Cerebral interstitial tissue oxygen tension, pH, HCO3, CO2

ELSEVIER

Technical Note

CEREBRAL INTERSTITIAL TISSUE OXYGEN TENSION, PH, HCO,, CO, Fady T. Charbel, M.D., William E. Hoffman, Ph.D., Mukesh Misra, M.D., Kelly Hannigan, B.S., and James 1. Ausman, M.D., Ph.D. Department of Neurosurgery, University of Illinois at Chicago, Chicago, Illinois

Charbel lT, Hoffman WE, Misra M, Hannigan K, Ausman JI. Cerebral interstitial tissue oxygen tension, pH, HCO,, CO,. Surg Neurol 1997;48:414-7. BACKGROUND

There are many techniques for monitoring the injured brain following trauma, subarachnoid hemorrhage, or surgery. It is thought that the major determinants for recovery of injured cerebral tissue are oxygen, glucose delivery, and the clearance of metabolites. These factors, at optimal levels, are probably responsible for the regaining of neuronal functions. These parameters are in turn dependent on the tissue’s blood flow and metabolism. METHODS

We have been using a single, compact, polyethylene sensor, the Paratrend 7TM,for the measurementof cerebral oxygen tension, CO,, pH, and temperature. This sensor is designedfor continuous blood gasanalysis to aid in monitoring neurosurgical patients, both during surgery and in the intensive care unit. RESULTS

Using the Paratrend 7TMsensor, we found the normal range of values to be: PO, 33 ? 11 mm Hg; PCO, 48 & 7 mm Hg; pH 7.19 + 0.11. Critical measurementsare considered to be tissue PO, 60 mm Hg, and pH <6.8. We have had no complications with this device; the risks are similar to those of placing a parenchymal intracranial pressure monitor. CONCLUSIONS

We believe that assessmentof interstitial cerebral oxygen saturation can be of great value both intraoperatively and postoperatively. In our experience, the Paratrend 7TMsystem is an effective method of measuring tissue cerebral oxygen tension, along with carbon dioxide levels, pH, and temperature. 0 1997by Elsevier Science Inc. KEY

WORDS

Carbon dioxide; cerebral oxygen tension; hypoxia; ischemia; monitoring.

V

arious intracranial monitoring devices have gained popularity and interest in recent years, so much so that monitoring intracranial pressure Address reprint requests to: Fady T. Charbel, M.D., University of Illinois at Chicago, Department of Neurosurgery (M/C 799), 912 South Wood Street, Chicago, IL 60612-7329. Received April 22, 1996; accepted September 5, 1996. 00903019/97/$17.00 PII SOO90-3019(96)00473-9

(ICP) and the treatment of raised ICP is now routine. Attention has also been focused on calculating cerebral perfusion pressure (CPP) as one guideline used in the management of neurosurgical patients [5,6]. The importance of measuring ICP and CPP follows the realization that injury to the brain is directly related to raised ICP, which in turn results in decrease in cerebral blood flow (CBF) and regional cerebral oxygenation (rSO& Until recently, there were no routinely used intracranial cerebral oxygen-measuring devices available that had proved their efficacy in animal studies [4,9]. However, we have recently been measuring rS0, transcranially using near-infrared (NIR) [ 11. There are also studies advocating the use of jugular bulb oxygen saturation as a measure of cerebral oxygen saturation [2]. We have found that the Paratrend 7TM system (Biomedical Sensors, Pfizer Inc, New York, New York) is an effective method of measuring tissue cerebral oxygen tension (POJ along with carbon dioxide levels (CO& pH, and temperature. The Paratrend 7TM is primarily designed for continuous blood gas analysis as a way of monitoring neurosurgical patients and evaluating their progress during surgery and follow-up in the neurosurgical intensive care unit.

INSTRUMENTSPECIFICATIONS The Paratrend consists of:

7TM monitoring

system

(Figure

1)

A microprocessor-based device incorporating a screen for continuous data display; keys for selecting data, calibration, and printout; and a printer. Patient Data Module (PDMJ This provides the interface between the Paratrend 7TM sensor and the monitor. It contains a battery backup, signaldetection circuitry, and nonvolatile memory to retain patient trend data and calibrated data, Monitor:

655 Avenue

0 1997 by Elsevier Science Inc. of the Americas, New York, NY 10010

Cerebral Interstitial

Two position

Hard keys

Surg Neurol 1997;48:414-7

Monitoring

4 15

Intravascular

-

Postoperative CT scan showing El plied during surgery.

braked castor

Paratrend 7TM system. b

which are the baseline values the machine establishes during the warm-up period. Paratrend 7 Multiparameter Sensor: This is a disposable, sterile, single-use device for continuously monitoring POz, CO*, pH, and bicarbonate levels. Calibration Stand: For mounting the monitor and incorporating the calibration gas cylinders. The system works in the range of loo-120 V, 220-240 V; there is a 50/60 Hz battery backup for calibration and patient-trend data. The electroluminescent display screen is 640 X 400 pixels with a screen size of 200 mm x 120 mm. It has a fully isolated RS 232-compatible data output source. The system uses an innovative combination of fiberop tic and electrochemical sensing elements.

The sensor is primarily made of polyethylene with a covalently bonded bioactive surface treatment (Carmeda, Taby, Sweden). It measures PO,, CO,, bicarbonate level (I-ICO& and temperature. The response time is 5180 seconds at 37°C (at 100 seconds, accuracy is 90%). The sensor is approximately 0.5 mm (outer diameter). When stored in a

sensor in situ ap

cool, dry place, it has a shelf life of about 12 months. The sensors can be sterilized by gamma irradiation ~25 kGy, although the sensors are presterilized and are intended for single use only (we resterilize the probes before use in the brain). The highly sensitive and accurate in vitro sensor calibrating system is an integral part of the monitor. Monitoring PO,, CO,, HCOa, pH, and temperature can be done simultaneously by placing the sensor in the brain parenchyma just under the dura. The system can be routinely used in the operating room by inserting the sensor after opening the dura mater, and is kept ready for use after initial calibration. Monitoring can be continued after surgery in the neurosurgery intensive care unit by keeping the sensor well anchored in situ. The position of the sensor can be confirmed by the postoperative follow-up computed tomography (CT) scan (Figure 2). Concomitant monitoring of the ICP, CPP, and cerebral tissue oxygen saturation helps to define the pathophysiology in the brain. In the case of closed diffuse head injury, the sensor could be inserted via a burr hole or twist drill, although this method of placement is technically more problematic, due to the soft and fragile nature of the probe. The risks and complications of using this device are similar to those of placement of a parenchymal ICP monitor, although so far we have not encountered any.

THEPARATREND~~~ MONITOR Measurements are clearly displayed on the large screen in “trend” format for the previous 24 hours of continuous patient data or as a large digital display. The system is very easy to calibrate and op-

4 16

Charbel et al

Surg Neural

1997;48:414-7

, 7.32

70,

7.24

7.2

" r 0

7.16 10

20

30

“/w

oxygen saturation

is

(1) transcranial cerebral oximetry by using nearinfrared (NIR), (2) measuring jugular oxygen saturation by placing a catheter in the internal jugular vein, and (3) measuring tissue-oxygen tension by placing a sensor within the brain parenchyma. 02

CO2

I

20 10

DISCUSSION The assessment of cerebral mainly done in three ways:

lime (min)

0

48 2 7; and pH 7.19 ? 0.11. Tissue PO, ~10 mm Hg, PCO, >60 mm Hg, and pH ~6.8 are considered critical. Under baseline conditions, the patient in figure 3 had a tissue PO, of 52 mm Hg, which was higher than the normal nonischemic levels (approximately 35 mm Hg) usually seen. However, the presence of normal tissue PCO, and pH in this patient suggested that there was no tissue hyperperfusion.

xl

30

Tme (min) Graphic representation of changes in tissue PO,, Q PCO,, pH, during an increase in PaCO, and PO,. End tidal (ET) CO, was increased by decreasing ventilation. Oxygen was increased by increasing PfO, from 0.4 to 1.0. The changes in PCO, and PO, were selective for each challenge. (Although this patient’s tissue PO, is higher than the normal nonischemic level of 35 mm Hg, the fact that PCO, and pH are in the normal range suggeststhat there is no tissue hyperperfusion.)

erate (“intuitive”). The information key (i) helps with calibration and system setup. The selection of soft (screen-defined) and hard (function-specific) keys gives instant access and precise information immediately. The alarm selection can be easily defined according to individual selection for each parameter. The system is very flexible and a portable patient/monitor interface unit allows it to be easily transferred with the patient between departments with no loss of calibration or data. The printout of the data/graph on the monitor is available at the touch of a button. The system can be easily connected to other hospital computers or database systems to fully maximize its potential. The digital stored or recorded data can also be used to reproduce a graphic representation of the events, if required (Figure 3). We have determined the normal range of values to be: PO, 33 + 11 mm Hg; PCO,

The main difference between jugular bulb venous oxygen and near-infrared spectroscopy is that the former tends to reflect global cerebral saturation, whereas the latter measures oxygen saturation within a localized region of the brain. TCCO is a comparatively simple, noninvasive, and safe technique for measuring rS0, transcranially, and it has demonstrated its efficacy in various neurosurgical and endovascular procedures [7,8]. The measure ment of jugular bulb oxygen saturation requires jugular vein puncture and can lead to injury. Direct measurement of PO* in the brain tissue or cerebrospinal fluid (CSF’) is believed to be the most effective way of measuring regional oxygen saturation [3,4,9]. The hesitation on the part of some clinicians to embrace this technique is most likely due to its invasiveness and the nonavailability of validated data regarding its influence on outcome. However, we believe that assessment of interstitial cerebral oxygen saturation could be of great value, both intraoperatively (especially during temporary clipping and vessel sacrifice) and postoperatively. We view cerebral interstitial tissue measurements as a mainstay for monitoring neurosurgical patients, although more clinical trials are needed to accurately assess its efficacy under a variety of procedures and conditions. Although the Paratrend 7TM system must undergo rigorous trials and modifications in order to make a definitive evaluation, we have been using the system for about a year with promising results. We have found that the diagnosis and management of cerebral ischemia can be optimized using the interstitial data provided by the

Cerebral Interstitial

Surg Neurol 1997;48:414-7

Monitoring

Paratrend 7TM system, especially during and following various neurosurgical procedures.

4 17

11. Zauner A, Bullock R, Di X, Young H. Oxygen, CO,, and temperature monitoring: evaluation in the feline brain. Neurosurgery 1995;37(6):1168-77.

REFERENCES

1. Ausman JI, McCormick PW, Stewart M, Lewis G, Dujovny M, Balkrishna G, Malik GM, Ghaly RF. Cerebral oxygen metabolism during hypothermic circulatory arrest in humans. J Neurosurg 1993;79:810-5. 2. Dearden NM. Jugular bulb venous oxygen saturation monitoring in the management of severe head injury. Curr Opin Anaesthesiol. 1991;4:279-86. 3. Hoffman WE, Charbel FT, Edelman G, Hannigan K, Ausman JI. Brain tissue oxygen pressure, carbon dioxide pressure and pH during ischemia. Neurol Res 1996;18(1):54-6. 4. Meixensberger J, Dings J, Kuhnigk, Roosen K. Studies in tissue PO, in normal and pathological human brain cortex. Acta Neurochir (Wien) 1993;59:58-63(Suppl). 5. Mendelow AD, Allcutt DA, Chambers IR, Jenkins A, Crawford PJ, Sultan H. Intracranial and cerebral perfusion pressure monitoring in the head injured patients: which Index? In: Avezaat CJJ, Eijindhoven JHMV, Maas AIR, Tans JTJ, eds. Intracranial pressure, Vol VIII. Berlin, Heidelberg: Springer-Verlag, 1993:

544-8. 6. Rosner MJ, Rosner SD. Cerebral perfusion pressure

management I: Results. In: Nagai H, Kamiya K, lshii RS, eds. Intracranial pressure, Vol IX. Tokyo: SpringerVerlag, 1994:218-21. 7. Sheinberg M, Kanter MJ, Robertson CS, Contant CF, Narayan RK, Grossman RG. Continuous monitoring of jugular venous oxygen saturation in head-injured patients. J Neurosurg 1992;76:212-7. 8. Slavin KV, Dujovny M, Ausman JI, Hernandez GA, Leur M, Stoddart H. Clinical experience with transcranial cerebral oximetry. Surg Neurol 1994;42:531-40. 9. Stocchetti N, Paparella A, Briedelli F, Bacchi M, Pizza P, Zuccoli P. Cerebral venous oxygen saturation studied with bilateral samples in the internal jugular veins. Neurosurgery 1994;34:38-44. 10. Williams IM, McCollum C. Cerebral oximetry in carotid endarterectomy and acute stroke. In: Greenhalgh RM, Hollier LH, eds. Surgery for stroke. London: WB Saunders, 1988;933:184-92.

COMMENTARY

Many clinical conditions following acute brain injury and operative neurosurgical procedures have the potential to cause brain ischemia. Therefore, sensitive continuous monitoring techniques are necessary to detect changes of cerebral circulation and metabolism. The authors introduce a multiparameter single polyethylene sensor, primarily designed for continuous blood gas analysis, which allows monitoring of tissue oxygen tension, pH, CO,, and bicarbonate levels after placement in the brain parenchyma. They used the sensor intraoperatively as well as postoperatively in the intensive care unit to study changes in tissue oxygen tension, pH, COz, and bicarbonate levels. There seems to be no doubt that the sensor is practical and reflects changes in cerebral microcirculation during temporary clipping of major vessels. Additionally, there is no evidence of increased risk of complications (infection, bleeding) after intraparenchymal place ment. Their first experience allows us the conclusion that we will obtain more insight into the pathophysiology of ischemia leading to infarction using this device in more clinical trials. This knowledge might give us a new and important basis to detect critical ischemia and to find new strategies for treatment. At least, this will improve the outcome of our neurosurgical patients. Prof. Dr. Jiirgen

Meixensberger

Neurosurgery Clinic University of Wiinburg Wiinburg, Germany