Bench-to-bedside review: Permissive hypercapnia

Impact of AKI on metabolic compensation for respiratory acidosis in ICU patients with AECOPD

PURPOSE

Acute exacerbation of chronic obstructive pulmonary disease (AECOPD) can result in severe respiratory acidosis. Metabolic compensation is primarily achieved by renal retention of bicarbonate. The extent to which acute kidney injury (AKI) impairs the kidney's capacity to compensate for respiratory acidosis remains unclear.

MATERIALS AND METHODS

This retrospective analysis covers clinical data between January 2009 and December 2021 for 498 ICU patients with AECOPD and need for respiratory support.

RESULTS

278 patients (55.8%) presented with or developed AKI. Patients with AKI exhibited higher 30-day-mortality rates (14.5% vs. 4.5% p = 0.001), longer duration of mechanical ventilation (median 90 h vs. 14 h; p = 0.001) and more severe hypercapnic acidosis (pH 7.23 vs. 7.28; pCO2 68.5 mmHg vs. 61.8 mmHg). Patients with higher AKI stages exhibited lower HCO3-/pCO2 ratios and did not reach expected HCO3- levels. In a mixed model analysis with random intercept per patient we analyzed the association of pCO2 (independent) and HCO3- (dependent variable). Lower estimates for averaged change in HCO3- were observed in patients with more severe AKI.

CONCLUSION

AKI leads to poor outcomes and compromises metabolic compensation of respiratory acidosis in ICU patients with AECOPD. While buffering agents may aid compensation for severe AKI, their use should be approached with caution.

Impact of healthcare system strain on the implementation of ICU sedation practices and encephalopathy burden during the early COVID-19 pandemic

The COVID-19 pandemic posed unprecedented challenges to healthcare systems worldwide, particularly in managing critically ill patients requiring mechanical ventilation early in the pandemic. Surging patient volumes strained hospital resources and complicated the implementation of standard-of-care intensive care unit (ICU) practices, including sedation management. The objective of this study was to evaluate the impact of an evidence-based ICU sedation bundle during the early COVID-19 pandemic. The bundle was designed by a multi-disciplinary collaborative to reinforce best clinical practices related to ICU sedation. The bundle was implemented prospectively with retrospective analysis of electronic medical record data. The setting was the ICUs of a single-center tertiary hospital. The patients were the ICU patients requiring mechanical ventilation for confirmed COVID-19 between March and June 2020. A learning health collaborative developed a sedation bundle encouraging goal-directed sedation and use of adjunctive strategies to avoid excessive sedative administration. Implementation strategies included structured in-service training, audit and feedback, and continuous improvement. Sedative utilization and clinical outcomes were compared between patients admitted before and after the sedation bundle implementation. Quasi-experimental interrupted time-series analyses of pre and post intervention sedative utilization, hospital length of stay, and number of days free of delirium, coma, or death in 21 days (as a quantitative measure of encephalopathy burden). The analysis used the time duration between start of the COVID-19 wave and ICU admission to identify a "breakpoint" indicating a change in observed trends. A total of 183 patients (age 59.0 ± 15.9 years) were included, with 83 (45%) admitted before the intervention began. Benzodiazepine utilization increased for patients admitted after the bundle implementation, while agents intended to reduce benzodiazepine use showed no greater utilization. No "breakpoint" was identified to suggest the bundle impacted any endpoint measure. However, increasing time between COVID-19 wave start and ICU admission was associated with fewer delirium, coma, and death-free days (β =  - 0.044 [95% CI - 0.085, - 0.003] days/wave day); more days of benzodiazepine infusion (β = 0.056 [95% CI 0.025, 0.088] days/wave day); and a higher maximum benzodiazepine infusion rate (β = 0.079 [95% CI 0.037, 0.120] mg/h/wave day). The evidence-based practice bundle did not significantly alter sedation utilization patterns during the first COVID-19 wave. Sedation practices deteriorated and encephalopathy burden increased over time, highlighting that strategies to reinforce clinical practices may be hindered under conditions of extreme healthcare system strain.

Cerebral perfusion and metabolism with mild hypercapnia vs. normocapnia in a porcine post cardiac arrest model with and without targeted temperature management

Aim

To determine whether targeting mild hypercapnia (PaCO2 7 kPa) would yield improved cerebral blood flow and metabolism compared to normocapnia (PaCO2 5 kPa) with and without targeted temperature management to 33 °C (TTM33) in a porcine post-cardiac arrest model.

Methods

39 pigs were resuscitated after 10 minutes of cardiac arrest using cardiopulmonary bypass and randomised to TTM33 or no-TTM, and hypercapnia or normocapnia. TTM33 was managed with intravasal cooling. Animals were stabilized for 30 minutes followed by a two-hour intervention period. Hemodynamic parameters were measured continuously, and neuromonitoring included intracranial pressure (ICP), pressure reactivity index, cerebral blood flow, brain-tissue pCO2 and microdialysis. Measurements are reported as proportion of baseline, and areas under the curve during the 120 min intervention period were compared.

Results

Hypercapnia increased cerebral flow in both TTM33 and no-TTM groups, but also increased ICP (199% vs. 183% of baseline, p = 0.018) and reduced cerebral perfusion pressure (70% vs. 84% of baseline, p < 0.001) in no-TTM animals. Cerebral lactate (196% vs. 297% of baseline, p < 0.001), pyruvate (118% vs. 152% of baseline, p < 0.001), glycerol and lactate/pyruvate ratios were lower with hypercapnia in the TTM33 group, but only pyruvate (133% vs. 150% of baseline, p = 0.002) was lower with hypercapnia among no-TTM animals.

Conclusion

In this porcine post-arrest model, hypercapnia led to increased cerebral flow both with and without hypothermia, but also increased ICP and reduced cerebral perfusion pressure in no-TTM animals. The effects of hypercapnia were different with and without TTM.(Institutional protocol number: FOTS, id 14931).

Future directions in ventilator-induced lung injury associated cognitive impairment: a new sight

Mechanical ventilation is a widely used short-term life support technique, but an accompanying adverse consequence can be pulmonary damage which is called ventilator-induced lung injury (VILI). Mechanical ventilation can potentially affect the central nervous system and lead to long-term cognitive impairment. In recent years, many studies revealed that VILI, as a common lung injury, may be involved in the central pathogenesis of cognitive impairment by inducing hypoxia, inflammation, and changes in neural pathways. In addition, VILI has received attention in affecting the treatment of cognitive impairment and provides new insights into individualized therapy. The combination of lung protective ventilation and drug therapy can overcome the inevitable problems of poor prognosis from a new perspective. In this review, we summarized VILI and non-VILI factors as risk factors for cognitive impairment and concluded the latest mechanisms. Moreover, we retrospectively explored the role of improving VILI in cognitive impairment treatment. This work contributes to a better understanding of the pathogenesis of VILI-induced cognitive impairment and may provide future direction for the treatment and prognosis of cognitive impairment.

Chloride Reduction Therapy with Furosemide: Short-Term Effects in Children with Acute Respiratory Failure

From the perspective of the Stewart approach, it is known that expansion of the sodium chloride ion difference (SCD) induces alkalosis. We investigated the role of SCD expansion by furosemide-induced chloride reduction in pediatric patients with acute respiratory failure. We included patients admitted to our pediatric intensive care unit intubated for acute respiratory failure without underlying diseases, and excluded patients receiving extracorporeal circulation therapy (extracorporeal membrane oxygenation and/or renal replacement therapy). We classified eligible patients into the following two groups: case-those intubated who received furosemide within 24 hours, and control-those intubated who did not receive furosemide within 48 hours. Primary outcomes included SCD, partial pressure of carbon dioxide (PaCO 2 ), and pH results from arterial blood gas samples obtained over 48 hours following intubation. Multiple regression analysis was also performed to evaluate the effects of SCD and PaCO 2 changes on pH. Twenty-six patients were included of which 13 patients were assigned to each of the two groups. A total of 215 gas samples were analyzed. SCD (median [mEq/L] [interquartile range]) 48 hours after intubation significantly increased in the case group compared with the control group (37 [33-38] vs. 31 [30-34]; p  = 0.005). Although hypercapnia persisted in the case group, the pH (median [interquartile range]) remained unchanged in both groups (7.454 [7.420-7.467] vs. 7.425 [7.421-7.436]; p  = 0.089). SCD and PaCO 2 were independently associated with pH ( p  < 0.001 for each regression coefficient). As a result, we provide evidence that SCD expansion with furosemide may be useful in maintaining pH within the normal range in pediatric patients with acute respiratory failure complicated by concurrent metabolic acidosis.

Hypercapnia alters mitochondrial gene expression and acylcarnitine production in monocytes

CO2 is produced during aerobic respiration. Normally, levels of CO2 in the blood are tightly regulated but pCO2 can rise (hypercapnia, pCO2  > 45 mmHg) in patients with lung diseases, for example, chronic obstructive pulmonary disease (COPD). Hypercapnia is a risk factor in COPD but may be of benefit in the context of destructive inflammation. The effects of CO2 per se, on transcription, independent of pH change are poorly understood and warrant further investigation. Here we elucidate the influence of hypercapnia on monocytes and macrophages through integration of state-of-the-art RNA-sequencing, metabolic and metabolomic approaches. THP-1 monocytes and interleukin 4-polarized primary murine macrophages were exposed to 5% CO2 versus 10% CO2 for up to 24 h in pH-buffered conditions. In hypercapnia, we identified around 370 differentially expressed genes (DEGs) under basal and about 1889 DEGs under lipopolysaccharide-stimulated conditions in monocytes. Transcripts relating to both mitochondrial and nuclear-encoded gene expression were enhanced in hypercapnia in basal and lipopolysaccharide-stimulated cells. Mitochondrial DNA content was not enhanced, but acylcarnitine species and genes associated with fatty acid metabolism were increased in hypercapnia. Primary macrophages exposed to hypercapnia also increased activation of genes associated with fatty acid metabolism and reduced activation of genes associated with glycolysis. Thus, hypercapnia elicits metabolic shifts in lipid metabolism in monocytes and macrophages under pH-buffered conditions. These data indicate that CO2 is an important modulator of monocyte transcription that can influence immunometabolic signaling in immune cells in hypercapnia. These immunometabolic insights may be of benefit in the treatment of patients experiencing hypercapnia.

Impact of Arterial CO2 Retention in Patients With Moderate or Severe ARDS

BACKGROUND

Lung-protective ventilation (reduced tidal volume and limited plateau pressure) may lead to CO2 retention. Data about the impact of hypercapnia in patients with ARDS are scarce and conflicting.

METHODS

We performed a non-interventional cohort study with subjects with ARDS admitted from 2006 to 2021 and with PaO2 /FIO2 ≤ 150 mm Hg. We examined the association between severe hypercapnia (PaCO2 ≥ 50 mm Hg) on the first 5 days after the diagnosis of ARDS and death in ICU for 930 subjects. All the subjects received lung-protective ventilation.

RESULTS

Severe hypercapnia was noted in 552 subjects (59%) on the first day of ARDS (day 1); 323/930 (34.7%) died in the ICU. Severe hypercapnia on day 1 was associated with mortality in the unadjusted (odds ratio 1.54, 95% CI 1.16-1.63; P = .003) and adjusted (odds ratio 1.47, 95% CI 1.08-2.43; P = .004) models. In the Bayesian analysis, the posterior probability that severe hypercapnia was associated with ICU death was > 90% in 4 different priors, including a septic prior for this association. Sustained severe hypercapnia on day 5, defined as severe hypercapnia present from day 1 to day 5, was noted in 93 subjects (12%). After propensity score matching, severe hypercapnia on day 5 remained associated with ICU mortality (odds ratio 1.73, 95% CI 1.02-2.97; P = .047).

CONCLUSIONS

Severe hypercapnia was associated with mortality in subjects with ARDS who received lung-protective ventilation. Our results deserve further evaluation of the strategies and treatments that aim to control CO2 retention.

Brachial artery responses to acute hypercapnia: The roles of shear stress and adrenergic tone

NEW FINDINGS

What is the central question of this study? What are the contributions of shear stress and adrenergic tone to brachial artery vasodilatation during hypercapnia? What is the main finding and its importance? In healthy young adults, shear-mediated vasodilatation does not occur in the brachial artery during hypercapnia, as elevated α₁-adrenergic activity typically maintains vascular tone and offsets distal vasodilatation controlling flow.

ABSTRACT

We aimed to assess the shear stress dependency of brachial artery (BA) responses to hypercapnia, and the α₁-adrenergic restraint of these responses. We hypothesized that elevated shear stress during hypercapnia would cause BA vasodilatation, but where shear stress was prohibited (via arterial compression), the BA would not vasodilate (study 1); and, in the absence of α₁-adrenergic activity, blood flow, shear stress and BA vasodilatation would increase (study 2). In study 1, 14 healthy adults (7/7 male/female, 27 ± 4 years) underwent bilateral BA duplex ultrasound during hypercapnia (partial pressure of end-tidal carbon dioxide, +10.2 ± 0.3 mmHg above baseline, 12 min) via dynamic end-tidal forcing, and shear stress was reduced in one BA using manual compression (compression vs. control arm). Neither diameter nor blood flow was different between baseline and the last minute of hypercapnia (P = 0.423, P = 0.363, respectively) in either arm. The change values from baseline to the last minute, in diameter (%; P = 0.201), flow (ml/min; P = 0.234) and conductance (ml/min/mmHg; P = 0.503) were not different between arms. In study 2, 12 healthy adults (9/3 male/female, 26 ± 4 years) underwent the same design with and without α₁-adrenergic receptor blockade (prazosin; 0.05 mg/kg) in a placebo-controlled, double-blind and randomized design. BA flow, conductance and shear rate increased during hypercapnia in the prazosin control arm (interaction, P < 0.001), but in neither arm during placebo. Even in the absence of α₁-adrenergic restraint, downstream vasodilatation in the microvasculature during hypercapnia is insufficient to cause shear-mediated vasodilatation in the BA.

Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome (ARDS) occurs in up to 10% of patients with respiratory failure admitted through the emergency department. Use of noninvasive respiratory support has proliferated in recent years; clinicians must understand the relative merits and risks of these technologies and know how to recognize signs of failure. The cornerstone of ARDS care of the mechanically ventilated patient is low-tidal volume ventilation based on ideal body weight. Adjunctive therapies, such as prone positioning and neuromuscular blockade, may have a role in the emergency department management of ARDS depending on patient and department characteristics.

Carbon dioxide-dependent signal transduction in mammalian systems

Carbon dioxide (CO2) is a fundamental physiological gas known to profoundly influence the behaviour and health of millions of species within the plant and animal kingdoms in particular. A recent Royal Society meeting on the topic of 'Carbon dioxide detection in biological systems' was extremely revealing in terms of the multitude of roles that different levels of CO2 play in influencing plants and animals alike. While outstanding research has been performed by leading researchers in the area of plant biology, neuronal sensing, cell signalling, gas transport, inflammation, lung function and clinical medicine, there is still much to be learned about CO2-dependent sensing and signalling. Notably, while several key signal transduction pathways and nodes of activity have been identified in plants and animals respectively, the precise wiring and sensitivity of these pathways to CO2 remains to be fully elucidated. In this article, we will give an overview of the literature relating to CO2-dependent signal transduction in mammalian systems. We will highlight the main signal transduction hubs through which CO2-dependent signalling is elicited with a view to better understanding the complex physiological response to CO2 in mammalian systems. The main topics of discussion in this article relate to how changes in CO2 influence cellular function through modulation of signal transduction networks influenced by pH, mitochondrial function, adenylate cyclase, calcium, transcriptional regulators, the adenosine monophosphate-activated protein kinase pathway and direct CO2-dependent protein modifications. While each of these topics will be discussed independently, there is evidence of significant cross-talk between these signal transduction pathways as they respond to changes in CO2. In considering these core hubs of CO2-dependent signal transduction, we hope to delineate common elements and identify areas in which future research could be best directed.

Effects of hypercapnia in sepsis: A scoping review of clinical and pre-clinical data

BACKGROUND

Perform a scoping review of (1) pre-clinical studies testing the physiological effects of higher PaCO2 levels in the setting of sepsis models and (2) clinical investigations testing the effects of hypercapnia on clinical outcomes in mechanically ventilated patients with sepsis.

METHODS

We performed a search of CENTRAL, PUBMED, CINAHL, and EMBASE. Study inclusion criteria for pre-clinical studies were: (1) bacterial sepsis model (2) measurement of PaCO2 , and (3) comparison of outcome measure between different PaCO2 levels. Inclusion criteria for clinical studies were: (1) diagnosis of sepsis, (2) receiving invasive mechanical ventilation, (3) measurement of PaCO2 , and (4) comparison of outcomes between different PaCO2 levels. We performed a qualitative analysis to collate and summarize the physiological and clinical effects of hypercapnia according to the recommended methodology from the Cochrane Handbook.

RESULTS

Fifteen pre-clinical and nine clinical studies were included. Among pre-clinical studies, the individual studies found higher PaCO2 augments tissue blood flow and oxygenation, and attenuates inflammation and lung injury; however, all pre-clinical studies were found to have some degree of risk of bias. Six of the nine clinical studies were deemed to be good quality. Among clinical studies hypercapnia was associated with increased cerebral perfusion and oxygenation; however, there were conflicting results testing the association between hypercapnia and mortality.

CONCLUSION

While individual pre-clinical studies identified potential mechanisms by which changes in PaCO2 levels could affect pathophysiology in sepsis, there is a paucity of clinical data as to the optimal PaCO2 range, demonstrating a need for future research.

REGISTRATION

PROSPERO number CRD42018086703.

Sodium bicarbonate therapy for acute respiratory acidosis

PURPOSE OF REVIEW

Respiratory acidosis is commonly present in patients with respiratory failure. The usual treatment of hypercapnia is to increase ventilation. During the recent surge of COVID-19, respiratory acidosis unresponsive to increased mechanical ventilatory support was common. Increasing mechanical ventilation comes at the expense of barotrauma and hemodynamic compromise from increasing positive end-expiratory pressures or minute ventilation. Treating acute respiratory acidemia with sodium bicarbonate remains controversial.

RECENT FINDINGS

There are no randomized controlled trials of administration of sodium bicarbonate for respiratory acidemia. A recent review concluded that alkali therapy for mixed respiratory and metabolic acidosis might be useful but was based on the conflicting and not conclusive literature regarding metabolic acidosis. This strategy should not be extrapolated to treatment of respiratory acidemia. Low tidal volume ventilation in acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) has beneficial effects associated with permissive hypercapnia. Whether the putative benefits will be negated by administration of alkali is not known. Hypercapnic acidosis is well tolerated, with few adverse effects as long as tissue perfusion and oxygenation are maintained.

SUMMARY

There is a lack of clinical evidence that administration of sodium bicarbonate for respiratory acidosis has a net benefit; in fact, there are potential risks associated with it.

Veno-Venous Extracorporeal Lung Support as a Bridge to or Through Lung Volume Reduction Surgery in Patients with Severe Hypercapnia

Extracorporeal lung support (ECLS) represents an essential support tool especially for critically ill patients undergoing thoracic surgical procedures. Lung volume reduction surgery (LVRS) is an important treatment option for end-stage lung emphysema in carefully selected patients. Here, we report the efficacy of veno-venous ECLS (VV ECLS) as a bridge to or through LVRS in patients with end-stage lung emphysema and severe hypercapnia. Between January 2016 and May 2017, 125 patients with end-stage lung emphysema undergoing LVRS were prospectively enrolled into this study. Patients with severe hypercapnia caused by chronic respiratory failure were bridged to or through LVRS with low-flow VV ECLS (65 patients, group 1). Patients with preoperative normocapnia served as a control group (60 patients, group 2). In group 1, VV ECLS was implemented preoperatively in five patients and in 60 patients intraoperatively. Extracorporeal lung support was continued postoperatively in all 65 patients. Mean length of postoperative VV ECLS support was 3 ± 1 day. The 90 day mortality rate was 7.8% in group 1 compared with 5% in group 2 (p = 0.5). Postoperatively, a significant improvement was observed in quality of life, exercise capacity, and dyspnea symptoms in both groups. VV ECLS in patients with severe hypercapnia undergoing LVRS is an effective and well-tolerated treatment option. In particular, it increases the intraoperative safety, supports de-escalation of ventilatory strategies, and reduces the rate of postoperative complications in a cohort of patients considered "high risk" for LVRS in the current literature.

The effects of arterial CO2 on the injured brain: Two faces of the same coin

Serum levels of carbon dioxide (CO₂) closely regulate cerebral blood flow (CBF) and actively participate in different aspects of brain physiology such as hemodynamics, oxygenation, and metabolism. Fluctuations in the partial pressure of arterial CO₂ (PaCO₂) modify the aforementioned variables, and at the same time influence physiologic parameters in organs such as the lungs, heart, kidneys, and the gastrointestinal tract. In general, during acute brain injury (ABI), maintaining normal PaCO₂ is the target to be achieved. Both hypercapnia and hypocapnia may comprise secondary insults and should be avoided during ABI. The risks of hypocapnia mostly outweigh the potential benefits. Therefore, its therapeutic applicability is limited to transient and second-stage control of intracranial hypertension. On the other hand, inducing hypercapnia could be beneficial when certain specific situations require increasing CBF. The evidence supporting this claim is very weak. This review attempts providing an update on the physiology of CO₂, its risks, benefits, and potential utility in the neurocritical care setting.

Resuscitating the Crashing Pregnant Patient

Care of the critically ill pregnant patient is anxiety-provoking for those unprepared, as the emergency physician must consider not only the welfare of the immediate patient, but of the fetus as well. Familiarity with the physiologic changes of pregnancy and how they affect clinical presentation and management is key. Although some medications may be safer in pregnancy than others, stabilizing the pregnant patient is paramount. Emergency physicians should target pregnancy-specific oxygen and ventilation goals and hemodynamics and should be prepared to perform a perimortem cesarean section, should the mother lose pulses, to increase chances for maternal and fetal survival.

The Zentensivist Manifesto. Defining the Art of Critical Care

Evidence-based medicine asks us to integrate the best available evidence with clinical experience and patient values. In the modern intensive care unit, the primary focus is on complex technology and electronic health records, often away from the bedside. Excess interventionism is the norm. The term "intensivist" itself implies an intensive management strategy, which can lead us away from a patient-centered practice and toward iatrogenic harm. Under the hashtag #zentensivist, an international, multiprofessional group of clinicians has begun to discuss via Twitter how to apply key principles of history taking, physical examination, physiology, pharmacology, and clinical research in a competent, compassionate, and minimalist fashion. The term "zentensivist" intentionally combines concepts seemingly at odds-Zen philosophy and intensive care-to describe a holistic approach to the art of caring for the critically ill. We describe the key tenets of zentensivist practice and how we may inspire these actions in those we lead and educate.

Impact of low and high partial pressure of carbon dioxide on neuron-specific enolase derived from serum and cerebrospinal fluid in patients who underwent targeted temperature management after out-of-hospital cardiac arrest: A retrospective study

AIM

In a previous study, low and high-normal arterial carbon dioxide tension (PaCO₂) were not associated with serum neuron-specific enolase (NSE) in cardiac arrest survivors. We assessed the effect of PaCO₂ on NSE in cerebrospinal fluid (CSF) and serum.

METHODS

This was a retrospective study. PaCO₂ for the first 24 h was analysed in four means, qualitative exposure state (qES), time-weighted average (TWA), median, and minimum-maximum (Min-Max). These subgroups were divided into low (LCO₂) and high PaCO₂ (HCO₂) groups defined as PaCO₂ ≤ 35.3 and PaCO₂ > 43.5 mmHg, respectively. NSE was measured at 24, 48, and 72 h (sNSE_24,48,72 and cNSE_24,48,72) from return of spontaneous circulation (ROSC). The primary outcome was the association between PaCO₂ and the NSE measured at 24 h after ROSC.

RESULTS

Forty-two subjects (male, 33; 78.6%) were included in total cohort. PaCO₂ in TWA subgroup was associated with cNSE_24,48,72, while PaCO₂ in the other subgroup were only associated with cNSE₂₄. PaCO₂ and cNSE in qES subgroup showed good correlation (r = -0.61; p < 0.01), and in TWA, median, and Min-Max subgroup showed moderate correlations (r = -0.57, r = -0.48, and r = -0.60; p < 0.01). Contrastively, sNSE was not associated and correlated with PaCO₂ in all analysis. Poor neurological outcome in LCO₂ was significantly higher than HCO₂ in qES, TWA, and median subgroups (p < 0.01, p < 0.01, and p = 0.02).

CONCLUSION

Association was found between NSE and PaCO₂ using CSF, despite including normocapnic ranges; TWA of PaCO₂ may be most strongly associated with CSF NSE levels. A prospective, multi-centre study is required to confirm our results.

Spontaneous breathing anesthesia for cervical tracheal resection and reconstruction

Background

Spontaneous breathing anesthesia (SBA) may have advantages over general anesthesia for cervical tracheal resection and reconstruction (TRR), avoiding the difficulties and complication caused by endotracheal intubation and surgical cross-field intubation. This prospective study evaluates SBA for cervical TRR.

Methods

Date was obtained from 35 patients who had cervical TRR under SBA from May 2015 to March 2019. Intravenous sedation and ultrasound-guided bilateral superficial cervical plexus block (CPB) were applied to maintain effective analgesia and sedation.

Results

Thirty-two patients with tracheal tumors and 3 patients with post-intubation tracheal stenosis underwent TRR. After the airway was opened, 29 patients resumed stable spontaneous breathing, 1 patient needed high-frequency jet ventilation, and 1 patient needed anesthesia conversion for surgical reasons.

Conclusions

Spontaneous breathing anesthesia is feasible for the cervical TRR. It can be an alternative anesthetic technique for certain patients.

Increased effort during partial ventilatory support is not associated with lung damage in experimental acute lung injury

BACKGROUND

An on-going debate exists as to whether partial ventilatory support is lung protective in an acute phase of ARDS. So far, the effects of different respiratory efforts on the development of ventilator-associated lung injury (VALI) have been poorly understood. To test the hypothesis whether respiratory effort itself promotes VALI, acute lung injury (ALI) was induced in 48 Sprague Dawley rats by hydrochloric acid aspiration model. Hemodynamics, gas-exchange, and respiratory mechanics were measured after 4 h of ventilation in pressure control (PC), assist-control (AC), or pressure support with 100% (PS100), 60% (PS60), or 20% (PS20) of the driving pressure during PC. VALI was assessed by histological analysis and biological markers.

RESULTS

ALI was characterized by a decrease in PaO₂/FiO₂ from 447 ± 75 to 235 ± 90 mmHg (p < 0.001) and dynamic respiratory compliance from 0.53 ± 0.2 to 0.28 ± 0.1 ml/cmH₂O (p < 0.001). There were no differences in hemodynamics or respiratory function among groups at baseline or after 4 h of ventilation. The reduction of mechanical pressure support was associated with a compensatory increase in an inspiratory effort such that peak inspiratory transpulmonary pressures were equal in all groups. The diffuse alveolar damage score showed significant lung injury but was similar among groups. Pro- and anti-inflammatory proteins in the bronchial fluid were comparable among groups.

CONCLUSIONS

In experimental ALI in rodents, the respiratory effort was increased by reducing the pressure support during partial ventilatory support. In the presence of a constant peak inspiratory transpulmonary pressure, an increased respiratory effort was not associated with worsening ventilator-associated lung injury measured by histologic score and biologic markers.

Effects of hypercapnia in sepsis: protocol for a systematic review of clinical and preclinical data

BACKGROUND

Respiratory failure requiring mechanical ventilation is a common manifestation of end-organ damage among patients with sepsis and has a high morbidity and mortality rate, as well as substantial associated treatment costs. Considering the burden of this condition, there is great need to identify novel, pragmatic therapies to improve outcomes in this population. Hypercapnia has shown benefits in several different ex vivo and in vivo models of lung injury. However, it is currently unclear if hypercapnia can confer clinical benefit among patients with sepsis. The objective of this systematic review is to collate the biomedical literature of preclinical and clinical studies testing the effects of higher PaCO₂ levels in the setting of sepsis.

METHODS

We will perform a qualitative systematic review of preclinical and clinical studies evaluating the effects of hypercapnia in sepsis. We will search CENTRAL, PubMed, CINAHL, and EMBASE using a comprehensive strategy. We will screen the reference lists of the articles we select for inclusion to identify additional studies for potential inclusion. Two independent reviewers will review all search results. Upon inclusion of articles, we will extract data using a standardized form. We will use tables to describe the study type, population included, exposure and control groups, outcome measures, and effects of exposure on outcome measures compared to controls.

DISCUSSION

This systematic review aims to synthesize the world's literature on the effects of hypercapnia in the setting of sepsis. We expect this systematic review will find that majority of the studies will demonstrate a potential benefit of higher PaCO₂ levels in sepsis. The results of this systematic review will contribute to the understanding of the effects of hypercapnia in the setting of sepsis and promote future research of PaCO₂ management in mechanically ventilated patients with sepsis.

SYSTEMATIC REVIEW REGISTRATION

The systematic review is registered in the PROSPERO international prospective register of systematic review (PROSPERO # CRD42018086703 ).

Successful treatment of canine acute respiratory distress syndrome secondary to inhalant toxin exposure

OBJECTIVE

To describe the successful management of a dog with acute respiratory distress syndrome secondary to inhalant toxin exposure.

CASE SUMMARY

An 8-year-old male neutered Greyhound was referred with severe respiratory distress 56 hours after exposure to an aerosol toxicant. The patient developed respiratory difficulties requiring veterinary attention within 12 hours of initial exposure. Treatment at the referral hospital included mechanical ventilation and supportive care. The patient was discharged 5 days after admission to the referral hospital.

NEW OR UNIQUE INFORMATION

This is the first report, to the authors' knowledge, of canine acute respiratory distress syndrome secondary to inhalant toxin exposure not associated with smoke inhalation. The report summarizes the provided care and subsequent successful outcome.

Association of Hypercapnia and Hypercapnic Acidosis With Clinical Outcomes in Mechanically Ventilated Patients With Cerebral Injury

IMPORTANCE

Clinical studies investigating the effects of hypercapnia and hypercapnic acidosis in acute cerebral injury are limited. The studies performed so far have mainly focused on the outcomes in relation to the changes in partial pressure of carbon dioxide and pH in isolation and have not evaluated the effects of partial pressure of carbon dioxide and pH in conjunction.

OBJECTIVE

To review the association of compensated hypercapnia and hypercapnic acidosis during the first 24 hours of intensive care unit admission on hospital mortality in adult mechanically ventilated patients with cerebral injury.

DESIGN, SETTING, AND PARTICIPANTS

Multicenter, binational retrospective review of patients with cerebral injury (traumatic brain injury, cardiac arrest, and stroke) admitted to 167 intensive care units in Australia and New Zealand between January 2000 and December 2015. Patients were classified into 3 groups based on combination of arterial pH and arterial carbon dioxide (normocapnia and normal pH, compensated hypercapnia, and hypercapnic acidosis) during the first 24 hours of intensive care unit stay.

MAIN OUTCOMES AND MEASURES

Hospital mortality.

RESULTS

A total of 30 742 patients (mean age, 55 years; 21 827 men [71%]) were included. Unadjusted hospital mortality rates were highest in patients with hypercapnic acidosis. Multivariable logistic regression analysis and Cox proportional hazards analysis in 3 diagnostic categories showed increased odds of hospital mortality (cardiac arrest odds ratio [OR], 1.51; 95% CI, 1.34-1.71; stroke OR, 1.43; 95% CI, 1.27-1.6; and traumatic brain injury OR, 1.22; 95% CI, 1.06-1.42; P <.001) and hazard ratios (HR) (cardiac arrest HR, 1.23; 95% CI, 1.14-1.34; stroke HR, 1.3; 95% CI, 1.21-1.4; traumatic brain injury HR, 1.13; 95% CI, 1-1.27), in patients with hypercapnic acidosis compared with normocapnia and normal pH. There was no difference in mortality between patients who had compensated hypercapnia compared with patients who had normocapnia and normal pH. In patients with hypercapnic acidosis, the adjusted OR of hospital mortality increased with increasing partial pressure of carbon dioxide, while no such increase was noted in patients with compensated hypercapnia.

CONCLUSIONS AND RELEVANCE

Hypercapnic acidosis was associated with increased risk of hospital mortality in patients with cerebral injury. Hypercapnia, when compensated to normal pH during the first 24 hours of intensive care unit admission, may not be harmful in mechanically ventilated patients with cerebral injury.

Phosgene-induced acute lung injury (ALI): differences from chlorine-induced ALI and attempts to translate toxicology to clinical medicine

BACKGROUND

Phosgene (carbonyl dichloride) gas is an indispensable chemical inter-mediate used in numerous industrial processes. There is no clear consensus as to its time- and inhaled-dose-dependent etiopathologies and associated preventive or therapeutic treatment strategies.

METHODS

Cardiopulmonary function was examined in rats exposed by inhalation to the alveolar irritant phosgene or to the airway irritant chlorine during and following exposure. Terminal measurements focused on hematology, protein extravasation in bronchoalveolar lavage (BAL), and increased lung weight. Noninvasive diagnostic and prognostic endpoints in exhaled breath (carbon dioxide and nitric oxide) were used to detect the clinically occult stage of pulmonary edema.

RESULTS

The first event observed in rats following high but sublethal acute exposure to phosgene was the stimulation of alveolar nociceptive vagal receptors. This afferent stimulation resulted in dramatic changes in cardiopulmonary functions, ventilation: perfusion imbalances, and progressive pulmonary edema and phospholipoproteinosis. Hematology revealed hemoconcentration to be an early marker of pulmonary edema and fibrin as a discriminating endpoint that was positive for the airway irritant chlorine and negative for the alveolar irritant phosgene.

CONCLUSIONS

The application of each gas produced typical ALI/ARDS (acute lung injury/acute respiratory distress syndrome) characteristics. Phosgene-induced ALI showed evidence of persistent apnea periods, bradycardia, and shifts of vascular fluid from the peripheral to the pulmonary circulation. Carbon dioxide in expired gas was suggestive of increased ventilation dead space and appeared to be a harbinger of progressively developing lung edema. Treatment with the iNOS inhibitor aminoguanidine aerosol by inhalation reduced the severity of phosgene-induced ALI when applied at low dose-rates. Symptomatic treatment regimens were considered inferior to causal modes of treatment.

The Right Ventricle in ARDS

ARDS is associated with poor clinical outcomes, with a pooled mortality rate of approximately 40% despite best standards of care. Current therapeutic strategies are based on improving oxygenation and pulmonary compliance while minimizing ventilator-induced lung injury. It has been demonstrated that relative hypoxemia can be well tolerated, and improvements in oxygenation do not necessarily translate into survival benefit. Cardiac failure, in particular right ventricular dysfunction (RVD), is commonly encountered in moderate to severe ARDS and is reported to be one of the major determinants of mortality. The prevalence rate of echocardiographically evident RVD in ARDS varies across studies, ranging from 22% to 50%. Although there is no definitive causal relationship between RVD and mortality, severe RVD is associated with increased mortality. Factors that can adversely affect RV function include hypoxic pulmonary vasoconstriction, hypercapnia, and invasive ventilation with high driving pressure. It might be expected that early diagnosis of RVD would be of benefit; however, echocardiographic markers (qualitative and quantitative) used to prospectively evaluate the right ventricle in ARDS have not been tested in adequately powered studies. In this review, we examine the prognostic implications and pathophysiology of RVD in ARDS and discuss available diagnostic modalities and treatment options. We aim to identify gaps in knowledge and directions for future research that could potentially improve clinical outcomes in this patient population.

Arterial CO2 as a Potent Coronary Vasodilator: A Preclinical PET/MR Validation Study with Implications for Cardiac Stress Testing

Myocardial blood flow (MBF) is the critical determinant of cardiac function. However, its response to increases in partial pressure of arterial CO₂ (PaCO₂), particularly with respect to adenosine, is not well characterized because of challenges in blood gas control and limited availability of validated approaches to ascertain MBF in vivo. Methods: By prospectively and independently controlling PaCO₂ and combining it with ¹³N-ammonia PET measurements, we investigated whether a physiologically tolerable hypercapnic stimulus (∼25 mm Hg increase in PaCO₂) can increase MBF to that observed with adenosine in 3 groups of canines: without coronary stenosis, subjected to non-flow-limiting coronary stenosis, and after preadministration of caffeine. The extent of effect on MBF due to hypercapnia was compared with adenosine. Results: In the absence of stenosis, mean MBF under hypercapnia was 2.1 ± 0.9 mL/min/g and adenosine was 2.2 ± 1.1 mL/min/g; these were significantly higher than at rest (0.9 ± 0.5 mL/min/g, P < 0.05) and were not different from each other (P = 0.30). Under left-anterior descending coronary stenosis, MBF increased in response to hypercapnia and adenosine (P < 0.05, all territories), but the effect was significantly lower than in the left-anterior descending coronary territory (with hypercapnia and adenosine; both P < 0.05). Mean perfusion defect volumes measured with adenosine and hypercapnia were significantly correlated (R = 0.85) and were not different (P = 0.12). After preadministration of caffeine, a known inhibitor of adenosine, resting MBF decreased; and hypercapnia increased MBF but not adenosine (P < 0.05). Conclusion: Arterial blood CO₂ tension when increased by 25 mm Hg can induce MBF to the same level as a standard dose of adenosine. Prospectively targeted arterial CO₂ has the capability to evolve as an alternative to current pharmacologic vasodilators used for cardiac stress testing.

Management of blunt pulmonary injury

Thoracic injuries account for 25% of all civilian deaths. Blunt force injuries are a subset of thoracic injuries and include injuries of the tracheobronchial tree, pleural space, and lung parenchyma. Early identification of these injuries during initial assessment and resuscitation is essential to reduce associated morbidity and mortality rates. Management of airway injuries includes definitive airway control with identification and repair of tracheobronchial injuries. Management of pneumothorax and hemothorax includes pleural space drainage and control of ongoing hemorrhage, along with monitoring for complications such as empyema and chylothorax. Injuries of the lung parenchyma, such as pulmonary contusion, may require support of oxygenation and ventilation through both conventional and nonconventional mechanical ventilation strategies. General strategies to improve pulmonary function and gas exchange include balanced fluid resuscitation to targeted volume-based resuscitation end points, positioning therapy, and pain management.

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.

Applying a low-flow CO2 removal device in severe acute hypercapnic respiratory failure

A novel and portable extracorporeal CO2-removal device was evaluated to provide additional gas transfer, auxiliary to standard therapy in severe acute hypercapnic respiratory failure. A dual-lumen catheter was inserted percutaneously in five subjects (mean age 55 ± 0.4 years) and, subsequently, connected to the CO2-removal device. The median duration on support was 45 hours (interquartile range 26-156), with a blood flow rate of approximately 500 mL/min. The mean PaCO2 decreased from 95.8 ± 21.9 mmHg to 63.9 ± 19.6 mmHg with the pH improving from 7.11 ± 0.1 to 7.26 ± 0.1 in the initial 4 hours of support. Three subjects were directly weaned from the CO2-removal device and mechanical ventilation, one subject was converted to ECMO and one subject died following withdrawal of support. No systemic bleeding or device complications were observed. Low-flow CO2 removal adjuvant to standard therapy was effective in steadily removing CO2, limiting the progression of acidosis in subjects with severe acute hypercapnic respiratory failure.

High-frequency oscillation ventilation for hypercapnic failure of conventional ventilation in pulmonary acute respiratory distress syndrome

Introduction

High-frequency oscillation ventilation (HFOV) is regarded as particularly lung protective. Recently, HFOV has been shown to be not beneficial for acute respiratory distress syndrome (ARDS) patients in general. Due to its special physical effects, it could be beneficial, however, in inhomogeneous ARDS. This study evaluates the effect of HFOV on PaCO₂ removal in hypercapnic patients with ARDS of pulmonary origin.

Methods

Between October 2010 and June 2014 patients with ARDS of pulmonary origin with PaO₂/FiO₂ ratio >60 mmHg, but respiratory acidosis (pH <7.26) under optimized protective ventilation were switched to HFOV, using moderate airway pressure (adopting the mean airway pressure of the prior ventilation). Data from these patients were analyzed retrospectively; PaCO₂ and pH before, 1 h and 24 h after the start of HFOV were compared.

Results

Twenty-six patients with PaO₂/FiO₂ ratio 139 ± 49 and respiratory acidosis (PaCO₂ 68 ± 12 mmHg) were put on HFOV after 17 ± 22 h of conventional ventilation. Mean airway pressure was 19 cm H₂O (15 to 28). PaCO₂ decreased significantly: after 1 hour the mean difference was −14 ± 10 mmHg; P <0.01 and after 24 hours −17 ± 12 mmHg; P <0.01; n = 24. CO₂ clearance improved in all but two patients; in those, extracorporeal lung support was initiated. Oxygenation remained unchanged after 1 h and slightly increased after 24 h. No complications related to HFOV were observed. Twenty-two patients improved and could be weaned from HFOV. Twenty patients (77%) were alive on day 30.

Conclusions

HFOV could be a useful alternative in patients with ARDS of pulmonary origin with hypercapnic failure of lung-protective conventional ventilation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-015-0935-4) contains supplementary material, which is available to authorized users.

Veno-venous extracorporeal CO2 removal improves pulmonary hemodynamics in a porcine ARDS model

BACKGROUND

Protective lung ventilation is recommended in patients with acute respiratory distress syndrome (ARDS) to minimize additional injuries to the lung. However, hypercapnic acidosis resulting from ventilation at lower tidal volume enhances pulmonary hypertension and might induce right ventricular (RV) failure. We investigated if extracorporeal veno-venous CO2 removal therapy could have beneficial effects on pulmonary circulation and RV function.

METHODS

This study was performed on an experimental model of ARDS obtained in eight anaesthetized pigs connected to a volume-cycled ventilator. A micromanometer-tipped catheter was inserted into the main pulmonary artery and an admittance micromanometer-tipped catheter was inserted into the right ventricle. RV-arterial coupling was derived from RV pressure-volume loops. ARDS was obtained by repeated bronchoalveolar lavage. Protective ventilation was then achieved, and the pigs were connected to a pump-driven extracorporeal membrane oxygenator (PALP, Maquet, Germany) in order to achieve CO2 removal.

RESULTS

ARDS induced severe hypercapnic acidosis. Systolic pulmonary artery pressure significantly increased from 29.6±1.8 to 43.9±2.0 mmHg (P<0.001). After the PALP was started, acidosis was corrected and normocarbia was maintained despite protective ventilation. Pulmonary artery pressure significantly decreased to 31.6±3.2 mmHg (P<0.001) and RV-arterial coupling significantly improved (RV-arterial coupling index=1.03±0.33 vs. 0.55±0.41, P<0.05).

CONCLUSION

Veno-venous CO2 removal therapy enabled protective ventilation while maintaining normocarbia during ARDS. CO2 removal decreased pulmonary hypertension and improved RV function. This technique may be an effective lung- and RV-protective adjunct to mechanical ventilation.

Update on the role of extracorporeal CO₂ removal as an adjunct to mechanical ventilation in ARDS

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency Medicine 2015 and co-published as a series in Critical Care. Other articles in the series can be found online at http://ccforum.com/series/annualupdate2015. Further information about the Annual Update in Intensive Care and Emergency Medicine is available from http://www.springer.com/series/8901.

Management of Blunt Pulmonary Injury

Thoracic injuries account for 25% of all civilian deaths. Blunt force injuries are a subset of thoracic injuries and include injuries of the tracheobronchial tree, pleural space, and lung parenchyma. Early identification of these injuries during initial assessment and resuscitation is essential to reduce associated morbidity and mortality rates. Management of airway injuries includes definitive airway control with identification and repair of tracheobronchial injuries. Management of pneumothorax and hemothorax includes pleural space drainage and control of ongoing hemorrhage, along with monitoring for complications such as empyema and chylothorax. Injuries of the lung parenchyma, such as pulmonary contusion, may require support of oxygenation and ventilation through both conventional and nonconventional mechanical ventilation strategies. General strategies to improve pulmonary function and gas exchange include balanced fluid resuscitation to targeted volume-based resuscitation end points, positioning therapy, and pain management.

Permissive hypercapnia: Is there any upper limit?

A 19-year-old male presented with history of massive hemoptysis. The patient was kept on mechanical ventilation because of severe hypoxia. Lung protective ventilation with low tidal volume was given in view of very poor pulmonary compliance. During the course of treatment, the patient developed a very high CO₂ level of 373 mmHg. The patient was successfully weaned off on the 9^th day without any obvious adverse consequences.

Contributions of KATP and KCa channels to cerebral arteriolar dilation to hypercapnia in neonatal brain

Mechanisms by which Pco₂ controls cerebral vascular tone remain uncertain. We hypothesize that potassium channel activation contributes to the neonatal cerebrovascular dilation in response to increases in Paco₂. To test this hypothesis, experiments were performed on newborn pigs with surgically implanted, closed cranial windows. Hypercapnia was induced by ventilation with elevated Pco₂ gas in the absence and presence of the K_ATP channel inhibitor, glibenclamide and/or the K_Ca channel inhibitor, paxillin. Dilations to pinacidil, a selective K_ATP channel activator, without and with glibenclamide, were used to evaluate the efficacy of K_ATP channel inhibition. Dilations to NS1619, a selective K_Ca channel activator, without and with paxillin, were used to evaluate the efficacy of K_Ca channel inhibition. Cerebrovascular responses to the K_ATP and K_Ca channel activators, pinacidil and NS1619, respectively, cAMP‐dependent dilator, isoproterenol, and cGMP‐dependent dilator, sodium nitroprusside (SNP), were used to evaluate the selectivity of glibenclamide and paxillin. Glibenclamide blocked dilation to pinacidil, but did not inhibit dilations to NS1619, isoproterenol, or SNP. Glibenclamide prior to hypercapnia decreased mean pial arteriole dilation ~60%. Glibenclamide treatment during hypercapnia constricted arterioles ~35%. The level of hypercapnia, Paco₂ between 50 and 75 mmHg, did not appear to be involved in efficacy of glibenclamide in blocking dilation to Paco₂. Similarly to glibenclamide and K_ATP channel inhibition, paxillin blocked dilation to the K_Ca channel agonist, NS1619, and attenuated, but did not block, arteriolar dilation to hypercapnia. Treatment with both glibenclamide and paxillin abolished dilation to hypercapnia. Therefore, either glibenclamide or paxillin that block dilation to their channel agonists, pinacidil or NS1619, respectively, only partially inhibit dilation to hypercapnia. Block of both K_ATP and K_Ca channels completely prevent dilation hypercapnia. These data suggest hypercapnia activates both K_ATP and K_Ca channels leading to cerebral arteriolar dilation in newborn pigs.

Mechanisms by which Pco₂ controls vascular tone remain uncertain. We hypothesize K_ATP and K_Ca channel activation contributes to the neonatal cerebrovascular dilation in response to increases in Paco₂. Presented data support this hypothesis.

The role of inhaled nitric oxide beyond ARDS

Patients with traumatic brain injury complicated by acute respiratory distress syndrome (ARDS) are not uncommon in intensive care unit (ICU). The ventilatory management of patients combined with both of these catastrophic conditions is not straightforward. Evidence-based permissive hypercapnia strategy for ARDS could be fatal in patients with intracranial hypertension. Adjunctive use of inhaled nitric oxide (INO) is well-defined as a rescue therapy in severe ARDS, but its specific role in intracranial hypertension is somewhat uncertain. We report a case, which following traumatic brain injury developed both intracranial hypertension and ARDS. INO was given for ARDS, but coincidentally it also improved the raised intracranial pressure (ICP) and patient's neurological outcome. The case report will be followed by literature review on the role of INO in raised ICP.

Exploring for the safer ventilation method in laparoscopic urologic patients? Conventional or low tidal?

BACKGROUND

To study the effects of low tidal volume with positive end-expiratory pressure (PEEP) on arterial blood gases of patients undergoing laparoscopic urologic surgeries.

SUBJECTS AND METHODS

Eighty-six laparoscopic urologic patients were enrolled in this study. Patients were randomized into two groups according to the ventilatory settings. In the conventional group (Group C) (n=43), the tidal volume was 10 mL/kg, and the PEEP was set at 0 cm of H2O. In the low tidal volume with PEEP group (Group LP), the tidal volume was 6 mL/kg, with PEEP of 5 cm of H2O. In both groups total minute volume was 6 L/kg. Peak and plateau airway pressure (PPEAK and PPLAT, respectively) and arterial blood gases were recorded before pneumoperitoneum (PNP) (T1) and the first and third hour (T3) after PNP induction and also after extubation in the intensive care unit. Additionally, heart rate, mean arterial pressure, and peripheral O2 saturation of hemoglobin were recorded.

RESULTS

Heart rate, PPEAK, and PPLAT values were similar in both groups. Partial arterial O2 pressure values measured postoperatively were significantly higher in Group LP, whereas those measured before PNP induction were similar (P=.014 and P=.056, respectively). Compared with the baseline, partial arterial CO2 pressure values measured at T1 and at T3 after PNP induction were significantly higher in Group C than in Group LP (P<.001). The pH values of Group C at T1 and at T3 postoperatively were significantly lower than the values of Group LP (P<.001). Extubation times were significantly lower in Group LP.

CONCLUSIONS

The results of the present study suggest that low tidal volume with PEEP application may be a good alternative for preventing high CO2 levels and yielding better oxygenation and lower extubation times in patients undergoing prolonged laparoscopic urology.

Current perspectives for management of acute respiratory insufficiency in premature infants with acute respiratory syndrome

Current perspectives for management of acute respiratory insufficiency in premature infants with acute respiratory syndrome and the pathology of acute respiratory insufficiency in the preterm infant, including the current therapy modalities on disposition are presented. Since the therapeutical challenge and primary clinical goal are to normalize ventilation ratio and lung perfusion, when respiratory insufficiency occurs, it is very important to introduce the respiratory support as soon possible, in order to reduce development of pulmonary cyanosis and edema, and intrapulmonary or intracardial shunts. A characteristic respiratory instability that reflects through fluctuations in gas exchange and ventilation is often present in premature infants. Adapting the respiratory support on a continuous basis to the infant's needs is challenging and not always effective. Although a large number of ventilation strategies for the neonate are available, there is a need for additional consensus on management of acute respiratory distress syndrome in pediatric population lately redefined by Berlin definition criteria, in order to efficiently apply various modes of respiratory support in daily pediatrician clinical use.

Hypercapnia: is it protective in lung injury?

Hypercapnic acidosis has been regarded as a tolerated side effect of protective lung ventilation strategies. Various in vivo and ex vivo animal studies have shown beneficial effects in acute lung injury setting, but some recent work raised concerns about its anti-inflammatory properties. This mini-review article aims to expand the potential clinical spectrum of hypercapnic acidosis in critically ill patients with lung injury. Despite the proven benefits of hypercapnic acidosis, further safety studies including dose-effect, level-and-onset of anti-inflammatory effect, and safe applicability period need to be performed in various models of lung injury in animals and humans to further elucidate its protective role.

Measuring cerebrovascular reactivity: what stimulus to use?

Cerebrovascular reactivity is the change in cerebral blood flow in response to a vasodilatory or vasoconstrictive stimulus. Measuring variations of cerebrovascular reactivity between different regions of the brain has the potential to not only advance understanding of how the cerebral vasculature controls the distribution of blood flow but also to detect cerebrovascular pathophysiology. While there are standardized and repeatable methods for estimating the changes in cerebral blood flow in response to a vasoactive stimulus, the same cannot be said for the stimulus itself. Indeed, the wide variety of vasoactive challenges currently employed in these studies impedes comparisons between them. This review therefore critically examines the vasoactive stimuli in current use for their ability to provide a standard repeatable challenge and for the practicality of their implementation. Such challenges include induced reductions in systemic blood pressure, and the administration of vasoactive substances such as acetazolamide and carbon dioxide. We conclude that many of the stimuli in current use do not provide a standard stimulus comparable between individuals and in the same individual over time. We suggest that carbon dioxide is the most suitable vasoactive stimulus. We describe recently developed computer-controlled MRI compatible gas delivery systems which are capable of administering reliable and repeatable vasoactive CO2 stimuli.

Low-flow CO₂ removal integrated into a renal-replacement circuit can reduce acidosis and decrease vasopressor requirements

INTRODUCTION

Lung-protective ventilation in patients with ARDS and multiorgan failure, including renal failure, is often paralleled with a combined respiratory and metabolic acidosis. We assessed the effectiveness of a hollow-fiber gas exchanger integrated into a conventional renal-replacement circuit on CO₂ removal, acidosis, and hemodynamics.

METHODS

In ten ventilated critically ill patients with ARDS and AKI undergoing renal- and respiratory-replacement therapy, effects of low-flow CO₂ removal on respiratory acidosis compensation were tested by using a hollow-fiber gas exchanger added to the renal-replacement circuit. This was an observational study on safety, CO₂-removal capacity, effects on pH, ventilator settings, and hemodynamics.

RESULTS

CO₂ elimination in the low-flow circuit was safe and was well tolerated by all patients. After 4 hours of treatment, a mean reduction of 17.3 mm Hg (-28.1%) pCO₂ was observed, in line with an increase in pH. In hemodynamically instable patients, low-flow CO₂ elimination was paralleled by hemodynamic improvement, with an average reduction of vasopressors of 65% in five of six catecholamine-dependent patients during the first 24 hours.

CONCLUSIONS

Because no further catheters are needed, besides those for renal replacement, the implementation of a hollow-fiber gas exchanger in a renal circuit could be an attractive therapeutic tool with only a little additional trauma for patients with mild to moderate ARDS undergoing invasive ventilation with concomitant respiratory acidosis, as long as no severe oxygenation defects indicate ECMO therapy.

CO2 blood oxygen level-dependent MR mapping of cerebrovascular reserve in a clinical population: safety, tolerability, and technical feasibility

PURPOSE

To evaluate the safety, tolerability, and technical feasibility of mapping cerebrovascular reactivity (CVR) in a clinical population by using a precise prospectively targeted CO(2) stimulus and blood oxygen level-dependent (BOLD) magnetic resonance (MR) imaging.

MATERIALS AND METHODS

A chart review was performed of all CVR studies from institutional review board-approved projects at a tertiary care hospital between January 1, 2006, and December 1, 2010. Informed consent was obtained. Records were searched for the incidence of adverse events and failed examinations. CVR maps were evaluated for diagnostic quality by two blinded observers and were categorized as good, diagnostic but suboptimal, or nondiagnostic. Outcomes were presented as raw data and descriptive statistics (means ± standard deviations). Intraclass correlation coefficient was used to determine interobserver variability.

RESULTS

Four hundred thirty-four consecutive CVR examinations from 294 patients (51.8% female patients) were studied. Patient age ranged from 9 to 88 years (mean age, 45.9 years ± 20.6). Transient symptoms, such as shortness of breath, headache, and dizziness, were reported in 48 subjects (11.1% of studies) during hypercapnic phases only. There were no neurologic ischemic events, myocardial infarctions, or other major complications. The success rate in generating CVR maps was 83.9% (364 of 434). Of the 70 (16.1%) failed examinations, 25 (35.7%) were due to discomfort; eight (11.4%), to head motion; two (2.9%), to inability to cooperate; seven (10.0%), to technical difficulties with equipment; and 28 (40.0%), to unknown or unspecified conditions. Among the 364 remaining successful examinations, good quality CVR maps were obtained in 340 (93.4%); diagnostic but suboptimal, in 12 (3.3%); and nondiagnostic, in 12 (3.3%).

CONCLUSION

CVR mapping by using a prospectively targeted CO(2) stimulus and BOLD MR imaging is safe, well tolerated, and technically feasible in a clinical patient population.

Hypercapnic respiratory acidosis: a protective or harmful strategy for critically ill newborn foals?

This paper reviews both the beneficial and adverse effects of permissive hypercapnic respiratory acidosis in critically ill newborn foals. It has been shown that partial carbon dioxide pressure (PCO2) above the traditional safe range (hypercapnia), has beneficial effects on the physiology of the respiratory, cardiovascular, and nervous system in neonates. In human neonatal critical care medicine permissive hypercapnic acidosis is generally well-tolerated by patients and is more beneficial to their wellbeing than normal carbon dioxide (CO2) pressure or normocapnia. Even though adverse effects of hypercapnia have been reported, especially in patients with central nervous system pathology and/or chronic infection, critical care clinicians often artificially increase PCO2 to take advantage of its positive effects on compromised neonate tissues. This is referred to as therapeutic hypercapnia. Hypercapnic respiratory acidosis is common in critically ill newborn foals and has traditionally been considered as not beneficial. A search of online scientific databases was conducted to survey the literature on the effects of hypercapnia in neonates, with emphasis on newborn foals. The dynamic status of safety levels of PCO2 and data on the effectiveness of different carbon dioxide levels are not available for newborn foals and should be scientifically determined. Presently, permissive hypercapnia should be implemented or tolerated cautiously in compromised newborn foals and its use should be based on relevant data from adult horses and other species.

Clinical effectiveness and safety of permissive hypercapnia

Experimental and clinical data indicate that ventilator strategies with permissive hypercapnia may reduce lung injury by a variety of mechanisms. Seven randomized controlled trials in preterm neonates suggest that permissive hypercapnia started early, before the initiation of mechanical ventilation (in conjunction with continuous positive airway pressure), followed by prolonged permissive hypercapnia if mechanical ventilation is needed is an alternative to early ventilation and surfactant. Permissive hypercapnia may improve pulmonary outcomes and survival.

Low Tidal Volume Ventilation in Patients without Acute Respiratory Distress Syndrome: A Paradigm Shift in Mechanical Ventilation

Protective ventilation with low tidal volume has been shown to reduce morbidity and mortality in patients suffering from acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). Low tidal volume ventilation is associated with particular clinical challenges and is therefore often underutilized as a therapeutic option in clinical practice. Despite some potential difficulties, data have been published examining the application of protective ventilation in patients without lung injury. We will briefly review the physiologic rationale for low tidal volume ventilation and explore the current evidence for protective ventilation in patients without lung injury. In addition, we will explore some of the potential reasons for its underuse and provide strategies to overcome some of the associated clinical challenges.