Characterizing the Caudal Vena Cava
Measurements
Guidelines for caudal vena caval (CVC) absolute size in dogs of various weight classes have been created by the author from the data generously provided by Dr Elodie Darnis and colleagues (Darnis et al. 2018). More indepth CVC detail regarding measurements and formulas may be found in her co‐authored Chapter 26.
The expected CVC maximum heights for three weight classes of dogs taken in the longitudinal plane at the FAST DH view (subxiphoid) are shown in Table 7.6. The absolute height measurements should be combined with the “eyeball method” of evaluating respirophasic dynamic changes in the CVC. This gestalt “eyeball method” essentially assesses the CVC Collapsibility Index, which is the difference between maximum and minimum diameter divided by the maximum diameter multiplied by 100%.
The author has characterized the CVC as having a “bounce,” being “FAT” or “flat” for categorizing its clinical relevance to volume status. A “bounce” is a “fluid‐responsive” CVC; a “FAT” CVC is a distended CVC suggesting a “fluid‐intolerant” CVC reflective of an abnormally high central venous pressure (hypervolemia); and a “flat” CVC is a “fluid‐starved” CVC reflective of a “hypovolemic CVC.” The terms “FAT” and “flat” have been descriptively used in the human literature (Ferrada et al. 2012a,b) and many clinicians combine absolute maximum inferior vena cava height measurements with the “eyeball method” (FAT or flat). More and more, these same clinicians are incorporating basic echo views and lung ultrasound findings for more clinical integration to accurately assess volume status and thus guide fluid resuscitation in people (Ferrada et al. 2012a,b). Similar approaches are being investigated in veterinary medicine (Nelson et al. 2010; Lisciandro 2014a, 2016a, Lisciandro and Fosgate 2017; Bucci et al. 2017; Kwak et al. 2017; Tuplin et al. 2017; Darnis et al. 2018; Marshall et al. 2018; Cambournac et al. 2018) (see Chapters 26, 36, and 37 and also Figures 36.8–36.12). The terms “FAT” (fluid intolerant, high central venous pressure, inferior vena cava >2 cm) and “flat” (fluid starved, low central venous pressure, hypovolemia) are routinely used in human medicine in the San Antonio area (Ferrada et al. 2012a,b). The author has added the term “bounce” for a fluid‐responsive CVC. The suggested CVC measurements shown in Table 7.6 are at least a start and are easy to remember over formulas.
Table 7.6. Reference values for the caudal vena cava (CVC) measured in longitudinal at the subxiphoida view in 126 healthy dogs, grouped into three body weight classes.
| Size | Body weight (kg) | Expected CVC height measurement (cm) | CVC +/‐2 standard deviations (cm) | Suggested CVC maximum height (cm) for a “flat” or hypovolemic, fluid‐starved CVC | Suggested CVC maximum height (cm) for a “FAT” or fluid‐intolerant CVC (high central venous pressure) |
|---|---|---|---|---|---|
| Small/Toyb | <9 kg | 0.55 | (0.23–0.86) | <0.25 | >1.0 |
| Medium | >9–15 kg | 0.85 | (0.32–1.38) | <0.35 | >1.5 |
| Large/Giant | >15 kg | 0.96 | (0.51–1.4) | <0.50 | >1.5 |
Data from the study by Darnis et al. (2018) and measurements created with permission by Lisciandro GR and Vientós‐Plotts AI. These values are unproven but give some guidelines for veterinary clinicians to combine with the eyeball method – “bounce”, “FAT,” and “flat.”
a The subxiphoid view is analogous to the FAST DH view and the CVC imaged in its longitudinal plane.
b Suggested starting point for felines while awaiting current research findings.
Integrating Global FAST Information
The characterization of the CVC is key because it helps with clinical integration of information when sonographic striation of the gallbladder is found in acute collapse or weakness in a dog with a previous healthy history (Figure 7.12) (Lisciandro 2014a). In canine AX, the CVC is expected to be “flat” having small maximum diameter with little respirophasic diametrical change because of the severe AX‐related hypovolemia (see Figures 7.12, 36.8–36.12). In contrast, patients with pericardial effusion/tamponade and right‐sided congestive heart failure have a CVC that is expected to be “FAT” having a large maximum diameter with little respirophasic diametrical change because of the severe cardiac‐related hepatic venous congestion (see Figures 7.12, 36.8–36.12). The terms “flat” and “FAT” have been published as terms that similarly characterize the inferior vena cava (IVC) at the subxiphoid view in people (Ferrada et al. 2012a,b). Integration of other POCUS and FAST findings is imperative for accurate interpretation. More information regarding the CVC and its evaluation may be found in Chapters 19, 20, 26, 36, and 37.
Canine AX‐Related Heparin‐Induced Hemoabdomen – Single Witnessed or Unwitnessed Hymenoptera sp. Envenomation
Although we were the first group to describe the phenomenon in the veterinary literature (Lisciandro 2016b), all the credit goes to Dr Scott Johnson, of Austin, Texas. When Dr Johnson took our Global FAST course in 2010, he remarked that he had observed hemoabdomen in anaphylactic dogs, and that we should start looking during AFAST. We heeded his suggestion and have seen close to 100 canine anaphylactic dogs with positive fluid scores and dozens with confirmed hemoabdomen that responded to medical treatment (Lisciandro 2014a, 2016b; Hnatusko et al. 2019). Importantly, these are witnessed or unwitnessed events likely caused by a presumed single Hymenoptera species envenomation (not massive bee envenomation). The great majority of anaphylactic dogs have no obvious cutaneous signs (Lisciandro 2016b; Hnatusko et al. 2019).
Heparin, a clinically tangible constituent of mast cells, likely plays a major role, thus the addition of “heparin‐induced” by the author to its descriptor (Lisciandro 2016b). The importance of recognizing this AX‐related heparin‐induced hemoabdomen is that these dogs are medically treated (Lisciandro 2014a, 2016b; Caldwell et al. 2018; Birkbeck
