Fluid administration plays a critical role in perioperative patient care, including hydration, electrolyte balance, blood product transfusion, and medication delivery. Accurate monitoring of the fluid infusion rates is essential to ensure optimal patient management. Here, we briefly introduce a pilot study to measure the rate of fluid administration that is a method for calculating the number of drops using a pulse oximeter wrapped around the drip chamber.

A 1,000 ml bag of 0.9% normal saline (HK inno.N) without medication was used. The normal saline bag was suspended at the manufacturer’s recommended height of 100 cm. A pulse oximeter (Nellcor^TM SpO₂ Adhesive Sensors, Medtronics, Neonatal/Adult < 3 kg or > 40 kg) was wrapped around the drip chamber, and the fluid flow was controlled using an intravenous infusion flow regulator (IIFR) set (Innofuser; SUNGWON MEDICAL Co., Ltd.). The pulse oximeter was monitored by connecting to an IntelliVue MP70 instrument (Philips). Drop rates were measured using a pulse oximeter and recorded at different numerical scales on the IIFR dial (Supplementary Video 1). The expected and measured volumes were calculated and the deviations between the IIFR and pulse oximeter measurements were compared. Three IIFR products of the same type from the same manufacturer were used. Each trial was initiated by opening the tubing roller clamp and the infusion was run for exactly 5 min, at which point the roller clamp was closed. Each fluid volume in the beaker was calculated indirectly by using the relative density (kg/L) of the fluids that had been previously measured by recording the weight of 50 ml at 20°C. All experiments were conducted by a single researcher.

The drop rates measured by the pulse oximeter were consistent for infusion rates above 100 ml/h on the IIFR dial (Table 1). Maximum volume deviations ranged from –2.83 to 3.1 for the IIFR and from –0.4 to 0.2 for the pulse oximeter. The percentage of maximum volume deviation varied from –15.72% to 19.9% for the IIFR and from –3.66% to 0.76% for the pulse oximeter. In all trials, the drop rate measured by the pulse oximeter showed lower deviations than the IIFR.

Manual IIFRs are popular because of their simplicity; however, variations in fluid injection have been reported [1,2]. Although computer-controlled infusion pumps offer precise measurements, their high cost and bulkiness limit their popular use. This pilot study used the light source of a pulse oximeter, and a study have measured the fluid infusion rate using light sources [3]. As far as the authors searched, there were no studies using the pulse oximeter. This study introduces the feasibility of using a pulse oximeter, a device readily available in clinical settings, as an alternative method for measuring infusion rates. The limitations of this study include the use of a specific IIFR product, measurement restrictions to rates above 100 ml/h, and the dependence on specific monitoring and oximeter devices. However, the ability of a pulse oximeter to capture drop rates accurately offers a simple and accessible method for monitoring fluid administration. Thus, this method is advantageous in small clinics or emergency situations that lack electronic infusion devices.