Perioperative transcutaneous oxygen monitoring in thoracic anaesthesia

Chubra-Smith etal.: Ptc 0 M O N I T O R I N G 0 0 From the Department of Anaesthesiology, The Uni- versity of British Columbia and Vancouver General Hospital , Vancouver , British Columbia. Department of Anaesthesia, Burnaby General Hospital , 3935 Kincaid Street, Burnaby, British Columbia , Canada V5G 2X6 Transcutaneous oxygen tension (Ptc02) was measured in 30 patients scheduled for elective pulmonary resection requiring one-lung ventilation during anaesr Simultaneous Ptc02 and arterial oxygen tension (PaO2) measurements were taken preoperatively (preop), intraoperatively during two-lung endotracheal (ET) and onelung endobronchial ventilation (EB), and postoperatively (postop). There was a significant correlation (r) between PtcOz and PaO2 at all time periods: 0.97 (preop); 0.91 (ET); 0.83 (EB); 0.81 (postop). There were no significant differences among the transcutaneous oxygen indices (tc02 index = PtcO2/Pa02) in the preop (0.69 +- 0.09), ET (0.68  0.10) andpostop (0.71  0.12) time period. The tc02 index was significantly lower during one-lung anaesthesia (0.61  0.14). The Ptc02 was consistently lower than the corresponding PaOz measurement, thus providing a continuous estimation of the "'minimum" Pa02 level throughout anaesthesia and recovery. In four patients a marked drop in Ptc02 occurred just after the initiation of one-lung ventilation. In three, this was associated with arterial hypoxaemia and in one, haemodynamic compromise. In allfour cases the Ptc02 was the Perioperative transcutaneous o x y g e n monitoring in thoracic anaesthesia first monitored parameter to change. As there is a substantial risk of developing hypoxaemia during thoracic anaesthesia, PtcO2 monitoring provides valuable early warning of impending hypoxaemia or haemodynamic compromise, thereby facilitating early therapeutic intervention. During anaesthesia for thoracotomy, one-lung endobronchial ventilation is not infrequently associated with marked decreases in PaO2. Hypoxaemia may result from intrapulmonary shunting, from changes in hypoxic pulmonary vasoconstricton, from atelectasis in the dependent lung and from surgical manipulation impairing ventilation or cardiac output, l Previous studies have shown that in haemodynamically stable adults transcutaneous oxygen tension (PtcO2) correlates well with arterial oxygen tension (Pa02). 2'3 In patients with cardiac compromise PtcO2 is more a reflection of cardiac output and oxygen delivery to the tissues than of PAO2.4'5 Transcutaneous oxygen monitoring during anaesthesia for thoracic surgery has been shown to be a valuable trend indicator when two-lung ventilation is utilized. 6 Previous investigators have also suggested that PtcO2 monitoring is of value during one-lung ventilation. 7's In the latter study, however, only two or three paired measurements of PtcO2 and PaO2 were made in each patient during one-lung ventilation, s The purpose of the present study was to examine the relationship between PtcO2 and PaO2 in patients undergoing thoracotomy where one-lung ventilation was utilized, and to examine whether or not that relationship was altered by changing from two-lung ventilation to one-lung ventilation. Methods Thirty ASA physical status II to IV patients aged 41 to 76 years admitted for elective thoracotomy and lung resection were studied. Patients with a history of cardiac failure or with any degree of cardiac compromise preoperatively were excluded. The study was approved by the Screening Committee for Research Involving Human Subjects of The University of British Columbia and by the Vancouver General Hospital Clinical Research Committee. Written informed consent was obtained from each patient prior to inclusion in the study. Patients were assessed the day before surgery and blood pressure, heart rate (HR) and oral temperature were recorded. A combined transcutaneous oxygen (PtcO2) and carbon dioxide monitor, Biochem Lifespan #100 (Waukesha, WI), was used for measuring PtcO2. The oxygen sensor, a polarographic electrode with a platinum cathode and silver anode, polarized with 0.6 volts and covered with a potassium chloride electrolyte and semi-permeable polypropylene membrane, was calibrated at 44~ to an internal electronic zero and to 21 per cent by exposure to room air. Electrode temperature was monitored and maintained at 44~ by an internal thermistor. The patients' shoulders or infraclavicular areas were used for placement of the PtcO2 sensors. The site was wiped and alcohol, a drop of contact gel was placed on the skin and the Ptc02 sensor was fixed to the site using a double-sided adhesive O-ring. Twenty minutes were allowed for warm up and stabilization of the PtcO2 sensor before a measurement with the patient breathing room air was recorded. At the same time an arterial blood sample was drawn by percutaneous puncture of a radial artery with a preheparinized syringe. The blood sample was buried in ice and analyzed within 20 minutes by the hospital laboratory with a Radiometer ABL 3 analyzer. Results were corrected for patient temperature and haemoglobin values. After recording the first measurements, patients were placed on supplemental oxygen by Venturi mask. The first ten patients received an inspired oxygen concentration (FxO2) of 0.3, the next eight patients 0.5, and the final eight 1.0. After waiting 15 minutes for stabilization, the PtcO2 was recorded and another arterial blood sample was drawn for measurement of PaO2. Four patients refused to allow a second arterial blood gas measurement. CANADIAN ANAESTHETISTS ~ SOCIETY JOURNAL On the day of surgery the patients were premedicated with a benzodiazepine one hour preoperatively. In the operating room the PtcO2 sensor was calibrated and placed on the patient's shoulders in the same fashion as described above. A #20 gauge catheter was placed percutaneously in a radial artery prior to anaesthetic induction; heart rate and blood pressure were monitored continuously utilizing an Electronics for Medicine PM-2B monitor and Cobe disposable pressure transducer. Placement of the PtcO2 sensor was restricted to the patients' shoulders and infraclavicular areas of the chest. Sites were changed and prepared every four hours, as recommended by the manufacturer. The sensor underwent two-point calibration with each sensor site change. A continuous strip recording of PtcO2 for the duration of the study period was obtained for each patient. Anaesthesia was induced with thiopentone and fentanyl. Endobronchial intubation with a double lumen tube (National Catheter Broncho-Cath) was facilitated by administration of succinylcholine. Correct positioning of the double lumen tube was confirmed using a paediatric fiberoptic bronchoscope. Anaesthesia was maintained with oxygen, isoflurane, nitrous oxide, fentanyl and pancuronium. Patients were mechanically ventilated with a tidal volume of 8 - 1 0 m l ' k g - l . Ventilation was adjusted to maintain the arterial carbon dioxide tens (...truncated)