Almitrine and doxapram in experimental lung injury

Effect of position, nitric oxide, and almitrine on lung perfusion in a porcine model of acute lung injury

In a porcine model of oleic acid-induced lung injury, the effects of inhaled nitric oxide (iNO) and intravenous almitrine bismesylate (ivALM), which enhances the hypoxic pulmonary vasoconstriction on the distribution of regional pulmonary blood flow (PBF), were assessed. After injection of 0.12 ml/kg oleic acid, 20 anesthetized and mechanically ventilated piglets [weight of 25 +/- 2.6 (SD) kg] were randomly divided into four groups: supine position, prone position, and 10 ppm iNO for 40 min followed by 4 microg x kg(-1) x min(-1) ivALM for 40 min in supine position and in prone position. PBF was measured with positron emission tomography and H(2)15O. The redistribution of PBF was studied on a pixel-by-pixel basis. Positron emission tomography scans were performed before and then 120, 160, and 200 min after injury. With prone position alone, although PBF remained prevalent in the dorsal regions it was significantly redistributed toward the ventral regions (P < 0.001). A ventral redistribution of PBF was also obtained with iNO regardless of the position (P = 0.043). Adjunction of ivALM had no further effect on PBF redistribution. PP and iNO have an additive effect on ventral redistribution of PBF.

Right ventricular response to high-dose almitrine infusion in patients with severe hypoxemia related to acute respiratory distress syndrome

OBJECTIVE

To evaluate the effects of high-dose almitrine infusion on gas exchange and right ventricular function in patients with severe hypoxemia related to acute respiratory distress syndrome (ARDS).

DESIGN

Prospective study.

SETTING

Medicosurgical intensive care department (ten beds).

PATIENTS

Nine patients with ARDS and severe hypoxemia (PaO2/FIO2 ratio, <150 torr [20 kPa]).

INTERVENTION

High-dose almitrine infusion (16 microg/kg/min for 30 mins).

MEASUREMENTS AND MAIN RESULTS

Gas exchange and hemodynamic parameters were recorded before and after almitrine infusion. Right ventricular function was evaluated by using a fast response thermistor pulmonary artery catheter that allowed measurement of right ventricular ejection fraction and calculation of right ventricular end-diastolic and end-systolic volumes. Almitrine did not significantly alter arterial oxygenation and intrapulmonary shunt. Almitrine increased mean pulmonary arterial pressure (MPAP) from 31 +/- 4 to 33 +/- 4 mm Hg (p < .05), pulmonary vascular resistance index from 353 +/- 63 to 397 +/- 100 dyne x sec/ cm5 x m2 (p < .05), and right ventricular end-systolic volume index from 71 +/- 22 to 77 +/- 21 mL/m2 (p < .05); almitrine decreased right ventricular ejection fraction from 36% +/- 7% to 34% +/- 8% (p < .05). Stroke volume index and cardiac index did not change. The almitrine-induced changes in right ventricular ejection fraction were closely correlated with the baseline MPAP (r2 = .71, p < .01).

CONCLUSION

In patients with severe hypoxemia related to ARDS, high-dose almitrine infusion did not improve arterial oxygenation and impaired the loading conditions of the right ventricle. The decrease in right ventricular ejection fraction induced by almitrine was correlated with the baseline MPAP. Thus, high-dose almitrine infusion may be harmful in ARDS patients with severe hypoxemia and pulmonary hypertension.

Inhaled nitric oxide and vasoconstrictors in acute respiratory distress syndrome

It has been suggested that the increase in PO(2) observed with nitric oxide (NO) should be enhanced by the addition of a vasoconstrictor agent. The vasoconstrictor used in combination with NO should mimic or enhance hypoxic vasoconstriction. The aim of this study was to evaluate the respiratory and hemodynamic effects of norepinephrine (a nonspecific vasoconstrictor), almitrine bismesylate (a specific pulmonary vasoconstrictor), and inhaled NO, alone or together. During a 6-mo period, 16 patients presenting with ARDS were prospectively investigated. On inclusion, no patient was receiving cardiovasoactive drugs. The protocol consisted of seven consecutive phases: baseline, norepinephrine (in order to obtain a 3 mm Hg rise in mean pulmonary arterial pressure [Ppa]), almitrine bismesylate (16 micrograms/kg/min), inhaled NO (20 ppm delivered during inspiration), norepinephrine + inhaled NO, almitrine bismesylate + inhaled NO, almitrine bismesylate + norepinephrine + inhaled NO. General factorial analysis of variance showed that inhaled NO and almitrine bismesylate increased oxygenation (p < 0.0001). Norepinephrine had no effect on oxygenation. A synergistic effect between inhaled NO and almitrine bismesylate was found (p < 0.05), whereas norepinephrine did not affect the response to inhaled NO. Nitric oxide produced a significant decrease in Ppa and pulmonary vascular resistances (PVRI) (p < 0.0001). Both almitrine bismesylate and norepinephrine induced an increase in Ppa (p < 0.0001). Norepinephrine increased PVRI (p < 0.002), whereas almitrine bismesylate had no effect on PVRI. The present results support the hypothesis that a selective pulmonary vasoconstrictor enhances the increase in oxygenation induced by inhaled NO, whereas norepinephrine attenuates this effect.

Intravenous almitrine combined with inhaled nitric oxide for acute respiratory distress syndrome. The NO Almitrine Study Group

Inhaled nitric oxide (iNO), a selective pulmonary vasodilator and intravenously administered almitrine, a selective pulmonary vasoconstrictor, have been shown to increase PaO2 in patients with acute respiratory distress syndrome (ARDS). This prospective study was undertaken to assess the cardiopulmonary effects of combining both drugs. In 48 consecutive patients with early ARDS, cardiorespiratory parameters were measured at control, after iNO 5 ppm, after almitrine 4 micrograms. kg-1. min-1, and after the combination of both drugs. In 30 patients, dose response to 2, 4, and 16 micrograms. kg-1. min-1 of almitrine with and without NO was determined. Almitrine and lactate plasma concentrations were measured in 17 patients. Using pure O2, PaO2 increased by 75 +/- 8 mm Hg after iNO, by 101 +/- 12 mm Hg after almitrine 4 micrograms. kg-1. min-1, and by 175 +/- 18 mm Hg after almitrine combined with iNO (p < 0.001). In 63% of the patients, PaO2 increased by more than 100% with the combination of both drugs. Mean pulmonary artery pressure (Ppa) increased by 1.4 +/- 0.2 mm Hg with almitrine 4 micrograms/kg/ min (p < 0.001) and decreased by 3.4 +/- 0.4 mm Hg with iNO and by 1.5 +/- 0.3 mm Hg with the combination (p < 0.001). The maximum increase in PaO2 was obtained at almitrine concentrations <= 4 micrograms. kg-1. min-1, whereas almitrine increased Ppa dose-dependently. Almitrine plasma concentrations also increased dose-dependently and returned to values close to zero after 12 h. In many patients with early ARDS, the combination of iNO 5 ppm and almitrine 4 micrograms. kg-1. min-1 dramatically increases PaO2 without apparent deleterious effect allowing a rapid reduction in inspired fraction of O2. The long-term consequences of this immediate beneficial effect remain to be determined.

Effect of modulators of hypoxic pulmonary vasoconstriction on the response to inhaled nitric oxide in a neonatal model of severe pulmonary atelectasis

Hypoxic pulmonary vasoconstriction (HPV) is an intrinsic mechanism that facilitates ventilation to perfusion matching and preservation of oxygenation. We investigated the neonatal HPV response from extensive atelectasis and tested the hypothesis that (I) the resulting hypoxemia is corrected by inhaled nitric oxide (NO); (2) the "pulmonary steal" of blood away from hypoxic area is further improved by modulators of the HPV. Intratracheal injection of steel beads in 32 piglets (7 to 20 days) resulted in atelectasis of 50% to 75% of the lungs. The piglets were then randomized to receive saline (control), indomethacin (IND) 2 mg/kg, doxapram (DOX) 0.5 mg/kg/h or almitrine (ALM) 4 micrograms/kg/min. After 30 minutes, all animals were subjected to NO at 40 ppm. Atelectasis resulted in severe impairment in oxygenation (PaO2 - 105 +/- 6 mm Hg, AaDO2 = 536 +/- 9 mm Hg; shunt fraction = 31% +/- 2%) and moderate pulmonary hypertension. Mean pulmonary artery pressure (PAP) increased to 35 +/- 0.8 mm Hg. NO reduced pulmonary vascular resistance (PVR) from 128 +/- 14 mm Hg/kg/mL/min to 74 +/- 9 mm Hg/kg/mL/min and improved gas exchange (PaO2 = 180 +/- 50 and AaDO2 = 438 +/- 50 mm Hg). Following the development of atelectasis, the peripheral chemoreceptor agonists (ALM and DOX) did not modify gas exchange and had no significant cardiovascular effect. ALM and DOX failed to enhance the response to NO. IND did not alter HPV, but prevented the improvement in gas exchange associated with NO-induced pulmonary vasodilation.

Beneficial effects of a novel anti-hypoxemic agent, TEI-7322, on bleomycin-induced experimental hypoxemia in rats

Almitrine bismesylate is known to be an anti-hypoxemic agent that acts via the enhancement of hypoxic pulmonary vasoconstriction. However, screening for this class of compounds has been minimal, owing, in part, to a lack of convenient hypoxemic models in small animals. The present study was designed to establish a convenient model of hypoxemia induced by bleomycin and to evaluate anti-hypoxemic agents including a newly synthesized compound. TEI-7322, 2-allylamino-4-tert-butyl-amino-7-methyl-7H-pyrrolo[2,3- d]pyrimidine hydrochloride by using this model. Bleomycin was intratracheally instilled into rats. After 3 weeks, the arterial blood gas pressures were monitored in the animals in the conscious state. Then, prednisolone, doxapram, almitrine or TEI-7322 was administered to the bleomycin-treated rats to monitor changes in arterial blood gas pressures. Bleomycin-treated rats showed a decrease in the arterial blood O2 pressure (PaO2). The blood CO2 pressure (PaCO2) increased, along with an increase in the alveolar-arterial oxygen difference (AaDO2). These blood gas pressures in bleomycin-treated rats were not affected by treatment with prednisolone. Doxapram decreased the PaCO2 but did not change the PaO2. However, administration of almitrine or TEI-7322 significantly improved the PaO2 of bleomycin-treated rats with a decrease in the PaCO2. In conclusion, (1) bleomycin-induced lung injury causes hypoxemia in rats, probably resulting from ventilation-perfusion inequality; thus this model may be useful for evaluating anti-hypoxemic agents; and (2) TEI-7322, as well as almitrine, showed anti-hypoxemic effects in this model with different properties from those of doxapram, possibly due to improvement of ventilation-perfusion inequality, indicating that TEI-7322 may be a potent candidate for the treatment of hypoxemia.

Additive effect on gas exchange of inhaled nitric oxide and intravenous almitrine bismesylate in the adult respiratory distress syndrome

OBJECTIVE

To assess the additive effect of inhaled nitric oxide (NO) and intravenous almitrine bismesylate (ALM) on gas exchange.

DESIGN

Prospective self-controlled study.

SETTING

3 medico-surgical intensive care units.

PATIENTS

17 patients with severe hypoxemia (PaO2/FIO2 ratio: 88 +/- 30 mmHg, venous admixture: 47 +/- 7%) and elevated mean pulmonary artery pressure (MPAP: 30 +/- 5 mmHg) due to adult respiratory distress syndrome (ARDS).

INTERVENTIONS

5 conditions were studied: 1) baseline, 2) 5 to 10 ppm of NO during 30 min, 3) discontinuation of NO during 30 min, 4) ALM infusion (0.5 mg/kg) during 30 min, 5) ALM infusion (0.5 mg/kg) during 30 min in combination with 5 to 10 ppm of NO.

MEASUREMENT AND RESULTS

The PaO2/FIO2 ratio rose from 88 +/- 30 to 98 +/- 37 mmHg (NS) with NO alone, and from 92 +/- 25 to 130 +/- 56 mmHg (p < 0.01) with NO + ALM (p < 0.05 vs NO alone). Seven patients were considered as "NO-responders" (rise in PaO2/FIO2 ratio of 10 mmHg or more with NO); in this subgroup the PaO2/FIO2 ratio rose from 87 +/- 30 to 128 +/- 39 mmHg (p < 0.05) with NO alone, and from 93 +/- 20 to 169 +/- 51 mmHg (p < 0.01) with NO + ALM (p < 0.05 versus NO alone). MPAP decreased from 30 +/- 5 to 26 +/- 5 mmHg (p < 0.01) with NO alone, increased slightly from 28 +/- 5 to 31 +/- 5 mmHg (NS) with ALM alone and decreased to 27 +/- 5 mmHg (p < 0.05) with NO + ALM.

CONCLUSIONS

NO + ALM had additive effects on gas exchange while decreasing MPAP in patients with ARDS. The effects of NO alone were small and non significant, except in a subgroup of 7 patients in whom the combination of both therapies had the more pronounced results.