Anne-Maree KellyProfessor and DirectorJoseph Epstein Centre for Emergency Medicine Research @Western Health
I received financial support for travel and accommodation from Radiometer Pty Ltd to present a similar presentation at 4th International Symposium on Blood Gas and Critical Care in France in 2008.
I am undertaking some research with A/Prof Rees into calculated values which may be commercialised. I have no pecuniary interest in this program.
I have not received industry funding for any of my blood gas research projects.
To share a research journey
To describe how venous blood gas analysis might fit into clinical care of selected patients
An emergency physician, an educator and a clinical researcher
My research journey started when a ‘rep’ came to the ED with a transcutaneous CO2 monitor and I wanted to know if it worked in an ED population.
My questions come from my clinical practice – with a focus on working smarter for better patient outcomes
Venous blood gases is one of my research streams
How we work
Clinical focus: ED, prehospital care and related
Small team◦ Myself◦ Research nurse◦ Registrars, students
Collaborative approach
Pain management in ED Acute respiratory disease: asthma, COPD and
pneumothorax Estimating children’s weight in emergencies Intranasal naloxone for heroin overdose Acute cardiology and resuscitation, especially
chest pain in ED Clinical decision rules Implementation science and EBM
2001: Accuracy of pulse oximeters in resp. disease 2001: Arteriovenous pH agreement 2002: Venous pH and pCO2 as screening tests for
hypercarbia (derivation) 2004: Agreement for K+, bicarbonate 2005: Validation screening VBG for hypercarbia 2006: ICU studies 2011-13: Meta-analyses and systematic reviews 2012-13: Arteriovenous agreement and clinical utility in
patients undergoing NIV 2013: External validation of mathematical prediction
model (in collaboration with Aalborg University, Denmark)
Year Patient population
Paper
2001 General ED population Kelly AM, McAlpine R, Kyle E. Venous pH can safely replace arterial pH in the initial evaluation of patients in the emergency department. Emerg Med J 2001; 18:340-2
2002 Acute respiratory disease Kelly AM, Kyle E, McAlpine R. Venous pH and pCO2 can be used to screen for significant hypercarbia in emergency patients with acute respiratory disease. J Emerg Med 2002; 15-19.
2004 General ED population Fu P, Douros G, Kelly AM. Does potassium concentration measured on blood gas analysis agree with serum potassium in patients with diabetic ketoacidosis? Emerg Med Austral 2004; 16:280-3.
2004 General ED population Kelly AM, McAlpine R, Kyle E. Agreement between bicarbonate measured on arterial and venous blood gases. Emerg Med Australas 2004; 16:407-9.
2005 COAD Kelly AM, Kerr D, Middleton P. Validation of venous pCO2 to screen for arterial hypercarbia in patients with chronic obstructive airways disease. J Emerg Med 2005; 28;4:377-9.
2006 ICU Middleton P, Kelly AM, Brown J, Robertson M. Agreement Between Arterial And Venous Values For pH, Bicarbonate, Base Excess and Lactate Emerg Med J 2006; 23:622-4.
2010 COAD Lim BL, Kelly AM. A meta-analysis on the utility of peripheral venous blood gas analyses in exacerbations of chronic obstructive pulmonary disease in the emergency department. Eur J Emerg Med 2010; 17:246-8.
2010 General ED population Lim BL, Kelly AM. How useful is transcutaneous carbon dioxide monitoring in the adult emergency department? Hong Kong J Emerg Med 2010; 17:82-4
2011 NIV Kelly AM, Klim S. Agreement between arterial and transcutaneous pCO2 in patients undergoing non-invasive ventilation Respir Med 2011;105:226-9.
2013 NIV Kelly A, Klim S. Agreement between arterial and venous pH and pCO2 in patients undergoing non-invasive ventilation in the emergency department Emerg Med Australas [at press]
2013 NIV Agreement Between Mathematically Arterialized Venous vs. Arterial Blood Gas Values in Patients Undergoing Non-invasive Ventilation [submitted]
2013 NIV Can trend of pH and pCO2 be used to monitor progress in patient undergoing non-invasive ventilation? A prospective cohort study
Establishing acid-base status◦ Mainly pH; but also bicarbonate
Measuring respiratory function/ ventilation Mainly pCO2; but also pH
‘Quick check’ potassium, haematocrit, some electrolytes◦ Not addressed in this presentation
Less pain for patients Fewer complications, especially vascular and
infection Fewer needle-stick injuries Easier blood draw Minimal training requirement
JANE TRAN
◦ 26 year old, insulin dependent diabetic
◦ 2 days of vomiting and diarrhoea.
◦ Pulse 120 bpm, BP 100/60, bedside glucose ‘hi’
◦ 74 year old COAD◦ Acute respiratory
distress. ◦ Pulse 110, BP 140/-,
oxygen saturation (on air) 88%
Can we ◦ Exclude / diagnose◦ Monitor progress of◦ Base therapeutic decisions for
Metabolic acidosis or acute respiratory failure using venous blood gas analysis rather than arterial?
Outcome of interest is how closely venous and arterial values agree, not how well they correlate
Weighted mean difference gives an estimate of the accuracy between the methods
95% limits of agreement give information about precision
Arterial value
Venous value
95% LoA
There is limited data about the tolerance clinicians have with respect to agreement between arterial and venous values of blood gas parameters
Depending on this tolerance, the degree of agreement may be acceptable or unacceptable
This is included in a University of Melbourne Scholarly Selective project late 2013
Patient cohorts in the published literature are highly varied
Patient groups of interest are those at high risk of acidosis or hypercarbia◦ Reporting does not always report this detail◦ Data may to be dominated by patients with normal pH,
pCO2 and blood pressure
◦ Need for research focussed on high risk patient groups
13 studies◦ Range from 44 to 346 patients; Several JECEMR
Various conditions◦ DKA (3), COAD (4), trauma (1)
2009 patients
Weighted mean difference of 0.033 pH units
95% limits of agreement (7 studies) generally within +/- 0.1 pH units
DKA COAD
◦ 3 studies (265 patients)
◦ Weighted mean difference = 0.02 pH units
◦ 95% limits of agreement = -0.009 to 0.02 pH units (1 study)
◦ 5 studies (643 patients)
◦ Weighted mean difference= 0.034 pH units
◦ 95% limits of agreement generally +/- 0.1 pH units (3 studies)
One ICU-based study suggests that as hypotension increases, AV pH agreement deteriorates◦ Very small patient numbers◦ Finding not yet validated
University of Melbourne scholarly selective 2013◦ Arteriovenous blood gas agreement in varying
levels of shock and cardiac output
We know:◦ Generally close AV agreement in both respiratory and
metabolic disease
Evidence gaps:◦ AV agreement in various levels and types of shock◦ AV difference in toxicology scenarios (1 small study in
TCA OD only)◦ AV difference in mixed acid-base disease
8 studies
965 patients
Various conditions (COAD 4)
Weighted mean difference = 6.2 mmHg
95% limits of agreement: up to -17.4 to +23.9 mmHg◦ 5/7 studies reporting LoA report LoA band >20mmHg
4 studies
452 patients
Weighted man difference = 7.26 mmHg
95% limits of agreement: up to -14 to +26 mmHg◦ All 3 studies that reported LoA report LoA band
>20mmHg
Author, year No. Screening cut-off
Sens. Spec. NPV %ABG avoided
Kelly, 2002 196 45 100 57 100 43
Kelly, 2005 107 45 100 47 100 29
Ak, 2006 132 45 100 * 100 33
McCanny, 2011
94 45 100 34 100 23
POOLED DATA
529
45 100 (95% CI 97-100)
53(95% CI 57-58)
100(95% CI 97-100)
35%(95% CI 32-41)
Data limited to studies in cohorts with respiratory disease
Data recently submitted for publication
47 comparisons in 34 patients
Average arteriovenous difference for change in pH (v-a) was 0.001pH units (LoA -0.7 to +0.7).
Average arteriovenous difference between change in pCO2 (v-a) was 0.04mmHg (LoA -17.3 to +18.2).
For both pH and pCO2, in the majority of cases the direction of change was the same although the magnitude was variable.
We know: AV agreement is NOT good enough for clinical inter-
changeability Wide limits of agreement
Venous pCO2 has utility as a screening test for hypercarbia Excellent NPV
Evidence gaps: Whether trend in venous pCO2 and pH can safely drive a care pathway
for COAD Subject of current international research project (JECEMR is a partner)
8 studies
1211 patients
Various conditions (COAD 2)
Weighted mean difference = -1.3mmol/l
95% limits of agreement : up to +/- 5mmol/l (3 studies)
Two studies only
Data not suitable for pooling
JANE TRAN
◦DKA
◦ AV agreement is acceptable; at least in non-shocked patients
◦ Can use venous pH to diagnose/ monitor
◦ Acute respiratory distress
◦ pH agreement good but pCO2 has considerable imprecision
◦ Can use venous pCO2 as a screening test for hypercarbia
◦ ? Can monitor trend*
Team from Center for Model Based Medical Decision Support Systems, Dept of Health Science and Technology, Aalborg University, Denmark (A/Prof Steven Rees)
Developed venous to arterial conversion method using venous blood gas variables and pulse oximetry
Designed to be incorporated into blood gas analysers
The method calculates arterial values using mathematical models
Assumes:◦ Constant value of the
respiratory quotient of 0.82◦ Change in base excess
from arterial to venous blood is 0 mmol/l
Rees SE, Toftegaard M, Andreassen S. A method for calculation of arterial acid–base and blood gas status from measurements in the peripheral venous blood. Comp Methods Programs Biomed. 2006, Vol 81, 18-25.
Respiratory patients◦ Arterial-calculated pH difference = -0.001pH units (95% LoA -
0.026 to +0.026)◦ Arterial-calculated pCO2 difference = -0.68mmHg (95% LoA -
4.81 to +3.45 mmHg)
ICU◦ Arterial-calculated pH difference = -0.002pH units (95% LoA -
0.029 to +0.025)◦ Arterial-calculated pCO2 difference = 0.3mmHg (95% LoA -3.58
to +4.18 mmHg)
ED◦ pH can be calculated to within 0.02 pH units (95% LoA)◦ pCO2 can be calculated to within 4mmHg (0.5kPa)
82 sample-pairs (60 patients)
Mean difference for arterial pH (actual-calculated) was 0.01 pH units (95% limits of agreement: -0.04, 0.06).
Mean difference for pCO2 (actual-calculated) was -0.45mmHg (95% limits of agreement: -10, +9).
pH and bicarbonate◦ Probably close enough agreement for clinical purposes
in DKA, acute respiratory failure, isolated metabolic acidosis
◦ More work needed in toxicology, shock, mixed disease
◦ Scholarly selective addressing agreement in shock and with varying levels of cardiac output
pCO2◦ NOT enough agreement for clinical purposes, either as one-off
or to monitor change
◦ Data suggests venous pCO2 is useful as a screening test
Base excess◦ Probably not enough agreement for clinical purposes
Mathematical modelling approaches might be more accurate especially for pCO2
For broad applicability an app/ similar would be more feasible than integration into blood gas machines
More work needed to prove accuracy and precision in high risk groups
JECEMR has led research into arteriovenous blood gas agreement
Our >10 year journey has steadily added pieces to build understanding of agreement in different disease states
The accumulated data has changed practice both ‘home’ and ‘away’
Questions?
Questions?
Questions?
Follow JECEMR research:
@kellyam_jec
Subscribe to quarterly e-newsletter: Email ‘subscribe’ to [email protected]