The Relationship between PaCO2 - PETCO2 Difference and SpO2 in Patients with Congenital Cyanotic Heart Disease / 대한마취과학회지

BACKGROUND: In neonates and infants with congenital cyanotic heart disease, venous blood, rich in CO2 and poor in O2, is mixed with pulmonary venous blood at left heart. As a consequence, any given degree of decreases in SpO2 is accompanied by obligatory increase in PaCO2 - PETCO2 difference. This study was designed to evaluate these relationship in 20 pediatric patients. METHODS: After endotracheal intubation with high dose fentanyl and pancuroniun, PETCO2 was measured by capnometer (side stream, sample gas flow rate of 200 ml/min; sampling site at elbow connector area) and SpO2 probe was attached at toe or finger. Observations were made 4 or 5 times before initiation of CPB. Ventilation was controlled by pressure type ventilator, partial rebreathing circuit at frequency of 25-35 breaths/min, an inspiratory time of 25% with an end-inspiratory pause of 10%, and peak airway pressure of 20 +/- 2 cmH2O. RESULT : Mean values of PaCO2 - PETCO2 difference were increased linely with decreases in SpO2. The regression equation is mean (PaCO2 - PETCO2) (mmHg) = 23.9 0.22 mean SpO2 (r= 0.51, p=0.028) CONCLUSIONS: The relationship between PaCO2 - PETCO2 was found to agree with that predicted by theory confirming that in congenital cyanotic heart patients, PaCO2 increases by 2-5 mmHg for every 10% reduction in SpO2. This relationship may be useful when attemping to estimate PaCO2 from PETCO2 in the management of congenital cyanotic heart patients.

Monitoring of Tracheal CO2 Tension during High Frequency Jet Ventilation for Laryngomicrosurgery / 대한마취과학회지

BACKGROUND: The monitoring of end-tidal CO2 tension (PETCO2) during high frequency jet ventilation (HFJV) has been unsatisfactory because of a small tidal volume and slow response time of CO2 analyser, although several authors have reported strategies of successful PETCO2 measurement during HFJV. The aim of this study was to assess the validity of tracheal CO2 tension (PtCO2) as a PaCO2 during HFJV. METHODS: We studied 24 patients undergoing laryngomicrosurgery during HFJV (rates: 100/min; I:E= 0.2; driving pressure: 0.25-0.35 MPa) through a 12 Fr. polyethylene injector placed 6-7 cm below the vocal cord. A gas sampling line was placed longitudinally against the injector and they were wrapped with aluminum foil. Continuous capnography was recorded during 20 minutes of HFJV. Every 5 minutes of HFJV, PtCO2 was obtained from the plateau value of CO2 wave after the stopping of JV and arterial blood gas analysis was done at 20 minutes of HFJV comparing PaCO2 to PtCO2. A Pearson's product moment correlation and regression analysis between PtCO2 and PaCO2 and the agreement between the two methods using Bland-Altman method were assessed. RESULTS: A regression analysis (R2=0.928) and a Pearson's product moment correlation (r=0.965, P<0.001) indicated a strong correlation of PtCO2 and PaCO2 during HFJV. The difference against a mean scatter diagram showed a relative good agreement between the two method (mean difference: 1.58 (SD 2.22) mmHg; limit of agreement: 2.86 and -6.02). CONCLUSIONS: PtCO2 obtained from a plateau of CO2 wave on capnography after interruption of HFJV can accurately reflect PaCO2 during HFJV in relative.

The Differences between PETCO2 Values According to the Measuring Sites / 대한마취과학회지

Backgrounds: End-tidal CO2 (PETCO2) monitoring is becoming one of essential respiratory monitoring systems during anesthesia. In this study, the differences between PETCO2 values measured from the 4 different sites were evaluated. METHODS: Healthy adult patients were studied (n=30). During N2O-O2-Enflurane anesthesia, PETCO2 was measured from the 4 possible monitoring sites, 3 from the breathing circuit and 1 from the monitoring lumen site of the specialized endotracheal tube connected to the distal endotracheal tube. After intubation, repeated PETCO2 measurements at 15mins (T15), 30mins (T30), 60mins (T60) and 90mins (T90) and ABGAs at T30 and T90 were done and the differences between arterial Pco2 and PETCO2 (P (a-ET)CO2) were calculated. In addition, to study the effect of changing fresh gas flow rate upon the PETCO2 values, PETCO2 measurements were done by varying the total gas flow rate from 4 L/min to 2 L/min to 6 L/min at T60. RESULTS: The Y-connector area (PETCO2- (1)) showed the lowest PETCO2 value, the elbow connector (PETCO2- (2)) and heat-moisture exchanger (PETCO2- (3)) areas, the intermediate, and the distal endotracheal site (PETCO2- (4)), the highest. The difference between the most proximal and distal sites was varied 2.4 to 3.0 mmHg and not statistically significant. PETCO2 values showed significant decreasing trend with time at each site (p<0.05). At T30 and T90, PaCO2 was not significantly different from PETCO2- (4) but significantly different from PETCO2- (1), (2), (3). The effect of changing fresh gas flow rate upon the amount of PETCO2 values of the different sites was not statistically significant. CONCLUSION: PaCO2 was significantly different from PETCO2 values measured from the breathing circuit sites but not significantly different from those measured from the distal endotracheal tube. It might be said that we have to pay special attention to these differences if we want to estimate real P (a-ET)CO2 difference.

Difference between Arterial Carbon Dioxide Tension and End-tidal Carbon Dioxide Tension in Neurosurgical Patients during Craniotomy / 대한마취과학회지

BACKGROUND: During craniotomy operations, the PaCO2 has therapeutic implications because hyperventilation is often used to lower intracranial pressure. PETCO2 is often used as an estimate of PaCO2, with the assumption that P(a-ET)CO2 is relatively constant. To clarify the relationship between PaCO2 and PETCO2, sixty patients undergoing elective craniotomies were studied. METHODS: Arterial blood gases were measured from 30 minutes after endotracheal intubation to skin closure at an interval of 30 minutes in thirty patients, and at random interval in another thirty patients. PETCO2 was simultaneously determined with infrared capnography(Datex AS/3TM, Filand). RESULTS: The PaCO2 was 31.7+/-3.0 mmHg and PETCO2, 26.3+/-2.5 mmHg, with a P(a-ET)CO2 of 5.5+/-2.7 mmHg(n = 431, range between 0-13.5). There was a significant positive correlation between PaCO2 and PETCO2(r = 0.537, slope = 0.440, P<0.001) and between P(a-ET)CO2 and PaCO2(r = 0.625, slope = 0.555, P<0.001). Although changes in the pooled data of PaCO2 and PETCO2 correlated statistically, comparisons in 43 of 60(71.6%) individuals were not correlated. On comparisons of subsequent measurements, 17.0% of changes in PaCO2 and PETCO2 were in opposite directions. P(a-ET)CO2 had a tendency to increase with time during surgery(slope = 0.0082), but there was no statistically significant difference between the measurements. CONCLUSION: The PETCO2 measured with infrared capnography does not provide a stable reflection of PaCO2 in many patients undergoing craniotomy. Therefore, we concluded that capnography must be used in conjuction with arterial blood gas measurements for monitoring the respiratory acid-base status of mechanically ventilated neurosurgical patients undergoing craniotomy.