Brazilian Journal of Anesthesiology
https://bjan-sba.org/article/doi/10.1016/j.bjane.2021.07.025
Brazilian Journal of Anesthesiology
Original Investigation

Role of Pv-aCO2 gradient and Pv-aCO2/Ca-vO2 ratio during cardiac surgery: a retrospective observational study

Papel do gradiente Pv-aCO2 e da relação Pv-aCO2/Ca-vO2 durante cirurgia cardíaca: um estudo observacional retrospectivo

Juan P. Bouchacourt; F. Javier Hurtado; Eduardo Kohn; Laura Illescas; Arnaldo Dubin; Juan A. Riva

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Abstract

Introduction
Arterial lactate, mixed venous O2 saturation, venous minus arterial CO2 partial pressure (Pv-aCO2) and the ratio between this gradient and the arterial minus venous oxygen content (Pv-aCO2/Ca-vO2) were proposed as markers of tissue hypoperfusion and oxygenation. The main goals were to characterize the determinants of Pv-aCO2 and Pv-aCO2/Ca-vO2, and the interchangeability of the variables calculated from mixed and central venous samples.

Methods
35 cardiac surgery patients were included. Variables were measured or calculated: after anesthesia induction (T1), end of surgery (T2), and at 6-8 hours intervals after ICU admission (T3 and T4).

Results
Macrohemodynamics was characterized by increased cardiac index and low systemic vascular resistances after surgery (p < 0.05). Hemoglobin, arterial-pH, lactate, and systemic O2 metabolism showed significant changes during the study (p < 0.05). Pv-aCO2 remained high and without changes, Pv-aCO2/Ca-vO2 was also high and decreased at T4 (p < 0.05). A significant correlation was observed globally and at each time interval, between Pv-aCO2 or Pv-aCO2/Ca-vO2 with factors that may affect the CO2 hemoglobin dissociation. A multilevel linear regression model with Pv-aCO2 and Pv-aCO2/Ca-vO2 as outcome variables showed a significant association for Pv-aCO2 with SvO2, and BE (p < 0.05), while Pv-aCO2/Ca-vO2 was significantly associated with Hb, SvO2, and BE (p < 0.05) but not with cardiac output. Measurements and calculations from mixed and central venous blood were not interchangeable.

Conclusions
Pv-aCO2 and Pv-aCO2/Ca-vO2 could be influenced by different factors that affect the CO2 dissociation curve, these variables should be considered with caution in cardiac surgery patients. Finally, central venous and mixed values were not interchangeable.

Keywords

Anaerobiosis;  Carbon dioxide;  Cardiac surgical procedures;  Perfusions

Resumo

Introdução

Lactato arterial, saturação venosa mista de O2, pressão parcial de CO2 venoso menos arterial (Pv-aCO2) e a relação entre esse gradiente e o conteúdo de oxigênio arterial menos venoso (Pv-aCO2/Ca-vO2) foram propostos como marcadores de hipoperfusão e oxigenação tecidual. Os principais objetivos foram caracterizar os determinantes de Pv-aCO2 e Pv-aCO2/Ca-vO2, e a intercambialidade das variáveis calculadas a partir de amostras venosas mistas e centrais.

Métodos

Foram incluídos 35 pacientes de cirurgia cardíaca. As variáveis ​​foram medidas ou calculadas: após a indução anestésica (T1), final da cirurgia (T2) e em intervalos de 6 a 8 horas após a admissão na UTI (T3 e T4).

Resultados

A macrohemodinâmica foi caracterizada por aumento do índice cardíaco e baixas resistências vasculares sistêmicas após a cirurgia (p < 0,05). A hemoglobina, o pH arterial, o lactato e o metabolismo sistêmico do O2 apresentaram alterações significativas durante o estudo (p < 0,05). A Pv-aCO2 permaneceu elevada e sem alterações, a Pv-aCO2/Ca-vO2 também esteve elevada e diminuiu em T4 (p < 0,05). Uma correlação significativa foi observada globalmente e em cada intervalo de tempo, entre Pv-aCO2 ou Pv-aCO2/Ca-vO2 com fatores que podem afetar a dissociação da hemoglobina CO2. Um modelo de regressão linear multinível com Pv-aCO2 e Pv-aCO2/Ca-vO2 como variáveis de desfecho mostrou uma associação significativa para Pv-aCO2 com SvO2 e BE (p < 0,05), enquanto Pv-aCO2/Ca-vO2 foi significativamente associado com Hb, SvO2 e BE (p < 0,05), mas não com débito cardíaco. As medições e cálculos de sangue venoso central e misto não eram intercambiáveis.

Conclusão

Pv-aCO2 e Pv-aCO2/Ca-vO2 podem ser influenciados por diferentes fatores que afetam a curva de dissociação de CO2, essas variáveis devem ser consideradas com cautela em pacientes de cirurgia cardíaca. Finalmente, os valores venosos centrais e mistos não eram intercambiáveis.

Palavras-chave

Anaerobiose; Dióxido de carbono; Procedimentos cirúrgicos cardíacos; Perfusões

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