Evaluation of the caudal vena cava diameter to abdominal aortic diameter ratio and the caudal vena cava respiratory collapsibility for predicting fluid responsiveness in a heterogeneous population of hospitalized conscious dogs

Ultrasonographic measurement of caudal vena cava to aorta ratio during fluid resuscitation of dogs with spontaneous circulatory shock

OBJECTIVES

To describe the change in the caudal vena cava to aorta ratio (CVC:Ao) ratio during fluid resuscitation of circulatory shock in dogs and compare these results with those of the physical examination and blood lactate.

MATERIALS AND METHODS

Perfusion parameters and blood lactate were recorded at admission. An abdominal point-of-care ultrasound protocol was performed, during which the caudal vena cava to aorta ratio was measured on the spleno-renal view. Measurements were performed within 5 minutes before and after a 10 mL/kg crystalloid fluid bolus. Investigators were not blinded to therapeutic interventions.

RESULTS

Twenty-nine dogs with physical signs of circulatory shock were enrolled. Caudal vena cava to aorta ratios were below reference interval in 28 of 29 dogs. After bolus administration, median caudal vena cava diameter increased by 0.14 cm (0.69 to 0.83 cm) and median aorta diameter increased by 0.03 cm (0.87 to 0.90 cm) and caudal vena cava to aorta ratio returned to within reference range in 65% of dogs (13/29). Bolus administration was associated with an increase in median caudal vena cava to aorta ratio of 0.10 (95% CI:0.05 to 0.16, P=0.0005). Blood lactate did not change significantly. Heart rate and capillary refill time decreased significantly after fluid bolus (heart rate: estimate=-19 bpm, 95% CI:-30 to -8, P=0.002; capillary refill time: estimate=-1.0 s, 95% CI:-1.3 to -0.7, P < 0.0001).

CLINICAL SIGNIFICANCE

In this population of dogs with circulatory shock, the caudal vena cava to aorta ratio significantly increased after a fluid bolus. Future studies that implement blinding of the outcome assessors are warranted to confirm these findings.

Efficacy of ultrasonographic caudal vena cava to aorta ratios for quantifying canine parvoviral enteritis rehydration

Quantifying changes in intravascular fluid volume is important for treatment planning and follow-up assessment in dogs with dehydration. Recently, it has been reported that current standard methods used to estimate intravascular fluid volume in dogs are inadequate, invasive, or have complications such as thrombosis. The ultrasonographic ratio of dimensions for the caudal vena cava relative to the aorta (CVC/Ao) has been previously described as a promising, noninvasive method for quantifying changes in blood volume in dogs. This prospective observational study aimed to describe ultrasonographic CVC/Ao values before and after fluid replacement in a sample of dogs with varying degrees of dehydration due to naturally-occurring canine parvoviral enteritis (CPE), test correlations between this measure and clinical dehydration scores and determine the clinical efficacy of this measure for fluid therapy follow-up. The clinical dehydration score of 30 dogs naturally infected with canine parvovirus was determined at the first admission using standard clinical scoring methods, and then CVC/Ao was measured ultrasonographically. Following initial fluid therapy, the clinical dehydration scores and ultrasonographic CVC/Ao values were remeasured. On the basis of receiver operating characteristic analyses, ultrasonographic CVC/Ao was found to be a more sensitive and specific indicator than physical examination-based methods for estimating intravascular fluid alterations in dogs with dehydration due to parvovirus and rehydration following fluid therapy. Findings supported the use of this measure for treatment planning and follow-up in future dogs presenting with dehydration.

Ecografía de la vena cava caudal pre, trans y post quirúrgica como determinación de hipotensión en perros

El volumen sanguíneo es un factor fundamental en la funcionabilidad hemodinámica determinante de la correcta homeostasis en los seres vivos. La hipovolemia, así como la hipervolemia son factores perjudiciales en el paciente que los padece. La medición del índice de colapsabilidad de la vena cava caudal (ICVCC) es un marcador predictor de ciertos trastornos, que pueden ser corregidos mediante la administración intravenosa de fluidos y así poder evaluar su adecuada respuesta mediante el uso de la ultrasonografía. Mediante el uso de la ultrasonografía, realizando una medición del diámetro máximo y mínimo de la VCC usando el modo M del equipo ecográfico, permite medir el diámetro interno de la VCC, antes, durante y después del procedimiento quirúrgico. En los pacientes que se evidenció un colapso de la VCC, independientemente del momento quirúrgico se administró una solución de Ringer Lactato para posteriormente medir nuevamente la VCC y verificar que fueron responsivos a la fluidoterapia.

Evaluation of caudal vena cava size using computed tomography in dogs under general anesthesia

This study investigated the association between caudal vena cava (CVC) size and circulatory dynamics in dogs using computed tomography (CT) under general anesthesia. The subjects were 104 dogs who had undergone CT under general anesthesia in the past. The ratio of short diameter of the CVC to aortic diameter (CVC_S/Ao) and the ratio of long to short diameter of the CVC (CVC_L/CVC_S) in the thorax and abdomen, respectively, were calculated using factors such as mean blood pressure (MBP), shock index (SI), anemia, hypoproteinemia, presence of intra-abdominal mass, and cardiac disease. There was a significant but negligible negative correlation between CVC_S/Ao and MBP. In contrast, no significant correlation was found between CVC size and SI. The low MBP group had significantly higher CVC_S/Ao of the thorax than the normal MBP group. The group with intra-abdominal mass had significantly lower CVC_S/Ao of the abdomen than the group without intra-abdominal mass. The group with cardiac disease had significantly lower CVC_L/CVC_S of the thorax than the group without cardiac disease. In multiple regression analysis, low MBP, cardiac disease, intra-abdominal mass, and anemia were significant factors for CVC_S/Ao of the thorax, CVC_L/CVC_S of the thorax, CVC_S/Ao of the abdomen, and CVC_L/CVC_S of the abdomen, respectively. In conclusion, CVC size assessment using CT in dogs under general anesthesia is influenced by various factors.

Development and comparison of an esophageal Doppler monitoring-based treatment algorithm with a heart rate and blood pressure-based treatment algorithm for goal-directed fluid therapy in anesthetized dogs: A pilot study

The objective of this pilot study was to determine the feasibility of a study comparing the efficacy of an esophageal Doppler monitor (EDM)-based fluid therapy algorithm with a heart rate (HR)- and mean arterial blood pressure (MAP)-based algorithm in reducing hypotension and fluid load in anesthetized dogs. Client-owned dogs undergoing general anesthesia for surgical procedures were randomized to two groups. An EDM probe for monitoring blood flow in the descending aorta was placed in each dog before receiving a crystalloid bolus (5 mL/kg) over 5 min. Fluids were repeated in case of fluid responsiveness defined by increasing Velocity Time Integral (VTI) ≥ 10% in group EDM and by decreasing HR ≥ 5 beats/min and/or increasing MAP ≥ 3 mmHg in group standard. The feasibility outcomes included the proportion of dogs completing the study and the clinical applicability of the algorithms. The clinical outcomes were the total administered fluid volume and the duration of hypotension defined as MAP < 60 mmHg. Data was compared between groups with Mann-Whitney U-test. p < 0.05 were deemed significant. Of 25 dogs screened, 14 completed the study (56%). There were no differences in the proportion of recorded time spent in hypotension in group standard [2 (0–39)% (median (range))] and EDM [0 (0–63) %, p = 1], or the total volume of fluids [standard 8 (5–14) mL/kg/h, EDM 11 (4–20) mL/kg/h, p = 0.3]. This study declined the feasibility of a study comparing the impact of two newly developed fluid therapy algorithms on hypotension and fluid load in their current form. Clinical outcome analyses were underpowered and no differences in treatment efficacy between the groups could be determined. The conclusions drawn from this pilot study provide important information for future study designs.

Clinical Application of the Fluid Challenge Approach in Goal-Directed Fluid Therapy: What Can We Learn From Human Studies?

Resuscitative fluid therapy aims to increase stroke volume (SV) and cardiac output (CO) and restore/improve tissue oxygen delivery in patients with circulatory failure. In individualized goal-directed fluid therapy (GDFT), fluids are titrated based on the assessment of responsiveness status (i.e., the ability of an individual to increase SV and CO in response to volume expansion). Fluid administration may increase venous return, SV and CO, but these effects may not be predictable in the clinical setting. The fluid challenge (FC) approach, which consists on the intravenous administration of small aliquots of fluids, over a relatively short period of time, to test if a patient has a preload reserve (i.e., the relative position on the Frank-Starling curve), has been used to guide fluid administration in critically ill humans. In responders to volume expansion (defined as individuals where SV or CO increases ≥10–15% from pre FC values), FC administration is repeated until the individual no longer presents a preload reserve (i.e., until increases in SV or CO are <10–15% from values preceding each FC) or until other signs of shock are resolved (e.g., hypotension). Even with the most recent technological developments, reliable and practical measurement of the response variable (SV or CO changes induced by a FC) has posed a challenge in GDFT. Among the methods used to evaluate fluid responsiveness in the human medical field, measurement of aortic flow velocity time integral by point-of-care echocardiography has been implemented as a surrogate of SV changes induced by a FC and seems a promising non-invasive tool to guide FC administration in animals with signs of circulatory failure. This narrative review discusses the development of GDFT based on the FC approach and the response variables used to assess fluid responsiveness status in humans and animals, aiming to open new perspectives on the application of this concept to the veterinary field.

Fluid Overload

Fluid overload (FO) is characterized by hypervolemia, edema, or both. In clinical practice it is usually suspected when a patient shows evidence of pulmonary edema, peripheral edema, or body cavity effusion. FO may be a consequence of spontaneous disease, or may be a complication of intravenous fluid therapy. Most clinical studies of the association of FO with fluid therapy and risk of harm define it in terms of an increase in body weight of at least 5–10%, or a positive fluid balance of the same magnitude when fluid intake and urine output are measured. Numerous observational clinical studies in humans have demonstrated an association between FO, adverse events, and mortality, as have two retrospective observational studies in dogs and cats. The risk of FO may be minimized by limiting resuscitation fluid to the smallest amount needed to optimize cardiac output and then limiting maintenance fluid to the amount needed to replace ongoing normal and pathological losses of water and sodium.

Assessment of Volume Status and Fluid Responsiveness in Small Animals

Intravenous fluids are an essential component of shock management in human and veterinary emergency and critical care to increase cardiac output and improve tissue perfusion. Unfortunately, there are very few evidence-based guidelines to help direct fluid therapy in the clinical setting. Giving insufficient fluids and/or administering fluids too slowly to hypotensive patients with hypovolemia can contribute to continued hypoperfusion and increased morbidity and mortality. Similarly, giving excessive fluids to a volume unresponsive patient can contribute to volume overload and can equally increase morbidity and mortality. Therefore, assessing a patient's volume status and fluid responsiveness, and monitoring patient's response to fluid administration is critical in maintaining the balance between meeting a patient's fluid needs vs. contributing to complications of volume overload. This article will focus on the physiology behind fluid responsiveness and the methodologies used to estimate volume status and fluid responsiveness in the clinical setting.