Intensive Care Med (1990) 16:184-188

Intensive Care Medicine 9 Springer-Verlag 1990

Continuous monitoring of cerebral tissue pressure in neurosurgical practice - experiences with 100 patients J. Piek and W.J. Bock Neurosurgical Clinic, University of DUsseldorf, D~sseldorf, FRG Received: 4 April 1989; accepted: 18 July 1989

Abstract. T h e a u t h o r s present their experience with the use o f c o n t i n u o u s m o n i t o r i n g o f cerebral tissue pressure ( C T P ) in a neurosurgical intensive care unit. T h e C T P was m o n i t o r e d in 100 patients with a variety o f n e u r o surgical diseases. I n 13 p a t i e n t s s i m u l t a n e o u s recording o f the v e n t r i c u l a r fluid pressure ( V F P ) was c a r r i e d o u t for u p to 134 h. I n 21 patients i n t r a h e m i s p h e r i c gradients o f C T P were r e c o r d e d a n d in 66 p a t i e n t s C T P a l o n e was r e c o r d e d (59 s u p r a t e n t o r i a l , 7 infratentorial). I n general C T P m o n i t o r i n g gave excellent results with no a d d i t i o n a l risk to the p a t i e n t a n d low costs for the m o n i t o r i n g system. T h e b e h a v i o u r o f C T P in v a r i o u s clinical c o n d i t i o n s a n d the i n d i c a t i o n s a n d l i m i t a t i o n s o f C T P m o n i t o r i n g c o m p a r e d with V F P o r e p i d u r a l pressure m o n i t o r i n g are outlined. T h e a u t h o r s r e c o m m e n d m o n i t o r i n g o f V F P as the m e t h o d o f choice in I C P supervision. C o n t i n u o u s m o n i t o r i n g o f C T P is the preferred m e t h o d in the posterior fossa, after large craniectomies, for p o s t o p e r a t i v e sup e r v i s i o n following o p e n surgery a n d in cases o f narrowed ventricles.

Key words: I n t r a c r a n i a l pressure - Cerebral tissue pressure -

Monitoring -

Neurosurgery

F o l l o w i n g the p i o n e e r i n g w o r k o f A d s o n a n d Lillie [1], G u i l l a u m e a n d J a n n y [2], a n d L u n d b e r g [3] c o n t i n u o u s m o n i t o r i n g o f i n t r a c r a n i a l pressure (ICP) has b e c o m e a r o u t i n e m e t h o d in m a n y intensive care units. W h e n e v e r elevated I C P is suspected m o n i t o r i n g o f I C P is indicated. I n a d u l t p a t i e n t s I C P m o n i t o r i n g is u s u a l l y p e r f o r m e d using ventricular, s u b d u r a l / s u b a r a c h n o i d a l [ 4 - 7 ] o r epid u r a l catheters [8, 9 - 1 5 ] using a variety o f t r a n s d u c e r s

[5-10, 13-181. T h e a d v a n t a g e s o f the ventricular m e t h o d , besides its p r o v e n reliability in t h o u s a n d s o f patients, are t h a t it provides a m e t h o d for in vivo c a l i b r a t i o n a n d it makes it p o s sible to w i t h d r a w ventricular fluid either for r e d u c t i o n o f elevated I C P o r c e r e b r o s p i n a l fluid analysis (e.g. lactate,

free a m i n o acids). T h e d i s a d v a n t a g e s are the need for t r a n s c e r e b r a l p u n c t u r e [19] a n d a n increased infection rate [9, 20]. In p a t i e n t s with n a r r o w e d ventricles a n d ext r e m e l y high I C P it is p a r t i c u l a r l y difficult to establish or to m a i n t a i n pressure recordings [3, 9]. I m p l a n t a b l e microt r a n s d u c e r s for e p i d u r a l m o n i t o r i n g m a y reduce infection rates a n d are widely used in clinical practice. They are, however, expensive a n d p r o b l e m s m a y arise in p o s t e r i o r fossa I C P recordings as well as after extensive craniectomies o r where the d u r a m a t e r has been destroyed. To overcome these p r o b l e m s c o n t i n u o u s recording of cerebral tissue pressure ( C T P ) has b e e n i n t r o d u c e d by our g r o u p as a r o u t i n e m e t h o d for I C P m o n i t o r i n g [21]. We now r e p o r t 2 years experience with C T P recordings in 100 patients with neurosurgical disease.

Materials and methods

Transducer An implantable microtransducer (Sensodyn, B. Braun AG, D-350~ Melsungen, FRG) was used for CTP monitoring in all cases. The trans. ducer (Fig. 1) contains a Wheatstone bridge of 4 silicium chips coverec with silicone. Pressures are transmitted via a piezoresistive technique Electrical characteristics of the transducer are given in Table 1. Th~ catheter with one or more (if required) transducer(s) at its tip is avail able in a diameter of 3 to 8 French gauge. After mechanical cleanin~ and resterilization the catheter may be reused. To avoid offset failure~ a zero-point simulator has to be used before inserting the catheter foJ rezeroing the transducer when connecting it to a new monitor.

Monitoring technique To establish pressure recordings in the operating theatre the catheter off set is determined intraoperatively by the zero-point simulator. The tiI of the catheter is then placed approximately 1.5 em into the brain tissue Pressure recordings may be done anywhere in the brain. For ICP record ing following a closed head injury or subarachnoid haemorrhage w~ prefer to use a frontal burr-hole. For pressure recordings following opei surgery (e.g. for brain tumours, subdural or intracerebraI haematoma the catheter tip is simply placed into the surrounding brain tissue. In th~ intensive care unit the catheter is connected to the monitoring system af ter re-zeroing.

J. Pick and W.J. Bock: Monitoring of cerebral tissue pressure

185

7b

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Fig. 1. a - c . a, h Catheter used for C T P monitoring; c Catheter tip with transducer (5 French)

Patients and recording details

Results

We have used this m e t h o d in 100 patients who h a d a variety o f clinical conditions (Table 2). In 13 patients we carried out simultaneous recording of ventricular fluid pressure (VFP) and C T P using a method previously described [20]. The duration of these recordings ranged from 1 8 - 1 3 4 h with a mean duration of 49 h. In 21 patients we performed parallel recording o f C T P with two transducers as previously described [22]. In 66 patients C T P was recorded alone in the supratentorial (59 patients) or the infratentorial space (7 patients). Pressure recordings ranged from 4 to 126 m m H g , and measurements were carried out for up to 17 days depending on the clinical situation.

Establishing and maintaining of pressure recordings

Table

1. Technical characteristics

Total pressure range: - 3 0 0 to +300 m m H g M a x i m u m pressure permitted: 4000 m m Hg Nonlinearity and hysteresis: max. 0.5~ of end pressure Temperature effect on zero point: max. 0.075m H g / ~ Operating temperature: 22 to 42 ~ Zero point drift in water: max. 3 m m Hg after the first 16 h; less than I m m Hg thereafter

In all cases we were able to establish pressure recording postoperatively. In simple burr-hole procedures no additional complications occurred until the end of the m o n T a b l e 2.

Recording details in the patients

Type of recording

N u m b e r of patients

Parallel recordings o f C T P and VFP

13

Intrahemispheric C T P gradients - head injury/subarachnoid haemorrhage - brain t u m o r

21

CTP alone - supratentorial - infratentorial

66

Total

2 19 59 7 100

M a x i m u m recording time = 288h; m a x i m u m pressure recorded = 149 m m Hg

186

J. Piek and W.J. Bock: Monitoring of cerebral tissue pressure

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surgery (in most cases following the removal of large meningiomas) or for I C P monitoring via a burr-hole after subarachnoid hemorrhage or head injury.

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Clinical application A. Parallel recordings of VFP and CTP. Parallel recordings were performed in 13 patients (Fig. 2). In the supratentorial space C T P and VFP correlated closely with the C T P continuously 4 - 8 m m Hg below VFP. As previously noted this was the case at all pressure ranges [21]. All typical I C P waves were recorded (Fig. 3). Usually the pulse-wave shape is different when C T P is compared to VFP. As VFP is transmitted by a fluid-filled system the pulse wave amplitude is higher due to the phenomenon of resonance. Compared with VFP, C T P showed different changes with therapeutic interventions. With barbiturate injection the VFP started to fall up to 2 min after CTP, which usually fell 5 - 15 s following the injection. Mannitol infusions also reduced the C T P first and VFP second. The causes for these observations are unclear and require further study. In 2 patients with extremely high ICP ( > 50 m m H g ) VFP recordings failed because of obliteration of the ventricular catheter by detritus.

B. Recordings of CTP alone. In 60 cases C P T was recorded either to assist postoperative supervision after open

frontal burr-hole 1.5 cm into the brain, typical behaviour and ICP waveforms were observed. Pupil dilatation was noted in 12 patients with C T P pressures ranging from 48 to 71 m m H g . In 11 of these patients the rise in C T P was caused by brain oedema. Plateau waves were recorded in all of these cases and were subsequently treated by mannitol infusions and barbiturate coma. In one patient a steep rise in C T P without any pathological waveforms occurring 4 h after evacuation of a right temporal epidural h a e m a t o m a was the first sign of the development of a frontal extradural h a e m a t o m a on the same side. In 3 cases C T P was monitored ipsilaterally after fashioning of large osteoclastic trauma flaps. Although high C T P values were recorded no Plateau waves occurred. This may be explained by the pathogenesis of these waves [9].

2. CTP after brain tumour operations. The typical course following surgery for a brain tumour was for there to be a low C T P during the first postoperative day, with a slight elevation to 25 m m H g on days 2 and 3 and a reduction afterwards. B waves were recorded in approximately half o f these cases. Postoperative oedema resulted in an elevation of C T P which was accompanied by pathological waves. Postoperative hemorrhage in 3 patients result-

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Fig. 4. Postoperative h e m o r r h a g e detected by CTP. Following surgery for a large m e n i n g i o m a (OP) a rise in C T P leads to a CT scan. This shows a large postoperative hemorrhage. After operative evacuation of the h a e m a t o m a (Re OP) C T P remains n o r m a l

ed in a steep rise of I C P without pathological waves and this always occurred during the first 8 h following operation (Fig. 4).

3. CTP in the posterior fossa. The C T P was recorded in 7 patients for up to 5 days after removal of infratentorial tumours. In 4 patients the postoperative course was uneventful. In a further patient a postoperative hemorrhage was detected by a steep rise in C T P similar to that observed in the supratrentorial space. One patient showed a massive infratentorial swelling after removal of a large ependymoma, the C T P did not react to barbiturates and mannitol: the patient recovered after 3 weeks of coma. Subsequently a supratentorial hydrocephalus was treated with a ventricular drain. Severe changes in the auditory evoked potentials were observed which were due to transient transtentorial herniation and which recovered after normalisation of infratentorial C T P (Fig. 5 a - c ) . In one patient the C T P was recorded following evacuation of a warfarin-induced spontaneous h a e m a t o m a in the left cerebellar hemisphere. In this case C T P values up to a mean of 23 m m H g were recorded, mainly B waves.

4. Gradients of CTP. In 21 patients C T P gradients were recorded with 2 transducers on one catheter placed intrahemispherically following surgery for brain tumours (19 cases) or after head injury (2 cases). The results of these recordings have previously been published [22]. Whereas C T P gradients up to 28 m m Hg were observed after t u m o r surgery this was not the case in catheters placed at a depth of 1.5 cm and 3.5 cm in the frontal cortex following trauma. Complications No infections were noted as a result of C T P recording although no prophylactic antibiotics had been given to our patients. Bacteriological examination of the catheter tip was routinely performed only in the first 30 of our 100 patients; Staphylococcus albus was found in 4 cases and enterococcus species in I case; antibiotics (ampicillin) were given only in this last case. Besides postoperative hemorrhage following tumour surgery no additional intracranial bleeds were observed as a consequence of C T P recordings. Eight of the catheters were damaged, in all of these cases this was due to mechanical problems caused by the staff while implanting, removing, or cleaning the catheter.

Costs The initital costs were about 1900 DM for a catheter with one transducer, 400 DM for the zero-point simulator and 250 DM for the monitor adapter. We used our catheters up to 12 times, thus an average of 250 DM per I C P recording is a realistic value which should be minimized by a careful handling of the catheters. Discussion

Although some attempts have been made [18, 21 - 2 3 ] to continuously record the C T P this new method of I C P monitoring is only used in a few hospitals. Our results clearly show that for the control of I C P it is a safe and reliable method with low costs. In spite of new microtransducers for continuous monitoring of I C P in the subdural or epidural space or via a ventricular catheter some problems associated with I C P recordings with these conventional methods remain unsolved. In the posterior fossa routine infratentorial ICP recordings are possible only in selected cases especially following craniectomies. After such operations C T P recordings can easily be performed by placing the catheter tip into the cerebellar brain tissue. The C T P recordings may demonstrate postoperative complications such as hemorrhage and oedma and appear to correlate with electrophysiological methods. In patients undergoing large craniectomies or following open head injuries with destruction of the dura, ipsilateral I C P recordings in the epidural spare are not possible, here C T P recordings are an alternative method. Ventricular catheters for VFP measurement often require an extra burr-hole at the end of a t u m o r operation with an additional risk to the patient [19]. In cases of closed head injury and narrow ventricles ventricular puncture is not possible in up to 15~ of the cases [3] or catheter placement may lead to extensive trauma to the brain tissue [19], and infection rates may be as high as 3 - 4 % [9]. Occlusion of the catheter due to blood or brain tissue occurs, especially in cases of elevated ICP. Recordings of the C T P can maintain I C P monitoring in nearly all of these cases. In our experience C T P has a lower infection rate and requires less penetration of the catheter into the brain (CTP: 1.5 cm vs. VFP: approx. 4 cm). The greatest advantage of ventricular catheters is that they can be used for fluid drainage to reduce elevated I C E From approximately 150 VFP recordings per year and our experiences with C T P measurement, VFP recording

J. Piek and W.J. Bock: Monitoring of cerebral tissue pressure

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Fig. 5 a - c . Transtentorial herniation by infratentorial brain swelling at different CTP levels in the posterior fossa following removal of a large ependymoma, a Nearly normal latencies (upper values) and amplitudes (lower values) of brain stem auditory evoked potentials (BAEP) on the 1st postoperative day (CTP 14 mmHg), b Latencies and amplitudes of BAEP on the 3rd postoperative day. CTP is now 28 mmHg. Waves 3 - 5 are nearly extinguished but c start to recover on day I 1

still remains the method of choice of ICP recording. However, in cases where extremely high values of ICP are expected, in patients with narrow ventricles or with intraventricular blood, after large craniectomies or open head injuries, and in posterior fossa, CTP recordings should be regarded as the technique of choice.

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Dr. J. Piek Neurochirurgische Universit~tsklinik Moorenstrage 5 D-4000 Dasseldorf, FRG