Capillary lactic acid validation in an ED
a b s t r a c t
Introduction: One of the most used methods to evaluate patients with a high risk not responding to clinical treatment is the measurement of blood levels of lactic acid (LA). The objective of this study was to compare the sensitivity and specificity of an LA test for capillary and venous blood with LA test for arterial blood in a population of patients with tissue hypoperfusion and to evaluate the time needed for each test.
Materials and Methods: The following factors were evaluated: the performance of venous and capillary LA in relation to arterial LA, and the time needed to elicit each method from patient admission to mortality according to initial LA. Results: Seventy-nine patients with a median age of 58 years were admitted. The area under the curve for capillary LA was 82% (95% confidence interval [CI], 73-91). The best cutoff point was 2.35, with a sensitivity of 81% (95% CI, 65- 90) and a specificity of 70% (95% CI, 53-83). The average time from patient admission until arterial, venous, and capillary LA values were obtained was 112, 117, and 77 minutes, respectively. The patients who died within 3, 30, and 60 days showed an average arterial LA of 5.9, 1.9, and 2.2, respectively.
Conclusion: The utilization of capillary and venous LA is an effective method of evaluation and risk stratification for patients with different degrees of tissue hypoperfusion. The time needed to elicit capillary LA proved much faster with respect to arterial and venous LA.
(C) 2013
Introduction
The emergency services are one of the busiest and most converged places in hospitals. Generally, they face the problem of patient overpopulation due to different factors: lack of available beds for hospitalization, orders of multiple studies, and the delay of the latter. A minority of patients present critical situations in which precision and speed are necessary. Previous studies have shown that by reducing the time needed for diagnosis and treatment in sepsis and trauma, morbidity/mortality decreases [1].
Many laboratory tests and enzymatic markers have been used for patient risk stratification. One of the most widely used for Patient evaluation with high suspicion of bad clinical evolution is lactic acid (LA) [2]. Many clinical parameters such as artery tension, heart rate, and diuresis could represent clear parameters of clinical severity but also be normal in those patients, for example, with occult shock [3]. In emerging situations of tissue hypoperfusion, the aerobic cell metab- olism is altered anaerobically, increasing the production of LA. At the same time, just as in sepsis, LA clearance diminishes, which leads to LA blood increase [4]. In practice, it is technically easy to determine the LA circulating; it is commonly used and relatively quickly obtained. Lactic acid evaluation has finally been adopted as a Predictive tool in patients with sepsis, trauma, surgery, and burns; and it predicts mortality in this group of serious patients.
E-mail addresses: [email protected], [email protected] (L. Seoane).
Because of all these factors, the prompt evaluation of LA in the emergency services is important because it is the first place where the patient becomes aware of his illness and where his morbidity/ mortality depends on Prompt diagnosis and treatment.
Lactic acid evaluation can be performed in venous and arterial blood and by means of new methods such as those using the patient’s capillary blood through reflectance photometry. Lactic acid equivalent values in central vein, peripheral, artery, and pulmonary blood have been evaluated [5,6]; but there is no literature correlating prompt detection methods of LA as, for example, the one of capillary blood in emergency service.
Hypothesis
There are no studies comparing the 3 diagnostic methods; therefore, our hypothesis is that the determination of LA through capillary puncture has a high correlation with other methods of determination (arterial and venous) in patients with tissue hypoperfusion.
Purpose
Main
The main purpose was to evaluate the sensitivity, specificity, and correlation of different methods of measurement for LA–capillary, venous, and arterial–in a population of patients with different degrees of tissue hypoperfusion.
0735-6757/$ – see front matter (C) 2013 http://dx.doi.org/10.1016/j.ajem.2013.06.015
1366 L. Seoane et al. / American Journal of Emergency Medicine 31 (2013) 1365–1367
Secondary
The secondary purpose was to evaluate the time needed for each method.
Material and methods
The emergency service at Hospital Universitario Austral offers a high-complexity level service that assists 12,000 patients per month. The study cohort design was prospective. Inclusion criteria adopted included patients older than 18 years with signs of peripheral tissue hypoperfusion, shocks of any kind, serious sepsis, serious trauma, acute myocardial infarction, neurological disorders with Glasgow scale less than or equal to 12, and heart and respiratory failure signs. Exclusion criteria included HIV-positive patients treated with Protease inhibitors
(they increase LA considerably without any signs of hypoperfusion).
Definitions
Shock: has systolic blood pressure less than 100 mm Hg.
Serious sepsis: meets systemic inflammatory response syndrome criteria with an infectious focus plus one of the following: systolic blood pressure less than 90 o medium blood pressure less than 65 or fall greater than 40 of basal blood pressure that recovers with fluids; bilirubin greater than 2 mg/dL; platelets less than 100,000; international normalized ratio greater than 1.5 or KPTT greater than 60?; creatinine greater than 2 mg/ dL; pulmonary bilateral infiltration with PaFi less than 300.
Heart failure: according to the Framingham criteria (2 main criteria or a main criterion and 2 secondary criteria):
Main criteria: paroxysmal nocturnal dyspnea, jugular engorge- ment, wheezing, radiographic cardiomegaly, acute pulmonary edema, gallop rhythm or third heart sound, hepatojugular reflux, weight loss greater than 4.5 kg in 5 days as Treatment response. Secondary criteria: bilateral edema of the lower limbs, night time coughs, exertional dyspnea, hepatomegaly, pleural effusion, reduced vital capacity to one-third of maximum capacity, tachycardia greater than 120 beats per minute.
Ventilatory failure: one of the following: respiration rates greater than 30 per minute3, use of accessory muscles, intercostal retraction, added bilateral lung sounds, PO2 less than 60 mm Hg.
Acute myocardial infarction: must meet 2 of the following criteria:
ST elevation of at least 2 mm in contiguous derivations, acute chest pain, or increased creatine kinase.
Basal characteristics
Characteristics |
(n) |
Male |
66% (52) |
Immunosuppression |
31% (24) |
Pregnancy |
3% (2) |
24% (19) |
|
15% (12) |
|
Smoking |
10% (8) |
Obesity |
8% (6) |
Neurologic |
8%(6) |
Diabetes |
9% (7) |
Cirrhosis |
9%(7) |
Inclusion criteria Hypoperfusion |
19%(15) |
Cardiogenic shock |
1% (1) |
4%(3) |
|
18%(14) |
|
Severe sepsis |
18% (14) |
Trauma |
1% (1) |
Acute myocardial infarction |
0 |
Glasgow b12 |
5% (4) |
Ventilatory failure |
32%(25) |
1%(1) |
Fig. 1. ROC curve: venous LA.
Lactic acid analysis by means of 3 different methods was performed on each patient: capillary, venous, and arterial blood simultaneously. Capillary blood collection was performed on earlobes. Artery blood collection was performed preferably on the radial or femoral artery with a preheparinized syringe and vein sample collection through a peripheral vein puncture on upper limbs. The blood was placed in a tube with lithium heparin for further analysis. The time from triage admission to final result was recorded, and the results’ sensitivity and specificity according to methods used were
analyzed. An LA level lower than 2 mmol/L was considered normal.
The different methods of LA evaluation were analyzed with the following equipment:
- Lactic acid evaluation devices through capillary blood, Accutrend Plus, Roche Products SAQ e I (point-of-care device).
- Multiparameter analyserde Cobas b 221 (Roche),”amperometric- enzymatic method.”
Statistical analysis
The analysis was descriptive, expressing continuous quantitative variables on average and standard deviation or median and interquartile interval according to observed distribution. Categorical variables were expressed as proportions with their absolute
Fig. 2. ROC curve: capillary LA.
L. Seoane et al. / American Journal of Emergency Medicine 31 (2013) 1365–1367 1367
frequency. receiver operating characteristic curves were used to assess venous and capillary LA with respect to arterial LA (considered the criterion standard). The area under ROC curve was expressed and determined at cutoff point with the best specificity, sensitivity, positive predictive value (PPV), and negative predictive value (NPV) with their 98% confidence intervals (95% CIs). A value lower than .005 was considered statistically significant. IBM SPSS version 19 was used.
Results
The study included 79 male patients with a median age of 58 (IR 40-66) years; 66% (52/79) were male. Patient characteristics, history, and inclusion criteria are shown on the Table.
Venous LA showed an area under the curve of 86% (95% CI, 78-94). Relevant cutoff point found was 2.5, with a 76% sensitivity (95% CI, 62- 87) 78% specificity (95% CI, 58-90), PPV 86 (95% CI, 72-94), and NPV
64 (95% CI, 46-79). The area under the curve for capillary LA was 82% (95% CI, 73-91). Relevant cutoff point was 2.35, with an 81% sensitivity (95% CI, 65-90), 70% specificity (95% CI, 53-83), PPV 75 (95% CI, 60-
87), and NPV 76 (95% CI, 56-89) (Figs. 1 and 2).
The average time from patient admission until arterial, venous, and capillary LA values were obtained was 112, 117, and 77 minutes, respectively. The time difference gained between artery LA and capillary LA was 35 minutes. Patients who died within 3, 30, and 60 days showed an average artery LA of 5.9, 1.9, and 2.2, respectively.
Discussion
Initial LA levels have been proven to predict mortality in emergency services [2,7], as well as in sepsis [7], trauma [8,9], shock [10-12], burn victims [13], surgical intensive care unit [9,14], and general intensive care unit [15].
Even in patients who present trauma with normal or almost normal CF, LA levels higher than 2.5 mmol/L have been able to predict morbidity and mortality as well as worsening with persisting high LA [3]. This case of high LA with no overt shock has been called occult shock or occult hypoperfusion.
In “Early goal-directed therapy in the treatment of severe sepsis and septic shock” by Rivers et al [16], patients who presented sepsis in the emergency department (with LA N 4 mmol/L) were selected for a conducted early treatment within 6 hours. This therapy reduced in- hospital mortality from 46% to 30% at day 28; that is, there was an absolute mortality decrease of 16%. This led to the Surviving Sepsis Campaign [17], which recommends this therapy, among others.
In our study, capillary and venous LA sensitivity and specificity, compared with the criterion standard arterial LA, were evaluated through radial puncture. In our population, both LA evaluations perform effectively to diagnose hyperlactacidemia in patients with signs of tissue hypoperfusion. A small difference in favor of capillary LA vs venous LA specificity was found, which did not prove statistically significant (P = .46).
The time needed to obtain arterial, capillary, and venous LA was evaluated from patient admission until final results; the outcomes were 112, 117, and 77 minutes, respectively. The difference in “time gained” between arterial LA and capillary LA was 35 minutes. This correlates with the studies of Goyal et al [18,19], wherein a time gained of 65 minutes between capillary and arterial leads to time gained for patient location in shock room, medical evaluation, diagnosis tests, and earlier beginning of therapy (expansion with crystalloids and antibiotics). It should be mentioned that, for the latter studies, the samples were collected from the soft part of the finger at triage rooms. In our experience, the sample was obtained from the
earlobe so as to reduce the interference of a possible regional hypoperfusion factor.
The LA evaluation method from triage proves faster with respect to our sample collection after being placed in a box. In the context of a national overpopulation of emergency departments, the time reduced through a quick evaluation method for critical patients impacts dramatically on triage classification and immediate assistance to more complicated cases.
It should be noted that not only is capillary evaluation comparable to artery LA but also the speed in obtaining results and action taken greatly favor quick-yielding methods in emergencies, for instance, devices such as “point of care.” Another important benefit is 90% cost saving for each determination.
Lastly, mortality evaluation according to initial artery LA shows that values greater than5 mmol/L present a high mortality 3 days after with respect to those patients who died 30 and 60 days after clinical presentation, as also shown by Shapiro’s series [2].
Conclusion
The use of capillary and venous LA is very effective; that is, they are high-performance methods to evaluate patients with different de- grees of tissue hypoperfusion with respect to arterial LA and stratify their risks. The time to obtain capillary LA proved much faster than that for artery LA and venous LA.
References
- Wang HE, Shapiro NI, Angus DC, et al. National estimates of severe sepsis in United States emergency departments. Crit Care Med 2007;35:1928e36.
- Shapiro NI, Howell MD, Talmor D, et al. Serum lactate as a predictor of mortality in emergency department patients with infection. Ann Emerg Med 2005;45:524-8.
- Blow O, Magliore L, Claridge JA, et al. The golden hour and the silver day: detection and correction of occult hypoperfusion within 24 hours improves outcome from major trauma. J Trauma 1999;47:964-9.
- Levraut J, Ciebiera JP, Chave S, et al. Mild hyperlactatemia in stable septic patients is due to impaired Lactate clearance rather than overproduction. Am J Respir Crit Care Med 1998;157:1021-6.
- Lavery RF, Livingston DH, Tortella BJ, et al. The utility of venous lactate to triage injured patients in the trauma center. J Am Coll Surg 2000;190:656-64.
- Weil MH, Michaels S, Rackow EC. Comparison of blood lactate concentrations in central venous, pulmonary artery, and arterial blood. Crit Care Med 1987;15: 489-90.
- Nguyen HB, Rivers EP, Knoblich BP, et al. Early lactate clearance is associated with improved outcome in severe sepsis and septic shock. Crit Care Med 2004;32: 1637-42.
- Dunne JR, Tracy JK, Scalea TM, et al. Lactate and Base deficit in trauma: does alcohol or drug use impair their predictive accuracy? J Trauma 2005;58:959-66.
- Husain FA, Martin MJ, Mullenix PS, et al. Serum lactate and base deficit as predictors of mortality and morbidity. Am J Surg 2003;185:485-91.
- Cowan BN, Burns HJ, Boyle P, et al. The relative prognostic value of lactate and haemodynamic measurements in early shock. Anaesthesia 1984;39:750-5.
- Marecaux G, Pinsky MR, Dupont E, et al. Blood lactate levels are better prognostic indicators than TNF and IL-6 levels in patients with septic shock. Intensive Care Med 1996;22:404-8.
- Vincent JL, Dufaye P, Berre J, et al. Serial lactate determinations during circulatory shock. Crit Care Med 1983;11:449-51.
- Kamolz LP, Andel H, Schramm W, et al. Lactate: early predictor of morbidity and mortality in patients with severe burns. Burns 2005;31:986-90.
- McNelis J, Marini CP, Jurkiewicz A, et al. Prolonged lactate clearance is associated with increased mortality in the surgical intensive careunit. Am J Surg 2001;182: 481-5.
- Stacpoole PW, Wright EC, Baumgartner TG, et al. Natural history and course of acquired lactic acidosis in adults. DCA-Lactic Acidosis Study Group. Am J Med 1994;97:47-54.
- Rivers E, Nguyen B, Havstad S, et al. Early goal-directed therapy in the treatment of severe sepsis and septic shock. N Engl J Med 2001;345:1368-77.
- Dellinger RP, Carlet JM, Masur H, et al. Surviving sepsis campaign guidelines for management of severe sepsis and septic shock. Crit Care Med 2004;32:858-73.
- Goyal M, Fuchs BD, Shofer FS, Drumheller BC, Zogby K, Gaieski DF. Validation of point-of-care fingertip lactate measurement in the emergency department. Ann Emerg Med 2006;48(4S):2.
- Goyal M, Pines JM, Drumheller BC, and Gaieski DF. Point-of-care testing at triage decreases time to lactate level in.