Continuous monitoring of intrathecal pO2, pCO2 and pH during surgical replacement of type II thoracoabdominal aortic aneurysm

Eur J VascEndovascSurg 15, 78-81 (1998)

TECHNICAL

NOTE

Continuous Monitoring of Intrathecal pO2, pCO2 and pH During Surgical Replacement of Type II Thoracoabdominal Aortic Aneurysm L. Christiansson ~1, S. Karacagil 2, S. Thelin 3, A. Hellberg 2, H. Tyden .1, L. Wiklund ~1 and D. Bergqvist ~2 Departments of ,1Anaesthesiology, 2Surgery and 3Thoracic Surgery, University Hospital, Uppsala, Sweden Key Words: Aortic surgery; Thoracoabdominal aneurysm; Paraplegia; Spinal cord ischaemia; h~trathecal monitoring.

Introduction

measure oxygen pressure (pO2), carbon-dioxide pressure pCO2), temperature and pH. For the first time The surgical management of a thoracoabdominal aortic this system has been used to monitor CSF oxygenation aneurysm is a challenging task both for the surgeon during thoracoabdominal aortic aneurysm repair. This and the anaesthesiologist, not only because of serious catheter was orignally validated for continuous systemic haemodynamic consequences during repair intra-arterial monitoring of blood gases 1 but the prinbut also because it may be complicated by spinal cord ciples of the sensor is valid also for measurements in injury. Apart from a long aortic clamping time, failure tissue. 2 to identify and reconstruct the blood supply to the The intrathecal sensor used in the present patient spinal cord may cause irreversible ischaemic injury was designed for intra-arterial onqine blood gas monand lead to paraplegia. itoring and contains two modified optical fibres for Recently, we have studied the use of continuous the measurements of pCO2 and pH; a miniaturised measurement of cerebrospinal fluid (CSF) oxygen ten- polarographic Clark oxygen electrode and a thermosion during thoracic aortic cross-clamping in an ex- couple, for temperature measurement. The void beperimental model in pigs as a sensitive method of tween each sensor is filled with acrylamide gel monitoring ischaemic changes in the spinal cord (un- containing phenol red (Fig. 1). The cylindrical conpublished data). We report a patient with a type II struction of the sensor allows measurement over the thoracoabdominal aortic aneurysm in whom the same entire surface of the probe. The diameter of the probe method of continuous intrathecal pO2, pCO2 and pH is 0.5 mm and the four sensing components are located monitoring during aneurysm repair was used. at different intervals along the distal 4 cm of the polyethylene probe permeable for O2 and CO2. The outer surface of the probe is coated with covalently bonded heparin to prevent fibrin deposition. Technique The monitor displays on-line pH, pCOa, pO 2 and temperature. The readings from the thermocouple corBy using a combined electrode-fibreoptic system, a rect all measured values to 37 °C, or if chosen, to the multiparameter sensor (Paratrend 7; Biomedical patient's temperature. After calibration for 30 rain, the Sensors, High Wycombe, U.K.) can simultaneously sensor must be inserted within 8 h. The catheter construction allows sterile placement with a touch-free technique. For the lumbar puncture at L1-L2 level, *Please address all correspondence to: L. Christiansson, Department of Anaesthesiology, University Hospital, Uppsala, we used a 18G/1.2 x 90ram Secalon-T over-needle S-751 85, Sweden. catheter (Ohmeda, Swindon, U.K.). 1078-5884/98/010078+04 $12.00/0 © 1998 W.B.Saunders CompanyLtd.

pO2, pCO2 and pH Monitoring During Aortic Aneurysm Surgery

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A 65-year-old male with hypertension underwent emergency surgical repair of an infrarenal abdominal aortic aneurysm in December 1996 and preoperative computed tomography (CT) scanning demonstrated an associated type II thoracoabdominal aortic aneurysm with a maximum aortic diameter of 5 cm just above the diaphragm. After uneventful recovery from the infrarenal aortic grafting, CT scanning in January 1997 revealed progress of the thoracoabdominal aortic aneurysm with a maximum diameter of 7 cm at the distal thoracic aorta. The patient underwent surgical repair of the entire descending thoracic aorta to the abdominal aortic graft using mild hypothermia and femorofemoral bypass. Sequential aortic clamping and retrograde perfusion of the aorta was applied during

performance of the proximal anastomosis, reattachment of one intercostal artery in the T10 region and reconstruction of the visceral arteries with Crawford technique. One intercostal artery was spared above the proximal anastomosis and three proximal (T6-8) and one distal intercostal arteries (T12) were ligated. To maintain the CSF pressure below 12 mmHg, a total of 60 ml fluid was withdrawn during the procedure. Figure 2 shows baseline CSF readings after a short stabilisation period. The relation between pO2, pCO2, pH at various stages during replacement together with other events are summarised in Fig. 3. In a compressed time scale, a number of events during the complete peroperative course are shown. In the pre-clamping period two hyperoxic and one short Eur J Vasc Endovasc Surg Vo] 15, January 1998

L. Christiansson et al.

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Fig. 3. Preoperative registration (8 h trend). 1 - Hyperoxaemia-FiO21.0; 2 - Start of surgery; 3 - Start of one-lung anaesthesia-FiO2 1.0; 4 - Hypotension;5 - proximal clamping;6 - splanchnicreperfusion;7 - declamping;8 - reperfusion-hypotension;9 - circulatorystabilisation.

hypotensive episode were noted without simultaneous changes in pH of pCO2. During aortic clamping we registered a decrease in pO2, an increase in pCO2 and a moderate acidification. After declamping, pO2 remained low during the hypotensive reperfusion period, but the metabolic parameters slowly started to normalise. Not until circulatory stability was reached (more than I h after declamping) did the oxygen pressure resume the level recorded before clamping. The patient m a d e an uneventful recovery without any neurological deficit.

Discussion

Paraplegia following thoracoabdominal aortic aneurysm repair is an unpredictable, devastating complication and has been correlated with prolonged cross-clamping time, interruption of critical blood supply to the spinal cord, hypotension and the extent of the aneurysm. The role of various adjunctive measures for prevention of spinal cord ischaemia is still controversial as well as methods for monitoring spinal Eur J Vasc Endovasc Surg Vol 15, January 1998

cord function during aortic replacement. Reliable continuous monitoring of spinal cord circulation during aortic replacement might not only provide better understanding of factors affecting spinal cord perfusion, but might also help to identify critical intercostal arteries to be implanted into the aortic graft. No technique is available for continuous measurement of spinal cord perfusion during surgical replacement of thoracic aorta in humans. The preliminary results of an ongoing experimental study in pigs with thoracic aortic clamping have demonstrated a strong correlation between the morphological degree of spinal cord ischaemia, laser Doppler derived flow measurement in the spinal cord and CSF oxygenation using the aforementioned multiparameter pO2, pCO2 and pH sensor. For the first time, this probe has been applied in a clinical situation to the patient reported in this article during surgical replacement of type II thoracoabdominal aortic aneurysm. There are no reports on normal CSF pO2, pCO2 and pH values in h u m a n s measured with the same technique. Baseline readings in our patient are in agreement with our experimental data. In the animal model, electron microscopy verified that a significant degree of spinal

pO2, pCO2 and pH Monitoring During Aortic Aneurysm Surgery

cord ischaemia developed at pO2 readings less than approximately 1.5 kPa but simultaneously there were metabolic changes (increase in pCO2 and decrease in pH). In our patient there were changes in CSF oxygen tension durng graft replacement with normalisation at the end of the reperfusion period. CSF pO2 was also influenced by variations in systemic blood pressure during replacement. Only during the clamping and reperfusion hypotensive period were concomitant metabolic changes observed, but the decrease in pO 2 never reached critical levels and the patient showed no signs of postoperative neurological deficit. The results from the pig experiments indicate that the method might also be useful to rapidly identify the critical blood supply to the spinal cord by segmental clamping of the aorta. It has also been possible to investigate the importance of proximal pressure as well as the effect of distal clamping or shunting on spinal cord oxygenation. We believe that continuous CSF oxygen tension monitoring with the above mentioned technique might be a useful adjunct in the perioperative management of patients during thoracoabdominal aortic replacement. Further clinical and

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experimental research is needed for validation of the method and interpretation of the data. To conclude, the combined results from this patient and the pig experiments obtained so far indicate that we have a method in the multiparameter sensor, which might help in the prevention of spinal cord ischaemia during extensive aortic grafting.

Acknowledgement

Swedish Medical Research Council 00759. The Laerdal Foundation for Acute Medicine 1460/96.

References 1 VENKATESHB, BROCKTH, HENDRYSP. A multiparameter sensor for continuous intra-arterial blood gas monitoring: a prospective evaluation. Crit CareMed 1994;22: 588-593. 2 HOFFMANWE, CHARBELFT, EDELMANG. Brain tissue oxygen, carbon-dioxide and pH in neurosurgical patients at risk for ischaemia. Anesth Analg 1996; 82: 582-586. Accepted 28 May 1997

Eur J Vasc Endovasc Surg Vol 15, January 1998