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Lecture 20
20. Cerebral Compartmental Compliances Cerebral arterial inflow CBFa(t) Cerebral arterial blood volume (CaBV) mean CBFa 0 CBFv(t) Cerebral venous outflow CBV(t) t mean CBV ΔCBV (CBFa (t) CBFv (t))dt + t0 t1 t2 t Cerebral blood volume R-R interval Thanks to Dr.M.Kasprowicz of ECG Avezaat CJ, van Eijndhoven JH. (1986) The role of the pulsatile pressure variations in intracranial pressure monitoring. Neurosurg Rev 9:113-120 Cerebral arterial blood volume Assumptions: • Diameter of the MCA artery unchanged during the cardiac cycle • Venous outflow constant during the cardiac cycle Thanks to Dr. E.Carrera CBV Thanks to Dr. M.Kasprowicz CaBV pulsation and shape of pulse waveorm of ICP ? Thanks to Dr. E.Carrera Thanks to Dr. E.Carrera Thanks to Dr. E.Carrera Thanks to Dr. E.Carrera Compartmental compliances of brain Cerebral arterial compliance (Ca) Ca = AmpCaBV Amp ABP Cerebrospinal + venous compliance (Ci) AmpCaBV Ci = Thanks to Dr. E.Carrera AmpICP Change of Cerebral Compliance (Ci) during infusion study Thanks to Dr.DJ Kim Compartmental compliances (Ca, Ci) Thanks to Dr.DJ Kim Thanks to Dr.E.Carrera Thanks to Dr.E.Carrera Thanks to Dr.E.Carrera Thanks to Dr.E.Carrera Stenotic disease- reaction to Diamox (Toulouse study) Thanks to Dr.N.Nasr Thanks to Dr.N.Nasr Thanks to Dr.E.Carrera Hypocapnia in TBI Example :18 yo woman GCS =7 Baseline characteristics Age (years) 39.5 ± 3.4 Gender (women) 6 (22%) GCS 5 (3-8) Physiological variables ABP (mmHg) 97 ± 9 ICP (mmHg) 18 ± 7 CPP (mmHg) 79 ± 8 PaCO2 (mmHg) 38 ± 0.5 ABP Thanks to Dr.E.Carrera “Early” hyperventilation • CSF compartment ICP Results – Significant increase in Ci – Decrease in ICP correlated with the increase in Ci (r2=0.2; p=0.02) • Arterial compartment Ci mmHg; p<0.001) CBFV – Reduction in ICP: (17.5 to 13.9 – Reduction in CBFV (75 to 63 cm/s; – Significant decrease in Ca – Reduction in CBFV correlated with the reduction in Ca (r2=0.2; p=0.02). Ca p<0.001) “Sustained” hyperventilation ICP Results ABP Thanks to Dr.E.Carrera – Re-increase in ICP (13.9 to 15.3 mmHg; p<0.001) – No significant change in Ci CBFV • CSF compartment – No changes in CBFV (63 vs 62 Ci • Arterial compartment cm/s; p=0.3) Ca – No significant change in Ca Thanks to Dr. DJ Kim • Monro-Kellie doctrine Definition When the volume of one compartment increases, there must be a corresponding and compensatory decrease in the volume of the other compartment Brain volume [Vbrain] arterial blood Venous blood Volume [Va-blood] Volume [Vv-blood] Ca . Skull – rigid body Cb Brain volume [Vbrain] Ci CSF volume [Vcsf] Thanks to Dr. DJ Kim Algorithm to estimate ICC Negative ICC Positive ICC - Inverse relationship between Ca% and Ci% - Direct proportional relationship between Ca% and Ci% - Monro-Kellie doctrine is obeyed - Monro-Kellie doctrine is not followed Thanks to Dr. DJ Kim Observation II Plateau waves (transient changes in cerebral blood volume) 105 ABP 100 [mmHg] 95 90 ICP [mmHg] 60 50 40 30 20 80 CBFva [cm/s] Strong haemodynamic exitation (Sudden decrease cerebral blood volume) 60 40 20 1 0.5 ICC 0 -0.5 -1 400 Ca% [%] 250 100 400 Ci% [%] 300 200 100 0 0 4 8 12 16 20 Time [min] Findings: Ca% and Ci% change in opposite directions, which makes ICC solidly negative Thanks to Dr. DJ Kim Observation I Arterial hypertension (transient changes in arterial blood pressure) 120 Strong haemodynamic exitation (Sudden increase arterial blood pressure) 110 ABP 100 [mmHg] 90 ICP [mmHg] 35 30 25 20 15 10 60 CBFva [cm/s] 50 Conpensating mechanism (i.e. autoregulation) 40 ICC 0 -0.5 110 Ca% [%] 90 70 50 130 Ci% [%] 110 90 70 0 3 6 9 12 15 Time [min] Findings: Ca% and Ci% change in opposite directions, which makes ICC solidly negative Thanks to Dr. DJ Kim Observation III Intracranial hypertension (traumatic brain injury) ABP [mmHg] 84 82 80 78 76 74 38 ICP [mmHg] 36 34 32 36 CBFva [cm/s] 32 28 1 0.5 ICC 0 -0.5 -1 Ca% [%] Ci% [%] 100 80 60 40 20 120 100 80 60 40 20 0 5 10 15 20 25 Time [min] Findings: Ca% and Ci% change in same directions, which makes ICC positive Outcome I Distribution of ICC with different outcome cohorts P (Kruskall-Wallis test ) < 0.004 Survived Fatal Thanks to Dr. DJ Kim Outcome II Change in ICC over time Weight Fatal Survived ICC is significantly greater in patients who died, particularly over the first few days after head injury Thanks to Dr. DJ Kim Correlation I Relationship between ICC and ICP Corr. R=0.65; p<0.001 Thanks to Dr. DJ Kim Outcome III Regression of ICC vs mortality rate ICC=0.7 Intracranial hypertension (IH) -Average ICP > 20 mmHg for entrie NCCU stay IH (30% ) IH (65% ) Messages to take home •Relative changes in compartmental compliances may be assessed with TCD and ABP/ICP waveforms •Absolute values unknown- we do not know cross-sectional area of MCA •During plateau wave Ca increases and Ci decreases •During hyperventilation in TBI Ci increases and Ca decreases •Reactivity of Ca to change in PaCO2 is useful in carotid artery stenosis •Relative changes in Ca and Ci : monitoring of Monro-Kelly Doctrine?
