is the major player in each case. However, heparin must play a role because some dogs have obvious discordance in coagulation times with a much higher aPTT than PT time (consistent with heparinization). Mast cell granules contain heparin. Additional factors likely playing a role include histamine, bradykinin, tryptase, platelet‐activating factor, and others (Lisciandro 2016b; Caldwell et al. 2018; Hnatusko et al. 2019).
Therapy for Canine Anaphylaxis
The human case and these AX‐related factors are important to recognize for effective therapy. It is equally important to recognize that in people 4–5% (range ~2–20%) experience the “second episode of AX” in which inflammatory by‐products create a second wave of inflammation (Simons et al. 2015). The “second episode of AX” is countered therapeutically through the use of histamine‐2 receptor blockers (e.g., famotidine) and glucocorticoids, often continued over several days post AX. Histamine‐2 receptor blockers are readily available and help mitigate oozing of blood and plasma into the abdominal cavity. Glucocorticoids are important on several fronts, most importantly including: mitigating mast cell degranulation (stopping release of heparin and histamine), and indirectly attenuating the wind‐up of bradykinin (BK) through (a) blocking phospholipase A2 and the arachidonic acid pathway and (b) mitigating circulating heparin (Hnatusko et al. 2019) (see Table 7.7). Of note, maropitant and pantoprazole, commonly used drugs for gastrointestinal signs, do not treat AX and are ineffective for mitigating the “second episode of anaphylaxis” and treating the AX‐acquired coagulopathy.
In a recent case series of four dogs with AX‐hemoabdomen, three of the four dogs had small‐volume peritoneal effusion at the DH view and these three had short hospitalization courses (<48 hours). However, the fourth case had progression of the abdominal effusion and became unstable, requiring vasopressors and multiple units of FFP, surviving but hospitalized for five days. None of these four dogs received glucocorticoids or antihistamines to mitigate the “second episode of anaphylaxis.” The first three arguably got better on their own and were unlikely to progress no matter the treatment. However, the fourth dog arguably risked a poor outcome (death or euthanasia) and presumably had a large bill for its five days of intensive care with transfusion products and vasopressors (Birkbeck et al. 2019). One has to wonder if treating for the “second episode of AX” would have shortened the patient's course and curbed its complications and still would have been a low‐risk, high‐benefit, cost‐effective preventive therapy for the first three dogs. Moreover, performing a standardized AFAST and assigning an AFS would have provided more clinically relevant patient information rather than performing an unspecified POCUS abdominal exam using subjective descriptive terms for the ascites.
Pearl: Anaphylactic dogs commonly have AFAST‐positive fluid scores (AFS of 1 and 2, modified AFS system <3) with some developing large‐volume medically treated coagulopathic hemoabdomens (AFS 3 and 4, modified AFS system ≥3). Misdiagnosing and taking to surgery likely will be a fatal event.
Pearl: All canine AX‐hemoabdomen cases need to have as part of their work‐up a Global FAST and POCUS spleen evaluation to avoid “satisfaction of search error.” The combined evaluation will (1) semiquantitate volume of blood (AFS), (2) screen for gallbladder wall edema (AFAST), (3) screen for pericardial and pleural effusion (TFAST), (4) screen for right‐sided heart problems and dilated cardiomyopathy (TFAST), and (5) screen for a splenic mass (focused spleen). This combination of Global FAST and POCUS increases the probability of obtaining an accurate working diagnosis in the acutely collapsed or weak dog.
AFAST DH View for Pericardial Effusion
Anatomy and Advantages over TFAST Transthoracic Views
The premise is simple – always, always, always look cranial to the diaphragm at the FAST DH view (Figure 7.13; see also Figures 6.8 and 6.9) (Lisciandro 2016a, 2019). The use of the DH view for pericardial effusion (PCE) avoids air interference (ultrasound cannot transit through air) from lung at transthoracic views, especially since dogs and cats (and people) often have respiratory distress as their chief complaint. In fact, the subcostal FAST view in human medicine is the number 1 view for PCE that may be used a single view because the heart is so well imaged through the acoustic window provided by the liver and gallbladder into the thorax. In dogs and cats, the observation of the “racetrack sign” is essentially pathognomonic for PCE (Lisciandro 2014a, 2016a) (see Figure 7.13).
The best way to comprehend the relevant anatomy at the DH view is to look at an inverted canine (and feline) lateral thoracic radiograph (TXR). The TXR helps in learning the relative locations of the major structures, including the location of the muscular apex of the heart, called the “cardiac bump,” the expected positioning of heart chambers relative to the diaphragm, location of the CVC, and the expected location of the canine and feline gallbladder (Figure 7.14; see also Figures 6.11 and 6.12). The “cardiac bump” is the descriptor used for the observation of the beating heart and its muscular apex immediately against and, in dogs, often indenting the surface of the diaphragm where the heart and diaphragm come into contact (see Figures 7.14, 6.11, and 39.5). From our retrospective case series in which the methodology did not establish whether transthoracic TFAST views or the DH view was first performed, ~85% of PCE cases were imaged via the DH view (Lisciandro 2016a). In a prospective case series with subsequent improvements in training since our study, likely the DH view would prove to be nearly 100% sensitive and 100% specific for PCE in standing/sternal positioning in both dogs and cats. In other words, the DH view is a very good screening test.
Interestingly, the cardiac and diaphragmatic interface differs between people and dogs and cats. The human heart has its right ventricle and right atrium closest to the diaphragm whereas it is the left ventricle and left atrium in dogs and cats (see Figure 7.14). This is important when imaging the CVC because in people, the analogous IVC may be imaged as it enters the right atrium whereas in dogs and cats, the closest the CVC may be imaged to the right atrium is where the CVC passes through the diaphragm. Learning the DH view's cardiac orientation is a good add‐on skill. The DH cardiac view is helpful in PCE cases that have a left atrial tear/rupture from chronic mitral valve disease because the severely enlarged left atrium is commonly obvious here (conversely finding a small left atrium), and the DH view is generally less stressful and a better acoustic window for respiratory distressed patients.
Use for Cardiac Tamponade
The noncardiologist sonographer will grapple with this clinical question that often causes marked degrees of anxiety – does my patient have cardiac tamponade? And, taking it a step further – does my patient need emergent pericardiocentesis?
The diagnosis of cardiac tamponade is discussed in more detail in Chapters 18 and 21. Most importantly for the AFAST chapter, there exists a nonecho option, the characterization of the patient's CVC (see
