Changes in intracranial pressure and epidural pulse waveform following cold injury

Assessment of a Non-Invasive Brain Pulse Monitor to Measure Intra-Cranial Pressure Following Acute Brain Injury

Background

Intracranial pressure (ICP) monitoring requires placing a hole in the skull through which an invasive pressure monitor is inserted into the brain. This approach has risks for the patient and is expensive. We have developed a non-invasive brain pulse monitor that uses red light to detect a photoplethysmographic (PPG) signal arising from the blood vessels on the brain's cortical surface. The brain PPG and the invasive ICP waveform share morphological features which may allow measurement of the intracranial pressure.

Methods

We enrolled critically ill patients with an acute brain injury with invasive ICP monitoring to assess the new monitor. A total of 24 simultaneous invasive ICP and brain pulse monitor PPG measurements were undertaken in 12 patients over a range of ICP levels.

Results

The waveform morphologies were similar for the invasive ICP and brain pulse monitor PPG approach. Both methods demonstrated a progressive increase in the amplitude of P2 relative to P1 with increasing ICP levels. An automated algorithm was developed to assess the PPG morphological features in relation to the ICP level. A correlation was demonstrated between the brain pulse waveform morphology and ICP levels, R²=0.66, P < 0.001.

Conclusion

The brain pulse monitor's PPG waveform demonstrated morphological features were similar to the invasive ICP waveform over a range of ICP levels, these features may provide a method to measure ICP levels.

Trial Registration

ACTRN12620000828921.

Simultaneous measurements of intracranial pressure parameters in the epidural space and in brain parenchyma in patients with hydrocephalus

Object

In this study, the authors compare simultaneous measurements of static and pulsatile pressure parameters in the epidural space and brain parenchyma of hydrocephalic patients.

Methods

Simultaneous intracranial pressure (ICP) signals from the epidural space (ICPEPI) and the brain parenchyma (ICPPAR) were compared in 12 patients undergoing continuous ICP monitoring as part of their diagnostic workup for hydrocephalus. The static ICP was characterized by mean ICP and the frequency of B waves quantified in the time domain, while the pulsatile ICP was determined from the cardiac beat–induced single ICP waves and expressed by the ICP pulse pressure amplitude (dP) and latency (dT; that is, rise time).

Results

The 12 patients underwent a median of 22.5 hours (range 5.9–24.8 hours) of ICP monitoring. Considering the total recording period of each patient, the mean ICP (static ICP) differed between the 2 compartments by ≥ 5 mm Hg in 8 patients (67%) and by ≥ 10 mm Hg in 4 patients (33%). In contrast, for every patient the ICP pulse pressure readings from the 2 compartments showed near-identical results. Consequently, when sorting patients to shunt/no shunt treatment according to pulsatile ICP values, selection was independent of sensor placement. The frequency of B waves also compared well between the 2 compartments.

Conclusions

The pulsatile ICP is measured with equal confidence from the ICPEPI and ICPPAR signals. When using the pulsatile ICP for evaluation of hydrocephalic patients, valid measurements may thus be obtained from pressure monitoring in the epidural space. Recorded differences in the mean ICP between the epidural space and the brain parenchyma are best explained by differences in the zero setting of different sensors.

Comparison of simultaneous continuous intracranial pressure (ICP) signals from ICP sensors placed within the brain parenchyma and the epidural space

Simultaneous continuous intracranial pressure (ICP) signals from two different ICP sensors (Codman ICP MicroSensor; Johnson & Johnson, Raynham, MA) placed within the brain parenchyma and the epidural space were compared in ten patients with idiopathic normal pressure hydrocephalus (iNPH). Comparisons were made at the single ICP wave level by determining differences in mean pressure, and pulse pressure amplitude (dP) and latency (dT, i.e. rise time). Differences for the parameters mean ICP, mean ICP wave amplitude and mean ICP wave latency were also determined during consecutive 6-s time windows. The ICP sensors located within the brain parenchyma and epidural space showed marked differences in mean pressure. On the contrary, there were minor differences between sensors in 8 of 10 patients regarding single wave pulse pressure amplitude (dP) and single wave latency (dT, i.e. rise time), and also with regard to the parameters mean ICP wave amplitude and mean ICP wave latency. The levels of mean ICP wave amplitudes used for predicting shunt response in iNPH patients were independent of sensor location in 9 of 10 patients. These results extend previous data that epidural ICP monitoring cannot be used to reliably determine mean ICP, however, epidural ICP monitoring is very useful for determining ICP waveform parameters such as pulse pressure amplitude (dP) and mean ICP wave amplitude. It is suggested that epidural ICP monitoring with determination of mean ICP wave amplitude can be used to predict shunt response in iNPH, though an ICP sensor designed for epidural ICP monitoring would be preferable.

Intracranial pressure waveform indices in transient and refractory intracranial hypertension

Analysis of data obtained by continuous computerized monitoring of intracranial pressure (ICP) in 109 adult patients with severe head trauma was performed to examine the pattern of change in indices of the ICP waveform. Indices derived from direct measurement of the ICP wave and obtained from a Fast Fourier Transform (FFT) were examined. Concurrent physiologic measurements were made. Two types of intracranial hypertension (ICH) were defined for comparison. 'Transient intracranial hypertension' occurred when an abrupt rise in ICP was followed by a return to below 25 mm Hg (n = 63). Increases in ICP that were progressive and led to neurologic deterioration and death were termed 'refractory intracranial hypertension' (n = 18). During transient ICH heart rate, arterial pressure, end-tidal carbon dioxide and jugular venous oxygen saturation all increased, while these measures either were unchanged or decreased during refractory ICH. The pulse amplitude of the ICP wave increased in both types of ICHtn. Other changes in the waveform indices were consistent with this change in pulse amplitude. HFC responded differently to the two types of changes, with an increase during the transient changes and a decrease during the refractory changes. The differences in changes in physiologic measurements as ICH occurred in the 2 groups suggest that in refractory ICH cerebral blood flow is maintained against the mounting ICP, while in transient ICH the hypertension is caused by an increase in cerebral blood flow. The waveform indices do not discriminate between the two types of changes.