Multimodal monitoring in laboratory requires computer support. Various protocols in different centers have been used. Apart from classical signals like in TBI, monitors like laser Doppler flowmetry, rheoencephalography, NIRS, diffused correlation spectroscopy, etc., are verified. Various novel secondary indices can be designed and tested in an experimental environment.
The software ICM (a previous version of ICM+) was used for the collection and processing of data from animal models during the years of 1995 and 1996 in Cambridge in accordance with guidelines of the United Kingdom Animals (Scientific Procedures) Act of 1986. During this time, data from several cohorts of New Zealand rabbits was collected and has been under scrutiny until recently.
- One of these cohorts was a population of 28 rabbits, anesthetised and ventilated, where severe intracranial hypertension was induced until the Cushing response occurred. These rabbits were being monitored by ICM during the duration of the experiment. Here, high-resolution data of ICP, ABP, Fv in the middle cerebral artery (MCA), Laser Doppler Flowetry (LDF)and PaCO2 signals were collected.
Several retrospective studies were performed using the data generated by this cohort.
One example of this was published by Donnelly et al., where it was found that Fv was unchanged for ICP pressures up to 41 mmHg, ABP increased, and LDF and wall tension decreased. For higher pressures, the ABP kept increasing and the Fv started decreasing alongside LDF, but wall tension remained the same. This helped to demonstrate two intracranial pressure-dependent cerebroprotective mechanisms: with moderate increases in intracranial pressure, wall tension decreased and arterial blood pressure increased, while with severe increases in intracranial pressure, an arterial blood pressure increase predominated.
In another study on this data from the same cohort of rabbits published by Robba et al, where new techniques to access ICP non-invasively were studied: Gosling’s pulsatility index PI (gPI), Aaslid’s method (AaICP), and a method based on diastolic blood flow velocity (FVdICP). All methods proved to produce a nICP value significantly correlated with the real ICP. It was also shown that, even though non-invasive methods do not generate accurate values for the real ICP, they are very good in detecting the changes of ICP in time. In this work, ICM+ was used to process the raw data and calculate the nICP value using the three algorithms.
- In another cohort consisting of 29 male rabbits, anesthetized and ventilated where Hartman’s solution was infused into the spinal subarachnoid space, generating episodes of intracranial hypertension. In addition to this, arterial hypotension was induced by using trimetaphan to a part of the cohort and to the other, periods of hypo and hypercapnia were induced by changing the arterial PaCO2. These rabbits also were being monitored by ICM during all the duration of the experiment and high resolution data of ICP, ABP, Fv in the MCA, Laser Doppler Flowetry LDF and PaCO2 was collected.
Similar to the data in the previous cohort of rabbits, several studies were published using the data collected. One example is the work presented by Varsos et al where a new method for calculating for Critical Closing Pressure (CCP) was compared with the most accepted method CCP1. This new method calculated CCP using CPP, ABP, HR and cerebrovascular time constant. On the other side, the most accepted method used ABP and Fv for CCP calculation. The values generated by the new method proved to be highly correlated with the values generated by CCP1. Due to the nature of the variables used to calculate CCP, the new method is capable of generating physiological values for CPP for moments where CCP1 failed in doing so.
Shunt Evaluation Laboratory
ICM+ supports the Cambridge Shunt Evaluation Laboratory. It is used for evaluating hydrocephalus shunts and novel pressure transducers. Flow and pressure are measured and compared to each other using different protocols (depending on the construction of the shunt or transducer). Here, the rig from a project comparing Codman ICP transducer to Pressio 2 is presented as an example.