An apparatus is provided for monitoring a predetermined parameter of a patient's
body fluid while infusing an infusion fluid into the patient. The apparatus comprises an infusion line and a
catheter configured for
insertion into a
blood vessel of the patient, and a reversible
infusion pump connected between a source of an infusion fluid and the infusion line and
catheter. The apparatus further comprises a
body fluid sensor
assembly mounted in fluid communication with the infusion line and which includes a first sensor and a sample
cell. The first sensor provides a
signal indicative of a predetermined parameter of any fluid present in the infusion line. The sample
cell is substantially transmissive to light comprising a
wavelength λ. The apparatus further comprises a controller that is configured to operate the
infusion pump in a forward direction so as to pump the infusion fluid through the infusion line and
catheter for infusion into the patient. The controller is configured to intermittently interrupt its operating of the
infusion pump in the forward direction to operate the infusion pump in a rearward direction so as to draw a
body fluid sample from the patient through the catheter and infusion line. The
body fluid sample drawn from the patient is disposed such that a first portion of the
body fluid sample is in sensing contact with the first sensor of the body fluid sensor
assembly, and a second portion of the
body fluid sample is disposed within the sample
cell of the body fluid sensor
assembly. The controller further is configured to monitor the
signal provided by the first sensor of the body fluid sensor assembly and to detect a change in the
signal indicative of the arrival of the body fluid sample at the first sensor. The controller, in response to detecting the arrival of the body fluid sample at the first sensor, is configured to cease its operating of the infusion pump in the rearward direction. The signal produced by the first sensor provides an indication of a predetermined parameter of the patient's body fluid when the body fluid sample is in sensing contact with the first sensor.