. Author manuscript; available in PMC: 2018 Nov 1.

Published in final edited form as: Crit Care Med. 2017 Nov;45(11):1907–1914. doi: 10.1097/CCM.0000000000002619

Table 2.

PbtO₂ and Intracranial Pressure parameters by study group.

PbtO₂ metric	ICP Only (N=58)	PbtO₂ + ICP (N=55)	p-value
Proportion of time below 20 mmHg	.44 (.31) Median .45	.15 (.21) Median .07	.0000147
Average depth (mmHg)	3.6 (3.9) Median 2.3	1.0 (2.0) Median 0.2	.0000005
Area [over] the curve (mmHg^*hrs)^**	255 (291) Median 187	58 (97) Median 14	.0000002

Intracranial Pressure metric	ICP Only (N=57)	PbtO₂ + ICP (N=55)	p-value
Proportion of time above 20mmHg	.15 (.19) Median .10	.12 (.19) Median .04	.115
Average depth (mmHg)	1.6 (6.9)^* Median 0.4	0.7 (1.3)^* Median 0.3	.194
Average depth (mmHg) (excluding the 2 extreme outliers)	0.7 (0.9) Median 0.4	0.6 (0.9) Median 0.2	.195
Area under the curve (mmHg^*hrs)^**	103 (408)^* Median 36	50 (88)^* Median 17	.113
Area under the curve (mmHg^*hrs)^** (excluding the 2 extreme outliers)	50 (56) Median 34	41 (59) Median 15	.115

One extreme outlier in each group is dominating the Mean(SD) estimate

^**

The “area under the curve” analysis does not adjust for inconsistent monitoring durations, thus a low AUC value could be due to normal PbtO₂ values or a short duration of monitoring. (This pitfall is avoided with the “average depth” analysis, in which the AUC value is subsequently divided by the duration of monitoring. It also yields a more interpretable metric.)