北海道脳神経疾患研究所医誌第21巻

2010．12．P55〜58

Continuation Measurement of Thoracic Epidural Pressure
Satoshi OMORI, M.D., Shingo FURUSE, M.D.
Department of Anesthesiology, Nakamura Memorial Hospital and Hokkaido Brain Research Foundation, Sapporo,Japan
Abstract:[Purpose] The aim of this study was to examine whether the epidural pressure can be measured for a long period oftime using the continuation epidural infusion via the thorax.
[Materials and Methods] Ten adult patients undergoing surgery had an epidural catheter inserted via the thoracic
interspaced. After induction of general anesthesia, continuous infusion of local anesthetic (0.2% ropivacaine) at arate of 6 mL/h was applied epidural space. A pressure transducer was connected to the epidural catheter and theepidural pressure was measured. During surgery, changes in the epidural pressure were monitored at 0, 5, and 10
cmH20 of positive end-expiratory pressure (PEEP). On postoperative day 1, and 2, the epidural pressure was measured in the supine position, the Queckenstedt test, and the 30º head-up position.
[Results] The epidural pressure was measured continuously and stably during surgery and until postoperative day
2, it increased significantly at 5 and 10 cm H20 PEEP, and increased and decreased significantly in the Queckenstedt test and the head-up position, respectively.
[Conclusion] Continuous epidural infusion at a rate of 6 mL/h via the thorax allows stable measurement of theepidural pressure over a long period of time.

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INTRODUCTION
Epidural pressure is measured commonly by injecting a small volume of saline as a single injection into
the epidural space through an epidural catheter connected to a pressure transducer 1,2) . Because theepidural space is a non-fluid-filled environment, thistraditional method dose not allow for long-term, stable, and continuation of measurement of the epiduralpressure 3) . To allows stable measurement of theepidural pressure, Iwama et al suggested that the single injection of saline should be changed to a continuous infusion at relatively high flow rate3). According
to this concept, we examined whether the epiduralpressure measured via the T10-T12 levels thorax canbe measured stably for a long period of time.
PATIENTS AND METHODS
Ten adults patients classified as ASA 1-2 undergoing surgery who provided informed consent wereenrolled in this study. The Institutional Committee
approved this study.
All patients received cephalic insertion of an 18gauge multi-orifice epidural catheter (PERIFIX. BBRAUN. Tokyo, Japan) via the thoracic interspaced
between the T10-T11 and the T11-T12 levels. Subsequently, anesthesia was induced with propofol, oxygen,and sevoflurane, and laryngeal mask insertion wasfacilitated vecuronium. The anesthesia was maintainedwith oxygen and sevoflurane with mechanical ventilation of 8 to 12 mL/kg tidal volume, respiratory rate of 10
bpm. After induction and several minutes before thestart of surgery, 6±1 mL of 0.75% ropivacaine wasinjected epidural space. And a continuous epidural
infusion of 0.2% ropivacaine at a rate of 6 mL/h was initiated using a disposable portable pump connected tothe epidural catheter by a 3-way stopcock. A pressuretransducer available for monitoring arterial pressure(Life Kit: Ohmeda, Singapore) was then connected tothe side pore of this stopcock and placed on the posterior axillary's line, and the epidural pressure was measured continuously in the supine position. About 5±1mL of 0.75% ropivacaine was injected epidural space at
60-minutes interval until completion of surgery. The
continuous epidural infusion was continued until post-operative day 2 for postoperative pain relief.
In the supine position and 15 minutes after the second epidural injection of 0.75% ropivacaine, the PEEP
level was increased from 0 to 5 cm H 2 0 using athreshold resistance expiratory pressure valve. Ten
minutes later, this level was increased to 10 cm H20,
followed up 10 minutes later by returning to 0 cm
H20. The mean epidural pressure level was recorded
before the application of PEEP, and 10 minutes after
application of 5 and 10 cm H20 PEEP.
After complication of surgery, the laryngeal mask
was removed from patients, who subsequently
entered the intensive care unit. The epidural pressure measurement system and the continuous epidural infusion system were maintained until postoperative day 2. The pressure transducer was placed on
the lateral upper abdomen where the midaxillary'sline crossed the horizontal line of the ensiform
process. On postoperative day 1, and 2, the epiduralpressure was recorded with patient in the position,receiving jugular venous compression (Queckenstedttest), and a 30° head-up position. After these measurements, the epidural catheter was removed.
Changes in epidural pressure levels during analyzed by repeated measure one-way analysis of variance, followed up by Fisher's protected least significant difference for multi-comparison. Change in
epidural pressure levels in the supine position.
Queckenstedt test, and head-up position were analyzed by t test. P < 0.05 was considered significant.
RESULTS
The age, height, and weight of the patients was
58±10 years, 156±12 cm, and 52±9 kg, respectively,expressed as mean ± SD. Six patients were womenand four patients were men. The position of insertionof the epidural catheter was T10-T11 in 4 patients,
T11-T12 in 6 patients.
During surgery, the epidural pressure was successfully monitored continuously except for the time when
the intermittent epidural injection was performed.
Changes in the epidural pressure levels during theapplication of PEEP are shown in Table 1. The
epidural pressure was increased significantly at 5 cm
H20 PEEP, and further increased at 10 cm H20 PEEP.

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After surgery, postoperative analgesia was clinically satisfactory in all patients, and the epidural pressure was successfully monitored continuously until
postoperative day 2. The time course of the epiduralpressure is shown in Table 2. The epidural pressure
did not change significantly during this period when
the patient was in the supine position. During theQueckenstedt test, the epidural pressure wasincreased significantly on each measurement day.
After the patient was positioned 30º head up, theepidural pressure was decreased significantly on eachmeasurement day. The record of epidural pressure
waves in the supine position, Queckenstedt test, andhead-up position is shown in Fig. 1.
DISCUSSION

Table 1 Changes in epidural pressure during application ofPEEP

Table 2 Time course of epidural pressure after surgery andits changes during the Queckenstedt test or thehead-up position

Fig. 1 Measurement of Epidural pressure during thesupine position, Queckenstedt, and 30º head-up
position.

This study shown that injection of a fluid volume
into the thoracic epidural space at about 6 mL/hallows stable monitoring of the epidural pressure up
to 2 days. This result suggests that the epiduralspace becomes a fluid-filled environment, so that theintraspinal pressure may be easily transmitted to theepidural space. Intracranial pressure (ICP) is known
to increase during the application of PEEP, whichshould result in an augmentation of the intraspinal
pressure, except in the conditions with a blockage ofthe spinal canal. Furthermore, the ICP is increased
and decreased during the Queckenstedt test and in
the head-up position, respectively. To test whether
the epidural pressure obtained in this study reflected
the ICP, we examined changes in the epidural pressure during these procedures and the results wereconsistent with the known responses in ICP describedearlier. In fact, there has been some report suggesting a correlation between the epidural pressure andICP1-3,5). We have also measured both types of pressure simultaneously in 2 patients and documented
similar records3).
Measurement of ICP involves the measurement ofintraventricular pressure, brain tissue pressure, subarachnoid pressure, and intracranial epidural pressure. Clinically, intraventricular pressure has been
often used for ICP measurement, and, recently, acatheter with a pressure transducer attached at thetip has been developed, which commonly measuressubarachnoid pressure. All of these methods requirea burr hole open at the skull, which may have moreinvasion than measurement of the epidural pressure
requiring epidural placement of the catheter. The
primary use of ICP monitoring is in management of−57−

intracranial hypertension; however, the question as towhich pressure indicates the ICP has not beenanswered, and significant differences in pressure
between various measurement sites are observed6).
Another method, measurement of lumbar spinal pressure by subarachnoid catheterization, has beenreported2) in which cerebrospinal fluid drainage as atherapeutic maneuver is often combined. In thismethod, communication between the cranial andspinal subarachnoid spaces is necessary, but may beoccluded depending on the severity of intracranial
hypertension. Because the epidural pressure by ourmethodology seems to be identical to the intraspinalpressure, this limitation should be considered. Moreover, because a large volume of epidural injection
causes ICP to increase significantly, epidural infusion
at a relatively high flow rate may also be contraindicated in patients with severe intracranial hypertension. Taking these implications into consideration, an
application of the epidural pressure as a possible indicator for estimation of the intracranial pressure
should be limited to patients with mild to moderate
intracranial hypertension, possibly to detect early
onset of brain swelling or to determine the need forconventional ICP monitoring.
In this study, the pressure transducer was placedon the posterior axillary's line during surgery, andwas placed on the midaxillary's line after surgery.
This difference could be the cause of the difference inthe epidural pressure values obtained during surgery
and after surgery. We believe that the pressuretransducer should be placed at the same height as the
epidural catheter tip because the pressure at thecatheter tip site is the most accurate indicator ofepidural pressure. However, it is relatively difficult
to determine this site. Because the patient moves
appropriately after surgery, we recommend thattransducer be placed on the lateral side of the upper
abdomen when the epidural pressure is measured via
the thoracic epidural catheter. Although an optimal
spine level to monitor the epidural pressure is
unknown, successful recording of the epidural pressure has been reported via the cervix or lumbus2,3).
In this study, there was no apparent difference in
epidural pressure with epidural location from T11T12 to T10-T11. This suggests that measurement at
any epidural level in the spine may provide satisfacto-

ry monitoring of the epidural pressure. Because theT10-T12 thorax is an easy site for epidural catheterization even in critically ill patients, we believe that
the T10-T12 thoracic epidural space is one of the suitable sites for measurement of epidural pressure.
In conclusion, continuous fluid infusion at a rate of
6 mL/h into the thoracic epidural space allows stable
monitoring of the epidural pressure for up to 2 days.
The epidural pressure values appear sensitive to clinical maneuvers known to ICP. Monitoring of theepidural pressure may have use as a less invasive
early detector of intracranial hypertension than conventional ICP monitoring.
REFERENCES
1）Shah JL: Influence of cerebrospinal fluid on
epidural pressure. Anaesthesia, 1981; 36: 627-631.
2） Mimura M, Kumeta Y, Echizenya K: Spinal
epidural pressure as a less-invasive monitoring ofintracranial pressure, Report of two cases ofencephalitis. Journal of Anesthesia, 1997; 11: 237238.
3）Iwama H: Simultaneous record of epidural andintracranial pressure. Acta Anaesthesiol Scand,
1997; 41: 800.
4）Shah JL: Positive lumbar extradural space pressure. Br J Anaesth, 1994; 73: 309-314.
5）Hilt H, Gramm HJ, Link J: Changes in intracranial pressure associated with extradural anaesthesia. Br J Anaesth, 1986; 58: 676-680.
6）Kosteljanetz M, Borgesen SE, Stjernolm P, et al:
Clinical evaluation of a simple epidral pressure
sensor. Acta Neurochir (Wien), 1986; 83: 108-111.

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