How to Draw Vbg From Central Line TUTORIAL

Clin J Am Soc Nephrol. 2010 Mar; five(3): 390–394.

Original Manufactures

Agreement between Central Venous and Arterial Blood Gas Measurements in the Intensive Care Unit

Richard Treger

^*Departments of Nephrology and Emergency Medicine, Veterans Affairs Greater Los Angeles Healthcare System, Los Angeles, California;

^†David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California

Shahriar Pirouz

^‡Internal Medicine, and

^†David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California

Nader Kamangar

^§Pulmonary/Critical Care, Olive View-UCLA Medical Middle, Sylmar, California; and

^†David Geffen Schoolhouse of Medicine, University of California, Los Angeles, Los Angeles, California

Dalila Corry

Departments of ^‖Nephrology,

^†David Geffen Schoolhouse of Medicine, Academy of California, Los Angeles, Los Angeles, California

Received 2009 Jan 17; Accepted 2009 Nov 17.

Abstract

Background and objectives: Venous claret gas (VBG) assay is a safer procedure than arterial blood gas (ABG) assay and may be an culling for determining acid-base status. The objective of this written report was to examine the agreement betwixt ABG and primal VBG samples for all normally used parameters in a medical intensive care unit (ICU) population.

Design, setting, participants, & measurements: We performed a single-middle, prospective trial to assess the agreement between arterial and central VBG measurements in a medical ICU. Developed patients who were admitted to the ICU and required both a central venous line and an arterial line were enrolled. When an ABG was performed, a key venous sample was obtained to examine the understanding amongst the pH, Pco ₂, and bicarbonate. Data comparing cardinal and peripheral VBG values were also obtained.

Results: The mean arterial minus venous divergence for pH, Pco ₂, and bicarbonate was 0.027, −3.8, and −0.lxxx, respectively. Bland-Altman plots for agreement of pH, Pco ₂, and bicarbonate showed 95% limits of agreement of −0.028 to 0.081, −12.three to 4.eight, and −iv.0 to 2.iv, respectively. Regression equations were derived to predict arterial values from venous values as follows: Arterial pH = −0.307 + 1.05 × venous pH, arterial Pco ₂ = 0.805 + 0.936 × venous Pco _ii, and arterial bicarbonate = 0.513 + 0.945 × venous bicarbonate. The mean central minus peripheral differences for pH, Pco ₂, and bicarbonate were non clinically of import.

Conclusions: Peripheral or fundamental venous pH, Pco ₂, and bicarbonate tin can replace their arterial equivalents in many clinical contexts encountered in the ICU.

Arterial blood gas (ABG) analysis is a normally performed procedure that is often used to decide the acid-base and respiratory status of critical patients; however, this examination tin can result in patient discomfort too every bit complications such as arterial injury, thrombosis or embolization, hematoma, aneurysm germination, and reflex sympathetic dystrophy (1–3). In addition, the process has a small just observable risk for needlestick injury to wellness care workers. Venous claret gas (VBG) analysis requires fewer punctures, is a relatively safer procedure for both the patient and the health intendance provider, and may be an alternative to ABG analysis for acrid-base status. Although a few studies accept expressed reservations regarding the accuracy of VBG values (iv–6), at that place is emerging evidence to suggest that there is agreement between ABG and VBG values (vii–15). To our knowledge, no previous report has examined the agreement among all of the commonly used parameters in arterial and central VBG samples in a diverse population of medical intensive care unit (ICU) patients. As well, no previous study has specifically obtained multiple paired ABG and VBG samples from each patient throughout their ICU class to evaluate whether the agreement between ABG and VBG values is acceptable throughout the dynamic acrid-base and respiratory weather condition encountered in the ICU. The principal objective of this study was to examine the agreement betwixt ABG and central VBG samples for all commonly used parameters (pH, Pco _two, and bicarbonate) in a pathologically various ICU patient population, specifically analyzing multiple paired arterial and venous samples from each patient. In addition, a secondary objective was to compare central and peripheral VBG values with respect to pH, Pco _two, and bicarbonate.

Materials and Methods

Nosotros performed a single-center, prospective trial to assess the understanding between arterial and central VBG measurements. This study was conducted in the medical ICU at Olive View-UCLA Medical Eye, a 377-bed county hospital that serves primarily low-income and indigent patients. All developed patients who were admitted to the ICU and had been determined by their treating clinicians to crave both a central venous line and an arterial line were enrolled in the study. Given that only minimal blood was required to perform this study, a waiver of consent was granted from our review board. When an ABG was accounted to be necessary as part of ICU management, a primal venous sample was also obtained within two minutes. All of the samples were analyzed using the same Bayer Rapid Signal 405 blood gas analyzer every bit apace as possible. A maximum of x paired ABG-VBG samples were obtained per patient to foreclose a unmarried patient from dominating the data set up. Additional data collected on a standardized information drove form included chief diagnosis, intubation status, use of inotropic agents, and hypotension (defined as a systolic BP <90 mmHg). Data comparing primal and peripheral VBG values were also obtained. Paired central and peripheral venous samples were drawn inside 2 minutes of i another in ICU patients with both central venous lines and peripheral intravenous lines already in identify.

Statistical Analysis

The Bland-Altman method was used to assess agreement between arterial (A) and primal venous (5) measurements of pH, Pco ₂, and bicarbonate. The A-V departure versus the average value ([A+V]/2) was plotted. Means, SDs, and 95% prediction intervals (limits of understanding) of the A-Five differences are reported as well as the Pearson correlation between A-Five and (A+Five)/ii. If there is no tendency in the A-V differences, and so this correlation should be 0. In improver, Pearson correlations betwixt the arterial and primal venous values are reported and linear regression was used to establish equations for interpretation of arterial values from central venous values. Considering there were multiple A and 5 measurements for a single patient, components of variance computations were carried out to determine whether there was between-patient SD heterogeneity, and a random slope and intercept model was used to determine whether there was between-patient heterogeneity in the regression analyses. A sample size of 40 patients was based on estimating the central venous minus arterial differences (lack of agreement) and their SD (SD_e) to within ±23% with 95% conviction for Pco ₂, bicarbonate, or pH differences.

Results

The study involved 40 patients with a total of 221 paired ABG-VBG samples. Thirty-one paired samples were excluded (xiii samples considering of clerical errors, 16 samples because of being run on different blood gas analyzers, and 2 samples because the arterial and venous samples were drawn >ii minutes apart); therefore, 190 paired samples were included in the assay. Table 1 shows the patient characteristics. The patient population consisted of roughly equal numbers of men and women, with a mean ± SD age of 57 ± 16 years. The most common presenting diagnosis was sepsis (72.5%), although a number of other weather condition that oftentimes are encountered in the ICU were present. The vast majority of enrolled patients were intubated, hypotensive, and on inotropic agents. None of the patients in the study were receiving bicarbonate.

Tabular array ane.

Patient characteristics

Characteristic	Value
Age (years; mean ± SD)	57 ± xvi
Gender (male person/female; due north [%])	22 (55)/xviii (45)
Intubated (n/N [%])	36/40 (90)
Hypotensive (n/N [%])	36/40 (90)
Inotropic agent utilise (n/Northward [%])	35/40 (87.5)
Primary diagnosis (%)
sepsis	72.5
interstitial lung illness	2.five
altered mental status	2.5
upper gastrointestinal bleed	2.5
renal failure	ii.5
congestive middle failure	2.5
pulmonary tuberculosis	2.5
pneumocystis pneumonia	2.5
pancreatitis	two.5
diabetic ketoacidosis	ii.5
cor pulmonale	two.5
respiratory failure of unclear cause	ii.5

Arterial versus central venous intercept and gradient homogeneity tests for pH, Pco ₂, and bicarbonate had P values of 0.995, 0.122, and 0.497, respectively (information non shown). Thus, all 190 observations could exist combined (see the Word section).

The arterial pH values ranged from 6.73 to seven.63, the arterial Pco ₂ values ranged from 16 to 79 mmHg, and arterial bicarbonate values ranged from 2 to 45 mEq/L. Table 2 shows the mean values and SDs for arterial and key venous pH, Pco ₂, and bicarbonate, as well as for the arterial minus central venous difference of these parameters.

Table 2.

Arterial and primal venous blood gas values (n = 190)

Parameter	ABG (Mean ± SD)	VBG (Mean ± SD)	A-V Difference (Mean ± SD) a
pH	7.370 ± 0.138	vii.340 ± 0.134	0.027 ± 0.027
Pco 2 (mmHg)	38.four ± 12.4	42.3 ± 12.6	−three.eight ± 4.iii
Bicarbonate (mEq/50)	22.40 ± 7.threescore	23.20 ± seven.eighty	−0.lxxx ± 1.58

Figures 1, ​ two, and ​ 3 show the Bland-Altman plots for pH, Pco ₂, and bicarbonate with their 95% limits of agreement (95% prediction intervals), respectively. Figures 4, ​ 5, and ​ half-dozen bear witness the correlation betwixt central venous and arterial blood gas values for pH, Pco _ii, and bicarbonate, respectively. Regression equations were derived to predict arterial values from cardinal venous values every bit follows:

• Arterial pH = −0.307 + 1.05 × venous pH (R ² = 0.945)

• Arterial Pco _two = 0.805 + 0.936 × venous Pco ₂ (R ^two = 0.883)

• Arterial bicarbonate = 0.513 + 0.945 × venous bicarbonate (R ² = 0.950)

Banal-Altman plot of arterial and central venous blood pH showing the regression line (solid line) and the 95% limits of agreement of −0.028 to 0.081 (dotted lines) for the A-V difference. r = 0.296, R ^two = 0.088.

Bland-Altman plot of arterial and primal venous blood Pco _ii showing the regression line (solid line) and the 95% limits of agreement of −12.3 to four.8 mmHg (dotted lines) for the A-V departure. r = −0.01, R ² = 0.0001.

Bland-Altman plot of arterial and central venous claret HCO₃ showing the regression line (solid line) and the 95% limits of agreement of −4.0 to 2.four mEq/L (dotted lines) for the A-V difference. r = −0.136, R ^two = 0.018.

Correlation between fundamental venous and arterial blood gas values for pH. R ^two = 0.95.

Correlation between central venous and arterial claret gas values for Pco _two. R ² = 0.88.

Correlation between primal venous and arterial blood gas values for HCO₃. R ² = 0.95.

Multivariate regression was used to establish whether using all iii of the central venous variables (pH, Pco ₂, and bicarbonate) in a unmarried equation tin be used to predict amend the arterial values for pH, Pco ₂, and bicarbonate. The multivariate regression equations are as follows:

• Arterial pH = 0.545 + 0.0288 × venous pH − 0.00139 × venous Pco ₂ + 0.00269 × venous HCO₃ (R ⁱⁱ = 0.948)

• Arterial Pco ₂ = −120.1 + sixteen.498 × venous pH + 1.193 × venous Pco ₂ −0.553 × venous HCO₃ (R ⁱⁱ = 0.895)

• Arterial HCO₃ = −23.666 + 3.268 × venous pH + 0.053 × venous Pco ₂ + 0.855 × venous HCO₃ (R ^two = 0.951)

A total of xiv paired samples comparing central and peripheral VBG values were drawn from xiv patients (ane paired sample per patient). For pH, the mean central venous value was 7.34 and the mean peripheral venous value was seven.34 with a mean central minus peripheral difference of −0.001 (−0.01%). For Pco ₂, the mean central venous value was 37.52 mmHg and the mean peripheral venous value was 36.80 mmHg with a mean central minus peripheral difference of 0.72 mmHg (1.94%). For bicarbonate, the mean cardinal venous value was 21.18 mEq/L and the hateful peripheral venous value was 20.87 mEq/L with a mean central minus peripheral departure of 0.31 mEq/Fifty (ane.46%).

Discussion

VBG analysis conspicuously does not replace ABG analysis in determining exact Po ₂ condition, and arterial puncture may still be required for invasive arterial BP monitoring, only given the well-accepted accuracy of pulse oximetry, VBG analysis may exist a safer culling to ABG analysis for determining acid-base status, reducing the need for frequent invasive arterial sampling. A number of studies take suggested that there is agreement betwixt ABG and VBG values, although virtually of the previous studies were express past specific patient group samples (e.one thousand., patients with diabetic ketoacidosis), assay of only one or some parameters rather than all commonly used parameters (e.g., pH, Pco _ii, and bicarbonate), or test of merely one ABG and VBG sample per patient (seven–15). A few authors even expressed doubts about the use of VBG values in lieu of arterial values (4–vi). The aim of this study was to investigate the agreement between ABG and central VBG samples for all ordinarily used parameters (pH, Pco ₂, and bicarbonate) in a pathologically diverse ICU patient population.

Although the presenting diagnosis for patients in the study was predominantly sepsis, at that place was a range of other pathophysiology present. This patient population seems to be fairly representative of the disease processes encountered in many medical ICUs.

No previous study has assessed whether all patients share a mutual relationship betwixt arterial and key venous pH, Pco _two, and bicarbonate. Factors that are intrinsic to each individual patient, as well every bit their differing pathophysiologic states, could result in differential CO₂ unloading at the tissue level; therefore, it cannot be assumed a priori that all patients have a common relationship between ABG and VBG values. Obtaining multiple paired arterial and primal venous samples from each patient allowed us to perform homogeneity tests, which revealed that arterial versus venous intercept and slope for pH, Pco _ii, and bicarbonate had P values of 0.995, 0.122, and 0.497, respectively; therefore, in that location is a common relationship between arterial and fundamental venous pH, Pco ₂, and bicarbonate for all patients, allowing all 190 observations to be pooled for the remainder of the assay.

There is first-class understanding between arterial and fundamental venous values for pH and bicarbonate, which is consistent with the results of other studies in the literature (four–xi,xiii–xv). In regard to pH, the mean arterial minus central venous departure was 0.027 (SD 0.027) with a 95% limits of agreement of −0.028 to 0.081 (Figure 1). Previous studies have shown a mean arterial minus venous difference for pH ranging from −0.04 to 0.05 (4–6,8–xi,thirteen–15). With respect to bicarbonate, the mean arterial minus central venous departure was −0.eighty (SD one.58) with a 95% limits of agreement of −four.0 to ii.iv (Figure 3). Previous studies have shown a mean arterial minus venous difference for bicarbonate ranging from −ane.88 to −0.52 (5–seven,ten,11,13–15). There is acceptable agreement between arterial and key venous values for Pco _two; the hateful arterial minus cardinal venous divergence was −three.eight (SD 4.3) with a 95% limits of understanding of −12.3 to 4.eight (Effigy 2). Previous literature showed a mean arterial minus venous difference for Pco ₂ ranging from −half-dozen.6 to −3.0 (4–half dozen,fourteen,15). Comparing the results of our study with other studies that also reported 95% limits of agreement, the arterial and primal venous values for Pco _ii in our study showed better agreement than the study by Kelly et al. (five), which demonstrated a mean arterial minus venous difference of −5.viii with a 95% limits of agreement of −8.viii to xx.5; however, there was less agreement in our report compared with studies past Malinoski et al. (4), which showed a mean arterial minus venous deviation of −iv.36 with a 95% limits of agreement of −ii.20 to 10.ninety and Malatesha et al. (15), which revealed a mean arterial minus venous difference of −3.0 with a 95% limits of understanding of −7.half-dozen to vi.8. Overall, the results of our report in regard to Pco ₂ are consistent with the existing literature. Given that blood gas values should be interpreted in the context of the private patient's clinical condition and that ofttimes series claret gases are obtained to aid assess a patient'due south grade, primal venous Pco _two largely should exist able to supersede arterial Pco ₂ in most clinical circumstances.

Comparing the bivariate R ² values to the multivariate R ² values shows that the multivariate models exercise not account for significantly more variation than the respective uncomplicated linear regression equations. This demonstrates that there is no advantage in using the more complicated multivariate equations. For example, the R ⁱⁱ for arterial pH using only fundamental venous pH is R ⁱⁱ = 0.945. Using central venous pH, central venous Pco _ii, and central venous bicarbonate simultaneously to predict arterial pH only increases this to R ² = 0.948. We obtained boosted information comparison central and peripheral VBG values and found that the mean central minus peripheral differences for pH, Pco ₂, and bicarbonate were non clinically of import; therefore, peripheral every bit well every bit central venous samples have acceptable agreement with ABG values.

To our knowledge, our study is the offset report to examine the agreement among all of the commonly used parameters in arterial and central VBG samples in a diverse population of medical ICU patients; however, the study does have some limitations. The first twoscore patients that met written report inclusion criteria were enrolled. Although patient selection did not involve formal random sampling, this is unlikely to have resulted in systematic bias, because our demographics are like to a typical report population in a medical ICU and the ranges of arterial and venous values bridge the clinically important range. Second, although the enrolled patients did seem to be adequately representative of the disease processes encountered in many ICUs, there was a prevalence of sepsis. As a event, other pathophysiologic states, such every bit pure hypovolemic shock and cardiogenic shock, were underrepresented. Information technology is unlikely that any of these pathophysiologic states would accept a different human relationship betwixt arterial and venous values in the absence of severe circulatory failure, which was shown by Adrogue et al. (sixteen) in previous piece of work to upshot in poorer understanding between arterial and venous values. However, that the patient population in the study had a predominance of patients with sepsis does limit the generalizability of our results, especially in patients with very low cardiac output. Third, the study did use central venous samples obtained from a central line, not peripheral venous samples; however, given that our study establish adequate agreement between arterial and cardinal venous values, it would be expected that similar agreement would be institute if peripheral venous samples were used, which in fact has been confirmed by both our own results and those of other studies (vii–10,12–fifteen). Final, even though the report did include a wide range of acid-base status, including arterial pH values that ranged from 6.73 to 7.63, arterial Pco _two values that ranged from 16 to 79 mmHg, and arterial bicarbonate values that ranged from 2 to 45 mEq/L, in that location were fewer values at the extremes. For case, just three samples had a pH <7 and only 10 samples had a pH >seven.5. On the ground of the middle 95% range of the Banal-Altman plots, the human relationship between arterial and central venous values holds between the ranges of vii.12 to vii.52, 24.5 to 74.i (mmHg), and 12 to 41 (mEq/L) for pH, Pco ₂, and bicarbonate, respectively. These ranges cover near of the values commonly encountered in an ICU setting, although there clearly is less certainty most the human relationship between arterial and venous values at the extremes of pH, Pco ₂, and bicarbonate beyond these ranges.

Conclusions

Peripheral or fundamental venous pH, Pco _two and bicarbonate can replace their arterial equivalents in many clinical contexts that are encountered in the ICU. Further work needs to be done to define better the human relationship betwixt ABG and VBG values in low-cardiac-output states.

Acknowledgments

This project was supported by a seed grant from the Olive-View-UCLA Education and Enquiry Institute.

Nosotros acknowledge Dr. Jeffrey Gornbein's help with the statistical analysis, as well as Dr. Constance Chen and the entire ICU and respiratory therapy staff at Olive View-UCLA Medical Eye.

Footnotes

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