Article

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.

* Corresponding author.

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) 13651367

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.

Table

Basal characteristics

Characteristics

(n)

Male

66% (52)

Immunosuppression

31% (24)

Pregnancy

3% (2)

Cardiovascular history

24% (19)

asthma/chronic obstructive pulmonary disease

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)

hemodynamic shock

4%(3)

distributive shock

18%(14)

Severe sepsis

18% (14)

Trauma

1% (1)

Acute myocardial infarction

0

Glasgow b12

5% (4)

Ventilatory failure

32%(25)

cardiac failure

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:

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