Bench-to-bedside review: carbon dioxide

Partial pressure of arterial carbon dioxide and survival to hospital discharge among patients requiring acute mechanical ventilation: A cohort study

PURPOSE

To describe the prevalence of hypocapnia and hypercapnia during the earliest period of mechanical ventilation, and determine the association between PaCO2 and mortality.

MATERIALS AND METHODS

A cohort study using an emergency department registry of mechanically ventilated patients. PaCO2 was categorized: hypocapnia (<35mmHg), normocapnia (35-45mmHg), and hypercapnia (>45mmHg). The primary outcome was survival to hospital discharge.

RESULTS

A total of 1,491 patients were included. Hypocapnia occurred in 375 (25%) patients and hypercapnia in 569 (38%). Hypercapnia (85%) had higher survival rate compared to normocapnia (74%) and hypocapnia (66%), P<0.001. PaCO2 was an independent predictor of survival to hospital discharge [hypocapnia (aOR 0.65 (95% confidence interval [CI] 0.48-0.89), normocapnia (reference category), hypercapnia (aOR 1.83 (95% CI 1.32-2.54)]. Over ascending ranges of PaCO2, there was a linear trend of increasing survival up to a PaCO2 range of 66-75mmHg, which had the strongest survival association, aOR 3.18 (95% CI 1.35-7.50).

CONCLUSIONS

Hypocapnia and hypercapnia occurred frequently after initiation of mechanical ventilation. Higher PaCO2 levels were associated with increased survival. These data provide rationale for a trial examining the optimal PaCO2 in the critically ill.

Effects of Hypercapnia and Hypercapnic Acidosis on Hospital Mortality in Mechanically Ventilated Patients

OBJECTIVES

Lung-protective ventilation is used to prevent further lung injury in patients on invasive mechanical ventilation. However, lung-protective ventilation can cause hypercapnia and hypercapnic acidosis. There are no large clinical studies evaluating the effects of hypercapnia and hypercapnic acidosis in patients requiring mechanical ventilation.

DESIGN

Multicenter, binational, retrospective study aimed to assess the impact of compensated hypercapnia and hypercapnic acidosis in patients receiving mechanical ventilation.

SETTINGS

Data were extracted from the Australian and New Zealand Intensive Care Society Centre for Outcome and Resource Evaluation Adult Patient Database over a 14-year period where 171 ICUs contributed deidentified data.

PATIENTS

Patients were classified into three groups based on a combination of pH and carbon dioxide levels (normocapnia and normal pH, compensated hypercapnia [normal pH with elevated carbon dioxide], and hypercapnic acidosis) during the first 24 hours of ICU stay. Logistic regression analysis was used to identify the independent association of hypercapnia and hypercapnic acidosis with hospital mortality.

INTERVENTIONS

Nil.

MEASUREMENTS AND MAIN RESULTS

A total of 252,812 patients (normocapnia and normal pH, 110,104; compensated hypercapnia, 20,463; and hypercapnic acidosis, 122,245) were included in analysis. Patients with compensated hypercapnia and hypercapnic acidosis had higher Acute Physiology and Chronic Health Evaluation III scores (49.2 vs 53.2 vs 68.6; p < 0.01). The mortality was higher in hypercapnic acidosis patients when compared with other groups, with the lowest mortality in patients with normocapnia and normal pH. After adjusting for severity of illness, the adjusted odds ratio for hospital mortality was higher in hypercapnic acidosis patients (odds ratio, 1.74; 95% CI, 1.62-1.88) and compensated hypercapnia (odds ratio, 1.18; 95% CI, 1.10-1.26) when compared with patients with normocapnia and normal pH (p < 0.001). In patients with hypercapnic acidosis, the mortality increased with increasing PCO2 until 65 mm Hg after which the mortality plateaued.

CONCLUSIONS

Hypercapnic acidosis during the first 24 hours of intensive care admission is more strongly associated with increased hospital mortality than compensated hypercapnia or normocapnia.

Inflammatory Mediators in Tracheal Aspirates of Preterm Infants Participating in a Randomized Trial of Permissive Hypercapnia

BACKGROUND

Ventilator-induced lung injury is considered to be a main factor in the pathogenesis of bronchopulmonary dysplasia (BPD). Optimizing ventilator strategies may reduce respiratory morbidities in preterm infants. Permissive hypercapnia has been suggested to attenuate lung injury. We aimed to determine if a higher PCO₂ target range results in less lung injury compared to the control target range and possibly reduces pro-inflammatory cytokines and acid sphingomyelinase (ASM) in tracheal aspirates (TA), which has not been addressed before.

METHODS

During a multicenter trial of permissive hypercapnia in extremely low birthweight infants (PHELBI), preterm infants (birthweight 400-1,000 g, gestational age 23 0/7-28 6/7 weeks) requiring mechanical ventilation within 24 h of birth were randomly assigned to a high PCO₂ target or a control group. The high target group aimed at PCO₂ values of 55-65, 60-70, and 65-75 mmHg and the control group at PCO₂ values of 40-50, 45-55 and 50-60 mmHg on postnatal days 1-3, 4-6, and 7-14, respectively. TA was analyzed for pro-inflammatory cytokines from postnatal day 2-21. BPD was determined at a postmenstrual age of 36 weeks ± 2 days.

MAIN FINDINGS

Levels of inflammatory cytokines and ASM were similar in both groups: interleukin (IL)-6 (p = 0.14), IL-8 (p = 0.43), IL-10 (p = 0.24), IL-1β (p = 0.11), macrophage inflammatory protein 1α (p = 0.44), albumin (p = 0.41), neuropeptide Y (p = 0.52), leukotriene B₄ (p = 0.11), transforming growth factor-β₁ (p = 0.68), nitrite (p = 0.15), and ASM (p = 0.94). Furthermore, most inflammatory mediators were strongly affected by the age of the infants and increased from postnatal day 2 to 21. BPD or death was observed in 14 out of 62 infants, who were distributed evenly between both groups.

CONCLUSION

The results suggest that high PCO₂ target levels did not result in lower pulmonary inflammatory activity and thus reflect clinical results. This indicates that high PCO₂ target ranges are not effective in reducing ventilator-induced lung injury in preterm infants, as compared to control targets.

TRIAL REGISTRATION

ISRCTN56143743.

Carbon dioxide: Global warning for nephrologists

The large prevalence of respiratory acid-base disorders overlapping metabolic acidosis in hemodialysis population should prompt nephrologists to deal with the partial pressure of carbon dioxide (pCO2) complying with the reduced bicarbonate concentration. What the most suitable formula to compute pCO2 is reviewed. Then, the neglected issue of CO2 content in the dialysis fluid is under the spotlight. In fact, a considerable amount of CO2 comes to patients' bloodstream every hemodialysis treatment and "acidosis by dialysate" may occur if lungs do not properly clear away this burden of CO2. Moreover, vascular access recirculation may be easy diagnosed by detecting CO2 in the arterial line of extracorporeal circuit if CO2-enriched blood from the filter reenters arterial needle.

Yogic breathing when compared to attention control reduces the levels of pro-inflammatory biomarkers in saliva: a pilot randomized controlled trial

Background

Self-report measures indicate that Yoga practices are perceived to reduce stress; however, molecular mechanisms through which YB affects stress are just beginning to be understood. While invasive sampling such as blood has been widely used to measure biological indicators such as pro-inflammatory biomarkers, the use of saliva to measure changes in various biomolecules has been increasingly recognized. As Yoga practice stimulates salivary secretion, and saliva is considered a source of biomarkers, changes in salivary cytokines before and after Yogic breathing exercise as specified in an ancient Tamil script, Thirumanthiram, were examined using a Cytokine Multiplex to compare to Attention Control (AC) group.

Methods

Twenty healthy volunteers were randomized into two groups stratified by gender (N = 10 per YB and AC groups); The YB group performed two YB exercises, each for ten minutes, for a total of twenty minutes in a single session as directed by a trained Yoga instructor. The AC group read a text of their choice for 20 min. Saliva was collected immediately after YB training at 0, 5, 10, 15 and 20 min and analyzed by Multiplex enzyme linked immunosorbent assay (ELISA).

Results

The levels of interleukin (IL)-1β, IL-8, and monocyte chemotactic protein −1 (MCP-1) were significantly reduced in YB group when compared to AC group. The level of reduction of IL-8 was significant at all time points tested, whereas IL-1β showed reduction at 15 and 20 min time points (p < 0.05), and MCP-1 level was marginally different at 5–20 min. There were no significant differences between YB and AC groups in the salivary levels of IL-1RA, IL-6, IL-10, IL-17, IP-10, MIP-1b, and TNF-α.

Conclusions

These data are the first to demonstrate the feasibility of detecting salivary cytokines using multiplex assay in response to a Yoga practice. This study was registered in Clinical Trials.gov # NCT02108769.

Electronic supplementary material

The online version of this article (doi:10.1186/s12906-016-1286-7) contains supplementary material, which is available to authorized users.

Community-acquired pneumonia and survival of critically ill acute exacerbation of COPD patients in respiratory intensive care units

PURPOSE

The aim of this study was to appraise the effect of community-acquired pneumonia (CAP) on inhospital mortality in critically ill acute exacerbation of COPD (AECOPD) patients admitted to a respiratory intensive care unit.

PATIENTS AND METHODS

A retrospective observational study was performed. Consecutive critically ill AECOPD patients receiving treatment in a respiratory intensive care unit were reviewed from September 1, 2012, to August 31, 2015. Categorical variables were analyzed using chi-square tests, and continuous variables were analyzed by Mann-Whitney U-test. Kaplan-Meier analysis was used to assess the association of CAP with survival of critically ill AECOPD patients for univariate analysis. Cox's proportional hazards regression model was performed to identify risk factors for multivariate analysis.

RESULTS

A total of 80 consecutive eligible individuals were reviewed. These included 38 patients with CAP and 42 patients without CAP. Patients with CAP had a higher inhospital rate of mortality than patients without CAP (42% vs 33.3%, P<0.05). Kaplan-Meier survival analysis showed that patients with CAP had a worse survival rate than patients without CAP (P<0.05). Clinical characteristics, including Acute Physiology and Chronic Health Evaluation II (APACHE II) score, C-reactive protein, and CAP, were found to be closely associated with survival of AECOPD individuals. Further multivariate Cox regression analysis confirmed that CAP and APACHE II were independent risk factors for inhospital mortality in critically ill AECOPD patients (CAP: hazard ratio, 5.29; 95% CI, 1.50-18.47, P<0.01 and APACHE II: hazard ratio, 1.20; 95% CI, 1.06-1.37, P<0.01).

CONCLUSION

CAP may be an independent risk factor for higher inhospital mortality in critically ill AECOPD patients.

Influence of α-stat and pH-stat blood gas management strategies on cerebral blood flow and oxygenation in patients treated with therapeutic hypothermia after out-of-hospital cardiac arrest: a crossover study

OBJECTIVES

In patients treated with therapeutic hypothermia after out-of-hospital cardiac arrest, two blood gas management strategies are used regarding the PaCO2 target: α-stat or pH-stat. We aimed to compare the effects of these strategies on cerebral blood flow and oxygenation.

DESIGN

Prospective observational single-center crossover study.

SETTING

ICU of University hospital.

PATIENTS

Twenty-one therapeutic hypothermia-treated patients after out-of-hospital cardiac arrest more than 18 years old without history of cerebrovascular disease were included.

INTERVENTIONS

Cerebral perfusion and oxygenation variables were compared in α-stat (PaCO2 measured at 37 °C) versus pH-stat (PaCO2 measured at 32-34 °C), both strategies maintaining physiological PaCO2 values: 4.8-5.6 kPa (36-42 torr).

MEASUREMENTS AND MAIN RESULTS

Bilateral transcranial middle cerebral artery flow velocities using Doppler and jugular vein oxygen saturation were measured in both strategies 18 hours (14-23 hr) after the return of spontaneous circulation. Pulsatility and resistance indexes and cerebral oxygen extraction were calculated. Data are expressed as median (interquartile range 25-75) in α-stat versus pH-stat. No differences were found in temperature, arterial blood pressure, and oxygenation between α-stat and pH-stat. Significant differences were found in minute ventilation (p = 0.006), temperature-corrected PaCO2 (4.4 kPa [4.1-4.6 kPa] vs. 5.1 kPa [5.0-5.3 kPa], p = 0.0001), and temperature-uncorrected PaCO2 (p = 0.0001). No differences were found in cerebral blood velocities and pulsatility and resistance indexes in the overall population. Significant differences were found in jugular vein oxygen saturation (83.2% [79.2-87.6%] vs. 86.7% [83.2-88.2%], p = 0.009) and cerebral oxygen extraction (15% [11-20%] vs. 12% [10-16%], p = 0.01), respectively. In survivors, diastolic blood velocities were 25 cm/s (19-30 cm/s) versus 29 cm/s (23-35 cm/s) (p = 0.004), pulsatility index was 1.10 (0.97-1.18) versus 0.94 (0.89-1.05) (p = 0.027), jugular vein oxygen saturation was 79.2 (71.1-81.8) versus 83.3% (76.6-87.8) (p = 0.033), respectively. However, similar results were not found in nonsurvivors.

CONCLUSIONS

In therapeutic hypothermia-treated patients after out-of-hospital cardiac arrest at physiological PaCO2, α-stat strategy increases jugular vein blood desaturation and cerebral oxygen extraction compared with pH-stat strategy and decreases cerebral blood flow velocities in survivors.

Targeted therapeutic mild hypercapnia after cardiac arrest: A phase II multi-centre randomised controlled trial (the CCC trial)

BACKGROUND

In intensive care observational studies, hypercapnia after cardiac arrest (CA) is independently associated with improved neurological outcome. However, the safety and feasibility of delivering targeted therapeutic mild hypercapnia (TTMH) for such patients is untested.

METHODS

In a phase II safety and feasibility multi-centre, randomised controlled trial, we allocated ICU patients after CA to 24h of targeted normocapnia (TN) (PaCO2 35-45mmHg) or TTMH (PaCO2 50-55mmHg). The primary outcome was serum neuron specific enolase (NSE) and S100b protein concentrations over the first 72h assessed in the first 50 patients surviving to day three. Secondary end-points included global measure of function assessment at six months and mortality for all patients.

RESULTS

We enrolled 86 patients. Their median age was 61 years (58, 64 years) and 66 (79%) were male. Of these, 50 patients (58%) survived to day three for full biomarker assessment. NSE concentrations increased in the TTMH group (p=0.02) and TN group (p=0.005) over time, with the increase being significantly more pronounced in the TN group (p(interaction)=0.04). S100b concentrations decreased over time in the TTMH group (p<0.001) but not in the TN group (p=0.68). However, the S100b change over time did not differ between the groups (p(interaction)=0.23). At six months, 23 (59%) TTMH patients had good functional recovery compared with 18 (46%) TN patients. Hospital mortality occurred in 11 (26%) TTMH patients and 15 (37%) TN patients (p=0.31).

CONCLUSIONS

In CA patients admitted to the ICU, TTMH was feasible, appeared safe and attenuated the release of NSE compared with TN. These findings justify further investigation of this novel treatment.

Advances in the support of respiratory failure: putting all the evidence together

Considerable progress has been made recently in the understanding of how best to accomplish safe and effective ventilation of patients with acute lung injury. Mechanical and nonmechanical factors contribute to causation of ventilator-associated lung injury. Intervention timing helps determine the therapeutic efficacy and outcome, and the stage and severity of the disease process may determine the patient's vulnerability as well as an intervention's value. Reducing oxygen consumption and ventilatory demands are key to a successful strategy for respiratory support of acute respiratory distress syndrome. Results from major clinical trials can be understood against the background of the complex physiology of ventilator-induced lung injury.

Transcutaneous PTCCO2 measurement in combination with arterial blood gas analysis provides superior accuracy and reliability in ICU patients

Hyper or hypoventilation may have serious clinical consequences in critically ill patients and should be generally avoided, especially in neurosurgical patients. Therefore, monitoring of carbon dioxide partial pressure by intermittent arterial blood gas analysis (PaCO₂) has become standard in intensive care units (ICUs). However, several additional methods are available to determine PCO₂ including end-tidal (PETCO₂) and transcutaneous (PTCCO₂) measurements. The aim of this study was to compare the accuracy and reliability of different methods to determine PCO₂ in mechanically ventilated patients on ICU. After approval of the local ethics committee PCO₂ was determined in n = 32 ICU consecutive patients requiring mechanical ventilation: (1) arterial PaCO₂ blood gas analysis with Radiometer ABL 625 (ABL; gold standard), (2) arterial PaCO₂ analysis with Immediate Response Mobile Analyzer (IRMA), (3) end-tidal PETCO₂ by a Propaq 106 EL monitor and (4) transcutaneous PTCCO₂ determination by a Tina TCM4. Bland-Altman method was used for statistical analysis; p < 0.05 was considered statistically significant. Statistical analysis revealed good correlation between PaCO₂ by IRMA and ABL (R² = 0.766; p < 0.01) as well as between PTCCO₂ and ABL (R² = 0.619; p < 0.01), whereas correlation between PETCO₂ and ABL was weaker (R² = 0.405; p < 0.01). Bland-Altman analysis revealed a bias and precision of 2.0 ± 3.7 mmHg for the IRMA, 2.2 ± 5.7 mmHg for transcutaneous, and -5.5 ± 5.6 mmHg for end-tidal measurement. Arterial CO₂ partial pressure by IRMA (PaCO₂) and PTCCO₂ provided greater accuracy compared to the reference measurement (ABL) than the end-tidal CO₂ measurements in critically ill in mechanically ventilated patients patients.

Carbon Dioxide and the Heart: Physiology and Clinical Implications

Carbon dioxide (CO2) is an end product of aerobic cellular respiration. In healthy persons, PaCO2 is maintained by physiologic mechanisms within a narrow range (35-45 mm Hg). Both hypercapnia and hypocapnia are encountered in myriad clinical situations. In recent years, the number of hypercapnic patients has increased by the use of smaller tidal volumes to limit lung stretch and injury during mechanical ventilation, so-called permissive hypercapnia. A knowledge and appreciation of the effects of CO2 in the heart are necessary for optimal clinical management in the perioperative and critical care settings. This article reviews, from a historical perspective: (1) the effects of CO2 on coronary blood flow and the mechanisms underlying these effects; (2) the role of endogenously produced CO2 in metabolic control of coronary blood flow and the matching of myocardial oxygen supply to demand; and (3) the direct and reflexogenic actions of CO2 on myocardial contractile function. Clinically relevant issues are addressed, including the role of increased myocardial tissue PCO2 (PmCO2) in the decline in myocardial contractility during coronary hypoperfusion and the increased vulnerability to CO2-induced cardiac depression in patients receiving a β-adrenergic receptor antagonist or with otherwise compromised inotropic reserve. The potential use of real-time measurements of PmO2 to monitor the adequacy of myocardial perfusion in the perioperative period is discussed.

Ventilation and gas exchange management after cardiac arrest

For several decades, physicians had integrated several interventions aiming to improve the outcomes in post-cardiac arrest patients. However, the mortality rate after cardiac arrest is still as high as 50%. Post-cardiac arrest syndrome is associated with high morbidity and mortality due to not only poor neurological outcome and cardiovascular failure but also respiratory dysfunction. To minimize ventilator-associated lung injury, protective mechanical ventilation by using low tidal volume ventilation and driving pressure may decrease pulmonary complications and improve survival. Low level of positive end-expiratory pressure (PEEP) can be initiated and titrated with careful cardiac output and respiratory mechanics monitoring. Furthermore, optimizing gas exchange by avoiding hypoxia and hyperoxia as well as maintaining normocarbia may improve neurological and survival outcome. Early multidisciplinary cardiac rehabilitation intervention is recommended. Minimally invasive monitoring techniques, that is, echocardiography, transpulmonary thermodilution method measuring extravascular lung water, as well as transcranial Doppler ultrasound, might be useful to improve appropriate management of post-cardiac arrest patients.

Blood flow/pump rotation ratio as an artificial lung performance monitoring tool during extracorporeal respiratory support using centrifugal pumps

Objective

To analyze the correlations of the blood flow/pump rotation ratio and the transmembrane pressure, CO₂ and O₂ transfer during the extracorporeal respiratory support.

Methods

Five animals were instrumented and submitted to extracorporeal membrane oxygenation in a five-step protocol, including abdominal sepsis and lung injury.

Results

This study showed that blood flow/pump rotations ratio variations are dependent on extracorporeal membrane oxygenation blood flow in a positive logarithmic fashion. Blood flow/pump rotation ratio variations are negatively associated with transmembrane pressure (R² = 0.5 for blood flow = 1500mL/minute and R² = 0.4 for blood flow = 3500mL/minute, both with p < 0.001) and positively associated with CO₂ transfer variations (R² = 0.2 for sweep gas flow ≤ 6L/minute, p < 0.001, and R² = 0.1 for sweep gas flow > 6L/minute, p = 0.006), and the blood flow/pump rotation ratio is not associated with O₂ transfer variations (R² = 0.01 for blood flow = 1500mL/minute, p = 0.19, and R² = - 0.01 for blood flow = 3500 mL/minute, p = 0.46).

Conclusion

Blood flow/pump rotation ratio variation is negatively associated with transmembrane pressure and positively associated with CO₂ transfer in this animal model. According to the clinical situation, a decrease in the blood flow/pump rotation ratio can indicate artificial lung dysfunction without the occurrence of hypoxemia.

Permissive hypercapnia in extremely low birthweight infants (PHELBI): a randomised controlled multicentre trial

BACKGROUND

Tolerating higher partial pressure of carbon dioxide (pCO2) in mechanically ventilated, extremely low birthweight infants might reduce ventilator-induced lung injury and bronchopulmonary dysplasia. We aimed to test the hypothesis that higher target ranges for pCO2 decrease the rate of bronchopulmonary dysplasia or death.

METHODS

In this randomised multicentre trial, we recruited infants from 16 tertiary care perinatal centres in Germany with birthweight between 400 g and 1000 g and gestational age 23-28 weeks plus 6 days, who needed endotracheal intubation and mechanical ventilation within 24 h of birth. Infants were randomly assigned to either a high target or control group. The high target group aimed at pCO2 values of 55-65 mm Hg on postnatal days 1-3, 60-70 mm Hg on days 4-6, and 65-75 mm Hg on days 7-14, and the control target at pCO2 40-50 mmHg on days 1-3, 45-55 mm Hg on days 4-6, and 50-60 mm Hg on days 7-14. The primary outcome was death or moderate to severe bronchopulmonary dysplasia, defined as need for mechanical pressure support or supplemental oxygen at 36 weeks postmenstrual age. Cranial ultrasonograms were assessed centrally by a masked paediatric radiologist. This trial is registered with the ISRCTN registry, number ISRCTN56143743.

RESULTS

Between March 1, 2008, and July 31, 2012, we recruited 362 patients of whom three dropped out, leaving 179 patients in the high target and 180 in the control group. The trial was stopped after an interim analysis (n=359). The rate of bronchopulmonary dysplasia or death in the high target group (65/179 [36%]) did not differ significantly from the control group (54/180 [30%]; p=0·18). Mortality was 25 (14%) in the high target group and 19 (11%; p=0·32) in the control group, grade 3-4 intraventricular haemorrhage was 26 (15%) and 21 (12%; p=0·30), and the rate of severe retinopathy recorded was 20 (11%) and 26 (14%; p=0·36).

INTERPRETATION

Targeting a higher pCO2 did not decrease the rate of bronchopulmonary dysplasia or death in ventilated preterm infants. The rates of mortality, intraventricular haemorrhage, and retinopathy did not differ between groups. These results suggest that higher pCO2 targets than in the slightly hypercapnic control group do not confer increased benefits such as lung protection.

FUNDING

Deutsche Forschungsgemeinschaft.

Carbon Dioxide and Acetate-Free Biofiltration: A Relationship to be Investigated

As the name reveals, acetate-free biofiltration (AFB) is featured by lack of acetate and this would seem to allow better hemodynamic stability. However, AFB also has a unique characteristic of carbon dioxide (CO2 )-free dialysate, whereas all other modern dialysis techniques imply an overload of CO2 from dialysate to the patient. This notwithstanding the role of CO2 in tolerance to dialysis treatment, both AFB and all other dialysis techniques seem not investigated in due depth. Specifically, the amount of CO2 coming back to the patient's bloodstream during AFB and bicarbonate dialysis (BD) is unknown. We measured partial pressure of CO2 (pCO2 ) in blood samples withdrawn from the venous line of the extracorporeal circuit during BD and subsequently during AFB in 22 stable chronic hemodialysis outpatients. The amount of CO2 coming back to the patient's bloodstream is higher in BD (59.1 ± 4.0 mmol/L) than in AFB (42.8 ± 4.5 mmol/L, P < 0.0001). Such difference exceeds 30%. Moreover, shifting from BD to AFB shows, notably for each patient, the reduction of pCO2 toward physiological values. BD implies CO2 overload from dialysate, whereas AFB does not. Further studies are required to evaluate if AFB would be the most appropriate dialysis technique in patients affected by chronic, but especially acute, lung diseases.

A pilot feasibility, safety and biological efficacy multicentre trial of therapeutic hypercapnia after cardiac arrest: study protocol for a randomized controlled trial

BACKGROUND

Cardiac arrest causes ischaemic brain injury. Arterial carbon dioxide tension (PaCO2) is a major determinant of cerebral blood flow. Thus, mild hypercapnia in the 24 h following cardiac arrest may increase cerebral blood flow and attenuate such injury. We describe the Carbon Control and Cardiac Arrest (CCC) trial.

METHODS/DESIGN

The CCC trial is a pilot multicentre feasibility, safety and biological efficacy randomized controlled trial recruiting adult cardiac arrest patients admitted to the intensive care unit after return of spontaneous circulation. At admission, using concealed allocation, participants are randomized to 24 h of either normocapnia (PaCO2 35 to 45 mmHg) or mild hypercapnia (PaCO2 50 to 55 mmHg). Key feasibility outcomes are recruitment rate and protocol compliance rate. The primary biological efficacy and biological safety measures are the between-groups difference in serum neuron-specific enolase and S100b protein levels at 24 h, 48 h and 72 h. Secondary outcome measure include adverse events, in-hospital mortality, and neurological assessment at 6 months.

DISCUSSION

The trial commenced in December 2012 and, when completed, will provide clinical evidence as to whether targeting mild hypercapnia for 24 h following intensive care unit admission for cardiac arrest patients is feasible and safe and whether it results in decreased concentrations of neurological injury biomarkers compared with normocapnia. Trial results will also be used to determine whether a phase IIb study powered for survival at 90 days is feasible and justified.

TRIAL REGISTRATION

Australian New Zealand Clinical Trials Registry ACTRN12612000690853 .

The use of elements of the Stewart model (Strong Ion Approach) for the diagnostics of respiratory acidosis on the basis of the calculation of a value of a modified anion gap (AGm) in brachycephalic dogs

Apart from the HH equation, the acid-base balance of an organism is also described by the Stewart model, which assumes that the proper insight into the ABB of the organism is given by an analysis of: pCO2, the difference of concentrations of strong cations and anions in the blood serum – SID, and the total concentration of nonvolatile weak acids – Acid total. The notion of an anion gap (AG), or the apparent lack of ions, is closely related to the acid-base balance described according to the HH equation. Its value mainly consists of negatively charged proteins, phosphates, and sulphates in blood. In the human medicine, a modified anion gap is used, which, including the concentration of the protein buffer of blood, is, in fact, the combination of the apparent lack of ions derived from the classic model and the Stewart model. In brachycephalic dogs, respiratory acidosis often occurs, which is caused by an overgrowth of the soft palate, making it impossible for a free air flow and causing an increase in pCO2– carbonic acid anhydride The aim of the present paper was an attempt to answer the question whether, in the case of systemic respiratory acidosis, changes in the concentration of buffering ions can also be seen. The study was carried out on 60 adult dogs of boxer breed in which, on the basis of the results of endoscopic examination, a strong overgrowth of the soft palate requiring a surgical correction was found. For each dog, the value of the anion gap before and after the palate correction procedure was calculated according to the following equation: AG = ([Na+mmol/l] + [K+mmol/l]) – ([Cl−mmol/l]+[HCO3−mmol/l]) as well as the value of the modified AG – according to the following equation: AGm= calculated AG + 2.5 × (albuminsr– albuminsd). The values of AG calculated for the dogs before and after the procedure fell within the limits of the reference values and did not differ significantly whereas the values of AGmcalculated for the dogs before and after the procedure differed from each other significantly. Conclusions: 1) On the basis of the values of AGmobtained it should be stated that in spite of finding respiratory acidosis in the examined dogs, changes in ion concentration can also be seen, which, according to the Stewart theory, compensate metabolic ABB disorders 2) In spite of the fact that all the values used for calculation of AGmwere within the limits of reference values, the values of AGmin dogs before and after the soft palate correction procedure differed from each other significantly, which proves high sensitivity and usefulness of the AGmcalculation as a diagnostic method.

Post return of spontaneous circulation factors associated with mortality in pediatric in-hospital cardiac arrest: a prospective multicenter multinational observational study

INTRODUCTION

Most studies have analyzed pre-arrest and resuscitation factors associated with mortality after cardiac arrest (CA) in children, but many patients that reach return of spontaneous circulation die within the next days or weeks. The objective of our study was to analyze post-return of spontaneous circulation factors associated with in-hospital mortality after cardiac arrest in children.

METHODS

A prospective multicenter, multinational, observational study in 48 hospitals from 12 countries was performed. A total of 502 children aged between 1 month and 18 years with in-hospital cardiac arrest were analyzed. The primary endpoint was survival to hospital discharge. Univariate and multivariate logistic regression analyses were performed to assess the influence of each post-return of spontaneous circulation factor on mortality.

RESULTS

Return of spontaneous circulation was achieved in 69.5% of patients; 39.2% survived to hospital discharge and 88.9% of survivors had good neurological outcome. In the univariate analysis, post- return of spontaneous circulation factors related with mortality were pH, base deficit, lactic acid, bicarbonate, FiO2, need for inotropic support, inotropic index, dose of dopamine and dobutamine at 1 hour and at 24 hours after return of spontaneous circulation as well as Pediatric Intensive Care Unit and total hospital length of stay. In the multivariate analysis factors associated with mortality at 1 hour after return of spontaneous circulation were PaCO2 < 30 mmHg and >50 mmHg, inotropic index >14 and lactic acid >5 mmol/L. Factors associated with mortality at 24 hours after return of spontaneous circulation were PaCO2 > 50 mmHg, inotropic index >14 and FiO2 ≥ 0.80.

CONCLUSIONS

Secondary in-hospital mortality among the initial survivors of CA is high. Hypoventilation, hyperventilation, FiO2 ≥ 0.80, the need for high doses of inotropic support, and high levels of lactic acid were the most important post-return of spontaneous circulation factors associated with in-hospital mortality in children in our population.

Hypercapnia attenuates ventilator-induced lung injury via a disintegrin and metalloprotease-17

Hypercapnic acidosis, common in mechanically ventilated patients, has been reported to exert both beneficial and harmful effects in models of lung injury. Understanding its effects at the molecular level may provide insight into mechanisms of injury and protection. The aim of this study was to establish the effects of hypercapnic acidosis on mitogen‐activated protein kinase (MAPK) activation, and determine the relevant signalling pathways. p44/42 MAPK activation in a murine model of ventilator‐induced lung injury (VILI) correlated with injury and was reduced in hypercapnia. When cultured rat alveolar epithelial cells were subjected to cyclic stretch, activation of p44/42 MAPK was dependent on epidermal growth factor receptor (EGFR) activity and on shedding of EGFR ligands; exposure to 12% CO2 without additional buffering blocked ligand shedding, as well as EGFR and p44/42 MAPK activation. The EGFR ligands are known substrates of the matrix metalloprotease ADAM17, suggesting stretch activates and hypercapnic acidosis blocks stretch‐mediated activation of ADAM17. This was corroborated in the isolated perfused mouse lung, where elevated CO2 also inhibited stretch‐activated shedding of the ADAM17 substrate TNFR1 from airway epithelial cells. Finally, in vivo confirmation was obtained in a two‐hit murine model of VILI where pharmacological inhibition of ADAM17 reduced both injury and p44/42 MAPK activation. Thus, ADAM17 is an important proximal mediator of VILI; its inhibition is one mechanism of hypercapnic protection and may be a target for clinical therapy.

Dietary methanol regulates human gene activity

Methanol (MeOH) is considered to be a poison in humans because of the alcohol dehydrogenase (ADH)-mediated conversion of MeOH to formaldehyde (FA), which is toxic. Our recent genome-wide analysis of the mouse brain demonstrated that an increase in endogenous MeOH after ADH inhibition led to a significant increase in the plasma MeOH concentration and a modification of mRNA synthesis. These findings suggest endogenous MeOH involvement in homeostasis regulation by controlling mRNA levels. Here, we demonstrate directly that study volunteers displayed increasing concentrations of MeOH and FA in their blood plasma when consuming citrus pectin, ethanol and red wine. A microarray analysis of white blood cells (WBC) from volunteers after pectin intake showed various responses for 30 significantly differentially regulated mRNAs, most of which were somehow involved in the pathogenesis of Alzheimer's disease (AD). There was also a decreased synthesis of hemoglobin mRNA, HBA and HBB, the presence of which in WBC RNA was not a result of red blood cells contamination because erythrocyte-specific marker genes were not significantly expressed. A qRT-PCR analysis of volunteer WBCs after pectin and red wine intake confirmed the complicated relationship between the plasma MeOH content and the mRNA accumulation of both genes that were previously identified, namely, GAPDH and SNX27, and genes revealed in this study, including MME, SORL1, DDIT4, HBA and HBB. We hypothesized that human plasma MeOH has an impact on the WBC mRNA levels of genes involved in cell signaling.

[Veno-venous extracorporeal support to treat acute respiratory distress syndrome: Rationale and clinical objectives]

Les techniques de circulation extracorporelle (CEC) peuvent être utilisées dans les défaillances respiratoires graves des syndromes de détresse respiratoire aiguë (SDRA) avec trois objectifs : 1) assurer une oxygénation satisfaisante en court-circuitant le poumon malade grâce à une circulation veinoveineuse à haut débit ; cette technique assure sans difficulté l’épuration de CO₂ ; 2) assurer avant tout une élimination partielle de CO₂ dans le but de protéger le poumon d’une ventilation mécanique dangereuse. Des débits sanguins quatre à cinq fois plus faibles sont suffisants avec une circulation veinoveineuse ou artérioveineuse sans pompe ; 3) exceptionnellement, la prise en charge d’une défaillance cardiaque associée peut nécessiter une circulation veinoartérielle à haut débit. Des études physiologiques détaillées et des essais cliniques sont indispensables pour mieux connaître les indications de ces techniques.

Adherence to oxygenation and ventilation targets in mechanically ventilated premature and sick newborns: a retrospective study

Background

Ventilator treatment exposes newborns to both hyperoxemia and hyperventilation. It is not known how common hyperoxemia and hyperventilation are in neonatal intensive care units in Norway. The purpose of this study was to assess the quality of current care by studying deviations from the target range of charted oxygenation and ventilation parameters in newborns receiving mechanical ventilation.

Methods

Single centre, retrospective chart review that focused on oxygen and ventilator treatment practices.

Results

The bedside intensive care charts of 138 newborns reflected 4978 hours of ventilator time. Arterial blood gases were charted in 1170 samples. In oxygen-supplemented newborns, high arterial pressure of oxygen (PaO₂) values were observed in 87/609 (14%) samples. In extremely premature newborns only 5% of the recorded PaO₂ values were high. Low arterial pressure of CO₂ (PaCO₂) values were recorded in 187/1170 (16%) samples, and 64 (34%) of these were < 4 kPa. Half of all low values were measured in extremely premature newborns. Tidal volumes above the target range were noted in 22% of premature and 20% of full-term newborns.

Conclusions

There was a low prevalence of high PaO₂ values in premature newborns, which increased significantly with gestational age (GA). The prevalence of low PaCO₂ values was highest among extremely premature newborns and decreased with increasing GA. Further studies are needed to identify whether adherence to oxygenation and ventilation targets can be improved by clearer communication and allocation of responsibilities between nurses and physicians.

Cardiac index and oxygen delivery during low and high tidal volume ventilation strategies in patients with acute respiratory distress syndrome: a crossover randomized clinical trial

INTRODUCTION

The beneficial effect of low tidal volume (TV) ventilation strategy on mortality in patients with acute respiratory distress syndrome (ARDS) has been attributed to the protective effect on ventilator-induced lung injury, and yet its effect on cardiovascular function might also play an important role. The aim of this study was to assess whether low TV ventilation improves cardiac output and oxygen delivery compared with high TV ventilation strategy in patients with ARDS.

METHODS

In this crossover randomized clinical trial 16 ARDS patients were recruited in an intensive care unit at a university-affiliated hospital. Each patient was ventilated for 30 min with low (6 mL/kg) and 30 min with high (12 mL/kg) TV. The two experimental periods, applied in random order and with allocation concealment, were separated by 30 min of basal ventilation. Minute ventilation was constantly maintained by appropriate respiratory rate changes.

RESULTS

Compared with high TV ventilation, low TV ventilation showed decreased pH (7.37 vs. 7.41, P = 0.001) and increased PaCO₂ (49 vs. 43 mmHg; P = 0.002). Cardiac index and oxygen delivery index were increased with low compared with high TV ventilation (3.9 vs. 3.5 L.min⁻¹.m⁻², P = 0.012, and 521 vs. 463 mL.min⁻¹.m⁻², P = 0.002, respectively), while oxygen extraction ratio decreased (0.36 vs. 0.44, P = 0.027). In four patients oxygen extraction ratio was >0.5 during high TV but not during low TV strategy. The magnitude of the change in cardiac index was positively associated with PaCO₂ variation (P = 0.004), while it was unrelated to the magnitude of changes in TV and airway pressure. The decrease of cardiac index was predicted by PaCO₂ reduction, with and area under ROC curve of 0.72.

CONCLUSIONS

Our findings suggest that a low TV ventilation strategy increases cardiac index and oxygen delivery, thus supporting the hypothesis that the beneficial effect of low TV ventilation in patients with ARDS could be partially explained by hemodynamic improvement. In other words, low tidal volume ventilation could be protective also for the cardiovascular system and not only for the lung. The slight increase of PaCO₂ during low TV ventilation seems to predict the increase of cardiac index.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT00713713.

Incidence of hypo- and hyper-capnia in a cross-sectional European cohort of ventilated newborn infants

OBJECTIVE

To determine the incidence of hypo- and hyper-capnia in a European cohort of ventilated newborn infants.

DESIGN AND SETTING

Two-point cross-sectional prospective study in 173 European neonatal intensive care units.

PATIENTS AND METHODS

Patient characteristics, ventilator settings and measurements, and blood gas analyses were collected for endotracheally ventilated newborn infants on two separate dates.

RESULTS

A total of 1569 blood gas analyses were performed in 508 included patients with a mean±SD Pco2 of 48±12 mm Hg or 6.4±1.6 kPa (range 17-104 mm Hg or 2.3-13.9 kPa). Hypocapnia (Pco2<30 mm Hg or 4 kPa) and hypercapnia (Pco2>52 mm Hg or 7 kPa) was present in, respectively, 69 (4%) and 492 (31%) of the blood gases. Hypocapnia was most common in the first 3 days of life (7.3%) and hypercapnia after the first week of life (42.6%). Pco2 was significantly higher in preterm infants (49 mm Hg or 6.5 kPa) than term infants (43 mm Hg or 5.7 kPa) and significantly lower during pressure-limited ventilation (47 mm Hg or 6.3±1.6 kPa) compared with volume-targeted ventilation (51 mm Hg or 6.8±1.7 kPa) and high-frequency ventilation (50 mm Hg or 6.7±1.7 kPa).

CONCLUSIONS

This study shows that hypocapnia is a relatively uncommon finding during neonatal ventilation. The higher incidence of hypercapnia may suggest that permissive hypercapnia has found its way into daily clinical practice.

Aerodynamic profiles of women with muscle tension dysphonia/aphonia

PURPOSE

In this study, the authors aimed to (a) determine whether phonatory airflows and estimated subglottal pressures (est-Psub) for women with primary muscle tension dysphonia/aphonia (MTD/A) differ from those for healthy speakers; (b) identify different aerodynamic profile patterns within the MTD/A subject group; and (c) determine whether results suggest new understanding of pathogenesis in MTD/A.

METHOD

Retrospective review of aerodynamic data collected from 90 women at the time of primary MTD/A diagnosis.

RESULTS

Aerodynamic profiles were significantly different for women with MTD/A as compared with healthy speakers. Five distinct profiles were identified: (a) normal flow, normal est-Psub; (b) high flow, high est-Psub; (c) low flow, normal est-Psub; (d) normal flow, high est-Psub; and (e) high flow, normal est-Psub.

CONCLUSIONS

This study is the first to identify distinct subgroups of aerodynamic profiles in women with MTD/A and to quantitatively identify a clinical phenomenon sometimes described in association with it-"breath holding"-that is shown by low airflow with normal est-Psub. Results were consistent with clinical claims that diverse respiratory and laryngeal functions may underlie phonatory patterns associated with MTD/A. One potential mechanism, based in psychobiological theory, is introduced to explain some of the variability in aerodynamic profiles of women with MTD/A.

Carbon dioxide clearance in critical care

Lung protective ventilation limiting tidal volumes and airway pressures were proven to reduce mortality in patients with acute severe respiratory failure. Hypercapnia and hypercapnic acidosis is often noted with lung protective ventilation. While the protective effects of lung protective ventilation are well recognised, the role of hypercapnia and hypercapnic acidosis remains debatable. Some clinicians argue that hypercapnia and hypercapnic acidosis protect the lungs and may be associated with improved outcomes. To the contrary, some clinicians do not tolerate hypercapnic acidosis and use various techniques including extracorporeal carbon dioxide elimination to treat hypercapnia and acidosis. This review aims at defining the effects of hypercapnia and hypercapnic acidosis with a focus on the pros and cons of clearing carbon dioxide and the modalities that may enhance carbon dioxide clearance.

Mitochondrial-targeted DNA repair enzyme 8-oxoguanine DNA glycosylase 1 protects against ventilator-induced lung injury in intact mice

This study tested the hypothesis that oxidative mitochondrial-targeted DNA (mtDNA) damage triggered ventilator-induced lung injury (VILI). Control mice and mice infused with a fusion protein targeting the DNA repair enzyme, 8-oxoguanine-DNA glycosylase 1 (OGG1) to mitochondria were mechanically ventilated with a range of peak inflation pressures (PIP) for specified durations. In minimal VILI (1 h at 40 cmH(2)O PIP), lung total extravascular albumin space increased 2.8-fold even though neither lung wet/dry (W/D) weight ratios nor bronchoalveolar lavage (BAL) macrophage inflammatory protein (MIP)-2 or IL-6 failed to differ from nonventilated or low PIP controls. This increase in albumin space was attenuated by OGG1. Moderately severe VILI (2 h at 40 cmH(2)O PIP) produced a 25-fold increase in total extravascular albumin space, a 60% increase in W/D weight ratio and marked increases in BAL MIP-2 and IL-6, accompanied by oxidative mitochondrial DNA damage, as well as decreases in the total tissue glutathione (GSH) and GSH/GSSH ratio compared with nonventilated lungs. All of these injury indices were attenuated in OGG1-treated mice. At the highest level of VILI (2 h at 50 cmH(2)O PIP), OGG1 failed to protect against massive lung edema and BAL cytokines or against depletion of the tissue GSH pool. Interestingly, whereas untreated mice died before completing the 2-h protocol, OGG1-treated mice lived for the duration of observation. Thus mitochondrially targeted OGG1 prevented VILI over a range of ventilation times and pressures and enhanced survival in the most severely injured group. These findings support the concept that oxidative mtDNA damage caused by high PIP triggers induction of acute lung inflammation and injury.

Hypocapnia and hypercapnia are predictors for ICU admission and mortality in hospitalized patients with community-acquired pneumonia

OBJECTIVE

The purpose of our study was to examine in patients hospitalized with community acquired pneumonia (CAP) the association between abnormal Pa CO 2 and ICU admission and 30-day mortality.

METHODS

A retrospective cohort study was conducted at two tertiary teaching hospitals. Eligible subjects were admitted with a diagnosis of CAP. Arterial blood gas analyses were obtained with measurement of PaCO2 on admission. Multivariate analyses were performed using 30-day mortality and ICU admission as the dependent measures.

RESULTS

Data were abstracted on 453 subjects with a documented arterial blood gas analysis. One hundred eighty-nine patients (41%) had normal PaCO2 (35-45 mm Hg), 194 patients (42%) had aPa CO 2 , 35 mm Hg (hypocapnic), and 70 patients (15%) had a Pa CO 2 . 45 mm Hg (hypercapnic).In the multivariate analysis, after adjusting for severity of illness, hypocapnic patients had greater 30-day mortality (OR= 2.84; 95% CI, 1.28-6.30) and a higher need for ICU admission (OR= 2.88;95% CI, 1.68-4.95) compared with patients with normal PaCO2. In addition, hypercapnic patients had a greater 30-day mortality (OR= 3.38; 95% CI, 1.38-8.30) and a higher need for ICU admission(OR =5.35; 95% CI, 2.80-10.23). When patients with COPD were excluded from the analysis,the differences persisted between groups.

CONCLUSION

In hospitalized patients with CAP, both hypocapnia and hypercapnia were associated with an increased need for ICU admission and higher 30-day mortality. These findings persisted after excluding patients with CAP and with COPD. Therefore, PaCO2 should be considered for inclusion in future severity stratification criteria to appropriate identified patients who will require a higher level of care and are at risk for increased mortality.

Hypercapnia accelerates wound healing in endothelial cell monolayers exposed to hypoxia

INTRODUCTION

While tissue hypoxia is known to play a critical role in the process of vascular injury and repair, the effect of hypercapnia on this process remains uncertain. We investigated whether hypercapnia might influence endothelial cell wound healing under the influence of hypoxia.

MATERIALS AND METHODOLOGY

Monolayers of human umbilical venous endothelial cells (HUVECs) were scratch-wounded and incubated under different levels of O2, CO2, and pH in the environment.

RESULTS

Inhibition of wound healing was observed in the HUVEC monolayers under the hypoxic condition as compared to the normoxic condition. Both hypercapnic acidosis and buffered hypercapnia, but not normocapnic acidosis improved the rate of wound healing under the influence of hypoxia. The beneficial effect of hypercapnia was associated with stimulation of cell proliferation, without effects on cell adhesion, migration or apoptosis. On the other hand, the stimulatory effect of hypercapnia on wound healing and cell proliferation was not noted under normoxic conditions.

CONCLUSION

These results suggest that hypercapnia, rather than acidosis per se, accelerated the wound healing in HUVEC monolayers cultured under hypoxic conditions. The effect of hypercapnia on wound healing was due, at least in part, to the stimulation of cell proliferation by hypercapnia.

Bench to bedside review: Extracorporeal carbon dioxide removal, past present and future

Acute respiratory distress syndrome (ARDS) has a substantial mortality rate and annually affects more than 140,000 people in the USA alone. Standard management includes lung protective ventilation but this impairs carbon dioxide clearance and may lead to right heart dysfunction or increased intracranial pressure. Extracorporeal carbon dioxide removal has the potential to optimize lung protective ventilation by uncoupling oxygenation and carbon dioxide clearance. The aim of this article is to review the carbon dioxide removal strategies that are likely to be widely available in the near future. Relevant published literature was identified using PubMed and Medline searches. Queries were performed by using the search terms ECCOR, AVCO2R, VVCO2R, respiratory dialysis, and by combining carbon dioxide removal and ARDS. The only search limitation imposed was English language. Additional articles were identified from reference lists in the studies that were reviewed. Several novel strategies to achieve carbon dioxide removal were identified, some of which are already commercially available whereas others are in advanced stages of development.

Monitoring in the intensive care

In critical care, the monitoring is essential to the daily care of ICU patients, as the optimization of patient's hemodynamic, ventilation, temperature, nutrition, and metabolism is the key to improve patients' survival. Indeed, the decisive endpoint is the supply of oxygen to tissues according to their metabolic needs in order to fuel mitochondrial respiration and, therefore, life. In this sense, both oxygenation and perfusion must be monitored in the implementation of any resuscitation strategy. The emerging concept has been the enhancement of macrocirculation through sequential optimization of heart function and then judging the adequacy of perfusion/oxygenation on specific parameters in a strategy which was aptly coined “goal directed therapy.” On the other hand, the maintenance of normal temperature is critical and should be regularly monitored. Regarding respiratory monitoring of ventilated ICU patients, it includes serial assessment of gas exchange, of respiratory system mechanics, and of patients' readiness for liberation from invasive positive pressure ventilation. Also, the monitoring of nutritional and metabolic care should allow controlling nutrients delivery, adequation between energy needs and delivery, and blood glucose. The present paper will describe the physiological basis, interpretation of, and clinical use of the major endpoints of perfusion/oxygenation adequacy and of temperature, respiratory, nutritional, and metabolic monitorings.

Perioperative lung protection strategies in cardiothoracic anesthesia: are they useful?

Patients are at risk for several types of lung injury in the perioperative period. These injuries include atelectasis, pneumonia, pneumothorax, bronchopleural fistula, acute lung injury, and acute respiratory distress syndrome. Anesthetic management can cause, exacerbate, or ameliorate most of these injuries. Lung-protective ventilation strategies using more physiologic tidal volumes and appropriate levels of positive end-expiratory pressure can decrease the extent of this injury. This review discusses the effects of mechanical ventilation and its role in ventilator-induced lung injury with specific reference to cardiothoracic anesthesia.

Hypercapnia induces cleavage and nuclear localization of RelB protein, giving insight into CO2 sensing and signaling

Carbon dioxide (CO₂) is increasingly being appreciated as an intracellular signaling molecule that affects inflammatory and immune responses. Elevated arterial CO₂ (hypercapnia) is encountered in a range of clinical conditions, including chronic obstructive pulmonary disease, and as a consequence of therapeutic ventilation in acute respiratory distress syndrome. In patients suffering from this syndrome, therapeutic hypoventilation strategy designed to reduce mechanical damage to the lungs is accompanied by systemic hypercapnia and associated acidosis, which are associated with improved patient outcome. However, the molecular mechanisms underlying the beneficial effects of hypercapnia and the relative contribution of elevated CO₂ or associated acidosis to this response remain poorly understood. Recently, a role for the non-canonical NF-κB pathway has been postulated to be important in signaling the cellular transcriptional response to CO₂. In this study, we demonstrate that in cells exposed to elevated CO₂, the NF-κB family member RelB was cleaved to a lower molecular weight form and translocated to the nucleus in both mouse embryonic fibroblasts and human pulmonary epithelial cells (A549). Furthermore, elevated nuclear RelB was observed in vivo and correlated with hypercapnia-induced protection against LPS-induced lung injury. Hypercapnia-induced RelB processing was sensitive to proteasomal inhibition by MG-132 but was independent of the activity of glycogen synthase kinase 3β or MALT-1, both of which have been previously shown to mediate RelB processing. Taken together, these data demonstrate that RelB is a CO₂-sensitive NF-κB family member that may contribute to the beneficial effects of hypercapnia in inflammatory diseases of the lung.

Systemic inflammation impairs respiratory chemoreflexes and plasticity

Many lung and central nervous system disorders require robust and appropriate physiological responses to assure adequate breathing. Factors undermining the efficacy of ventilatory control will diminish the ability to compensate for pathology, threatening life itself. Although most of these same disorders are associated with systemic and/or neuroinflammation, and inflammation affects neural function, we are only beginning to understand interactions between inflammation and any aspect of ventilatory control (e.g. sensory receptors, rhythm generation, chemoreflexes, plasticity). Here we review available evidence, and present limited new data suggesting that systemic (or neural) inflammation impairs two key elements of ventilatory control: chemoreflexes and respiratory motor (versus sensory) plasticity. Achieving an understanding of mechanisms whereby inflammation undermines ventilatory control is fundamental since inflammation may diminish the capacity for natural, compensatory responses during pathological states, and the ability to harness respiratory plasticity as a therapeutic strategy in the treatment of devastating breathing disorders, such as during cervical spinal injury or motor neuron disease.

Lung protective strategies in anaesthesia

Patients are at risk for several types of lung injury in the perioperative period including atelectasis, pneumonia, pneumothorax, acute lung injury, and acute respiratory distress syndrome. Anaesthetic management can cause, exacerbate, or ameliorate these injuries. This review examines the effects of perioperative mechanical ventilation and its role in ventilator-induced lung injury. Lung protective ventilatory strategies to specific clinical situations such as cardiopulmonary bypass and one-lung ventilation along with newer novel lung protective strategies are discussed.