← Back
A phosphorescent cyclometalated iridium(III) complex as mitochondria-targeted theranostic anticancer agent
Anesth Pain Med. 2018 June; 8(3):e74243.
doi: 10.5812/aapm.74243.
Research Article
Published online 2018 June 23.
The Relationship between Arterial and Central Venous Blood Gases
Values in Patients Undergoing Mechanical Ventilation after Cardiac
Surgery
Mohammadamin Valizad Hassanloei,1 Alireza Mahoori,1 Nazli Karami,1,* and Venus Sina1
1
Anesthesiology Department of Urmia University of Medical Sciences, Urmia, Iran
*
Corresponding author: Nazli Karami, Imam Khomeini Teaching Hospital, Ershad St. Urmia, Iran. Tel: +98-9122179344, Fax: +98-44 33468967, E-mail: nazlikarami@yahoo.com
Received 2018 May 03; Revised 2018 June 08; Accepted 2018 June 11.
Abstract
Background: The most straightforward method of ascertaining arterial PO2 , PCO2 , and other components of blood gas is to measure
them directly from a blood sample. In situations in which arterial puncture cannot be achieved or may be technically difficult, the
venous blood sample can be used.
Methods: In a prospective analytical study, 80 patients undergoing mechanical ventilation after open-heart surgery in the intensive care unit were evaluated. Simultaneous, matched arterial and central venous blood gas samples were taken from radial artery
line and central vein, respectively, when the ABG (arterial blood gases) assessment was needed. Arterial and central venous blood
samples were analyzed and data were expressed as mean and ± SD.
Results: The Pearson correlation coefficient for pH, PCO2 , HCO3 , and SatO2 was 0.898, 0.940, 0.840, and 0.567, respectively. There
was a significant correlation between arterial and central venous values of pH, PCO2 , and HCO3 (P < 0.0001). The mean difference
between arterial and central venous PCO2 was -2.44 ± 2.6 mmHg, and the mean venous pH value was only 0.021 ± 0.037 units lower
than the mean arterial value. In addition, the calculated mean bicarbonate concentration in venous blood was only about 0.06 ±
1.5 mEq.L higher than the mean arterial value.
Conclusions: The central venous PCO2 , pH, and HCO3 measured during mechanical ventilation in the intensive care unit approximate arterial values closely enough to permit the estimation of the adequacy of ventilation and acid-base status. The central venous
Sat O2 does not reliably parallel the arterial Sat O2 . In conclusion, venous blood sampling can potentially reduce the requirement
for ABG sampling in special situations.
Keywords: Arteries, Central Venous, Blood Gas, Mechanical Ventilation, Surgery
1. Background
Arterial blood gas (ABG) analysis is used to assess oxygenation, ventilation, and acid-base status (1-3). ABG measurement is the most frequently ordered test in intensive
care units. Therefore, taking an appropriate approach to
this clinical test is important for the optimal care of the
patients (4). The history of using and expanding arterial
blood gases analysis is attributed to Severinghaus and Astrup (5, 6). Arterial blood gas analysis is a standard method
for the assessment of oxygenation, ventilation, and the status of acids and bases in the body. The blood sample is
usually taken through puncturing the arteries or through
the implanted arterial catheter, which is accompanied by
some complications such as hematoma, aneurysm formation, thrombosis, embolism, and the possibility of needle
stick injury (7, 8).
When it is difficult or technically impossible, an alternative method is venous blood gas measurement. With
both methods, we can obtain pH, oxygen pressure, carbon dioxide pressure, oxygen saturation, and the level of
HCO3 . Venous blood sampling is done easily while doing
routine blood tests painlessly and without complications
of arterial blood sampling. Various studies have been conducted regarding the relationship between arterial and venous blood values. Undoubtedly, determining the average
of the difference in PCO2 , HCO3 , and pH of arterial and venous blood can be useful for managing the patients undergoing mechanical ventilation and for their weaning (9, 10).
A study in 2012 showed venous pH and HCO3 values had
an excellent correlation with the values of arterial samples
(11). On the other hand, a systematic review in 2014 showed
that the peripheral venous and arterial PCO2 were not com-
Copyright © 2018, Author(s). This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International License
(http://creativecommons.org/licenses/by-nc/4.0/) which permits copy and redistribute the material just in noncommercial usages, provided the original work is properly
cited
Valizad Hassanloei M et al.
7.500
7.400
Arterial pH
parable (12).
We assume that the central venous blood has a close relationship with arterial blood. The purpose of this study
was to examine this relationship in the patients who were
candidates for open-heart surgery. In this study, data gathering did not impose any extra procedure because in patients under open-heart surgery, central venous and arterial catheter preparations are necessary for monitoring.
2. Methods
3. Results
In this prospective analytic study, 80 ASA II - III patients,
who were transferred to the cardiac ICU to receive mechanical ventilation, were enrolled. Their arterial and central
venous blood samples were analyzed. The mean age was
62.18 ± 11.57 years; 56 (70%) patients were male and 24
(30%) were female. The mean arterial and central venous
blood pH values were 7.38 ± 0.03 and 7.36 ± 0.08, respectively, that were significantly correlated with each other (P
= 0.0001 and R = 0.898). The mean difference between central venous and arterial blood pH was 0.021 ± 0.037 and
95% CI (Confidence Interval) regarding the difference in pH
was 0.013 to 0.029. This indicates that the arterial pH was
about 0.013 to 0.029 unit higher than the central venous
pH (Figure 1 and Table 1).
Mean arterial and central venous PCO2 were 36.3 ± 8.7
mmHg and 39.8 ± 8.9 mmHg, respectively, which were significantly correlated with each other (P = 0.0001, R = 0.954).
2
7.200
R sq Linear = 0.806
7.100
7.100
7.200
7.300
7.400
7.500
Venouse pH
Figure 1. The correlation between arterial and central venous blood pH. Pearson correlation coefficient shows the intensity of correlation. If the correlation was perfect
(-1 or 1), in this case, all circles would be on a straight line.
The mean difference between arterial and central venous
PCO2 was -2.44 ± 2.6 mmHg and 95% CI regarding PCO2 difference was 1.84 to 3.03 mmHg. Thus, arterial PCO2 was approximately 1.84 to 3.03 mmHg less than the central venous
PCO2 (Figure 2 and Table 1).
70.00
60.00
50.00
PaCO2
This study was conducted with the approval of the scientific and ethical review boards of Urmia University of
Medical Sciences. 80 patients, who were admitted to the intensive care unit after cardiac surgery, were enrolled in our
prospective analytic study. All patients were ASA (American
society of anesthesiologists) physical status II - III according to the ASA’s classification system. Patients with ASA IV
or more, with fever, with unstable hemodynamics, pneumothorax, hemothorax, respiratory, and heart failure were
excluded from the study. In all patients, to check blood
gases, samples were taken from arterial and central venous
lines that were prepared in the operation room. Arterial
samples were taken with 2 cc syringes, containing 0.1 cc
heparin as an anticoagulant. First, air bubbles were removed and then were analyzed in 5 minutes. Simultaneously, central venous blood samples were taken and analyzed by using Nova biomedical model phox plus. All gathered data were statistically analyzed via chi-square and
independent t-tests, or Fisher’s exact and Mann-Whitney
U tests where needed by using SPSS version 20 software
(Chicago, IL).
7.300
40.00
30.00
R sq Linear = 0.91
20.00
20.00
30.00
40.00
50.00
60.00
70.00
PvCO2
Figure 2. The correlation between arterial and central venous blood PCO2 . Pearson
correlation coefficient shows the intensity of correlation. If the correlation was perfect (-1 or 1), in this case, all circles would be on a straight line.
Mean arterial and venous HCO3 was 22.1 ± 2.8 and 22.1
± 2.4 mEq per liter, respectively. Arterial and central venous HCO3 were significantly correlated with each other (P
= 0.0001, R = 0.840). The mean difference between arterial
and central venous HCO3 was -0.06 ± 1.5 mEq per liter and
Anesth Pain Med. 2018; 8(3):e74243.
Valizad Hassanloei M et al.
Table 1. Values of Arterial and Venous Blood Dataa
Analysis
Arterial Blood
Venous Blood
Difference
CI 95%
R
pH
7.38 ± 0..8
7.36 ± 0.08
0.021 ± 0.037
0.29 to 0.013
0.898
PCO2 , mmHg
36.3 ± 8.7
39.8 ± 8.9
-2.44 ± 2.6
1.84 to 3.03
0.940
HCO3 , mEq.L
22.1 ± 2.8
22.1 ± 2.4
-0.06 ± 1.5
-0.4 to 0.2
0.840
Sao2 , %
95.9 ± 4.7
89.4 ± 9.3
6.55 ± 7.76
4.8 to 8.2
0.567
a
Values are expressed as mean ± SD.
95% CI was -0.4 to 0.2 mEq/L in this regard (Figure 3 and Table 1).
27.50
HCO3a
25.00
22.50
20.00
R sq Linear = 0.705
R sq Linear = 0.705
17.50
18.00
20.00
22.00
24.00
26.00
28.00
HCO3v
Figure 3. The correlation between arterial and central venous blood HCO3 . Pearson
correlation coefficient shows the intensity of correlation. If the correlation was perfect (-1 or 1), in this case, all of the circles would be on a straight line.
When FiO2 was approximately 50%, the mean arterial
and central venous blood oxygen saturation (Scvo2 ) were
95.9 ± 4.7 and 89.4 ± 9.3, respectively. In this regard, the
relationship between these amounts was very poor (R =
0.567) (Table 1).
4. Discussion
ABG analysis is a standard method for determining
acid and basis status and adjusting mechanical ventilation
based on oxygen pressure, arterial blood carbon dioxide,
and pH. Arterial blood sampling as previously mentioned
may be followed by some complications and even may lead
to contaminated needles in the hands of staff and those
who care patients during blood sampling (1, 7, 8). Patients
who were candidates for open-heart surgery had a central
venous line and an arterial line. Our goal was to study the
relationship between pH, PO2 , PCO2 , and HCO3 between
central venous and arterial blood in these patients. We
hope if desired results are achieved, central venous blood
Anesth Pain Med. 2018; 8(3):e74243.
sampling will be used instead of arterial blood sampling
for arterial blood gas analysis. In this study, arterial and
central venous blood samples were correlated regarding
PCO2 , pH, and HCO3 and 95% Confidence Intervals were
very close and could be easily used in the results of ABG and
central VBG.
In 1961, Gombino compared capillary blood and
brachial arterial blood of patients who had referred for
pulmonary tests and reported that there was no significant difference between them (13). Kim et al. in 2012
in Korea determined peripheral venous and arterial
blood gas correlation in ICU patients and reported that
peripheral venous pH, PCO2 , and HCO3 may be used as
alternatives to their arterial equivalents in many clinical
contexts encountered in the ICU (14). Our study results
do not correlate with their studies. The difference of our
study is that the blood sample was taken from the central
vein and, as their studies showed, they could be taken
from the central VBG in cases where ABG is not available.
Nevertheless, we had a weak correlation between the mean
oxygen saturation of the arterial and central venous blood.
The monitoring of the mixed venous oxygen saturation
(SMVO2 ) has been used for delivery and consumption of
oxygen in critically ill patients. Most critically ill patients
have a central venous catheter and the central venous
oxygen saturation (SCVO2 ) has been used as an alternative
to the SMVO2 . A few studies were conducted for hemodynamic monitoring with SCVO2 , but their results in various
situations were different (2, 15, 16). Based on these data, the
surviving sepsis campaign has recommended achieving a
SMVO2 level of 65% or a SCVO2 level of 70% in septic shock
patients.
Various studies have been done to evaluate patients
under different conditions. For example, Kelly et al. (17)
studied the correlation between arterial and venous HCO3 in patients in emergency wards who had respiratory or
metabolic disorders and announced that measuring venous blood bicarbonate could be a good alternative for estimating arterial HCO3 . On the other hand, the correlation
between arterial and venous blood gases was studied in patients with acute exacerbations of chronic obstructive pulmonary disease (COPD), patients poisoned by tricyclic antidepressants, patients with acute respiratory failure un3
Valizad Hassanloei M et al.
dergoing mechanical ventilation, trauma patients undergoing mechanical ventilation, and children. Based on the
results, there is a correlation between arterial and venous
blood gases, and VBG can be used to evaluate and estimate
their values in ABG (18-21). None of the above studies, except Maliaoski et al. (22) study, used central venous blood
and none of them was done after open-heart surgery.
In the present study, the correlation between arterial
and central venous blood oxygen saturation was poor. In
the study of Yildizdas et al. (19), a similar correlation in this
regard was reported. The results of this study help us in
different situations by adding or subtracting the amounts
of central venous blood gases, and their values can be estimated in arterial blood. Nevertheless, it is not recommended for estimating Pvo2 or Sat O2 of venous blood. In
conclusion, our results showed a significant correlation
between PO2 , pH, and PCO2 of arterial and central venous
blood in patients undergoing open-heart surgery. Further
study was done on these patients because both arterial and
central venous lines are required for the process of anesthesia for cardiac surgery and no more procedures were
imposed on patients. In addition, patients were not punctured for taking arterial and venous blood and thus, the results of this study can be used in similar cases. In this study,
the correlation between Sat O2 of arterial and central venous blood (SCVO2 ) was poor. Perhaps it could be better to
use some devices such as pulse oximetry for the evaluation
of these indices and regarding other blood gases, the analysis of venous blood gases can be applied. In conclusion,
it seems that other similar studies can be done in patients
who have hemodynamic instability or long-term hypotension or even in patients undergoing cardiopulmonary resuscitation in order to examine the correlation rate in this
regard.
References
1. Chitilian HV, Kaczka D, Vidalmelo MF. Respiratory Monitoring. In:
Miller RD, editor. Miller’s Anesthesia. Philadelphia: Elsevier Saunders;
2015. p. 1541–79.
2. Bazzazi A, Hasanloei MA, Mahoori A, Gholamnejad M, Tarverdipour
H. Correlation between arterial blood gas analysis and outcome
in patients with severe head trauma. Ulus Travma Acil Cerrahi Derg.
2014;20(4):236–40. doi: 10.5505/tjtes.2014.57089. [PubMed: 25135016].
3. Singh V, Khatana S, Gupta P. Blood gas analysis for bedside diagnosis.
Natl J Maxillofac Surg. 2013;4(2):136–41. doi: 10.4103/0975-5950.127641.
[PubMed: 24665166]. [PubMed Central: PMC3961885].
4. Kaynar AM. Arterial blood gas interpretation. In: Vincent JL, editor.
Text book of critical care. Elsevier; 2017. p. 167–74.
5. Severinghaus JW, Astrup P, Murray JF. Blood gas analysis and critical
care medicine. Am J Respir Crit Care Med. 1998;157(4 Pt 2):S114–22. doi:
10.1164/ajrccm.157.4.nhlb1-9. [PubMed: 9563770].
6. Severinghaus JW. First electrodes for blood PO2 and PCO2 determination. J Appl Physiol (1985). 2004;97(5):1599–600. doi: 10.1152/classicessays.00021.2004. [PubMed: 15475549].
4
7. Mortensen JD. Clinical sequelae from arterial needle puncture,
cannulation, and incision. Circulation. 1967;35(6):1118–23. [PubMed:
6026202].
8. Kelly AM, Kyle E, McAlpine R. Venous pCO(2) and pH can be used to
screen for significant hypercarbia in emergency patients with acute
respiratory disease. J Emerg Med. 2002;22(1):15–9. [PubMed: 11809551].
9. Bilan N, Behbahan AG, Khosroshahi AJ. Validity of venous blood gas
analysis for diagnosis of acid-base imbalance in children admitted
to pediatric intensive care unit. World J Pediatr. 2008;4(2):114–7. doi:
10.1007/s12519-008-0022-x. [PubMed: 18661766].
10. Razi E, Moosavi GA. Comparison of arterial and venous blood gases
analysis in patients with exacerbation of chronic obstructive pulmonary disease. Saudi Med J. 2007;28(6):862–5. [PubMed: 17530100].
11. McCanny P, Bennett K, Staunton P, McMahon G. Venous vs arterial
blood gases in the assessment of patients presenting with an exacerbation of chronic obstructive pulmonary disease. Am J Emerg
Med. 2012;30(6):896–900. doi: 10.1016/j.ajem.2011.06.011. [PubMed:
21908141].
12. Byrne AL, Bennett M, Chatterji R, Symons R, Pace NL, Thomas PS. Peripheral venous and arterial blood gas analysis in adults: are they
comparable? A systematic review and meta-analysis. Respirology.
2014;19(2):168–75. doi: 10.1111/resp.12225. [PubMed: 24383789].
13. Gambino SR. Collection of Capillary Blood for Simultaneous Determinations of Arterial pH, CO2 Content, pCO2, And Oxygen Saturation.
Am J Clin Pathol. 1961;35(2_ts):175–83. doi: 10.1093/ajcp/35.2_ts.175.
14. Kim BR, Park SJ, Shin HS, Jung YS, Rim H. Correlation between peripheral venous and arterial blood gas measurements in patients
admitted to the intensive care unit: A single-center study. Kidney
Res Clin Pract. 2013;32(1):32–8. doi: 10.1016/j.krcp.2013.01.002. [PubMed:
26889435]. [PubMed Central: PMC4716110].
15. Futier E, Robin E, Jabaudon M, Guerin R, Petit A, Bazin JE, et al.
Central venous O(2) saturation and venous-to-arterial CO(2) difference as complementary tools for goal-directed therapy during highrisk surgery. Crit Care. 2010;14(5):R193. doi: 10.1186/cc9310. [PubMed:
21034476]. [PubMed Central: PMC3219300].
16. Habicher M, von Heymann C, Spies CD, Wernecke KD, Sander M. Central Venous-Arterial pCO2 Difference Identifies Microcirculatory Hypoperfusion in Cardiac Surgical Patients With Normal Central Venous Oxygen Saturation: A Retrospective Analysis. J Cardiothorac Vasc
Anesth. 2015;29(3):646–55. doi: 10.1053/j.jvca.2014.09.006. [PubMed:
25575410].
17. Kelly AM, McAlpine R, Kyle E. Agreement between bicarbonate measured on arterial and venous blood gases. Emerg Med Australas.
2004;16(5-6):407–9. doi: 10.1111/j.1742-6723.2004.00642.x. [PubMed:
15537402].
18. Eizadi-Mood N, Moein N, Saghaei M. Evaluation of relationship between arterial and venous blood gas values in the patients with tricyclic antidepressant poisoning. Clin Toxicol (Phila). 2005;43(5):357–
60. [PubMed: 16235510].
19. Yildizdas D, Yapicioglu H, Yilmaz HL, Sertdemir Y. Correlation
of simultaneously obtained capillary, venous, and arterial blood
gases of patients in a paediatric intensive care unit. Arch Dis
Child. 2004;89(2):176–80. [PubMed: 14736638]. [PubMed Central:
PMC1719810].
20. Chu YC, Chen CZ, Lee CH, Chen CW, Chang HY, Hsiue TR. Prediction
of arterial blood gas values from venous blood gas values in patients
with acute respiratory failure receiving mechanical ventilation. J Formos Med Assoc. 2003;102(8):539–43. [PubMed: 14569318].
21. Ak A, Ogun CO, Bayir A, Kayis SA, Koylu R. Prediction of arterial blood
gas values from venous blood gas values in patients with acute exacerbation of chronic obstructive pulmonary disease. Tohoku J Exp Med.
2006;210(4):285–90. [PubMed: 17146193].
22. Malinoski DJ, Todd SR, Slone S, Mullins RJ, Schreiber MA. Correlation of central venous and arterial blood gas measurements in mechanically ventilated trauma patients. Arch Surg. 2005;140(11):1122–5.
[PubMed: 16342377].
Anesth Pain Med. 2018; 8(3):e74243.