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Free How to undertake intravenous infusion calculations
Jane Brindley Senior lecturer in adult nursing, School of Nursing, Faculty of Health and Wellbeing, Canterbury Christ Church University, Kent, England
• To refresh your knowledge of the steps involved in undertaking intravenous infusion calculations
• To understand the role of the nurse in reducing medication errors
• To recognise the importance of organisational culture in preserving patient safety and preventing harm
Rationale and key points
This article provides a step-wise, practical approach to undertaking intravenous (IV) infusion calculations. It also explores the evidence base behind medication errors in relation to calculations.
• Medication errors are the most common type of error affecting patient safety and the most common single, preventable cause of adverse events.
• Medicines calculations can assist in preventing an inaccurate medicines dose from being administered to the patient, which could result in suboptimal therapeutic benefit and/or possible harm to the patient.
• It is crucial for IV infusion calculations to be accurate, because these medicines directly enter the venous system and generally have a prompt action. Therefore, there is limited possibility of removing the medicine if an error is made.
• Individual nurses and healthcare organisations must ensure that medicines calculation skills are developed and maintained in practice.
‘How to’ articles can help to update your practice and ensure it remains evidence-based. Apply this article to your practice. Reflect on and write a short account of:
1. How this article might improve your practice when undertaking IV infusion calculations.
2. How you could use this information to educate nursing students or your colleagues on the appropriate methods to use when undertaking an IV infusion calculation.
Nursing Standard. doi: 10.7748/ns.2020.e11444Peer review
This article has been subject to external double-blind peer review and checked for plagiarism using automated software
Brindley J (2020) How to undertake intravenous infusion calculations. Nursing Standard. doi: 10.7748/ns.2020.e11444Disclaimer
Please note that information provided by Nursing Standard is not sufficient to make the reader competent to perform the task. All clinical skills should be formally assessed at the bedside by a nurse educator or mentor. It is the nurse’s responsibility to ensure their practice remains up to date and reflects the latest evidence
Published online: 13 January 2020
Preparation and equipment
• When calculating and administering intravenous (IV) infusions, the nurse must ensure that they follow national and local policies, procedures and protocols, for example by checking a calculation result with another healthcare practitioner if required. For controlled medicines, the National Institute for Health and Care Excellence (NICE) (2016) guidelines recommend that a second healthcare practitioner independently checks any dose calculations.
• The nurse must understand how to undertake IV infusion calculations accurately, and have completed any IV infusion training requirements specific to their clinical area of practice. They should reflect on their skills, knowledge and competence in relation to calculating and administering IV infusions, and take steps to address any deficits or uncertainty in relation to these areas. If the nurse is unsure about any aspect of IV infusion calculation or administration, they must ask questions or seek clarity from another qualified healthcare practitioner.
• Where possible, the nurse should find a quiet, undisturbed area to undertake medicines calculations. To minimise distractions and interruptions, the nurse should inform their colleagues of what they are doing and ask that they are not disturbed.
• There is minimal equipment required to undertake medicines calculations. The nurse will require the patient’s medicines chart to check the prescription information and dose. The use of a pen, paper and calculator may assist the nurse with the mathematics involved in the calculation.
• There is a higher risk of patient harm if medication errors are made for the IV route than for other routes of administration. This is because IV infusions directly enter the venous system, so the effects will be more immediate than for other routes. Furthermore, unlike in oral medicines, it will not be possible to remove the medicine once it has been administered, for example through stomach aspiration. The mathematical calculations involved in IV infusions are also more complex than for other routes of medicines administration, so nurses’ anxieties may be increased when undertaking these calculations (Sneck et al 2016).
• Computerised infusion devices (smart pumps) are commonly used in clinical settings and aim to reduce IV medication errors and enhance patient safety. These devices use a dose error reduction system (DERS), which is a software programme that provides a customised medicines library, alerting users to programmed minimum and maximum dose limits for each medicine (Reston 2013). However, even when smart pumps are used, there remains a risk of human error (Harding 2011); for example, a medication error would occur if the smart pump were incorrectly programmed by the nurse. Therefore, it is essential for nurses to use manual calculations to check that these dosages are accurate.
• When calculating and administering intravenous (IV) infusions, the nurse must ensure that they follow national and local policies, procedures and protocols, for example by checking a calculation result with another healthcare practitioner if required
• There is a higher risk of patient harm if medication errors are made for the IV route than for other routes of administration. This is because IV infusions directly enter the venous system, so the effects will be more immediate than for other routes
• Errors in IV medicines administration commonly result from initial errors, for example a mistake within a patient’s prescription that the nurse did not identify
• Medication errors can be reduced and patient safety enhanced by fostering a culture of openness in which healthcare practitioners at all levels can question suboptimal practice and mistakes, and in which thorough checking is encouraged
1. Ensure the prescription on the patient’s medicines chart is correct and written legibly, and that it remains appropriate to administer the medicine. If there is any doubt about what is written, or whether the medicine is still required, do not administer the medicine and immediately seek assistance and advice from the prescriber or pharmacist.
2. Check the prescribed route of administration on the patient’s medicines chart, since the medicines calculation will vary between the IV route and other routes.
3. Check the IV infusion information on the patient’s medicines chart before undertaking the calculation – for example the date and time commenced, fluid type, volume and rate, and the units used in the prescription and for the infusion. Ensure that the medicine is due to be administered, to avoid spending unnecessary time working out the calculation.
4. Select the appropriate formula to use for the calculation. The formula used will differ, depending on whether it is:
5. For a prescribed volume of IV fluid that needs to be administered to a patient over a specified time period, usually several hours. The infusion can be administered either manually (gravitationally) using an IV giving set, or using an electronic device such as a smart pump. Box 1 details the formula used to calculate the drop rate for an IV infusion that will be administered manually, while Box 2 details the formula used to calculate the flow rate for an IV infusion that will be administered using a smart pump.
6. For a prescribed dose of an IV medicine that needs to be administered over a specified time period, and will be related to the patient’s weight. These calculations are generally used in critical care settings or high dependency units for highly potent medicines, such as positive inotropes, which increase the contractility of the myocardium (Adam et al 2017). Box 3 outlines the process used to calculate the flow rate of an IV infusion required to deliver the prescribed dose of a medicine.
7. For checking an IV infusion already in progress to ensure the prescribed dose is being delivered to the patient. This will be related to the patient’s weight and a specified time period, and is often stated in mcg/kg/min (for the purpose of this article and ease of reading, the abbreviation mcg is used for micrograms. However, NICE (2017) guidelines state that micrograms and nanograms should not be abbreviated in clinical practice, to avoid medication errors during prescribing and administration). Box 4 outlines the process used to calculate the dose of a medicine being delivered by an IV infusion already in progress.
8. Check the calculation result carefully. If necessary, undertake the calculation again to ensure it is correct. Consider if the result looks illogical or incorrect, for example if it would require an unusually large or small volume of fluid to be administered, or an unusually fast or slow infusion rate. Check the result with a colleague, if this is the local policy, or if you are unsure of the accuracy of the result. If in any doubt, do not administer the medicine and seek expert advice, for example from the nurse in charge or the pharmacist. Document any medicine that is not administered, in accordance with local policy.
Formula used to calculate the drop rate for an intravenous (IV) infusion that will be administered manually
A manual IV infusion must be set according to drops per minute (drops/min) – counting the drops as they drip into the chamber of the giving set. Identify the type of fluid that will be infused, because different types of fluid will have different rates of drops per mL (drops/mL). For instance, giving sets for administering crystalloid solutions, such as 0.9% sodium chloride, are usually 20 drops/mL, while giving sets for administering blood are usually 15 drops/mL. Check the packaging or manufacturer’s instructions to obtain this information.
Use the following formula to calculate the drop rate in mL per hour (mL/hr) for an IV infusion that will be administered manually:
For example, 1.5L of 0.9% sodium chloride is prescribed for manual IV infusion over eight hours. To calculate how many drops/min this infusion needs to run at, first convert 1.5L to mL: 1.5 × 1,000 = 1,500. Then use the formula as follows:
Round this figure up to 63 drops/min*
*When calculations result in decimal places, if the first number after the decimal point is 5 or above it should be rounded up to the next whole number. If it is below 5, it should be rounded down to the lower whole number
Formula used to calculate the flow rate for an intravenous (IV) infusion that will be administered using a smart pump
Use the following formula to calculate the flow rate in mL per hour (mL/hr) for an IV infusion that will be administered using a smart pump:
For example, gentamicin 100mg in 100mL is prescribed to be infused over 30 minutes using a smart pump. Use the formula to calculate the flow rate as follows:
Calculating the flow rate of an intravenous (IV) infusion required to deliver the prescribed dose of a medicine
The following process is used to calculate the flow rate required; that is, how many mL/hr to run the syringe driver or infusion pump to deliver the prescribed dose of a medicine. It should be used if the nurse needs to administer an IV infusion and knows the prescribed dose range to be administered, usually related to the patient’s weight and a specified time period, and also knows the dose of the medicine and fluid volume in the syringe or fluid bag.
For example, the patient is prescribed a dobutamine infusion of 2.5-10mcg/kg/min, titrated to effect, but this is not yet in progress. Local policy and the prescription require 250mg dobutamine to be added to 50mL of 5% glucose solution. The patient’s weight is 85kg.
• The prescription will be a range based on the patient’s clinical presentation, so confirm precisely how many mcg/kg/min needs to be administered. For example, 5mcg/kg/min may be chosen, then titrated as required
• Convert 5mcg/kg/min to mg/hr as follows:
• Convert mcg to mg, by dividing by 1,000: 5mcg/kg/min / 1,000 = 0.005mg
• Multiply this by the patient’s weight in kilograms, which is 85kg: 0.005mg × 85kg = 0.425mg
• Multiply this by 60, to relate it to each hour rather than each minute: 0.425mg × 60 = 25.5mg/hr
• Calculate how many mg per mL are in the constituted solution as follows: 250mg / 50mL = 5mg in 1mL of solution. 25.5mg / 5 = 5.1mL
• Therefore, the syringe driver needs to be run at 5.1mL/hr
Calculating the dose of a medicine being delivered by an intravenous (IV) infusion already in progress
The following process is used if the nurse needs to check the dose of a medicine being delivered by an IV infusion, often stated in mcg/kg/min, and based on the mL per hour (mL/hr) being infused. This involves working backwards from the process detailed in Box 3.
For example, 4mg of noradrenaline (norepinephrine) in 50mL of 5% glucose solution is running at 5mL/hr. The prescription is for a range of 0.05-0.1mcg/kg/min of noradrenaline to be delivered. The patient’s weight is 75kg.
• Calculate how many mg per hour (mg/hr) are being delivered: 4mg / 50mL = 0.08mg in 1mL of solution
• Multiply this by 5mL/hr: 0.08mg × 5mL = 0.4mg/hr
• Convert 0.4mg/hr to mcg/kg/min:
• Convert mg to mcg, by multiplying by 1,000: 0.4mg × 1,000 = 400mcg/hr
• Divide this by the patient’s weight in kilograms, which is 75kg: 400mcg/hr / 75kg = 5.3mcg/kg/hr
• Divide this by 60 to relate it to each minute rather than each hour: 5.3mcg/kg/hr / 60 = 0.09mcg/kg/min
• Therefore, the IV infusion is being delivered within the prescribed range of 0.05-0.1mcg/kg/min
The severity of IV medication errors should be emphasised in all clinical settings, because the harm to patients is more severe if the incorrect dose is administered compared with other routes of administration. Errors in IV medicines administration commonly result from initial errors, for example a mistake within a patient’s prescription that the nurse did not identify (Keers et al 2015). Schnock et al (2017) identified that the most frequent errors arising from the use of smart pumps were user errors and violations of policy, such as bypassing the use of the pump or setting an incorrect infusion rate. Medication errors can also occur as a result of:
• Environmental factors, such as distractions and interruptions. While it may not be possible to prevent all distractions and interruptions, the nurse should attempt to minimise and manage these (Hayes et al 2015), for example by finding a quiet area to undertake a medicines calculation.
• Institutional factors, for example a lack of checking processes in place. Nurses and healthcare organisations should ensure checking processes for medicines are thorough; for example, assumptions should not be made about colleagues’ competence in checking calculations, since this might subconsciously reduce the integrity of checking and result in calculation errors (Brindley 2018).
• Individual factors, for example the nurse having false confidence that using a smart pump protects against all errors (Schnock et al 2017).
Nurses should reflect on any medicines calculation errors that occur in their practice and ensure that strategies are implemented to prevent their reoccurrence. Such strategies could include ensuring robust checking processes and policies are in place, or the nurse developing and maintaining their skills in calculating and administering IV infusions. Nurses must also ensure that they adhere to the guidance and requirements of their regulatory body; for example The Code: Professional Standards of Practice and Behaviour for Nurses, Midwives and Nursing Associates (Nursing and Midwifery Council (NMC) 2018) states that nurses must ‘advise on, prescribe, supply, dispense or administer medicines within the limits of your training and competence, the law, our guidance and other relevant policies, guidance and regulations’. The NMC (2018) also emphasises the need for nurses to ‘be aware of, and reduce as far as possible, any potential for harm associated with your practice.’
Role of organisational culture
The organisational culture is also important in preventing medication errors. Leveson et al (2016) examined the wider systems approach to managing adverse events such as medication errors. They proposed a non-punitive environment, in which systems are designed to prevent unsafe behaviour. Healthcare practitioners, including nurses, should ideally be practising within an organisational culture that provides a supportive learning environment, education, role clarity and appropriate constructive feedback mechanisms to aid reflection. Medication errors can be reduced and patient safety enhanced by fostering a culture of openness in which healthcare practitioners at all levels can question suboptimal practice and mistakes, and in which thorough checking is encouraged. Furthermore, Wright (2012) asserted that a wider exploration of the reasons for medication errors is required, which would involve examining the system of medicines management and addressing issues in the way that medicines are managed in the healthcare setting.
In the UK, the launch of the draft Health Service Safety Investigations Bill in 2017 has been part of a move to establish a culture of openness and transparency across the NHS, in which patients feel supported to raise concerns about their medicines (Department of Health and Social Care 2018). The bill aims to identify the whole-system changes that can be made to support learning when significant clinical errors occur, and to ensure that investigations focus on what can be learned from patient safety incidents in the NHS, to prevent their reoccurrence. An organisational culture should be established where wider learning occurs after a medication error has been identified; for example, investigating the factors that may lead to medication errors should be encouraged so that these can be addressed.
Gluyas (2018) asserted that healthcare organisations have a responsibility to ensure that user-friendly systems are in place in relation to medicines calculations and administration, which offer support and education to nurses to enable them to practise safely and effectively.
Adam S, Osborne S, Welch J (Eds) (2017) Critical Care Nursing: Science and Practice. Third edition. Oxford University Press, Oxford.
Brindley J (2018) Undertaking drug calculations for intravenous medications and infusions. Nursing Standard. 32, 20, 55-63. doi: 10.7748/ns.2018.e11029.
Department of Health and Social Care (2018) The Report of the Short Life Working Group on Reducing Medication-Related Harm. The Stationery Office, London.
Gluyas H (2018) Understanding the human and system factors involved in medication errors. Nursing Standard. doi: 10.7748/ ns.2018.e11176.
Harding A (2011) Use of intravenous smart pumps for patient safety. Journal of Emergency Nursing. 37, 1, 71-72. doi: 10.1016/j.jen.2010.07.006.
Hayes C, Power T, Davidson PM et al (2015) Nurse interrupted: development of a realistic medication administration simulation for undergraduate nurses. Nurse Education Today. 35, 9, 981-986. doi: 10.1016/j.nedt.2015.07.002.
Keers RN, Williams SD, Cooke J et al (2015) Understanding the causes of intravenous medication administration errors in hospitals: a qualitative critical incident study. BMJ Open. 5, 3, e005948. doi: 10.1136/bmjopen-2014-005948.
Leveson N, Samost A, Dekker S et al (2016) A systems approach to analyzing and preventing hospital adverse events. Journal of Patient Safety. doi: 10.1097/PTS.0000000000000263.
National Institute for Health and Care Excellence (2016) Controlled Drugs: Safe Use and Management. NICE guideline No. 46. NICE, London.
National Institute for Health and Care Excellence (2017) Prescription Writing. http://bnf.nice.org.uk/guidance/prescription-writing.html (Last accessed: 23 July 2019.)
Nursing and Midwifery Council (2018) The Code: Professional Standards of Practice and Behaviour for Nurses, Midwives and Nursing Associates. NMC, London.
Reston J (2013) Smart pumps and other protocols for infusion pumps: brief review. In Shekelle PG, Wachter RM, Pronovost PJ et al (Eds) Making Health Care Safer II: An Updated Critical Analysis of the Evidence for Patient Safety Practices. Agency for Healthcare Research and Quality, Rockville MD, 48-54.
Schnock KO, Dykes PC, Albert J et al (2017) The frequency of intravenous medication administration errors related to smart infusion pumps: a multihospital observational study. BMJ Quality & Safety. 26, 2, 131-140. doi: 10.1136/bmjqs-2015-004465.
Sneck S, Saarnio R, Isola A et al (2016) Medication competency of nurses according to theoretical and drug calculation online exams: a descriptive correlational study. Nurse Education Today. 36, 195-201. doi: 10.1016/j.nedt.2015.10.006.
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