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Syringe pump displacement alters line internal pressure and flow

[Le déplacement verticalde la pompe à perfusion modifie la pression interne du cathéter et le débit]

Hiroshi Igarashi, MD^*, Yukako Obata, MD^*, Yoshiki Nakajima, MD PhD^*, Takasumi Katoh, MD PhD^*, Koji Morita, PhD and Shigehito Sato, MD PhD^*

^* From the Department of Anesthesiology and Intensive Care, and
the Surgical Center, Hamamatsu University School of Medicine, Hamamatsu, Japan.

Address correspondence to: Dr. Hiroshi Igarashi, Anesthesiology and Intensive Care, Hamamatsu University School of Medicine, 1-20-1 Handayama, Hamamatsu, 431-3192, Japan. Phone and Fax: +81-53-435-2284; E-mail: igaiga{at}hama-med.ac.jp

Purpose: It has been reported that the actual flow from a syringe pump changes due to vertical movement of the pump in vitro, but a direct study of the in vivo effects of fluid delivery irregularities caused by vertical pump displacement has not been performed. The aim of this study was to assess the influence of positional changes of the syringe pump on the internal pressure (IP) and flow from the circuit, and to examine blood pressure changes caused by pump movement in animals with or without hemorrhagic shock.

Methods: To simulate clinical conditions, we used a rabbit model. We first measured the changes in line IP and flow from the syringe pump after moving the pump 50 cm vertically upwards or downwards. With the same animal, we then recorded the blood pressure changes under these conditions during norepinephrine (NE) infusion, using a rabbit hemorrhagic shock (HS) model.

Results: Following downward movement of the syringe pump, the IP increased by 37.5 ± 4.0 mmHg and IP decreased by 37.3 ± 3.1 mmHg following upward movement of the syringe pump. In the rabbit HS model, movement downwards decreased systolic blood pressure (SBP) by -17 ± 6.9% (P < 0.001), while upward movement raised SBP by 45.7 ± 21.5% (P < 0.001) from baseline values.

Conclusions: Vertical displacement of the syringe pump alters the flow due to a change of line IP, and blood pressure can be affected by pump movement during NE infusion.