Introduction

In ICU, the continuous monitoring of CO₂ and pH of the patient who is under mechanical ventilation is as important as SPO₂ monitoring. Nowadays SPO₂ can be monitored by non invasive method in a safe and practical manner; however machines which can measure non invasive CO₂ are being tried and hence being further improved. Furthermore, same method and machine is under trial to measure pH. In our study, we compared practicality and trustworthiness of invasive arterial blood gas (PCO₂, SatO₂), noninvasive ventilator monitoring (ETCO₂, SPO₂, PR), transcutaneous monitoring (PtcCO₂, SPO₂, PR) and pulse oxymeter (SPO₂, PR) on the patients whom we applied mechanical ventilation in ICU.

Methods

The study included 100 synchronous measures including arterial blood gas, ventilator monitor measures, transcutaneous monitor measures and patient side monitor measures of patients whom we applied mechanical ventilation in ICU due to various reasons. Arterial blood CO₂ pressure (PCO₂) and arterial blood O₂ saturation (SatO₂) in arterial blood gas are measured with Chiron/Diagnostic 865. End tidal CO₂ (ETCO₂), peripheral O₂ saturation [SPO2(V)], peripheral pulse [PR(V)] are measured with Drager Evita 4 (Lubeck,Germany) ventilator monitor. Transcutaneous CO₂ (PtcCO₂), peripheral O₂ saturation [SPO2(T)], peripheral pulse [PR(T)] are measured with Sen Tec Digital Monitor System (V-Sign). Peripheral O₂ saturation [SPO2(M)] and peripheral pulse [PR(M)] are measured with Drager Infinity Kappa (Germany) monitor saturation probe. All of these are measured and recorded synchronously and compared with each other.

Before starting the measures, the required calibration of transcutaneous monitor and ventilator is made. In all the measures, the probe of transcutaneous machine is fixed to the right ear lobe of the patient with the probe’s clip. Before the measures, it’s ensured that the ear lobe is clean. Difficulties such as the need for frequent calibration, re-fixation of the probe’s position, and the occurrence of unexplainable errors at unexpected times are encountered. During the evaluation of the findings of the study, the SPPS for Windows 10.0 software is used for statistical analysis. During the evaluation of the data from the study, Pearson correlation analysis is used to calculate the correlation of the quantitative data along with the descriptive statistical methods (average, standard deviation). Conclusions are evaluated within the 95% confidence interval and at p<0.05.

Results

A positive and very good level of statistically significant correlation is found between the values of arterial blood O₂ saturation (SatO₂), peripheral O₂ saturation with ventilator monitor [SPO2(V)], peripheral O₂ saturation with Transcutaneous monitor [SPO₂(T)], peripheral O₂ saturation with patient side monitor saturation probe. (p<0.01) (Table 1)

Figure 1

Table 1: SPO(V), SPO(M), SPO(T) ve SatO corelations

A positive and very good level of statistically significant correlation is found between the measured values of ventilator monitor and peripheral pulse [PR(V)], transcutaneous monitor and peripheral pulse [PR(T)], patient side monitor probe and peripheral pulse [PR(M)] (p<0.01) (Table 2)

Figure 2

Table 2: PR(V), PR(M) ve PR(T) corelations

No statistically significant correlation is found between ETCO₂ and PtcCO₂ as well as ETCO₂ and blood gas PCO₂ measures. (p>0.05), (Table 3).

Figure 3

Table 3: ETCO, PtcCO ve PCO corelations

A positive and good level of statistically significant correlation is found between PtcCO₂ and blood gas PCO₂ measures. (p<0.01) (Graphic 1)

Figure 4

Graphic 1: PtcCO ile PCO corelation

Discussion

For the patients who are under mechanical ventilation in ICU as well as for the ones who are under anesthesia, the O₂ and CO₂ monitoring are the “must be performed” ones. Although monitoring with the arterial blood gas is trustable, because of the fact that it’s invasive and does not allow continuous monitoring, it is unpractical to apply. In this case, the importance of continuous noninvasive monitoring is once again highlighted. In this subject, SPO₂ monitoring with saturation probes and ETCO₂ monitoring with gas sample taken from the expiratory branch of the ventilator circuit are the methods that have been in use for a long time. It’s also a fact that ETCO₂ does not always move in parallel with the arterial CO₂. Also our findings did not find any correlation between ETCO₂ and arterial CO₂. Because of these reasons, search for non invasive CO₂ measure methods is continuing. In the recent years, due to ease of use, monitors tracking transcutaneous PtcCO₂ monitoring and SPO₂ through non invasive ear probe have started to be utilized (₁,₂,₃).

McCormack et al. (₂) investigated the clinical utility of transcutaneous carbon dioxide monitoring in the postoperative period, and quantified the effects of different perioperative analgesic regimens on postoperative respiratory function. They found that; the transcutaneous capnometer successfully recorded data for 98 % of the total time when it was applied to patients.

Casati A et al. (₃) compared end tidal carbon dioxide (ETCO₂) with transcutaneous CO₂ measurements during mechanical ventilation in elderly patients. They reported that; transcutaneous monitoring of CO₂ partial pressure gave a more accurate estimation of arterial CO₂ partial pressure than end tidal carbon dioxide (ETCO₂) did.

Dullenkopf et al. (₄) compared SPO₂ with ETCO₂ from patient side monitor and SPO₂ with PtcCO₂ from transcutaneous monitor ear probe with 111 blood gas sample taken from 60 children patients who had anesthesia. As a result, they found that transcutaneous measures were correlated with arterial blood gas and other monitor measures. They reported that transcutaneous measures can be used in anesthesia applications.

Griffin et al. (₅) compared arterial blood gas PaCO₂ measures with ETCO₂ and PtcCO₂ measures in 30 morbid obese patients who had gastric bypass operation and found a better correlation between PtcCO₂ and PaCO₂ than ETCO₂. As a result of our study, we found the same significant correlation between PtcCO₂ and PaCO₂.

Oshibushi et al. (₆) found a correlation between PtcCO₂ and ETCO₂ in 26 patients who had thorax surgery.

Nelson et al. (₇) showed that they detected hypoventilation, which they could not detect prior by using only SPO₂ monitoring, by using transcutaneous SPO₂ / PtcCO₂ monitor in patients whom they applied sedation during ERCP. Tatevossian et al. (₈) utilized SPO₂ PtcCO₂ monitor during early resuscitation stage of trauma patients who had ARDS. They reported that high PtcCO₂ and low SPO₂ are important as early indicators of poor tissue perfusion in patients who died at that stage and that it can be used in daily routine.

Janssens et al. (₉) found correlation between blood gas measures and monitor measures in a study in which they evaluated trustworthiness and ease of use of the transcutaneous SPO₂ / PtcCO₂ monitor. They reported that they did not have problems with the probe they fixed to the same ear for 8 hours and had no skin burns. We also did not have any skin burns during our study but we had unwanted difficulties such as no measuring or incorrect measuring. We overcame these difficulties with simple methods such as recalibration or changing the place of clip on the ear. These methods which seem simple were discouraging and time consuming.

As a conclusion of our study, as the PtcCO₂ values which were measured with transcutaneous SPO₂ / PtcCO₂ monitor were fully correlated with blood gas CO₂ values, PtcCO₂ values are found to be superior to ETCO₂ values.

Compared to blood gas monitoring, transcutaneous CO₂ monitoring is evaluated to be more comfortable for the patient and more practical for the doctor since it’s non invasive and allows continuous monitoring. However the difficulties that the machine brings to users such as probe maintenance, sensor sensitivity, need for frequent calibration and need for extensive maintenance requirements in long term usage can be underestimated. It’s a fact that once technical difficulties are overcame, this method will be an essential monitoring device for ICUs.

Correspondence to

GULDEM TURAN M.D. Barbaros M. Ihlamur S. Uphill Court B 5 D: 2 Atasehir - Istanbul TURKEY Post Code: 34746 Tel : +900 216 4144545-1499 Fax: +900 216 3360565 E-mail: gturanmd@yahoo.com