EFFECT OF TIME ON THE ARTERIAL BLOOD GAS ANALYSIS

The present study was done to find out whether there is any change occurring during delay in ABG analysis. In our study we first took baseline reading and from the remaining blood sample, stored at room temperature, repeat analysis were done from it after 30minute, 60 minute and after 90 minute and the change in result is compared with the baseline result. In our study if the sample is stored for more than 30 minutes at room temperature there is no significant changes occurs in pH, PCO2, but there is significant change in the PO2. The value of PO2 increase 20.23 mmHg if the sample is stored for more than 30 minutes at room temperature. In our study although the changes in pH, PCO2 are statistically greater in sample kept at room temperature, those changes do not appear to have major clinical significance until the time of analysis after arterial puncture exceeds 90 minutes. The PCO2 remained very stable with the different sampling methods. In our study there is no significance change found in Hco3 and O2sat if sample is stored for more than 30 minutes at room temperature.


INTRODUCTION:
An arterial blood gas (ABG) is a blood test that is performed using blood collected from an artery.The test is used to determine the pH of the blood, the partial pressure of carbon dioxide and oxygen and the bicarbonate level.This test is used to check how well your lungs are able to move oxygen into the blood and remove carbon dioxide from the blood.Carbon dioxide is produced during normal cell metabolism and is released into the blood stream where it is transported to the kidneys and lungs for excretion.CO 2 is transported through the blood as bicarbonate ,dissolved CO 2 , and carbonic acid.

PO 2 :
Oxygen is essential for cell and tissue metabolism in the body.The cardiopulmonary system is responsible for transporting oxygen to the cells.Oxygen transport involves four major steps: convection and diffusion from the air into the pulmonary circulation, combination of O 2 from the lungs with haemoglobin in red blood cells ,and finally the release into the tissues and utilization of O 2 cellular level.

Bicarbonate Ion (HCO 3 ) -:
Bicarbonate is the major buffer substance present in the body, and play a major role in maintaining the pH level in blood.It is present in large amount in the blood as a result of the dynamic state of CO 2 in the blood .The majority of CO 2 is transported as HCO 3 -.

Oxygen Saturation:
Oxygen saturation is a ratio, expressed as a percentage of the volume of oxygen carried to the maximum volume that can be carried.Knowledge of oxygen saturation is useful for predicting the amount of oxygen actually available for the tissues and can be used to determine the effectiveness of oxygen therapy.

MATERIAL AND METHOD
The study was carried out at Cardiac Centre of Shree Krishna Hospital, and Biochemistry department of Pramukh Swami Medical College Karamsad.The procedures followed were in accordance with the Clinical Research Ethics Committee of Pramukh Swami Medical College, Karamsad.The study include total 100 patients who was admitted in the MICU, SICU, CICU, PICU, NICU & TEC at the Shree Krishna Hospital Karamsd.
 Duration of the study: April 2010 to February 2011  Sample collection:

Arterial Blood:
An arterial blood gas (ABG) is a blood test that is performed using blood from an artery.It involves puncturing an artery with a thin needle and syringe and drawing a small volume of blood.The most common puncture site is the radial artery at the wrist.

Arterial puncture:
Blood is usually withdrawn from the radial artery as it is easy to palpate and has a good collateral supply.The patient's arm is placed palm-up on a flat surface, with the wrist at 45°.A towel may be placed under the wrist for support.

Calibration:
The 348 automatically calibrates at a specified interval.The interval is user selectable, and can be 30 or 40 minutes.A one point calibration is carried out at every interval.A full two point calibration is carried out at every fourth interval.Hct slope check is prompted at least every 25 days.

Calibration Gases:
Two gas standards are used to calibrate the pCo 2 and po 2 sensors.Gas1(cal) provides the calibration point for 1 & 2 point PCO 2 and PO 2 calibration.The cal gas cartridge contains 5.00% carbon dioxide & 12.00% oxygen balanced with nitrogen & is NBS traceable.

RESULT AND DISCUSSION:
The study comprises of 100 patients and all the cases were studied in department of Biochemistry, at CDL (Clinical biochemistry), Shree Krishna Hospital, Karamsad.

Statistical analysis:
Statistical analysis was performed using statistical software the mean value, the mean difference between groups, and the 95% confidence intervals were determined.A Bland and Altman plot was used to plot the mean difference between base line and after half hours, one hours, and after one and half hours of pH, PCO 2 , PO 2 , HCO - 3std O 2 sat..

Bland -Altman Analysis:
Bland-Altman Analysis was performed for pH, PCO 2 , PO 2 , HCO - 3std , and O 2 sat for base line verses half hour, base line verses one hour and baseline verses one and half hour.The bias and corresponding limits of agreement for different value of arterial blood gas are listed in Table 1.Total number of sample N=100   Total number of sample N=100  Total number of sample N=10  Total number of sample N=100

CONCLUSION
There is no significant change found in pH, PCO 2, HCO 3 -and in O 2 sat even if the estimation is get delay for 90 minutes.A significant change was found in PO 2 , If the sample was stored for more than 30 minutes at room temperature.Although the changes were not that significant which could change the management of the patient.

Figure 1 :
Figure 1: Performing an arterial puncture2.3Processing of the sample:Syringes should be kept and rolled between the two palms and gently inverted to mix the blood.Open the probe lever up to second position and insert the syringe.If syringe is inserted press: 1 No. key

Figure 3 :
Figure 3: BOX and WHISKER plot

Figure 4 :
Figure 4: pH half hour and pH baseline plot Figure-4 show the average of pH half hour and pH baseline and the pH half hour and baseline difference.the mean difference and SD are represented as the line between two doted line and doted line respectively.Mean value is -0.005 and standard deviation is 0.019.if the sample is stored for half hour pH is decrease 0.005 which is clinically not significant.

Figure 5 :
Figure 5: Distribution of pO 2 value at base line Figure-5 show distribution of pO 2 value at base line, after half hour, one hour and after one and half hour.The distribution of pO 2 is 30mmHg to 430mmHg.Analysis delay led to a gradual rise in measured PO 2 that became statistically and clinically significant.

Figure 6 :
Figure 6: Distribution of HCO 3 -value at base line Figure-6 show distribution of HCO 3 -value at base line, after half hour, one hour and after one and half hour.The distribution of HCO 3 -is 8mmol/L to 40mmol/L.

Figure 7 :
Figure 7: Distribution of O 2 sat value at base line

Table 6 :
Descriptive Statistics for O 2 sat