Venous Blood Gas Samples Research Articles

Plastic Blood Gas Syringes and Measurement Error in Central Venous Oxygen Saturations.

Measurement of central venous oxygen (SvO2) levels remains an important method for the detection of circulatory shock. Plastic blood gas syringes have supplanted glass. These syringes are, however, permeable to atmospheric oxygen. Common sampling practices, including a delay between blood aspiration and analysis and continuous mixing of the sample, may promote equilibration of the blood sample with atmospheric oxygen and could result in over estimation of SvO2 levels. Pulmonary artery or central venous catheter blood samples were taken from 21 critically ill patients. Two venous blood gas samples were collected simultaneously in plastic syringes. One sample was continuously mixed through a gentle rotation. The other sample was not mixed. Blood gas analyses were undertaken on both samples at baseline and at 5, 10, 15, and 20 min. Compared with baseline levels, the SvO2 increased significantly over time for both continuously mixed and nonmixed samples (P < 0.0001). The rate of the increase was 2-fold greater for continuously mixed samples (P < 0.0001). For continuously mixed samples, the SvO2 was 63% at baseline, 65% at 5 min, 70% at 10 min, 74% at 15 min, and 78% at 20 min. For the nonmixed samples, the levels were 63%, 64%, 66%, 68%, and 70%, respectively. This is the first report documenting that plastic blood gas syringes systematically overestimate SvO2 levels when there is a delay in analysis or continuous mixing of the sample. Overestimation of SvO2 levels may harm patients as circulatory shock may not be recognized and treated.

Abstract: Perfusion Assessment of the Deep Inferior Epigastric Artery Perforator Flap: A Blood Gas Analysis

PURPOSE: Tissue oxygen saturation is a commonly used method to assess and evaluate free flap physiology. However, it is an indirect proxy, subject to variation by position, lighting, and other systemic factors. In this study of abdominally-based breast reconstruction free flaps, blood gas samples from the deep inferior epigastric vein (DIEV) and the superficial inferior epigastric vein (SIEV) are compared to systemic arterial and venous values. By doing so, the authors aim to demonstrate the direct impact of perforator selection on flap physiology. To our knowledge, no study to date has evaluated the in vivo blood gas variations for breast free flap reconstruction. METHODS/MATERIALS: Ten consecutive patients undergoing deep inferior epigastric artery perforator (DIEP) free flap breast reconstruction were prospectively included. Demographic data were collected preoperatively. Intraoperatively, systemic arterial blood gas (ABG), venous blood gas (VBG), FiO2, pulse oximetry, and end-tidal CO2 were measured. Simultaneously, VBG from the SIEV and DIEV were noted. Flap characteristics and intra- and post-operative complications were recorded, with at least 30 days of follow-up. RESULTS: Comparison of the venous blood gas samples demonstrated no statistical difference among the pH, PaCO2, and base excess of the DIEV, SIEV, and systemic blood samples. However, the PaO2 of the systemic blood samples was higher than its respective value in the DIEV and SIEV sample (p< 0.01). There were no cases of fat necrosis, partial flap loss, or total flap loss. CONCLUSIONS: The blood gas values, in particular oxygenation, of the DIEV and SIEV in DIEP flaps do differ from systemic values. DISCLOSURES:None of the authors have any disclosures.

Evaluation of adjusted central venous blood gases versus arterial blood gases of patients in post-operative paediatric cardiac surgical intensive care unit.

Background and Aims:Central venous catheters are in situ in most of the intensive care unit (ICU) patients, which may be an alternative for determining acid-base status and can reduce complications from prolonged arterial cannulation. The aim of this study was to examine the reliability between adjusted central venous blood gas (aVBG) and arterial blood gas (ABG) samples for pH, partial pressure of carbon-di-oxide (pCO2), bicarbonate (HCO3−), base excess (BE) and lactates in paediatric cardiac surgical ICU.Methods:We applied blood gas adjustment rule, that is aVBG pH = venous blood gas (VBG) pH +0.05, aVBG CO2 = VBG pCO2 - 5 mm Hg from the prior studies. In this study, we validated this relationship with simultaneous arterial and central venous blood obtained from 30 patients with four blood sample pairs each in paediatric cardiac surgical ICU patients.Results:There was a strong correlation (R i.e., Pearson's correlation) between ABG and aVBG for pH = 0.9544, pCO2 = 0.8738, lactate = 0.9741, HCO3− = 0.9650 and BE = 0.9778. Intraclass correlation co-efficients (ICCs) for agreement improved after applying the adjustment rule to venous pH (0.7505 to 0.9454) and pCO2 (0.4354 to 0.741). Bland Altman showed bias (and limits of agreement) for pH: 0.008 (−0.04 to + 0.057), pCO2: −3.52 (–9.68 to +2.65), lactate: −0.10 (−0.51 to +0.30), HCO3−: −2.3 (–5.11 to +0.50) and BE: −0.80 (−3.09 to +1.49).Conclusion:ABG and aVBG samples showed strong correlation, acceptable mean differences and improved agreement (high ICC) after adjusting the VBG. Hence, it can be promising to use trend values of VBG instead of ABG in conjunction with a correction factor under stable haemodynamic conditions.

Evaluation of intravascular microdialysis for continuous blood glucose monitoring in hypoglycemia: an animal model.

We have previously shown that intravascular microdialysis in a central vein is an accurate method for continuous glucose monitoring in patients undergoing cardiac surgery. However, no hypoglycemia occurred in our earlier studies, prompting further evaluation of the accuracy of intravascular microdialysis in the hypoglycemic range. Thus, this animal study was performed. A porcine model was developed; hypoglycemia was induced using insulin injections. The pigs were monitored with intravascular microdialysis integrated in a triple-lumen central venous catheter. As reference, venous blood gas samples were taken every 5 minutes and analyzed in a blood gas analyzer. Ethical permission for the animal experiments was obtained from the Stockholm Regional Ethical Committee, reference no N397/09. A total of 213 paired samples were obtained for analysis, and 126 (59.2%) of these were in the hypoglycemic range (<74 mg/dl). Using Clarke error grid analysis, 100% of the paired samples were in region AB and 99% in region A. The ISO standard (ISO15197) was met. Bland-Altman analysis showed bias (mean difference) ± limits of agreement was -0.18 ± 16.2 mg/dl. No influence from glucose infusions was seen. The microdialysis monitoring system was found to be very responsive in rapid changes in blood glucose concentration. This study shows that intravascular microdialysis in a central vein is an accurate method for continuous glucose monitoring in hypoglycemia in a porcine experimental model. Furthermore, the system was not influenced by glucose administration and was found to be responsive in rapid blood glucose fluctuations.

Can venous blood gas values be used instead of arterial blood gas values in respiratory alkalosis?

Objective: The increase in alveolar ventilation causes disposal of large amounts of carbon dioxide from the respiratory system resulting in hypocapnia and respiratory alkalosis. Hypocapnia reduces cerebral blood flow, alkalosis leads to a leftward shift in oxygen- hemoglobin dissociation curve causing reduced oxygen delivery to tissues. Therefore, immediate diagnosis and close monitoring of respiratory alkalosis is necessary in emergency situations. In this study, the comparison of arterial and venous blood gas parameters of patients with respiratory alkalosis, and the evaluation of the usability of venous blood gas instead of arterial blood gas in patients with respiratory alkalosis were aimed. Methods: Ninety patients with respiratory alkalosis were enrolled in this study prospectively. Arterial and venous blood gas samples of patients enrolled in the study were drawn simultaneously in room air without administering any treatment after admitting to the emergency department. Results: The correlation between the results of pH, partial pressure of carbon dioxide (pCO2), bicarbonate (HCO 3 ) and base excess (BE) (respectively, r= 0.764, r= 0.839, r= 0.843, r= 0.883) in arterial and venous blood gas samples were statistically significant (p 80 mmHg in 23 patients (25.6%), between 60-80 mmHg in 29 (32.2%) patients and <60 mmHg in 38 (42.2%) patients. A statistically significant correlation (r= 0.540, p<0.001) detected only between arterial and venous blood gas samples of patients with PaO 2 <60mmHg and O 2 saturation <90% among these three groups. Conclusion: In the follow-up of patients with respiratory alkalosis, if O2 saturation is ≥90%; pH, pCO 2 and HCO 3 of venous blood gas samples can be used instead of arterial blood gas samples. If patient's O2 saturation <90%; pH, pCO2, HCO3 and also pO2 values in venous blood gas sample can be used instead of arterial blood gas samples.

P182 COPD: Is it all in vein?

Introduction & ObjectivesIn patients with COPD, an arterial blood gas (ABG) is considered the gold standard method of directly measuring serum pH, pO2, pO2 and calculating bicarbonate (HCO3) levels. These...

Effect of Intravenous Infusion of Dexmedetomidine Combined with Inhalation of Isoflurane on Arterial Oxygenation and Intrapulmonary Shunt During Single-Lung Ventilation

To investigate the changes in arterial oxygenation and intrapulmonary shunt during one-lung ventilation (OLV) with intravenous infusion of dexmedetomidine combined with isoflurane inhalation. ASA I-II 60 patients aged 18-70 year, undergoing OLV during elective thoracic surgery were randomly allocated to two groups: (1) isoflurane + saline (group NISO, n = 30) and (2) isoflurane + dexmedetomidine (group DISO, n = 30). After induction, anesthesia was maintained with intravenous infusion of remifentanil 0.1-0.2 μg kg(-1) min(-1) and inhalation isoflurane (1.0-2.0%). In addition, anesthesia was maintained with intravenous infusion of dexmedetomidine 0.7 μg kg(-1) h(-1) in DISO group and saline 0.25 ml kg(-1) h(-1) in NISO group. Bispectral Index values were maintained within 40-60 by changing the concentration of isoflurane in all groups. Arterial blood gas samples and central venous blood gas samples were taken as follows: during two-lung ventilation before OLV and during the first 40 min of OLV. 45 Patients completed the study, with 23 patients in DISO group and 22 patients in NISO group. The two groups were comparable in terms of demographic variables, hemodynamic, PaO2, Qs/QT, end expiration isoflurane and BIS levels during the operation. Compared with patients in the group NISO, there were significant increases with PaO2, significant decrease with Qs/QT, significant decrease with end expiration isoflurane, and significant decrease with HR in the group DISO during the first 40 min of OLV (P < 0.05). Dexmedetomidine infusions decrease the requirement for isoflurane, decrease intrapulmonary shunt, and moderate the change in PaO2 and may be useful in managing OLV.

Correlation between peripheral venous and arterial blood gas measurements in patients admitted to the intensive care unit: A single-center study

BackgroundThe objective of this study was to examine the correlation between arterial blood gas (ABG) and peripheral venous blood gas (VBG) samples for all commonly used parameters in patients admitted to a medical intensive care unit (ICU). MethodsA single-center, prospective trial was carried out in a medical ICU in order to determine the level of correlation of ABG and peripheral VBG measurements. A maximum of five paired ABG–VBG samples were obtained per patient to prevent a single patient from dominating the data set. ResultsRegression equations were derived to predict arterial values from venous values as follows: arterial pH=−1.108+1.145×venous pH+0.008×PCO2−0.012×venous HCO3+0.002×venous total CO2 (R2=0.655), arterial PCO2=88.6−10.888×venous pH+0.150×PCO2+0.812×venous HCO3+0.124×venous total CO2 (R2=0.609), arterial HCO3=−89.266+12.677×venous pH+0.042×PCO2+0.675×venous HCO3+0.185×venous total CO2 (R2=0.782). The mean ABG minus peripheral VBG differences for pH, PCO2, and bicarbonates were not clinically important for between–person heterogeneity. ConclusionPeripheral venous pH, PCO2, bicarbonates, and total CO2 may be used as alternatives to their arterial equivalents in many clinical contexts encountered in the ICU.

Venoarterial PCO2 difference: a marker of postoperative cardiac output in children with congenital heart disease.

To determine the relationship between venoarterial carbon dioxide gradient (DeltapCO2) and central venous oxygen saturation (ScvO2) in children after cardiac surgery. A cohort study. The Paediatric cardiac intensive care unit of the Aga Khan University Hospital, Karachi, from June 2006 to May 2007. All children admitted in the paediatric cardiac intensive care after complete repair of congenital heart defect using cardiopulmonary bypass were included in the study. Simultaneous arterial and central venous blood gas samples were obtained from a catheter placed in the artery (either radial or femoral) and superior vena cava respectively. Linear regression analysis was performed between ScvO2 and DeltapCO2. Fifty seven children aged from 5 days to 14 years were included and 272-paired simultaneous arterial and central venous samples were analyzed. Mean venous pCO2 was 47.82+/-9.03 mmHg and mean arterial pCO2 was 40.50+/-9.06 mmHg. One hundred seventy four samples had ScvO2 > 70% with mean DeltapCO2 of 5.44+/-2.55 mmHg and 98 samples had ScvO2 < 70% with mean DeltapCO2 of 9.07+/-3.90 mmHg. With ScvO2 < 70%, 77 samples had DeltapCO2 of > 6 mmHg while only 21 samples had DeltapCO2 of < 6 mmHg (p < 0.001). On the contrary with ScvO2 > 70%, 71 samples had DeltapCO2 of > 6 mmHg and 103 samples had DeltapCO2 of < 6 mmHg. Coefficient of correlation (R2) between 0.340 was ScvO2 and DeltapCO2. Elevated DeltapCO2 is practical and can be utilized as a useful adjunct to low ScvO2 in the assessment of low cardiac output syndrome in children after cardiac surgery.

Venous vs arterial blood gases in the assessment of patients presenting with an exacerbation of chronic obstructive pulmonary disease

ObjectiveThe purpose of this study was to investigate the clinical correlation between arterial and venous blood gas (VBG) values in patients presenting to the emergency department (ED) with acute exacerbation of chronic obstructive pulmonary disease. MethodsA prospective study of patients with chronic obstructive pulmonary disease presenting to the ED with acute ventilatory compromise was done. Patients were included if their attending physician considered arterial blood gas sampling important in their initial assessment. Data from arterial and venous samples were compared using Spearman correlation and bias plot (Bland-Altman) methods. ResultsNinety-four patients were enrolled in the study. Eighty-nine patients had complete data sets for analysis. Arterial hypercarbia was present in 30 patients (33.7%; range, 51-140.19 mm Hg). All cases of arterial hypercarbia were detected using VBG sampling when a screening cutoff of 45 mm Hg was applied (sensitivity, 100%; 95% confidence interval, 88.7%-100% and specificity, 34%; 95% confidence interval, 23.1%-46.6%). Bias plot revealed moderate agreement between arterial and venous Pco2 with an average difference of 8.6 mm Hg and 95% limits of agreement of −7.84 to 25.05 mm Hg. For pH, mean difference between each group was 0.039 (range, −0.12 to 0.03). Linear regression analysis for pH demonstrated very close equivalence with a regression coefficient of 0.955, and Spearman correlation showed significant correlation of 0.826 (P = .001). ConclusionVenous pH and HCO3 values show excellent correlation with arterial values. Using a previously validated screening cutoff of 45 mm Hg, venous CO2 has 100% sensitivity in detecting arterial hypercarbia. There is insufficient agreement between venous and arterial CO2 for VBG to replace arterial blood gas in determining the degree of hypercarbia.

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

Venous blood gas (VBG) analysis is a safer procedure than arterial blood gas (ABG) analysis and may be an alternative for determining acid-base status. The objective of this study was to examine the agreement between ABG and central VBG samples for all commonly used parameters in a medical intensive care unit (ICU) population. We performed a single-center, prospective trial to assess the agreement between arterial and central VBG measurements in a medical ICU. Adult 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 central venous sample was obtained to examine the agreement among the pH, Pco(2), and bicarbonate. Data comparing central and peripheral VBG values were also obtained. The mean arterial minus venous difference for pH, Pco(2), and bicarbonate was 0.027, -3.8, and -0.80, respectively. Bland-Altman plots for agreement of pH, Pco(2), and bicarbonate showed 95% limits of agreement of -0.028 to 0.081, -12.3 to 4.8, and -4.0 to 2.4, respectively. Regression equations were derived to predict arterial values from venous values as follows: Arterial pH = -0.307 + 1.05 x venous pH, arterial Pco(2) = 0.805 + 0.936 x venous Pco(2), and arterial bicarbonate = 0.513 + 0.945 x venous bicarbonate. The mean central minus peripheral differences for pH, Pco(2), and bicarbonate were not clinically important. Peripheral or central venous pH, Pco(2), and bicarbonate can replace their arterial equivalents in many clinical contexts encountered in the ICU.

Long-acting oral phosphodiesterase inhibition preconditions against reperfusion injury in an experimental lung transplantation model

Ischemia-reperfusion injury remains a devastating complication of lung transplantation. Phosphodiesterase inhibitors have been shown to precondition tissues against ischemia-reperfusion injury. Little is known, however, about the utility of phosphodiesterase inhibition in reperfusion injury after lung transplantation. We evaluated the long-acting phosphodiesterase-5 inhibitor, tadalafil, in an ex vivo lung transplant model. New Zealand White rabbits (4 kg), were given oral tadalafil (n = 11) 24 hours before lung harvest and compared with rabbits given oral vehicle alone (n = 11). Lungs were recovered with Perfadex solution (Vitrolife, Kungsbacka, Sweden) and cold stored for 18 hours. After storage, lung blocks were reperfused with donor rabbit blood in an ex vivo apparatus. Pulmonary artery pressures were recorded with serial arterial and venous blood gas sampling and animals served as their own controls. Phosphodiesterase-5 and protein kinase G tissue activity assays confirmed drug effects. Luminol chemiluminescence assay was used to measure reactive oxygen species and levels of endothelial and inducible nitric oxide synthase were measured. Extended cold storage, followed by reperfusion produced a consistent reproducible decrease in oxygenation and increase in pulmonary pressure. Tadalafil-treated animals exhibited greater Pao(2) throughout the course of reperfusion (P = .001) Mean pulmonary artery pressure was lower in tadalafil-treated animals (22 vs 40 mm Hg; P = .04). Phosphodiesterase-5 activity was decreased (143 +/- 8 vs 205 +/- 32 mP; P < .001) with protein kinase G activity increased (25 +/- 12 vs 12 +/- 2.4 fU/microg; P = .01) in the experimental group confirming that oral pretreatment resulted in active phosphodiesterase inhibition in the lung tissue. Reactive oxygen species (as measured by luminol activity) were decreased in tadalafil-treated animals (7.8 +/- 1.5 vs 10.2 +/- 1.2 relative light units; P = .003). Our experimental model demonstrates that oral donor pretreatment with a long-acting phosphodiesterase inhibitor is an effective strategy for improving pulmonary performance after reperfusion. Importantly, phosphodiesterase enzymes and their downstream effectors may play a critical role in reperfusion injury after lung transplantation.

Lack of agreement between arterial and central venous blood glucose measurement in critically ill children

Dear Sir, We were interested to read the article by Critchell et al. [1] highlighting concerns about the accuracy of bedside capillary blood glucose measurements in critically ill patients. We would agree that the importance of sampling site for blood glucose measurement has been under-emphasized in the published studies on hyperglycaemia and tight glycaemic control. The majority of studies linking hyperglycaemia with adverse clinical outcome have not provided data on the site of sampling. We would like to share preliminary data regarding the use of central venous blood sampling for glucose measurement in critically ill children. The objective of this preliminary study was to compare blood glucose concentrations in simultaneously drawn arterial and central venous blood glucose samples taken for clinical purposes. Paired arterial and central venous blood gas samples were taken to obtain information about oxygen extraction and the results were prospectively documented. Blood glucose was measured on a blood gas analyzer (Bayer Rapidlab; electrochemical biosensor), which is subject to strict quality control by the Clinical Chemistry department. No glucose containing solution was infused into either the arterial or the central venous sampling lines. A total of 245 paired arterial and central venous blood samples were obtained from 71 children, age range 5 days–14 years, between January and October 2006. The majority of cases were children post cardiac surgery, reflecting a group of patients in whom regular assessment of oxygen extraction is undertaken. The median number of samples per patient was 2 (range 1–22). The samples included a wide range of arterial blood glucose values, from 2.4 to 23 mmol/l. There was poor agreement between arterial and central venous blood glucose (Fig. 1). The central venous blood glucose was frequently higher than the arterial blood glucose (median 0.4 mmol/l, CI 0.3–0.5, P \ 0.001 Wilcoxon Signed Rank test). On occasions, the difference exceeded 5 mmol/l. The implications of these findings for titration of insulin therapy are obvious. Inappropriate adjustments to insulin therapy could be made and, importantly, hypoglycaemia could go undetected if central venous sampling is used to monitor blood glucose in this population of critically ill children. It is common for a child to be managed without an arterial line once their cardio-respiratory condition has stabilized, and for bloods to be taken through a central line, if present, to avoid the need for venepuncture. In contrast with our findings, a recent study by Evron et al. [2] found no difference between arterial and central venous blood glucose concentration in adult patients undergoing major orthopaedic or colon surgery though these patients were all studied in the context of general anaesthesia and surgery and were not critically ill. It is possible that glucose containing fluids infused into a vein peripheral to the central venous line or infused via one of the other central venous line lumens could have contaminated the central venous sample that was taken. As this was an opportunistic study performed under uncontrolled conditions information about glucose infusions was not collected, other than confirmation that no glucose containing fluid was infused into either the arterial or central venous sampling lines. However, alternative explanations are possible in that glucose may be generated in peripheral tissues, most notably in muscle, during critical illness and released into the venous system [3, 4]. 0 5 10 15 20 25

A surgical technique for catheterization of the sagittal sinus in pigs

The purpose of our study was to describe an efficient, reliable and inexpensive surgical method for cerebral venous blood gas sampling in acutely instrumented pigs in a research setting. Parameters from the blood samples are used to monitor brain perfusion and oxygenation in different animal models. To the authors' knowledge, this is the first detailed description of an accurate surgical technique for catheterization of the sagittal sinus in pigs.

Clinical evaluation of an instrument to measure carbon dioxide tension at the oxygenator gas outlet in cardiopulmonary bypass

This paper presents the clinical testing of a new capnograph designed to measure the carbon dioxide tension at the oxygenator exhaust outlet in cardiopulmonary bypass (CPB). During CPB, there is a need for reliable, accurate and instant estimates of the arterial blood CO2 tension (PaCO2) in the patient. Currently, the standard practice for measuring PaCO2 involves the manual collection of intermittent blood samples, followed by a separate analysis performed by a blood gas analyser. Probes for inline blood gas measurement exist, but they are expensive and, thus, unsuitable for routine use. A well-known method is to measure PexCO2, ie, the partial pressure of CO2 in the exhaust gas output from the oxygenator and use this as an indirect estimate for PaCO2. Based on a commercially available CO2 sensor circuit board, a laminar flow capnograph was developed. A standard sample line with integrated water trap was connected to the oxygenator exhaust port. Fifty patients were divided into six different groups with respect to oxygenator type and temperature range. Both arterial and venous blood gas samples were drawn from the CPB circuit at various temperatures. Alfa-stat corrected pCO2 values were obtained by running a linear regression for each group based on the arterial temperature and then correcting the PexCO2 accordingly. The accuracy of the six groups was found to be (+/- SD): +/- 4.3, +/- 4.8, +/- 5.7, +/- 1.0, +/- 3.7 and +/- 2.1%. These results suggest that oxygenator exhaust capnography is a simple, inexpensive and reliable method of estimating the PaCO2 in both adult and pediatric patients at all relevant-temperatures.

Mixed Venous Blood Gas Sampling Is Not Influenced by the Speed of Withdrawal in Cardiac Surgery Patients

Mixed Venous Blood Gas Sampling Is Not Influenced by the Speed of Withdrawal in Cardiac Surgery Patients

Validation of venous pCO 2 to screen for arterial hypercarbia in patients with chronic obstructive airways disease

To validate a previously derived venous pCO 2 (pvCO 2) cut-off for ruling out arterial hypercarbia in patients with chronic obstructive pulmonary disease (COPD), matched arterial and venous blood gas samples were taken from a convenience sample of patients who presented to the Emergency Department (ED) with COPD deemed by their treating doctor to require arterial blood gas (ABG) analysis as part of their care. The screening cut-off was defined as pvCO 2 of > 45 mm Hg and arterial hypercarbia was defined as arterial pCO 2 (paCO 2) of > 50 mm Hg. Descriptive statistics were employed. Sensitivity, specificity and negative predictive value were calculated. There were 112 patients enrolled in the study, of whom 107 had complete data for analysis. Forty-three patients had arterial hypercarbia (range of 51 to 90mm Hg, median 60 mm Hg). All cases of arterial hypercarbia were detected by the screening cut-off (sensitivity 100%; 43/43; 95% CI 91–100%; specificity 47%, 95% CI 35–59%). The negative predictive value of pvCO 2 < 45 mm Hg was 100% (30/30, 95% CI 89–100%). Assuming the ABG was performed to assess hypercarbia, 29% of ABGs potentially could have been avoided if a venous screening test was employed. In conclusion, pvCO 2 can be used as a screening test for arterial hypercarbia, and if employed, can potentially reduce the requirement for ABG sampling.

Evaluation of Relationship Between Arterial and Venous Blood Gas Values in the Patients with Tricyclic Antidepressant Poisoning

Introduction. Determination of arterial blood gas (ABG) values is essential in the evaluation of patients with TCA poisoning. The relationship between arterial and venous blood gas pH has not been established in TCA poisoning. In TCA poisoning, blood vessels vasodilatation due to antidepressant-induced α-blockade and also metabolic acidosis may lead to arterialization of venous blood, which in turn enhances the relationship between ABG and VBG parameters. Therefore this study was designed to evaluate the relationship between ABG and VBG pH values in TCA poisoned patients. Methods. This prospective study was performed in the Poisoning Emergency Department of Noor Hospital, Isfahan, Iran. Samples for arterial and venous blood gas analysis were obtained during initial evaluation of TCA-poisoned patients and 30 min after treatment with sodium bicarbonate. The venous blood gas samples were collected with samples for other blood tests at the time of intravenous line insertion. Laboratory data were recorded on a database form initiated in the emergency department and analyzed by paired student t-test. The degree of agreement between the arterial and venous pH measurements was evaluated by Bland and Altman method. Results. Data from 50 TCA-poisoned patients were analyzed. There were significant differences between mean differences of ABG and VBG parameter values on the initial evaluation. There was also a relationship between arterial and venous pH on the initial evaluation. Conclusion. In TCA poisoning, the peripheral venous pH measurement is a valid and reliable substitute for arterial pH.

The correlation of carboxyhemoglobin levels between venous and arterial blood gas samples

Study objectives: In suspected carbon monoxide poisoning, carboxyhemoglobin levels are commonly obtained from arterial blood gas samplings. Arterial puncture is associated with increased risks (ie, hematoma, thrombosis, pseudoaneurysm) and is more painful compared with venipuncture. This study assesses the reliability of carboxyhemoglobin levels obtained by venous blood gas sampling compared with arterial blood gas samplings. Methods: A cross-sectional study of 98 patients in the emergency department of an urban, inner-city hospital was performed. Paired samples of arterial and venous blood were obtained within a 15-minute interval. Arteriovenous differences were analyzed for multiple variables (ie, Na, K, hemoglobin, glucose, and lactate), including carboxyhemoglobin. Statistical analysis was performed using a paired sample t test, and Pearson correlation coefficient was determined for confirmation. Results: Within the entire data set (n=98), the mean difference between arterial and venous carboxyhemoglobin levels was 0.40±0.44 ( P =.0001), with a Pearson correlation of r =0.97 ( P Conclusion: There is excellent correlation in the measurement of carboxyhemoglobin between venous and arterial blood gas samples. These data should lend support to the use of venous blood gas analysis for the determination of carboxyhemoglobin levels when arterial blood gas sampling is otherwise not required, is difficult, or is not desired by the patient. One limitation of this study, however, is the lack of carboxyhemoglobin levels in toxic ranges (ie, >20%); further prospective investigation in a population with suspected carbon monoxide poisoning is warranted.

Arterial and venous ionized calcium measurements: Is there a difference?

Study objectives: In critically ill patients, the ionized calcium level has commonly been obtained from arterial blood gas samplings. Arterial puncture is associated with increased risks (ie, pseudoaneurysm) and is more painful compared with venipuncture. This study will assess the reliability of ionized calcium levels obtained by venous blood gas sampling compared with arterial blood gas samplings. Methods: A cross-sectional study of 102 patients in the emergency department of an urban, inner-city hospital was performed. Paired samples of arterial and venous blood were obtained within a 15-minute interval. Arteriovenous differences were analyzed for multiple variables (ie, Na, K, hemoglobin, glucose, and lactate), including ionized calcium. Statistical analysis was performed on the entire data set, as well as subsets, according to acidosis (pH <7.35) and alkalosis (pH >7.45). A paired sample <i>t</i> test was used, and Pearson correlation coefficient was determined for confirmation. Results: Within the entire data set (n=102), the mean difference between venous and arterial ionized calcium measurements was 0.015±0.045 (<i>P</i>=.001) with a Pearson correlation of <i>r</i>=0.94 (<i>P</i><.0001). When the arterial pH was acidotic (n=18), the mean difference between venous and arterial ionized calcium was 0.014±0.030 (<i>P</i>=.069), with a Pearson correlation of <i>r</i>=0.98 (<i>P</i><.0001). Under alkalotic states (n=20), the mean difference between venous and arterial ionized calcium was 0.036±0.039 (<i>P</i>=.0007), with a Pearson correlation of <i>r</i>=0.98 (<i>P</i><.0001). Conclusion: There is excellent correlation in the measurement of ionized calcium between venous and arterial blood gas samples, including both acidotic and alkalotic states. These data should lend support to the use of venous blood gas analysis for the determination of ionized calcium levels when arterial blood gas sampling is otherwise not required, is difficult, or is not desired by the patient.