Introduction

Cardiopulmonary resuscitation (CPR) is a comprehensive term used to describe the fundamental rules of cardiopulmonary resuscitation, life support, and post-resuscitation care. There are many excellent resources on CPR in the veterinary patient, however there is very little specific information about CPR in exotic animal species. Although the principles of resuscitation are the same for all species, there are important species-specific considerations related to patient disposition, anatomy, and physiology (Fig 1).

 

Preparation

A “crash cart” with emergency supplies should be readily available (Fig 2) (Table 1), as well as a dosing chart for resuscitation drugs (Table 2). Before handling a critically ill patient or performing any anesthetic procedure, it is prudent to gather all tools and emergency drugs beforehand. Calculate drug doses, particularly for tiny patients that will require dilution of emergency drugs for safe and accurate drug delivery. Many exotic animal veterinarians draw up drug doses ahead of time (Fig 3).

 

 

Table 1. Crash cart supplies (Source: Dr. Marla Lichtenberger)
Supplies to be kept WITHIN the crash cart	Supplies to be kept NEAR the crash cart
Epinephrine	CPR Drug Resuscitation Protocol
Vasopressin	Defibrillator
Atropine	Syringe pump
Glycopyrrolate	Warming equipment for patient
Doxapram	Bag valve mask (e.g. Ambu bag)
1, 2, and 3-mm endotracheal tubes	Crystalloids and colloids
3-0 absorbable suture	1 bag of crystalloids (i.e., LRS)
3-cc syringes	Indirect blood pressure equipment
24-gauge catheters	Pulse oximeter
Heparin and saline (saline used to flush drugs into endotracheal tube)
3-cc syringes filled with saline flush
Scissors to cut wide part of red rubber tubes
5 and 8 French red rubber tubes
1-inch porous tape
1-cc syringes with 25-gauge needles (or smaller)
Tuberculin syringes
25, 22, 20 and 18-gauge intraosseous catheters

Table 2. Dosing chart for resuscitation drugs based on body weight of small exotic pets
Drug (concentration)	Dose	mL/50 g	mL/100 g	mL/kg	mL/2 kg
Epinephrine (1:1000) (1 mg/mL)	0.01 mg/kg	0.0005	0.001	0.01	0.02
Atropine (0.54 mg/mL)	0.02 mg/kg	0.002	0.004	0.037	0.074
Glycopyrrolate (0.2 mg/mL)	0.02 mg/kg	0.005	0.01	0.1	0.2
50% Dextrose (diluted 50% with saline)	0.25 ml/kg	0.05	0.1	1.0	2.0
Calcium gluconate (100 mg/mL)	50 mg/kg	0.025	0.05	0.5	1.0
Doxapram (20 mg/mL)	2.0 mg/kg	0.005	0.01	0.1	0.2
Vasopressin (20 U/mL)	0.8 U/kg	0.002	0.004	0.04	0.08
External defibrillation	2–10 Joules/kg	n/a	1	2	4
Naloxone (0.4 mg/mL)	0.02 mg/kg IV 0.04 mg/kg IM	0.0025 0.005	0.005 0.01	0.05 0.1	0.1 0.2
Atipamezole	Same volume as medetomidine; IM only	---	---	---	-

Early recognition of cardiovascular instability is imperative in exotic animal patients. Anesthetized animals should ideally be monitored with an electrocardiogram and Doppler blood pressure measurements at minimum. Bradycardia is often observed just prior to CPA (Lichtenberger and Lennox 2012).

Early recognition of a problem is particularly challenging in the reptile patient. General anesthesia normally induces respiratory arrest and the heart rate will fall as body temperature falls. At lower temperatures, cardiac output is typically maintained by an increase in stroke volume (O’Malley 2011).

 

Prognosis

The prognosis for respiratory arrest is good, especially when caused by an overdose of isoflurane or sevoflurane anesthesia. Otherwise the expected outcome for CPR of the exotic animal patient can be grim, particularly in patients suffering from chronic diseases. Cardiac arrest in birds carries a poor prognosis because direct compression of the heart is not possible due to the overlying sternum. Additionally, birds and reptiles lack a diaphragm and closed-chest compressions cannot utilize the thoracic pump mechanism to increase overall negative intrathoracic pressure. Nevertheless, positive outcomes can and do occur with conventional CPR techniques (Fernandez et al 2013, Buckley et al 2011).

 

Basic principles

The basic principles of CPR can be applied to exotic animal species (Table 3). Download the CPR flowchart shared by Dr. Marla Lichtenberger circa 2007.

Table 3. Basic principles of cardiopulmonary resuscitation Source: Dr. Marla Lichtenberger
Airway	Intubate using an endotracheal tube or catheter
Breathing	Positive pressure ventilation is performed. Consider doxapram to stimulate higher respiratory centers in select patients when mechanical ventilation is suboptimal or not possible (Daly 2015).
Circulation	Cardiac compression (Although this is not possible in the bird due to the overlying sternum, the action is still performed to force air through the air sacs).
Drugs	Epinephrine 1:1000 IV, IO, IT Atropine IV, IO, IT Glucose is given at 0.25 ml/kg of 50% dextrose with an equal volume of saline IV, IO Calcium is given in documented hypocalcemia cases only at 100 mg/kg IV, IO Vasopressin 0.8 U/kg IV or IO is considered in asystole
ECG	Monitor the patient using ECG, Doppler, and carbon dioxide levels
IV: intravenous IO: intraosseous (ulna preferred site) IT: intratracheal

 

Airway

If the patient is anesthetized, immediately halt anesthesia. If any reversible sedatives have been administered, reversal agents like flumazenil (0.01 mg/kg IV, IO) for benzodiazepines and atipamizole (0.05 mg/kg IV, IO) or yohimbine (0.11 mg/kg IV/IO) for alpha-2 agonists can also be beneficial (Fletcher and Boller 2015).

If an endotracheal tube is not already in place, intubation is the first step for respiratory arrest however patient size and anatomy can make this vital step extremely challenging. Most birds and reptiles can be easily intubated using a non-cuffed endotracheal tube. A catheter or feeding tube of appropriate size can be used instead of a commercially available tube if patient size dictates. Air sac cannula placement into the caudal thoracic or abdominal air sac is also an option for airway control in birds. If the patient is already intubated, ensure the airway is clear as mucus plugs are a common problem in birds and reptiles.

There are multiple techniques described for endotracheal intubation of the rabbit. Although the blind technique is quite popular, proficiency with at least one other technique that utilizes visualization will be needed for resuscitation. Unless your intubation skills in rabbits and rodents are stellar, forced mask high flow oxygen ventilation may be the best technique to successfully ventilate the small mammal (Mans 2013, Lichtenberger and Lennox 2012, Lennox 2012, Buckley et al 2011, O’Malley 2011). This technique relies upon the fact that rabbits and rodents are obligate nasal breathers.

To employ forced mask high flow oxygen ventilation in the rabbit or rodent, place a tight-fitting mask over the nose and mouth and ventilate the patient. Potential complications can include failure to ventilate due to poor seal, and accumulation of air into the stomach. Bloat can limit expansion of the diaphragm, however this problem can be addressed after successful resuscitation.

Nasotracheal intubation is another option for airway control, and as a last resort, tracheostomy can be performed (Lichtenberger and Lennox 2012, Lennox 2012, O’Malley 2011).

 

Breathing

Reptiles can survive long periods using anaerobic metabolism. While 100% oxygen is always delivered to birds and small mammals during respiratory arrest, a reduced partial pressure of oxygen stimulates respiration in the reptile. Therefore, lower levels of oxygen (no more than 30-40%) or even room air delivered via a bag valve mask (e.g. Ambu bag) is preferable in the reptile patient. Although all small patients should be provided with supplemental heat, reptiles should be maintained at their preferred optimum temperature zone in an effort to trigger spontaneous respiration (O’Malley 2011).

Recommended ventilation rates vary widely (Table 4). Approximately 10 breaths per minute (bpm) is the target rate in cats and dogs. In small birds or mammals with higher metabolic rates, approximately 20-40 bpm have been recommended. Perform sternal compressions in the bird to push air through the bellows-like air sac system by placing a hand or finger on each side of the sternum. In reptiles, anywhere from 1-6 bpm have been described (Whiteside 2015, O’Malley 2011). Avoid hyperventilation in all species, being careful not to overinflate the lungs. A peak positive ventilation pressure not exceeding 8 cm H2O has been recommended in reptiles (Whiteside 2015). Avoidance of hyerpventilation is particularly important in reptiles as this can raise the partial pressure of oxygen (PO2), further depressing respiration.

Table 4. Recommended positive-pressure ventilation rates (Whiteside 2015, O’Malley 2011)
Taxonomic group	Ventilation rate (breaths per minute)
Exotic companion ammals	20-40
Birds	20-40
Dogs and cats	10
Reptiles	1-6

 

Circulation

If no heartbeat is ausculted, perform chest or sternal compressions to support circulation. The chest of many small patients is highly compliant, so take care not to overcompress the chest (Fletcher and Boller 2015). Compressions are generally performed at a depth of one third to one half the width of the chest, delivered in uninterrupted cycles of 2 minutes (Fletcher and Boller 2015).

Mammals

Small mammals are best placed in lateral recumbency. Perform compressions in these patients by wrapping a hand around the sternum over the heart or placing a hand (or finger) directly over the heart (Fletcher and Boller 2015). In dogs and cats, chest compressions are performed between 100-120 times per minute (Fletcher and Boller 2015). Based on rapid resting heart rates, effective chest compression rates are assumed to be extremely high in exotic pets. Recommended ranges of 80-100 and 100-120 times per minute have been described in the literature (Table 5) (Lennox 2012, O’Malley 2011).

Table 5. Recommendations for chest or sternal compressions (Lennox 2012, O’Malley 2011)
Taxonomic group	Recumbency	Rate (per minute)
Exotic companion mammals	Lateral	80-120
Birds	Dorsal	60-80
Dogs and cats	Lateral, dorsal*	100-120
Reptiles (lizards, snakes)	Lateral	---
*Dorsal recumbency is recommended for barrel-chested dogs like the bulldog

Birds and reptiles

The avian patient is best placed in dorsal recumbency and sternal compressions are made at a rate of 60-80 or 80-100 times per minute (Table 5). Direct compression of the avian heart is not possible due to the overlying sternum or keel, and again this compression serves mainly to pump air through the air sac system. Also, since birds and reptiles lack a diaphragm, closed-chest compressions cannot utilize the thoracic pump mechanism to increase overall negative intrathoracic pressure.

I could find no recommendations for chest compressions in reptiles. The reptile heart rate depends on many factors, including temperature, body size, and respiratory rate. Heart rate falls during periods of apnea and is generally much lower in reptiles than in mammals (O’Malley 2011).

Management of life-threatening cardiac dysrhythmias

Defibrillation is not recommended for birds or mammals less than 1 kg body weight. When external defibrillation is performed, values ranging from 2-10 joules/kg have been described for small mammals (Lennox 2012) (Table 2).

Fluid therapy

While one team member is performing chest compressions, another should obtain vascular access. If the patient is hypovolemic, administer intravenous (IV) or intraosseous (IO) isotonic crystalloid fluid boluses during CPR (Lennox 2012). Recommended fluid bolus rates have ranged from 10-25 ml/kg IV, IO over 5-7 minutes for the avian patient or 25 ml/kg in the rabbit (Mans 2013). A bolus infusion of 7.2-7.5% hypertonic saline (3 ml/kg IV, IO) over 10 minutes has also been described (Lichtenberger and Lennox 2012). Fluid boluses can be harmful to patients with fluid overload or even normovolemic individuals so careful patient selection and monitoring is crucial (Fletcher and Boller 2015). Remember that small patient size means that supplemental heat and warmed fluids are also critical!

For advice on catheter placement in the exotic animal patient, view videos and text in LafeberVet’s Intravenous Catheter Placement in Small Mammals, Intraosseous Catheter Placement in Small Mammals, Intravenous Catheter Placement in the Bird, Intraosseous Catheter Placement in the Bird, and Catheters in Reptiles, as well as the article Intravenous Catheter Placement in Rabbits.

Drugs

Cardiac output during CPR is often 30% or less of normal (Fletcher and Boller 2015). Life support interventions for asystole and pulseless electrical activity include vasopressor therapy, such as epinephrine or vasopressin, and parasympathetic therapy, like atropine, especially in cases of bradycardic arrest secondary to high vagal tone (Fletcher and Boller 2015).

Many but not all rabbits possess atropine esterases. Atropine only briefly induces a moderate tachycardia, unless higher doses are used, which in turn increases the risk of ventricular arrhythmia. Glycopyrrolate is used for longer effects (Allweiler 2016, Mans 2013).

Vasopressor therapy

The best-studied vasopressor during CPR is the catecholamine epinephrine, which causes peripheral vasoconstriction. Epinephrine and other catecholamines lose much of their effectiveness when the body is in a state of hypoxia and acidosis (Lichtenberger and Lennox 2012). Vasopressin may be more effective under these conditions and can improve the rate for restoration of spontaneous circulation and survival (Fletcher and Boller 2015). Vasopressin can be used interchangeably or in combination with epinephrine during CPR, and because of its positive effects vasopressin should be administered first, followed by epinephrine (Fletcher and Boller 2015). Both vasopressin and epinephrine should ideally be given by IV or IO routes, however these drugs can also be administered via endotracheal tube. Avoid intracardiac injections because of the risk of lacerating coronary vessels. Use of both vasopressin and epinephrine use have been described in exotic companion mammals.

The drugs selected and doses used during CPR in exotic animal are directly extrapolated from those used in dogs and cats (Table 6). Although different species may require different drug doses to produce the same physiologic effect, empirical information is lacking in all but the rare laboratory specimen (Chen et al 2010, Chen et al 2009, Chen et al 2006, Chen et al 2006b). Effects of low, medium, and high-dose vasopressin were compared in a study with 40 male Sprague-Dawley rats. Findings indicate that these different doses of vasopressin resulted in a similar outcome of CPR, with no additional benefits afforded by high-dose vasopressin during or after CPR (Chen et al 2009). In another study comparing high and low-dose epinephrine during CPR in a rat model (Chen et al 2010), different doses of epinephrine produced a similar rate of restoration of spontaneous circulation, but high-dose epinephrine inhibited the recovery of spontaneous ventilation and caused relative bradycardia after CPR. Low and medium doses of epinephrine were optimal for CPR in the rat (Chen et al 2010, Sharman and Meert 2005). To achieve low- or medium-doses in small mammals, keep the diluted 1:10,000 concentration of epinephrine in stock to reduce the potential risk of accidental overdose. Finally, the administration of naloxone alone or in combination with epinephrine (0.4 mg/kg IV) was found to improve the resuscitation rate following asphyxial cardiac arrest in rats (Chen et al 2006).

Dextrose

Just as in kittens and puppies, small body size also means that hypoglycemia is an important concern in both birds and small mammals. Glucose can be given at 0.25 ml/kg of 50% dextrose with an equal volume of saline IV or IO.

Steroids

The use of glucocorticoids in the treatment of shock is controversial as the potential adverse effects of these drugs (immunosuppression, gastric ulceration) can outweigh their benefits in select patients. The use of steroids in shock caused by hemorrhage and hypovolemia is not currently recommended.

Table 6. Drugs commonly used in emergencies
Drug	Dosage	Route	Comments
Atropine sulfate (0.54 mg/ml)	0.02-0.04 mg/kg 0.04 (bird) mg/kg	IV, IO	Recommended for bradycardic arrest and high vagal tone
	0.01-0.04 mg/kg	IV, IO, IM	Sugar glider (McLaughlin 2016)
	0.05-0.2 mg/kg	IV, IO, IM	Hedgehog (McLaughlin 2016)
	0.05-0.4 mg/kg	IV, IO, IM	Small rodents (McLaughlin 2016)
	0.1-0.5 mg/kg	IV, IO	Rabbit (Huynh 2016) May not be effective in the rabbit due to the presence of atropinase or high doses may be required, which in turn increases the risk of tachycardia and ventricular arrhythmia. Consider glycopyrrolate instead.
	0.2 mg/kg	IV, IO, IM	Birds
	0.08 mg/kg	IT
	0.01-0.2 mg/kg	IV, IM	Reptiles
	0.5 mg/kg	IV IO, IM, IT	Turtles and tortoises, snakes (Mans 2013)
Calcium gluconate	100 mg/kg	IV, IO slow bolus	Only give in documented cases of hypocalcemia
Dexamethasone sodium phosphate	2-4 mg/kg	IV, IO	Use with caution. Steroids are not recommended in shock caused by hemorrhage and hypovolemia.
Dextrose (50%)	0.25 ml/kg	IV, IO	Dilute with equal volume of saline
	1 ml/kg	IV
Doxapram	1-2 mg/kg	IV, IO, IM	Stimulates respiratory centers but also increases oxygen consumption and carbon dioxide production (Daly 2015). Administer only when absolutely necessary as when mechanical ventilation is suboptimal or not possible
	2-10 mg/kg	IV, IM	Hedgehog
	5 mg/kg	IM, IV	Reptiles
	5-10 mg/kg	IM, IV	Small rodents (McLaughlin 2016)
	2-4 mg/kg	IT	Lennox 2012
Epinephrine (1:1000) (1 mg/mL)	0.01 mg/kg	IV, IO
	0.02 mg/kg	IT
	0.1 mg/kg	IV	Reptiles
	0.003 mg/kg	IV, IO	Small rodent, hedgehog, sugar glider (McLaughlin 2016)
Glycopyrrolate (0.2 mg/ml)	0.01-0.02 mg/kg	IV, IM	30-60 second onset of action
Lidocaine (20 mg/ml)	1-2 mg/kg	IV	Rabbit dose for treatment of ventricular tachycardia (McLaughlin 2016)
Naloxone (0.4 mg/ml)	1 mg/kg	IV
Vasopressin (20 U/ml)	0.8 U/kg	IV, IO	Use as an alternative or with epinephrine in asystole Every other cycle of CPR
	1.6 U/kg	IT
IV: intravenous IO: intraosseous IM: intramuscular IT: intratracheal (insert a tom cat catheter or red rubber tube down the endotracheal tube)

 

Monitoring

Minimize the risk of another arrest by ensuring optimal ventilation, oxygenation, and tissue perfusion. Also work to recognize and address reversible causes of CPA (Fletcher and Boller 2015). Use an electrocardiogram, blood pressure measurements, and end-tidal carbon dioxide (CO2) levels to evaluate the effectiveness of CPR. End-tidal CO2 monitoring can be particularly useful because this parameter is resistant to motion artifact (Fletcher and Boller 2015, Tourma and Davies 2013, Grmec 2001). In many species, once rectal temperature approaches (98°F (36.7°C) adrenergic receptors begin to respond to catecholamines and fluid therapy (Lichtenberger and Lennox 2012, Rudloff 2001). Monitor core body temperature and provide supplemental heat and warmed fluids.

 

Conclusion

There is little empirical information available on CPR in most exotic animals. Fortunately, the basic principles of CPR are the same for all species, however there are important species-specific considerations. The ease of establishing airway control can vary dramatically. Most birds and reptiles can be intubated relatively easily whereas gaining control of the rabbit or rodent airway can be quite challenging. There are multiple techniques described for intubation, all of which require significant amounts of practice for proficiency. Additional techniques used to ventilate exotic companion mammals include nasotracheal intubation in the rabbit, a tight-fitting mask over the nose and mouth in rabbits and rodents, and even tracheostomy. The prognosis for cardiac arrest is particularly poor for the bird because the sternum or keel makes direct compression of the heart impossible. Birds and reptiles also lack a diaphragm, therefore closed-chest compressions cannot utilize the thoracic pump mechanism to increase overall negative intrathoracic pressure. Emergency drug doses are directly extrapolated from dog and cat medicine; however, atropine may not be effective in the rabbit due to the presence of atropinase.

 

References