Response of pulmonary vascular segments to angiotensin and norepinephrine

Angiotensin II treatment is associated with improved oxygenation in ARDS patients with refractory vasodilatory shock

BACKGROUND

The physiological effects of renin-angiotensin system modulation in acute respiratory distress syndrome (ARDS) remain controversial and have not been investigated in randomized trials. We sought to determine whether angiotensin-II treatment is associated with improved oxygenation in shock-associated ARDS.

METHODS

Post-hoc subgroup analysis of the Angiotensin Therapy for High Output Shock (ATHOS-3) trial. We studied patients who met modified Berlin ARDS criteria at enrollment. The primary outcome was PaO2/FiO2-ratio (P:F) at 48-h adjusted for baseline P:F. Secondary outcomes included oxygenation index, ventilatory ratio, PEEP, minute-ventilation, hemodynamic measures, patients alive and ventilator-free by day-7, and mortality.

RESULTS

Of 81 ARDS patients, 34 (42%) and 47 (58%) were randomized to angiotensin-II or placebo, respectively. In angiotensin-II patients, mean P:F increased from 155 mmHg (SD: 69) at baseline to 265 mmHg (SD: 160) at hour-48 compared with no change with placebo (148 mmHg (SD: 63) at baseline versus 164 mmHg (SD: 74) at hour-48)(baseline-adjusted difference: + 98.4 mmHg [95%CI 35.2-161.5], p = 0.0028). Similarly, oxygenation index decreased by - 6.0 cmH2O/mmHg at hour-48 with angiotensin-II versus - 0.4 cmH2O/mmHg with placebo (baseline-adjusted difference: -4.8 cmH2O/mmHg, [95%CI - 8.6 to - 1.1], p = 0.0273). There was no difference in PEEP, minute ventilation, or ventilatory ratio. Twenty-two (64.7%) angiotensin-II patients had sustained hemodynamic response to treatment at hour-3 versus 17 (36.2%) placebo patients (absolute risk-difference: 28.5% [95%CI 6.5-47.0%], p = 0.0120). At day-7, 7/34 (20.6%) angiotensin-II patients were alive and ventilator-free versus 5/47(10.6%) placebo patients. Day-28 mortality was 55.9% in the angiotensin-II group versus 68.1% in the placebo group.

CONCLUSIONS

In post-hoc analysis of the ATHOS-3 trial, angiotensin-II was associated with improved oxygenation versus placebo among patients with ARDS and catecholamine-refractory vasodilatory shock. These findings provide a physiologic rationale for trials of angiotensin-II as treatment for ARDS with vasodilatory shock.

TRIAL REGISTRATION

ClinicalTrials.Gov Identifier: NCT02338843 (Registered January 14th 2015).

Heterogeneity of endothelium-dependent and independent responses among large and small porcine pulmonary arteries

To determine whether heterogeneity of endothelium-dependent or independent responsiveness exists between large and small pulmonary arteries, isolated rings (3-4 mm long) from large (5-7 mm in diameter) and small (2-3 mm in diameter) intralobar pulmonary arteries were prepared from normal swine and studied in vitro. Rings, with and without endothelium, were suspended in modified Krebs-Ringer bicarbonate solution, bubbled with 95% O2-5% CO2, maintained at 37 degrees C and studied in parallel. Contractions to phenylephrine, norepinephrine and histamine were significantly potentiated in small rings, with or without endothelium, compared to large pulmonary artery rings with or without endothelium. The alpha-adrenergic agonist, UK 14304, however, caused comparable contractions in rings without endothelium taken from large and small vessels. Contractions to potassium chloride in rings without endothelium were also comparable. Relaxant responses were assessed in rings incubated with indomethacin and contracted with phenylephrine or prostaglandin F2 alpha. Acetylcholine, bradykinin, the calcium ionophore A23187 and UK 14304 elicited endothelium-dependent relaxations in rings from both large and small vessels. Relaxations induced by acetylcholine and bradykinin but not those by A23187 were significantly shifted downward in small versus large pulmonary-artery rings. Isoproterenol also caused endothelium-augmented relaxations but in rings from small vessels only. Sodium nitroprusside and nitric oxide caused similar relaxations in rings from both orders. These results demonstrate that a heterogeneity in endothelium-dependent and independent responsiveness exists between large and small pulmonary arteries.

Increased pulmonary vascular resistance with systemic hypertension. Effect of minoxidil and other antihypertensive agents

Recent case reports suggest that pulmonary hypertension could be caused by minoxidil, a new potent vasodilating antihypertensive drug. Therefore, we evaluated the incidence and severity of pulmonary hypertension in 110 patients with systemic hypertension. Fourteen patients were treated with minoxidil for 2 to 35 months (mean 19.9 months), 15 were treated with no drugs, and the remaining 81 patients received conventional antihypertensive agents of several types. Pulmonary vascular resistance correlated positively (P is less than 0.05) with systemic vascular resistance. Minoxidil-treated patients with hypertension previously refractory to conventional therapy had slightly lower pulmonary vascular resistance than other hypertensive subjects. There was no correlation between pulmonary vascular resistance and duration of minoxidil therapy or other types of antihypertensive regimens. The positive correlation between pulmonary and systemic vascular resistance suggests the possibility of a causal hypertension relation in the two vascular beds.