Ventricular dilation is associated with improved cardiovascular performance and survival in sepsis.

OBJECTIVES: Myocardial dysfunction in sepsis may be associated with changes in left ventricular (LV) size. The goal of this study was to evaluate the impact of myocardial dysfunction and changes in LV diameter on hemodynamics and survival in a murine model of sepsis. METHODS: C57Bl/6 mice (N = 30) were used. Septic mice (n = 24) had cecal ligation and puncture (CLP) followed by fluid and antibiotic resuscitation and control mice (n = 6) received sham ligation. Echocardiography with a 30-mHz probe was performed at baseline and at frequent predefined time points after CLP. Stroke volume (SV), cardiac output (CO), LV internal diameter in diastole (LVIDd), and fractional shortening (FS) were measured. LV dilation was prospectively defined as an increase in LVIDd ≥ 5% from baseline values. Septic animals were classified as dilators or nondilators. RESULTS: Among septic animals, 37% were dilators and 63% were nondilators. After CLP, SV and CO decreased early in both groups. With resuscitation, SV and CO improved to a greater extent in dilators than nondilators (for SV, 46.0 ± 8.2 vs 36.1 ± 12.7 µL at 24 h, P = .05; for CO, 20.4 ± 4.8 vs 14.8 ± 6.7 mL/min, P = .04). Survival at 72 h was significantly improved in dilators compared with nondilators (88% vs 40%, P = .01). CONCLUSIONS: In a clinically relevant murine model of sepsis, animals with LV dilation had better cardiovascular performance and increased survival. Our results suggest that LV dilation is associated with improved SV and CO, a pattern resulting in greatly improved survival. These studies highlight the importance of diastolic function in septic shock.

Fluid resuscitation influences cardiovascular performance and mortality in a murine model of sepsis.

RATIONALE: Current murine models of sepsis do not account for the effects of aggressive fluid resuscitation on hemodynamics and mortality. OBJECTIVES: Evaluate the impact of fluid resuscitation regimens on cardiovascular performance and survival in a murine model of sepsis. METHODS: Mice (n = 90) were made septic by cecal ligation and puncture (CLP), and received antibiotics plus Low, Intermediate, or High fluid resuscitation regimens. Stroke volume (SV), cardiac output (CO), and fractional shortening (FS) were measured by echocardiography at predefined time points. MEASUREMENTS AND MAIN RESULTS: Baseline echocardiographic measurements were similar in all groups. After CLP, SV and CO decreased early in all groups; High: 57.2 +/- 9.2 to 23.9 +/- 7.2 microL, and 26.8 +/- 4.9 to 13.1 +/- 5.8 ml/min; Intermediate: 52.1 +/- 7.0 to 21.5 +/- 6.6 microL, and 24.9 +/- 4.1 to 11.9 +/- 3.9 ml/min; Low: 54.0 +/- 7.0 to 20.3 +/- 5.6 microL, and 25.8 +/- 4.0 to 11.3 +/- 3.9 ml/min (P < 0.05 for all vs. baseline). With resuscitation there was a dose-dependent improvement in SV and CO (P < 0.05). At 24 h SV and CO were 44.0 +/- 13.8 microL and 20.7 +/- 8.5 ml/min in the High group, 39.8 +/- 12.3 microL and 16.7 +/- 6.5 ml/min in the Intermediate group, and 30.1 +/- 12.4 microL and 14.0 +/- 7.2 ml/min in the Low group. Survival was improved in the High fluid group (75%) compared to the Intermediate (58%) and the Low (35%) resuscitation groups (P < 0.05). CONCLUSIONS: In this model, as in human sepsis, the intensity of fluid resuscitation modulates hemodynamic response and mortality. Incorporation of early and aggressive fluid resuscitation can significantly enhances the clinical relevance of murine models of sepsis.

Discordance between microvascular permeability and leukocyte dynamics in septic inducible nitric oxide synthase deficient mice.

INTRODUCTION: Microvascular dysfunction causing intravascular leakage of fluid and protein contributes to hypotension and shock in sepsis. We tested the hypothesis that abrogation of inducible nitric oxide synthase (iNOS) activation would decrease leukocyte rolling, leukocyte adhesion, and microvascular leakage in sepsis. We compared wild-type mice made septic by cecal ligation and puncture with mice deficient in iNOS. METHODS: Leukocyte dynamics and microvascular permeability were assessed simultaneously by fluorescence intravital microscopy in the cremaster muscle 15 to 20 hours after induction of sepsis by cecal ligation and puncture in C57Bl/6 mice. Rolling and adhesion of leukocytes labeled with rhodamine and leakage of fluorescein isothiocyanate-conjugated albumin was measured in single nonbranching venules (25 to 40 microm) and compared among septic wild-type, septic iNOS-deficient transgenic, and sham-operated control mice. RESULTS: Leukocyte rolling and adhesion were increased in septic animals (61.6 +/- 14.4 cells/minute and 4.1 +/- 0.6 cells/100 microm per minute, respectively) as compared with control animals (8.5 +/- 2.3 cells/minute and 1.1 +/- 0.2 cells/100 microm per minute, respectively; P < 0.001 for both). Rolling increased in iNOS-deficient septic mice (to 105.5 +/- 30.0 cells/minute, P = 0.048, versus wild-type septic); adhesion was unchanged (5.1 +/- 0.5 cells/100 microm per minute, P = 0.30). Sepsis produced an increase in leakage ratio in wild-type septic mice compared with controls (0.36 +/- 0.05 versus 0.08 +/- 0.01, P < 0.001). Leakage was attenuated in iNOS-deficient septic mice (0.12 +/- 0.02, P < 0.001, versus wild-type septic mice). CONCLUSION: Leukocyte adhesion and vascular leakage were discordant in this setting. The finding that septic iNOS-deficient mice exhibited less microvascular leakage than wild-type septic mice despite equivalent increases in leukocyte adhesion suggests an important role for nitric oxide in modulating vascular permeability during sepsis.

Effects of the beach chair position, positive end-expiratory pressure, and pneumoperitoneum on respiratory function in morbidly obese patients during anesthesia and paralysis.

BACKGROUND: The authors studied the effects of the beach chair (BC) position, 10 cm H2O positive end-expiratory pressure (PEEP), and pneumoperitoneum on respiratory function in morbidly obese patients undergoing laparoscopic gastric banding. METHODS: The authors studied 20 patients (body mass index 42 +/- 5 kg/m2) during the supine and BC positions, before and after pneumoperitoneum was instituted (13.6 +/- 1.2 mmHg). PEEP was applied during each combination of position and pneumoperitoneum. The authors measured elastance (E,rs) of the respiratory system, end-expiratory lung volume (helium technique), and arterial oxygen tension. Pressure-volume curves were also taken (occlusion technique). Patients were paralyzed during total intravenous anesthesia. Tidal volume (10.5 +/- 1 ml/kg ideal body weight) and respiratory rate (11 +/- 1 breaths/min) were kept constant throughout. RESULTS: In the supine position, respiratory function was abnormal: E,rs was 21.71 +/- 5.26 cm H2O/l, and end-expiratory lung volume was 0.46 +/- 0.1 l. Both the BC position and PEEP improved E,rs (P < 0.01). End-expiratory lung volume almost doubled (0.83 +/- 0.3 and 0.85 +/- 0.3 l, BC and PEEP, respectively; P < 0.01 vs. supine zero end-expiratory pressure), with no evidence of lung recruitment (0.04 +/- 0.1 l in the supine and 0.07 +/- 0.2 in the BC position). PEEP was associated with higher airway pressures than the BC position (22.1 +/- 2.01 vs. 13.8 +/- 1.8 cm H2O; P < 0.01). Pneumoperitoneum further worsened E,rs (31.59 +/- 6.73; P < 0.01) and end-expiratory lung volume (0.35 +/- 0.1 l; P < 0.01). Changes of lung volume correlated with changes of oxygenation (linear regression, R2 = 0.524, P < 0.001) so that during pneumoperitoneum, only the combination of the BC position and PEEP improved oxygenation. CONCLUSIONS: The BC position and PEEP counteracted the major derangements of respiratory function produced by anesthesia and paralysis. During pneumoperitoneum, only the combination of the two maneuvers improved oxygenation.

Pulse doppler and M-mode to assess viability of cardiac allografts using heterotopic femoral heart transplantation in rats.

Noninvasive assessment of heterotopic heart transplants using Doppler echocardiography was first described in two patients by Allen at Stanford in 1981. Since then, numerous experiments studying heterotopic heart transplantation in humans and large animals have confirmed its utility by employing either an intra-abdominal or cervical model. In rats, however, prior research investigating intra-abdominal heterotopic hearts has showed echocardiography to be ineffective. We have recently developed a new technique for heterotopic femoral heart transplantation in rats, which employs the novel use of trans-femoral echocardiography. Therefore, our goal was to re-examine the efficacy of echocardiography for detection of graft rejection.

A new modified technique for heterotopic femoral heart transplantation in rats.

BACKGROUND: Abbott developed the first experimental accessory heart transplant rat model in 1964. This intra-abdominal model required a labor-intensive aortic anastomosis. In 1971, Heron modified the operation by using sutureless cervical vessel anastomoses. Rao and Lisitza developed a femoral heart accessory transplant model in 1985. Our goal was to improve this femoral model for the study of cardiac transplantation between both syngeneic and allogeneic rats. METHODS: ACI and Lewis rats weighing 150 to 350 g were used as donors and recipients (n = 12). The left common carotid and left pulmonary arteries were anastomosed to the femoral artery and vein in an end-to-end fashion, respectively. Improved modifications included the use of hemostatic vessel clips, heparinization of both donor and recipient, a ventricular prolene stay-suture for secure graft placement, and transfemoral echocardiography (TFE). Total operative time averaged 61 +/- 12 minutes. RESULTS: Femoral accessory transplanted hearts (FATHs) allowed easier pulse palpation and access for TFE versus previously described cervical and intra-abdominal models. This modification allows precise detection of acute graft rejection (AGR) and is defined as absent ventricular contraction in the presence of anastomostic patency. CONCLUSIONS: Our new modified technique for heterotopic femoral heart transplantation in rats is a relatively easily learned and reproduced procedure that allows superior allograft access for palpation and improved echocardiographic assessment. Femoral heterotopic heart transplantation remains an effective model for allograft transplantation study.

Early microcirculatory perfusion derangements in patients with severe sepsis and septic shock: relationship to hemodynamics, oxygen transport, and survival.

STUDY OBJECTIVE: To study early microcirculatory perfusion indices in patients with severe sepsis/septic shock, compare early microcirculatory indices in sepsis survivors versus nonsurvivors, and identify systemic hemodynamic/oxygen transport variables that correlate with early microcirculatory perfusion indices. METHODS: This prospective observational study used orthogonal polarization spectral imaging to directly visualize the sublingual microcirculation in patients with severe sepsis/septic shock treated with early goal-directed therapy. We performed initial imaging within 6 hours of early goal-directed therapy initiation and late follow-up studies at 24-hour intervals until death or resolution of organ dysfunction. We imaged 5 sublingual sites and analyzed the data offline in a blinded fashion. We calculated 3 microcirculatory perfusion indices: flow velocity score, flow heterogeneity index, and capillary density. We analyzed early data to compare survivors versus nonsurvivors and examine correlations with systemic hemodynamic measurements. We used a linear mixed-effects model for longitudinal analyses. RESULTS: We performed 66 orthogonal polarization spectral studies in 26 sepsis patients. Early microcirculatory indices were more markedly impaired (lower flow velocity and more heterogeneous perfusion) in nonsurvivors compared with survivors. These same early indices, flow velocity and heterogeneity, were also more markedly impaired with increasing severity of systemic cardiovascular dysfunction (lower arterial pressure or increasing vasopressor requirement). CONCLUSION: Early microcirculatory perfusion indices in severe sepsis and septic shock are more markedly impaired in nonsurvivors compared with survivors and with increasing severity of global cardiovascular dysfunction.

Prone position delays the progression of ventilator-induced lung injury in rats: does lung strain distribution play a role?

OBJECTIVE: To investigate if prone position delays the progression of experimental ventilator-induced lung injury, possibly due to a more homogeneous distribution of strain within lung parenchyma. DESIGN: Prospective, randomized, controlled trial. SETTING: Animal laboratory of a university hospital. SUBJECTS: Thirty-five Sprague Dawley male rats (weight 257 +/- 45 g). INTERVENTIONS: Mechanical ventilation in either supine or prone position and computed tomography scan analysis. MEASUREMENTS: : Animals were ventilated in supine (n = 15) or prone (n = 15) position until a similar ventilator-induced lung injury was reached. To do so, experiments were interrupted when respiratory system elastance was 150% of baseline. Ventilator-induced lung injury was assessed as lung wet-to-dry ratio and histology. Time to reach lung injury was considered as a main outcome measure. In five additional animals, computed tomography scans (GE Light Speed QX/I, thickness 1.25 mm, interval 0.6 mm, 100 MA, 100 Kv) were randomly taken at end-expiration and end-inspiration in both positions, and quantitative analysis was performed. Data are shown as mean +/- sd. MEASUREMENTS AND MAIN RESULTS: Similar ventilator-induced lung injury was reached (respiratory system elastance, wet-to-dry ratio, and histology). The time taken to achieve the target ventilator-induced lung injury was longer with prone position (73 +/- 37 mins vs. 112 +/- 42, supine vs. prone, p = .011). Computed tomography scan analysis performed before lung injury revealed that at end-expiration, the lung was wider in prone position (p = .004) and somewhat shorter (p = .09), despite similar lung volumes (p = .455). Lung density along the vertical axis increased significantly only in supine position (p = .002). Lung strain was greater in supine as opposed to prone position (width strain, 7.8 +/- 1.8% vs. 5.6 +/- 0.9, supine vs. prone, p = .029). CONCLUSIONS: Prone position delays the progression of ventilator-induced lung injury. Computed tomography scan analysis suggests that a more homogeneous distribution of strain may be implicated in the protective role of prone position against ventilator-induced lung injury.

Effects of continuous negative extra-abdominal pressure on cardiorespiratory function during abdominal hypertension: an experimental study.

OBJECTIVE: To investigate whether negative extra-abdominal pressure (NEXAP) improves respiratory function and induces a blood shift from the intrathoracic compartment and to assess whether these effects are influenced by abdominal pressure. DESIGN AND SETTING: Prospective, randomized, controlled trial in the animal laboratory of a university hospital. SUBJECTS: Eight sedated and paralyzed pigs (19.6+/-3.4 kg). INTERVENTIONS: Application of NEXAP (-20 cmH(2)O). MEASUREMENTS AND RESULTS: Airway, esophageal, gastric and central venous pressures were recorded simultaneously. Intrathoracic blood volume was assessed by PiCCO. The effects of NEXAP were assessed with and without abdominal hypertension by intraperitoneal insufflation of helium. NEXAP caused a lasting drop of gastric (1.97+/-2.26 mmHg) and esophageal (1.21+/-0.67 mmHg) pressures, while end-expiratory airway pressure was similar, hence transpulmonary pressure increased. Intrathoracic blood volume dropped from 358+/-47 to 314+/-47 ml. The fall was associated with a decrease in central venous pressure (R(2)=0.820). When peritoneal pressure was raised (24.7+/-5.5 mmHg), the effects were less marked. However, the difference between negative pressure around the abdomen and the pressure inside the abdomen (effective NEXAP) was correlated with the proportional changes in intrathoracic blood volume (R(2)=0.648), being greater with more negative effective NEXAP. NEXAP improved chest wall elastance during abdominal hypertension (from 0.067+/-0.023 to 0.056+/-0.021 cmH(2)O/ml). CONCLUSIONS: NEXAP increases lung volume and causes a shift of blood from the intrathoracic compartment. It needs to be tailored against abdominal pressure to be effective.

Positive end-expiratory pressure delays the progression of lung injury during ventilator strategies involving high airway pressure and lung overdistention.

OBJECTIVE: Many studies have investigated the protective role of positive end-expiratory pressure (PEEP) on ventilator-induced lung injury. Most assessed lung injury in protocols involving different ventilation strategies applied for the same length of time. This study, however, set out to investigate the protective role of PEEP with respect to the time needed to reach similar levels of lung injury. DESIGN: Prospective, randomized laboratory animal investigation. SETTING: The University Laboratory of Ospedale Maggiore, Milano, IRCCS. SUBJECTS: Anesthetized, paralyzed, and mechanically ventilated Sprague-Dawley rats. INTERVENTIONS: Three groups of five Sprague-Dawley rats were ventilated using zero end-expiratory pressure ZEEP (PEEP of 0 cm H(2)O) and PEEP of 3 and 6 cm H(2)O and a similar index of lung overdistension (Paw(p)/P(100) congruent with 1.1; where Paw(p) is peak airway pressure and P(100) is the pressure corresponding to total lung capacity). To obtain this, tidal volume was reduced depending on the PEEP. To reach similar levels of lung injury, we measured respiratory system elastance while ventilating the animals and killed them when respiratory system elastance was 150% of baseline. Once target respiratory system elastance was reached, the lung wet-to-dry ratio was obtained. RESULTS: Rats were ventilated with comparable high airway pressure (Paw(p) of 42.8 +/- 3.1, 43.5 +/- 2.6, and 46.2 +/- 4.4, respectively, for PEEP 0, 3, and 6) obtaining similar overdistension (Paw(p)/P(100) - index of overdistension: 1.17 +/- 0.2, 1.06 +/- 0.1, and 1.19 +/- 0.2). The respiratory system elastance target was reached and wet-to-dry ratio was not different in the three groups, suggesting a similar degree of lung damage. The time taken to achieve the target respiratory system elastance was three times longer with PEEP 3 and 6 (55 +/- 14 mins and 60 +/- 17) as compared with zero end-expiratory pressure (18 +/- 3 mins, p <.001). CONCLUSION: These findings confirm that PEEP is protective against ventilator-induced lung injury and may enable the clinician to "buy time" in the progression of lung injury.

Equal increases in respiratory system elastance reflect similar lung damage in experimental ventilator-induced lung injury.

OBJECTIVE: We hypothesized that a 50% increase in respiratory system elastance (Ers) would indicate similar degree of lung damage (equi-damage, ED), independently of ventilation strategy. DESIGN AND SETTING: A prospective, randomized animal laboratory investigation at a university hospital laboratory. SUBJECTS: 35 anesthetized, paralyzed, mechanically ventilated male Sprague-Dawley rats. INTERVENTIONS: Each rat was ventilated with a different combination of tidal volume, positive end-expiratory pressure, and inspired fraction of oxygen. Ers was determined throughout the experiment; the studies were interrupted when Ers reached 150% (ED) of its baseline value, or after 5 h. MEASUREMENTS AND RESULTS: Lung wet to dry weight ratio (W/D) was assessed. Morphological damage of the lung was scored on a grading of perivascular edema, hemorrhage, and breaks in the alveolar septa to obtain a total injury score. Twenty-four rats achieved an Ers of 150%: nine within 1 h (class 1), nine in 1-2 h (class 2), and six in 2-5 h (class 3). Eleven rats did not reach the target 50% increase in Ers (class 4). W/D was higher in rats that reached the target than in those that did not. W/D did not differ among rats that reached ED. Similarly, the total injury score did not differ among classes 1-3 but was higher than class 4. CONCLUSIONS: In the setting of VILI a 50% increase in Ers corresponds to an equal level of lung damage, irrespective of ventilatory setting and time of ventilation.