Infusion Rate Calculation

Intravenous fluid flow rate is calculated via the drop rate.1  The drop factor is the number of drops it takes to make up one ml of fluid and relates to the size of each drop; this cannot be altered. There are two sizes; 20 drops per ml and 15 drops per ml, although 20 drops per ml is much more common with 15 drops per ml typically used for thicker fluids. When using electronic infusion controllers, the flow rate needs to be set. The rate is the volume (ml) divided by the duration in hours (mls/hour). This forms the basis of infusion rate calculation.

Issues in IV administration

Whether paper and pen or a calculator is used to calculate the volume and rate at which an intravenous drug is to be administered, the aim is to ensure that it is delivered safely and in accordance with the written prescription. Historically, this does not always happen. The National Institute for Health and Care Excellence (NICE),2 cites a 1999 report, which showed a significant number of hospitalised patients dying as a result of infusion of too much or too little fluid. Further, NICE suggests that ‘…it is likely that as many as 1 in 5 patients on IV fluids and electrolytes suffer complications or morbidity due to their inappropriate administration.’2

Cousins et al’s3 study of intravenous drug administration found one error in dose or infusion volume and 132 (48% of nurses studied) errors in administration rate; errors in administration rate were also found by Taxis and Barber4 and Tissot et al.4

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Bruce and Wong6 and Han et al7 found that infusions were being administered slower than prescribed because nurses were not monitoring gravity infusion systems (i.e. no pump) nor were they readjusting the rate to take account of changes in gravity if the patient altered their position.

Some studies indicate that infusion rate calculation errors are due to miscalculation of infusion rates. Calabrese et al.8 observed medication administration in five intensive care units and found 75 errors out of 187 were due to wrong infusion rate calculations; at least three of these errors were due to miscalculation of the infusion rate required.

Volumetric Pumps

Currently, powered volumetric infusion pumps aim to provide an accurate flow of fluids over a prescribed period. These employ a linear peristaltic pumping mechanism applied to the infusion tubing (‘giving set’) to control the speed of infusion over a specified time. However, these require specialist administration sets, which are more expensive than simple gravity administration sets where the infusion rate calculation is set by the health care professional.  

Additionally, shortages of pumps are common in many UK Hospitals – a problem that was exacerbated during the initial surge of COVID-19 infections early in 2020. The National Infusion and Vascular Access Society (NIVAS) published the COVID-19 Gravity Infusion and Bolus Admin Guidance earlier in 2020 in anticipation of increased pump shortages.9

Such studies, coupled with current guidance on IV infusion safety suggest that a simple but effective method of fluid delivery and monitoring is required both to save resources and improve patient safety.

Towards a solution

The Monidrop® (Monidor Finland) IV fluid Monitor allows for accurate delivery in infusion speed, target volume and speed and total volume infused (Figure 1). The system is portable, chargeable, and compatible with most commonly used drip sets (20 drops/ml). Additionally, when used in conjunction with the IV Screen remote monitoring software application, allows Nurses to remotely monitor details of several infusions in real-time on a computer or mobile device. The Monidrop device attaches to the drip chamber and shows on the screen:

  • Infusion speed
  • Total volume
  • Treatment duration

Flow rate can be adjusted by using the administration set’s roller clamp - the infusion speed is shown on the system’s screen (ml/h). Monidrop® monitors the infusion but does not adjust it. It has a series of built-in alarms which indicate if it is outside the measurement range of 6ml/h to 1200ml/h, or if the battery is low.

The wireless connection enables remote monitoring, thus allowing the system to be used in both acute and home care settings. The information obtained from the Monidrop device is transmitted wirelessly to the IV Screen and from there, Nursing staff can set target speeds for each patient by inputting the total volume of fluids they would like to infuse and over how long. If the infusion then starts to run too fast or too slow, this will flag up on the screen and prompt the Nurse to adjust the infusion speed. Trials are currently ongoing for COVID-19 patients in isolation with positive results showing a reduction in unnecessary patient contact to monitor infusion speed.

Cost savings

Currently, a commonly used volumetric pump set for blood and blood components costs £2.91 per unit when purchased through NHS supply chain. Capital outlay will also be required for the actual pump. In a typical 400-bed hospital which uses on average, 9039 blood administration sets, the cost would be £26,303.49 per annum. A theoretical reduction in use of these sets by 10%, 15%, 20% or 50% would result in savings of £2,630.35, £3,945.52, £5,260.70 and £13,151.75, respectively. A reduction in the use of volumetric pumps and associated costly administration sets could be realised using the Monidrop system as it facilitates effective blood product administration, as well as other fluids and medications, using a standard administration set costing £0.61.

The purpose of Monidrop is not to directly replace the function of volumetric pumps as they are a mandatory requirement for certain fluids and medications, and in certain scenarios. However, by increasing Nurses confidence to administer IV therapy with gravity and, as a result, increasing patient safety, the overall requirement for pumps is reduced, leading to cost-savings and other efficiencies.

The Future

Monidrop development plans in remote monitoring are already producing great results and will fit well with the NHS desire to adopt digital healthcare solutions. Other exciting developments include the addition of a dedicated low-cost dial infusion set designed to deliver stable, consistent, and accurate delivery volume for hours. This will be in the form of a dial-slow giving set, however, there will be no numbers printed on the dial and users will instead take the speed of infusion from the Monidrop screen. Initial testing indicates a far greater consistency of infusion speed in comparison to traditional gravity sets with roller clamp control.

Conclusion

The Monidrop® system is simple yet effective. Early results from the three-month clinical trial suggest that using the system can prevent over/under delivery of IV fluid. Accurate administration will prevent complications and thus shorter hospital stay and reduced costs. Monidrop also clearly offers significant advantages in patient safety and fits well with NHS plans to adopt digital solutions with remote monitoring functions.

References

  1. Royal College of Nursing (RCN). Clinical topics. Flow rate and IV drugs. 2018. Available at: https://www.rcn.org.uk/clinical-topics/safety-in-numbers/flow-rate-and-iv-drugs
  2. National Institute for Health and Care Excellence. Intravenous fluid therapy in adults in hospital. Clinical guideline [CG174]. 2017 (Update). 

Available at: https://www.nice.org.uk/guidance/cg174 

  1. Cousins D, Sabatier B, Begue D, et al. Medication errors in intravenous drug preparation and administration: a multicentre audit in the UK, Germany and France. Quality and Safety in Health Care. 2005;(14):190–195
  2. Taxis K, Barber N. Incidence and severity of intravenous drug errors in a German Hospital. European Journal and Clinical Pharmacology. 2004;59(11):815–817
  3. Tissot E, Cornette Limat S, Mourand J, Becker M, et al. Observational study of potential risk factors to medication administration errors. Pharmacy World and Science. 2003:25(6):264–268
  4. Bruce J, Wong I. Parenteral drug administration errors by nursing staff on an acute medical admissions ward during day duty. Drug Safety. 2001;24(11):855–862
  1. Han P, Coombes I, Green B. Factors predictive of intravenous fluid administration errors in Australian surgical care wards. Quality and Safety in Health Care. 2005;14(3):179–184
  2. Calabrese A, Erstad B, Brand K, et al. Medication errors in adult patients in the ICU. Intensive Care Medicine. 2001;27(10): 592–1598
  1. COVID19: NIVAS Gravity infusion and Bolus IV drug administration guidance. Available at https://nivas.org.uk/contentimages/main/NIVAS-COVID19-Gravity-Infusion-Bolus-Admin-Giuidance-2-converted-SH.pdf