Complement activation contributes to ventilator-induced lung injury in rats.

The complement system contributes to ventilator induced lung injury (VILI). We hypothesized that pretreatment with the C1 esterase inhibitor (C1INH) Berinert® constrains complement activation consecutively inducing improvements in arterial oxygenation and histological pulmonary damage. At baseline, male Sprague-Dawley rats underwent mechanical ventilation in a conventional mode (PIP 13 cm H2O, PEEP 3 cm H2O). In the Control group, the ventilator setting was maintained (Control, n = 15). The other animals randomly received intravenous pretreatment with either 100 units/kg of the C1-INH Berinert® (VILI-C1INH group, n = 15) or 1 ml saline solution (VILI-C group, n = 15). VILI was induced by invasive ventilation (PIP 35 cm H2O, PEEP 0 cm H2O). After two hours of mechanical ventilation, the complement component C3a remained low in the Control group (258 ± 82 ng/ml) but increased in both VILI groups (VILI-C: 1017 ± 283 ng/ml; VILIC1INH: 817 ± 293 ng/ml; P < 0.05 for both VILI groups versus Control). VILI caused a profound deterioration of arterial oxygen tension (VILI-C: 193 ± 167 mmHg; VILI/C1-INH: 154 ± 115 mmHg), whereas arterial oxygen tension remained unaltered in the Control group (569 ± 26 mmHg; P < 0.05 versus both VILI groups). Histological investigation revealed prominent overdistension and interstitial edema in both VILI groups compared to the Control group. C3a plasma level in the VILI group were inversely correlated with arterial oxygen tension (R = -0.734; P < 0.001). We conclude that in our animal model of VILI the complement system was activated in parallel with the impairment in arterial oxygenation and that pretreatment with 100 units/kg Berinert® did neither prevent systemic complement activation nor lung injury.

Charge heterogeneity study of a Fc-fusion protein, abatacept, using two-dimensional gel electrophoresis.

Medicinal products obtained by recombinant DNA technology are complex molecules and demonstrate a high degree of molecular heterogeneity. Charge heterogeneity and isoform pattern of this class of medicines, are parameters important for their quality, safety, and efficacy. In this study we report the application of two-dimensional gel electrophoresis (2-D electrophoresis) for the quality assessment, identification, charge heterogeneity and isoform pattern study of recombinant protein, CTLA4-Ig (abatacept), which has been selected as an example of the drug class, known as Fc-fusion proteins. In order to achieve an efficient separation of this complex analyte,2-D electrophoresis was optimized employing different experimental conditions regarding the selection of an immobilized pH gradient (IPG), sample pretreatment, presentation and detection procedure. Experimental datadocumented that 2-D electrophoresis is a suitable method for the assessment of identity, purity, structural integrity, isoform pattern and to monitor charge heterogeneity and post-translational glycosylation of the Fc-fusion protein, abatacept.

Determination of acarbose by capillary zone electrophoresis.

Acarbose (Glucobay, Bayer AG) acts as a potent alpha-glucosidase-inhibitor, which delays the intestinal starch digestion resulting in a reduction of postprandial blood glucose and insulin levels. Acarbose is a pseudo-tetrasaccharide, with two D-glucose units linked via an alpha 1-->4 glycosidic bond to acarviosin, which is a N-glycoside composed of an unsaturated cyclitol and 4-amino-4,6-dideoxy-alpha-D-glucopyranose. Several methods for the determination of acarbose by capillary electrophoresis can be found in literature. They are based either on the derivatisation with 7-aminonaphthalene-1,3-disulfonic acid (ANDS) or on the detection of the unsaturated cyclitol at wavelengths below 200 nm. The aim of our work was the determination of acarbose making use of a previously developed method based on reductive amination with S-phenylethylamine. The aminoalditols generated in the reaction formed differently charged borate-complexes depending on the configuration of the sugar. After successful method optimisation we were able to separate two potential impurities of acarbose, D-maltose und D-glucose. For the quantitation of acarbose in Glucobay tablets an additional borate-buffer system was established, reducing the total time of analysis to less than 10 min.

Lactic acid oligomers (OLAs) as prodrug moieties.

In this paper we propose the use of lactic acid oligomers (OLAs) as prodrug moieties. Two synthetic approaches are presented, on the one hand a non selective oligomerisation of lactic acid and on the other hand a block synthesis to tetramers of lactic acid. Dimers of lactic acid were investigated with respect to their plasma stability and their adsorption to albumine. Ibuprofen was chosen as the first drug for OLAylation. The ester 19 of LA(1)-ibuprofen was evaluated with respect to the degradation to human plasma and the adsorption to albumine. All results indicate that lactic acid oligomers are promising prodrug moieties.

Blood-brain barrier in vitro models as tools in drug discovery: assessment of the transport ranking of antihistaminic drugs.

In the course of our validation program testing blood-brain barrier (BBB) in vitro models for their usability as tools in drug discovery it was evaluated whether an established Transwell model based on porcine cell line PBMEC/C1-2 was able to differentiate between the transport properties of first and second generation antihistaminic drugs. First generation antihistamines can permeate the BBB and act in the central nervous system (CNS), whereas entry to the CNS of second generation antihistamines is restricted by efflux pumps such as P-glycoprotein (P-gP) located in brain endothelial cells. P-gP functionality of PBMEC/C1-2 cells grown on Transwell filter inserts was proven by transport studies with P-gP substrate rhodamine 123 and P-gP blocker verapamil. Subsequent drug transport studies with the first generation antihistamines promethazine, diphenhydramine and pheniramine and the second generation antihistamines astemizole, ceterizine, fexofenadine and loratadine were accomplished in single substance as well as in group studies. Results were normalised to diazepam, an internal standard for the transcellular transport route. Moreover, effects after addition of P-gP inhibitor verapamil were investigated. First generation antihistamine pheniramine permeated as fastest followed by diphenhydramine, diazepam, promethazine and second generation antihistaminic drugs ceterizine, fexofenadine, astemizole and loratadine reflecting the BBB in vivo permeability ranking well. Verapamil increased the transport rates of all second generation antihistamines, which suggested involvement of P-gP during their permeation across the BBB model. The ranking after addition of verapamil was significantly changed, only fexofenadine and ceterizine penetrated slower than internal standard diazepam in the presence of verapamil. In summary, permeability data showed that the BBB model based on porcine cell line PBMEC/C1-2 was able to reflect the BBB in vivo situation for the transport of antihistaminc drugs and to distinguish between first and second generation antihistamines.

Evaluation of a short stability-indicating HPLC method for diclofenac sodium gels.

A fast and reproducible high performance liquid chromatography method has been developed for the determination of diclofenac sodium and its degradation products in commercial and in in-house produced ointments. The method employs a RP-LiChrospher select B (C8) column with a mobile phase containing methanol/water (63:37, v/v) and detection at 220 nm. This rapid and simple HPLC assay was used for QA/QC of large scale in-house produced diclofenac gel. The validation protocol was designed following international guidelines, e. g. ICH Q2(R1). Selectivity tests also included the separation of synthesis related by-products like 1-(2,6-dichlorphenyl)indoline-2-one (impurity A) and indoline-2-one (impurity E), and in addition selectivity with regard to several photodegradation products produced by both UV and simulated sunlight irradiation has been shown.

Evaluation of different preparation methods for a preservative free triamcinolone acetonide preparation for intravitreal administration: a validated stability indicating HPLC-method.

Intravitreally applied triamcinolone acetonide (TA) is used to treat a variety of macular diseases. Commercially available products of TA are mainly intended for intramuscular application and contain benzyl alcohol (BA) as a bacteriostatic preservative. Since this agent damages ocular tissues, different methods such as filtration techniques and centrifugation are usually used to eliminate BA from commercial products (40 mg/mL TA, 9.9 mg/mL BA). In this study, we evaluated these methods in regard to their ability to eliminate benzyl alcohol and to guarantee standard doses of triamcinolone acetonide. A new formulation without BA (TA 40 mg/mL) was developped according to the following criteria: autoclavability, stability, and suitability for intravitreal use. For QA/QC evaluation a new rapid and simple HPLC procedure (C18 RP column, mobile phase consisting of methanol-water, 48:52, v/v) to quantify the respective compounds was developed and validated according to ICH guidelines. The HPLC method was proven to be selective, linear, precise and accurate. Analysis of preparations based on commercial products undergoing different filtration techniques showed variable results: TA concentrations of 22-80% of the declared amount were found, and BA content was not reduced to safe levels (up to 39% of initial content remained). Centrifugation methods decreased the concentration of the preservative adequately, however agglomerated TA crystals were observed, leading to irreproducible and deviating particle sizes that are potentially harmful with ocular use. The newly developed preservative free formulation (TA 40 mg/mL) delivered uniform doses of TA, revealed no drug loss during forced light exposure and was proven to be stable, sterile and bacterial endotoxin free after autoclaving and after storage for three months,. The new formulation may offer an alternative for the in-house production of intravitreally applicable TA preparations in hospital pharmacies and should enhance medication safety.

Additives in intravenous anesthesia modulate pulmonary inflammation in a model of LPS-induced respiratory distress.

BACKGROUND: It has been suggested that propofol with ethylenediaminetetraacetic acid (EDTA) can modulate the systemic inflammatory response. Prolonged higher levels of pulmonary inflammation are associated with poor outcome of patients with acute lung injury. In the present study, we hypothesized that pulmonary inflammation could be modulated by propofol with EDTA compared with propofol with sulfite. METHODS: Respiratory distress was induced in rats (n=25) by intratracheal nebulization of lipopolysaccharide (LPS). After 24 h, animals were randomized to either propofol with EDTA (Propofol(EDTA)), propofol with sulfite (Propofol(sulfite)) or ketamine/midazolam (Ket/Mid); control animals received saline (n=30). Animals were ventilated for 4 h and blood gases were measured hourly. Bronchoalveolar lavage (BAL) was performed for cytokine analysis of: tumor necrosis factor (TNF), interleukin (IL)-6 and macrophage inflammatory protein (MIP)-2. RESULTS: LPS led to increased pulmonary inflammation in all groups compared with the control groups. Gas exchange deteriorated over time only in the LPS Propofol(sulfite) group and was significantly lower than the Ket/Mid group. Only IL-6 was significantly higher in the LPS Propofol(sulfite) group compared with both the Ket/Mid group and the Propofol(EDTA) group. CONCLUSION: Pulmonary IL-6 can be modulated by additives in systemic anesthesia. IMPLICATION STATEMENT: This study demonstrates that pulmonary inflammation caused by direct lung injury can be modulated by intravenous anesthesia used in critically ill patients.

ACE mediates ventilator-induced lung injury in rats via angiotensin II but not bradykinin.

Ventilator-induced lung injury is characterised by inflammation and apoptosis, but the underlying mechanisms are poorly understood. The present study proposed a role for angiotensin-converting enzyme (ACE) via angiotensin II (Ang II) and/or bradykinin in acute lung injury. The authors assessed whether ACE and, if so, Ang II and/or bradykinin are implicated in inflammation and apoptosis by mechanical ventilation. Rats were ventilated for 4 h with low- or high-pressure amplitudes in the absence or presence of the ACE inhibitor captopril. Nonventilated animals served as controls. ACE activity, Ang II and bradykinin levels, as well as inflammatory parameters (total protein, macrophage inflammatory protein-2 and interleukin-6) were determined. Apoptosis was assessed by the number of activated caspase-3 and TUNEL (terminal deoxynucleotidyltransferase-mediated deoxyuridine triphosphate nick-end labelling)-positive cells. Bronchoalveolar lavage fluid ACE activity, levels of total protein, inflammatory parameters and the number of apoptotic cells were increased in the high-pressure amplitude group as compared with the control group. Blocking ACE activity by captopril attenuated inflammation and apoptosis in the latter group. Similar results were obtained by blocking Ang II receptors, but blocking bradykinin receptors did not attenuate the anti-inflammatory and anti-apoptotic effects of captopril. The current authors conclude that inflammation and apoptosis in ventilator-induced lung injury is, at least in part, due to angiotensin-converting enzyme-mediated angiotensin II production.

Determination of (R,R)-glycopyrronium bromide and its related impurities by ion-pair HPLC.

A simple, rapid and specific ion-pair HPLC method for the determination of (R,R)-glycopyrronium bromide and its related impurities is presented, and parameters affecting the chromatographic properties of these compounds are discussed. Optimal analyte separation was achieved on base deactivated Nucleosil at 40 degrees C, using phosphate buffer pH 2.30 with sodium-1-decanesulfonate (0.01 M)/methanol (35/65; v/v) as eluent for isocratic elution at a flow rate 1 ml x min(-1). The analytical assay was validated according to international guidelines. The methodis suitable for in-process control and as stability indicating assay.

Effect of SP-B peptides on the uptake of liposomes by alveolar cells.

BACKGROUND: Exogenous surfactant has been accepted worldwide as a therapy of RDS in premature and term infants. Exogenous surfactant is usually derived from lung extracts containing phospholipids and the surfactant proteins SP-B and SP-C. Synthetic peptides of SP-B and SP-C are being tested with the aim to develop a completely synthetic surfactant preparation. Nevertheless, the effects of these peptides on the endogenous surfactant metabolism remain unknown. OBJECTIVES: The effect of synthetic SP-B peptides on uptake of surfactant-like liposomes was investigated in alveolar cells. Native SP-B and seven SP-B peptides were included: monomeric and dimeric SP-B(1-25) (Cys-11 --> Ala-11), SP-B(63-78)and Ala-SP-B(63-78) (Cys-71 --> Ala-71;Cys-77 --> Ala-77)and their serine mutants. METHODS: In vitro, alveolar macrophages (AM) and alveolar type II cells (ATII) were incubated with liposomes containing SP-B or one of its peptides. In vivo, rats received intratracheally various SP-B peptides (SP-B/lipid ratio 1:33 w/w) incorporated in fluorescent surfactant-like liposomes. One hour after instillation, AM and ATII were isolated and cell-associated fluorescence was determined using flow cytometry. Confocal laser microscopy was performed to ensure internalization of the liposomes. RESULTS: In vitro uptake by AM or ATII was not influenced by the SP-B peptides. In vivo, SP-B(1-25) and Ser-SP-B(1-25) increased the uptake by AM whereas dSP-B(1-25) decreased the uptake. Neither SP-B(1-25) nor dSP-B(1-25 )affected total uptake by ATII. The overall uptake by SP-B(63-78) variants was not changed. CONCLUSIONS: Surface-active synthetic SP-B peptides do not interfere with the normal uptake of surfactant by ATII.

Surfactant as a carrier: influence of immunosuppressive agents on surfactant activity.

INTRODUCTION: It has been proposed that exogenous pulmonary surfactant can be used as a drug delivery system for immunosuppressive agents to the alveolar compartment of the lung while reducing the risk of systemic toxicity. Before using this combination, however, alterations in activity of both substances should be examined. Therefore, this study investigated whether the activity of a natural derived surfactant preparation is changed after it is mixed with cyclosporine A (CsA) or rapamycin (RPM). METHODS: A surfactant suspension was mixed with CsA or RPM and minimal surface tension of these mixtures was measured in vitro. Surfactant activity was evaluated in vivo by its capacity to restore gas exchange in an established model of surfactant deficiency in rats. CsA-surfactant, RPM-surfactant or surfactant alone was instilled intratracheally and blood gases were measured under standardized ventilatory conditions. RESULTS: Minimal surface tension of surfactant-CsA was comparable with that of surfactant alone, whereas minimal surface tension of the surfactant-RPM mixture was increased. In vivo partial arterial oxygen pressure levels increased immediately to prelavage values after instillation of CsA-surfactant, RPM-surfactant and surfactant only and were comparable during the entire study period. CONCLUSION: The activity of a naturally derived surfactant was affected when mixed with RPM but not when mixed with CsA at the used concentrations.

Liver-type fatty acid binding protein in serum and broncho-alveolar lavage in a model of acute respiratory failure because of surfactant depletion--a possible marker for lung damage?

INTRODUCTION: Liver-type fatty acid binding proteins (L-FABP) have been shown to be present in alveolar macrophages and type II pneumocytes of the lung. This study determined levels of L-FABP in serum and broncho-alveolar lavage (BAL) during experimental acute respiratory failure (ARF) to evaluate whether this molecule can serve as a marker for lung damage. METHODS: Male Sprague-Dawley rats (n = 24) were ventilated and either lung lavaged or lavaged and treated with surfactant, and compared to ventilated, non-lavaged controls. Blood samples were drawn every hour for 4 h to measure L-FABP concentrations in serum. At the end of the experiment a BAL was performed to determine L-FABP levels in BAL fluid. L-FABP was measured with a sandwich enzyme-linked immunosorbent assays. RESULTS: Serum L-FABP concentrations rose significantly during the first 2 h of ventilation in all groups compared with baseline values. After 2 h L-FABP levels were significantly higher in lavaged animals compared with the ventilated controls and to animals treated with surfactant. After 4 h of ventilation, L-FABP in BAL was significantly higher in lavaged, non-surfactant treated animals compared with the ventilated controls. CONCLUSION: In the early phase of experimental ARF serum L-FABP levels correlate well with the degree of lung injury.

Mechanical ventilation affects alveolar fibrinolysis in LPS-induced lung injury.

The aim of the present study was to determine the effects of mechanical ventilation on alveolar fibrin turnover in lipopolysaccharide (LPS)-induced lung injury. In a randomised controlled trial, Sprague-Dawley rats (n = 61) were allocated to three ventilation groups after intratracheal LPS (Salmonella enteritidis) instillations. Group I animals were subjected to 16 cmH(2)O positive inspiratory pressure (PIP) and 5 cmH(2)O positive end-expiratory pressure (PEEP); group II animals to 26 cmH(2)O PIP and 5 cmH(2)O PEEP; and group III animals to 35 cmH(2)O PIP and 5 cmH(2)O PEEP. Control rats (not mechanically ventilated) received LPS. Healthy rats served as a reference group. Levels of thrombin-antithrombin complex (TATc), D-dimer, plasminogen activator inhibitor (PAI) activity and PAI-1 antigen in bronchoalveolar lavage fluid were measured. LPS-induced lung injury increased TATc, D-dimer and PAI activity and PAI-1 antigen levels versus healthy animals. High pressure-amplitude ventilation increased TATc concentrations. D-dimer concentrations were not significantly raised. Instead, PAI activity increased with the amplitude of the pressure, from 0.7 U.mL(-1) in group I to 3.4 U.mL(-1) in group II and 5.0 U.mL(-1) in group III. There was no change in PAI-1 antigen levels. In conclusion, mechanical ventilation creates an alveolar/pulmonary anti-fibrinolytic milieu in endotoxin-induced lung injury which, at least in part, might be due to an increase in plasminogen activator inhibitor activity.

Respiratory inductive plethysmography accuracy at varying PEEP levels and degrees of acute lung injury.

BACKGROUND AND OBJECTIVE: This study was performed to assess the accuracy of respiratory inductive plethysmographic (RIP) estimated lung volume changes at varying positive end-expiratory pressures (PEEP) during different degrees of acute respiratory failure. METHODS: Measurements of inspiratory tidal volume were validated in eight piglets during constant volume ventilation at incremental and decremental PEEP levels and with increasing severity of pulmonary injury. RIP accuracy was assessed with calibration from the healthy state, from the disease state as the measurement error was assessed, and at various PEEP levels. RESULTS: Best results (bias 3%, precision 7%) were obtained in healthy animals. RIP accuracy decreased with progressing degrees of acute respiratory failure and was PEEP dependent, unless RIP was calibrated again. When calibration was performed in the disease state as the measurement error was assessed, bias was reduced but precision did not improve (bias -2%, precision 9%). CONCLUSIONS: RIP accuracy is within the accuracy range found in monitoring devices currently in clinical use. Most reliable results with RIP are obtained when measurements are preceded by calibration in pulmonary conditions that are comparable to the measurement period. When RIP calibration is not possible, fixed weighting of the RIP signals with species and subject size adequate factors is an alternative. Measurement errors should be taken into account with interpretation of small volume changes.

Small-dose perfluorocarbon reduces the recruitment pressure needed to open surfactant-deficient atelectatic lungs.

BACKGROUND: This study was undertaken to investigate the effect of a small dose of perfluorocarbon on the recruitment pressure needed to open atelectatic lung areas. METHODS: In 12 Yorkshire pigs (body weight, 9 kg), lung injury was induced by whole lung lavage. After 1 h of conventional ventilation, an open lung maneuver was performed to obtain PaO2 values equal to the pre-lavage PaO2 values (+/-10%). After 1 h of ventilation at the lowest possible airway pressure that stabilized the recruited lung volume, the animals were disconnected from the ventilator to allow the lung to collapse. Six animals received a 5 ml/kg intratracheal dose of perfluorocarbon and a second open lung maneuver was performed. Six animals served as controls and received no perfluorocarbon but also underwent a second open lung maneuver. RESULTS: In both groups, an open lung maneuver resulted in a significant increase in oxygenation. The peak pressures needed to open the lung after 1 h of mechanical ventilation in the perfluorocarbon and control groups were 43.8 +/- 8.4 cmH2O and 46.6 +/- 4 cmH2O, respectively. The addition of perfluorocarbon significantly reduced the opening pressure to 34.5 +/- 6.3 cmH2O (P < 0.01), whereas the opening pressure in the control group, 45.0 +/- 0.2 cmH2O, did not change. CONCLUSION: The instillation of a small amount of perfluorocarbon significantly reduces the opening pressures needed to recruit atelectatic lung areas.

Lung protective ventilation in ARDS: the open lung maneuver.

This review addresses the current state of lung protective strategies and their physiological rationale. Lung protective ventilation can reduce mortality in adult respiratory distress syndrome (ARDS) patients. We review the latest knowledge on the progression of lung injury by mechanical ventilation. Results from clinical studies on mechanical ventilation are compared with results obtained in experimental studies. Furthermore, we discuss possible future improvements to mechanical ventilation; especially the open lung maneuver. The rationale behind the open lung maneuver and steps to accomplish an open lung are described, as well as data from animal and human studies. Finally, guidelines for future strategies and/or investigations are presented.

Effect of ventilation strategy and surfactant on inflammation in experimental pneumonia.

This study explored, the inflammatory response during experimental pneumonia in surfactant-depleted animals as a function of ventilation strategies and surfactant treatment. Following intratracheal instillation of Group B streptococci (GBS), surfactant-depleted piglets were treated with conventional (positive-end expiratory pressure (PEEP) of 5 cmH2O, tidal volume 7 mL x kg(-1)) or open lung ventilation. During the latter, collapsed alveoli were recruited by applying high peak inspiratory pressures for a short period of time, combined with high levels of PEEP and the smallest possible pressure amplitude. Subgroups in both ventilation arms also received exogenous surfactant. Conventionally ventilated healthy animals receiving GBS and surfactant-depleted animals receiving saline served as controls. In contrast with both control groups, surfactant-depleted animals challenged with GBS and conventional ventilation showed high levels of interleukin (IL)-8, tumour necrosis factor (TNF)-alpha and myeloperoxidase in bronchoalveolar lavage fluid after 5 h of ventilation. Open lung ventilation attenuated this inflammatory response, but exogenous surfactant did not. Systemic dissemination of the inflammatory response was minimal, as indicated by low serum levels of IL-8 and TNF-alpha. In conclusion, the current study indicates that the ventilation strategy, but not exogenous surfactant, is an important modulator of the inflammation during Group B streptococci pneumonia in mechanically ventilated surfactant-depleted animals.

Influence of phosphatidylglycerol on the uptake of liposomes by alveolar cells and on lung function.

The effect of phosphatidylglycerol on the uptake of surfactant-like liposomes by alveolar type II cells and alveolar macrophages as well as the effect on endogenous surfactant function was studied in vivo. Healthy ventilated rats were intratracheally instilled with fluorescent labeled liposomes with different concentrations of phosphatidylglycerol. Lung function was determined by monitoring arterial oxygenation and, at the end of the experiment, by recording static pressure-volume curves. In addition, alveolar cells were isolated, and cell-associated fluorescence was determined using flow cytometry. The results show that, in the presence of cofactors (Ca(2+), Mg(2+)), phosphatidylglycerol stimulates the uptake by alveolar macrophages but hardly affects the uptake by alveolar type II cells. High concentrations of phosphatidylglycerol reduce the number of alveolar macrophages in the alveolar space and deteriorate lung function. On the other hand, the presence of cofactors protects the lung against the negative effects of phosphatidylglycerol on endogenous surfactant and alveolar macrophages. This study indicates that the phosphatidylglycerol concentration may play a fundamental role in the surfactant function and metabolism depending on the presence of so-called cofactors like calcium and magnesium; further study is needed to clarify the mechanisms involved.

Brain glucose and lactate levels during ventilator-induced hypo- and hypercapnia.

OBJECTIVE: Levels of glucose and lactate were measured in the brain by means of microdialysis in order to evaluate the effects of ventilator-induced hypocapnia and hypercapnia on brain metabolism in healthy non-brain-traumatized animals. DESIGN AND SETTING: Prospective animal study in a university laboratory. SUBJECTS: Eight adult Landrace/Yorkshire pigs. INTERVENTIONS: The microdialysis probe was inserted in the brain along with a multiparameter sensor and intracranial pressure (ICP) probe. The animals were ventilated in a pressure-controlled mode according to the open lung concept with an inspired oxygen fraction of 0.4/1.0. Starting at normoventilation (PaCO(2) +/-40 mmHg) two steps of both hypercapnia (PCO(2) +/- 70 and 100 mmHg) and hypocapnia (PaCO(2) +/- 20 and 30 mmHg) were performed. Under these conditions, brain glucose and lactate levels as well as brain oxygen (PbrO(2)), brain carbon dioxide (PbrCO(2)), brain pH (brpH), brain temperature and ICP were measured. RESULTS: At hypercapnia (PaCO(2) = 102.7 mmHg) there were no significant changes in brain glucose and lactate but there was a significant increase in PbrCO(2), PbrO(2) and ICP. In contrast, at hypocapnia (PCO(2) = 19.8 mmHg) there was a significant increase in brain lactate and a significant decrease in both brain glucose and PbrCO(2). CONCLUSIONS: Hypocapnia decreases brain glucose and increases brain lactate concentration, indicating anaerobic metabolism, whereas hypercapnia has no influence on levels of brain glucose and brain lactate.