Agreement and correlation of pH, bicarbonate, base excess and lactate measurements in venous and arterial blood of premature and term infants

BACKGROUND AND OBJECTIVES: Determine the extent of agreement and correlation between arterial samples and venous (obtained from a venous umbilical catheter), with respect to measurements of pH, bicarbonate, base excess and lactate, in critically ill term and premature newborns. METHODS: Arterial blood samples (0.5-1 mL) were obtained for gas analysis by radial artery puncture, and, within the limit of 5 minutes, samples were obtained from venous umbilical catheters. Bland-Altman plots were used to depict agreement between arterial and venous measurements. Limits of agreement were defined as the mean difference ± 2SD (Standard Deviation). Correlation was assessed by Pearson's method. RESULTS: A hundred and six samples (53 pairs) were taken from 53 patients for analysis of bicarbonate, pH and base excess. Lactate was analyzed in 49 pairs of samples. Differences were within the limits of agreement in 94.3 percent of pairs of samples for pH, and the same percentage was observed for bicarbonate. There was agreement in 96.2 percent of pairs for base excess, and in 91.8 percent for lactate. Mean differences were 0.03 units for pH, -1.2 mmol/L for bicarbonate, -0.24 mmol/L for base excess and 0.33 mmol/L for lactate. Pearson's correlation coefficients (r) were 0.87 for pH, 0.76 for bicarbonate, 0.86 for base excess and 0.95 for lactate. CONCLUSIONS: Although single venous values cannot be used as equivalent to arterial for assessing acid base status in newborns, venous blood samples can be used serially for monitoring trends over time.

JUSTIFICATIVA E OBJETIVOS: Determinar o grau de concordância e correlação entre amostras arteriais e as obtidas através de um cateter venoso umbilical, com relação ao pH, bicarbonato, excesso de base (BE) e lactato, em recém-nascidos prematuros e de termo, criticamente doentes. MÉTODO: Foram obtidas amostras para gasometria (0,5 - 1 mL), por punção de artéria radial, e, dentro do limite de 5 minutos, do cateter venoso umbilical. O método de Bland-Altman foi utilizado para demonstrar a concordância entre as medidas. Os limites de concordância foram definidos como a diferença média ± 2 DP. Para as correlações foi utilizado o método de Pearson. RESULTADOS: Cento e seis amostras (53 pares) de 53 pacientes foram analisadas para bicarbonato, pH e BE. Foi dosado lactato em 49 pares de amostras. Houve concordância em 94,3 por cento dos pares de amostras para o pH, e este mesmo percentual foi observado para o bicarbonato. Para o excesso de base, a concordância foi de 96,2 por cento, e de 91,8 por cento para o lactato. As diferenças médias foram 0,03 unidade para o pH, -1,2 mmol/L para o bicarbonato, -0,24 mmol/L para o excesso de base e 0,33 mmol/L para o lactato. Os coeficientes de correlação de Pearson (r) foram 0,87 para o pH, 0,76 para o bicarbonato, 0,86 para o excesso de base e 0,95 para o lactato. CONCLUSÕES: Os valores venosos isolados não podem ser usados como equivalentes aos arteriais para a avaliação do estado ácido-básico em recém-nascidos. As amostras venosas poderiam ser usadas de forma serial, para monitorizar tendências ao longo do tempo.

Cefepime restriction improves gram-negative overall resistance patterns in neonatal intensive care unit

Antibiotic restriction can be useful in maintaining bacterial susceptibility. The objective of this study was verify if restriction of cefepime, the most frequently used cephalosporin in our neonatal intensive care unit (NICU), would ameliorate broad-spectrum susceptibility of Gram-negative isolates. Nine hundred and ninety-five premature and term newborns were divided into 3 cohorts, according to the prevalence of cefepime use in the unit: Group 1 (n=396) comprised patients admitted from January 2002 to December 2003, period in which cefepime was the most used broad-spectrum antibiotic. Patients in Group 2 (n=349) were admitted when piperacillin/tazobactam replaced cefepime (January to December 2004) and in Group 3 (n=250) when cefepime was reintroduced (January to September 2005). Meropenem was the alternative third-line antibiotic for all groups. Multiresistance was defined as resistance to 2 or more unrelated antibiotics, including necessarily a third or fourth generation cephalosporin, piperacillin/tazobactam or meropenem. Statistics involved Kruskal-Wallis, Mann-Whitney and logrank tests, Kaplan-Meier analysis. Groups were comparable in length of stay, time of mechanical ventilation, gestational age and birth weight. Ninety-eight Gram-negative isolates were analyzed. Patients were more likely to remain free of multiresistant isolates by Kaplan-Meier analysis in Group 2 when compared to Group 1 (p=0.017) and Group 3 (p=0.003). There was also a significant difference in meropenem resistance rates. Cefepime has a greater propensity to select multiresistant Gram-negative pathogens than piperacillin/tazobactam and should not be used extensively in neonatal intensive care.