IV Infusion in Critical Care: Essential Knowledge for Nurses

At the Elaine Marieb Center for Nursing and Engineering Innovation, we have an active and ongoing program of research to improve the safety and usability of intravenous smart infusion pumps (IVSPs) (Giuliano, 2018a, 2018b; Giuliano et al., 2021). This blog focuses on secondary infusion.

What Is Secondary Infusion?

Secondary infusion involves connecting a secondary fluid bag to the primary IV line using a Y-connector located above the infusion. During secondary infusion, the primary infusion pauses to allow the secondary to infuse and should resume automatically once the secondary infusion is complete.

• This process is commonly used for large-volume IV smart pumps (LVPs).
  • Two types of LVP technology are used in U.S. healthcare, linear peristaltic pumps, which depend on the required head height of the fluid for accurate flow (BD Alaris, Baxter Sigma, B. Braun) and cassette systems (ICU Medical Plum 360 and Plum Duo, Ivenix), which do not have specific head-height requirements.
• IVSP systems were designed to provide accurate administration of fluids and medications.
• The process of using the most common head-height dependent IVSP systems requires multiple manual steps and a specific manufacturer-required system setup in order to provide accurate flow (Karen K. Giuliano, Jeannine WC Blake, et al., 2021).
• There is a general lack of knowledge on the specific manufacturer setup requirements among nurses and pharmacists (Giuliano & Blake, 2021).
• Observational studies have found that during real-world clinical use, there is limited adherence to manufacturer setup requirements, and in many cases correct setup is not possible in the hospital due to limitations in space and ergonomics (Karen K. Giuliano, Daleen Penoyer, et al., 2021).

What Are the Differences With Secondary Infusion Between Head-Height Dependent and Cassette IV Smart Pump Infusion Systems?

• 1Head-Height Differential Method

  To achieve accurate flow, the head-height differential method (BD/Alaris, Baxter Sigma, B. Braun) requires specific positioning of the primary and secondary fluid containers both during and after secondary medication administration (Giuliano & Blake, 2021).

  System Setup Requirements (Figure 1):

  Figure 1. Required components for secondary medication infusion for head-height dependent systems (copyright Giuliano).
  1. A one-way check-valve and Y-port in the primary tubing located above the pumping segment
  2. A minimum head-height differential (as specified by the pump manufacturer) between the primary fluid level and secondary fluid level throughout the duration of secondary infusion
  3. The roller clamp on the secondary tubing, which must be OPEN during secondary infusion and priming but CLOSED during primary infusion

  Key Considerations

  • Ensure the primary bag is lowered using a fully extended provided hanger (typically longer than 9.5 inches). At higher flow rates (≥300 mL/hr), additional hangers may be necessary.
  • Inadequate head-height differentials will result in underinfusion of the secondary medication, unintentional simultaneous infusion from both the primary and secondary fluids, or fluid backflow from the secondary fluid bag into the primary bag.
  • If the secondary clamp is left closed during secondary infusion, the IVSP will infuse from the primary fluid instead of the secondary, and no alarm will sound.

• 2Cassette Method

  The cassette method (ICU Medical Plum 360 and Plum Duo, Ivenix) uses a pump-operated valve system to direct flow between the primary and secondary bags. This method eliminates the need for bag-positioning adjustments for accurate secondary infusion delivery.

  Setup Requirements (Figure 2):

  Figure 2: Required components for secondary medication infusion using the cassette method (copyright Giuliano)
  1. A cassette tubing with a secondary port and internal valves
  2. Secondary tubing with a roller clamp for priming purposes
  3. No required back-check valve or specific head height

  Key Considerations

  • An alarm will alert the clinician if the secondary clamp is unintentionally left closed.
  • There should be no potential for unintended simultaneous flow from the primary fluid bag.
  • The Ivenix pump has a new "infuse to empty" feature, which is designed to ensure that the complete dose of the secondary medication is administered before resuming primary fluid flow.
  • The ICU Medical Plum 360 and Plum Duo are capable of programmed concurrent flow of both the primary and secondary fluids when allowable in the drug library, eliminating the need to pause the primary fluid, if required.

Common Errors in Secondary Infusion

Secondary infusion using the head-height dependent system is vulnerable to a number of errors due to the complexity of setup and programming.

• 1Failure to Open the Secondary Clamp

  Leaving the secondary roller clamp closed prevents the secondary fluid from infusing. The system defaults to pulling fluid from the primary bag without triggering an alarm to alert the clinician (Karen K. Giuliano, Jeannine WC Blake, et al., 2021; Karen K. Giuliano, Daleen Penoyer, et al., 2021).

  Clinical Example: A preoperative cefazolin dose for surgical site infection prophylaxis was delayed, because the roller clamp on the secondary tubing was left closed. This error was not detected until the next dose was due, resulting in a completely missed dose and an increased risk of postoperative infection or delay in a scheduled surgical procedure.

• 2Volume to Be Infused

  Volume to Be Infused (VTBI) refers to the total amount of fluid or medication programmed into an IVSP for the patient during a specific infusion session. It is a key parameter used by healthcare providers during ordering and administration processes for IV therapies, such as fluids, electrolytes or medications.

  Use of VTBI in Clinical Practice

  • Once the IVSP reaches the programmed VTBI, the pump will alert to "infusion complete" or switch to another mode, such as a "keep vein open" (KVO) rate, to prevent air from entering the line or overdosing.
  • VTBI was originally designed to ensure the patient receives the correct amount of medication or fluid over the prescribed time, to minimize under- or overdosing risks.
  • Programming the VTBI for an amount larger than the volume in the secondary bag may result in air-in-line alarms or require back-priming to remove air bubbles. However, in IVSPs where under-delivery is frequently experienced, RNs have reported over-programming VTBI as a strategy to avoid being called to the pump despite fluid still remaining in the bag. Some hospitals have protocols that recommend this method or even have added VTBI in their drug library programming parameters to compensate.
  • During secondary infusion, VTBI should be set for the entire volume of the secondary bag (i.e., 100 mL over 30 min) to ensure complete delivery before resuming the primary infusion.
    • In reality, VTBI is actually a time measurement, not a volume measurement, which can lead to errors in IV medication administration that are difficult to detect. If the secondary administration is programmed to deliver in 30 minutes, the rate will revert back to the primary rate regardless of the volume left in the secondary bag, and the remaining secondary medication will be delivered at the primary rate.

  Clinical Example: A critically ill patient has an order to receive vancomycin by secondary IV infusion (1 g/250 mL) to be administered over 1 hr. The IVSP secondary VTBI is programmed to 250 mL to deliver vancomycin over 60 min, to be followed automatically by a fluid bolus of 250 mL over 30 min from the primary normal saline infusion. After 60 min, even though there was still approximately 20 mL left in the secondary IV bag, the IVSP switches to the primary, and the remaining 20 mL of vancomycin is delivered to the patient at a rate of 500 mL/hr, placing the patient at significant risk for the intense and itchy rash associated with vancomycin flushing syndrome (VFS).

  The proper dose of IV vancomycin should be administered slowly over at least 60 min at a rate of 10 mg/min to prevent adverse infusion reactions.

• 3Check Valve Failure

  A check valve on an IV line, in this case termed a "back-check valve," is a small, one-way valve designed to prevent the backward flow of fluid from the secondary tubing up into the primary tubing. The primary purpose of a check valve is to ensure that fluid flows in only one direction — from the IV bag to the patient — preventing unintended mixing or contamination of fluids. The key functions of a back-check valve include the following:

  Prevent Backflow: The back-check valve is designed to prevent fluid from flowing backward into the primary IV bag during secondary infusion when using head-height dependent systems. Preventing backflow is especially important during secondary infusions where the secondary medication needs to flow to the patient without mixing into the primary IV solution.

  Prevent Primary Fluid Flow During Secondary Infusion: The back-check valve creates a resistance in the primary fluid path when the secondary fluid container is hung at a sufficient head-height differential above the secondary fluid level.

  Using head-height dependent systems, if the check valve fails or the distance between primary and secondary fluids is inadequate to trigger the check valve to close, the secondary will flow into the primary bag instead of into the patient, resulting in an occult medication administration error that is completely undetectable to the clinician.

  Clinical Example: An occult error occurred when a replacement dose of potassium flowed into the primary bag instead of into the patient. Once the VTBI for the potassium was complete, the system reverted back to the primary infusion bag, which was then programmed for a 250 mL fluid bolus. This resulted in a life-threatening medication administration error, because the potassium, which was now in the primary bag, was administered too rapidly, placing the patient at significant risk for sudden cardiac arrest.

• 4Simultaneous Flow Issues

  Inadequate head-height differential, restrictions in the secondary fluid path or high flow rates can all cause simultaneous flow from both bags, delaying secondary medication delivery and infusing fluid that was not intended to be delivered.

  Clinical Example: A critically ill patient with congestive heart failure, requiring potassium replacement, experienced delayed infusion due to insufficient head-height differential, prolonging the correction of life-threatening hypokalemia. Additionally, the patient received fluid volume that was not ordered due to the unintended sympathetic flow from the primary fluid bag leading to inaccurate intake and output volumes.

• 5Air-in-Line Alarms (Cassette Method)

  Programming secondary VTBI beyond the actual fluid volume can introduce air into the cassette, leading to alarms and treatment delays.

  Clinical Example: During outpatient chemotherapy, air entered the cassette when the nurse programmed VTBI higher than the volume of medication in the secondary bag. Clearing the alarm using back-priming and interruptions added 20 minutes to the patient's treatment, wasting time for the nurse, potentially impacting treatment efficacy for the patient, extending their stay in the outpatient center, and leading to a delay in the initiation of treatment for all subsequent patients who were scheduled after this patient's discharge.

Best Practices for Secondary Infusion

• When using head-height dependent systems, make sure you know and adhere to manufacturer setup requirements for both the primary and secondary IV bags.
• Ensure that the VTBI is set for the volume in the secondary bag.
• Ensure that the roller clamp on the secondary tubing is open at the start of the secondary infusion.
• Be sure to check the secondary infusion at the time it should be completed to assess whether the full dose has been delivered and, if not, make sure the remaining volume in the secondary bag is not infusing at the primary rate.
• Always set the primary flow rate that is programmed to automatically start following the completion of a high-risk secondary medication to the same or lower programmed flow rate as the secondary medication programmed rate, until full completion of the secondary medication has been checked. This process will ensure that any remaining secondary medication is then not infused at a dangerously elevated flow rate.

Conclusion

Secondary infusion using IVSP is a common practice for IV medication administration in acute and critical care settings. However, when secondary infusion is used with head-height dependent IVSP systems, it is important to understand specific manufacturer setup requirements as well as the associated common errors. By understanding the differences between the head-height differential and cassette methods, recognizing common errors and following best practices, healthcare providers can help to ensure the safest and most effective administration of IV medications and fluids.

Errors related to improper head-height positioning, secondary clamp closure, incorrect VTBI programming and check-valve failures can lead to IV medication administration errors that are difficult to detect and can be serious or life-threatening. These errors include delayed or incomplete IV medication delivery or unintended over-delivery.

Because head-height dependent systems require ongoing adjustments in the system setup to support both primary and secondary infusions, it is up to frontline nurses to mitigate risks and enhance patient safety. Ongoing education and awareness of best practices are essential to optimize secondary infusion accuracy and improve overall patient outcomes.

Acknowledgements

This blog is part of a series that shares some of the practical knowledge we have gained with critical care nurses at the front lines of care. I specifically acknowledge the collaboration and support for this blog series from IV smart pump researchers Jeannine Blake, PhD, RN, UMass doctoral student Karen Meade, and the Elaine Marieb Center for Nursing and Engineering Innovation.