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The effect of baseline pressure errors on an intracranial pressure-derived index: results of a prospective observational study.

Eide PK, Sorteberg A, Meling TR, Sorteberg W - Biomed Eng Online (2014)

Bottom Line: We compared this approach with a method of calculating RAP using a 4-min moving window updated every 6 seconds (method 2).The two methods of calculating RAP produced similar results.As differences in RAP are of magnitudes that may alter patient management, we do not advocate the use of RAP in the management of neurosurgical patients.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Neurosurgery, Oslo University Hospital, Rikshospitalet, Oslo, Norway. p.k.eide@medisin.uio.no.

ABSTRACT

Background: In order to characterize the intracranial pressure-volume reserve capacity, the correlation coefficient (R) between the ICP wave amplitude (A) and the mean ICP level (P), the RAP index, has been used to improve the diagnostic value of ICP monitoring. Baseline pressure errors (BPEs), caused by spontaneous shifts or drifts in baseline pressure, cause erroneous readings of mean ICP. Consequently, BPEs could also affect ICP indices such as the RAP where in the mean ICP is incorporated.

Methods: A prospective, observational study was carried out on patients with aneurysmal subarachnoid hemorrhage (aSAH) undergoing ICP monitoring as part of their surveillance. Via the same burr hole in the scull, two separate ICP sensors were placed close to each other. For each consecutive 6-sec time window, the dynamic mean ICP wave amplitude (MWA; measure of the amplitude of the single pressure waves) and the static mean ICP, were computed. The RAP index was computed as the Pearson correlation coefficient between the MWA and the mean ICP for 40 6-sec time windows, i.e. every subsequent 4-min period (method 1). We compared this approach with a method of calculating RAP using a 4-min moving window updated every 6 seconds (method 2).

Results: The study included 16 aSAH patients. We compared 43,653 4-min RAP observations of signals 1 and 2 (method 1), and 1,727,000 6-sec RAP observations (method 2). The two methods of calculating RAP produced similar results. Differences in RAP ≥ 0.4 in at least 7% of observations were seen in 5/16 (31%) patients. Moreover, the combination of a RAP of ≥ 0.6 in one signal and <0.6 in the other was seen in ≥ 13% of RAP-observations in 4/16 (25%) patients, and in ≥ 8% in another 4/16 (25%) patients. The frequency of differences in RAP >0.2 was significantly associated with the frequency of BPEs (5 mmHg ≤ BPE <10 mmHg).

Conclusions: Simultaneous monitoring from two separate, close-by ICP sensors reveals significant differences in RAP that correspond to the occurrence of BPEs. As differences in RAP are of magnitudes that may alter patient management, we do not advocate the use of RAP in the management of neurosurgical patients.

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Illustration of the method of determining the RAP [correlation coefficient (R) between the intracranial pressure (ICP) wave amplitude (A) and the mean ICP level (P)] in patient 2. Following automatic identification of the cardiac induced single intracranial pressure (ICP) waves, the mean ICP and mean wave amplitude (MWA) are determined for every consecutive 6-sec time window. Trend plots of mean ICP and MWA determined during the same 6-sec time windows are shown for Signals 1 (a) and 2 (b) over subsequent 12 min periods (representing three 4-min periods, and 120 6-sec time windows). For Signal 1 (a) the average (± standard deviation) of mean ICP was 7.9 ± 1.2 mmHg and of MWA 4.6 ± 0.5 mmHg; while for Signal 2 (b) mean ICP -0.9 ± 1.9 mmHg and MWA 4.4 + 0.5 mmHg (mean difference of ICP -8.8 ± 2.2 mmHg; mean difference of MWA -0.2 ± 0.2 mmHg). In (c) one single 6-sec time window is shown, demonstrating the individual single ICP waves, each wave being characterized by the amplitude (dP), rise time (dT), and rise time coefficient (RT) (indicated for single wave 3). RAP is determined as the Pearson correlation coefficient between MWA and the mean ICP during subsequent 4 min periods (representing 40 6-sec time windows). In the patients included in this study, we compared the RAP values during identical 4-min periods for Signals 1 and 2 (referred to as method 1). This was performed for every consecutive 4-min period. For the three consecutive 4-min periods shown in (a) and (b), the corresponding scatter plots and RAP-values are presented in (d), (e), and (f), respectively. The differences in RAP were associated with marked differences in mean ICP between Signals 1 and 2 whereas the MWA was close to identical.
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Figure 1: Illustration of the method of determining the RAP [correlation coefficient (R) between the intracranial pressure (ICP) wave amplitude (A) and the mean ICP level (P)] in patient 2. Following automatic identification of the cardiac induced single intracranial pressure (ICP) waves, the mean ICP and mean wave amplitude (MWA) are determined for every consecutive 6-sec time window. Trend plots of mean ICP and MWA determined during the same 6-sec time windows are shown for Signals 1 (a) and 2 (b) over subsequent 12 min periods (representing three 4-min periods, and 120 6-sec time windows). For Signal 1 (a) the average (± standard deviation) of mean ICP was 7.9 ± 1.2 mmHg and of MWA 4.6 ± 0.5 mmHg; while for Signal 2 (b) mean ICP -0.9 ± 1.9 mmHg and MWA 4.4 + 0.5 mmHg (mean difference of ICP -8.8 ± 2.2 mmHg; mean difference of MWA -0.2 ± 0.2 mmHg). In (c) one single 6-sec time window is shown, demonstrating the individual single ICP waves, each wave being characterized by the amplitude (dP), rise time (dT), and rise time coefficient (RT) (indicated for single wave 3). RAP is determined as the Pearson correlation coefficient between MWA and the mean ICP during subsequent 4 min periods (representing 40 6-sec time windows). In the patients included in this study, we compared the RAP values during identical 4-min periods for Signals 1 and 2 (referred to as method 1). This was performed for every consecutive 4-min period. For the three consecutive 4-min periods shown in (a) and (b), the corresponding scatter plots and RAP-values are presented in (d), (e), and (f), respectively. The differences in RAP were associated with marked differences in mean ICP between Signals 1 and 2 whereas the MWA was close to identical.

Mentions: As previously described, the ICP signals were analyzed according to the methodology implemented in Sensometrics Software (Figure 1) [17]. An automatic method identifies the heartbeat-induced single ICP waves, differentiating them from the pressure waves of other origins (noise or various artifacts). Each heartbeat-induced single ICP wave is characterized by the following wave parameters: the amplitude (dP), rise time (dT), and the rise-time coefficient (dP/dT) (Figure 1c). Only 6-sec time windows containing a minimum of four cardiac-beat-induced waves were included for further analysis. The MWA is computed in consecutive 6-sec time window (Figure 1c). During the same 6-sec time windows, the mean ICP is determined as the sum of sample values divided by the number of samples.


The effect of baseline pressure errors on an intracranial pressure-derived index: results of a prospective observational study.

Eide PK, Sorteberg A, Meling TR, Sorteberg W - Biomed Eng Online (2014)

Illustration of the method of determining the RAP [correlation coefficient (R) between the intracranial pressure (ICP) wave amplitude (A) and the mean ICP level (P)] in patient 2. Following automatic identification of the cardiac induced single intracranial pressure (ICP) waves, the mean ICP and mean wave amplitude (MWA) are determined for every consecutive 6-sec time window. Trend plots of mean ICP and MWA determined during the same 6-sec time windows are shown for Signals 1 (a) and 2 (b) over subsequent 12 min periods (representing three 4-min periods, and 120 6-sec time windows). For Signal 1 (a) the average (± standard deviation) of mean ICP was 7.9 ± 1.2 mmHg and of MWA 4.6 ± 0.5 mmHg; while for Signal 2 (b) mean ICP -0.9 ± 1.9 mmHg and MWA 4.4 + 0.5 mmHg (mean difference of ICP -8.8 ± 2.2 mmHg; mean difference of MWA -0.2 ± 0.2 mmHg). In (c) one single 6-sec time window is shown, demonstrating the individual single ICP waves, each wave being characterized by the amplitude (dP), rise time (dT), and rise time coefficient (RT) (indicated for single wave 3). RAP is determined as the Pearson correlation coefficient between MWA and the mean ICP during subsequent 4 min periods (representing 40 6-sec time windows). In the patients included in this study, we compared the RAP values during identical 4-min periods for Signals 1 and 2 (referred to as method 1). This was performed for every consecutive 4-min period. For the three consecutive 4-min periods shown in (a) and (b), the corresponding scatter plots and RAP-values are presented in (d), (e), and (f), respectively. The differences in RAP were associated with marked differences in mean ICP between Signals 1 and 2 whereas the MWA was close to identical.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4125597&req=5

Figure 1: Illustration of the method of determining the RAP [correlation coefficient (R) between the intracranial pressure (ICP) wave amplitude (A) and the mean ICP level (P)] in patient 2. Following automatic identification of the cardiac induced single intracranial pressure (ICP) waves, the mean ICP and mean wave amplitude (MWA) are determined for every consecutive 6-sec time window. Trend plots of mean ICP and MWA determined during the same 6-sec time windows are shown for Signals 1 (a) and 2 (b) over subsequent 12 min periods (representing three 4-min periods, and 120 6-sec time windows). For Signal 1 (a) the average (± standard deviation) of mean ICP was 7.9 ± 1.2 mmHg and of MWA 4.6 ± 0.5 mmHg; while for Signal 2 (b) mean ICP -0.9 ± 1.9 mmHg and MWA 4.4 + 0.5 mmHg (mean difference of ICP -8.8 ± 2.2 mmHg; mean difference of MWA -0.2 ± 0.2 mmHg). In (c) one single 6-sec time window is shown, demonstrating the individual single ICP waves, each wave being characterized by the amplitude (dP), rise time (dT), and rise time coefficient (RT) (indicated for single wave 3). RAP is determined as the Pearson correlation coefficient between MWA and the mean ICP during subsequent 4 min periods (representing 40 6-sec time windows). In the patients included in this study, we compared the RAP values during identical 4-min periods for Signals 1 and 2 (referred to as method 1). This was performed for every consecutive 4-min period. For the three consecutive 4-min periods shown in (a) and (b), the corresponding scatter plots and RAP-values are presented in (d), (e), and (f), respectively. The differences in RAP were associated with marked differences in mean ICP between Signals 1 and 2 whereas the MWA was close to identical.
Mentions: As previously described, the ICP signals were analyzed according to the methodology implemented in Sensometrics Software (Figure 1) [17]. An automatic method identifies the heartbeat-induced single ICP waves, differentiating them from the pressure waves of other origins (noise or various artifacts). Each heartbeat-induced single ICP wave is characterized by the following wave parameters: the amplitude (dP), rise time (dT), and the rise-time coefficient (dP/dT) (Figure 1c). Only 6-sec time windows containing a minimum of four cardiac-beat-induced waves were included for further analysis. The MWA is computed in consecutive 6-sec time window (Figure 1c). During the same 6-sec time windows, the mean ICP is determined as the sum of sample values divided by the number of samples.

Bottom Line: We compared this approach with a method of calculating RAP using a 4-min moving window updated every 6 seconds (method 2).The two methods of calculating RAP produced similar results.As differences in RAP are of magnitudes that may alter patient management, we do not advocate the use of RAP in the management of neurosurgical patients.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Neurosurgery, Oslo University Hospital, Rikshospitalet, Oslo, Norway. p.k.eide@medisin.uio.no.

ABSTRACT

Background: In order to characterize the intracranial pressure-volume reserve capacity, the correlation coefficient (R) between the ICP wave amplitude (A) and the mean ICP level (P), the RAP index, has been used to improve the diagnostic value of ICP monitoring. Baseline pressure errors (BPEs), caused by spontaneous shifts or drifts in baseline pressure, cause erroneous readings of mean ICP. Consequently, BPEs could also affect ICP indices such as the RAP where in the mean ICP is incorporated.

Methods: A prospective, observational study was carried out on patients with aneurysmal subarachnoid hemorrhage (aSAH) undergoing ICP monitoring as part of their surveillance. Via the same burr hole in the scull, two separate ICP sensors were placed close to each other. For each consecutive 6-sec time window, the dynamic mean ICP wave amplitude (MWA; measure of the amplitude of the single pressure waves) and the static mean ICP, were computed. The RAP index was computed as the Pearson correlation coefficient between the MWA and the mean ICP for 40 6-sec time windows, i.e. every subsequent 4-min period (method 1). We compared this approach with a method of calculating RAP using a 4-min moving window updated every 6 seconds (method 2).

Results: The study included 16 aSAH patients. We compared 43,653 4-min RAP observations of signals 1 and 2 (method 1), and 1,727,000 6-sec RAP observations (method 2). The two methods of calculating RAP produced similar results. Differences in RAP ≥ 0.4 in at least 7% of observations were seen in 5/16 (31%) patients. Moreover, the combination of a RAP of ≥ 0.6 in one signal and <0.6 in the other was seen in ≥ 13% of RAP-observations in 4/16 (25%) patients, and in ≥ 8% in another 4/16 (25%) patients. The frequency of differences in RAP >0.2 was significantly associated with the frequency of BPEs (5 mmHg ≤ BPE <10 mmHg).

Conclusions: Simultaneous monitoring from two separate, close-by ICP sensors reveals significant differences in RAP that correspond to the occurrence of BPEs. As differences in RAP are of magnitudes that may alter patient management, we do not advocate the use of RAP in the management of neurosurgical patients.

Show MeSH
Related in: MedlinePlus