The authors have investigated the relationships between the amplitude
of the ICP pulse wave, the mean values of ICP and CPP, and the outcome
of 56 head injured ventilated patients. The ICP was monitored continu
ously using a Camino transducer (35 patients) or subdural catheter (21
patients). The mean Glasgow Coma Score was 6 (range 3-13; 5 patients
had a GCS > 8 after resuscitation). Patients were grouped according to
their Glasgow Outcome Score assessed at 12 months after injury. The a
mplitude of ICP pulse waveform was assessed using the fundamental harm
onic of the pulse waveform (AMP) to avoid distortion caused by differe
nt frequency responses of the pressure transducers used in the study.
Statistical analysis revealed that in patients with fatal outcome the
ICP pulse amplitude increased when the mean ICP increased to 25 mmHg a
nd then began to decrease. The upper breakpoint of the AMP-ICP relatio
nship was not present in patients with good/moderate outcome. The movi
ng correlation coefficient between the fundamental harmonic of ICP pul
se wave and the mean ICP (RAP: R-symbol of correlation between A-ampli
tude and P-pressure) was introduced to describe the time-dependent cha
nges in correlation between amplitude and mean ICP. The RAP was signif
icantly lower in patients who died or remained in the vegetative state
. In 7 patients who died from uncontrollable intracranial hypertension
RAP was oscillating or decreased to 0 or negative values well before
brain-stem herniation. The combination of an ICP above 20 mmHg for a p
eriod longer than 6 hours with low correlation between the amplitude a
nd pressure (RAP < 0.5) was described as an predictive index of an unf
avourable outcome.