Uterine Relaxants

P2-adrenoceptor agonists relax the uterus and are given by i.v. infusion by obstetricians to inhibit premature labour, e.g. isoxsuprine, terbutaline, ritodrine, salbutamol. Their use is complicated by the expected cardiovascular effects, including tachycardia, hypotension. Less easy to explain, but more devastating on occasion to the patient, is severe left ventricular failure. Possibly the combination of fluid overload (due to the vehicle) and increased oxygen demand by the heart are factors,

20 Oxytocin should be used in standard dilutions of 10 units/500 ml (infusing 3 ml/hour delivers 0.001 unit/minute) or, for higher doses, 30 units/500 ml (infusing

1 ml/hour delivers 0.001 unit/minute).

and the risk is higher in the presence of multiple pregnancy, pre-existing cardiac disease or maternal infection. It is important to administer the P2-agonist with minimum fluid volume using a syringe pump with 5% dextrose (not saline) as diluent, and to monitor the patient closely for signs of fluid overload.

The dose of ritodrine for intravenous administration is: initially 50 micrograms/minute, increased gradually according to response by 50 micrograms/ minute every 10 minutes until contractions stop or maternal heart rate reaches 140 beats per minute; continue for 12-48 hours after contractions cease (usual rate 150-350 micrograms/minute).

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Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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