The patient presented to the practice in a semi-collapsed condition, the owner reported this happened suddenly while the dog was out walking. On examination it became clear the patient was in shock but the cause was unknown.
Signalment
Species: Canine
Breed: Labrador
Age: 1 year
Sex: Female (neutered)
Weight: 27 kg
Initial patient triage/major body systems assessment
The patient was triaged by assessing the major body systems.
Cardiovascular
Heart rate was 140 beats/minute (normal 60–140 beats/minute) with weak peripheral pulses, heart sounded muffled. Mean blood pressure (MAP) 81 mmHg (normal 60–85 mmHg). Mucous membranes were pale pink/muddy coloured in appearance with a capillary refill time of 2 seconds (normal 1–2 seconds). Patient was hyperthermic with a temperature of 39.5°C (normal 38.3–39.2°C).
Respiratory
The patient had an increased respiratory effort with a rate of 36 breaths/minute (normal 10–30 breaths/minute). Oxygen saturation was measured with a pulse oximeter as 99% (normal 95%).
Neurological
Patient was dull with obtunded mentation, unable to ambulate and was hypersalivating.
Veterinary investigations and treatment
Blood was taken for biochemistry, haematology and electrolytes: platelet count was low (anaphylaxis causes platelet aggregation), all other parameters were within normal limits. Blood gases were not taken as the practice lacks this facility. An intravenous catheter was placed, Hartmann's solution was administered intravenously at a rate of 270 ml/hour; the patient's response was assessed every 10 minutes. A FAST Scan (focused assessment with sonography for trauma) showed the heart appeared normal, no free fluid was seen, and minor pulmonary oedema was present. The patient's clinical signs continued to deteriorate in the imaging suite: heart rate increased to 160 beats/minute, MAP dropped to 48 mmHg, respiratory effort and rate increased, temperature decreased to 38.8°C, chest continued to sound muffled and it was difficult to auscultate the heart, pulses were still poor, and the patient appeared weaker. While the light was off the patient had developed generalised urticaria which was only noted when the light was turned on. Chlorphenamine (10 mg/kg) and dexamethasone (0.5 mg/kg) were administered intravenously. The patient's clinical signs quickly began to improve, and once stabilised she was transferred to the general ward and monitored every 2 hours. The patient was discharged 4 hours after the initial incident.
Discussion of nursing interventions
Anaphylactic shock is the result of considerable vasodilation secondary to mast cell degranulation, histamine release and the quick release of inflammatory and vasoactive mediators; these mediators then cause vasodilation, which decreases perfusion and therefore oxygen delivery to the organs. The body's response is for the spleen to contract, the heart rate will increase, which in combination leads to myocardial and cerebral hypoxaemia, cardiovascular collapse and death (Lyons and Scherk, 2017). It is a severe condition, which must be treated immediately, but it is rare, can be difficult to diagnose and is often overlooked. There is inconsistency in the differentiation of diagnosing anaphylaxis versus an allergic reaction. This is partly because of a lack of specific criteria to diagnose anaphylactic shock, and research into the epidemiology, pathophysiology and management of this condition is lacking. Consistency in its diagnoses and treatment is variable, despite quick action being crucial to a positive patient outcome (Lyons and Scherk, 2017). In humans a universal clinical criterion for classifying anaphylaxis has recently been defined (Sampson and Muñoz-Furlong, 2006) (Table 1). However, nothing has been established in any other species (Shmuel and Cortes, 2013). These criteria could be used as a reference in dogs; the patient in this case had clinical signs which were comparable and if these criteria were used then the likelihood of anaphylaxis as a diagnosis would be high. A study by Quantz et al (2009) concluded that increased alanine transaminase (ALT) and gallbladder wall oedema were biomarkers commonly associated with anaphylaxis in dogs. Although this patient had a FAST scan, this could have been overlooked and this information is useful to know for diagnosis of any future cases.
Table 1. Likelihood of anaphylaxis in humans
| Anaphylaxis is highly likely when any one of the following three criteria is fulfilled: |
|---|
| 1. Acute onset of an illness (minutes to several hours) with involvement of the skin, mucosal tissue, or both (e.g. generalised hives; pruritus or flushing; swollen lips, tongue, vulva) |
And at least 1 of the following:
|
2. Two or more of the following that occur rapidly after exposure to a likely allergen (minutes to several hours):
|
3. Reduced BP after exposure to a known allergen (minutes to several hours):
|
The physiology of shock is complex and understanding this is advantageous, but being able to recognise shock irrespective of its type, is invaluable (Wemple, 2010). The status of critically ill patients can be extremely dynamic (Andrews-Jones and Boags, 2015), therefore, the registered veterinary nurse (RVN) plays a vital role in patient monitoring and reporting changes so they can be acted on swiftly. Early detection of deterioration or complications can greatly impact the outcome of the patient (Andrews-Jones and Boag, 2015). Patient monitoring, fluid therapy and medication will be discussed in further detail. Additional patient care was carried out (Table 2), but is not within the scope of this patient care report.
Table 2. Care plan
| Activity | Patient ability | Nurse intervention |
|---|---|---|
| Eat | Appetite normal before incident | Offer food once patient mentation has improved and she is able to eat without assistance |
| Drink | No perceived problems | Water to be offered once patient mentation has improved and she is able to drink without assistance |
| Urinate | No perceived problems | Walk hourly once patient can walk to allow elimination. Provide incontinence pad under Vetbed so patient stays dry, if does urinate. Ensure bedding stays clean and dry |
| Defecate | No perceived problems | As for urination |
| Breathe normally | Patient is dyspnoeic, mucous membranes pale/muddy coloured | Provide oxygen via mask, record respiration rate and depth every 10 minutes, then 2 hourly once stable and transferred to wardPatient is hypersalivating — monitor for worsening as may affect respirationKeep patient in sternal or turn every 2 hours if lateralUse pulse oximeter while critical |
| Maintain body temperature | Hyperthermia | Take temperature every 30 minutes. Provide ice packs/fan if temperature increasesKeep room at ambient temperature (18–22oC) |
| Circulation | Tachycardia, mucous membranes pale/muddy coloured, hypotensive | Constant monitor of heart rate and sounds, record every 10–30 minutesMonitor blood pressure every 10–30 minutesCheck mucous membranes and capillary refill time every 10–30 minutesOnce normalised can monitor every hourAlert veterinarian if any changes |
| Groom and clean itself | Urinates on bed | Provide incontinence pad under Vetbed so stays dry if urinates on bedEnsure clean and dry if urinates on bed. Brush daily |
| Mobilise adequately | Patient is flat, currently in sternal as prefers this | Keep in sternal or turn every 2 hoursOnce stable can be walked |
| Sleep and rest adequately | No perceived problems | Provide comfortable bedding |
| Express normal behaviour | Obtunded can lift head | Monitor patient until mentation returns to normal, groom and fuss patient |
| Intravenous fluid therapy | Monitoring (discussed in extended patient care report), catheter care, check catheter site and change bandage twice daily. Monitor for signs of phlebitis (redness at site of insertion, temperature, fluids not flowing properly or infusion pump regularly occluding) |
Monitoring
The patient was experiencing the following abnormalities which can give an indication of the cardiovascular system. These are consistent with poor tissue perfusion and can lead to a reduction in oxygen delivery to tissues (Table 3, Reineke, 2014):
- Pale mucous membranes
- Tachycardia
- Quiet heart sounds
- Poor pulses
- Prolonged capillary refill time
- Weak femoral and pedal pulses
- Low MAP
- Quiet demeanour
- Dyspnoea.
Table 3. Physical examination and diagnostic parameters consistent with shock parameter
| Parameter | Value |
|---|---|
| Mentation | Depressed |
| Mucous membranes | Pale pink, white, injected |
| Capillary refill time | >2 seconds |
| Heart rate | Small-breed dogs: >160 beats/minute; large-breed dogs: >100 beats/minute |
| Respiratory rate | >40 breaths/minute |
| Pulse quality | Absent or weak femoral or metatarsal pulse narrow or wide pulse pressure |
| Blood pressure | Systolic: <90 mmHg; mean: <60 mmHg |
| Lactate | >2.5 mmol/litre |
These findings were measured and recorded every 10–30 minutes on the patient's hospitalisation forms as recommended by Reineke (2014). If poor tissue perfusion is not identified and treated immediately it can result in hypoxia, multiple organ dysfunction and death (Reineke 2014).
Hypotension is the main cardiovascular sign in anaphylaxis; this is intensified by fluid extravasation because of an increase in vascular permeability, which can lead to as much as a 35% reduction in blood volume (Lyons and Scherk, 2017). Combining this with the extreme vasodilation a mixed distributive-hypovolaemic shock pattern develops (Lyons and Scherk, 2017). This is likely the cause of the mild pulmonary oedema seen on ultrasound and why the patient's chest sounded dull, which the author had auscultated during triage. Additionally, a compensatory tachycardia may be seen as a result of hypovolaemia (Shmuel and Cortes, 2013), this was noted alongside a cardiac arrythmia. Epinephrine is the usual choice for cases of anaphylactic shock. It is essential in the treatment of anaphylaxis because of the benefits discussed in the ‘medication’ section of this case report, but in this case would have caused further complications (Lyons and Scherk, 2017).
Bradycardia although not present in this patient can be seen because of increased vagal activity and is worth noting for future patients. A tall and narrow pulse profile is often seen in cardiogenic shock, a pulse oximeter was used, and this sign was not noted, however, as the patient had a weak pulse rather than a bounding one, this may not have shown up on the pulse oximeter. The patient's oxygen saturation was 97–100%, but she was dyspnoeic, so oxygen was supplemented via an oxygen mask. Excessive mucus production, bronchoconstriction, laryngeal and pharyngeal oedema can all contribute to dyspnoea in anaphylactic shock (Shmuel and Cortes, 2013). MAP was monitored using an oscillometric machine, the cuff selected was 30% of the circumference of the limb and placed securely round the patient's left forelimb. The author recorded the patient's MAP, it may have been beneficial to record systolic blood pressure (BP) although this would not have changed the patient's treatment. Changes were reported to the veterinarian. It is important to monitor the patient's BP as discussed above, and it is also used in conjunction with other monitoring to decide on the intravenous fluid rate (Shmuel and Cortes, 2013).
The most common clinical signs of an allergic reaction are often cutaneous (erythema, urticaria, pruritus, wheals and angioedema), however this is often a precursor for more severe reactions, such as anaphylaxis (Lyons and Scherk, 2017). It is important to remember severe anaphylaxis can have a rapid onset and cutaneous signs may be absent or delayed (Lyons and Scherk, 2017). Hives were present in this patient, but their onset was delayed — hives can be caused by many triggers including drugs, foods and insect stings. Physical stimuli, such as exposure to heat and exercise, have also been reported, although these reactions usually only affect the skin and tend to be mild. However, some patients can develop an anaphylactic reaction, but there is little information published in the veterinary or human field (Lieberman et al, 2015). On admission to the hospital the patient was hyperthermic, although hypothermia is more common in shock patients; therefore, physical stimuli may have been the source, however, as there are few reports of physical stimuli causing anaphylaxis in published literature, it is difficult to know if this was the cause.
The patient should not have been transferred to the ward and discharged so quickly. Patients experiencing anaphylactic shock should be hospitalised for a minimum of 48 hours (Lyons and Scherk, 2017), in order to continue observation, as organs involved in the initial reaction can deteriorate quickly and should be monitored closely. Clinical signs can subside and reappear rapidly after several hours. This is known as a biphasic response and can increase mortality if not recognised and treated accordingly (Lyons and Scherk, 2017).
Fluid therapy
Aggressive fluid resuscitation is recommended for patients in shock, as they will be hypotensive, and should be administered as soon as clinical signs are recognised to reduce the risk of cardiovascular collapse (Shmuel and Cortes, 2013). A 22-gauge catheter was placed in the patient's right cephalic vein and Hartmann's solution was administered at 10 ml/kg/hour, for 45 minutes. Recommended shock rates of intravenous fluid therapy (IVFT) vary throughout veterinary publications; Lyons and Scherk (2017) recommended a shock dose of 10–20 ml/kg, given as a bolus over 5–15 minutes, which can be repeated up to 90 ml/kg. Shmuel and Cortes (2013) suggested 90 ml/kg, but do not advise how quickly this should be given, and Davis et al (2013) advised 80–90 ml/kg given rapidly over 25% increments. The patient could have received a higher rate than was administered, but it is difficult to know whether this would have led to a quicker recovery in this patient. All agree the most important thing to do when administering shock doses is to assess the patient's response regularly throughout administration. The patient's response to fluids was assessed and recorded by monitoring the parameters listed in Table 4 every 10 minutes using a timer. Davis et al (2013) recommended further monitoring, which was not carried out, including serum lactate which would have been a valuable diagnostic test to assess the patient's perfusion status (Reineke, 2017). Unfortunately, the practice does not have the facilities to carry out this test or blood gases. Other parameters not continually monitored include packed cell volume, total protein, creatinine, blood urea nitrogen and electrolytes; these were measured on admission, but could have been repeated while the patient was receiving fluids to gain more knowledge regarding the patient's perfusion status. Colloids can also be useful for fluid resuscitation as they can work quickly and have a more prolonged effect than crystalloid fluids such as Hartmann's solution (Davis et al, 2013). Colloids should be considered if there is not sufficient improvement in the patient's parameters following the administration of Hartmann's. Davis et al (2013) advised administration of colloids should occur once the patient has received 50% of the calculated fluid requirement. They should have been considered as despite receiving fluid therapy, the patient's vitals (including cardiovascular, respiratory and neurological systems) continued to decline. Heart rate had increased and was difficult to auscultate, pulses were still poor, blood pressure decreased and respiration rate and effort had worsened, and it was not until she received medications that any improvement was seen. Colloids must be used with caution as patients with anaphylaxis are at an increased risk of acute kidney injury as a result of dehydration, and their use is contraindicated in cases of renal failure.
Table 4. Evaluation and monitoring parameters that may be used for patients receiving fluid therapy
| Parameters monitored | Parameters not monitored |
|---|---|
| Pulse rate and quality | Packed cell volume/total solids |
| Capillary refill time | Total protein |
| Mucous membrane colour | Serum lactate |
| Respiratory rate and effort | Urine specific gravity |
| Lung sounds | Blood urea nitrogen |
| Skin turgor | Creatinine |
| Bodyweight | Electrolytes |
| Urine output | Venous or arterial blood gases |
| Mental status | |
| Extremity temperature | |
| BP | |
| O2 saturation |
Medication
The choice of medications used is ultimately the veterinarian's decision, but it is useful to know which drugs may be used in anaphylactic shock in order to be prepared and to know the reactions the drugs may cause for monitoring purposes. The patient was administered dexamethasone and chlorphenamine intravenously and discharged with prednisolone and chlorphenamine tablets. Dexamethasone and prednisolone are corticosteroids, which suppress the inflammatory process; side effects are not usually seen in short-term use <1 week. Epinephrine is usually the first drug used in anaphylaxis because of its adrenergenic effects — it causes bronchodilation which will increase tissue oxygenation, vasoconstriction which will therefore, increase BP and can decrease oedema, it increases cardiac output and inhibits histamine and cytokine release (Lyons and Scherk, 2017). The veterinarian decided not to use epinephrine initially because the patient already had tachycardia and an arrythmia, which are potential adverse reactions of epinephrine, so its use could have caused symptoms to worsen. Within a few minutes of administering chlorphenamine and dexadresson the patient began to improve. Her heart rate decreased, her pulses were stronger, her respiration rate decreased and effort improved, her blood pressure improved, mucous membranes became pink and capillary refill time normalised. The patient's demeanour improved slightly but she was still collapsed. Chlorphenamine is an antihistamine that can depress the central nervous system, so the patient being mentally dull was not surprising and ongoing monitoring is recommended (Lyons and Scherk, 2017).
The patient was discharged 4 hours after being admitted and has been healthy since the anaphylactic episode. The owner did not know what caused the symptoms.
Conclusion
The RVN should know the signs of shock and although the diagnosis in anaphylactic shock is variable, it is important to know the signs discussed in order to monitor effectively, as the patient's parameters can change quickly. Reporting and acting rapidly while monitoring a critical patient is vital to a positive outcome. Monitoring is recommended for up to 72 hours following anaphylaxis because of the potential for biphasic reactions and the author will suggest this to the veterinary team for future cases. Hypotension will occur in anaphylaxis and fluid therapy is essential in supporting the cardiovascular system. Rates should be tailored to the individual patient and monitoring of perfusion parameters can help determine whether the patient's fluid rate needs adjusting. A higher fluid rate or colloids should have been considered in this patient as an improvement was not seen. It is beneficial for the RVN to know which drugs may be used and their effects, in order to be efficient in an emergency situation. Patients in anaphylactic shock must receive treatment quickly, but further research is needed in this field so that patients can be diagnosed and treated in a consistent manner.
KEY POINTS
- Anaphylaxis is a rare life-threatening emergency, which can be difficult to diagnose as specific criteria for diagnoses, is yet to be determined in the veterinary field.
- The most common clinical signs of an allergic reaction are often cutaneous (erythema, urticaria, pruritus, wheals and angioedema), however, this is often a precursor for more severe reactions, such as anaphylaxis.
- The registered veterinary nurse (RVN) should know the signs of shock and monitor patients closely as their condition can deteriorate quickly, early detection can impact treatment decisions and patient outcome.
- Fluid therapy plays a vital part in the treatment of anaphylaxis, as patients can develop a mixed distributive-hypovolaemic shock with hypotension. The rate should be patient dependent following monitoring and evaluation of parameters.
- The RVN should be familiar with the drugs used in anaphylactic shock, to be prepared and understand the pharmacology for monitoring purposes.
- Monitoring is recommended for up to 72 hours following anaphylaxis because of the risk of biphasic reactions.