Using Oximeter For Weak Pulse

Using Pulse Oximeter in Low Perfusion Environment


Weak pulse can cause issues for oximeters. There are several ways one can mitigate the problem.

Pulse oximeter works by shining two lights though a translucent portion of the patient's body and measuring the variation in light absorption caused by the changes in blood flow. The total light absorbance is the sum of a constant component and a pulsating component, which is almost exclusively the result of arteriolar bed pulsations. Perfusion index is the ratio of the pulsating blood flow to the nonpulsating component in peripheral tissue.

When the patient has weak pulses or low perfusion index, the pulsating component can be weak and irregular. Identification and isolation of the pulsating component from noise and other signals would be difficult and would decrease the accuracy and reliability of the measurements.

Using a handheld pulse oximeter would help as it is normally more sensitive to fingertip oximeters.

Here are some steps that may help you when taking readings:

  1. Select a sensor that is appropriate for the patient's size and site. For smaller fingers, use a pediatric pulse oximeter or a Y multi-site oximeter sensor.
  2. Select a location that is steady and has adequate circulation. If the pulse oximeter provides plethysmograph, perfusion index or pulse strength, use it to find a location that has the best circulation. This step is critical.
  3. Clean the area with an alcohol wipe and make sure the area is clean and dry.
  4. Make sure the oximeter sensor is clean. It should be cleaned regularly.
  5. Align the LED and photo detector on the sensor properly so they are exactly opposite each other.
  6. Evaluate the plethysmograph and signal strength to assess the accuracy of data. A strong signal would ensure the reliability of the readings. For some oximeters, each sweep corresponds to about 5 seconds; if you see exactly six complete cycles, this means the heart beats 6 times in 5 seconds or 72 times in one minute.
  7. Relax the hand and avoid any pressure on the finger as this would reduce blood flow.

With the introduction of new technology, pulse oximeter has improved significantly. Now, a pulse oximeter is capable of isolating venous blood pulsations from arterial blood pulsations resulting in more accurate readings. The use of brighter LEDs also helps.