Animal Monitoring in the Laboratory with Pulse Oximetry
Several types of pulse oximeters were developed in the mid 1900’s, but the modern version used throughout hospitals today was invented in 1972. In 1980, modern pulse oximetry was first commercialized, making it readily available – it quickly grew in popularity.
Because of its ease-of-use, low cost and non-invasive nature, pulse oximetry is mandated in nearly all hospital and home care patient care guidelines. In the hospital, this includes first responders to post-operative and critical care monitoring.
While common in the healthcare setting, pulse oximetry monitoring wasn’t easily available for small animal research. Some researchers would modify a human pulse oximeter for mice and rats but the results weren’t accurate because of the right shift of the oxyhemoglobin dissociation curve and the heart rate limit of human pulse oximeters.
What is Pulse Oximetry?
Pulse oximetry is a technique for monitoring the level of oxygen carried to the tissues on hemoglobin molecules in red blood cells.
Since 97% of oxygen is carried on hemoglobin, pulse oximetry provides a very robust assessment of arterial oxygenation. This is fortunate, because the alternative for monitoring arterial oxygen, an indwelling arterial catheter, is highly undesirable.
In pulse oximetry, the saturation is measured directly (not through a table or other function) with the use of 2 different wavelengths of light. One is red, which you can see, and the other is infrared, which you cannot. The absorption of light by hemoglobin changes based on the degree of oxygen bound to the hemoglobin.
Most people are familiar with the fact that de-oxygenated blood appears much darker than fresh blood. These variations can be tied back to the level of hemoglobin saturation through calibration that can be performed by the manufacturer,obviating the need for the user to do so.
Moreover, the word “pulse” in pulse oximetry refers to the fact that the light absorption received by a pulse-ox sensor oscillates with the cardiac pulsation. Because blood pulsation is completely damped by the time blood enters the capillary bed, the pulsating signal can only arise from the arterial system, and therefore measurements are made only on arterial blood and not on tissues, capillary blood or venous blood.
Mouse, Rat & Small Animal Pulse Oximeter
It wasn’t until 2006, when the MouseOx came to the market, that there was a clinically validated pulse oximeter for mice and rats. Besides being calibrated to consider of the difference of the oxyhemoglobin dissociation curve, the MouseOx is able to accurately monitor small animals with heart rates up to 900 bpm.
In 2011 the National Research Council updated their Guide for the Care and Use of Animals for the first time since 1996. Among the changes and additions was that “the use of a pulse oximeter precision vaporizers and monitoring equipment, e.g., pulse oximeter for determining arterial blood oxygen saturation levels, increases the safety and choices of anesthetic agents for use in rodents and other small species.”
Download the MouseOx Validation Papers
What Animals Can a Pulse Oximeter Be Used On?
When deciding if a pulse oximeter can be used in your animal research model, consideration of the species and heart rate must be taken into effect. Furthermore, darker pigmented skin or fur decrease the light signal due to absorption.
Researchers have successfully used small animal pulse oximetry on many species with heart rates in the range of 90 – 900 bpm.
- Guinea Pigs
- Rhesus Monkeys
- Tree Shrews
Using a Pulse Oximeter for Anesthetized & Surgical Animal Monitoring
Types of Anesthetized Monitoring:
- Surgery (multiple sensor options to accommodate different locations and accessibility)
- Surgical recovery
- Neonatal monitoring
- Lung injury and mechanical ventilation
- Shock models
- Stroke and brain injury
- Hypoxia and inhalation studies
When monitoring mice, rats and other small animals during anesthesia and surgical procedures, a multi-parameter pulse-oximeter that can monitor the cardio-pulmonary health of mice, rats and other small laboratory animals (heart rats 90 to 900 bpm), is perfect for collecting data of anesthetized animals during research and monitoring vital signs during surgery including
- Arterial Oxygen Saturation (SpO2)
- Heart Rate
- Breath Rate
- Pulse Distention (indicator of local blood flow and signal quality)
- Breath Distention (surrogate for intrapleural pressure)
- Core Temperature
Can You Monitor Conscious Unrestrained Animals with Pulse Oximetry?
Conscious monitoring of unrestrained mice and rats is possible with software that can filter out the noise of the animal moving and with a sensor designed for conscious monitoring.
Our MouseOx Plus has been used in many studies to monitor conscious animals using our Collar sensor.
Benefits of Pulse Oximetry Monitoring in Conscious Unrestrained Animals
Types of Conscious Unrestrained Monitoring Studies
- Influenza, Pneumonia, RSV & Other Acute Respiratory Disorders
- Lung Injury
- Lung Cancer, COPD, Sleep Apnea & Other Chronic Respiratory Disorders
- Shock Models
- Stroke & Brain Injury
- Hypertension, Hypotension & Other Cardiovascular Disorders
- Hypoxia & Inhalation Studies
- Vital Signs Monitoring During Imaging
- Vital Signs Monitoring During Surgery & Experiments Requiring Anesthesia
- Pharmacology & Toxicology
Pulse oximetry is not only beneficial as a anesthesia and surgical monitor. Researchers studying lung injury, shock, influenza, hypoxia and inhalation, just to name a few, have benefited by monitoring pulse oximetry in conscious and unrestrained animal.
- 3 of 5 vital signs from one monitor
- Heart Rate
- Breath Rate
- Activity/Motion Flag
- Record measurements on completely unstressed subjects.
- Conscious Measurement Enclosures available
- Make measurements on unstressed animals
- Monitor 24 hours or longer without direct contact with the animal
- Measurement from a single collar clip – no anesthesia, no surgery
- Animals are unrestrained and can be left unattended
- Food and water available ad libitum
- 2 Sizes – for mice and rats
- Low-torque slip-ring to allow animal to spin without winding wires
- Counterbalanced load – subject feels no weight from wires
Understanding the Limitations of Monitoring Conscious Unrestrained Animals
A small animal pulse oximeter such as the MouseOx Plus can measure vital signs in mice, rats and other small laboratory
animals that are conscious and unrestrained. However, there are some limitations to its use such as movement.
While measurement of pulse rate can be maintained during moderate movement, it must be understood that oxygen saturation cannot be measured while the animal is moving.
The nature of pulse oximetry that allows calculations of oxygen saturation to be obtained from absorption of light measurements requires that the distance between the sensor pads not change. When the animal moves, or even flexes muscles under the skin without obvious surface movement of the sensor pads, this assumption is violated preventing the measurement of oxygen saturation. Thus, an animal that is conscious and unrestrained, must also be still while the saturation measurement is being made.
Final Thoughts on Animal Monitoring in the Laboratory with Pulse Oximetry
Since 2006, a clinically validated small animal pulse oximetry has been available for mice, rats and other small animals with heart rate ranges of 90 -900 bpm. Five years later, the NRC stated that the use of pulse oximetry benefits the animals care during anesthesia use.
With a special collar sensor and software, a pulse oximeter, such as the MouseOx Plus, can provide vital sign monitoring on conscious and unrestrained subjects.
With the advent of the small animal pulse oximeter, pulse oximetry has furthered life science research by offering a noninvasive way to monitor and measure conscious and anesthetized animals.