sponge

32. SUMMARY
•
•
Baby lung is actually small lung open at end expiration
It may become larger during inspiration due to newly recruited tissue
•
•
Baby lung is not healthy but aerated
Smaller the baby lung the greater the potential for VILI
Ubaidur Rahaman, S.R., CCM, SGPGIMS, Lucknow
Rahaman,

33. The third ENLIGHTENMENT
CONCEPT OF
Protective lung ventilation

34. Low mortality associated with low volume pressure limited ventilation with
permissive hypercapnia in severe adult respiratory distress syndrome.
Hickling KG, Henderson SJ, Jackson R. Intensive Care Med. 1990;16(6):372-7.
50 patients
LIS ≥ 2.5, mean PaO2/FiO2 = 94
managed with low tidal volume, disregarding hypercapnia
hospital mortality was significantly lower than predicted.
Only one death was due to respiratory failure, caused by pneumocystis pneumonia.
10 patients had a "ventilator score" greater than 80,
which has previously predicted 100% mortality from respiratory failure.
Only 2 died, neither from respiratory failure.

35. The true ENLIGHTENMENT
was not the use of low tidal volume but the CHANGE OF GOAL
NORMAL OXYGENATION AND VENTILATION ( PaCO2)
ADEQUATE OXYGENATION AND PERMISSIVE HYPERCAPNIA
.The concept of "baby lung".
Gattinoni L, Pesenti A. Intensive Care Med. 2005 Jun;31(6):776-84. Epub 2005 Apr 6

36. Much has been said about end expiratory pressure
What happens at end inspiration:
concept of recruitment

37. •During inspiration only part of the lung is recruited
•Opening pressures are widely and normally distributed throughout lung
parenchyma
•Some lung regions usually most dependent may require higher opening
pressure
•If the Pplat is limited, collapsed tissues with higher opening pressure stay
closed throughout the respiratory cycle.
•At end expiration PEEP, if adequate will keep open only the lung regions
already opened by applied Pplat
Applied physiology of intensive care medicine. Pinsky, Mancebo, pg 307
Ubaidur Rahaman, S.R., CCM, SGPGIMS, Lucknow
Rahaman,

38. Recruitment and Derecruitment during Acute Respiratory Failure: A Clinical Study
S Crotti, D Mascheroni, P PelosiI, J J. Marini, L Gattinoni.
Am J Respir Crit Care Med 2001,Vol 164. pp 131–140, 2001
recruitment occurs along entire VP curve of respiratory system, even beyond the UIP
derecruitment is also a continuous process, but is most prevalent over a pressure
range (0–10cm H2O) lower than the pressure range over which recruitment occur

39. Venegas JG, Harris RS, Simon BA. A comprehensive equation for the pulmonary pressure-volume curve.
J Appl Physiol 1998;84:389–395.

40. ARDSNET TRIALS
Result of
confluence of basic and clinical research

41. BASIC RESEARCH
Experimental pulmonary oedema due to intermittent positive pressure ventilation with high
Inflation pressures: protection by positive end expiratory pressure.
Webb HH, Tierney DG. Am Rev Respir Dis 1974; 110: 556
Rats were ventilated with varying level of PIP and PEEP
PIP
PEEP
14 cmH2O
0
No pathological or physiological changes
30 cmH2O
0
Perivascular odema; no alveolar odema
45 cmH2O
0
Alveolar and perivascular odema, decreased compliance,
hypoxaemia and gross anatomical changes
45 cmH2O
10
No alveolar odema
BAROTRAUMA
Ubaidur Rahaman, S.R., CCM, SGPGIMS, Lucknow
Rahaman,

42. BASIC RESEARCH
High inflation pressure pulmonary odema. Respective effects of high airway pressure,
high tidal volume and positive end expiratory pressure.
Dreyfuss D, Basset G, Soler P, Saumon G. Am Rev Respir dis, 1988; 137:1159
Ventilated rats with high Paw with and without chest wall strapped
Rats with strapped chest
Paw - very high
VT – modest
No lung damage
Rats without strapped chest
Paw - very high
VT – very high
Dramatic changes in lung
TRANSPULMONARY PRESSURE- VOLUTRAUMA
PEEP effective in preventing damage in large VT rats
Ubaidur Rahaman, S.R., CCM, SGPGIMS, Lucknow
Rahaman,

43. BASIC RESEARCH
INFERENCE
1.
High tidal volume ventilation causes acute lung injury
2.
3.
PEEP exerts a protective effect against this injury
High tidal volume ventilation can result in distant organ
injury
Ubaidur Rahaman, S.R., CCM, SGPGIMS, Lucknow
Rahaman,

44. CLINICAL RESEARCH
CT SCAN CORRELATED WITH LUNG MECHANICS
INFERENCE
1.
Lung is non- homogenous
2.
3.
Lung is small not stiff
Compartment of aerated alveoli ( baby lung) is subject to
overdistension
Ubaidur Rahaman, S.R., CCM, SGPGIMS, Lucknow
Rahaman,

45. HYPOTHESIS
End inspiratory lung volume should be limited
to avoid alveolar overdistension (volutrauma)
Sufficient PEEP should be applied to prevent
cycles of end expiratory derecruitment following inspiratory recruitment
(avoid biotrauma and atelectotrauma)
Ubaidur Rahaman, S.R., CCM, SGPGIMS, Lucknow
Rahaman,

46. 3 multicenter RCTs
Authers
Year
published/
enrollment
No.
patient
s
Mortality
Low VT
Mortality
High VT
p Value
Amato et al
1998
(1990-1995)
53
38%*
45%**
71%*
71%**
<0.000
1
Brochard et al
1998
(1994-1996)
116
46.5%^
37.9%^
0.39
Stewart et al
1998
(1995-1996)
120
50%ª
47%ª
0.72
*mortality at 28 days
**mortality at hospital discharge
^mortality at 60 days
ªmortality at hospital discharge

47. Open lung
approach
Amato et al, 1998, NEJM
Conventional ventilation
lowest PEEP for acceptable oxygenation
VT - 12 ml/ kg actual bw
PaCO2:35-38 mm Hg
Protective ventilation
PEEP above LIP on static P/V curve
VT < 6 ml/ kg actual bw
Pplat < 20 cmH2O above PEEP
Permissive hypercapnia,
Brochard et al, 1998, AJRCCM
Conventional ventilation
PEEP – 10 cmH2O
Pplat – 31 cmH2O
VT - 10 ml/ kg actual bw
PaCO2:53-60 mm Hg
Protective ventilation
PEEP – 10 cmH2O
Ppat – 25 cmH2O
VT - 7 ml/ kg actual bw
PaCO2:41-44 mm Hg
Stewart et al, 1998, NEJM
Conventional ventilation
PEEP – 7-8 cmH2O
Pplat – 26-28 cmH2O
VT - 10 ml/ kg actual bw
PaCO2:45 mm Hg
Protective ventilation
PEEP – 8 cmH2O
Pplat – 22 cmH2O
VT - 7 ml/ kg actual bw
PaCO2:54 mm Hg
Ubaidur Rahaman, S.R., CCM, SGPGIMS, Lucknow
Rahaman,

48. Acute Respiratory Distress Syndrome Clinical Network
(ARDSNet)
• NIH-funded, NHLBI sponsored, consortium of 10 centers, 24
hospitals, 75 intensive care units
• Goal to design large RCTs to determine effective treatments
• Key ARDSnet studies:
–
–
–
–
Tidal volume- low vs high - 2000
PEEP- low vs high - 2004
Steroids - 2006
Fluid volume management/PA catheter - 2006

49. Ventilation with lower tidal volume as compared to traditional tidal volume for
acute lung injury and the acute respiratory distress syndrome- ARMA STUDY
NEJM 2000, 342;18
861 patients
Conventional ventilation
PEEP- 5-24 cm H2O
Pplat ≤ 50 cm H2O
VT – 10-12 ml/ kg IBW
PaCO2- 35 mm Hg
22% relative mortality reduction
9% absolute mortality reduction
Protective ventilation
PEEP- 5-24 cm H2O
Pplat ≤ 30 cm H2O
VT – 6-8 ml/ kg IBW
PaCO2- 40 mm Hg
Permissive hypercapnia and acidosis

50. Higher versus Lower Positive End-Expiratory Pressures in Patients with the
Acute Respiratory Distress Syndrome- ALVEOLI STUDY
NEJM, 2004, 351;4
549 patients
HIGHER PEEP
LOWER PEEP
PEEP- 13±3 cm H2O
PEEP- 8±3 cm H2O
Pplat ≤ 26±7 cm H2O
Pplat ≤ 24±6 cm H2O
VT – 5.8±1 ml/ kg IBW
VT – 6±1 ml/ kg IBW
PaO2/FiO2- 206±76
PaO2/FiO2 - 169±69
Mortality – 27%
Mortality – 24.9%%
similar mortality rate despite significant improvement in PaO2/FiO2
Higher PEEP group had higher Pplat despite lower TV
? Benefit of higher PEEP negated by overdistension

51. Efficacy and Safety of Corticosteroids for Persistent Acute Respiratory Distress Syndrome
NEJM, 2006, 354;16
180 patients
>7days of unresolving ARDS
methylprednisolone 2mg/kg iv stat followed by 0.5 mg/kg q6h for 14 days then
tapering to 0.5 mg/kg q12h for 7 days
•no survival benefit
•If given ≥ 2 weeks after onset of ARDS - significantly increased mortality
•improved cardiopulmonary physiology within 3-7 days after their
initiation and altered the course of ARDS
• increased number of ventilator-free days, ICU-free days, and shockfree days during the first 28 days

52. Comparison of Two Fluid-Management Strategies in Acute Lung Injury
N EJM, 2006;354:2564-75
1000 patients
•no significant difference in 60-day mortality
•conservative strategy improved lung function and shortened the
duration of mechanical ventilation and intensive care without
increasing non pulmonary-organ failures

53. Pulmonary-Artery versus Central Venous Catheter to Guide Treatment of Acute Lung Injury
NEJM, 2006,354;21
1000 patients
PAC-guided therapy did not improve survival or organ function
but
associated with more complications than CVC-guided therapy

54. I would rather discover a single fact, even a small one,
than debate the great issues at length without discovering
anything at all.
Galileo Galilei

55. VENTILATOR SCORE
Smith and Gordon-1986
•
•
age
• PA-aO2
mean peak airway pressure

56. Am. J. Respir. Crit. Care Med., Vol 149, No. 1, 01 1994, 8-13.
Respir. Crit.
8-
Vertical gradient of regional lung inflation in adult respiratory
distress syndrome
P Pelosi, L D'Andrea, G Vitale, A Pesenti and L Gattinoni
D'Andrea,
We obtained chest CT sections in 12 normal subjects (controls) and 17 patients with ARDS to
investigate regional lung inflation.
A basal CT section (just above the diaphragm) was obtained in the supine position at ZEEP.
In each CT section the distance from ventral to dorsal surface (hT) was divided into 10 equal
intervals, and 10 lung levels from ventral (no. 1) to dorsal (no. 10) were defined.
Knowing the average density and the volume of each level, we computed: (1) the tissue volume;
(2) the gas/tissue (g/t) ratio (index of regional inflation); (3) the hydrostatic pressure
superimposed on each level (SPL), estimated as density x height.
The total volume of the basal CT section was 49 +/- 2.5 ml x m-2 (mean +/- SE) in control subjects
and 43 +/- 2.3 ml x m-2 in patients with ARDS (p = not significant [NS]).
The tissue volume, however, was 16.7 +/- 0.8 ml x m-2 in control subjects and 31.6 +/- 1.7 ml x
m-2 in patients with ARDS (p < 0.01).
The g/t ratio in level 1 averaged 4.7 +/- 0.5 in control subjects and 1.2 +/- 0.2 in patients with
ARDS (p < 0.01), and this ratio decreased exponentially from level 1 to level 10, both in controls
and patients with ARDS. The Kd constant of the exponential decrease was 13.9 +/- 1.3 cm in
control subjects and 7.8 +/- 0.8 cm in patients with ARDS (p < 0.01).(ABSTRACT TRUNCATED AT
250 WORDS)
Ubaidur Rahaman, S.R., CCM, SGPGIMS, Lucknow
Rahaman,