The use of electrical impedance tomography (EIT) to evaluate pulse rate in anaesthetised horses.

The study investigates the potential use of electrical impedance tomography (EIT) as a tool to measure pulse rate in anaesthetised horses under different blood pressure conditions.

Study Objectives and Methodology

• This research aimed to examine if EIT, a technique for imaging lung conditions, could also provide valuable data about the cardiovascular system, particularly the pulse rate (PR) in anaesthetised horses. The investigation considered normal physiological conditions as well as states of high and low blood pressure.
• The study involved seven horses, each anaesthetised and laid on their back (dorsal recumbency), for the collection of EIT data and pulse rate measurements. The data were collected over one-minute periods during both mechanical ventilation and a state of no breathing (apnoea).
• Data were gathered before and during the administration of certain medications (nitroprusside and phenylephrine) to artificially induce changes in blood pressure. These measurements allowed the researchers to examine how the EIT data might vary under different blood pressure conditions.
• An innovative algorithm was used to detect peak changes in impedance, related to cardiac function, in specific sections of the EIT image. These figures were then compared with the PR measured through a more traditional, invasive method.

Key Findings

• The researchers collected and analysed 288 paired datasets from six of the seven horses. The analysis used a statistical method known as Bland-Altman assessment suitable for comparing measurements that come from different methods.
• The results showed remarkable consistency between the EIT-derived pulse rates and the traditionally measured rates under normal physiological conditions, high blood pressure (hypertension), and low blood pressure (hypotension). This indicates that EIT can indeed be used to evaluate PR using cardiac-related impedance changes.
• A minor bias was detected, currently unaccounted for, that might impact measurements under different conditions or in horses with different positioning during anaesthesia. This necessitates further investigation.

Implications and Future Directions

• This study suggests that EIT could be a useful tool for measuring pulse rate in anaesthetised horses, offering an additional source of valuable cardiovascular information that could help enhance clinical assessments.
• The emergence of a slight bias under specific untested situations means further research is required to fully understand all potential deviations and to further validate the versatility and accuracy of EIT in different clinical conditions and positions.