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Original article
Available online 24 June 2024
Lack of correlation between central venous minus arterial PCO2 to arterial minus central venous O2 content ratio and respiratory quotient in patients with septic shock: A prospective observational study
Falta de correlación entre la relación PCO2 venosa central-arterial/contenido arterial-venoso central de O2 y cociente respiratorio en pacientes con shock séptico: Estudio prospectivo observacional
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Facundo J. Gutierreza, Mario O. Pozoa, Matías Mugnob, Sebastián P. Chapelac,d, Natalia Lloberad, María J. Reberendod, Gastón E. Muriasa, Paolo N. Rubatto Birrib, Vanina S. Kanoore Edulb, Arnaldo Dubinb,e,
Corresponding author
dubina@otamendi.com.ar

Corresponding author.
a Servicio de Terapia Intensiva, Hospital Británico, Perdriel 74 (C1280AEB), Ciudad Autónoma de Buenos Aires, Argentina
b Servicio de Terapia Intensiva, Sanatorio Otamendi, Azcuénaga 870 (C1115AAB), Ciudad Autónoma de Buenos Aires, Argentina
c Departamento de Bioquímica, Facultad de Medicina, Universidad de Buenos Aires, Paraguay 2155 (C1121ABG), Ciudad Autónoma de Buenos Aires, Argentina
d Equipo de Soporte Nutricional, Hospital Británico, Perdriel 74 (C1280AEB), Ciudad Autónoma de Buenos Aires, Argentina
e Cátedras de Terapia Intensiva y Farmacología Aplicada, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, Av.60 y Av. 120 (B1900), La Plata, Argentina
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Received 25 March 2024. Accepted 28 May 2024
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Figures (1)
Tables (3)
Table 1. Clinical and epidemiologic characteristics of the patients.
Table 2. Values of arterial and central venous gases, co-oximetry, CO2-derived variables, and expired gases analysis.
Table 3. Multiple linear regression model for central venous-arterial PCO2 to arterial minus central venous O2 content ratio (Pcv-aCO2/Ca-cvO2).
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Abstract
Objective

Central venous-arterial PCO2 to arterial-central venous O2 content ratio (Pcv-aCO2/Ca-cvO2) is commonly used as a surrogate for respiratory quotient (RQ) and tissue oxygenation. Although Pcv-aCO2/Ca-cvO2 might be associated with hyperlactatemia and outcome, neither the interchangeability with RQ nor the correlation with conclusive variables of anaerobic metabolism has never been demonstrated in septic shock. Our goal was to compare Pcv-aCO2/Ca-cvO2 and RQ in patients with septic shock.

Design

Prospective, observational study.

Setting

Two adult ICUs.

Patients

Forty-seven patients with septic shock on mechanical ventilation with stable respiratory settings and vasopressor dose after initial resuscitation.

Interventions

None.

Main variables of interest

We measured arterial and central venous gases, Hb, and O2Hb. Pcv-aCO2/Ca-cvO2 and the ratio of central venous-arterial CO2 content to arterial-central venous O2 content (Ccv-aCO2/Ca-cvO2) were calculated. RQ was determined by indirect calorimetry.

Results

Pcv-aCO2/Ca-cvO2 and Ccv-aCO2/Ca-cvO2 were not correlated with RQ (R2 = 0.01, P = 0.50 and R2 = 0.01, P = 0.58, respectively), showing large bias and wide 95 % limits of agreement with RQ (1.09, -1.10−3.27 and 0.42, -1.53−2.37). A multiple linear regression model showed Hb, and central venous PCO2 and O2Hb, but not RQ, as Pcv-aCO2/Ca-cvO2 determinants (R2 = 0.36, P = 0.0007).

Conclusions

In patients with septic shock, Pcv-aCO2/Ca-cvO2 did not correlate with RQ and was mainly determined by factors that modify the dissociation of CO2 from Hb. Pcv-aCO2/Ca-cvO2 seems to be a poor surrogate for RQ; therefore, its values should be interpreted with caution.

Keywords:
Carbon dioxide production
Oxygen consumption
Anaerobic metabolism
Respiratory quotient
Resumen
Objetivo

La relación entre la PCO2 venosa central-arterial y el contenido arterial-venoso central de O2 (Pvc-aCO2/Ca-vcO2) se emplea comúnmente como sustituto del cociente respiratorio (CR). Aunque la Pvc-aCO2/Ca-vcO2 puede asociarse a hiperlactacidemia y mayor mortalidad, la intercambiabilidad con CR y la correlación con variables definidas de metabolismo anaeróbico no se han demostrado en el shock séptico. Nuestro objetivo fue comparar Pvc-aCO2/Ca-vcO2 y CR en pacientes con shock séptico.

Diseño

Estudio observacional y prospectivo.

Ámbito

Dos UCIs de adultos.

Pacientes

Cuarenta y siete pacientes con shock séptico, ventilados mecánicamente, y con condiciones respiratorias y dosis de vasopresores estables, luego de la resucitación inicial.

Intervenciones

Ninguna.

Variables de interés principales

Se midieron gases arteriales y venosos centrales, Hb y O2Hb. Se calcularon Pcv-aCO2/Ca-cvO2 y la relación entre contenido venoso central-arterial de CO2 y el contenido arterial-venoso central de O2 (Cvc-aCO2/Ca-vcO2). El CR se determinó por calorimetría indirecta.

Resultados

Pvc-aCO2/Ca-vcO2 y Cvc-aCO2/Ca-vcO2 no correlacionaron con CR (R2 = 0.01, P = 0.50 and R2 = 0.01, P = 0.58, respectivamente) y tuvieron amplios sesgos y límites de concordancia del 95 % (1.09, -1.10−3.27 y 0.42, -1.53−2.37). El modelo de regresión lineal múltiple encontró Hb, PCO2 venosa central y O2Hb, pero no CR, como determinantes de Pvc-aCO2/Ca-vcO2 (R2 = 0.36, P = 0.0007).

Conclusiones

In pacientes con shock séptico, Pvc-aCO2/Ca-vcO2 no tuvo correlación con CR y estuvo determinada principalmente por factores que modifican la disociación de CO2 desde la Hb. Pvc-aCO2/Ca-vcO2 parece ser un pobre sustituto de CR y sus valores deben interpretarse con precaución.

Palabras clave:
Producción de dióxido de carbono
Consumo de oxígeno
Metabolismo anaeróbico
Cociente respiratorio

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