journal of neurosurgery volume 76 issue 2 1992 [doi 10.3171%2fjns.1992.76.2.0207] feldman, zeev_...

8/16/2019 Journal of Neurosurgery Volume 76 issue 2 1992 [doi 10.3171%2Fjns.1992.76.2.0207] Feldman, Zeev_ Kanter, Ma…

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J

Neurosurg

7 6 : 2 0 7 - 2 1 1 , 1 9 9 2

Effect of h ead e levat ion on intracranial pressure cerebral

per fus ion pressure and cerebra l b lood f low in h ead-

injured patients

ZEEV FELDMANM . D . , MALCOLM . KANTER M . D . , CLAUDIAS. ROBERTSON M . D . ,

C H A R L E S

F . C O N T A N T , P H .D . ,

C HR I S TOP HER HAYES , P . A . - C , M I C HAEL A. S HEI Na ER G, B . S . ,

C Y N T H I A A . VILLAREALM . D . , R A J K . NARAYANM . D . , A N D R O B E R T G . GROSSMAN M . D .

Department of Neurological Surgery Baylor College of Medicine Houston Texas

v- T he t radi t iona l pract ice of e levating the head in ord er to lower intracranial pressure (ICP) in head-injured

pat ien ts has been chal lenged in recen t years . Som e invest igators argue that pat ients w ith intracranial hyp erten-

s ion should b e placed in a horizontal posi t ion, the ra t ionale being that th is wil l increase the cerebral perfusion

pressure (CPP) an d there by imp rov e cerebral b lood f low (CBF). How ever , IC P is general ly s ignif icant ly higher

wh en the pat ient is in the horizontal posi t ion. Th is s tudy was und ertaken t o c lari fy the issue of opt im al head

posi t ion in the care of head-injured pat ients . Th e effect of 13 and 30* head elevat ion on ICP, CPP, C BF, m ean

carot id pressure , and other cerebral and systemic physiological param eters was studied in 22 head-injured

pat ients . Th e m ean c arot id pressure w as s ignif icant ly lower when the pa t ient ' s head w as e levated at 30 ~ than

at 0* (84.3 _+ 14.5 ra ta H g vs . 895 _ 14.6 ram Hg), as was the me an IC P ( 14.1 _ 6 .7 ra ta H g vs~ 19.7 -+ 8 .3

m m Hg). Th ere was no s ta t is tical ly s ignif icant change in CPP, C BF, cerebral me tabol ic ra te of oxygen,

ar ter iov enou s difference of lacta te , or cerebrovascular res is tance associated with the change in head posi t ion.

Th e data indicate tha t head elevat ion to 30 ~significant ly reduced IC P in the m ajori ty of the 22 patients witho ut

reducing CP P o r CBF.

K E Y W O R D S h e a d i n j u r y 9 h e a d e l e v a t i o n 9 c e r e b r al p e r f u s i o n p r e s s u r e 9

c e r e b r a l b l o o d f l o w 9 i n t r a c r a n i a l p r e s s u r e

L E VA T ED i n t r a c r a n i a l p r e s s u r e ( I C P ) o r i n a d e -

q u a t e c e r e b r a l p e r f u s i o n p r e s s u r e ( C P P ) a n d c e -

r e b r al b l o o d f lo w ( C B F ) a re c o m m o n c a u s e s o f

s e c o n d a r y b r a i n d a m a g e i n h e a d - i n j u r e d p a t i e n t s . I n

p a t i e n t s w i t h r a i s e d I C P , i t i s a c o m m o n p r a c t i c e t o

p o s i t i o n t h e p a t i e n t i n b e d w i t h t h e h e a d e l e v a t e d a b o v e

t h e l e v e l o f t h e h e a r t . K e n n i n g , et a[. , 4 r e p o r t e d t h a t

e l e v a t i n g t h e h e a d t o 4 5 * o r 9 0 * s i g n i f i c a n t l y r e d u c e d

I C P . H o w e v e r , s o m e s t u d ie s s u g g e st t h a t h e a d e l e v a t i o n

m a y a l s o l o w e r th e C P P . D u r w a r d , et al.,2 s t u d i e d t h e

e f f e c t o f h e a d e l e v a t i o n a t 0 ~ ( h o r i z o n t a l ) , 1 5 , 3 0 * , o r

6 0 ~ o n I C P , s y s t e m i c a n d p u l m o n a r y p r e ss u r e, a n d C P P

i n p a t i e n t s w i t h in t r a c r a n i a l h y p e r t e n s i o n . T h e y c o n -

c l u d e d t h a t 1 5 o r 3 0 * o f h e a d e l e v a t i o n s i g n i fi c a n t ly

r e d u c e d I C P w h i le m a i n t a i n i n g C P P a n d c a r d ia c o u t -

p u t . H o w e v e r , f u r t h e r e l e v a t i o n o f t h e h e a d t o 6 0 *

c a u s e d a n i n c r e a s e i n I C P a n d a s i g n i f i c a n t d e c r e a s e i n

C P P a n d c a r d i a c o u t p u t . M o r e r e ce n t ly , R o s n e r , e t

a/. 16-19

h a v e e m p h a s i z e d t h e i m p o r t a n c e o f a d e q u a t e

C P P a n d h a v e p r o v i d e d p h y s i o l o g i c a l a n d c l i n i c a l e v i -

d e n c e s u g ge s ti n g t h a t C P P i s m a x i m u m w h e n p a t i e n ts

a r e in t h e h o r i z o n t a l p o s i t i o n , e v e n t h o u g h I C P is

u s u a l l y h i g h e r i n t h i s p o s i t i o n . D a v e n p o r t , e t a l . , a s -

s e s s e d t h e r o l e o f h e a d e l e v a t i o n a t 2 0 , 4 0 , o r 6 0 ~ i n

e i g h t p a t i e n t s s u f f e r i n g f r o m h e p a t i c c o m a . T h e y f o u n d

i n c o n s i s t e n t e f f e c t s o f h e a d e l e v a t i o n o n I C P b u t a

s i g n i f i c a n t d e c r e a s e i n m e a n a r t e r i a l b l o o d p r e s s u r e

( M A B P ) a n d C P P a t 40 * a n d 6 0* . N o s t u d y h a s y e t

m e a s u r e d C B F w h e n e v a l u a t in g t h e e f f ec t s o f p o s t u r a l

c h a n g e s o n c e r e b r al p e r f us i o n . A s m a i n t e n a n c e o f a d -

e q u a t e C B F i s t h e p r i m a r y r a t io n a l e f o r m a i n t a i n i n g

a d e q u a t e C P P i n p a t i e n t s w i t h i n c r e a s e d I C P , w e h a v e

s t u d i e d t h e c h a n g e s i n C B F , a s w e l l a s c h a n g e s i n I C P ,

C P P , a n d o t h e r c e r e b r a l a n d s y s t e m i c p h y s i o l o g i c a l

p a r a m e t e r s i n d u c e d b y c h a n g e s i n h e a d p o s i t io n i n

p a t i e n t s w i t h h e a d i n j u r y .

C l i n i c a l M a t e r i a l a n d M e t h o d s

T w e n t y - t w o h e a d - i n j u r e d p a t i e n t s a d m i t t e d t o t h e

n e u r o s u rg i c a l i n t en s i v e c a r e u n i t a t B e n T a u b G e n e r a l

J . Neurosurg. / Volu me 76 /Feb rua ry , 1992 9 0 7


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TABLE

Characteristics qf 22 head-injured patients

Characteristic Category No.

sex (M:F) 19:3

mean age (yrs) 35

age range 18-75

pathology

subdural hematoma 8

cerebral contusion 5

intracerebral hematoma 2

epidural hematoma 2

diffuse axonal njury 2

gunshot wound o head 2

traumatic subarachnoidhemorrhage 1

initialGCS score

3-5 3

6-8 14

9-12 5

CBF (ml/100 gm/min)

low (< 35) 7

normal (35-60) 9

high (> 60) 6

outcome

good recovery 6

moderately disabled 7

severely disabled 5

vegetative state 1

dead 3

* GCS = GlasgowComa Scale; CBF = cerebral blood flow.

Hospital between January, 1990, and January, 1991,

were studied. The demographic characteristics of the

patients are given in Table 1. The mean age of the

patients was 35 years (range 18 to 75 years). The pri-

mary diagnosis was subdural hematoma in eight pa-

tients, cerebral contusion in five, intracerebral hema-

toma in two, epidural hematoma in two, diffuse axonal

injury in two, gunshot wound to the head in two, and

traumatic sub arachnoid hemorrhage in one. Postresus-

citation Glasgow Coma Scale scores were 3 to 5 in three

patients, 6 to 8 in 14, and 9 to 12 in five. At 3 months

after injury, six patients bad a good recovery, seven

were moderately disabled, five were severely disabled,

one was in a permanent vegetative state, and three had

died (Table 1).

Z. Feldman

e t a l

All patients were treated accordi ng to a protocol that

emphasized early intubation and respiratory support,

prompt ev acuation of intracranial hematomas, and pre-

vent ion of s econdary in sults to the brain. 13 The patients

were initially ventilated to m ain tai n a PaO2 of 100 mm

Hg or above and a PaCO2 of 30 to 35 mm Hg. Intra-

cranial pressure greater than 20 mm Hg was treated by

cerebrospinal fluid (CSF) drainage, hyperventilation

(PaCO2 25 to 30 mm Hg), sedation, paralysis, and

administration of mannitol. Barbiturate coma was in-

duced only if ICP was refractory to the above treat-

ment. 3 Medications included morphi ne for sedation,

panc uron ium for paralysis, and phenytoin for seizure

prophylaxis. The treatm ent protocols were approved by

the Ins titut iona l Review Board of Baylor College of

Medicine, and informed consent for each patient was

obtained from the next of kin.

With in 72 hours after injur y, two consecutive sets of

physiological measurements were performed. In the

first 13 patients, the initial set of measurements was

performed with the head elevated to 300; in the subse-

que nt n ine patients, the initial set was taken at 0* head

elevation. The patient's head elevation was changed

after the initial set of measurements and a second set

of me asurements was taken 45 minutes later. Measure-

ments were made of CBF (using the Kety-Schmidt

N20 techniqueS-7), ICP ( measure d with the tra nsduce r

zeroed at the level of the foramen of Monro), arterio-

venous oxygen difference, cerebral metabolic rate of

oxygen (CMRO2), oxygen sa turat ion in the jugula r bulb,

cerebrovascular resistance (CVR), PaCO2, PaO2, arte-

rioveno us difference of lactate, and MABP. The MABP

was measured with the tra nsduc er zeroed at the level of

the foramen of Monro, giving an estimate of the mea n

carotid pressure (MCP), which was then used for cal-

culation of the CPP.

Differences were computed by subtracting the value

obtaine d when the pat ient was lying flat from the value

obtain ed when the hea d was elevated to 30 ~ These

differences were evalua ted using the paired t-test. Com-

parisons among subgroups of patients were made using

analysis of varianc e of the indiv idual differences.

TABLE

2

Effects of head elevation on cerebral and systemic pkysiologicat parameters in 22 patients

Parameter 30~Head Elevation 0~ Head Elevation MeanDifference P Value

mean carotid pressure (mm Hg)

intracranialpressure (ram Hg)

cerebral perfusionpressure (CPP) (mm Hg)

cerebral blood flow (CBF) (ml/100gm/min)

cerebrovascular resistance(CPP/CBF)

cerebral metabolic ate of oxygen (zmol/100 gm/min)

arteriovenousoxygendifference(umol/ml)

PaCO2 (mm Hg)

arteriovenousdifferenceof lactate (umol/ml)

oxygen saturation n jugularbulb (%)

84.3 _+ 14.5 89.5 -+ 14.6 -5 .2 --. 8.1 0.0062

14.1 + 6.7 19.7 __. 8.3 -5.7 _-X-5.6 0.0001

70.2 +__18.1 69.7 _+ 18.7 0.45 - 8.8 0.8

47.8 _+ 16.9 48.9 --- 20.4 -1.03 + 10.8 0,657

1.72 _ 0.8 1.72 + 0.9 -0.0014 --- 0.356 0.9844

1.35 - 0.59 1.28 + 0.53 0.075 _+ 0.23 0.14

1.81 _+ 0.63 1.72 _+ 0.73 0.093 + 0.35 0.23

32.34 _+ 5.89 32.46 -+ 6.4 -0.1 + 1.9 0.77

-0.05 + 0.05 -0.05 _+ 0.06 -0 .0 00 2 0.06 0.18

69.9 _+ 9 70.3 + 10 .2 -0 .0 04 3+ 0.042 0.63

* Values represent mean _+ standard deviation.

208

J. Neurosu rg. / Vol um e 76 / February , 1992


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Effects of head elevation in head injured patients

FIG. 1. Gra ph showing cere bral and systemic physiological p aram eters at head elevatio ns of 0 ~ and 30 ~ in

22 patients with head injury. At 30 , the intracranial pressure (ICP) was lower in 77% of patients, higher in

14%, and the same in 9%; mean carotid pressure (MCP) was lower in 59%, higher in 23%, and the same in

18%; cerebral perfusion pressure (CPP) was lower in 55% and higher in 45%; an d ce rebral blood flow (CBF)

was lower in 36%, highe r in 36%, and the sam e in 14%. See text for analysis of the significance of the

differences.

esults

The effects of head elevat ion on ICP, MCP, CPP,

and C BF are i l lust rated in Fig . 1 and are g iven in Ta ble

2 fo r a l l paramet er s measu red . The mean va l ues (+

standard deviat ion) for the MCP and ICP were s igni f i -

cant ly low er at 30 ~ head elevat ion tha n at 0 : 84 .3 +

14.5 mm Hg versus 89.5 + 14.6 mm Hg for MCP, and

14.1 + 6.7 m m Hg versus 19.7 + 8.3 mm Hg for ICP.

The m ean va l ues fo r CPP and CBF were unaf f ec t ed by

head eleva tion: 70.2 ___ 18.1 mm Hg at 30 ~ and 69.7 +

18.7 mm Hg a t 0 ~ for CPP, and 47.8 _+ 16.9 ml /100

gm /m in at 30* and 48.9 _+ 20.4 m l /100 gm /m in at 0 ~

fo r CBF. N one o f t he o t her para met er s showed a s t at is -

t ical ly s igni f icant d if ference between head elevat ions at

30* and at 0 ~ T he resul t s were not af fected by w hether

the hea d was a t 30* or at 0* for the in i t ial measurem ents .

Correlat ion analysis revealed a s igni f icant relat ion-

ship between the ICP level at 0* head elevat ion and the

amount of change in ICP af ter 30* head elevat ion ( r =

-0 .5890) . The h i gher t he ICP wi t h t he pa t i en t i n t he

hor izonta l posi t ion (0*) , the greater the reduc t ion in

ICP at head elevat ion of 30* (Fig . 2) . The effect of head

FIG. 2. Corre lation between the level of intrac rania l pres-

sure (ICP) at 0 ~ head elevation and the amo unt of change in

ICP after hea d elevation to 30 ~ T he higher the IC P level in

the horizontal position (0~ the greater was the reduction in

ICP at 30~ of head elevation (r = -0.5890).

J. Neurosurg. / Volume 76/F ebruary , 1992

909


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Z. Feldman

e t a l

T A B L E 3

Ef fe c t s o f he ad e le v at ion on c e rebra and sy s te m ic phy s io logic al parame te rs" in s i x pat i e n t s w i th ICP gre ate r than 25 m m Hg*

P a r a m e t e r 3 0 ~ H e a d E l e v a t i o n 0 ~ H e a d E l e v a t i o n M e a n D i f f e r e n c e P V a l u e

m e a n c a r o t i d p r e s s u r e ( r a m H g ) 7 4 . 7 _+ 1 4 . 5 8 3 . 7 + 1 5 .1 - 9 _+ 5 . 3 0 . 0 8 5

i n t r a c r a n i a I p r e s s u r e ( I C P ) ( r a m H g ) 2 0 . 3 + 3 . 9 3 0 . 7 _+ 3 . 3 - 1 0 . 3 3 + 5 . 9 0 . 0 0 7 9

c e r e b r a l p e r f u s i o n p r e s s u r e ( C P P ) ( m m H g ) 5 4 . 3 _+ 1 2 . 8 5 3 + 1 7 .1 1 . 3 + 4 . 8 0 . 5 3 0 1

c e r e b r a l b l o o d f l o w ( C B F ) ( m l / 1 0 0 g m / m i n ) 5 5 . 9 + 9 . 6 5 9 . 8 _+ 2 6 . 4 - 3 . 9 - + 1 7 . 2 6 0 . 6 0 4 2

c e r e b r o v a s c u l a r r e s i st a n c e ( C P P / C B F ) 0 . 9 9 2 + 0 . 2 2 6 0 . 9 7 6 _+ 0 . 3 9 8 0 . 0 1 6 _+ 0 . 2 1 9 0 . 8 6 3 9

* V a l u e s r e p r e s e n t m e a n + s t a n d a r d d e v i a t i o n o f t h e m e a n .

e l e v a t i o n o n I C P i n t h e s i x p a t i e n t s w h o h a d a n I C P

g r e a t e r t h a n 2 5 m m H g c o m p a r e d w i t h t h e e f f e c t o b -

se rved in the o the r 16 pa t i en t s revea led tha t the dec rease

in ICP obse rved was s ign i f i can t in the pa t i en t s wi th

ra i s ed ICP . The m ean reduc t ion in ICP wi th head

elevat io n was - 10.33 _+ 5.9 m m Hg in these s ix pat ients ,

c o m p a r e d w i t h - 3 . 9 _+ 8 .6 m m H g f o r th e r e m a i n i n g

16 pat ients (p < 0.05) (Table 3) . In these s ix pat ients ,

the ICP fe ll f rom a m ea n o f 30 .7 m m Hg a t 0* to 20 . 3

m m H g a t 3 0 *.

A l t h o u g h C B F w a s u n c h a n g e d w i t h h e a d e l e v a t i o n

to 30 ~ when the da ta fo r a l l 22 pa t i en t s were ave raged ,

in f ive pa t i en t s the CBF fe l l by m ore than 5 m l /100

gm /m in wi th head e leva t ion . In these f ive , CBF fe l l

f r o m a m e a n o f 6 7 .2 + 2 6 m l / 1 0 0 g m / m i n a t 0 ~ o 5 0 .7

_+ 16.5 ml/10 0 gin /ra in a t 30 ~ (p < 0.05). The refore ,

we t r i ed to iden t i fy phys io log ica l pa ram ete rs tha t would

pred ic t such a fa l l . The CMRO2 was a l so lower a f t e r

head e levat ion in these f ive pat ients , fa l l ing from 1.09

+ 0 . 5 #m ol /100 gm /m in a t 0* to 0 .9 _ 0 .5 ~m ol /100

g m / m i n a t 3 0 * . A s i n t h e e n ti r e g ro u p , M C P a n d I C P

were lower wi th the head e leva ted : 83. 2 _ 13 . 2 m m Hg

versus 90 .8 _ 11 . 9 m m Hg for MCP , and 18 +_ 3 .7 m m

H g v e r s u s 2 2. 4 _+ 7 m m H g f o r I C P . T h e C V R w a s

higher a t 30* elevat io n tha n a t 0 : 1 .51 _+ 0.56 versus

1.22 _+ 0.49, respect ively. Co m par iso n o f the chan ges

in these f ive pa t i en t s to those occ ur r ing in the o the r 17

pa t i en t s revea led tha t the changes in CBF , CMRO2,

and CVR were s ign i f i can t (p = 0 . 0001 fo r CBF , p =

0 .01 fo r CMRO2, and p = 0 .0221 fo r CVR ) . Al though

the dec rease in CP P in these f ive pa t i en t s was no t

s ign i f i can t ly d i f fe ren t f rom tha t obse rved in the o the r

pa t i en t s (p = 0 . 119), the c om bina t io n o f inc reased CV R

and dec reased CP P resu l t ed in a dec rease in CBF .

F ur the r ana lys i s revea led tha t in fo ur o f these pa t i en t s ,

the CBF , a l though lower a t 30 ~ head e leva t ion , was s t il l

w i t h i n t h e n o r m a l r a n g e ( > 3 5 m l / 1 0 0 g m / m i n ) . I n

o n l y o n e o f t h e f i ve p a ti e n t s d i d t h e C B F d r o p b e l o w

35 m l /100 g in / ra in ( f rom 37 to 25 m l /100 g in / ra in ) . In

th i s pa t i en t , the CP P was low: 59 m m Hg a t 0 ~ and 50

m m Hg a t 30 ~ In te re s t ing ly , the IC P rose m arg ina l ly

in th i s pa t i en t f rom 12 m m Hg a t 0 ~ head e leva t ion to

14 m m Hg a t 30 ~ Othe r than the sugges tion tha t a low

CP P m ay be a s soc ia ted wi th a fa l l in CBF wi th head

e leva t ion , the f ive pa t i en t s in wh om head e leva t ion

p r o d u c e d a d e c r e a s e i n C B F o f m o r e t h a n 5 m l / 1 0 0

gm /m in had no d i s t ingu i sh ing fea tu res .

i s c u s s i o n

The idea l head p os i t ion fo r pa t i en t s wi th head in ju ry

has been d i spu ted in recen t yea rs . R osne r 16 prov ided

ev idence tha t p la teau waves a re t r igge red by a fa l l in

C P P a n d t h a t m a i n t a i ni n g C P P a b o v e 7 0 to 8 0 m m H g

preven ted p la teau waves . In pa t i en t s wi th in t rac ran ia l

h y p e r t e n s i o n , R o s n e r a n d c o w o r k e r s l s 1 9 a d v o c a t e d

keep ing the pa t i en t ' s h ead a t 0 ~ e leva t ion and us ing

f l ui d e x p a n s i o n o r p h a r m a c o l o g i c a l m e a n s t o m a i n t a i n

CP P . O ur da ta ind ica te tha t , a l though the M CP i s lower

a t 30 ~ head e leva t ion tha n a t 0 , CP P and CBF a re no t

s ign i fi can t ly a l te red in m os t pa t i en t s b y head e leva t ion

to 30*.

Because the MCP could no t be ob ta ined by d i rec t

m easurem ent o f the in te rna l ca ro t id a r t e ry p res sure in

the pa t i en t s we s tud ied , we used the MABP recorded

wi th the t ransduce r p laced a t the l eve l o f the fo ram en

o f M o n r o a s a n e s t i m a t e o f t h e M C P , a t e c h n i q u e

c o m m o n l y u s e d t o c o m p u t e C P P ? 8 H o w e v e r , t h e r e -

su l ts o f a s tudy by W oischneck , et al . 22 suggest that th e

fal l in M CP th a t we obse rved a t 30* head e leva t ion m ay

be l a rge ly an a r t i fac t o f th i s m easurem ent t echn ique .

I n t h e i r s t u d y a d d r e ss i n g t h e a c c u r a c y o f C P P m e a s u r e -

m ents , they found the p res sure in the supe r f i c ia l t em -

pora l a r t e ry to be a lm os t iden t i ca l to the p res sure in the

in te rna l ca ro t id a r t e ry . Whe n eva lua t ing the e f fec t o f

h e a d e l e v a t io n o n C P P , c o m p u t e d u s i n g t h e p r e ss u r e o f

the supe r f i c ia l t em pora l a r t e ry , they found the CP P to

be cons tan t when the h ead w as e leva ted f rom 0* to 30* .

I f o u r m e a s u r e m e n t t e c h n iq u e i m p l i e d a fa ll i n M C P

tha t d id no t ac tua l ly occur , i t would sugges t tha t the

CP P m ight ac tua l ly inc rease a t 30 ~ o f head e leva t ion

and exp la in the l ack o f change in CBF seen in our

pa t i en t s wi th head e leva t ion .

We have a l so dem ons t ra ted a d i rec t re la t ionsh ip be -

tween the ICP leve l and the change in ICP a f te r head

e leva t ion . Ou r da ta suggest tha t in head - in ju red pa t i en t s

wi th nor m a l ICP , head p os i t ion does no t g rea t ly a f fec t

ICP and tha t these pa t i en t s can be pos i t ioned e i the r

hor izon ta l ly o r wi th the he ad e leva ted to 30 ~ Ho weve r ,

when the ICP i s inc reased , e leva t ion o f the h ead i s ve ry

e f fec tive in reduc ing the ICP . T his i s appa ren t ly d ue to :

1 ) hydros ta t i c d i sp lacem ent o f the CS F f rom the c ran ia l

cav i ty to the sp ina l sub a rachno id space ;4 and 2) faci l i -

tated ve no us ou tflo w fr om the brain.S-10'14'ls'2LT h e c o n -

t r ib u t i o n s o f C S F d i s p l a c e m e n t a n d c h a n g e s in v e n o u s

volu m e to the reduc t ion in IC P in head- in ju red p a t i en t s

910 J . N eurosurg . / V o lum e 76 /F eb rua ry 1992


5/5

Effects of h ead elevation in head injured patients

a f t e r h e a d e l e v a t i o n m a y d e p e n d u p o n t h e r e l a t i v e s i ze

o f e a c h i n tr a c r a n i a l c o m p a r t m e n t a t t h e t i m e o f h e a d

e le v a t io n , m .~v In p a t i e n t s w i th r a i s e d IC P , th e in t r a c ra -

n ia l c o m p l i a n c e d e c re a s e s , t~ 12,20 a n d s m a l l e r c h a n g e s

i n i n t r a c r a n i a l v o l u m e , s u c h a s t h o s e p r o d u c e d b y C S F

d i s p l a c e m e n t , w i l l p r o d u c e g r e a t e r c h a n g e s i n I C P .

A l t h o u g h t h e o v e r a l l r e s ul t s o f t h e p r e s e n t s t u d y s h o w

n o e f f e c t o f h e a d e l e v a t i o n o n C B F , o n e m u s t b e a r i n

m i n d t h a t o u r m e a s u r e m e n t s a r e o f g lo b a l C B F a n d

t h a t r e g i o n a l a r e a s o f d e c r e a se d C B F m a y e x i s t i n t h e

p r e s e n c e o f n o r m a l g l o b a l b l o o d f l o w m e a s u r e m e n t s .

O n l y i n o n e p a t i e n t d i d t h e C B F f a l l t o i s c h e m i c l e v e l s

a f t e r h e a d e l e v a t i o n , a n d t h e v a s o d i l a t o r y c a sc a d e s u g -

g e s t ed b y R o s n e r t< ~7 s e e m e d t o b e d e m o n s t r a b l e . I n

t h i s p a t i e n t , t h e lo w C P P 5 9 m m H g ) e m p h a s i z e s o n c e

m o r e t h e i m p o r t a n c e o f m a i n t a i n i n g a d e q u a t e l e v e ls o f

C P P . T h e r e s u l t s o f t h e p r e s e n t s t u d y s u g g e s t t h a t , i n

g e n e r a l , h e a d - i n j u r e d p a t i e n t s w i t h r a i s e d I C P s h o u l d

b e m a i n t a i n e d w i t h t h e h e a d e l e v a t e d t o 3 0 ~ w h i c h w i l l

p r o d u c e a f a l l in I C P w i t h o u t a s i g n i f ic a n t d e c r ea s e i n

C B F i n t h e m a j o r i t y o f t h e s e p a t ie n t s .

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Ma nuscript received May 19, 1991.

This s tudy was supported in pa r t by Na t iona l Ins t i tu tes o f

Health G rant PO 1-NS27616.

Some portions of this paper were presented at the Eighth

In te rna t iona l Sympos ium on In trac ran ia l Pressure, in Rot te r-

dam , The Netherlands, in June, 1991.

Address reprint requests to: Robert G. Grossman , M.D. ,

Dep artm ent of Neurosurgery, Baylor College of Medicine ,

One Baylor Plaza, H ouston, T exas 77030.

J . Neurosurg . / Vo lume 76 /Fe bru ary 1992 211

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