Holger Schiffmann

Monitoring Regional Lung Ventilation by Functional Electrical Impedance Tomography during Assisted Ventilationa

Abstract: A new approach in discriminating the regional air volume changes in the lungs associated with either spontaneous or mechanical ventilation during assisted ventilation is presented. Impedance data are obtained by conventional electrical impedance tomography (EIT). The data are filtered in the range of either the spontaneous or the ventilator rate and processed by the functional EIT (f‐EIT) evaluation technique, whereby the variation of the respective EIT data with time is determined and imaged. EIT measurements performed in an infant during synchronized intermittent mandatory ventilation were evaluated with this method and indicated that the specific local lung volume swings related to spontaneous and mechanical inhalations can be separated and imaged as tomograms. This noninvasive approach may become useful in optimizing the ventilatory pattern during advanced forms of artificial ventilation and may help the clinician in the therapy management of individual patients.

Randomized, controlled trial of amoxicillin prophylaxis for prevention of catheter-related infections in newborn infants with central venous silicone elastomer catheters☆☆☆★

OBJECTIVE To clarify the effectiveness of amoxicillin prophylaxis in the prevention of catheter-related infections. METHOD We performed a randomized, controlled, sequential, prospective trial in newborn infants undergoing percutaneous central venous catheterization. RESULTS Seventy-five infants (median birth weight, 1240 gm; median age at catheter insertion, 3 days) received prophylactic amoxicillin (100 mg/kg per day); 73 infants in the control group (median birth weight, 1170 gm; median age, 2 days) received no routine prophylactic antibiotic treatment. No infant receiving amoxicillin had septicemia, whereas two infants (2.7%) in the control group did; suspected septicemia (positive clinical and laboratory findings but negative blood culture results) was found in 3 infants in the amoxicillin group and in 6 of the control group (not significantly). Bacterial contamination of the catheter tip at removal was significantly reduced in the amoxicillin group (13.3% vs 28.8% in control subjects; p < 0.05). Negligible differences were found in duration of catheterization (median, 15 days in both groups), or the number of thrombotic (9.3% vs 2.7% in control subjects) and other catheter-related complications between the groups. CONCLUSION A low incidence of catheter-related infections can be achieved in neonates with central venous catheters without using prophylaxis with an antibiotic.

Airway humidification in mechanically ventilated neonates and infants: A comparative study of a heat and moisture exchanger vs. a heated humidifier using a new fast-response capacitive humidity sensor

OBJECTIVE To study the efficiency of a heated humidifier and a heat and moisture exchanger in mechanically ventilated neonates and infants. DESIGN Prospective, controlled, clinical study. SETTING University pediatric intensive care unit. PATIENTS Forty neonates and infants who needed mechanical ventilation were enrolled in the study. INTERVENTIONS None. MEASUREMENTS AND MAIN RESULTS A heat and moisture exchanger and active airway humidification were alternately used in the same patients to exclude interindividual differences in airway humidification. Airway humidity was measured by a new fast-response capacitive humidity sensor which measures airway humidity with an acquisition rate of 20 Hz throughout the respiratory cycle. The humidity sensor was placed at the endotracheal tube adapter. Measurements were done at the beginning and at the end of three consecutive sessions of passive, active, and again passive airway humidification, each session lasting 6 hrs. There was no significant difference between mean inspiratory airway humidity with the heated humidifier (33.8 +/- 2.9 mg/L) and with the heat and moisture exchanger (34.0 +/- 2.6 mg/L). Moreover, the mode of airway humidification did not significantly influence body temperature or PCO2. No serious side effects such as endotracheal tube occlusion were observed. CONCLUSIONS Passive airway humidification by a heat and moisture exchanger is effective in mechanically ventilated neonates and infants over a 6-hr period. However, the performance and safety of a heat and moisture exchanger in prolonged mechanical ventilation remain to be proven.

Effects of epinephrine on the myocardial performance and haemodynamics of the isolated rat heart during moderate hypothermia — importance of calcium homeostasis

Controversies exist concerning myocardial performance in hypothermia. We have studied the effects of epinephrine on myocardial function at various calcium concentrations in moderate hypothermia (28 degrees C) and normothermia (37 degrees C) using an isolated antegrade perfused rat heart. The maximum pressure velocity (dP/dt(max)) developed was significantly higher in normothermia compared with hypothermia and was improved by the addition of calcium in both circumstances. Peak negative pressure velocity (dP/dt(min)) was significantly higher at 37 degrees C compared with 28 degrees C, and was increased by the addition of calcium in normothermia; in contrast to hypothermia, in which no change of dP/dt(min) was observed. A reduction in cardiac output and stroke volume by hypercalcaemia was observed in hypothermia. The addition of epinephrine improved dP/dt(max) and dP/dt(min), but had a depressive effect on stroke volume and cardiac output at normal and elevated calcium concentrations. Myocardial efficiency was significantly higher during hypothermia compared with normothermia, but was impaired by epinephrine during hypothermia. The variable or even paradoxical effects of epinephrine suggest the need for careful haemodynamic monitoring and determination of calcium levels in hypothermia. The impairment of myocardial performance may be explained by impaired diastolic relaxation and calcium overload.

Determination of airway humidification in high-frequency oscillatory ventilation using an artificial neonatal lung model : Comparison of a heated humidifier and a heat and moisture exchanger

Objective: Thus far only few data are available on airway humidification during high-frequency oscillatory ventilation (HFOV). Therefore, we studied the performance and efficiency of a heated humidifier (HH) and a heat and moisture exchanger (HME) in HFOV using an artificial lung model. Methods: Experiments were performed with a pediatric high-frequency oscillatory ventilator. The artificial lung contained a sponge saturated with water to simulate evaporation and was placed in an incubator heated to 37 °C to prevent condensation. The airway humidity was measured using a capacitive humidity sensor. The water loss of the lung model was determined gravimetrically. Results: The water loss of the lung model varied between 2.14 and 3.1 g/h during active humidification; it was 2.85 g/h with passive humidification and 7.56 g/h without humidification. The humidity at the tube connector varied between 34.2 and 42.5 mg/l, depending on the temperature of the HH and the ventilator setting during active humidification, and between 37 and 39.9 mg/l with passive humidification. Conclusion: In general, HH and HME are suitable devices for airway humidification in HFOV. The performance of the ventilator was not significantly influenced by the mode of humidification. However, the adequacy of humidification and safety of the HME remains to be demonstrated in clinical practice.

Effects of different inotropic interventions on myocardial function in the developing rabbit heart

Abstract The development of the mammalian heart is characterized by substantial changes in myocardial performance. We studied the ontogeny of myocardial function with and without various inotropic interventions in the developing isolated, antegrade-perfused rabbit heart (2d, 8d, 14d, 28d, n = 96). Myocardial function was related to the protein expression of the sarcolemmal Na+-Ca2+ exchanger and to the sarcoplasmic Ca2+-ATPase.In neonatal hearts an age-dependent increase in maximal developed pressure velocity (dP/dtmax) by 45 % and peak negative pressure velocity (dP/dtmin) by 75 % within days 2 to 8 were observed. In response to inotropic intervention with isoproterenol, ouabain, calcium and the Na+-channel modulator BDF 9148, dP/dtmax and dP/dtmin increased in a concentration dependent manner. Significant differences between neonatal, juvenile and adult hearts could be demonstrated in a repeated measurement ANOVA model on the concentration-response curves for BDF 9148 (dP/dtmax and dP/dtmin), ouabain (dP/dtmin) and calcium (dP/dtmin), but not for isoproterenol. At the maximum isoproterenol concentration of 1 μmol/l, the increase in dP/dtmax and dP/dtmin was significantly higher in adult compared to neonatal hearts (t-test, p < 0.01). The significant decline of the Na+-Ca2+ exchanger protein expression from neonatal (1822 ± 171) to adult hearts (411 ± 96 S.E.M. [units per 20 μg protein], p < 0.01) was related to an increase in myocardial function (dP/dtmax r = 0.63, p < 0.01, dP/dtmin r = 0.62, p < 0.01).Contractility, relaxation and the observed positive inotropic effects were in general significantly lower in neonatal compared to adult hearts. In the individual heart an increase in contractility and relaxation was related to a decrease in Na+-Ca2+ exchanger expression.

Gene expression of the Na-Ca2+ exchanger, SERCA2a and calsequestrin after myocardial ischemia in the neonatal rabbit heart.

Background: Neonatal hearts are less susceptible to developing myocardial dysfunction after hypoxia and/or ischemia than adult hearts. Differences in intracellular calcium homeostasis may be responsible for reduced calcium overload of the immature myocardium leading to the observed protection against ischemia. Objective: To assess differences in baseline and post-ischemic gene expression of calcium handling proteins after ischemia in neonatal and adult rabbit hearts. Methods: We used isolated antegrade perfused rabbit hearts (age 2 days, 28 days, n = 32), which were exposed to ischemia and hypothermia simulating myocardial stunning comparable to neonatal asphyxia. Gene and protein expression of the sodium–calcium exchanger (NCX), the sarco-endoplasmatic reticulum Ca2+-ATPase 2a (SERCA) and calsequestrin (CSQ) were measured using quantitative real-time PCR and Western blotting. Results: After ischemia and reperfusion in neonatal and adult hearts, a significant decrease in myocardial performance was recorded. At the mRNA level, significant differences in the baseline expression of NCX, SERCA and CSQ between neonatal and adult hearts were observed. In neonatal post-ischemic hearts, NCX and CSQ expression were significantly higher at the mRNA level than in controls. In contrast, SERCA expression remained unchanged in neonatal hearts and decreased in adult hearts compared to the non-ischemic controls. Conclusion: These findings suggest that changes in gene expression of calcium handling proteins may be involved in the different susceptibility of neonatal compared to adult hearts to developing myocardial dysfunction after ischemia.

Na+-channel modulation, a new principle of inotropic intervention: Effects on hemodynamic and myocardial energetics in the immature rabbit heart

Na+-channel modulators exert their positive inotropic action without affecting the adenylate-cyclase pathway by an increase in the open probability of the sarcolemmal Na+ channels. Although inotropic effects in neonatal hearts are less pronounced compared with adult hearts, the Na+-channel modulator BDF 9148 increases contractility and relaxation velocity in immature myocardium. Effects on hemodynamics and myocardial energetics are not known. Therefore, we studied the Na+-channel modulator BDF 9148 in isolated antegrade perfused rabbit hearts of different ages (2-28 d) and compared the effects with isoproterenol, enoximone, and ouabain. ANOVA showed significant effects in the concentration response curves for heart rate, stroke volume, cardiac output, and oxygen consumption but not for myocardial efficiency (p = 0.06). Age-dependent differences were observed for heart rate and stroke volume. Administration of BDF 9148 resulted in a maximal increase in stroke volume and cardiac output up to 25% in neonatal and 40% to 60% in adult preparations. Heart rate decreased by 15% in adult hearts only. Myocardial oxygen consumption was increased in a concentration-dependent manner between 25% in neonatal and 50% in adult hearts. Myocardial efficiency was increased by 35% in adult and by 10% in neonatal preparations. Although positive hemodynamic and energetic effects were less pronounced in immature compared with adult hearts, neonatal hearts also profited from the administration of the Na+-channel modulator BDF 9148. Further studies are necessary to clarify the risk of arrhythmia during application of Na+-channel modulators such as BDF 9148.