Real-time detection of pneumothorax using electrical impedance tomogyaphy

Objectives: Pneumothorax is a frequent complication during mechanical ventilation. Electrical impedance tomography (EIT) is a noninvasive tool that allows real-time imaging of regional ventilation. The purpose of this study was to 1) identify characteristic changes in the EIT signals associated with pneumothoraces; 2) develop and fine-tune an algorithm for their automatic detection; and 3) prospectively evaluate this algorithm for its sensitivity and specificity in detecting pneumothoraces in real time. Design: Prospective controlled laboratory animal investigation. Setting: Experimental Pulmonology Laboratory of the University of Sao Paulo. Subjects: Thirty-nine anesthetized mechanically ventilated supine pigs (31.0 +/- 3.2 kg, mean +/- SD). Interventions. In a first group of 18 animals monitored by EIT, we either injected progressive amounts of air (from 20 to 500 mL) through chest tubes or applied large positive end-expiratory pressure (PEEP) increments to simulate extreme lung overdistension. This first data set was used to calibrate an EIT-based pneumothorax detection algorithm. Subsequently, we evaluated the real-time performance of the detection algorithm in 21 additional animals (with normal or preinjured lungs), submitted to multiple ventilatory interventions or traumatic punctures of the lung. Measurements and Main Results: Primary EIT relative images were acquired online (50 images/sec) and processed according to a few imaging-analysis routines running automatically and in parallel. Pneumothoraces as small as 20 mL could be detected with a sensitivity of 100% and specificity 95% and could be easily distinguished from parenchymal overdistension induced by PEEP or recruiting maneuvers, Their location was correctly identified in all cases, with a total delay of only three respiratory cycles. Conclusions. We created an EIT-based algorithm capable of detecting early signs of pneumothoraces in high-risk situations, which also identifies its location. It requires that the pneumothorax occurs or enlarges at least minimally during the monitoring period. Such detection was operator-free and in quasi real-time, opening opportunities for improving patient safety during mechanical ventilation.

Computed tomographic assessment of lung weights in trauma patients with early posttraumatic lung dysfunction

Introduction: Quantitative computed tomography (qCT)-based assessment of total lung weight (M(lung)) has the potential to differentiate atelectasis from consolidation and could thus provide valuable information for managing trauma patients fulfilling commonly used criteria for acute lung injury (ALI). We hypothesized that qCT would identify atelectasis as a frequent mimic of early posttraumatic ALI. Methods: In this prospective observational study, M(lung) was calculated by qCT in 78 mechanically ventilated trauma patients fulfilling the ALI criteria at admission. A reference interval for M(lung) was derived from 74 trauma patients with morphologically and functionally normal lungs (reference). Results are given as medians with interquartile ranges. Results: The ratio of arterial partial pressure of oxygen to the fraction of inspired oxygen was 560 (506 to 616) mmHg in reference patients and 169 (95 to 240) mmHg in ALI patients. The median reference M(lung) value was 885 (771 to 973) g, and the reference interval for M(lung) was 584 to 1164 g, which matched that of previous reports. Despite the significantly greater median M(lung) value (1088 (862 to 1,342) g) in the ALI group, 46 (59%) ALI patients had M(lung) values within the reference interval and thus most likely had atelectasis. In only 17 patients (22%), Mlung was increased to the range previously reported for ALI patients and compatible with lung consolidation. Statistically significant differences between atelectasis and consolidation patients were found for age, Lung Injury Score, Glasgow Coma Scale score, total lung volume, mass of the nonaerated lung compartment, ventilator-free days and intensive care unit-free days. Conclusions: Atelectasis is a frequent cause of early posttraumatic lung dysfunction. Differentiation between atelectasis and consolidation from other causes of lung damage by using qCT may help to identify patients who could benefit from management strategies such as damage control surgery and lung-protective mechanical ventilation that focus on the prevention of pulmonary complications.

Extrapolation from ten sections can make CT-based quantification of lung aeration more practicable

Clinical applications of quantitative computed tomography (qCT) in patients with pulmonary opacifications are hindered by the radiation exposure and by the arduous manual image processing. We hypothesized that extrapolation from only ten thoracic CT sections will provide reliable information on the aeration of the entire lung. CTs of 72 patients with normal and 85 patients with opacified lungs were studied retrospectively. Volumes and masses of the lung and its differently aerated compartments were obtained from all CT sections. Then only the most cranial and caudal sections and a further eight evenly spaced sections between them were selected. The results from these ten sections were extrapolated to the entire lung. The agreement between both methods was assessed with Bland-Altman plots. Median (range) total lung volume and mass were 3,738 (1,311-6,768) ml and 957 (545-3,019) g, the corresponding bias (limits of agreement) were 26 (-42 to 95) ml and 8 (-21 to 38) g, respectively. The median volumes (range) of differently aerated compartments (percentage of total lung volume) were 1 (0-54)% for the nonaerated, 5 (1-44)% for the poorly aerated, 85 (28-98)% for the normally aerated, and 4 (0-48)% for the hyperaerated subvolume. The agreement between the extrapolated results and those from all CT sections was excellent. All bias values were below 1% of the total lung volume or mass, the limits of agreement never exceeded +/- 2%. The extrapolation method can reduce radiation exposure and shorten the time required for qCT analysis of lung aeration.

Transfusion Requirements After Cardiac Surgery The TRACS Randomized Controlled Trial

Context Perioperative red blood cell transfusion is commonly used to address anemia, an independent risk factor for morbidity and mortality after cardiac operations; however, evidence regarding optimal blood transfusion practice in patients undergoing cardiac surgery is lacking. Objective To define whether a restrictive perioperative red blood cell transfusion strategy is as safe as a liberal strategy in patients undergoing elective cardiac surgery. Design, Setting, and Patients The Transfusion Requirements After Cardiac Surgery (TRACS) study, a prospective, randomized, controlled clinical noninferiority trial conducted between February 2009 and February 2010 in an intensive care unit at a university hospital cardiac surgery referral center in Brazil. Consecutive adult patients (n=502) who underwent cardiac surgery with cardiopulmonary bypass were eligible; analysis was by intention-to-treat. Intervention Patients were randomly assigned to a liberal strategy of blood transfusion (to maintain a hematocrit >= 30%) or to a restrictive strategy (hematocrit >= 24%). Main Outcome Measure Composite end point of 30-day all-cause mortality and severe morbidity (cardiogenic shock, acute respiratory distress syndrome, or acute renal injury requiring dialysis or hemofiltration) occurring during the hospital stay. The noninferiority margin was predefined at -8% (ie, 8% minimal clinically important increase in occurrence of the composite end point). Results Hemoglobin concentrations were maintained at a mean of 10.5 g/dL(95% confidence interval [CI], 10.4-10.6) in the liberal-strategy group and 9.1 g/dL (95% CI, 9.09.2) in the restrictive-strategy group (P<.001). A total of 198 of 253 patients (78%) in the liberal-strategy group and 118 of 249 (47%) in the restrictive-strategy group received a blood transfusion (P<.001). Occurrence of the primary end point was similar between groups (10% liberal vs 11% restrictive; between-group difference, 1% [95% CI, -6% to 4%]; P=.85). Independent of transfusion strategy, the number of transfused red blood cell units was an independent risk factor for clinical complications or death at 30 days (hazard ratio for each additional unit transfused, 1.2 [95% CI, 1.1-1.4]; P=.002). Conclusion Among patients undergoing cardiac surgery, the use of a restrictive perioperative transfusion strategy compared with a more liberal strategy resulted in noninferior rates of the combined outcome of 30-day all-cause mortality and severe morbidity. Trial Registration clinicaltrials.gov Identifier: NCT01021631 JAMA. 2010; 304(14):1559-1567 www.jama.com

Prone position prevents regional alveolar hyperinflation and mechanical stress and strain in mild experimental acute lung injury

Prone position may delay the development of ventilator-induced lung injury (VILI), but the mechanisms require better elucidation. In experimental mild acute lung injury (ALI), arterial oxygen partial pressure (Pa(O2)), lung mechanics and histology, inflammatory markers [interleukin (IL)-6 and IL-1 beta], and type III procollagen (PCIII) mRNA expressions were analysed in supine and prone position. Wistar rats were randomly divided into two groups. In controls, saline was intraperitoneally injected while ALI was induced by paraquat. After 24-h, the animals were mechanically ventilated for 1-h in supine or prone positions. In ALI, prone position led to a better blood flow/tissue ratio both in ventral and dorsal regions and was associated with a more homogeneous distribution of alveolar aeration/tissue ratio reducing lung static elastance and viscoelastic pressure, and increasing end-expiratory lung volume and Pa(O2). PCIII expression was higher in the ventral than dorsal region in supine position, with no regional changes in inflammatory markers. In conclusion, prone position may protect the lungs against VILI, thus reducing pulmonary stress and strain. (C) 2009 Elsevier B.V. All rights reserved.

Effects of frequency and inspiratory plateau pressure during recruitment manoeuvres on lung and distal organs in acute lung injury

To evaluate the effects of frequency and inspiratory plateau pressure (Pplat) during recruitment manoeuvres (RMs) on lung and distal organs in acute lung injury (ALI). We studied paraquat-induced ALI rats. At 24 h, rats were anesthetized and RMs were applied using continuous positive airway pressure (CPAP, 40 cmH(2)O/40 s) or three-different sigh strategies: (a) 180 sighs/h and Pplat = 40 cmH(2)O (S180/40), (b) 10 sighs/h and Pplat = 40 cmH(2)O (S10/40), and (c) 10 sighs/h and Pplat = 20 cmH(2)O (S10/20). S180/40 yielded alveolar hyperinflation and increased lung and kidney epithelial cell apoptosis as well as type III procollagen (PCIII) mRNA expression. S10/40 resulted in a reduction in epithelial cell apoptosis and PCIII expression. Static elastance and alveolar collapse were higher in S10/20 than S10/40. The reduction in sigh frequency led to a protective effect on lung and distal organs, while the combination with reduced Pplat worsened lung mechanics and histology.

Pulmonary lesion induced by low and high positive end-expiratory pressure levels during protective ventilation in experimental acute lung injury

Objective: To investigate the effects of low and high levels of positive end-expiratory pressure (PEEP), without recruitment maneuvers, during lung protective ventilation in an experimental model of acute lung injury (ALI). Design: Prospective, randomized, and controlled experimental study. Setting: University research laboratory. Subjects: Wistar rats were randomly assigned to control (C) [saline (0.1 ml), intraperitoneally] and ALI [paraquat (15 mg/kg), intra peritoneally] groups. Measurements and Main Results: After 24 hours, each group was further randomized into four groups (six rats each) at different PEEP levels = 1.5, 3, 4.5, or 6 cm H(2)O and ventilated with a constant tidal volume (6 mL/kg) and open thorax. Lung mechanics [static elastance (Est, L) and viscoelastic pressure (Delta P2, L)] and arterial blood gases were measured before (Pre) and at the end of 1-hour mechanical ventilation (Post). Pulmonary histology (light and electron microscopy) and type III procollagen (PCIII) messenger RNA (mRNA) expression were measured after 1 hour of mechanical ventilation. In ALI group, low and high PEEP levels induced a greater percentage of increase in Est, L (44% and 50%) and Delta P2, L (56% and 36%) in Post values related to Pre. Low PEEP yielded alveolar collapse whereas high PEEP caused overdistension and atelectasis, with both levels worsening oxygenation and increasing PCIII mRNA expression. Conclusions: In the present nonrecruited ALI model, protective mechanical ventilation with lower and higher PEEP levels than required for better oxygenation increased Est, L and Delta P2, L, the amount of atelectasis, and PCIII mRNA expression. PEEP selection titrated for a minimum elastance and maximum oxygenation may prevent lung injury while deviation from these settings may be harmful. (Crit Care Med 2009; 37:1011-1017)

Early short-term versus prolonged low-dose methylprednisolone therapy in acute lung injury

The present study compared the effects of early short-term with prolonged low-dose corticosteroid therapy in acute lung injury (ALI). In total, 120 BALB/c mice were randomly divided into five groups. In the control group, saline was intratracheally (i.t.) instilled. In the ALI group, mice received Escherichia coli lipopolysaccharide (10 mu g i.t.). ALI animals were further randomised into four subgroups to receive saline (0.1 mL i.v.) or methylprednisolone (2 mg center dot kg(-1) i.v.) at 6 h, 24 h or daily (for 7 days, beginning at day 1). At 1, 3 and 8 weeks, in vivo and in vitro lung mechanics and histology (light and electron microscopy), collagen and elastic fibre content, cytokines in bronchoalveolar lavage fluid and the expression of matrix metalloproteinase (MMP)-9 and -2 were measured. In vivo (static elastance and viscoelastic pressure) and in vitro (tissue elastance and resistance) lung mechanics, alveolar collapse, cell infiltration, collagen and elastic fibre content and the expression of MMP-9 and MMP-2 were increased in ALI at 1 week. Methylprednisolone led to a complete resolution of lung mechanics, avoided fibroelastogenesis and the increase in the expression of MMP-9 and MMP-2 independent of steroid treatment design. Thus, early short-term, low-dose methylprednisolone is as effective as prolonged therapy in acute lung injury.

Methylprednisolone improves lung mechanics and reduces the inflammatory response in pulmonary but not in extrapulmonary mild acute lung injury in mice

Objective: Gorticosteroids have been proposed to be effective in modulating the inflammatory response and pulmonary tissue remodeling in acute lung injury (ALI). We hypothesized that steroid treatment might act differently in models of pulmonary (p) or extrapulmonary (exp) ALI with similar mechanical compromise. Design: Prospective, randomized, controlled experimental study. Setting: University research laboratory. Subjects: One hundred twenty-eight BALB/c mice (20-25 g). Interventions: Mice were divided into six groups. In control animals sterile saline solution was intratracheally (0.05 mL, Cp) or intraperitoneally (0.5 mL, Gexp) injected, whereas ALI animals received Escherichia coli lipopolysaccharide intratracheally (10 mu g, ALIp) or intraperitoneally (125 mu g, ALIexp). Six hours after lipopolysaccharide administration, ALIp and ALlexp animals were further randomized into subgroups receiving saline (0.1 mL intravenously) or methylprednisolone (2 mg/kg intravenously, Mp and Mexp, respectively). Measurements and Main Results: At 24 hrs, lung state elastance, resistive and viscoelastic pressures, lung morphometry, and collagen fiber content were similar in both ALI groups. KC, interieukin-6, and transforming growth factor (TGF)-beta levels in bronchoatveolar lavage fluid, as well as tumor necrosis factor (TNF)-alpha, migration inhibitory factor (MIF), interferon (IFN)-gamma, TGF-beta 1 and TGF-beta 2 messenger RNA expression in lung tissue were higher in ALIp than in ALIexp animals. Methylprednisolone attenuated mechanical and morphometric changes, cytokine levels, and TNF-alpha, MIF, IFN gamma, and TGF-beta 2 messenger RNA expression only in ALIp animals, but prevented any changes in collagen fiber content in both ALI groups. Conclusions. Methylprednisolone is effective to inhibit fibrogenesis independent of the etiology of ALI, but its ability to attenuate inflammatory responses and lung mechanical changes varies according to the cause of ALI.

Recruitment maneuver in pulmonary and extrapulmonary experimental acute lung injury

Objective. The aim of this study is to test the hypothesis that recruitment maneuvers (RMs) might act differently in models of pulmonary (p) and extrapulmonary (exp) acute lung injury (ALI) with similar transpulmonary pressure changes. Design: Prospective, randomized, controlled experimental study. Setting. University research laboratory. Subjects: Wistar rats were randomly divided into four groups. In control groups, sterile saline solution was intratracheally (0.1 mL, Cp) or intraperitoneally (1 mL, Cexp) injected, whereas ALI animals received Escherichia coli lipopolysaccharide intratracheally (100 jig, ALIp) or intraperitoneally (1 mg, ALIexp). After 24 hrs, animals were mechanically ventilated (tidal volume, 6 mL/kg; positive end-expiratory pressure, 5 cm H2O) and three RMs (pressure inflations to 40 cm H2O for 40 secs, 1 min apart) applied. Measurements and Main Results. Pao(2), lung resistive and viscoelastic pressures, static elastance, lung histology (light and electron microscopy), and type III procollagen messenger RNA expression in pulmonary tissue were measured before RMs and at the end of 1 hr of mechanical ventilation. Mechanical variables, gas exchange, and the fraction of area of alveolar collapse were similar in both ALI groups. After RMs, lung resistive and viscoelastic pressures and static elastance decreased more in ALIexp (255%,180%, and 118%, respectively) than in ALIp (103%, 59%, and 89%, respectively). The amount of atelectasis decreased more in ALIexp than in ALIp (from 58% to 19% and from 59% to 33%, respectively). RMs augmented type III procollagen messenger RNA expression only in the ALIp group (19%), associated with worsening in alveolar epithelium injury but no capillary endothelium lesion, whereas the ALIexp group showed a minor detachment of the alveolar capillary membrane. Conclusions. Given the same transpulmonary pressures, RMs are more effective at opening collapsed alveoli in ALIexp than in ALIp, thus improving lung mechanics and oxygenation with limited damage to alveolar epithelium.

Recruitment maneuver in experimental acute lung injury: The role of alveolar collapse and edema

Objective: In acute lung injury, recruitment maneuvers have been used to open collapsed lungs and set positive end-expiratory pressure, but their effectiveness may depend on the degree of lung injury. This study uses a single experimental model with different degrees of lung injury and tests the hypothesis that recruitment maneuvers may have beneficial or deleterious effects depending on the severity of acute lung injury. We speculated that recruitment maneuvers may worsen lung mechanical stress in the presence of alveolar edema. Design: Prospective, randomized, controlled experimental study. Setting: University research laboratory. Subjects: Thirty-six Wistar rats randomly divided into three groups (n = 12 per group). Interventions: In the control group, saline was intraperitoneally injected, whereas moderate and severe acute lung injury animals received paraquat intraperitoneally (20 mg/kg [moderate acute lung injury] and 25 mg/kg [severe acute lung injury]). After 24 hrs, animals were further randomized into subgroups (n = 6/each) to be recruited (recruitment maneuvers: 40 cm H(2)O continuous positive airway pressure for 40 secs) or not, followed by 1 hr of protective mechanical ventilation (tidal volume, 6 mL/kg; positive end-expiratory pressure, 5 cm H(2)O). Measurements and Main Results: Only severe acute lung injury caused alveolar edema. The amounts of alveolar collapse were similar in the acute lung injury groups. Static lung elastance, viscoelastic pressure, hyperinflation, lung, liver, and kidney cell apoptosis, and type 3 procollagen and interleukin-6 mRNA expressions in lung tissue were more elevated in severe acute lung injury than in moderate acute lung injury. After recruitment maneuvers, static lung elastance, viscoelastic pressure, and alveolar collapse were lower in moderate acute lung injury than in severe acute lung injury. Recruitment maneuvers reduced interleukin-6 expression with a minor detachment of the alveolar capillary membrane in moderate acute lung injury. In severe acute lung injury, recruitment maneuvers were associated with hyperinflation, increased apoptosis of lung and kidney, expression of type 3 procollagen, and worsened alveolar capillary injury. Conclusions: In the presence of alveolar edema, regional mechanical heterogeneities, and hyperinflation, recruitment maneuvers promoted a modest but consistent increase in inflammatory and fibrogenic response, which may have worsened lung function and potentiated alveolar and renal epithelial injury. (Crit Care Med 2010; 38: 2207-2214)

Degree of endothelium injury promotes fibroelastogenesis in experimental acute lung injury

We tested the hypothesis that at the early phase of acute lung injury (ALI) the degree of endothelium injury may predict lung parenchyma remodelling For this purpose, two models of extrapulmonary ALI induced by Escherichia col: lipopolysaccharide (ALI-LPS) or cecal ligation and puncture (ALI-CLP) were developed in mice At day 1, these models had similar degrees of lung mechanical compromise, epithelial damage, and intraperitoneal inflammation, but endothelial lesion was greater in ALI-CLP A time course analysis revealed, at day 7 ALI-CLP had higher degrees of epithelial lesion, denudation of basement membrane, endothelial damage, elastic and collagen fibre content, neutrophils in bronchoalveolar lavage fluid (BALF), peritoneal fluid and blood, levels of interleukin-6, KC (murine analogue of IL-8), and transforming growth factor-beta in BALF Conversely, the number of lung apoptotic cells was similar in both groups In conclusion, the intensity of fibroelastogenesis was affected by endothelium injury in addition to the maintenance of epithelial damage and intraperitoneal inflammation. (C) 2010 Elsevier B V All rights reserved

Assisted ventilation modes reduce the expression of lung inflammatory and fibrogenic mediators in a model of mild acute lung injury

The goal of the study was to compare the effects of different assisted ventilation modes with pressure controlled ventilation (PCV) on lung histology, arterial blood gases, inflammatory and fibrogenic mediators in experimental acute lung injury (ALI). Paraquat-induced ALI rats were studied. At 24 h, animals were anaesthetised and further randomized as follows (n = 6/group): (1) pressure controlled ventilation mode (PCV) with tidal volume (V (T)) = 6 ml/kg and inspiratory to expiratory ratio (I:E) = 1:2; (2) three assisted ventilation modes: (a) assist-pressure controlled ventilation (APCV1:2) with I:E = 1:2, (b) APCV1:1 with I:E = 1:1; and (c) biphasic positive airway pressure and pressure support ventilation (BiVent + PSV), and (3) spontaneous breathing without PEEP in air. PCV, APCV1:1, and APCV1:2 were set with P (insp) = 10 cmH(2)O and PEEP = 5 cmH(2)O. BiVent + PSV was set with two levels of CPAP [inspiratory pressure (P (High) = 10 cmH(2)O) and positive end-expiratory pressure (P (Low) = 5 cmH(2)O)] and inspiratory/expiratory times: T (High) = 0.3 s and T (Low) = 0.3 s. PSV was set as follows: 2 cmH(2)O above P (High) and 7 cmH(2)O above P (Low). All rats were mechanically ventilated in air and PEEP = 5 cmH(2)O for 1 h. Assisted ventilation modes led to better functional improvement and less lung injury compared to PCV. APCV1:1 and BiVent + PSV presented similar oxygenation levels, which were higher than in APCV1:2. Bivent + PSV led to less alveolar epithelium injury and lower expression of tumour necrosis factor-alpha, interleukin-6, and type III procollagen. In this experimental ALI model, assisted ventilation modes presented greater beneficial effects on respiratory function and a reduction in lung injury compared to PCV. Among assisted ventilation modes, Bi-Vent + PSV demonstrated better functional results with less lung damage and expression of inflammatory mediators.

Hypervolemia induces and potentiates lung damage after recruitment maneuver in a model of sepsis-induced acute lung injury

Introduction: Recruitment maneuvers (RMs) seem to be more effective in extrapulmonary acute lung injury (ALI), caused mainly by sepsis, than in pulmonary ALI. Nevertheless, the maintenance of adequate volemic status is particularly challenging in sepsis. Since the interaction between volemic status and RMs is not well established, we investigated the effects of RMs on lung and distal organs in the presence of hypovolemia, normovolemia, and hypervolemia in a model of extrapulmonary lung injury induced by sepsis. Methods: ALI was induced by cecal ligation and puncture surgery in 66 Wistar rats. After 48 h, animals were anesthetized, mechanically ventilated and randomly assigned to 3 volemic status (n = 22/group): 1) hypovolemia induced by blood drainage at mean arterial pressure (MAP)approximate to 70 mmHg; 2) normovolemia (MAP approximate to 100 mmHg), and 3) hypervolemia with colloid administration to achieve a MAP approximate to 130 mmHg. In each group, animals were further randomized to be recruited (CPAP = 40 cm H(2)O for 40 s) or not (NR) (n = 11/group), followed by 1 h of protective mechanical ventilation. Echocardiography, arterial blood gases, static lung elastance (Est, L), histology (light and electron microscopy), lung wet-to-dry (W/D) ratio, interleukin (IL)-6, IL-1 beta, caspase-3, type III procollagen (PCIII), intercellular adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1) mRNA expressions in lung tissue, as well as lung and distal organ epithelial cell apoptosis were analyzed. Results: We observed that: 1) hypervolemia increased lung W/D ratio with impairment of oxygenation and Est, L, and was associated with alveolar and endothelial cell damage and increased IL-6, VCAM-1, and ICAM-1 mRNA expressions; and 2) RM reduced alveolar collapse independent of volemic status. In hypervolemic animals, RM improved oxygenation above the levels observed with the use of positive-end expiratory pressure (PEEP), but increased lung injury and led to higher inflammatory and fibrogenetic responses. Conclusions: Volemic status should be taken into account during RMs, since in this sepsis-induced ALI model hypervolemia promoted and potentiated lung injury compared to hypo-and normovolemia.

Heart-lung interactions with different ventilatory settings during acute lung injury and hypovolaemia: an experimental study

Background. The functional haemodynamic variables pulse pressure variation (PPV), stroke volume variation (SVV), and systolic pressure variation (SPV) are widely used to assess haemodynamic status. However, it is not known how these perform during acute lung injury (ALI). This study evaluated the effects of different ventilatory strategies on haemodynamic parameters in pigs with ALI during normovolaemia and hypovolaemia. Methods. Eight anaesthetized Agroceres pigs [40 (1.9) kg] were instrumented with pulmonary artery, PiCCO, and arterial catheters and ventilated. Three ventilatory settings were randomly assigned for 10 min each: tidal volume (VT) 15 ml kg(-1) and PEEP 5 cm H(2)O, VT 8 ml kg(-1) and PEEP 13 cm H(2)O, or VT 6 ml kg(-1) and PEEP 13 cm H(2)O. Data were collected at each setting at baseline, after ALI (lung lavage+Tween 1.5%), and ALI with hypovolaemia (haemorrhage to 30% of estimated blood volume). Results. At baseline, high VT increased PPV, SVV, and SPV (P < 0.05 for all). During ALI, high VT significantly increased PPV and SVV [(P = 0.002 and P = 0.008) respectively.]. After ALI with hypovolaemia, ventilation at VT 6 ml kg(-1) and PEEP 13 cm H(2)O decreased the accuracy of functional haemodynamic variables to predict hypovolaemia, with the exception of PPV (area under the curve 0.875). The parameters obtained by PiCCO were less influenced by ventilatory changes. Conclusions. VT is the ventilatory parameter which influences functional haemodynamics the most. During ventilation with low VT and high PEEP, most functional variables are less able to accurately predict hypovolaemia secondary to haemorrhage, with the exception of PPV.