Utility of routine methemoglobin laboratory assays in critically ill pediatric subjects receiving inhaled nitric oxide.

PURPOSE: Inhaled nitric oxide (iNO) has been associated with safety risks including reports of methemoglobinemia. While standard of care recommends routine monitoring of methemoglobin in subjects on iNO therapy, the utility of this practice remains unknown. MATERIALS AND METHODS: This retrospective chart review aimed to determine the frequency of methemoglobinemia in pediatric patients receiving iNO. Included subjects were under 18 years of age receiving iNO therapy with at least one methemoglobin concentration measured from 10/18/2014 to 11/18/2016. RESULTS: In total, 1809 methemoglobin concentrations were collected in 247 subjects during the study period. Median age was 0.33 (0.04-0.83) years. The mean methemoglobin concentration was 1.33% (±0.42) while receiving a mean iNO dose of 11.71 ppm (±7.97). Twenty-nine subjects had a total of 131 methemoglobin concentrations analyzed while receiving iNO doses above 20 ppm which were similar to the entire cohort at 1.33% (±0.42); (p = .95). CONCLUSIONS: Pediatric patients receiving iNO at doses below 40 ppm have minimal risk of developing clinically significant methemoglobinemia. Routine, ongoing monitoring of metHb levels in all pediatric subjects receiving iNO therapy at doses <40 ppm without the presence of risk factors predisposing the subject to increased risk of methemoglobinemia is unnecessary and should be avoided.

Effects of infusion of human methemoglobin solution following hydrogen sulfide poisoning.

RATIONALE: We have recently reported that infusion of a solution containing methemoglobin (MetHb) during exposure to hydrogen sulfide results in a rapid and large decrease in the concentration of the pool of soluble/diffusible H2S in the blood. However, since the pool of dissolved H2S disappears very quickly after H2S exposure, it is unclear if the ability of MetHb to "trap" sulfide in the blood has any clinical interest and relevance in the treatment of sulfide poisoning. METHODS: In anesthetized rats, repetition of short bouts of high level of H2S infusions was applied to allow the rapid development of an oxygen deficit. A solution containing MetHb (600 mg/kg) or its vehicle was administered 1 min and a half after the end of H2S intoxication. RESULTS: The injection of MetHb solution increased methemoglobinemia to about 6%, almost instantly, but was unable to affect the blood concentration of soluble H2S, which had already vanished at the time of infusion, or to increase combined H2S. In addition, H2S-induced O2 deficit and lactate production as well as the recovery of carotid blood flow and blood pressure were similar in treated and control animals. CONCLUSION: Our results do not support the view that administration of MetHb or drugs-induced methemoglobinemia during the recovery phase following severe H2S intoxication in sedated rats can restore cellular oxidative metabolism, as the pool of diffusible sulfide, accessible to MetHb, disappears rapidly from the blood after H2S exposure.

In vivo interactions between cobalt or ferric compounds and the pools of sulphide in the blood during and after H2S poisoning.

Hydrogen sulphide (H2S), a chemical hazard in oil and gas production, has recently become a dreadful method of suicide, posing specific risks and challenges for the first responders. Currently, there is no proven effective treatment against H2S poisoning and its severe neurological, respiratory or cardiac after-effects. We have recently described that H2S is present in various compartments, or pools, in the body during sulphide exposure, which have different levels of toxicity. The general goals of our study were to (1) determine the concentrations and kinetics of the various pools of hydrogen sulphide in the blood, i.e., gaseous (CgH2S) versus total sulphide, i.e., reacting with monobromobimane (CMBBH2S), during and following H2S exposure in a small and large mammal and (2) establish the interaction between the pools of H2S and a methemoglobin (MetHb) solution or a high dose of hydroxocobalamin (HyCo). We found that CgH2S during and following H2S infusion was similar in sedated sheep and rats at any given rate of infusion/kg and provoked symptoms, i.e., hyperpnea and apnea, at the same CgH2S. After H2S administration was stopped, CgH2S disappeared within 1 min. CMBBH2S also dropped to 2-3µM, but remained above baseline levels for at least 30 min. Infusion of a MetHb solution during H2S infusion produced an immediate reduction in the free/soluble pool of H2S only, whereas CMBBH2S increased by severalfold. HyCo (70 mg/kg) also decreased the concentrations of free/soluble H2S to almost zero; CgH2S returned to pre-HyCo levels within a maximum of 20 min, if H2S infusion is maintained. These results are discussed in the context of a relevant scenario, wherein antidotes can only be administered after H2S exposure.

Dosagem de metemoglobina em pacientes adultos com anemia falciforme: influência do tratamento com hidroxiureia / Methemoglobin measure in adult patients with sickle-cell anemia: influence of hydroxyurea therapy

Introduction: Hemoglobin S (HbS) is unstable hemoglobin that easily oxidizes, causing methemoglobin (MetHb) increased production in patients with sickle-cell anemia (SCA). Objectives: To determine MetHb levels and the influence of hydroxyurea (HU) therapy on this marker in patients with SCA. Materials and methods: Blood samples from 53 patients with SCA at the steady-state, with and without HU therapy, and 30 healthy individuals were collected to evaluate MetHb levels. The MetHb measurement was performed by spectrophotometry. Complete blood count, HU measurements, and fetal hemoglobin (HbF) and HbS concentrations were taken from medical records. Results: MetHb levels were statically higher in patients with SCA when compared to control group (p < 0.001). There was no statistical difference in MetHb level between SCA patients, either using or not HU. We obtained a positive correlation between MetHb measurements and HbS concentration (r = 0.2557; p = 0.0323). Conclusion: HbS presence favored hemoglobin breaking down, and consequently increased MetHb production. Treatment with HU, however, did not influence the levels of this marker...

Introdução: A hemoglobina S (HbS) é uma hemoglobina instável que facilmente se oxida, causando aumento da produção de metemoglobina (MetHb) em pacientes com anemia falciforme (AF). Objetivos: Determinar os níveis de MetHb e verificar a influência do tratamento com a hidroxiureia (HU) sobre as dosagens desse marcador em pacientes com AF. Materiais e métodos: Amostras de sangue de 53 pacientes adultos com AF em estado basal, em uso ou não de HU, e 30 indivíduos saudáveis foram coletadas para avaliar os níveis de MetHb. A dosagem de MetHb foi realizada pelo método espectrofotométrico. Os parâmetros hematológicos, a dosagem de HU e a concentração de hemoglobina F (HbF) e HbS foram retirados dos prontuários médicos. Resultados: Níveis de MetHb apresentaram-se mais elevados estatisticamente em pacientes com AF em relação ao grupo-controle (p < 0,0001). Não foi verificada diferença estatística nos níveis de MetHb entre pacientes em uso ou não de HU. Observou-se correlação positiva entre as dosagens de MetHb e a concentração de HbS (r = 0,2557; p = 0,0323). Conclusão: A presença da HbS favoreceu a degradação da hemoglobina, causando elevação da produção de MetHb. Tratamento com HU, entretanto, não influenciou nos níveis desse marcador...

Physical properties and stability mechanisms of poly(ethylene glycol) conjugated liposome encapsulated hemoglobin dispersions.

Liposomes encapsulating hemoglobin (LEHs) surface-conjugated with 2000 and 550 Da poly(ethylene glycol) (PEG) were produced via extrusion through 400, 200 and 100 nm pore diameter membranes in two types of phosphate buffer with different ionic strengths. The lipid bilayers were composed of dimyristoyl-phosphatidylcholine (DMPC), cholesterol, dimyristoyl-phosphoethanolamine-PEG (DMPE-PEG), dimyristoyl-phosphatidylglycerol (DMPG), and alpha-tocopherol (in a 43:40:10:5:2 mole ratio). N-acetyl-L-cysteine was coencapsulated in order to suppress hemoglobin (Hb) oxidation. Various physical properties of PEG-LEH dispersions were determined: size distribution, encapsulation efficiency, P50 (partial pressure of O2 where half of the oxygen binding sites are saturated with O2), cooperativity coefficient, and encapsulated methemoglobin (MetHb) level. In order to study the stabilization mechanism of these dispersions, the effective bending constant (KB) and the spontaneous radius of curvature (R0) of PEG-LEHs were extracted by fitting a mathematical model describing the size distribution of a liposome dispersion to the experimentally measured size distributions. We observed that liposome dispersions extruded in phosphate buffer (PB) were more monodisperse than liposomes extruded in phosphate buffered saline (PBS), and higher molecular weight PEG promoted the formation of narrower size distributions. Moreover, extrusion in PB and lipid conjugation with higher molecular weight PEG imparted higher bilayer rigidity (high KB), and stabilized the liposome dispersions by the spontaneous curvature mechanism, whereas the other liposome dispersions were stabilized by thermal undulations (low KB). The P50 and cooperativity coefficient of PEG-LEHs extruded in PBS and PB was comparable to that of human blood, and the encapsulated MetHb levels were less than 5%. The highest encapsulation efficiencies obtained were 27%-36% (82-109 mg Hb/mL) for LEH dispersions extruded in PBS and grafted with 2000 Da PEG. These dispersions yielded KBs' ranging from 7kT to 27kT, which indicated that these dispersions were stabilized by spontaneous curvature. Whereas the same lipid combination extruded in PBS, however, instead conjugated with 550 Da PEG resulted in KBs' ranging from 2 kT to 2.7 kT, which indicated that these dispersions were stabilized by thermal undulations. Thermal undulations permitted Hb leakage through the lipid bilayers, which in turn lowered the encapsulation efficiency to 1%-10.7% (3-32 mg Hb/mL). Taken together, the experimentally measured size distributions and encapsulation efficiencies of PEG-LEH dispersions can be readily explained through analysis of the magnitude of KB, which dictates the stability mechanism of the liposome dispersion.

Cell-free and erythrocytic S-nitrosohemoglobin inhibits human platelet aggregation.

BACKGROUND: Nitric oxide (NO) and related molecules are thought to inhibit human platelet aggregation by raising levels of cGMP. METHODS AND RESULTS: Both oxidative stress (reactive oxygen species) and hemoglobin (Hb) seem to oppose NO effects. A major fraction of NO in the blood is bound to thiols of Hb, forming S-nitrosohemoglobin (SNO-Hb), which releases the NO group on deoxygenation in the microcirculation. Here we show that (1) both cell-free and intraerythrocytic SNO-Hb (SNO-RBC) inhibit platelet aggregation, (2) the oxidation state of the hemes in Hb influences the response--SNO-metHb (which is functionally similar to SNO-deoxyHb) has greater platelet inhibitory effects than SNO-oxyHb, and (3) the mechanism of platelet inhibition by SNO-Hb is cGMP independent. CONCLUSIONS: We suggest that the RBC has evolved a means to counteract platelet activation in small vessels and the proaggregatory effects of oxidative stress by forming SNO-Hb.

[The experimental treatment of cyanide poisoning with a methemoglobin solution]. / Lechenie otravleniia tsianidami rastvorom metgemoglobina v éksperimente.

The stroma-free methemoglobin solution proved to be an effective antidote against acute cyanide poisoning in experiment. The poisoning was induced by intraperitoneal administration to rats of cyanide solutions in doses of 5, 10 and 15 mg/kg. Methemoglobin solutions were injected intravenously in doses of 2 and 4 g/kg. All the rats given methemoglobin solution after the administration of cyanide survived. Spectrophotometry of rat urine demonstrated rapid excretion of methemoglobin cyanide.

Etiology of cerebral vasospasm in primates.

A primate model was used to determine whether oxyhemoglobin (OxyHb), methemoglobin (MetHb), or bilirubin is likely to be responsible for cerebral vasospasm following subarachnoid hemorrhage (SAH). Forty cynomolgus monkeys were randomly assigned to one of five groups. On Day 0, each animal underwent angiography followed by right craniectomy and placement of an Ommaya reservoir with its catheter adjacent to the right middle cerebral artery (MCA). The animals received intrathecal injections twice a day for 6 days of one of the following solutions: mock cerebrospinal fluid (CSF); OxyHb; MetHb; bilirubin; or supernatant fluid from an incubated mixture of autologous blood and mock CSF. On Day 7, angiography was repeated and the animals were killed. Comparison of angiograms obtained on Day 0 and Day 7 of the experiment showed significant vasospasm of the right MCA and the right anterior cerebral and internal carotid arteries in the animal groups that had received OxyHb or supernatant fluid. There was a smaller reduction in diameter of the same vessels in the bilirubin group (not statistically significant), while no effects were observed in the groups receiving MetHb or mock CSF. Electron microscopy of the right MCA's gave results consistent with the angiographic findings. One monkey in the OxyHb group developed a delayed-onset right MCA infarction. These data suggest that OxyHb is the cause of cerebral vasospasm following SAH.

Stroma-free methemoglobin solution: an effective antidote for acute cyanide poisoning.

Several aspects of stroma-free methemoglobin solution (SFMS) as a cyanide antidote were investigated using a rat model. Stroma-free methemoglobin solution was more than 90% effective against multiples of the LD90 of cyanide up to and including four times the LD90 and approximately 50% effective against multiples up to and including eight times the LD90. Highly concentrated solutions of SFMS (33 g/dl) did not differ significantly from less concentrated solutions of SFMS (16 g/dl) when compared on the basis of efficacy. Administration of large doses of SFMS alone resulted in no apparent morbidity or mortality. It could be that SFMS is a safe and effective alternative antidote for the treatment of cyanide poisoning.

Stroma-free methemoglobin solution as an antidote for cyanide poisoning: a preliminary study.

Effective treatment of cyanide poisoning requires rapid diagnosis, good supportive treatment and the use of a specific antidote. The currently available antidotes offer demonstrated efficacy along with significant potential adverse side effects. We have investigated an alternate approach to antidote therapy for cyanide poisoning by using Stroma-Free Methemoglobin Solution ( SFMS ). Rats injected with an LD100 intravenous dose of cyanide were treated with SFMS equal to 1.5% of their total body hemoglobin. There was a highly significant increase in the survival rate of the treated group compared to saline controls. The potential advantages of SFMS over current antidotes include an immediate onset of action, rapid elimination of cyanide from the body and a mode of action that doesn't compromise any of the patients' oxygen carrying capacity. SFMS shows promise as a significant adjunct in the treatment of cyanide poisoning.

Morphologic demonstration of tubular obstruction in acute renal failure.

We used the qualitative Hanssen technique in albino rats to seek morphologic demonstration of tubular obstruction in two types of acute renal failure: one induced by folic acid and another by methemoglobin. Immediately after the intravenous injection of folic acid, 250 mg/kg body weight, the animals became almost anuric. Two to three hours after the injection, sodium ferrocyanide remained within the proximal convoluted tubules. After the intravenous injection of methemoglobin, 0.5 to 1.0 g/kg body weight, the animals became oliguric but not anuric. Sodium ferrocyanide injected with methemoglobin was seen mainly in distal tubules and collecting ducts 2 to 3 hours after the injection. The degree of tubular dilatation was more marked in the former model than in the latter, in agreement with the degree of oliguria. These morphologic findings were taken to indicate that the above two types of acute renal failure were caused by tubular obstruction rather than by intrarenal vasoconstriction and subsequent cessation of glomerular filtration. (Am J Pathol 87:323-330, 1977).