[Development of a method of continuous monitoring of spontaneous respiration in the postoperative phase. 1. Normal values for cutaneous pO2- and pCO2-partial pressure together with pulse oximetry determined oxygen saturation in healthy young volunteers]

Abstract

Methods: Twenty-eight healthy volunteers of both sexes (14 male, 14 female, age 31 +/- 7 years, weight 70 +/- 12 kg) breathing room air were monitored for cutaneous partial pressures of oxygen and carbon dioxide (pctO2, pctCO2) and partial oxygen saturation (psO2) as determined by pulse oximetry. Data triplets were collected and stored by a personal computer at 30-s intervals during a 4-h resting period to establish a confidence range for the devices in use (TCM 3 with a combination electrode E 5270, and Pulse Oximeter, Radiometer). This data range was intended to be used in later noninvasive, continuous respiratory studies with postoperative patients. Means, standard deviations, and ranges were calculated for individual data and data pooled from 15-min intervals. Data distribution over time was calculated for 30-min intervals.

Results: Contrary to the saturation data delivered by pulse oximetry, the pctO2 and pctCO2 readings needed about 15 min to stabilize. The mean +/- SD of a total of 12,600 pctO2 measurements (77.2 +/- 10.9 mmHg) could not simply be compared with arterial normal values, whereas the pctCO2 measurements (39.9 +/- 3.6 mmHg) fit well with arterial data from the literature. Interestingly, pctCO2 values in unmedicated healthy adults were not uniformly distributed, suggesting individual differences in either skin permeability of central regulation of respiration. Additionally, the pctO2 readings were characterized by serious inter-subject variability, which confirms earlier studies that pctO2 is not suitable for routine monitoring procedures in adults, the mean +/- SD of a total of 4500 psO2 measurements was 94.9 +/- 1.6%. A statistically significant correlation was found between pctO2 and psO2 (r = 0.358). Cutaneous carbon dioxide readings of greater than 50 mmHg were observed in only 0.06% of all 12,600 data sets (maximum 51.3 mmHg; 28 volunteers), desaturations (less than 90%) in only 0.24% of all 4,500 saturation measurements (minimum 86%; 10 volunteers).

Discussion and conclusion: Monitoring of spontaneous respiration in the recovery room is regarded as essential to prevent serious complications resulting from surgery and anesthesia. This has become particularly true with newer analgesic techniques like spinal opiates or patient-controlled analgesia. Since minor degrees of opiate-induced respiratory depression are easily influenced by external stimulation, it is mandatory that any monitoring of spontaneous respiration must be nonstimulant, and prefereably noninvasive. The present communication is the first of a series of investigations to develop of monitoring technique for postoperative patients. Because normal values for the parameters studied are either lacking or dependent on the monitoring devices in use, the present paper defined the respective data ranges. It is concluded that pulse oximetry and pctCO2 measurement are both useful and sensitive for continuous, non-invasive respiratory monitoring in adults, whereas pctO2 measurements are of lesser value. Results in volunteers treated with opiates and postoperative patients under patient-controlled analgesia using the above mentioned equipment will be reported in following publications.