Potentiation of epinephrine-induced mesenteric vasoconstriction with beta-blockade

Labetalol Infusion Attenuates Paradoxical Hypertension and Decreases Plasma Renin Activity After Repair of Coarctation of the Aorta in Children

OBJECTIVE

Paradoxical hypertension after repair of coarctation of the aorta in children is associated with the release of catecholamines and activation of the renin-angiotensin system. The objective of the present study was to describe the effects of labetalol infusion on blood pressure, plasma catecholamine levels, and plasma renin activity in a series of children undergoing repair of coarctation of the aorta.

DESIGN

Prospective, observational cohort study.

SETTING

Tertiary children's hospital with university affiliation.

PARTICIPANTS

The study was comprised of 15 consecutive children older than 1 year undergoing repair of coarctation of the aorta.

INTERVENTIONS

Intravenous infusion of labetalol, up to 20 µg/kg/min, was administered when patients became hypertensive after release of the aortic cross-clamp. Supplementation with nitroprusside was allowed as needed.

MEASUREMENTS AND MAIN RESULTS

Blood pressure was maintained below baseline values throughout the labetalol infusion. Plasma norepinephrine increased from 160 ± 81 pg/mL (preoperative) to 657 ± 268 pg/mL (6 h after release of aortic cross-clamp). Plasma renin activity decreased from 16.6 ± 9.7 ng/kg/h (at cross-clamp release) to 2.2 ± 2.2 ng/kg/h (6 h after cross-clamp release). Nitroprusside was added for 12 patients, at a highest mean dose of 2.4 ± 2.5 μg/kg/min.

CONCLUSIONS

Labetalol inhibited activation of the renin-angiotensin system and helped control paradoxical hypertension after coarctation repair in children.

Fatal non-occlusive mesenteric ischemia and the use of propranolol in paediatric burns

Abdominal complications without abdominal injury are infrequently seen in children with major burns. They are divided into those that occur early during the emergency phase of treatment and those that occur late in the course of treatment. One of the most serious late onset complications is non-occlusive mesenteric ischaemia associated with the use of vasoactive drugs. We report on 2 children who late in the course of their burn injury developed ischaemic necrosis of their entire intestine. Both were on propranolol, the administration of which was continued with even during the periods of septic shock which preceded their demise. We are of the opinion that endogenous catecholamine release during hypotensive and septic episodes in conjunction with β-adrenergic blockage from propranolol could lead to severe splanchnic vasoconstriction from unopposed α-adrenergic activity and hence critical circulation impairment to the bowel in the 2 children.

Propranolol-Exacerbated Mesenteric Ischemia in a Patient with Hyperthyroidism

OBJECTIVE:

To report a case of acute mesenteric ischemia associated with the use of oral propranolol.

CASE SUMMARY:

A 59-year-old white man was admitted to the hospital with chronic diarrhea and weight loss. The patient was diagnosed as having hyperthyroidism. Therapy with propylthiouracil 100 mg 3 times daily and propranolol 20 mg twice daily was initiated on an outpatient basis. The following day, the patient was readmitted to our hospital with increased abdominal pain and bloody diarrhea. Angiography revealed superior mesenteric artery occlusion. Antegrade aorta-mesenteric bypass surgery was performed for revascularization, and the patient was discharged 10 days after the surgery. The patient was well both clinically and endoscopically at a follow-up visit 8 months later.

DISCUSSION:

Although mesenteric ischemia is a devastating illness of varied causes, drug-associated mesenteric ischemia is rarely seen. By decreasing cardiac output and selective vasodilatory receptor inhibition in the splanchnic circulation, propranolol can cause a decline in splanchnic blood flow. An objective causality assessment indicated that propranolol was the possible cause of the arterial occlusion.

CONCLUSIONS:

Propranolol may rarely be associated with mesenteric ischemia. In cases of newly developed acute abdomen undergoing propranolol therapy, physicians should be aware of this rare and serious adverse reaction to this drug.

Beta-adrenergic blockade and the gastrointestinal system

As beta-adrenergic blockers grow increasingly popular for the therapy of a wide variety of disorders, it becomes increasingly important to appreciate the spectrum of physiologic effects on the gastrointestinal system and the potential hazards associated with use of these agents. This review details the effects of the beta-adrenergic blocking agents on the gastrointestinal tract.

Effect of non-carbonic acidosis on total splanchnic perfusion and cardiac output during anaesthesia with O2-N2O-barbiturate-relaxant

Seven dogs were anaesthetized using mebumal natrium-O2-N2O-gallamonijdidum. The PaCO2 was kept at a constant level by means of mechanical ventilation, and non-carbonic acidosis was induced with HCl infusion (0.3 normal). The arterial pH varied from 7.45 to 6.88. During this acidosis, a rising arterio-venous oxygen difference was observed, with an unchanged total oxygen consumption. The pulse fell, but the mean pressures in the right atrium and aorta were unchanged. The peripheral resistance rose by 50%, whereas the fall in cardiac output of 20% was non-significant (0.10 greater than P greater than 0.05). The total splanchnic perfusion fell by 28%, and the change in flow was correlated to the change in pH. Total splanchnic perfusion (ml min-1) = -4078+655x pH (N = 42, r = 0.67, P less than 0.001). Total splanchnic perfusion as a fraction of the cardiac output remained unchanged. The resistance in the splanchnic area rose by 50%. The oxygen saturation in the portal vein and mixed venous blood changed in parallel. It is concluded that contraction of the blood vessels is the most important effect on the circulation resulting from non-carbonic acidosis during the anaesthesia employed here.