Nutrition in ICU - a lot of calculation...can be made simple

Nutrition in ICU is an important aspect of Critical management of patients..as they are all in a catabolic state due to the high levels of circulating Catecholamines, cytokines and lymphokines. It has been emphasized that nutrition (either parenteral or enteral ) be started  as early as possible..within 24 hours of ICU admission.

Which route --Enteral Vs Parenteral - This is not a big issue...as enteral is easier and less expensive & less complicated to start......and there is some evidence that using the gut might prevent bacterial translocation. Also splanchnic circulation increases with enteral feeding..preventing mucosal breakdown. Use parenteral if contraindication to enteral feeds. e.g - GI bleed, Pancreatitis etc
What food -- In US...many types of enteral feeds are in use depending on the clinical scenario.These are pre-prepared. They can be classified according to the calorie concntration..or based on special additives. Some e.g are Osmolite- 1Kcal/ml, Jevity- 1.2Kcal/ml, Twocal-2Kcal/ml. Useful in case fluid restriction is needed!. Secondly.... use Glucerna - Diabetes, Nepro for renal disease, Oxepa for ARDS etc (we will discuss these at a later date). 
How much -- Always start low @ 20ml/hr...and increase every 4-6 hours by 20ml..upto the goal. Sooooo what is the goal?? Well here is a rough calculation.... First calculate the calories needed
Basal Energy Expenditure : 66.5+(13.8 x wt in kg) + (5 x ht in cm) - (6.8 x age in yrs)     .........for men
                                                65.5 +( 9.6 x wt in kg) + (1.8 x ht in cm) - (4.7 x age in yrs) ..........for women


Rougly for a 60 yo male 6 ft tall and 80 kg....BEE will be around 1800 Kcal/day (or if the above formula is too complicated!.....simply use 25Kcal/kg/day)
The Total Energy Expenditure will be = BEE x 1.2 x stress factor ( I add 1.5- 2.0 for being in ICU- Sepsis) (Critical Care 2003)
For our gentleman above...it will be roughly 3200 kcal/day. 
Nitrogen Balance - This is how we assess response to nutirional response. Its simply... Nitrogen intake – Nitrogen losses. 
Nitrogen intake = Calculate as 1gm of Nitrogen for each 150 Kcal of feed ( eg. for 3200 Kcal /day,it is 21 gm nitrogen)
Nitrogen losses = Urinary Urea Nitrogen (g/day) + 4g ( this is for extra renal loss of Nitrogen - stools, sweat etc)
If net nitrogen balance is > 2gm...it can be called a positive nitrogen balance........if <2 gm negative NB.To do this calculation..we need the Urine urea Nitrogen (UUN....same as BUN...but in urine) - this is done on a 24 hr collection of urine( can be done easily in a ICU setting). Do it atleast 2 days after starting tube feeds. Do this once a week...and present the Nitrogen balance to your attending!!! ( you will look more smart!)