The effect of intraoperative methadone during pediatric cardiac surgery on postoperative opioid requirements.

BACKGROUND: Pain control in pediatric patients undergoing cardiac surgery presents a unique challenge. Postoperatively, many of these patients require long-term opioid infusions and sedation leading to need for prolonged weaning from opioids and longer hospital stays. We hypothesized that intravenous methadone as the sole opioid in children having cardiac surgery with cardiopulmonary bypass would improve perioperative pain control and decrease overall perioperative use of opioid analgesics and sedatives. METHODS: We instituted a practice change involving pediatric patients aged <18 years who underwent cardiac surgery with cardiopulmonary bypass over a 14-month period, comparing the patient population who had surgery prior to the institution of intraoperative methadone usage to patients who had surgery in the months following. We then separated patients into two groups: neonatal (aged < 30 days) and non-neonatal (aged > 30 days to 18 years). Our primary outcome was intraoperative and postoperative opioid requirements measured in morphine equivalents intraoperatively, during the first 24 hours postoperatively, and up to postoperative day 7. Secondary outcomes included extubation rates in the OR, pain and sedation scores, sedation requirements, and time to start of oxycodone. RESULTS: Patients in both groups had similar demographics. In neonatal patients, the postintervention group required significantly lower doses of intraoperative opioids. There was no statistically significant difference in postoperative opioid use. In non-neonatal patients, the postintervention group required significantly less intraoperative opioids. Postoperatively, those in the postintervention group required significantly less opioids in the first 24 hours. CONCLUSION: The use of intraoperative methadone appears to be a reasonable alternative to the use of fentanyl with potential other benefits both intra- and postoperatively of decreased total dose of opioids and other sedatives. Future studies will assess for any improvement in total postoperative opioid requirements during the total hospital stay, and potential use of methadone by the ICU team.

Cardiopulmonary bypass is associated with hemolysis and acute kidney injury in neonates, infants, and children*.

OBJECTIVES: This pilot study assesses the degree of hemolysis induced by cardiopulmonary bypass and determines its association with acute kidney injury in pediatric patients. Further, it evaluates the degree to which the use of urinary biomarkers neutrophil gelatinase-associated lipocalin and cystatin C correlate with the presence of acute kidney injury and hemolysis following cardiopulmonary bypass. DESIGN: Prospective observational study. SETTING: A 13-bed pediatric cardiac ICU in a university hospital. PATIENTS: Children undergoing cardiac surgery with the use of cardiopulmonary bypass. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Blood and urine samples were obtained at multiple time points before and after cardiopulmonary bypass. Hemolysis was assessed by measuring levels of plasma hemoglobin and haptoglobin. Acute kidney injury was defined as a doubling in serum creatinine from preoperative baseline and by using the pediatric-modified RIFLE criteria. Urinary neutrophil gelatinase-associated lipocalin and cystatin C levels were measured. A total of 40 patients (range, 3 d to 4.8 yr) were enrolled. Plasma hemoglobin levels increased markedly on separation from cardiopulmonary bypass with a concurrent decrease in haptoglobin. This was associated with an increase in protein oxidation in the plasma. Hemolysis was more evident in younger patients with a longer duration of bypass and in those requiring a blood-primed circuit. Forty percent of patients had a doubling in serum creatinine and acute kidney injury was developed in 88% of patients when defined by the pediatric-modified RIFLE criteria. Controlling for cardiopulmonary bypass time, persistently elevated levels of plasma hemoglobin were associated with a five-fold increase in acute kidney injury. Further, urinary neutrophil gelatinase-associated lipocalin measured 2 hours after separation from cardiopulmonary bypass was associated with acute kidney injury and with elevations in plasma hemoglobin. CONCLUSIONS: Cardiopulmonary bypass in pediatric patients results in significant hemolysis, which is associated with the development of acute kidney injury. The biomarker neutrophil gelatinase-associated lipocalin correlates with both acute kidney injury and hemolysis in this population.

Sequestration of mitochondrial iron by silica particle initiates a biological effect.

Inhalation of particulate matter has presented a challenge to human health for thousands of years. The underlying mechanism for biological effect following particle exposure is incompletely understood. We tested the postulate that particle sequestration of cell and mitochondrial iron is a pivotal event mediating oxidant generation and biological effect. In vitro exposure of human bronchial epithelial cells to silica reduced intracellular iron, which resulted in increases in both the importer divalent metal transporter 1 expression and metal uptake. Diminished mitochondrial (57)Fe concentrations following silica exposure confirmed particle sequestration of cell iron. Preincubation of cells with excess ferric ammonium citrate increased cell, nuclear, and mitochondrial metal concentrations and prevented significant iron loss from mitochondria following silica exposure. Cell and mitochondrial oxidant generation increased after silica incubation, but pretreatment with iron diminished this generation of reactive oxygen species. Silica exposure activated MAP kinases (ERK and p38) and altered the expression of transcription factors (nF-κB and NF-E2-related factor 2), proinflammatory cytokines (interleukin-8 and -6), and apoptotic proteins. All of these changes in indexes of biological effect were either diminished or inhibited by cell pretreatment with iron. Finally, percentage of neutrophils and total protein concentrations in an animal model instilled with silica were decreased by concurrent exposure to iron. We conclude that an initiating event in the response to particulate matter is a sequestration of cell and mitochondrial iron by endocytosed particle. The resultant oxidative stress and biological response after particle exposure are either diminished or inhibited by increasing the cell iron concentration.

Transfusion-related biologic effects and free hemoglobin, heme, and iron.

BACKGROUND: Red blood cell (RBC) transfusion is common in intensive care unit (ICU) patients and is associated with complications that appear related to the duration of blood storage. We hypothesize that hemolysis of stored RBCs results in increases in the availability of non-heme-bound iron, which inhibits macrophage activation. STUDY DESIGN AND METHODS: RBCs were sampled at multiple time points to evaluate hemolysis and iron release. Activation of THP-1 monocytic cells was assessed in the presence of plasma from aged RBCs. Age of transfused blood in our pediatric intensive care unit (PICU) from 2001 to 2006 was analyzed to assess relevance to our patient population. RESULTS: Hemolysis increased significantly during storage time as demonstrated by increases in free heme and hemoglobin. While there was a trend toward elevated levels of non-heme-bound iron, this was not significant (p = 0.07). THP-1 cell activation was inhibited by exposures to both plasma and a ferric compound; the effect of plasma on macrophage activation was not reversed by the iron chelator desferroxamine. Thirty-one percent of our PICU patients received blood older than 2 weeks. CONCLUSION: Hemolysis products increased significantly over time in our stored RBCs. Ferric compounds and plasma from stored blood inhibit THP-1 cell activation. Plasma inhibition does not appear to be due primarily to increased iron. Further studies are needed to define the inhibitory effect of stored blood plasma on macrophage function. Complications related to blood storage are relevant to our PICU patients.

Disruption of iron homeostasis in mesothelial cells after talc pleurodesis.

The mechanism for biological effects after exposure to particles is incompletely understood. One postulate proposed to explain biological effects after exposure to particles involves altered iron homeostasis in the host. The fibro-inflammatory properties of mineral oxide particles are exploited therapeutically with the instillation of massive quantities of talc into the pleural space, to provide sclerosis. We tested the postulates that (1) in vitro exposure to talc induces a disruption in iron homeostasis, oxidative stress, and a biological effect, and (2) talc pleurodesis in humans alters iron homeostasis. In vitro exposures of both mesothelial and airway epithelial cells to 100 µg/ml talc significantly increased iron importation and concentrations of the storage protein ferritin. Using dichlorodihydrofluorescein, exposure to talc was associated with a time-dependent and concentration-dependent generation of oxidants in both cell types. The expression of proinflammatory mediators was also increased after in vitro exposures of mesothelial and airway epithelial cells to talc. Relative to control lung tissue, lung tissue from patients treated with sclerodesis demonstrated an accumulation of iron and increased expression of iron-related proteins, including ferritin, the importer divalent metal transport-1 and the exporter ferroportin-1. Talc was also observed to translocate to the parenchyma, and changes in iron homeostasis were focally distributed to sites of retention. We conclude that exposure to talc disrupts iron homeostasis, is associated with oxidative stress, and results in a biological effect (i.e., a fibro-inflammatory response). Talc pleurodesis can function as a model of the human response to mineral oxide particle exposure, albeit a massive one.

Hepcidin expression in human airway epithelial cells is regulated by interferon-γ.

BACKGROUND: Hepcidin serves as a major regulator of systemic iron metabolism and immune function. Airway epithelial cells have an extensive interface with the environment, and so must be able to respond locally to the presence of particulates, infection, and inflammation. Therefore, we hypothesized that hepcidin is expressed in airway epithelial cells and is regulated by early phase cytokines. METHODS: Primary, differentiated human bronchial epithelial (NHBE) cells were used to assess hepcidin gene expression in response to IFN-γ, TNF-α, IL-1ß, and IL-6, as well as to LPS + CD14. The role of the Janus Kinase-signal transducer and activator of transcription (JAK-STAT) pathway in IFN-γ-mediated hepcidin production was assessed by measuring JAK2 phophorylation and STAT1 nuclear translocation. Inductively coupled plasma mass spectroscopy (ICP-MS) was used to determine whether hepcidin altered iron transport in either NHBE cells or primary alveolar macrophages. RESULTS: We demonstrate that differentiated human airway epithelial cells express hepcidin mRNA and that its expression is augmented in response to IFN-γ via activation of STAT1. However, while IFN-γ induced hepcidin gene expression, we were not able to demonstrate diminished expression of the iron export protein, ferroportin (Fpn), at the cell surface, or iron accumulation in airway epithelial in the presence of exogenous hepcidin. CONCLUSION: These data demonstrate that airway epithelial cells express hepcidin in the lung in response to IFN-γ. The presence of hepcidin in the airway does not appear to alter cellular iron transport, but may serve as a protective factor via its direct antimicrobial effects.

Extending the radius of family-centered care in the pediatric cardiac intensive care unit through virtual rounding.

BACKGROUND: The arrival of COVID-19 brought urgent limitation of visitation in hospitals across the country. Family-centered care and its delivery rapidly changed and left the family behind-unable to actively participate in their loved one's care. LOCAL PROBLEM: A southeastern academic medical center pediatric cardiac intensive care unit (PCICU) needed to augment family-centered medical rounds when parents could not be at the bedside. No alternative to physical presence for daily medical rounds existed in the PCICU. METHODS: A virtual rounding (VR) program was implemented allowing parents of patients admitted to PCICU to join medical rounds remotely through teleconferencing. Preintervention and postintervention rounding times, staff perceptions of the program, and parental satisfaction scores using the Pediatric Family Satisfaction in the Intensive Care Unit (pFS-ICU) tool were measured. INTERVENTIONS: This quality improvement project implemented a VR program offered to all families of patients in the PCICU. RESULTS: VR did not increase rounding times after implementation (p = .673). Staff satisfaction surveys revealed that staff felt the VR program did not prolong rounding times (p ≤ 0.001), workload impact perceptions improved after intervention (p = <0.001), and staff felt VR should be offered to families in PCICU (p ≤ 0.001). Only nine pFS-ICU surveys were completed giving the family a limited voice in the evaluation of this project. CONCLUSIONS: This project demonstrates that VR can be successfully implemented for family engagement without increased burden on staff.

Iron overload following red blood cell transfusion and its impact on disease severity.

Transfusion of red blood cells can be a life-saving therapy both for patients with chronic anemias and for those who are critically ill with acute blood loss. However, transfusion has been associated with significant morbidity. Chronic transfusion results in accumulation of excess iron that surpasses the binding capacity of the major iron transport protein, transferrin. The resulting non-transferrin bound iron (NTBI) can catalyze the production of highly reactive oxygen species (ROS) leading to significant and wide spread injury to the liver, heart, and endocrine organs as well as increases in infection. Acute transfusion of red blood cells in critically ill patients likewise has significant effects including increased mortality, prolonged hospital stays, and elevated risk of nosocomial infection. These effects appear to be more profound with increasing age of stored blood. The progressive release of free iron associated with storage time suggests that morbidity following acute transfusion, like that seen in chronic transfusion, may be due in part to elevated levels of NTBI. It is clear that transfusion is necessary in many instances; however, its risks and benefits must be carefully balanced before proceeding to avoid unnecessary iron toxicity.

Circuit oxygenator contributes to extracorporeal membrane oxygenation-induced hemolysis.

Hemolysis can occur as a consequence of extracorporeal membrane oxygenation (ECMO) and is associated with increased mortality and morbidity. Shear stress generated by flow through the circuit and oxygenator is believed to cause ECMO-induced hemolysis. We hypothesize that either a smaller dimension oxygenator or an in-line hemofilter will increase ECMO-associated hemolysis. Circuits were configured with a Quadrox-D Adult oxygenator (surface area 1.8 m), Quadrox-iD Pediatric oxygenator (surface area 0.8 m), or Quadrox-D Adult oxygenator with an in-line hemofilter (N = 4) and ran for 6 hours. Samples were collected hourly from the ECMO circuit and a time-based hemolysis control. Plasma hemoglobin levels were assayed. Circuit-induced hemolysis at each time point was defined as the change in plasma hemoglobin standardized to the time-based hemolysis control. Plasma hemoglobin increased with the use of the smaller dimension pediatric oxygenator as compared with the adult oxygenator when controlling for ECMO run time (p = 0.02). Furthermore, there was a greater pressure gradient with the smaller dimension pediatric oxygenator (p < 0.05). Plasma hemoglobin did not change with the addition of the in-line hemofilter. The use of a smaller dimension pediatric oxygenator resulted in greater hemolysis and a higher pressure gradient. This may indicate that the increased shear forces augment ECMO-induced hemolysis.

The iron cycle and oxidative stress in the lung.

Iron is critical for many aspects of cellular function, but it can also generate reactive oxygen species that can damage biological macromolecules. To limit oxidative stress, iron acquisition and its distribution must be tightly regulated. In the lungs, which are continuously exposed to the atmosphere, the risk of oxidative damage is particularly high because of the high oxygen concentration and the presence of significant amounts of catalytically active iron in atmospheric particulates. An effective system of metal detoxification must exist to minimize the associated generation of oxidative stress in the lungs. Here we summarize the evidence that a number of specific proteins that control iron uptake in the gastrointestinal tract are also employed in the lung to transport iron into epithelial cells and sequester it in a catalytically inactive form in ferritin. Furthermore, these and other proteins facilitate ferritin release from lung cells to the epithelial and bronchial lining fluids for clearance by the mucociliary system or to the reticuloendothelial system for long-term storage of iron. These pathways seem to be the primary mechanism for control of oxidative stress presented by iron in the respiratory tract.

Iron accumulation in bronchial epithelial cells is dependent on concurrent sodium transport.

Airway epithelial cells prevent damaging effects of extracellular iron by taking up the metal and sequestering it within intracellular ferritin. Epithelial iron transport is associated with transcellular movement of other cations including changes in the expression or activity of Na, K-ATPase and epithelial Na(+) channel (ENaC). Given this relationship between iron and Na(+), we hypothesized that iron uptake by airway epithelial cells requires concurrent Na(+) transport. In preliminary studies, we found that Na(+)-free buffer blocked iron uptake by human airway epithelial cell. Na(+) channels inhibitors, including furosemide, bumetanide, and ethylisopropyl amiloride (EIPA) significantly decreased epithelial cell concentrations of non-heme iron suggesting that Na(+)-dependent iron accumulation involves generalized Na(+) flux into the cells rather than participation of one or more specific Na(+) channels. In addition, efflux of K(+) was detected during iron uptake, as was the influx of phosphate to balance the inward movement of cations. Together, these data demonstrate that intracellular iron accumulation by airway epithelium requires concurrent Na(+)/K(+)exchange.

Lung injury after ozone exposure is iron dependent.

We tested the hypothesis that oxidative stress and biological effect after ozone (O3) exposure are dependent on changes in iron homeostasis. After O3 exposure, healthy volunteers demonstrated increased lavage concentrations of iron, transferrin, lactoferrin, and ferritin. In normal rats, alterations of iron metabolism after O3 exposure were immediate and preceded the inflammatory influx. To test for participation of this disruption in iron homeostasis in lung injury following O3 inhalation, we exposed Belgrade rats, which are functionally deficient in divalent metal transporter 1 (DMT1) as a means of iron uptake, and controls to O3. Iron homeostasis was disrupted to a greater extent and the extent of injury was greater in Belgrade rats than in control rats. Nonheme iron and ferritin concentrations were higher in human bronchial epithelial (HBE) cells exposed to O3 than in HBE cells exposed to filtered air. Aldehyde generation and IL-8 release by the HBE cells was also elevated following O3 exposure. Human embryonic kidney (HEK 293) cells with elevated expression of a DMT1 construct were exposed to filtered air and O3. With exposure to O3, elevated DMT1 expression diminished oxidative stress (i.e., aldehyde generation) and IL-8 release. We conclude that iron participates critically in the oxidative stress and biological effects after O3 exposure.

Iron homeostasis in the lung.

Iron is essential for many aspects of cellular function. However, it also can generate oxygen-based free radicals that result in injury to biological molecules. For this reason, iron acquisition and distribution are tightly regulated. Constant exposure to the atmosphere results in significant exposure of the lungs to catalytically active iron. The lungs have a mechanism for detoxification to prevent associated generation of oxidative stress. Those same proteins that participate in iron uptake in the gut are also employed in the lung, to transport iron intracellularly and sequester it in an inactive form within ferritin. The release of metal is expedited (as transferrin and ferritin) from lung tissue to the respiratory lining fluid for clearance by the mucocilliary pathway or to the reticuloendothelial system for long-term storage. This pathway is likely to be the major method for the control of oxidative stress presented to the respiratory tract.

Duodenal cytochrome b: a novel ferrireductase in airway epithelial cells.

Catalytically active iron in the lung causes oxidative stress and promotes microbial growth that can be limited by intracellular sequestration of iron within ferritin. Because cellular iron uptake requires membrane ferrireductase activity that in the gut can be provided by duodenal cytochrome b (Dcytb), we sought Dcytb in the lung to test the hypothesis that it contributes to epithelial iron regulation by reducing Fe(3+) for cellular iron transport. Dcytb expression was found in respiratory epithelium in vitro and in vivo and was responsive to iron concentration. Iron transport was measured in human bronchial epithelial (HBE) cells using inductively coupled plasma atomic emission spectroscopy and was demonstrated to be partially inhibited in the presence of Dcytb-blocking antibody, suggesting that Dcytb reduces Fe(3+) for cellular iron transport. A definite source of reducing equivalents for Dcytb was sought but not identified. We found no evidence that ascorbate was involved but did demonstrate that O(2)(-). production decreased when Dcytb function was blocked. The presence of Dcytb in airway epithelial cells and its regulation by iron therefore may contribute to pulmonary cytoprotection.

Oxidative stress activates anion exchange protein 2 and AP-1 in airway epithelial cells.

Anion exchange protein 2 (AE2) is a membrane-bound protein that mediates chloride-bicarbonate exchange. In addition to regulating intracellular pH and cell volume, AE2 exports superoxide (O.) to the extracellular matrix in an HCO-dependent process. Given this ability to export O., we hypothesized that expression of AE2 in the lung is regulated by oxidative stress. AE2 mRNA and protein expression was measured by RT-PCR and Western blot analysis, respectively, in differentiated human bronchial epithelial cells exposed to H(2)O(2) (100 microM). Alterations in in vivo AE2 protein expression were evaluated in lung tissue of rats exposed to 70% O(2). The role of transcription factor activator protein (AP)-1 in oxidant regulation of AE2 was evaluated by EMSA and by immunoblotting of nuclear phospho-c-jun. Results show increased AE2 mRNA and protein expression after oxidant exposure. This was preceded by transient increases in DNA binding of AE2-specific AP-1 and phosphorylation of c-jun. This study demonstrates that AE2 expression is regulated by oxidative stress in airway epithelial cells and that this regulation correlates with activation of AP-1.

Iron homeostasis in the lung

Iron is essential for many aspects of cellular function. However, it also can generate oxygen-based free radicals that result in injury to biological molecules. For this reason, iron acquisition and distribution are tightly regulated. Constant exposure to the atmosphere results in significant exposure of the lungs to catalytically active iron. The lungs have a mechanism for detoxification to prevent associated generation of oxidative stress. Those same proteins that participate in iron uptake in the gut are also employed in the lung to transport iron intracellularly and sequester it in an inactive form within ferritin. The release of metal is expedited (as transferrin and ferritin) from lung tissue to the respiratory lining fluid for clearance by the mucocilliary pathway or to the reticuloendothelial system for long-term storage. This pathway is likely to be the major method for the control of oxidative stress presented to the respiratory tract.