Dopamine and Dobutamine Computations

for DOPAMINE, the constants are
single dose = 13.3 (translates to 200/250 or 400/500)
double dose = 26.6 (translates to 400/250 or 800/500)

... for DOBUTAMINE, the constants are
single dose = 16.6 (translates to 250/250 or 500/500)
double dose = 33.3 (translates to 500/250 or 1000/500)

the formula for the above computation is always...

DOSAGE x WT
___________
constant

FOR THE EXPLANATION OF CONSTANT:
notice in the sample computation of double-dose dopamine: pt wt. 176lbs. doctor ordered 5mcg/kg/MIN. available is 400/250 DOPAMINE in D5 water. how many ml/hr to give?

(5 mcg / kg min) x (80 kg) x
(250 ml / 400 mg) x (1 mg / 1000 mcg) x (60 min / 1 hr)

if we summarize the 2nd line, this can be reduced to:
(5 mcg / kg min) x (80 kg) x (0.0375 ml min / mcg hr)

the short-cut it is:

(5 mcg / kg min) x (80 kg)
________________________________
26.6 <-- (this is the RECIPROCAL of 0.0375)

: so in actuality the unit of 26.6 is (mcg hr / ml min)

WHY IS THERE A NEED TO KNOW THE CONSTANT?
IN SOME CASES, 400/250 IS NOT BEING MENTIONED IN NCLEX... SOMETIMES THE QUESTION WOULD BE LIKE

pt wt. 176lbs. doctor ordered 5mcg/kg/MIN. available is DOUBLE-DOSE DOPAMINE in D5 water. how many ml/hr to give? so in this case we know that we will be using 26.6...

for the rest of the computation... just remember to elimitate the UNITS thru multiplication process in order to come up with the CORRECT DESIRED UNITS... REMEMBER YOUR CONVERSION FACTORS FOR TIME,WEIGHT & VOLUME......

lets have an example...

Infuse Nitroprusside 25 mg in D5W 250 ml at 50mcg /min using microdrip tubing.Determine the ml/hr and the gtts/min.

Given:
25 mg/250 ml ( there is 25 mg NA Nitroprusside PER 250 ml...based on the given)
50 mcg/min
60 mcgtts/1 ml <---- microdrip

Find: ml/hr :
(250ml/25mg) x (1 mg/1000 mcg) x (50mcg/min)

= 0.5ml/min
= (0.5ml/min) x (60min/1 hr) = 30 ml/hr <---answer

Find: gtts/min :
(30ml/hr)x(60gtts/ml)x(1hr/60min)
= 30 gtts/min <----answer

example 2

Infuse Dobutamine 500 mg in 250 ml D5W at 5 mcg/kg/min using microdrip tubing.The client weighs 182 lbs. Determine the ml/hr and the gtts/min.

Given:
500mg/250ml (this is double-dose dobu)
5 mcg/kg/min
182 lbs
60gtts/ml <------- microdrip

Find:ml/hr
182 lbs x (1kg/2.2lbs) = 82.7kg

(5 mcg/kg min) x (82.7kg) = 413.5 mcg/min

413.5 mcg/min x 1mg/1000mcg = .4135 mg/min

.4135 mg/min x 250ml/500mg <--- ML is the numerator since were looking for ML/HR
= 0.20675ml/min

= 0.20675ml/min x (60 min / 1 hr) = 12.4 ml/hr <--ans

... using the short-cut: 33.3 is constant for double dose dobutamine...
5mcg/kg-min x 82.7kg divide by 33.3 = 12.41 ml/hr <--same answer.^^

Find: gtts/min
12.41 ml/hr x (1 hr/60 min) x (60gtts/ml) =
= 12 gtts/min... <---answer (Drops Per Minute MUST always be in WHOLE NUMBERS while ml/min, ml/hr,etc may have decimal points)