Effects of Perfluorohexan Vapor on Gas Exchange, Respiratory Mechanics, and Lung Histology in Pigs with Lung Injury after Endotoxin Infusion

Background: Inhaled perfluorohexan vapor has been shown to improve gas exchange and pulmonary mechanics in oleic acid- and ventilator-induced lung injury. However, in the clinical setting, lung injury frequently occurs in the context of systemic inflammation and consecutive lung injury, which may be induced experimentally by intravenous administration of endotoxin. The authors studied whether vaporized perfluorohexan is efficacious during endotoxin-induced lung injury in domestic pigs.

Methods: Twenty-two pigs (29 [23, 31] kg body weight [first, third interquartile]; tracheostomy) were anesthetized and mechanically ventilated. In the endotoxin (n = 8) and perfluorohexan groups (n = 7), we administered endotoxin of Escherichia coli 111:B4, 1 mg [middle dot] kg-1 [middle dot] h-1 for 1 h and 10 [mu]g [middle dot] kg-1 [middle dot] h-1 for 5 h in consecutive order. In the perfluorohexan group, inhalation of the test drug was started 2 h 30 min after the start of the intravenous endotoxin and terminated after 30 min. In a control group (n = 7), animals were instrumented and observed over time without further intervention. Oxygenation function was assessed from oxygen partial pressures (Po2, blood gases) and calculated shunt fraction. Respiratory compliance was calculated from airway pressure and tidal volume. Measurements were performed before and every hour during endotoxin infusion.

Results: After 6 h of endotoxin, gas exchange and pulmonary compliance were deteriorated in the endotoxin group (Pao2: 184 [114, 289] vs. 638 [615, 658] mmHg, pulmonary shunt fraction: 30 [23, 38] vs. 4 [3, 6]%, respiratory compliance: 12 [11, 14] vs. 22 [19, 23] ml/mbar; P < 0.05, endotoxin vs. control). Inhalation of vaporized perfluorohexan did not improve Pao 2 (107 [60, 221] mmHg), pulmonary shunt fraction (32 [26, 58]%), or respiratory compliance (14 [10, 17] ml/mbar) when compared with intravenous endotoxin (not significant, perfluorohexan vs. endotoxin).     

Inhaled nitric oxide (NO) for the treatment of early allograft failure after lung transplantation

Objective: Inhalation of high concentrations of nitric oxide (NO) has been shown to improve gas exchange and to reduce pulmonary vascular resistance in individuals with ischemia-reperfusion injury following orthotopic lung transplantation. We assessed the cardiopulmonary effects of low doses of NO in early allograft dysfunction following lung transplantion. Design: Prospective clinical dose- response study. Setting: Anesthesiological intensive care unit of a university hospital. Patients and participants: 8 patients following a single or double lung transplantation who had a mean pulmonary arterial pressure (PAP) in excess of 4.7 kPa (35 mmHg) or an arterial oxygen tension/fractional inspired oxygen ratio (PaO₂/FIO₂) of less than 13.3 kPa (100 mmHg). Interventions: Gaseous NO was inhaled in increasing concentrations (1, 4 and 8 parts per million, each for 15 min) via a Siemens Servo 300 ventilator. Measurements and results: Cardiorespiratory parameters were assessed at baseline, after each concentration of NO, and 15 min after withdrawal of the agent [statistics: median (25th/75th percentiles: Q1/Q3), rANOVA, Dunnett's test, p < 0.05]. Inhaled NO resulted in a significant, reversible, dose-dependent, selective reduction in PAP from 5.5(5.2/6.0) kPa at control to 5.1(4.7/5.6) kPa at 1 ppm, 4.9(4.3/5.3) kPa at 4 ppm, and to 4.7(4.1/5.1) kPa at 8 ppm. PaO₂ increased from 12.7(10.4/17.1) to 19.2(12.4/26.0) kPa at 1 ppm NO, to 23.9(4.67/26.7) kPa at 4 ppm NO and to 24.5(11.9/28.7) kPa at 8 ppm NO. All patients responded to NO inhalation (either with PAP or PaO₂), all were subject to long-term inhalation (1–19 days). All were successfully weaned from NO and were discharged from the intensive care unit. Conclusion: The present study demonstrates that low-dose inhaled NO may be an effective drug for symptomatic treatment of hypoxemia and/or pulmonary hypertension due to allograft dysfunction subsequent to lung transplantation. Received: 23 February 1998 Accepted: 20 August 1998     

Hyperoxic Ventilation Reduces 6-Hour Mortality at the Critical Hemoglobin Concentration

Background: Acute normovolemic hemodilution reduces the circulating erythrocyte mass and, thus, the hemoglobin concentration. After extreme acute normovolemic hemodilution to the critical hemoglobin concentration (Hbcrit), oxygen demand of the tissues is no longer met by oxygen supply, and death occurs with increasing oxygen debt. The aim of the current study was to investigate whether ventilation with 100% oxygen (fraction of inspired oxygen [Fio2] = 1.0; hyperoxic ventilation) initiated at Hbcrit could restore adequate tissue oxygenation and prevent death.

Methods: Fourteen anesthetized pigs ventilated with room air (Fio2 = 0.21) were hemodiluted by exchange of whole blood for 6% hydroxyethyl starch (200,000:0.5) until the individual Hbcrit was reached. Hbcrit was defined as the onset of oxygen supply dependency of oxygen consumption and was identified with indirect calorimetry. For the next 6 h, animals were either ventilated with an Fio2 of 0.21 (n = 7) or an Fio2 of 1.0 (n = 7).

Results: All animals in the 0.21 Fio2 group died within the first 3 h at Hbcrit (i.e., 6-h mortality 100%). Death was preceded by an increase of serum concentrations of lactate and catecholamines. In contrast to that, six of the seven animals of the 1.0 Fio2 group survived the complete 6-h observation period without lactacidosis and increased serum catecholamines (i.e., 6-h mortality 14%; Fio2 0.21 vs. Fio2 1.0, P <= 0.05). After 6 h at Hbcrit, the Fio2 was reduced from 1.0 to 0.21, and five of the six animals died within the next 3 h.     

Can we continue research in splenectomized dogs? Mycoplasma haemocanis: old problem--new insight

We report the appearance of a Mycoplasma haemocanis infection in laboratory dogs, which has been reported previously, yet, never before in Europe. Outbreak of the disease was triggered by a splenectomy intended to prepare the dogs for a hemorrhagic shock study. The clinical course of the dogs was dramatic including anorexia and hemolytic anemia. Treatment included allogeneic transfusion, prednisone, and oxytetracycline. Systematic follow-up (n = 12, blood smears, antibody testing and specific polymerase chain reaction) gives clear evidence that persistent eradication of M. haemocanis is unlikely. We, therefore, had to abandon the intended shock study. In the absence of effective surveillance and screening for M. haemocanis, the question arises whether it is prudent to continue shock research in splenectomized dogs.     

The prostaglandins epoprostenol and iloprost increase left ventricular contractility in vivo

OBJECTIVE: The principal effects of prostaglandin I(2) are vasodilation and inhibition of platelet aggregation induced by a rise in the intracellular second messenger cAMP. In the heart a rise in intracellular myocardial cAMP increases contractility. We examined whether prostaglandin I(2) increases left ventricular contractility in vivo. The effects of epoprostenol and iloprost on left ventricular contractility were assessed in vivo and compared to the effects of adenosine and sodium nitroprusside, which exerts vasodilatory properties independently of cAMP. DESIGN AND SETTING: Prospective, randomized, cross-over in a university laboratory. SUBJECTS: Eleven pigs (25.9+/-2.8 kg, balanced anesthesia). INTERVENTIONS: Each animal was exposed to intravenous sodium nitroprusside, adenosine, and epoprostenol in randomized order. Iloprost was administered at the end due to its longer half-life. The dose was titrated to achieve a 25% reduction in diastolic aortic pressure. MEASUREMENTS AND RESULTS: Left ventricular contractility was assessed before, during, and after each intervention by determination of the endsystolic elastance with the conductance method. While there was no change in endsystolic elastance upon the infusion of adenosine and sodium nitroprusside; endsystolic elastance increased in the case of epoprostenol (57%) and iloprost (71%). CONCLUSIONS: Left ventricular contractility is increased in vivo by epoprostenol and iloprost but not by adenosine or sodium nitroprusside at equipotent hypotensive dose. A contribution of sympathetic reflex activation of cardiac nerves on the increase in left ventricular contractility cannot be completely ruled out.     

Inhibition of glioblastoma growth in a highly invasive nude mouse model can be achieved by targeting epidermal growth factor receptor but not vascular endothelial growth factor receptor-2

PURPOSE: Major shortcomings of traditional mouse models based on xenografted human glioblastoma cell lines are that tumor cells do not invade and that genetic alterations, such as amplification of the epidermal growth factor receptor (EGFR) gene, are not maintained. Such models are thus of limited value for preclinical studies. We established a highly invasive model to evaluate the effect of antibodies against EGFR (cetuximab) and vascular endothelial growth factor receptor-2 (antibody DC101). EXPERIMENTAL DESIGN: After short-term culture, glioblastoma spheroids were implanted into the brains of nude mice. Animals were treated either i.c. with cetuximab or i.p. with DC101. Tumor burden was determined histologically using image analysis of 36 different landmark points on serial brain sections. RESULTS: Invasive xenografts were obtained from nine different glioblastomas. Three of seven cases treated with cetuximab responded with significant tumor growth inhibition, whereas four did not. All responsive tumors were derived from glioblastomas exhibiting EGFR amplification and expression of the truncated EGFRvIII variant, which were maintained in the xenografts. All nonresponsive tumors lacked EGFR amplification and EGFRvIII expression. The proportion of apoptotic cells was increased, whereas proliferation and invasion were decreased in responsive tumors. None of four xenograft cases treated with DC101 responded to treatment, and the diffusely invading tumors grew independent of angiogenesis. CONCLUSIONS: Inhibition of glioblastoma growth and invasion can be achieved using i.c. delivery of an anti-EGFR antibody, but tumor response depends on the presence of amplified and/or mutated EGFR. Antiangiogenic treatment with DC101 is not effective against diffusely invading tumors.     

Dosage of inhaled nitric oxide: a simple method for experimental studies

Few studies on treatment with inhaled nitric oxide (NOi) have been carried out in small laboratory animals yet, since commercially available dosing devices are not appropriate in this setting for technical or financial reasons. The aim of our study was to establish and validate a simple, cost-effective system for the application of NOi in small animals. The system mixes NOi with constant-flow inspiratory gas. A gas blender allows for a mixture of nitrogen, oxygen, and NO dissolved in nitrogen. A formula using the desired inspiratory oxygen fraction and the desired concentration of NOi as independent variables derives a somewhat higher inspiratory oxygen fraction, which is preset using an oximeter. Then the flow of NO in nitrogen is started, lowering the inspiratory oxygen fraction to the initially desired value, thereby adding NOi in the desired concentration. The method was validated by 153 adjustments, covering a variety of oxygen fractions and concentrations of NOi. NOi was measured by chemiluminescence as reference method. A close correlation (R=0.994) was found, and the regression line was close to the line of identity with y=-0.0994+1.048x. No systematic errors could be identified. We conclude that the method described may serve as a simple, cost-effective way to administer NOi to small animals.     

Diaspirin crosslinked hemoglobin enables extreme hemodilution beyond the critical hematocrit

BACKGROUND: Normovolemic hemodilution is an effective strategy to limit perioperative homologous blood transfusions. The reduction of hematocrit related to hemodilution results in reduced arterial oxygen content, which initially is compensated for by an increase in cardiac output and oxygen extraction ratio. To increase the efficacy of hemodilution, a low hematocrit should be aimed for; however, this implies the risk of myocardial ischemia and tissue hypoxia. OBJECTIVE: To assess whether hemodilution can be extended to lower hematocrit values by the use of a hemoglobin-based artificial oxygen carrier solution. DESIGN: Prospective, randomized, controlled. SETTING: Animal laboratory of a university hospital. SUBJECTS: Twelve anesthetized, mechanically ventilated pigs. INTERVENTIONS: Isovolemic hemodilution was performed with either 10% diaspirin crosslinked hemoglobin (DCLHb Baxter Healthcare, Boulder, CO; n = 6) or 8% human albumin solution (HSA, oncotically matched to DCLHb, Baxter Healthcare; n = 6) to a hematocrit of 15%, 8%, 4%, 2%, and 1%. MEASUREMENTS AND MAIN RESULTS: In both groups, measurements were performed at baseline at the previously mentioned preset hematocrit values and at the onset of myocardial ischemia characterized by critical hematocrit (significant ST-segment depression >0.1 mV and/or arrhythmia). To determine peripheral tissue oxygenation and myocardial perfusion and function, the following variables were evaluated: total body oxygen transport variables, tissue oxygen partial pressure (tPo2, MDO-Electrode, Eschweiler Kiel, Germany) on the surface of the skeletal muscle, coronary perfusion pressure, left ventricular (LV) end-diastolic pressure, global and regional myocardial contractility (maximal change in pressure over time, LV segmental shortening, microsonometry method), LV myocardial blood flow (fluorescent microsphere technique), LV oxygen delivery, and the ratio between LV subendocardial and subepicardial myocardial perfusion. In the HSA group, critical hematocrit was found at 6.1 (1.8)% (hemoglobin, 2 g x dL(-1)), whereas all DCLHb-treated animals survived hemodilution until hematocrit 1.2 (0.2)% (hemoglobin, 4.7 g x dL(-1)) was achieved without signs of hemodynamic instability. Although arterial oxygen content was higher in the DCLHb group at 1.2% hematocrit than in the HSA group at critical hematocrit (i.e., hematocrit, 6.1%; hemoglobin, 2 g.dL-1) neither oxygen delivery and oxygen uptake nor median tPo2 and hypoxic tPo2 values on the skeletal muscle were different between groups. In contrast, subendocardial ischemia was absent in DCLHb-diluted animals until 1.2% hematocrit was achieved. This was attributable to a higher coronary perfusion pressure (65 (22) mm Hg vs. 19 (8) mm Hg; p <.05), higher subendocardial perfusion (4.1 (2.6) mL.min-1.g-1 vs. 1.2 (0.4) mL x min(-1) x g(-1)), and subendocardial oxygen delivery (5.7 (2) mL x min(-1) x g(-1), p <.05) in DCLHb-diluted animals, resulting in superior myocardial contractility reflected by maximal change in pressure over time (3829 (1914) vs. 1678 (730); p <.05) and higher regional myocardial contractility (11 (8)% vs. 6 (2)%; p <.05). An increased LV end-diastolic pressure reflected LV myocardial pump failure in HSA-diluted animals but was unchanged in DCLHb-diluted animals. In the DCLHb group, systemic vascular resistance index remained at baseline values throughout the protocol, whereas coronary vascular resistance decreased. In contrast, both variables decreased in HSA-diluted animals. CONCLUSION: DCLHb as a diluent allowed for hemodilution beyond the hematocrit value, determined "critical" after hemodilution with HSA (6.1% (1.8)%). Even at 1.2% hematocrit (hemoglobin, 4.7 g x dL(-1)) myocardial perfusion and function were maintained, although at the expense of peripheral tissue oxygenation. This discrepancy in regional oxygenation might be caused by a redistribution of blood flow favoring the heart, which is related to a disproportionate decrease of coronary vascular resistance index during hemodilution with DCLHb.     

Causes of metabolic acidosis in canine hemorrhagic shock: role of unmeasured ions

Introduction

Metabolic acidosis during hemorrhagic shock is common and conventionally considered to be due to hyperlactatemia. There is increasing awareness, however, that other nonlactate, unmeasured anions contribute to this type of acidosis.

Methods

Eleven anesthetized dogs were hemorrhaged to a mean arterial pressure of 45 mm Hg and were kept at this level until a metabolic oxygen debt of 120 mLO₂/kg body weight had evolved. Blood pH, partial pressure of carbon dioxide, and concentrations of sodium, potassium, magnesium, calcium, chloride, lactate, albumin, and phosphate were measured at baseline, in shock, and during 3 hours post-therapy. Strong ion difference and the amount of weak plasma acid were calculated. To detect the presence of unmeasured anions, anion gap and strong ion gap were determined. Capillary electrophoresis was used to identify potential contributors to unmeasured anions.

Results

During induction of shock, pH decreased significantly from 7.41 to 7.19. The transient increase in lactate concentration from 1.5 to 5.5 mEq/L during shock was not sufficient to explain the transient increases in anion gap (+11.0 mEq/L) and strong ion gap (+7.1 mEq/L), suggesting that substantial amounts of unmeasured anions must have been generated. Capillary electrophoresis revealed increases in serum concentration of acetate (2.2 mEq/L), citrate (2.2 mEq/L), α-ketoglutarate (35.3 μEq/L), fumarate (6.2 μEq/L), sulfate (0.1 mEq/L), and urate (55.9 μEq/L) after shock induction.

Conclusion

Large amounts of unmeasured anions were generated after hemorrhage in this highly standardized model of hemorrhagic shock. Capillary electrophoresis suggested that the hitherto unmeasured anions citrate and acetate, but not sulfate, contributed significantly to the changes in strong ion gap associated with induction of shock.     

Positive end-expiratory pressure does not compromise myocardial contractility in myocardial ischemia/reperfusion

Therapy for severe myocardial ischemia/reperfusion sometimes necessitates intermittent positive pressure ventilation, which may impair left ventricular function by reduction of ventricular loading. It is unknown today whether positive airway pressure also affects contractile force after myocardial ischemia/reperfusion. The authors tested whether positive end-expiratory pressure (PEEP) impairs myocardial contractility in acute ischemic heart failure. In 11 anesthetized mechanically ventilated pigs (28 +/- 3 kg), cardiac output (CO, aortic flow probe), load-independent parameters of left ventricular contractility (conductance method: preload recruitable stroke work [PRSW] and end-systolic elastance [E(es)]) and preload (end-diastolic volume [EDV] conductance) were assessed before and after myocardial ischemia and reperfusion (left anterior descending artery occlusion, 60 min). Data were taken during PEEP 0, 5, and 10 cm H2O. Before myocardial ischemia, both PEEP 5 and 10 cm H2O reduced CO (P < 0.05) because of a reduction of EDV (P < 0.05, PEEP 10 cm H2O). The PRSW remained unchanged (not significant [NS]) and E(es) increased (P < 0.05, PEEP 10 cm H2O). After myocardial ischemia/reperfusion, CO and PRSW, but not E(es) (NS), deteriorated markedly. At the same time, PEEP 10 cm H2O reduced CO (P < 0.05) and, slightly, EDV (NS). Now, both PRSW (P < 0.05, PEEP 5 cm H2O) and E(es) (P < 0.05, PEEP 10 cm H2O) improved upon ventilation with PEEP. In our model, the administration of PEEP impaired global left ventricular function before and after myocardial ischemia/reperfusion. The observed impairment is not attributable to compromised contractility.