Waveform analysis of biphasic external defibrillators.

BACKGROUND AND OBJECTIVE: All internal defibrillators and some external defibrillators use biphasic waveforms. The study analysed the discharged waveform pulses of two manual and two semi-automated biphasic external defibrillators. METHODS AND RESULTS: The defibrillators were discharged into resistive loads of 25, 50 and 100 Omega simulating the patient's transthoracic impedance. The tested biphasic defibrillators differed in initial current as well as initial voltage, varying from 10.9 to 73.3 A and from 482.8 to 2140.0 V, respectively. The energies of the manual defibrillators set at 100, 150 and 200 J deviated by up to +19.1 or -28.9% from the selected energy. Impedance-normalised delivered energy varied from 1.0 to 12.5 J/Omega. Delivered energy, shock duration and charge flow were examined with respect to the total pulse, its splitting into positive and negative phases and their impedance dependence. For three defibrillators pulse duration increased with the resistive load, whereas one defibrillator always required 9.9 ms. All tested defibrillators showed a higher charge flow in the positive phase. Defibrillator capacitance varied between approximately 200 and 100 mu F and internal resistance varied from 2.0 to 7.6 Omega. Defibrillator waveform tilt ranged from -13.1 to 61.4%. CONCLUSIONS: The tested defibrillators showed remarkable differences in their waveform design and their varying dependence on transthoracic impedance.

Inotropic treatment and intestinal mucosal tissue oxygenation in a model of porcine endotoxemia.

OBJECTIVE: To evaluate the dose-related effects of dopamine, dopexamine, and dobutamine on intestinal mucosal tissue oxygenation following short-time infusion of Escherichia coli lipopolysaccharide, which has previously been shown to decrease mucosal tissue oxygenation by 60% of control values. DESIGN: Prospective, randomized, unblinded study. SETTING: Animal research laboratory. SUBJECTS: Anesthetized, mechanically ventilated domestic pigs. INTERVENTIONS: Pigs were infused with 2 microg/kg of E. coli lipopolysaccharide over 20 mins via the superior mesenteric artery. Pulmonary artery occlusion pressure was maintained near 15 mm Hg, using a mixed infusion regimen of Ringer's lactate solution and hydroxyethyl starch. Following endotoxemia, a small segment of the jejunal mucosa was exposed by midline laparotomy and antimesenteric incision. The control group (n = 7) received no further interventions. Pigs in the dopamine (n = 7), dopexamine (n = 7), and dobutamine (n = 7) groups were infused with 2.5, 5, 10, and 20 microg/kg/min of the respective drug via a central venous catheter. MEASUREMENTS AND MAIN RESULTS: Systemic hemodynamics as well as systemic, mesenteric, and femoral blood gas variables were measured using an arterial, a thermodilution pulmonary artery, a superior mesenteric venous, and a femoral venous catheter. Jejunal mucosal tissue PO2 was measured by means of two Clark-type surface oxygen electrodes. Oxygen saturation of jejunal mucosal microvascular hemoglobin was determined by tissue reflectance spectrophotometry. Infusion of endotoxin resulted in pulmonary hypertension. Systemic hemodynamics remained unchanged except for brief decreases in cardiac output and arterial blood pressure. Dopamine, dopexamine, and dobutamine increased systemic oxygen delivery in a dose-related manner by 80% (p < .01), 96% (p = .00), and 129% (p = .00) of values before inotropic treatment. Dopamine increased mucosal tissue PO2 by 109% (10-microg dose, p < .01) and 164% (20-microg dose, p = .00), and mucosal hemoglobin oxygen saturation by 61% (5-microg dose, p < .05), 102% (10-microg dose, p < 01) and 121% (20-microg dose, p = .00). Dopexamine increased mucosal tissue PO2 by 89% (20-microg dose, p < .01) and mucosal hemoglobin oxygen saturation by 26% (2.5-microg dose, p < .05) and 35% (5-, 10-, and 20-microg dose, p < .05). In the dobutamine and control groups, no significant effect on either mucosal tissue PO2 or hemoglobin oxygen saturation was observed. CONCLUSIONS: In this model of porcine endotoxemia, dopamine and, to a lesser extent, dopexamine increase intestinal mucosal tissue oxygenation. Of all three inotropes used, dobutamine has the most pronounced effect on systemic oxygen delivery, but it does not improve mucosal tissue oxygenation. Selective vasodilation within the intestinal mucosa, mediated mainly by dopamine-1 receptors, seems to explain the observed intestinal mucosal effect of dopamine and dopexamine.

Effects of short-term endotoxemia and dopamine on mucosal oxygenation in porcine jejunum.

Effects of Escherichia coli lipopolysaccharide (2 micrograms.kg-1.20 min-1; LPS), given systemically (S) or via superior mesenteric artery (M), and consecutive dopamine infusion (16 micrograms.kg-1.20 min-1) on jejunal mucosal tissue O2 tension (PO2muc) and serosal tissue O2 tension (PO2ser; Clark-type surface electrodes) and jejunal mucosal microvascular hemoglobin O2 saturation (HbO2muc; tissue reflectance spectrophotometry) were investigated in a hemodynamically stable pig model. Twenty-one pigs were anesthetized, paralyzed, and mechanically ventilated. After laparotomy, a mesenteric venous catheter was inserted and a jejunal antimesenteric enterotomy performed. LPS-infused animals developed similar degrees of pulmonary hypertension. No differences in cardiac output and mean arterial blood pressure between groups were found. PO2muc and HbO2muc were significantly lower in M animals compared with control (C) [210 min; PO2muc: 7.12 +/- 1.81 (M), 19.01 +/- 3.12 mmHg (C); HbO2muc: 28.78 +/- 3.36 (M), 49.09 +/- 3.84% (C)], whereas S animals ranged in between (PO2muc: 13.36 +/- 2.2 mmHg; HbO2muc: 40.68 +/- 4.43%). Of measured PO2muc values, 12.6 (C), 20.6 (S), and 46.3% (M) ranged from 0 to 5 mmHg. PO2ser was lower in LPS animals compared with control [59.43 +/- 5.4 (C), 45.00 +/- 6.12 (S), 47.33 +/- 4.34 (M) mmHg]. Dopamine increased PO2muc and HbO2muc to similar absolute values and significantly decreased frequency of PO2muc (0-5 mmHg) in M animals. We conclude that LPS impairs mucosal tissue oxygenation independently of systemic hemodynamics. Mucosal microvascular dysfunction depends on regional LPS concentrations. Under conditions of compromised tissue oxygenation, dopamine significantly improves PO2muc and HbO2muc.