Aortopulmonary collateral artery embolization during postoperative extracorporeal membrane oxygenation after arterial switch procedure

Aortopulmonary collateral arteries sometimes complicate cyanotic congenital heart defects. Combined with a relevant left-right shunt, this could result in massive airway bleeding during and after corrective surgery. A preoperatively diagnosed 1.2 mm small aortopulmonary collateral artery in a newborn suffering from transposition of the great arteries caused life-threatening airway bleeding during surgery. Postoperative extracorporeal membrane oxygenation (ECMO) was necessary, and coil embolization was performed on ECMO to terminate pulmonary bleeding.     

Termination of extracorporeal membrane oxygenation for cardiac support

The determination of when to stop extracorporeal membrane oxygenation (ECMO) rests upon demonstration of the return of adequate cardiac function to support vital organs and permit subsequent recovery. In general, patients with myocardial stun will recover function within several days. Factors that limit recovery include elevated end diastolic pressures leading to marginal myocardial perfusion, ongoing organ damage, massive anasarca, or progressive deterioration in lung function. Following a trial of slow weaning of ECMO support to condition the heart to take over the entire system flow requirements, decannulation can be accomplished in a standard fashion. When weaning is not successful and additional time does not lead to adequate recovery of cardiac function, physicians and nurses must be prepare to realistically advise families regarding such options as cardiac transplantation or withdrawal of support. It is critically important to provide an open and nonjudgmental environment for families to make these difficult decisions. The greatest difficulties involve ethical and emotional decisions that need to be made in a timely fashion to prevent undo burden on the patient when further ECMO support is futile.     

高压氧治疗小儿重型颅脑损伤(附68例报告)

６８例小儿重型颅脑损伤,在常规治疗基础上加用高压氧治疗３２例,治愈率达７１９％,总有效率９６．９％。与常规治疗组相比,疗效明显提高,经统计学处理有明显差异（Ｐ＜００１）。     

Twenty-four-hour venoarterial extracorporeal membrane oxygenation without systemic heparinization in dogs

Venoarterial extracorporeal membrane oxygenation (ECMO) was performed in five dogs without systemic heparinization to assess the feasibility of heparin-free ECMO. The surfaces of the inverted hollow-fiber-type oxygenator and circuit of the ECMO system were coated with heparin by the endpoint-attached (covalent-bonded) technique. No heparin was administered to the animal except for a small dose to maintain patency of the arterial line (1 IU/h). ECMO was run for 24 h at a pump flow of 50 ml/kg · min and was successful throughout the experiment in four of the five dogs. Scanning electron microscopy did not detect any blood clots in the oxygenator or circuit except for inside and outside the cannulas that were not coated with heparin in the carotid artery and jugular vein. Activated clotting time (ACT), fibrinogen, and anti-thrombin III (AT-III) activity remained within the normal physiological range. Serum heparin concentrations were low throughout the experiment, indicating minimal heparin release. Platelet levels decreased and fibrinopeptide B 15–42 (FPB 15–42) increased significantly after 6 h ECMO. D-dimer levels did not change throughout the experiment. ECMO was discontinued in one case after successful a 23-h run because of macroscopic clot formation at the oxygenator blood inlet. ACT had suddenly increased to 160 s approximately 1 h prior to this clot formation. These results suggest that the amount of systemic heparinization required can be substantially reduced by a heparin-coated ECMO system. Total abolishment of heparin administration in pediatric venoarterial ECMO may be possible by refinement of this technique. Monitoring of AT-III and FPB 15–42 in addition to ACT may be useful for early diagnosis of latent but ongoing coagulopathies during ECMO.     

How often is extracorporeal membrane oxygenation needed in cases of congenital diaphragmatic hernia?

Some newborns with congenital diaphragmatic hernia (CDH) and severe pulmonary hypertension cannot be saved by conventional treatment and may obtain some benefit from extracorporeal membrane oxygenation (ECMO) as a bridging measure until adequate hematosis is possible. Early prediction of the insufficiency of optimal assistance is still unclear; we reviewed our recent experience with CDH patients in an attempt to evaluate the real need for ECMO in our institution. Between 1987 and 1994, 47 newborns with CDH manifested in the first 24 h were treated with maximal ventilatory assistance (including high-frequency ventilation in 12 cases) and vasoactive drugs prior to surgical repair. In order to summarize the ventilatory and blood-gas parameters, we determined oxygenation index (OI) and ventilatory index (VI) and compared the results in survivors and nonsurvivors. Overall survival was 60% (2 cases of Fryns' syndrome were excluded from analysis). OI was 10.3±5.7 (mean ± SD) for survivors and 46.2 ± 37.8 for nonsurvivors (P < 0.01). VI was 460.9±303 and 1,532±500.6, respectively (P <0.01). Bayesian analysis and receiver operating characteristic curves enabled us to select a threshold value of OI of 20 as the best means of predicting survival in our current conditions (sensitivity: 0.7, specificity: 0.83). The generally accepted figure of 40 had a sensitivity of 1 but a specificity of only 0.44. For VI, the best threshold value was 1,100 (sensitivity: 0.93, specificity: 0.94), whereas the generally used figure of 1,000 had 0.89 and 1, respectively. According to our results, with our current management conditions, approximately 50% of our CDH patients might have obtained some benefit from ECMO.     

The effect of separate red blood cells on capillary tissue oxygenation calculated with a numerical model

Author to whom correspondence should be addressed In simplified models that describe large quantities of capillariesthe capillary content is considered to be homogeneous for oxygentransport; but, in reality, the capillaries contain discretered blood cells (RBCs), and this discreteness will affect oxygentransport from the capillary to the tissue. This was previouslyinvestigated with an analytical model, where RBCs were modelledas point-like sources. A numerical approach is used in thisinvestigation, and the results are compared with the analyticalmodel. In both models the effect of the particulate nature ofblood depends on the haematocrit and on the RBC velocity. Thereis only a minor difference between the two models. For rat hearts,the correction factor used in this study, the extraction pressure,can be up to 3 kPa (23 mmHg).     

Aerosolized prostacyclin and inhaled nitric oxide in septic shock — different effects on splanchnic oxygenation?

Objectives To compare the effects of inhaled nitric oxide and aerosolized prostacyclin (PGI₂) on hemodynamics and gas exchange as well as on the indocyanine-green plasma disappearance rate and gastric intramucosal pH in patients with septic shock.Design Prospective, randomized, interventional clinical study.Setting Intensive care unit in a university hospital.Patients Sixteen patients with pulmonary hypertension and septic shock according to the criteria of the ACCP/SCCM consensus conference all requiring norepinephrine and/or epinephrine to maintain mean arterial blood pressure above 65 mmHg.Methods and interventions Patients were randomly assigned to receive either nitric oxide or aerosolized prostacyclin. Nitric oxide was inhaled using a commercially available delivery system, prostacyclin was administered with a modified ultrasound nebulizer. Both nitric oxide and prostacyclin were incrementally adjusted to obtain a 15% decrease of mean pulmonary artery pressure. Hemodynamics and gas exchange as well as indocyaninegreen plasma disappearance rate and gastric intramucosal pH were determined at baseline after 90 min in steady state, after 90 min of nitric oxide inhalation or prostacyclin aerosol administration had elapsed in stable conditions, and after 90 min in stable conditions after nitric oxide or prostacyclin with-drawal.Results Both inhaled nitric oxide and aerosolized prostacyclin selectively reduced the mean pulmonary artery pressure from 35±4, 30±4 mmHg (p<0.05) and 34±4 to 30±3 mmHg (p<0.05) respectively; after removal of nitric oxide and prostacyclin, the mean pulmonary artery pressure returned to the baseline values. Systemic hemodynamics remained unaltered during the vasodilator treatment. While the mean PaO₂ was not significantly influenced, it increased in 4/8 of the NO- and 3/8 of the PGI₂ — treated patients. Neither of the drugs influenced indocyanine-green plasma disappearance rate, but prostacyclin — unlike nitric oxide — significantly increased gastric intramucosal pH (from 7.26±0.07 to 7.30±0.05,p<0.05) which remained elevated in four of these patients after prostacyclin removal, and decreased the arterial-gastric mucosal pressure of carbon dioxide gap from 19±6 to 15±4 mmHg (p<0.05).Conclusions Our data suggest that aerosolized prostacyclin — unlike nitric oxide — has similar beneficial effects on splanchnic perfusion and oxygenation as intravenous prostacyclin without detrimental effects on systemic hemodynamics. The different effects of prostacyclin and nitric oxide might be explained by the longer half-life of prostacyclin associated with a certain spillover into the systemic circulation.Presented in part at the Masterclass Symposium Sepsis in the ICU, Maastricht, June 27–29, 1995     

Dopamine,dopexamine and dobutamine in liver transplant recipients: a comparison of their effects on hemodynamics,oxygen transport and hepatic venous oxygen saturation

The purpose of this study was to determine the effects of vasoactive treatment with dopamine (DO), dopexamine (DX), and dobutamine (DOB) on hemodynamics, oxygen transport and hepatic venous oxygen saturation (SvhO₂) after orthotopic liver transplantation (OLT). A pulmonary artery catheter was inserted into the right hepatic vein of 17 OLT patients. Timed infusion of DO, DX, and DOB was performed at the following rates: DO at 4 and 8 g/kg per minute, and DOB at 5 and 10 g/kg per minute. Hemodynamics, oxygen transport variables, and SvhO₂ were assessed. Each catecholamine induced a significant increase in cardiac index, oxygen delivery, and SvhO₂. Mean arterial pressure was increased during DO and DOB, but significantly reduced during DX. Each inotrope increased oxygen delivery in parallel with SvhO₂, suggesting a corresponding increase in hepatic oxygen supply. Therefore, it appears that each vasoactive drug may be utilized in OLT patients to provide oxgen delivery without impairment of splanchnic oxygenation.     

Effects of synchronous pulsatile extracorporeal membrane oxygenation in an endotoxin-induced shock model: an experimental study

A synchronous pulsatile venoarterial device for extracorporeal membrane oxygenation (ECMO) was designed to accomplish more effective circulatory support for neonates. The effect of this device was studied using an endotoxin-induced shock model, compared with conventional nonpulsatile ECMO. Twenty puppies weighing 1.6 to 4.0 kg were given endotoxin (5 mg/kg) intravenously. Thirty minutes after the administration of endotoxin, 10 were placed on pulsatile ECMO, and the others were placed on nonpulsatile ECMO, and they were studied for an additional 180 min. Peak blood pressure, arterial pH, base excess, and renal blood flow were significantly higher in the pulsatile group than in the nonpulsatile group. Serum lactate and serum noradrenaline were significantly lower in the pulsatile group than in the nonpulsatile group. These results indicate that pulsatile ECMO may provide more effective cardiopulmonary support in the treatment of neonates with serious circulatory failure that has failed to be supported by nonpulsatile ECMO.     

Evaluation of high-frequency jet ventilation in oxygenation through an artificial membrane lung

The membrane oxygenator often develops impaired gas exchange after prolonged use because plasma proteins adhere to the membrane's surface and leak through its micropores. This study was performed to examine the efficacy of high-frequency jet ventilation (HFJV) in minimizing these problems in a "flat plate" type of membrane oxygenator. We first vibrated the membrane of the oxygenator by HFJV from 1 to 10 Hz to find the frequency most effective for optimal gas exchange in animals with partial extracorporeal circulation. These studies suggested that 6 Hz HFJV was preferable in our model. We subsequently performed in vivo extracorporeal oxygenation in dogs for 8 h using the membrane oxygenator with or without 6 Hz HFJV. Although the gas exchange capacity within the first 8 h was similar in the two groups, after 6 h a significant decrease in the red blood cell count and in the hematocrit was found in the group not receiving HFJV. Scanning electron microscopic examination of the membranes after 8 h of use disclosed that the membrane from the group receiving HFJV had less plasma protein and fibrin adhesion than that from the group not receiving HFJV. Moreover, it appears that with prolonged extracorporeal oxygenation, 6 Hz HFJV also protects against a decrease in the hematocrit of the passed blood and might lead to enhanced gas exchange. Our data suggest that good gas exchange can be maintained for periods even longer than 8 h if HFJV is used in conjunction with the membrane oxygenator.