Permissive hypercapnia in neonates: the case of the good, the bad, and the ugly

Hypercapnia Causes Injury of the Cerebral Cortex and Cognitive Deficits in Newborn Piglets

In critically ill newborns, exposure to hypercapnia (HC) is common and often accepted in neonatal intensive care units to prevent severe lung injury. However, as a "safe" range of arterial partial pressure of carbon dioxide levels in neonates has not been established, the potential impact of HC on the neurodevelopmental outcomes in these newborns remains a matter of concern. Here, in a newborn Yorkshire piglet model of either sex, we show that acute exposure to HC induced persistent cortical neuronal injury, associated cognitive and learning deficits, and long-term suppression of cortical electroencephalogram frequencies. HC induced a transient energy failure in cortical neurons, a persistent dysregulation of calcium-dependent proapoptotic signaling in the cerebral cortex, and activation of the apoptotic cascade, leading to nuclear deoxyribonucleic acid fragmentation. While neither 1 h of HC nor the rapid normalization of HC was associated with changes in cortical bioenergetics, rapid resuscitation resulted in a delayed onset of synaptosomal membrane lipid peroxidation, suggesting a dissociation between energy failure and the occurrence of synaptosomal lipid peroxidation. Even short durations of HC triggered biochemical responses at the subcellular level of the cortical neurons resulting in altered cortical activity and impaired neurobehavior. The deleterious effects of HC on the developing brain should be carefully considered as crucial elements of clinical decisions in the neonatal intensive care unit.

Carbon dioxide enhances sulphur-selective conjugate addition reactions

Sulphur-selective conjugate addition reactions play a central role in synthetic chemistry and chemical biology. A general tool for conjugate addition reactions should provide high selectivity in the presence of competing nucleophilic functional groups, namely nitrogen nucleophiles. We report CO₂-mediated chemoselective S-Michael addition reactions where CO₂ can reversibly control the reaction pHs, thus providing practical reaction conditions. The increased chemoselectivity for sulphur-alkylation products was ascribed to CO₂ as a temporary and traceless protecting group for nitrogen nucleophiles, while CO₂ efficiently provide higher conversion and selectivity sulphur nucleophiles on peptides and human serum albumin (HSA) with various electrophiles. This method offers simple reaction conditions for cysteine modification reactions when high chemoselectivity is required.

Transcutaneous carbon dioxide pattern and trend over time in preterm infants

BACKGROUND

Chronic lung disease remains a burden for extremely preterm infants. The changes in ventilation over time and optimal ventilatory management remains unknown. Newer, non-invasive technologies provide insight into these patterns.

METHODS

This single-center prospective cohort study enrolled infants ≤32 0/7 weeks. We obtained epochs of transcutaneous carbon dioxide (TcCO₂) measurements twice each week to describe the pattern of hypercarbia throughout their hospitalization.

RESULTS

Patterns of hypercarbia varied based on birth gestational age and post-menstrual age (PMA) (p = 0.03), regardless of respiratory support. Infants receiving the most respiratory support had values 16-21 mmHg higher than those on room air (p < 0.001). Infants born at the youngest gestational ages had the greatest total change but the rate of change was slower (p = 0.049) compared to infants born at later gestational ages. All infants had TcCO₂ values stabilize by 31-33 weeks PMA, when values were not significantly different compared to discharge. No rebound was observed when infants weaned off invasive support.

CONCLUSIONS

Hypercarbia improves as infants approached 31-33 weeks PMA. Hypercarbia was the highest in the most immature infants and improved with age and growth despite weaning respiratory support.

IMPACT

This study describes the evolution of hypercarbia as very preterm infants grow and develop. The pattern of ventilation is significantly different depending on the gestational age at birth and post-menstrual age. Average transcutaneous carbon dioxide (TCO₂) decreased over time as infants became more mature despite weaning respiratory support. This improvement was most significant in infants born at the lowest gestational ages.

Defining the momiome: Promiscuous information transfer by mobile mitochondria and the mitochondrial genome

Mitochondria are complex intracellular organelles that have long been identified as the powerhouses of eukaryotic cells because of the central role they play in oxidative metabolism. A resurgence of interest in the study of mitochondria during the past decade has revealed that mitochondria also play key roles in cell signaling, proliferation, cell metabolism and cell death, and that genetic and/or metabolic alterations in mitochondria contribute to a number of diseases, including cancer. Mitochondria have been identified as signaling organelles, capable of mediating bidirectional intracellular information transfer: anterograde (from nucleus to mitochondria) and retrograde (from mitochondria to nucleus). More recently, evidence is now building that the role of mitochondria extends to intercellular communication as well, and that the mitochondrial genome (mtDNA) and even whole mitochondria are indeed mobile and can mediate information transfer between cells. We define this promiscuous information transfer function of mitochondria and mtDNA as "momiome" to include all mobile functions of mitochondria and the mitochondrial genome. Herein, we review the "momiome" and explore its role in cancer development, progression, and treatment.

Lung-protective ventilatory strategies in intubated preterm neonates with RDS

This article provides a narrative review of lung-protective ventilatory strategies (LPVS) in intubated preterm infants with RDS. A description of strategies is followed by results on short-and long-term respiratory and neurodevelopmental outcomes. Strategies will include patient-triggered or synchronized ventilation, volume targeted ventilation, the technique of intubation, surfactant administration and rapid extubation to NCPAP (INSURE), the open lung concept, strategies of high-frequency ventilation, and permissive hypercapnia. Based on this review single recommendations on optimal LPVS cannot be made. Combinations of several strategies, individually applied, most probably minimize or avoid potential serious respiratory and cerebral complications like bronchopulmonary dysplasia and cerebral palsy.

A newborn tolerated severe hypercapnia during general anesthesia: a case report

Introduction

Severe hypercapnia is a rare but harmful complication of general anesthesia. We report the case of a newborn who developed severe hypercapnia with unknown reasons during general anesthesia but recovered well. This report will advance our understanding about the causes of severe hypercapnia during anesthesia, the possible compensatory mechanisms and the characteristics of neonatal respiratory physiology and intracellular buffering systems.

Case presentation

A 21-day-old Chinese baby girl who had an incarcerated hernia received an emergent exploratory operation under general anesthesia. She developed severe hypercapnia during surgery for unclear reasons. Arterial blood gas revealed a PCO₂ of 149mmHg. Troubleshooting and relevant measures were taken, but the level of CO₂ did not decrease. In spite of the high level of PCO₂, the newborn recovered well without any complications.

Conclusions

Neonates are vulnerable to hypercapnia during anesthesia for their characteristic respiratory physiology. Heat and moisture exchange should be used with caution in newborns under general anesthesia as it can increase dead space. Intracellular buffering systems play an important role in tolerating severe hypercapnia. Although this case raised a great challenge to the homeostatic mechanism of the body, measures should be taken to maintain PCO₂ values around the clinically acceptable level.

Dual-responsive nanoparticles that aggregate under the simultaneous action of light and CO2

Metallic nanoparticles co-functionalised with monolayers of UV- and CO₂-sensitive ligands were prepared and shown to respond to these two types of stimuli reversibly and in an orthogonal fashion.

NICU bedside caregivers sustain process improvement and decrease incidence of bronchopulmonary dysplasia in infants < 30 weeks gestation

BACKGROUND

The objective of this study was to investigate whether a respiratory care bundle, implemented through participation in the Vermont Oxford Network-sponsored Neonatal Intensive Care Quality Improvement Collaborative (NIC/Q 2005) and primarily dependent on bedside caregivers, resulted in sustained decrease in the incidence of bronchopulmonary dysplasia (BPD) in infants < 30 wk gestation.

METHODS

A retrospective cohort study was conducted. Infants inborn between 23 wk and 29 wk + 6 d of gestation were included. Patients with congenital heart disease, significant congenital or lung anomalies, or death before intubation were excluded. Four time periods (T1-T4) were identified: T1: September 1, 2002 to August 31, 2004; T2: September 1, 2004 to August 31, 2006; T3: September 1, 2006 to August 31, 2008; T4: September 1, 2008 to August 31, 2010.

RESULTS

A total of 1,050 infants were included in the study. BPD decreased significantly in T3 post-implementation of the respiratory bundle compared with T1 (29.9% vs 51.2%, respectively; adjusted odds ratio [aOR] = 0.06 [95% CI 0.03-0.13], P = < .001). The decrease was not sustained into T4. There was a significant increase in the rate of BPD-free survival to discharge in T3 compared with T1 (53.1% vs 47%; aOR = 1.68 [95% CI 1.11-2.56], P = .01) that was also not sustained. The rate of infants requiring O2 at 28 d of life decreased significantly in T3 versus T1 (40.3% vs 69.9%, respectively; aOR = 0.12 [95% CI 0.07-0.20], P = < .001). Increases in the rate of surfactant administration by 1 h of life and rate of caffeine use were observed in T4 versus T1, respectively. There was a significant decrease in median ventilator days and a significant increase in the median number of noninvasive CPAP days throughout the study period.

CONCLUSIONS

In this study, implementation of a respiratory bundle managed primarily by nurses and respiratory therapists was successful in increasing the use of less invasive respiratory support in a consistent manner among very low birthweight infants at a single institution. However, this study and others have failed to show sustained improvement in the incidence of BPD despite sustained process change.

Critical care in pregnancy--is it different?

In the first part of this review, the epidemiology of obstetric critical care is discussed. This includes the incidence of severe morbidity in pregnancy, identification of critically ill and potentially critically ill patients, the incidence of obstetric ICU admissions, the type of critical illness by stage of pregnancy, ICU admission diagnoses, the severity of illness in obstetric ICU patients compared to non-obstetric patients, ICU mortality of obstetric patients, the ICU proportion of total maternal mortality, and the causes of death for obstetric patients in ICU. In the second part, the management of obstetric patients who happen to be admitted to a general ICU is discussed. Rather than focusing on the management of particular obstetric conditions, general principles of ICU management will be discussed as applied to obstetric ICU patients. These include drug safety, monitoring the fetus, management of the airway, sedation, muscle relaxation, ventilation, cardiovascular support, thromboprophylaxis, and radiology and ethical issues.

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.

Protein kinase A-Iα regulates Na,K-ATPase endocytosis in alveolar epithelial cells exposed to high CO(2) concentrations

Elevated concentrations of CO2 (hypercapnia) lead to alveolar epithelial dysfunction by promoting Na,K-ATPase endocytosis. In the present report, we investigated whether the CO2/HCO3(-) activated soluble adenylyl cyclase (sAC) regulates this process. We found that hypercapnia increased the production of cyclic adenosine monophosphate (cAMP) and stimulated protein kinase A (PKA) activity via sAC, which was necessary for Na,K-ATPase endocytosis. During hypercapnia, cAMP was mainly produced in specific microdomains in the proximity of the plasma membrane, leading to PKA Type Iα activation. In alveolar epithelial cells exposed to high CO2 concentrations, PKA Type Iα regulated the time-dependent phosphorylation of the actin cytoskeleton component α-adducin at serine 726. Cells expressing small hairpin RNA for PKAc, dominant-negative PKA Type Iα, small interfering RNA for α-adducin, and α-adducin with serine 726 mutated to alanine prevented Na,K-ATPase endocytosis. In conclusion, we provide evidence for a new mechanism by which hypercapnia via sAC, cAMP, PKA Type Iα, and α-adducin regulates Na,K-ATPase endocytosis in alveolar epithelial cells.

Outcomes of preterm infants <29 weeks gestation over 10-year period in Canada: a cause for concern?

OBJECTIVE

To compare risk-adjusted changes in outcomes of preterm infants <29 weeks gestation born in 1996 to 1997 with those born in 2006 to 2007.

STUDY DESIGN

Observational retrospective comparison of data from 15 units that participated in the Canadian Neonatal Network during 1996 to 1997 and 2006 to 2007 was performed. Rates of mortality and common neonatal morbidities were compared after adjustment for confounders.

RESULT

Data on 1897 infants in 1996 to 1997 and 1866 infants in 2006 to 2007 were analyzed. A higher proportion of patients in the later cohort received antenatal steroids and had lower acuity of illness on admission. Unadjusted analyses revealed reduction in mortality (unadjusted odds ratio (UAOR): 0.83, 95% confidence interval (CI): 0.63, 0.98), severe retinopathy (UAOR: 0.68, 95% CI: 0.50 to 0.92), but increase in bronchopulmonary dysplasia (UAOR: 1.61, 95% CI: 1.39 to 1.86) and patent ductus arteriosus (UAOR: 1.22, 95% CI: 1.07 to 1.39). Adjusted analyses revealed increases in the later cohort for bronchopulmonary dysplasia (adjusted odds ratio (AOR): 1.88, 95% CI: 1.60 to 2.20) and severe neurological injury (AOR: 1.49, 95% CI: 1.22 to 1.80). However, the ascertainment methods for neurological findings and ductus arteriosus differed between the two time periods.

CONCLUSION

Improvements in prenatal care has resulted in improvement in the quality of care, as reflected by reduced severity of illness and mortality. However, after adjustment of prenatal factors, no improvement in any of the outcomes was observed and on the contrary bronchopulmonary dysplasia increased. There is need for identification and application of postnatal strategies to improve outcomes of extreme preterm infants.

Elevated CO(2) levels cause mitochondrial dysfunction and impair cell proliferation

Elevated CO(2) concentrations (hypercapnia) occur in patients with severe lung diseases. Here, we provide evidence that high CO(2) levels decrease O(2) consumption and ATP production and impair cell proliferation independently of acidosis and hypoxia in fibroblasts (N12) and alveolar epithelial cells (A549). Cells exposed to elevated CO(2) died in galactose medium as well as when glucose-6-phosphate isomerase was knocked down, suggesting mitochondrial dysfunction. High CO(2) levels led to increased levels of microRNA-183 (miR-183), which in turn decreased expression of IDH2 (isocitrate dehydrogenase 2). The high CO(2)-induced decrease in cell proliferation was rescued by α-ketoglutarate and overexpression of IDH2, whereas proliferation decreased in normocapnic cells transfected with siRNA for IDH2. Also, overexpression of miR-183 decreased IDH2 (mRNA and protein) as well as cell proliferation under normocapnic conditions, whereas inhibition of miR-183 rescued the normal proliferation phenotype in cells exposed to elevated levels of CO(2). Accordingly, we provide evidence that high CO(2) induces miR-183, which down-regulates IDH2, thus impairing mitochondrial function and cell proliferation. These results are of relevance to patients with hypercapnia such as those with chronic obstructive pulmonary disease, asthma, cystic fibrosis, bronchopulmonary dysplasia, and muscular dystrophies.

The management of the critically ill obstetric patient

Hypertensive disorders, postpartum hemorrhage, and sepsis are the most common indications for intensive care unit admission among obstetric patients. In general, ICU mortality is low, and better than would be predicted using available mortality prediction tools. Provision of care to this special population requires an intimate understanding of physiologic changes that occur during pregnancy. Clinicians must be aware of the way various diagnostic and treatment choices can affect the mother and fetus. Most clinically necessary radiographic tests can be safely performed and fall under the maternal radiation exposure limit of less than 0.05 Gray (Gy). Careful attention must be paid to acid-base status, oxygenation, and ventilation when faced with respiratory failure necessitating intubation. Cesarean delivery can be justified after 4 minutes of cardiac arrest and may improve fetal and maternal outcomes. The treatment of obstetric patients in the ICU introduces complexities and challenges that may be unfamiliar to many critical care physicians; teamwork and communication with obstetricians is crucial.

Impact of implementing 5 potentially better respiratory practices on neonatal outcomes and costs

OBJECTIVE

We implemented 5 potentially better practices to limit mechanical ventilation (MV), supplemental oxygen, and bronchopulmonary dysplasia in newborn infants born before 33 weeks' gestation.

METHODS

The methods used in this study included (1) exclusive use of bubble continuous positive airway pressure (bCPAP), (2) provision of bCPAP in the delivery room, (3) strict intubation criteria, (4) strict extubation criteria, and (5) prolonged CPAP to avoid supplemental oxygen. We excluded outborn infants and those with major anomalies and obstetric complications from analysis.

RESULTS

Demographics were similar in 61 infants born before and 60 born after implementation. For infants born at 26 to 32(6/7) weeks' gestation, intubation (first 72 hours) decreased from 52% to 11% (P < .0001) and surfactant use decreased from 48% to 14% (P=.0001). In all infants, the mean ± SD fraction of inspired oxygen requirement (first 24 hours) decreased from 0.27 ± 0.08 to 0.24 ± 0.05 (P=.0005), days of oxygen decreased from 23.5 ± 44.5 to 9.3 ± 22.0 (P=.04), and days of MV decreased from 8.8 ± 27.8 to 2.2 ± 6.2 (P=.005). Hypotension decreased from 33% to 15% (P=.03). The percentage of infants with bronchopulmonary dysplasia was 17% before and 8% after (P=.27). Nurse staffing ratios remained unchanged.

CONCLUSIONS

Implementation of these potentially better practices reduced the need for MV, surfactant, and supplemental oxygen as well as reduced hypotension among infants born before 33 weeks' gestation without adverse consequences. The costs for equipment and surfactant were lower.

Therapeutic effects of hypercapnia on chronic lung injury and vascular remodeling in neonatal rats

Permissive hypercapnia, achieved using low tidal volume ventilation, has been an effective protective strategy in patients with acute respiratory distress syndrome. To date, no such protective effect has been demonstrated for the chronic neonatal lung injury, bronchopulmonary dysplasia. The objective of our study was to determine whether evolving chronic neonatal lung injury, using a rat model, is resistant to the beneficial effects of hypercapnia or simply requires a less conservative approach to hypercapnia than that applied clinically to date. Neonatal rats inhaled air or 60% O2 for 14 days with or without 5.5% CO2. Lung parenchymal neutrophil and macrophage numbers were significantly increased by hyperoxia alone, which was associated with interstitial thickening and reduced secondary crest formation. The phagocyte influx, interstitial thickening, and impaired alveolar formation were significantly attenuated by concurrent hypercapnia. Hyperoxic pups that received 5.5% CO2 had a significant increase in alveolar number relative to air-exposed pups. Increased tyrosine nitration, a footprint for peroxynitrite-mediated reactions, arteriolar medial wall thickening, and both reduced small peripheral pulmonary vessel number and VEGF and angiopoietin-1 (Ang-1) expression, which were observed with hyperoxia, was attenuated by concurrent hypercapnia. We conclude that evolving chronic neonatal lung injury in a rat model is responsive to the beneficial effects of hypercapnia. Inhaled 5.5% CO2 provided a significant degree of protection against parenchymal and vascular injury in an animal model of chronic neonatal lung injury likely due, at least in part, to its inhibition of a phagocyte influx.

Hypercapnia and the neonate

'Permissive hypercapnia' is a familiar term in neonatal intensive care, given the widespread adoption of low-tidal-volume ventilation strategies applied with the goal of decreasing respiratory morbidity. Recent evidence suggesting that hypercapnic acidosis may itself have protective effects on the lung and other organs has led to the coining of a new phrase, 'therapeutic hypercapnia', which also encompasses the use of supplemental inspired CO(2).

CONCLUSION

Experimental evidence suggests that mild-moderate hypercapnia can improve tissue oxygenation and perfusion, which may ameliorate injury to the immature lung and brain. However, hypercapnia may also be associated with adverse outcomes, and the range of PaCO(2) levels that are both safe and effective for specific subsets of neonates has yet to be determined.

Permissive hypercapnia and risk for brain injury and developmental impairment

OBJECTIVE

Permissive hypercapnia is a respiratory-care strategy that is used to reduce the risk for lung injury. The goal of this study was to evaluate whether permissive hypercapnia is associated with higher risk for intraventricular hemorrhage and early childhood behavioral and functional problems than normocapnia among very low birth weight infants.

METHODS

Very low birth weight infants from a statewide cohort were eligible for this study when they were born at <32 weeks' gestational age and survived at least 24 hours. Infants were classified as receiving a permissive hypercapnia, normocapnia, or unclassifiable respiratory strategy during the first 24 hours after birth according to an algorithm based on Pco(2) values and respiratory-treatment decisions that were abstracted from medical charts. Intraventricular hemorrhage diagnosis was also abstracted from the medical chart. Behavioral and functional outcomes were assessed by parent interview at 2 to 3 years. Logistic regression was used to evaluate the relationship between intraventricular hemorrhage and respiratory strategy; ordinary linear regression was used to evaluate differences in behavior and function scores between children by respiratory strategy.

RESULTS

Infants who received a permissive hypercapnia strategy were not more likely to have intraventricular hemorrhage than those with normocapnia. There were no differences in any of the behavioral or functional scores among children according to respiratory strategy. There was a significant interaction between care strategy and 1-minute Apgar score, indicating that infants with lower Apgar scores may be at higher risk for intraventricular hemorrhage with permissive hypercapnia.

CONCLUSIONS

This study suggests that permissive hypercapnia does not increase risk for brain injury and impairment among very low birth weight children. The interaction between respiratory strategy and Apgar score is a potential worrisome exception to this conclusion. Future research should further evaluate the effect of elevated Pco(2) levels among those who are sickest at birth.

A randomized trial of delayed extubation for the reduction of reintubation in extremely preterm infants

OBJECTIVE

To compare immediate extubation versus delayed extubation after 36 hr in extremely low-birth weight infants receiving gentle mechanical ventilation and perinatal lung protective interventions. Our hypothesis was that a delayed extubation in this setting would decrease the rate of reintubation. STUDY DESIGN/METHODOLOGY: A prospective, unmasked, randomized, controlled trial to compare immediate extubation and delayed extubation after 36 hr. Optimized ventilation in both groups included continuous tracheal gas insufflation (CTGI), prophylactic surfactant administration, low oxygen saturation target and moderate permissive hypercapnia. Successful extubation for at least 7 days was the primary criterion and ventilatory support requirements until 36 weeks gestational age the main secondary criteria.

PATIENT SELECTION

Eighty-six infants under 28 weeks gestational age in a single neonatal intensive tertiary care unit.

RESULTS

Delayed extubation (1.9 +/- 0.8 days vs. 0.5 +/- 0.7 days) did not improve the rate of successful extubation but had no long-term adverse effects. CTGI and the lung protective strategy we describe resulted in a very gentle ventilation. The rate of survival without bronchopulmonary dysplasia (BPD, defined as any respiratory support at 36 weeks gestational age) was similar in the two groups and remarkably high for the global population (78%) and for the subgroup of infants <1,000 g at birth (75%).

CONCLUSIONS

Adding 36 hr of optimized mechanical ventilation before first extubation does not improve the rate of successful extubation but has no adverse effects.

Mechanisms of injury to the newborn brain

Preterm and ill term infants are at risk for brain injury and subsequent neurodevelopmental delay as a result of many perinatal factors. Outlined in this article are the basic science mechanisms by which hypoxia, hypocapnia, and hypercapnia may result in neuronal injury in the newborn brain.

Respiratory plasticity after perinatal hypercapnia in rats

Environmental conditions during early life may have profound effects on respiratory control development. We hypothesized that perinatal hypercapnia would exert lasting effects on the mammalian hypercapnic ventilatory response, but that these effects would differ between males and females. Rats were exposed to 5% CO2 from 1 to 3 days before birth through postnatal week 2 and ventilation was subsequently measured by whole-body plethysmography. In both male and female rats exposed to perinatal hypercapnia, a rapid, shallow breathing pattern was observed for the first 2 weeks after return to normocapnia, but ventilation was unchanged. Acute hypercapnic ventilatory responses (3% and 5% CO2) were reduced 27% immediately following perinatal hypercapnia, but these responses were normal after 2 weeks of recovery in both sexes and remained normal as adults. Collectively, these data suggest that perinatal hypercapnia elicits only transient respiratory plasticity in both male and female rats. This plasticity appears similar to that observed after chronic hypercapnia in adult animals and, therefore, is not unique to development.

Acute respiratory distress syndrome in pregnancy

OBJECTIVE

To summarize the pathophysiology and treatment of acute lung injury and acute respiratory distress syndrome (ARDS) during pregnancy.

DATA SOURCE

Review of select articles from MEDLINE, including published abstracts, case reports, observational studies, controlled trials, review articles, and institutional experience.

DATA SUMMARY

ARDS occurs in pregnancy and may have unique causes. Despite extensive clinical research to improve the management of ARDS, mortality remains high, and few strategies have shown a mortality benefit. Furthermore, in most published studies, pregnancy is an exclusionary criterion, and thus, few treatments have been adequately evaluated in obstetric populations. The treatment of ARDS in pregnancy is extrapolated from studies performed in the general ARDS patient population, with consideration given to the normal physiologic changes of pregnancy. In general, the best support of the fetus is support of the mother. From the age of viability (24-26 wks at most institutions) until full term, decisions regarding delivery should be made based primarily on the standard obstetric indications.

CONCLUSIONS

Little evidence exists regarding the management of ARDS specifically in pregnancy, and thus, treatment approaches must be drawn from studies performed in a general patient population. A multidisciplinary approach involving maternal-fetal medicine, neonatology, anesthesiology, and intensivist clinicians is essential to optimizing maternal and fetal outcomes.

Bronchopulmonary dysplasia in preterm infants: pathophysiology and management strategies

Bronchopulmonary dysplasia (BPD) has classically been described as including inflammation, architectural disruption, fibrosis, and disordered/delayed development of the infant lung. As infants born at progressively earlier gestations have begun to survive the neonatal period, a 'new' BPD, consisting primarily of disordered/delayed development, has emerged. BPD causes not only significant complications in the newborn period, but is associated with continuing mortality, cardiopulmonary dysfunction, re-hospitalization, growth failure, and poor neurodevelopmental outcome after hospital discharge. Four major risk factors for BPD include premature birth, respiratory failure, oxygen supplementation, and mechanical ventilation, although it is unclear whether any of these factors is absolutely necessary for development of the condition. Genetic susceptibility, infection, and patent ductus arteriosus have also been implicated in the pathogenesis of the disease. The strategies with the strongest evidence for effectiveness in preventing or lessening the severity of BPD include prevention of prematurity and closure of a clinically significant patent ductus arteriosus. Some evidence of effectiveness also exists for single-course therapy with antenatal glucocorticoids in women at risk for delivering premature infants, surfactant replacement therapy in intubated infants with respiratory distress syndrome, retinol (vitamin A) therapy, and modes of respiratory support designed to minimize 'volutrauma' and oxygen toxicity. The most effective treatments for ameliorating symptoms or preventing exacerbation in established BPD include oxygen therapy, inhaled glucocorticoid therapy, and vaccination against respiratory pathogens.Many other strategies for the prevention or treatment of BPD have been proposed, but have weaker or conflicting evidence of effectiveness. In addition, many therapies have significant side effects, including the possibility of worsening the disease despite symptom improvement. For instance, supraphysiologic systemic doses of glucocorticoids lessen the incidence of BPD in infants at risk for the disease, and promote weaning of oxygen and mechanical ventilation in infants with established BPD. However, the side effects of systemic glucocorticoid therapy, most notably the recently recognized adverse effects on neurodevelopment, preclude their routine use for the prevention or treatment of BPD. Future research in BPD will most probably focus on continued incremental improvements in outcome, which are likely to be achieved through the combined effects of many therapeutic modalities.

Hypercapnia-induced modifications of neuronal function in the cerebral cortex of newborn piglets

There is significant controversy over the effects of hypercapnia on the human newborn brain. Previous studies have shown that 1 h of an arterial CO2 pressure (Paco2) of 80 mm Hg alters brain cell membrane Na+K+-ATPase enzyme activity in the cerebral cortex of newborn piglets. The present study tests the hypothesis that hypercapnia (either a Paco2 of 65 or 80 mm Hg) results in decreased energy metabolism and alters neuronal nuclear enzyme activity and protein expression, specifically Ca++/calmodulin-dependent kinase (CaMK) IV activity, phosphorylation of cAMP response element binding protein (CREB), and expression of apoptotic proteins in cortical neuronal nuclei of newborn piglets. Studies were performed in 20 anesthetized normoxic piglets ventilated at either a Paco2 of 65 mm Hg, 80 mm Hg, or 40 mm Hg for 6 h. Energy metabolism was documented by ATP and phosphocreatine (PCr) levels. Results show ATP and PCr levels were significantly lower in the hypercapnic groups than the normocapnic. CaMK IV activity, phosphorylated CREB density, and Bax protein expression were all significantly higher in the hypercapnic groups than the normocapnic group. Bcl-2 protein was similar in all three groups, making the ratio of Bax/Bcl-2 significantly higher in the hypercapnic groups than in the normocapnic group. We conclude that hypercapnia alters neuronal energy metabolism, increases phosphorylation of transcription factors, and increases the expression of apoptotic proteins in the cerebral cortex of newborn piglets and therefore may be deleterious to the newborn brain.

Cardiovascular stability during arteriovenous extracorporeal therapy: a randomized controlled study in lambs with acute lung injury

INTRODUCTION

Clinical application of arteriovenous (AV) extracorporeal membrane oxygenation (ECMO) requires assessment of cardiovascular ability to respond adequately to the presence of an AV shunt in the face of acute lung injury (ALI). This ability may be age dependent and vary with the experimental model. We studied cardiovascular stability in a lamb model of severe ALI, comparing conventional mechanical ventilation (CMV) with AV-ECMO therapy.

METHODS

Seventeen lambs were anesthetized, tracheotomized, paralyzed, and ventilated to maintain normocapnia. Femoral and jugular veins, and femoral and carotid arteries were instrumented for the AV-ECMO circuit, systemic and pulmonary artery blood pressure monitoring, gas exchange, and cardiac output determination (thermodilution technique). A severe ALI (arterial oxygen tension/inspired fractional oxygen <200) was induced by lung lavage (repeated three times, each with 5 ml/kg saline) followed by tracheal instillation of 2.5 ml/kg of 0.1 N HCl. Lambs were consecutively assigned to CMV treatment (n = 8) or CMV plus AV-ECMO therapy using up to 15% of the cardiac output for the AV shunt flow during a 6-hour study period (n = 9). The outcome measures were the degree of inotropic and ventilator support needed to maintain hemodynamic stability and normocapnia, respectively.

RESULTS

Five of the nine lambs subjected to AV-ECMO therapy (56%) died before completion of the 6-hour study period, as compared with two out of eight lambs (25%) in the CMV group (P > 0.05; Fisher's exact test). Surviving and nonsurviving lambs in the AV-ECMO group, unlike the CMV group, required continuous volume expansion and inotropic support (P < 0.001; Fisher's exact test). Lambs in the AV-ECMO group were able to maintain normocapnia with a maximum of 30% reduction in the minute ventilation, as compared with the CMV group (P < 0.05).

CONCLUSION

AV-ECMO therapy in lambs subjected to severe ALI requires continuous hemodynamic support to maintain cardiovascular stability and normocapnia, as compared with lambs receiving CMV support.

Positive end expiratory pressure during resuscitation of premature lambs rapidly improves blood gases without adversely affecting arterial pressure

Positive end expiratory pressure (PEEP) is important for neonatal ventilation but is not considered in guidelines for resuscitation. Our aim was to investigate the effects of PEEP on cardiorespiratory parameters during resuscitation of very premature lambs delivered by hysterotomy at approximately 125 d gestation (term approximately 147 d). Before delivery, they were intubated and lung fluid was drained. Immediately after delivery, they were ventilated with a Dräger Babylog plus ventilator in volume guarantee mode with a tidal volume of 5 mL/kg. Lambs were randomized to receive 0, 4, 8, or 12 cm H(2)O of PEEP. They were ventilated for a 15-min resuscitation period followed by 2 h of stabilization at the same PEEP. Tidal volume, peak inspiratory pressure, PEEP, arterial pressure, oxygen saturation, and blood gases were measured regularly, and respiratory system compliance and alveolar/arterial oxygen differences were calculated. Lambs that received 12 cm H(2)O of PEEP died from pneumothoraces; all others survived without pneumothoraces. Oxygenation was significantly improved by 8 and 12 cm H(2)O of PEEP compared with 0 and 4 cm H(2)O of PEEP. Lambs with 0 PEEP did not oxygenate adequately. The compliance of the respiratory system was significantly higher at 4 and 8 cm H(2)O of PEEP than at 0 PEEP. There were no significant differences in partial pressure of carbon dioxide in arterial blood between groups. Arterial pressure was highest with 8 cm H(2)O of PEEP, and there was no cardiorespiratory compromise at any level of PEEP. Applying PEEP during resuscitation of very premature infants might be advantageous and merits further investigation.

Changing trends in the management of respiratory distress syndrome (RDS)

The management of respiratory distress syndrome (RDS) has advanced because of improvements in mechanical ventilators, promotion of antenatal steroids, availability of surfactant and overall advancements in neonatal intensive care. Intermittent mandatory ventilation still forms the mainstay of assisted ventilation. Newer modes of ventilation have not delivered the results as promised. Because of the continued high incidence of bronchopulmonary dysplasia, there is a renewed interest in non-invasive modes of ventilation like CPAP and nasal IPPV. The present trend is to follow gentle ventilatory strategies accepting higher arterial carbon dioxide and lower oxygen. The role of antenatal steroids has been established beyond doubt but still they fall short of universal acceptance. Surfactant replacement therapy is the standard of care for RDS but beyond the reach of majority in India. Postnatal steroids are out of vogue because of probable links with cerebral palsy and abnormal neurological outcomes.

Current perspectives on the prevention and management of chronic lung disease in preterm infants

Chronic lung disease (CLD) or bronchopulmonary dysplasia is a recognized sequel of preterm birth. With improving survival of infants at lower gestational ages, the incidence is on the rise. Pathological features of CLD include alveolar maldevelopment, with or without areas of pulmonary fibrosis. Assisted ventilation, infection/inflammation, oxygen administration, and fluid overload are the major risk factors in the evolution of CLD.Interventions, including the treatment of maternal infection, administration of prenatal glucocorticoids, and postnatal surfactant replacement therapy, improve the survival of preterm infants; however, their effect on CLD is difficult to determine. Strategies that have been effective in reducing CLD are the administration of retinol (vitamin A), high frequency oscillatory ventilation, and administration of glucocorticoids. Previous concerns regarding neurological problems associated with high frequency ventilation have not been substantiated in recent studies. Current recommendations do not advise the routine use of glucocorticoids due to concerns regarding long-term neurodevelopment. Therapies that were found to be ineffective in reducing the incidence of CLD include prenatal thyrotropin, cromolyn sodium (sodium cromoglycate), alpha-1 antitrypsin, superoxide dismutase, tocopherol (vitamin E), ascorbic acid (vitamin C), allopurinol, ambroxol, inositol, inhaled bronchodilators, and fluid restriction. Strategies that may be effective in reducing lung injury and subsequent CLD include avoiding assisted ventilation, lung protective ventilatory maneuvers, permissive hypercapnia, prevention of infection, early aggressive nutrition, and the treatment of a patent ductus arteriosus. The use of inhaled glucocorticoids improves pulmonary dynamics but long-term effects are unknown. The management of infants with established CLD has not been studied adequately, and the role of various ventilatory strategies for infants with established CLD is not clear. Adequate oxygenation should be maintained to prevent hypoxic episodes. Diuretics are helpful during acute decompensation; however, their long-term impact has not been well studied. Provision of adequate nutrition, immunization (routine and against respiratory syncytial virus), follow-up, and monitoring are the key elements in the long-term management of infants with CLD. Future research priorities should be to identify strategies to prevent/treat inflammation and promote the healing processes in the injured lung. The long-term effects of lung-protective ventilation strategies need to be studied.

Hypercapnic acidosis and compensated hypercapnia in control and pulmonary hypertensive piglets

Low tidal volume/inspiratory pressure ventilator strategies result in hypercapnia, which has been shown to increase pulmonary vasomotor tone. This may be particularly detrimental in infants and children with preexistent pulmonary hypertension. In this study, a piglet model of chronic hypoxia-induced pulmonary hypertension was used to test the hypotheses that: 1) the effects of hypercapnic acidosis are exaggerated by preexistent pulmonary hypertension; and 2) the pulmonary hemodynamic effects of hypercapnic acidosis are attenuated by normalizing pH. Pulmonary hypertension was induced by 2 weeks of hypoxia. Hemodynamic responses were measured in control and pulmonary hypertensive piglets during both normoxia and hypoxia under normocapnic, hypercapnic acidotic, and compensated hypercapnic conditions. We found that: 1) hypercapnic acidosis increased both normoxic and hypoxic pulmonary vascular resistance index (PVRI) in control piglets; 2) the pressor effects of hypercapnia were not attenuated by infusing bicarbonate to normalize the pH; and 3) piglets with chronic hypoxia-induced pulmonary hypertension had elevated baseline normoxic and hypoxic PVRI, but responded to hypercapnic acidosis and compensated hypercapnia in a similar way to control piglets. These data suggest that acute hypercapnic acidosis may have deleterious effects on the pulmonary hemodynamics of normal and pulmonary hypertensive subjects which may not be acutely reversed by buffering the pH.