iPhone app for managing drug infusions

Year: 2009-2010



ivDripRate was built upon the early research that I did during my Master's degree. I spent two years researching drug dose calculation errors in safety-critical situations. The vision for ivDripRate came from observations in the healthcare setting and the difficulties that practitioners face when carrying out intravenous infusions. During the early years of the iPhone, I saw an opportunity to design an app that could assist practitioners with drug administration wherever they are.


Board 1

Calculation errors are a leading factor to clinical incidents. In Europe around 120,000 hospital deaths per year are caused by drug calculation errors.

A detailed study carried out into mathematical skills for nurses in a large NHS hospital highlighted areas of concern and identified a lack of confidence in tackling basic infusion rate calculations. 

A calculator can be used if available, but there is still no guarantee that the you've used the right formula or entered everything correctly. Research has also shown how calculators make it easy for us to make mistakes and how they ignore human error, making them unreliable for specific tasks such as drug dose calculations. 

Contextual inquiry in the clinical setting

Research was carried out in a local NHS Hospital to gather an understanding of the social setting and the steps that practitioners need to make in order to administer drug infusions safely. 

Gravity Infusion is the most basic form of delivering fluids to a patient. It is delivered intravenously (into the vein) and can be used in cases where drug delivery pumps are not available. Nevertheless, there are many quite complex and error-prone steps involved in setting up a gravity infusion for the correct dose, and since there is no computer or similar technology involved to assist with the procedure, it can be difficult to guarantee the accuracy and consistency of the fluid delivery.

Calculating the drug dose

The first step in carrying out a gravity infusion is to calculate the correct dosage based on the patient’s prescription. There are several steps involved before the final answer can be obtained, also each variable in the calculation needs to be converted to the correct unit of measurement. Practitioners who do not regularly carry out this calculation can easily forget some of the steps involved.

Some nurses would use wooden tongue depressors to write down calculations and formulas, and keep them in their uniform pockets. One nurse created calculation pocket cards to help remember the different formulas and common infusion rates.

Board 2

Setting the rate

Once the drip-rate has been calculated, the practitioner can then begin to set up the gravity infusion. This involves hanging the bag of fluid on a steady drip stand and connecting the correct administration set from the bag to the patient. The administration set has a “drip chamber” (shown in the video) built on to it, which is used by the practitioner to measure the flow rate of the fluid (that is, watch the drips and time them against their watch) and adjust a roller clamp to make the flow rate correct. The flow rate is measured in drops per minute. One of the problems with this is that it can be time consuming; adjusting the roller clamp, looking at your pocket watch, counting the drops, and trying to adjust the clamp to achieve the precise drip-rate. Gravity infusion rates are often therefore approximated.

Co-creation, sketching and paper prototyping

I worked closely with experts in the NHS to sketch out scenarios and calculation steps. This allowed users to feed into the design process to develop a system that would suit their needs


Evaluating concepts

I led a workshop, consisting of seven registered nurses working for the NHS. The aim was to get feedback on early concepts and understand how these concepts could fit into their daily lives. A semi-structured questionnaire was also used for capturing individual data; demographics, confidence levels with example scenarios and questions relating to their job tasks.

Screen Shot 2018-07-01 at 17.12.39

Qualitative analysis


I studied the qualitative data that was gathered from the workshop and from interviewing nurses. This data was refined and categorised to form structure for the user needs and requirements. These new learnings could then be fed back into the design process to improve on the initial concepts.

User flows

I followed the recommendations of ISO Standard 14971,Medical devices – Application of risk management to medical devices and ISO Standard 62366 Medical devices – Application of usability engineering to medical devices.

Usability Engineering

I followed the classic Jakob Nielsen for usability heuristics for user interface design. The following summarises some of the error-prevention methods I engineered into the design to help carry out safer calculations for infusion drip-rates:

Minimize the user’s memory load

All steps of the calculation appear on the same screen. This reduces the memory load and allows users to see previous steps in the calculation, which lead to the answer.

Aesthetic and minimal design

Calculations are very clear to read by breaking down each calculation step and using a larger font for answers. The user interface contains only what is needed for the calculation.

Help guides

Located in the corner of the interface, the “information” icon opens the help features, which explain each calculation step to the user in case they get stuck or confused. It also includes the formula used by the app for the drip-rate calculation.

Error prevention

Units and conversions are automatically calculated. For example, if a practitioner needs to enter ’75 minutes’ as the total time, there is a feature to allow them to enter ’75’ as an option directly into the minutes input field. This also removes the need to convert 75 minutes into 1 hour and 15 minutes (which is also an acceptable input). Correct symbols and abbreviations have been used, and adhere to the Institute for Safe Medication Practices guidelines (ISMP 2006). For example “100mL” is correctly represented as “100 mL” with a space between the dose and unit of measure, and a capital L is used for litres, since l (the letter) is too easily confused with 1 (the digit). The space helps prevent the “m” from being mistaken as a zero or two zeros (e.g., when written badly by hand), risking a 10- to 100- fold overdose.

Each input field has been capped with a threshold to prevent any accidental lethal doses. “Total volume” cannot be bigger than 4 digits and the “hours” and “minutes” fields cannot be greater than 2 digits each. The “drop factor” can only be a value of 10 mL, 15 mL, 20 mL or 60 mL corresponding to the value on the administration set. For this I used graphical icons to represent the values, which matches what is printed on the administration set packaging. Only one value can be selected at a time and by default, no value is selected. When a value becomes selected, its button will change its state and display as highlighted. This eliminated the chances of a user entering an invalid value and saves time key pressing.

Decimal points have been removed from the number pad, as they are not needed in this type of calculation, eliminating the chances of decimal point errors.

Visibility of system status

The interface keeps the user informed about the state of the calculation by revealing an answer when all three parts of the calculation have been correctly entered. Also, whenever a user inputs a number, if the value is acceptable after a validation check the number will turn blue to indicate that it has been accepted and allow the user to progress to the next step in the calculation.

Recognition rather than recall

Each step in the calculation is visible and nothing is hidden. The user is not required to remember any information from one step to the next.

Agile development

Initial prototypes were coded early on to test out the different interactions of the design. The design/development process was carried out iteratively; refinments were made based on results from testing.

Board 7

The idea behind this feature was to guide practitioners better when setting up an IV drip. A practitioner can hold the simulation up against the real drip chamber and try to synchronise the accurate on-screen representation against the real one, which they try to achieve by increasing/decreasing the wheel of the roller clamp on the administration set. This can reduce practitioner workload by not having to count the drops and time manually, instead matching the rate of the app’s simulation.

Evaluation in clinical setting

Software features needed to be tested in the clinical setting where practitioners carry out drug calculations and infusions. This was tested in a ‘safe environment’ in the hospital where you can set up practice infusions.  


  • Download ivDripRate on the iOS app store (launched April 2010)
  • Over 20,000 downloads in over 25 countries worldwide
  • Reached top 10 medical apps in the UK app market during 2011
  • Read the Full research paper published at British HCI 2014
  • Used as a tool for teaching and training student nurses in Melbourne, Australia
  • Local newspapers in Wales wrote about the app

Selected Works

Just Eat | Rethinking the rating and reviewsHow we enhanced the existing ratings system and made it more reliable for our customers

Just Eat | Fixing the minimum spendHow we improved the usability of ordering food and increased conversion by 0.25% (270,000 extra orders per year)

Severn Trent | Digital transformationHow we transformed the digital experience, helping customers to self-serve better

ivDripRateiPhone app for managing drug infusions, which has generated more than 25,000 downloads and is used by healthcare practitioners globally


Hi, my name is Mark. I am a UX designer and researcher. Read more..


Hi, my name is Mark. I am a UX designer and researcher. Read more..

See my résumé


Find me elsewhere

© 2019 Mark Davies