CRRT: Providing Optimal Patient Care

BuckeyeICUNurse, BSN

Continuous Renal Replacement Therapy (CRRT) is commonly used in ICUs for patients that need dialysis and are hemodynamically unstable. CRRT allows for slower filtration and particle removal, creating smaller fluid shifts during therapy.

Here are the things I've learned from other Nurses and my experience at the bedside. The hospital I work at uses the Prismaflex system and the M150 filter. Our facility also does not use anticoagulation during CRRT, so this topic will not be included in this article.

CRRT provides four major things; it provides control of fluid status, cleans the blood, removes toxins that are usually excreted in urine, and controls electrolytes and acid/base balance.

The circuit is good to run for 72 hours total, and holds no greater than 300 mL of blood outside of the patient's body during therapy.

There Are 3 Modes Capable of Removing Fluid:

1. CVVHD Continuous Veno-Venous Hemodialysis

Works through diffusion. The patient's blood flows vertically up through the filter against dialysate which flows vertically down. Dialysate is used.

2. CVVH Continuous Veno-Venous Hemofiltration

Works through convection. Increased pressure is pushed through the filter, and replacement fluid is added before or after the filter (or both) to maintain fluid status. A higher filtrate flow equals increased particle removal. Replacement fluid is used. No dialysate is used.

3. CVVHDF Continuous Veno-Venous Hemodiafiltration

Most commonly used in the ICU, and uses both diffusion and convection

Replacement and dialysate fluid is used.

The Nephrologist will order different rates of flow depending on mode. When setting up therapy there will be areas where you will put in the information on the status screen. These terms will appear using CVVHDF mode and are ordered as a rate in mL per hour.

Blood: rate of blood flowing through the circuit in 1 hour.

Pre/Post-blood pump: Rate of the fluid that dilutes the blood from the access line (arterial) in 1 hour.

Replacement: Rate of fluid before or after the filter which restores volume and buffers the blood in 1 hour.

Before starting, always scan your bags into the MAR before you hook up the system. I have heard of incidences where bags were not scanned and the patient received the wrong concentration of electrolytes. This can cause harm to the patient if the bag concentrations are incorrect! Not to mention you need to change out the entire circuit.

Turn on the blood warmer before you start hooking the filter set into the machine. No one wants cold blood circulated into their body! Prevent hypothermia. The time it takes to set up everything will allow the warmer to get to optimum temperature before starting therapy. I tend to always turn it up the highest; there is a high limit for safety.

** Always, always, always select PRIME AND TEST** when you have your circuit ready to go before connecting to the patient. If you only select test, you will have to change out the entire circuit. I learned from experience!

What if my patient codes on therapy?

When you set up your filter set onto the machine, it is important to have supplies before starting therapy in case therapy needs stopped emergently. Have 2 sterile saline flushes, alcohol wipes, and a 1L 0.9NS bag at the bedside. *If a patient codes while on therapy, ALWAYS STOP therapy. During CPR, the machine will almost always be alarming due to differences in pressure and each time therapy is paused due to an alarm, the circuit is not running and the risk for the circuit clotting is increased. You do not want to be removing fluid from a patient or causing any fluid shifts, as they are already hemodynamically compromised at this point as well. *If* there is a Nurse available during the code that does not have a responsibility in resuscitation, the patient can be disconnected from the circuit. Both the access and return lines will need flushed and clamped to preserve line patency. The patient will lose the blood in the circuit (less than 300 mL) but can always be given back in IV fluids during resuscitation.

What if I need to return my patient's blood?

There are a couple reasons why returning blood may be needed. Transport off of the unit, or changing the filter set.

Indications for changing the filter set

TMP high alarm
Pressure Drop high alarm
Unable to run therapy after checking multiple causes
Circuit had to be stopped immediately and patient disconnected from set and then needs to re-start therapy

Starting Therapy

Allow and plan for 45 minutes on average from getting supplies to starting therapy.

You will need (for CVVHDF)

3 dialysate bags (concentrations in each bag are in the order on the MAR)
(2) 1 liter 0.9% Normal Saline bags
Spikes for priming
Filter set

Once the filter set is loaded and you are beginning to start therapy, the patient must be assessed for toleration.

Signs of tolerance during initiation and continuance include no large increase in vasopressors. If your patient needs CRRT and cannot tolerate HD, you will most likely always see the patient need vasopressors due to fluid shifts and workload on the heartin an already hemodynamically unstable ICU patient. The patient must have a stable MAP of 65 mmHg (or whatever MAP is ordered) consistently as well. Large increases in vasopressors, need for additional vasopressors, hemodynamic instability, EKG changes, mentation changes, and inability to stabilize MAP above goal are all signs that the patient is not tolerating therapy and providers need to be notified.

During therapy you will be checking hourly safety checks. These include but are not limited to

Total IV intake
Any additional intake (including tube feeding)
Total output (NG, drains, chest tube, Foley)
Access (Arterial) and Return (venous) pressures
TMP and pressure drop pressures
Effluent
Fluid removed last hour
Blood warmer temperature
Aeration chamber

Access and Return Pressures

Access and return pressures indicate how patent the arterial access and venous return line are. The most common causes for high pressure alarms for either are position of the catheters and the catheters or line being kinked or clamped accidentally. If you continue to get alarms for high access or return pressures, carefully put tension on the line (s) and reposition them close to the origin of access. Be sure to note and double check your lines are sutured before putting any tension on them, or they will dislodge.

TMP and Pressure Drop

TMP is the pressure that is exerted on the filter during therapy. Over time permeability of the filter decreases due to protein from the blood that naturally sticks to the filter and eventually the filter clogs.

I like to start thinking and planning a circuit/filter change when the TMP starts to reach 200. For the TMP to alarm high, numbers are on average between 250-300. Keep in mind though that the higher the TMP increases, the less chance you have of being able to re-turn the patient's blood. TMP trending upward related to a clogging problem.

Pressure Drop on the other hand is a clotting problem. Pressure drop is the pressure in the fibers of the filter itself. Over time micro clots can develop which makes the resistance increase as blood flows across the filter and through the filter fibers. Again, an increasing trend of Pressure Drop is a clotting problem.

I was personally taught to favor TMP over pressure drop when watching for trends and planning for circuit changes before the 72-hour expiration time.

Aeration Chamber

It is important to hourly check the aeration chamber that the fluid level is at the indicator line. This allows air to escape (air always rises) and prevents an air embolus or blood clot from getting into the circuit and going back to the patient. Luckily, the machine alarms and watches for those already, however the entire circuit most likely will need changed if detected.

Calculating Hourly Fluid Balance And Patient Fluid Removal

If ordered, the Nephrologist will order an hourly goal removal amount as patient is able to tolerate. Below are examples of different situations and how to calculate how much "patient fluid removal" needs to be entered in the machine hourly.

When calculating patient fluid removal, it is always important to be thinking ahead. It is important to know how much fluid your patient will receive during your entire shift and to prepare accordingly for optimum fluid removal.

Keep in mind, when you check how much fluid is precisely removed after each hour, you may be over or under goal, and that is okay. Try to achieve goal fluid removal per order to the best of your ability and as the patient tolerates. Also note that the amount of patient fluid removal might differ hour to hour.

How To run Even = No Extra Fluid Is Being Removed From The Patient

Patient Betty will receive 100 mL/hr from her continuous IV fluids/drips. She makes no urine, is not receiving tube feed, and has no other sources of output (drains, OG, chest tubes etc.). To run even, what comes in, must come out. In the "patient fluid removal" screen, you will type 100 mL. 100 mL going in, 100 mL out. The patient neither gains nor loses fluid.

*Tube feed counts as intake*

How To Calculate Goal Patient Fluid Removal Amount

The same patient Betty, who has only IV intake of 100 mL and no output for this hour, has a goal of 30 mL goal to be removed hourly. To run even, we know we have to take off at least 100 mL to run even. To run negative, we must add our goal amount to the amount we are removing; 100 +30 =130. Patient fluid removal amount is 130 mL for this hour.

How To Calculate Patient Fluid Removal Amount With Outputs Included

Betty now is making small amount of urine and has some output from her OG tube that is to suction. She has 30 mL in urine, and 10 mL from her OG.

IV intake: 100 mL

Output: 40 mL

Goal removal: 30 mL

Calculate fluid removal goal without output, which is already 130 mL to be removed this hour. Take the output amount and subtract from your number. 130-40= 90 mL. Your next hourly amount for patient fluid removal is 90 mL.

How To Calculate Patient Fluid Removal With Multiple IV Piggy Backs Throughout The Shift

Betty has antibiotics scheduled for your shift. Adding the total volumes for each med (you can find the volume on the MAR for each med) she has a total of 500 mL extra fluid she will be receiving on top of her hourly IVF/drips.

Say you are 1 hour into your shift and have 11 to go. We will take the volume and divide by 11 hours. Dividing the fluid volume will make it easier to remove from the patient then taking off 300 mL in one hour, which the patient may not tolerate. 500/11= 46 (rounded). We need to remove an additional 46 mL/hour to balance her I/O. To reach her goal, we determined our patient fluid goal amount needs to be 130 ml this hour. We will add 45 mL to each of the 11 hours, equaling 175 mL that need taken off each hour to still reach our goal of negative 30 mL each hour.

There may be an instance when an antibiotic or other piggyback is ordered off the fly, and you might only have 1 hour left in your shift. Do not try and add that entire volume and remove it in your last hour. Relay to the oncoming nurse how much she needs to add into her hourly patient fluid removal and the fluid can then be taken off safely over a longer period of time.

If you want to account for Betty's output along with her updated minimum patient fluid removal amount, simply subtract how much she had out this hour, from the 175 mL. Her patient fluid removal amount for next hour will now be 145 mL.

Your hourly checks will give you all the numbers you need to calculate the amount of patient fluid removal each hour. It will become easier with practice, I promise!

Remember, if it was easy, anyone could do it!