Dexmedetomidine protects against lung ischemia-reperfusion injury by the PI3K/Akt/HIF-1α signaling pathway

PURPOSE

To evaluate the role of the phosphatidylinositol 3 kinase (PI3K)/protein kinase B (Akt)/hypoxia-inducible factor 1α (HIF-1α) signaling pathway in the protection by dexmedetomidine against lung ischemia-reperfusion injury (IRI) in rats.

METHODS

Forty-eight male Sprague-Dawley rats weighing 250-350 g were randomly divided into six groups (n = 8 each group): sham group, IRI group, low-dose dexmedetomidine group (LD group), high-dose dexmedetomidine group (HD group), combined low-dose dexmedetomidine and LY294002 group (LDL group), and combined high-dose dexmedetomidine and LY294002 group (HDL group). A 30-min ischemia was induced by occluding the hilum of the left lung, followed by a 120-min reperfusion by removing occlusion of the hilum. After the left lung was removed, the wet/dry weight ratio (W/D) of the lung tissues was determined. Pathological changes of lung tissues were evaluated by light and electron microscopes and the expression of p-Akt and HIF-1α in the lung tissues was determined by western blotting.

RESULTS

Compared with the sham group, both the W/D ratio and lung injury were significantly increased, the p-Akt expression was down-regulated and HIF-1α expression was up-regulated in the five experimental groups. Compared with the LD and LDL groups, both the W/D ratio and lung injury were decreased, but the expression of p-Akt and HIF-1α was increased in the HD and HDL groups.

CONCLUSIONS

Administration of dexmedetomidine before ischemia can provide a protection against lung IRI by re-installing the PI3K/Akt/HIF-1α signaling pathway.

Low tidal volume ventilation preconditioning ameliorates lipopolysaccharide-induced acute lung injury in rats

BACKGROUND

Effects of low tidal volume (LTV) ventilation preconditioning in endotoxin-induced acute lung injury (ALI) have not been studied. We investigated the effect of LTV ventilation pre-treatment on ALI induced by lipopolysaccharide (LPS) in rats.

METHODS

Male Sprague-Dawley rats were assigned to four groups (n = 8 each): (1) sham rats injected (i.p.) with 0.9% (physiologic) saline; sham rats pre-treated with tidal volume 6 ml/kg ventilation for 1 h followed by injection (i.p.) of physiologic saline (mechanical ventilation; MV-saline group); (2) LPS group (rats injected with LPS (i.p.); rats pre-treated with tidal volume 6 ml/kg ventilation for 1 h before injection (i.p.) with LPS (MV-LPS group). Animals were observed for 6 h. ALI extent was evaluated by lung wet-to-dry ratio, Evans Blue Dye extravasation, and histologic examination. We measured levels of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6. Apoptotic index (AI) and the expression of pulmonary RhoA, ROCK2 mRNA, and ROCK1 protein in lung alveolar cells was determined.

RESULTS

Lipopolysaccharide caused severe ALI, as evidenced by increases in ALI extent, impairment of pulmonary functions, and increases in pulmonary levels of TNF-α, IL-1β, IL-6, and AI. LTV ventilation preconditioning mitigated LPS-induced increases in release of pulmonary pro-inflammatory cytokines and AI of alveolar cells. Expression of pulmonary RhoA, ROCK2 mRNA, and ROCK1 protein was upregulated by LPS and reduced by LTV ventilation pre-treatment.

CONCLUSION

Low tidal volume ventilation preconditioning can attenuate release of pulmonary pro-inflammatory cytokines and decrease the AI induced by severe sepsis. Early protection seems to be mediated partly through inhibition of activation of a Rho pathway.

A novel method for right one-lung ventilation modeling in rabbits

There is no standard method by which to establish a right one-lung ventilation (OLV) model in rabbits. In the present study, a novel method is proposed to compare with two other methods. After 0.5 h of baseline two-lung ventilation (TLV), 40 rabbits were randomly divided into sham group (TLV for 3 h as a contrast) and three right-OLV groups (right OLV for 3 h with different methods): Deep intubation group, clamp group and blocker group (deeply intubate the self-made bronchial blocker into the left main bronchus, the novel method). These three methods were compared using a number of variables: Circulation by heart rate (HR), mean arterial pressure (MAP); oxygenation by arterial blood gas analysis; airway pressure; lung injury by histopathology; and time, blood loss, success rate of modeling. Following OLV, compared with the sham group, arterial partial pressure of oxygen and arterial hemoglobin oxygen saturation decreased, peak pressure increased and lung injury scores were higher in three OLV groups at 3 h of OLV. All these indexes showed no differences between the three OLV groups. During right-OLV modeling, less time was spent in the blocker group (6±2 min), compared with the other two OLV groups (13±4 min in deep intubation group, P<0.05; 33±9 min in clamp group, P<0.001); more blood loss was observed in clamp group (11.7±2.8 ml), compared with the other two OLV groups (2.3±0.5 ml in deep intubation group, P<0.001; 2.1±0.6 ml in blocker group, P<0.001). The first-time and final success rate of modeling showed no differences among the three OLV groups. Deep intubation of the self-made bronchial blocker into the left main bronchus is an easy, effective and reliable method to establish a right-OLV model in rabbits.

Effects of methacholine infusion on desflurane pharmacokinetics in piglets

The data of a corresponding animal experiment demonstrates that nebulized methacholine (MCh) induced severe bronchoconstriction and significant inhomogeneous ventilation and pulmonary perfusion (V̇_A/Q̇) distribution in pigs, which is similar to findings in human asthma. The inhalation of MCh induced bronchoconstriction and delayed both uptake and elimination of desflurane (Kretzschmar et al., 2015) [1].

The objective of the present data is to determine V̇_A/Q̇ matching by Multiple Inert Gas Elimination Technique (MIGET) in piglets before and during methacholine- (MCh-) induced bronchoconstriction, induced by MCh infusion, and to assess the blood concentration profiles for desflurane (DES) by Micropore Membrane Inlet Mass Spectrometry (MMIMS).

Healthy piglets (n=4) under general anesthesia were instrumented with arterial, central venous, and pulmonary artery lines. The airway was secured via median tracheostomy with an endotracheal tube, and animals were mechanically ventilated with intermittent positive pressure ventilation (IPPV) with a FiO₂ of 0.4, tidal volume (V_T)=10 ml/kg and PEEP of 5cmH₂O using an open system. The determination of V._A/Q. was done by MIGET: before desflurane application and at plateau in both healthy state and during MCh infusion. Arterial blood was sampled at 0, 1, 2, 5, 10, 20, and 30 min during wash-in and washout, respectively.

Bronchoconstriction was established by MCH infusion aiming at doubling the peak airway pressure, after which wash-in and washout of the anesthetic gas was repeated. Anesthesia gas concentrations were measured by MMIMS. Data were analyzed by ANOVA, paired t-test, and by nonparametric Friedman׳s test and Wilcoxon׳s matched pairs test.

We measured airway pressures, pulmonary resistance, and mean paO₂ as well as hemodynamic variables in all pigs before desflurane application and at plateau in both healthy state and during methacholine administration by infusion. By MIGET, fractional alveolar ventilation and pulmonary perfusion in relation to the V.A/Q. compartments, data of logSDQ̇ and logSDV̇ (the second moments describing global dispersion, i.e. heterogeneity of distribution) were estimated prior to and after MCh infusion. The uptake and elimination of desflurane was determined by MMIMS.

Bronchoconstriction induced by inhaled methacholine delays desflurane uptake and elimination in a piglet model

Bronchoconstriction is a hallmark of asthma and impairs gas exchange. We hypothesized that pharmacokinetics of volatile anesthetics would be affected by bronchoconstriction. Ventilation/perfusion (VA/Q) ratios and pharmacokinetics of desflurane in both healthy state and during inhalational administration of methacholine (MCh) to double peak airway pressure were studied in a piglet model. In piglets, MCh administration by inhalation (100 μg/ml, n=6) increased respiratory resistance, impaired VA/Q distribution, increased shunt, and decreased paO2 in all animals. The uptake and elimination of desflurane in arterial blood was delayed by nebulization of MCh, as determined by Micropore Membrane Inlet Mass Spectrometry (wash-in time to P50, healthy vs. inhalation: 0.5 min vs. 1.1 min, to P90: 4.0 min vs. 14.8 min). Volatile elimination was accordingly delayed. Inhaled methacholine induced severe bronchoconstriction and marked inhomogeneous VA/Q distribution in pigs, which is similar to findings in human asthma exacerbation. Furthermore, MCh-induced bronchoconstriction delayed both uptake and elimination of desflurane. These findings might be considered when administering inhalational anesthesia to asthmatic patients.

Lung Injury After One-Lung Ventilation: A Review of the Pathophysiologic Mechanisms Affecting the Ventilated and the Collapsed Lung

Lung injury is the leading cause of death after thoracic surgery. Initially recognized after pneumonectomy, it has since been described after any period of 1-lung ventilation (OLV), even in the absence of lung resection. Overhydration and high tidal volumes were thought to be responsible at various points; however, it is now recognized that the pathophysiology is more complex and multifactorial. All causative mechanisms known to trigger ventilator-induced lung injury have been described in the OLV setting. The ventilated lung is exposed to high strain secondary to large, nonphysiologic tidal volumes and loss of the normal functional residual capacity. In addition, the ventilated lung experiences oxidative stress, as well as capillary shear stress because of hyperperfusion. Surgical manipulation and/or resection of the collapsed lung may induce lung injury. Re-expansion of the collapsed lung at the conclusion of OLV invariably induces duration-dependent, ischemia-reperfusion injury. Inflammatory cytokines are released in response to localized injury and may promote local and contralateral lung injury. Protective ventilation and volatile anesthesia lessen the degree of injury; however, increases in biochemical and histologic markers of lung injury appear unavoidable. The endothelial glycocalyx may represent a common pathway for lung injury creation during OLV, because it is damaged by most of the recognized lung injurious mechanisms. Experimental therapies to stabilize the endothelial glycocalyx may afford the ability to reduce lung injury in the future. In the interim, protective ventilation with tidal volumes of 4 to 5 mL/kg predicted body weight, positive end-expiratory pressure of 5 to 10 cm H2O, and routine lung recruitment should be used during OLV in an attempt to minimize harmful lung stress and strain. Additional strategies to reduce lung injury include routine volatile anesthesia and efforts to minimize OLV duration and hyperoxia.

Hypoxic pulmonary vasoconstriction: physiology and anesthetic implications

Hypoxic pulmonary vasoconstriction (HPV) represents a fundamental difference between the pulmonary and systemic circulations. HPV is active in utero, reducing pulmonary blood flow, and in adults helps to match regional ventilation and perfusion although it has little effect in healthy lungs. Many factors affect HPV including pH or PCO2, cardiac output, and several drugs, including antihypertensives. In patients with lung pathology and any patient having one-lung ventilation, HPV contributes to maintaining oxygenation, so anesthesiologists should be aware of the effects of anesthesia on this protective reflex. Intravenous anesthetic drugs have little effect on HPV, but it is attenuated by inhaled anesthetics, although less so with newer agents. The reflex is biphasic, and once the second phase becomes active after about an hour of hypoxia, this pulmonary vasoconstriction takes hours to reverse when normoxia returns. This has significant clinical implications for repeated periods of one-lung ventilation.

Oxidative lung injury correlates with one-lung ventilation time during pulmonary lobectomy: a study of exhaled breath condensate and blood

OBJECTIVES

During lung lobectomy, the operated lung is collapsed and hypoperfused; oxygen deprivation is accompanied by reactive hypoxic pulmonary vasoconstriction. After lung lobectomy, ischaemia present in the collapsed state is followed by expansion-reperfusion and lung injury attributed to the production of reactive oxygen species. The primary objective of this study was to investigate the time course of several markers of oxidative stress simultaneously in exhaled breath condensate and blood and to determine the relationship between oxidative stress and one-lung ventilation time in patients undergoing lung lobectomy.

METHODS

This single-centre, observational, prospective study included 28 patients with non-small-cell lung cancer who underwent lung lobectomy. We measured the levels of hydrogen peroxide, 8-iso-PGF2α, nitrites plus nitrates and pH in exhaled breath condensate (n = 25). The levels of 8-iso-PGF2α and nitrites plus nitrates were also measured in blood (n = 28). Blood samples and exhaled breath condensate samples were collected from all patients at five time points: preoperatively; during one-lung ventilation, immediately before resuming two-lung ventilation; immediately after resuming two-lung ventilation; 60 min after resuming two-lung ventilation and 180 min after resuming two-lung ventilation.

RESULTS

Both exhaled breath condensate and blood exhibited significant and simultaneous increases in oxidative-stress markers immediately before two-lung ventilation was resumed. However, all these values underwent larger increases immediately after resuming two-lung ventilation. In both exhaled breath condensate and blood, marker levels significantly and directly correlated with the duration of one-lung ventilation immediately before resuming two-lung ventilation and immediately after resuming two-lung ventilation. Although pH significantly decreased in exhaled breath condensate immediately after resuming two-lung ventilation, these pH values were inversely correlated with the duration of one-lung ventilation.

CONCLUSIONS

During lung lobectomy, the operated lung is collapsed and oxidative injury occurs, with the levels of markers of oxidative stress increasing simultaneously in exhaled breath condensate and blood during one-lung ventilation. These increases were larger after resuming two-lung ventilation. Increases immediately before resuming two-lung ventilation and immediately after resuming two-lung ventilation were directly correlated with the duration of one-lung ventilation.

Prophylactic methylprednisolone to reduce inflammation and improve outcomes from one lung ventilation in children: a randomized clinical trial

BACKGROUND

One lung ventilation (OLV) results in inflammatory and mechanical injury, leading to intraoperative and postoperative complications in children. No interventions have been studied in children to minimize such injury.

OBJECTIVE

We hypothesized that a single 2-mg·kg(-1) dose of methylprednisolone given 45-60 min prior to lung collapse would minimize injury from OLV and improve physiological stability.

METHODS

Twenty-eight children scheduled to undergo OLV were randomly assigned to receive 2 mg·kg(-1) methylprednisolone (MP) or normal saline (placebo group) prior to OLV. Anesthetic management was standardized, and data were collected for physiological stability (bronchospasm, respiratory resistance, and compliance). Plasma was assayed for inflammatory markers related to lung injury at timed intervals related to administration of methylprednisolone.

RESULTS

Three children in the placebo group experienced clinically significant intraoperative and postoperative respiratory complications. Respiratory resistance was lower (P = 0.04) in the methylprednisolone group. Pro-inflammatory cytokine IL-6 was lower (P = 0.01), and anti-inflammatory cytokine IL-10 was higher (P = 0.001) in the methylprednisolone group. Tryptase, measured before and after OLV, was lower (P = 0.03) in the methylprednisolone group while increased levels of tryptase were seen in placebo group after OLV (did not achieve significance). There were no side effects observed that could be attributed to methylprednisolone in this study.

CONCLUSIONS

Methylprednisolone at 2 mg·kg(-1) given as a single dose prior to OLV provides physiological stability to children undergoing OLV. In addition, methylprednisolone results in lower pro-inflammatory markers and higher anti-inflammatory markers in the children's plasma.

Reduced pulmonary blood flow in regions of injury 2 hours after acid aspiration in rats

BACKGROUND

Aspiration-induced lung injury can decrease gas exchange and increase mortality. Acute lung injury following acid aspiration is characterized by elevated pulmonary blood flow (PBF) in damaged lung areas in the early inflammation stage. Knowledge of PBF patterns after acid aspiration is important for targeting intravenous treatments. We examined PBF in an experimental model at a later stage (2 hours after injury).

METHODS

Anesthetized Wistar-Unilever rats (n = 5) underwent unilateral endobronchial instillation of hydrochloric acid. The PBF distribution was compared between injured and uninjured sides and with that of untreated control animals (n = 6). Changes in lung density after injury were measured using computed tomography (CT). Regional PBF distribution was determined quantitatively in vivo 2 hours after acid instillation by measuring the concentration of [(68)Ga]-radiolabeled microspheres using positron emission tomography.

RESULTS

CT scans revealed increased lung density in areas of acid aspiration. Lung injury was accompanied by impaired gas exchange. Acid aspiration decreased the arterial pressure of oxygen from 157 mmHg [139;165] to 74 mmHg [67;86] at 20 minutes and tended toward restoration to 109 mmHg [69;114] at 110 minutes (P < 0.001). The PBF ratio of the middle region of the injured versus uninjured lungs of the aspiration group (0.86 [0.7;0.9], median [25%;75%]) was significantly lower than the PBF ratio in the left versus right lung of the control group (1.02 [1.0;1.05]; P = 0.016).

CONCLUSIONS

The PBF pattern 2 hours after aspiration-induced lung injury showed a redistribution of PBF away from injured regions that was likely responsible for the partial recovery from hypoxemia over time. Treatments given intravenously 2 hours after acid-induced lung injury may not preferentially reach the injured lung regions, contrary to what occurs during the first hour of inflammation. Please see related article: http://dx.doi.org/10.1186/s12871-015-0014-z.

Real-time ventilation and perfusion distributions by electrical impedance tomography during one-lung ventilation with capnothorax

BACKGROUND

Carbon dioxide insufflation into the pleural cavity, capnothorax, with one-lung ventilation (OLV) may entail respiratory and hemodynamic impairments. We investigated the online physiological effects of OLV/capnothorax by electrical impedance tomography (EIT) in a porcine model mimicking the clinical setting.

METHODS

Five anesthetized, muscle-relaxed piglets were subjected to first right and then left capnothorax with an intra-pleural pressure of 19 cm H2 O. The contra-lateral lung was mechanically ventilated with a double-lumen tube at positive end-expiratory pressure 5 and subsequently 10 cm H2 O. Regional lung perfusion and ventilation were assessed by EIT. Hemodynamics, cerebral tissue oxygenation and lung gas exchange were also measured.

RESULTS

During right-sided capnothorax, mixed venous oxygen saturation (P = 0.018), as well as a tissue oxygenation index (P = 0.038) decreased. There was also an increase in central venous pressure (P = 0.006), and a decrease in mean arterial pressure (P = 0.045) and cardiac output (P = 0.017). During the left-sided capnothorax, the hemodynamic impairment was less than during the right side. EIT revealed that during the first period of OLV/capnothorax, no or very minor ventilation on the right side could be seen (3 ± 3% vs. 97 ± 3%, right vs. left, P = 0.007), perfusion decreased in the non-ventilated and increased in the ventilated lung (18 ± 2% vs. 82 ± 2%, right vs. left, P = 0.03). During the second OLV/capnothorax period, a similar distribution of perfusion was seen in the animals with successful separation (84 ± 4% vs. 16 ± 4%, right vs. left).

CONCLUSION

EIT detected in real-time dynamic changes in pulmonary ventilation and perfusion distributions. OLV to the left lung with right-sided capnothorax caused a decrease in cardiac output, arterial oxygenation and mixed venous saturation.

Sivelestat prevents cytoskeletal rearrangements in neutrophils resulting from lung re-expansion following one-lung ventilation during thoracic surgery

Patients undergoing lobectomy are at risk of developing acute lung injury resulting from one-lung ventilation (OLV) during surgery. We investigated the morphological and functional behavior of neutrophils in patients who underwent lobectomy and assessed the ability of sivelestat to inhibit neutrophil activity. This was a blinded randomized study. Sixteen patients who underwent lobectomy were given intravenous sivelestat (n = 8) or intravenous saline (n = 8). We studied the cytoskeletal rearrangements of circulating neutrophils by determining the localization of filamentous actin (F-actin). Pulmonary oxygenation was evaluated by measuring the partial pressure of arterial oxygen. We found that the number of circulating, F-actin-rimmed neutrophils increased during OLV and after lung re-expansion. Our results suggest that, in addition to the surgical procedure and OLV, re-expansion of the remaining lung after lobectomy increases the neutrophil activation levels. Furthermore, administration of sivelestat limited neutrophil activation and improved pulmonary oxygenation in our patients.

Pulmonary blood flow increases in damaged regions directly after acid aspiration in rats

BACKGROUND

After gastric aspiration events, patients are at risk of pulmonary dysfunction and the development of severe acute lung injury and acute respiratory distress syndrome, which may contribute to the development of an inflammatory reaction. The authors' aim in the current study was to investigate the role of the spatial distribution of pulmonary blood flow in the pathogenesis of pulmonary dysfunction during the early stages after acid aspiration.

METHODS

The authors analyzed the pulmonary distribution of radiolabeled microspheres in normal (n = 6) and injured (n = 12) anesthetized rat lungs using positron emission tomography, computed tomography, and histological examination.

RESULTS

Injured regions demonstrate increased pulmonary blood flow in association with reduced arterial pressure and the deterioration of arterial oxygenation. After acid aspiration, computed tomography scans revealed that lung density had increased in the injured regions and that these regions colocalized with areas of increased blood flow. The acid was instilled into the middle and basal regions of the lungs. The blood flow was significantly increased to these regions compared with the blood flow to uninjured lungs in the control animals (middle region: 1.23 [1.1; 1.4] (median [25%; 75%]) vs. 1.04 [1.0; 1.1] and basal region: 1.25 [1.2; 1.3] vs. 1.02 [1.0; 1.05], respectively). The increase in blood flow did not seem to be due to vascular leakage into these injured areas.

CONCLUSIONS

The data suggest that 10 min after acid aspiration, damaged areas are characterized by increased pulmonary blood flow. The results may impact further treatment strategies, such as drug targeting.

Respiratory function during anesthesia: effects on gas exchange

Anaesthesia causes a respiratory impairment, whether the patient is breathing spontaneously or is ventilated mechanically. This impairment impedes the matching of alveolar ventilation and perfusion and thus the oxygenation of arterial blood. A triggering factor is loss of muscle tone that causes a fall in the resting lung volume, functional residual capacity. This fall promotes airway closure and gas adsorption, leading eventually to alveolar collapse, that is, atelectasis. The higher the oxygen concentration, the faster will the gas be adsorbed and the aleveoli collapse. Preoxygenation is a major cause of atelectasis and continuing use of high oxygen concentration maintains or increases the lung collapse, that typically is 10% or more of the lung tissue. It can exceed 25% to 40%. Perfusion of the atelectasis causes shunt and cyclic airway closure causes regions with low ventilation/perfusion ratios, that add to impaired oxygenation. Ventilation with positive end-expiratory pressure reduces the atelectasis but oxygenation need not improve, because of shift of blood flow down the lung to any remaining atelectatic tissue. Inflation of the lung to an airway pressure of 40 cmH2O recruits almost all collapsed lung and the lung remains open if ventilation is with moderate oxygen concentration (< 40%) but recollapses within a few minutes if ventilation is with 100% oxygen. Severe obesity increases the lung collapse and obstructive lung disease and one-lung anesthesia increase the mismatch of ventilation and perfusion. CO2 pneumoperitoneum increases atelectasis formation but not shunt, likely explained by enhanced hypoxic pulmonary vasoconstriction by CO2. Atelectasis may persist in the postoperative period and contribute to pneumonia.

Immune response after systematic lymph node dissection in lung cancer surgery: changes of interleukin-6 level in serum, pleural lavage fluid, and lung supernatant in a dog model

BACKGROUND

Systematic nodal dissection (SND) is regarded as a core component of lung cancer surgery. However, there has been a concern on the increased morbidity associated with SND. This study was performed to investigate whether or not SND induces significant immune response.

METHODS

Sixteen dogs were divided into two groups; group 1 (n = 8) underwent thoracotomy only, and group 2 (n = 8) underwent SND after thoracotomy. We compared interleukin-6 (IL-6) levels in serum, pleural lavage fluid and lung supernatant at the time of thoracotomy (T0) and at 2 h(T1) after thoracotomy (group 1) or SND (group 2). Severity of inflammation and IL-6 expression in lung tissue were evaluated in a semi-quantitative manner.

RESULTS

The operative results were comparable. IL-6 was not detected in serum in either group. IL-6 in pleural lavage fluid marginally increased from 4.75 ± 3.74 pg/mL at T0 to 19.75 ± 8.67 pg/mL at T1 in group 1 (P = 0.112), and from 7.75 ± 5.35 pg/mL to 17.72 ± 8.58 pg/mL in group 2 (P = 0.068). IL-6 in lung supernatant increased from 0.36 ± 0.14 pg/mL/mg to 1.15 ± 0.17 pg/mL/mg in group 1 (P = 0.003), and from 0.25 ± 0.08 pg/mL/mg to 0.82 ± 0.17 pg/mL/mg in group 2 (P = 0.001). However, the degree of increase in IL-6 in pleural lavage fluid and lung supernatant were not different between two groups (P = 0.421 and P = 0.448). There was no difference in severity of inflammation and IL-6 expression between groups.

CONCLUSIONS

SND did not increase IL-6 in pleural lavage fluid and lung supernatant. This result suggests that SND could be routinely performed in lung cancer surgery without increasing the significant inflammatory response.

Acute lung injury in thoracic surgery

PURPOSE OF REVIEW

This review will analyze the risk factors of acute lung injury (ALI) in patients undergoing thoracic surgery. Evidence for the occurrence of lung injury following mechanical ventilation and one-lung ventilation (OLV) and the strategies to avoid it will also be discussed.

RECENT FINDINGS

Post-thoracotomy ALI has become one of the leading causes of operative death. The pathogenesis of ALI implicates a multiple-hit sequence of various triggering factors (e.g. preoperative conditions, surgery-induced inflammation, ventilator-induced injury, fluid overload, and transfusion). Conventional ventilation during OLV is performed with high tidal volumes equal to those being used in two-lung ventilation, high FiO(2), and without positive end-expiratory pressure. This practice was originally recommended to improve oxygenation and decrease shunt fraction during OLV. However, a number of recent studies using experimental models or human patients have shown low tidal volumes to be associated with a decrease in inflammatory mediators and a reduction in pulmonary postoperative complications. However, the application of such protective strategies could be harmful if not still properly used.

SUMMARY

The goal of ventilation is to minimize lung trauma by avoiding overdistension and repetitive alveolar collapse, while providing adequate oxygenation. Protective ventilation is not simply synonymous of low tidal volume ventilation, but it also involves positive end-expiratory pressure, lower FiO(2), recruitment maneuvers, and lower ventilatory pressures.

Lung re-expansion following one-lung ventilation induces neutrophil cytoskeletal rearrangements in rats

PURPOSE

To investigate the morphological and functional behavior of neutrophils during and after one-lung ventilation (OLV).

METHODS

We utilized an OLV rat model system and performed 3 hours of OLV followed by either re-expansion (RE) and 30 minutes of two-lung ventilation (TLV) (RE group), only two-lung ventilation (TLV group), or only OLV (OLV group). Cytoskeletal rearrangements of circulating neutrophils were assessed by determining the localization of filamentous actin (F-actin). In addition, the number of sequestered neutrophils in the lung capillary and the cytokine-induced neutrophil chemoattractant 1 (CINC-1) levels in the plasma were determined.

RESULTS

The F-actin rimmed neutrophils in the RE group increased after RE, but did not increase in the other groups. In the RE group, the sequestered neutrophils in the ventilated lung were significantly more numerous, and the plasma CINC-1 levels were significantly higher than in the other groups.

CONCLUSIONS

Lung RE following OLV induces cytoskeletal rearrangements in circulating neutrophils and would thereby promote their sequestration in the lung capillaries. The plasma CINC-1 elevation after RE can be involved in neutrophil recruitment.

Hyperoxia during one lung ventilation: inflammatory and oxidative responses

BACKGROUND

It is common practice during one lung ventilation (OLV) to use 100% oxygen, although this may cause hyperoxia- and oxidative stress-related lung injury. We hypothesized that lower oxygen (FiO(2) ) during OLV will result in less inflammatory and oxidative lung injury and improved lung function.

METHODS

Twenty pigs (8.88 ± 0.84 kg; 38 ± 4.6 days) were assigned to either the hyperoxia group (n = 10; FiO(2)  = 100%) or the normoxia group (n = 10; FiO(2)  < 50%). Both groups were subjected to 3 hr of OLV. Blood samples were tested for pro-inflammatory cytokines and lung tissue was tested for these cytokines and oxidative biomarkers.

RESULTS

There were no differences between groups for partial pressure of CO(2) , tidal volume, end-tidal CO(2) , plasma cytokines, or respiratory compliance. Total respiratory resistance was greater in the hyperoxia group (P = 0.02). There were higher levels of TNF-α, IL-1β, and IL-6 in the lung homogenates of the hyperoxia group than in the normoxia group (P ≤ 0.01, 0.001, and 0.001, respectively). Myeloperoxidase and protein carbonyls (PC) were higher (P = 0.03 and P = 0.01, respectively) and superoxide dismutase (SOD) was lower in the lung homogenates of the hyperoxia group (P ≤ 0.001).

CONCLUSION

Higher myeloperoxidase, PC, and cytokine levels, and lower SOD availability indicate a greater degree of injury in the lungs of the hyperoxia animals, possibly from using 100% oxygen. In this translational study using a pig model, FiO(2)  ≤ 50% during OLV reduced hyperoxic injury and improved function in the lungs.

Nuclear factor-kappa B mediates one-lung ventilation-induced acute lung injury in rabbits

INTRODUCTION

Several studies have revealed the adverse effect of one-lung ventilation (OLV) on pulmonary function. Nuclear factor-kappa B (NF-κB) is a principal transcription factor of proinflammatory genes. This study was designed to investigate the role of NF-κB in OLV-mediated lung injury.

METHODS

Male rabbits, weighing 2.2 ± 0.3 kg, were randomly divided into five groups: sham tracheostomized (Sham), OLV (V(T) = 10 ml/kg, FiO(2) = 1.0), two-lung ventilation (TLV, V(T) = 10 ml/kg, FiO(2) = 1.0), OLV preceded by the treatment with NF-κB inhibitor pyrrolidine dithiocarbamate (PDTC, 50 mg/kg, i.v.), and TLV with the PDTC pretreatment. Arterial blood gases, lung pathological changes, and production of proinflammatory cytokines (tumor necrosis factor-α and interleukin-8) were assessed. NF-κB activation was determined by electrophoretic mobility shift assay (EMSA) and western blotting of nuclear NF-κB p65.

RESULTS

The OLV significantly decreased the ratio of partial pressure of oxygen and fraction inspired oxygen (PaO(2)/FiO(2)) compared to the Sham group (p < .01). However, the TLV had no evident effect on the PaO(2)/FiO(2) ratio. The pretreatment with PDTC significantly reversed the OLV-induced reduction in the PaO(2)/FiO(2) ratio. The PDTC pretreatment also markedly attenuated the OLV-mediated lung injury and proinflammatory cytokine production. The OLV potentiated the NF-κB DNA binding activity assessed by EMSA and the NF-κB nuclear translocation. The OLV-mediated NF-κB activation was markedly inhibited by the PDTC pretreatment.

CONCLUSION

Our data collectively demonstrate that OLV can cause lung injury through the activation of NF-κB and the production of proinflammatory cytokines. Blocking NF-κB reduces lung inflammation and may be an effective strategy in the management of OLV-induced lung damage.

Regional lung perfusion estimated by electrical impedance tomography in a piglet model of lung collapse

The assessment of the regional match between alveolar ventilation and perfusion in critically ill patients requires simultaneous measurements of both parameters. Ideally, assessment of lung perfusion should be performed in real-time with an imaging technology that provides, through fast acquisition of sequential images, information about the regional dynamics or regional kinetics of an appropriate tracer. We present a novel electrical impedance tomography (EIT)-based method that quantitatively estimates regional lung perfusion based on first-pass kinetics of a bolus of hypertonic saline contrast. Pulmonary blood flow was measured in six piglets during control and unilateral or bilateral lung collapse conditions. The first-pass kinetics method showed good agreement with the estimates obtained by single-photon-emission computerized tomography (SPECT). The mean difference (SPECT minus EIT) between fractional blood flow to lung areas suffering atelectasis was -0.6%, with a SD of 2.9%. This method outperformed the estimates of lung perfusion based on impedance pulsatility. In conclusion, we describe a novel method based on EIT for estimating regional lung perfusion at the bedside. In both healthy and injured lung conditions, the distribution of pulmonary blood flow as assessed by EIT agreed well with the one obtained by SPECT. The method proposed in this study has the potential to contribute to a better understanding of the behavior of regional perfusion under different lung and therapeutic conditions.

Effects of Nondependent Lung Ventilation With Continuous Positive-Pressure Ventilation and High-Frequency Positive-Pressure Ventilation on Right-Ventricular Function During 1-Lung Ventilation

Background. The application of volume-controlled high frequency positive pressure ventilation (HFPPV) to the nondependent lung (NL) may have comparable effects to continuous positive airway pressure (CPAP) on the right ventricular (RV) function, oxygenation, and surgical conditions during one lung ventilation (OLV) for thoracotomy. Methods. After local ethics committee approval and informed consent, 75 patients scheduled for elective thoracotomy using OLV were randomly allocated to receive nondependent lung either CPAP 2 (CPAP2; n=25) or 5 (CPAP5; n=25) cm H2O pressure setting of the device or HFPPV using VT 3 mL-1, I: E ratio <0.3 and R.R 60/min (HFPPV; n=25), followed 15 min of OLV. Intraoperative changes in RV ejection fraction (REF), end-diastolic volume (RVEDVI) and stroke work (RVSWI), stroke volume (SVI), oxygen delivery (DO2), and uptake (VO2) indices and shunt fraction (Qs: Qt) were recorded without any surgical manipulation of the lung. Results. The application of NL-HFPPV resulted in improved REF by 33%, SVI and DO2 (P < 0.01) and reduced RVEDVI, RVSWI, PVRI, oxygen uptake, and shunt fraction by 24.8% (P < 0.01) than in the NL-CPAP groups. Conclusion. We concluded that the use of NL-HFPPV is a feasible option and offers improved RV function and oxygenation during OLV for open thoracotomy.

Management of mechanical ventilation during laparoscopic surgery

Laparoscopy is widely used in the surgical treatment of a number of diseases. Its advantages are generally believed to lie on its minimal invasiveness, better cosmetic outcome and shorter length of hospital stay based on surgical expertise and state-of-the-art equipment. Thousands of laparoscopic surgical procedures performed safely prove that mechanical ventilation during anaesthesia for laparoscopy is well tolerated by a vast majority of patients. However, the effects of pneumoperitoneum are particularly relevant to patients with underlying lung disease as well as to the increasing number of patients with higher-than-normal body mass index. Moreover, many surgical procedures are significantly longer in duration when performed with laparoscopic techniques. Taken together, these factors impose special care for the management of mechanical ventilation during laparoscopic surgery. The purpose of the review is to summarise the consequences of pneumoperitoneum on the standard monitoring of mechanical ventilation during anaesthesia and to discuss the rationale of using a protective ventilation strategy during laparoscopic surgery. The consequences of chest wall derangement occurring during pneumoperitoneum on airway pressure and central venous pressure, together with the role of end-tidal-CO2 monitoring are emphasised. Ventilatory and non-ventilatory strategies to protect the lung are discussed.

Acute lung injury and outcomes after thoracic surgery

PURPOSE OF REVIEW

The present review evaluates the evidence available in the literature tracking perioperative mortality and morbidity as well as the pathogenesis and management of acute lung injury (ALI) in patients undergoing thoracotomy.

RECENT FINDINGS

Over the last decade, despite increasing age and comorbid conditions, the operative mortality has remained unchanged for patients undergoing lung resection, whereas procedure-related complications have declined. Better clinical outcomes are achieved in high-volume hospitals and when procedures are performed by a thoracic surgeon. Postthoracotomy ALI has become the leading cause of operative death, its incidence has remained stable (2-5%) and earlier diagnosis can be made by assessing the extravascular lung water volume with the single-indicator dilution technique. The pathogenesis of ALI implicates a multiple-hit sequence of various triggering factors (e.g. oxidative stress and surgical-induced inflammation) in addition to injurious ventilatory settings and genetic predisposition.

SUMMARY

Knowledge of the perioperative risk factors of major complications and understanding of the mechanisms of postthoracotomy ALI enable anesthesiologists to implement 'protective' lung strategies including the use of low tidal volume (VT) with recruitment maneuvers, a goal-directed fluid approach and prophylactic treatment with inhaled beta2-adrenergic agonists.

Impact of intraoperative lung-protective interventions in patients undergoing lung cancer surgery

Introduction

In lung cancer surgery, large tidal volume and elevated inspiratory pressure are known risk factors of acute lung (ALI). Mechanical ventilation with low tidal volume has been shown to attenuate lung injuries in critically ill patients. In the current study, we assessed the impact of a protective lung ventilation (PLV) protocol in patients undergoing lung cancer resection.

Methods

We performed a secondary analysis of an observational cohort. Demographic, surgical, clinical and outcome data were prospectively collected over a 10-year period. The PLV protocol consisted of small tidal volume, limiting maximal pressure ventilation and adding end-expiratory positive pressure along with recruitment maneuvers. Multivariate analysis with logistic regression was performed and data were compared before and after implementation of the PLV protocol: from 1998 to 2003 (historical group, n = 533) and from 2003 to 2008 (protocol group, n = 558).

Results

Baseline patient characteristics were similar in the two cohorts, except for a higher cardiovascular risk profile in the intervention group. During one-lung ventilation, protocol-managed patients had lower tidal volume (5.3 ± 1.1 vs. 7.1 ± 1.2 ml/kg in historical controls, P = 0.013) and higher dynamic compliance (45 ± 8 vs. 32 ± 7 ml/cmH₂O, P = 0.011). After implementing PLV, there was a decreased incidence of acute lung injury (from 3.7% to 0.9%, P < 0.01) and atelectasis (from 8.8 to 5.0, P = 0.018), fewer admissions to the intensive care unit (from 9.4% vs. 2.5%, P < 0.001) and shorter hospital stay (from 14.5 ± 3.3 vs. 11.8 ± 4.1, P < 0.01). When adjusted for baseline characteristics, implementation of the open-lung protocol was associated with a reduced risk of acute lung injury (adjusted odds ratio of 0.34 with 95% confidence interval of 0.23 to 0.75; P = 0.002).

Conclusions

Implementing an intraoperative PLV protocol in patients undergoing lung cancer resection was associated with improved postoperative respiratory outcomes as evidence by significantly reduced incidences of acute lung injury and atelectasis along with reduced utilization of intensive care unit resources.