Neonatal emergencies: How to help patients survive the critical period
Knowing the common emergencies that occur in neonates and the differences between neonatal and adult physiology can help you manage these delicate patients in a manner that provides the highest possible survival rate.
Puppies and kittens are often the pride and joy of owners or breeders who only want the best for their animals. In certain cases, these animals have a high monetary value to the owner. To general veterinary practitioners, however, critically ill neonates can represent fear of the unfamiliar.
Knowing the common emergencies that occur in neonates and the differences between neonatal and adult physiology can help you manage these delicate patients in a manner that provides the highest possible survival rate. Although important decisions must often be made quickly, an intensive treatment effort will often be rewarded with lifelong loyal clients. In this article, we focus on the specific challenges of treating sick neonatal puppies and kittens, emphasizing the importance of addressing hypoxia, hypothermia, hypoglycemia, and dehydration to stabilize these patients.
FACTORS IN MORTALITY
The pediatric period in puppies and kittens is considered 0 to 12 weeks of age.1 This period is subdivided into three groups: neonates (0 to 2 weeks of age), infants (2 to 6 weeks of age), and juveniles (6 to 12 weeks of age).2 The overall mortality of healthy litters of kittens or puppies from a full-term birth to weaning should be no more than 15%.3
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Neonates face an increased risk of mortality if they are born to dams that are older or overweight, or both,4 if they are born to queens that are more than 3 years old,4 or if they are underweight at birth or fail to steadily gain weight thereafter.3 Low birth weight and rate of weight gain are the most important predictors of neonatal mortality.
In one study of 477 kittens, 60% of those with low birth weights died before weaning, while 68% of the remaining kittens that had a normal birth weight survived past the weaning period.5 Neonates born prematurely have low birth weights, have not reached their full physiologic maturity, have decreased lung surfactant, and are not ready to face environmental challenges.5 Also, puppies and kittens with lower birth weights, even if born full-term, can rapidly become hypothermic because of a higher body surface area to body mass ratio and, if too weak to nurse, may not be able to maintain proper blood glucose concentrations.6,7
A normal birth weight for a medium-sized dog (about 30 to 60 lb adult weight) is 500 ± 150 g (varies greatly among breeds and individuals) and for a kitten is 100 ± 10 g.8 Neonates may lose about 10% their body weight within the first 24 hours after birth because of water evaporation from the body, but they should gain weight steadily thereafter. Puppies and kittens should gain roughly 10% of their body weight per day during the neonatal period.8 Monitoring weight at least twice a day will detect neonates that are failing to gain weight.
Other factors that can contribute to neonatal mortality include genetics (e.g. feline neonatal isoerythrolysis), environmental factors (dystocia, maternal neglect, neonatal management), and viral diseases (e.g. canine herpesvirus and parvovirus infections; canine distemper; infectious canine hepatitis; feline herpesvirus, feline leukemia virus, and feline calicivirus infections; feline panleukopenia).
SIGNS OF ILLNESS
A thriving neonatal puppy or kitten is warm, plump, vigorous, and hungry. Until age 4 to 7 days, a healthy neonate's mucous membranes are hyperemic because of increased numbers of circulating erythrocytes.9 A normal packed cell volume for the first few days postpartum is around 60%.10
Most neonates that are apparently healthy at birth but decline in status have several features in common, regardless of the cause of their illness. These animals are often suffering from one or more of the following conditions: hypoxemia, hypothermia, dehydration, and hypoglycemia.3,11-14 They do not gain weight at the same rate as their littermates do (or, if the entire litter is affected, they do not gain as much weight as is average for their breed or species). They are not active or searching for food, and they lack the normal suckling and flexor reflexes. Dams will often isolate sick animals from the rest of the litter, exacerbating their problems.
Once it has been determined that a neonate needs veterinary care, treatment must be multifaceted and address each challenge the neonate is facing in order to provide the best chance for full recovery. Once the critical stage has passed, further diagnostic tests can be considered to determine the inciting cause.
POSTPARTUM NEONATAL RESUSCITATION
Ideally, parturition should be relatively uneventful and can be completed at a client's residence. However, veterinarians will sometimes manage delivery in a clinical setting because of either a high-risk pregnancy expected to result in dystocia or a planned cesarean section. Or problems may occur at home, and an owner may bring in the dam or newborn puppies or kittens for evaluation. Thus, the veterinarian and clinic staff need to be prepared for examination and possible resuscitation of one or more neonates.
Special care must be taken with handling and equipment to prevent nosocomial infection of the neonate. Wear gloves when handling neonates, and sterilize equipment before and after contact with the neonate.
Hypoxia and hypothermia
The main cause of fetal stress and depression associated with dystocia or cesarean section is hypoxia. Hypoxia can result from physical blockage of the respiratory tract or umbilicus during dystocia when a neonate is trapped in the vaginal canal, or from respiratory depression caused by anesthetic agents administered to the dam during surgery.15 In stark contrast to hypoxic adults, hypoxic neonates exhibit bradycardia, decreased respiratory rate, and reduced thoracic wall movement.15 This is likely an autoregulatory response carried over from the fetal period into the first few weeks postnatally in order to conserve energy and oxygen.15
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Hypothermia also adversely affects neonatal physiological functions. Hypothermia leads to further bradycardia (in an attempt to decrease metabolic demand),3 which worsens tissue hypoxia and leads to metabolic acidosis.1 Hypothermia is important to address in decompensating neonates (see "Hypothermia"). The shivering and vasoconstrictive responses are not present until about a week of age,13 normal adult central thermoregulation does not fully develop until 28 days of age,16 and neonates lack insulating fat.
If the dam is undergoing a cesarean section, the risk of neonatal hypothermia can be decreased by ensuring that the dam maintains a normal body temperature throughout the surgery. Hypothermia of the dam can translate to hypothermia of the offspring, especially in cats and small dogs that can dissipate body heat rapidly while anesthesitized.15
Keeping a newborn puppy or kitten at the ideal body temperature and stimulating the skin by rubbing it with a warm towel may be enough to arouse a newborn neonate to have normal respirations,15 especially if the dam is still anesthetized and unable to care for the newborns. The normal respiration rate for a newborn puppy or kitten is 10 to 18 breaths/min.8 If the animal is hypothermic, the respiration rate will be depressed.
If a newborn puppy or kitten is completely unresponsive after warming and stimulation efforts, follow the same steps of adult veterinary patient resuscitation (airway, breathing, and circulation).
Airway and breathing. The newborn may need assistance in clearing its airway with a towel, and rubbing the skin over the lumbar area may help stimulate it to cry, further clearing the airway.15 If the airway is still plugged, apply gentle suction with a rubber bulb syringe to the nose and mouth.15 Swinging or slinging is not recommended to clear the airways, as it can result in dropping the animal, cerebral hemorrhage, or aspiration of stomach contents,15 leading to pneumonia.
If a neonate remains unresponsive after the airway has been cleared, administer supplemental oxygen. Use a tight-fitting mask, size 1 or 2 uncuffed endotracheal tube, or size 12- to 16-ga intravenous catheter, and ventilate (applying 20 to 30 cm H2O pressure) until the chest wall expands.15 Once the lungs have been inflated, continue ventilation at a rate of 30 breaths/min at no more than 10 cm H2O pressure, pausing intermittently to check for spontaneous breathing.15 Discontinue ventilatory support after the neonate is breathing on its own. Continue to rub the neonate with a warm towel to help stimulate spontaneous respiration. A 25-ga needle inserted into the nasal philtrum, known as the Renzhong, Jenchung, or GV 26 acupuncture point, is another method that can be attempted to produce spontaneous respiration.17
Circulation. Once a clear airway and breathing have been established, circulation is the next priority for unresponsive neonates. The normal heart rate in newborn puppies and kittens is > 200 beats/min.1 Unlike in adults, bradycardia in neonates does not appear to be vagally mediated.8 The principal reasons for bradycardia in neonates are hypothermia and hypoxia, and addressing these issues with external temperature control and supplemental oxygen will often resolve any circulatory problems. However, if bradycardia persists, perform chest compressions with the thumb and forefinger at a rate of 1 to 2 compressions per second, allowing pauses for breathing.15
Drug administration. Options for drug administration during or after resuscitation are similar to those of adult animals. In neonates, the jugular and umbilical veins are easiest to access.18 Dilute drugs administered in the umbilical vein into a volume large enough to aid in diffusion18 (0.5 ml of a diluent such as 0.9% sodium chloride solution).
Naloxone can be administered to neonates experiencing respiratory depression if opioids were given to the dam before parturition. Naloxone can be given at a dose of 0.1 mg/kg intravenously, intraosseously, intramuscularly, subcutaneously, sublingually, or by endotracheal administration.18
If a neonate is completely unresponsive and has not responded to chest compressions, epinephrine can be given at a dose of 0.1 to 0.3 mg/kg intravenously or intraosseously.15 Doxapram, which is thought to be a central stimulant, has uncertain usefulness in veterinary medicine,15 but it can be attempted at a dose of 0.1 ml of the 20 mg/ml formulation given intravenously or sublingually12 if other means of resuscitation are ineffective.
Atropine is not recommended to treat bradycardia in neonates. These animals are likely bradycardic because of myocardial hypoxia, and further demand placed on the heart only worsens myocardial damage due to increased oxygen demand.8,15
Keep in mind that if any of these drugs are administered without increasing cardiac output, their effect will be minimal as they will not reach peripheral tissues. Perform chest compressions while administering drugs in patients with cardiac arrest.15
Consider fluid therapy in neonates experiencing cardiovascular collapse, no matter the cause. Neonates are more prone to dehydration because of immature renal function, increased surface area to mass ratio, and more permeable skin.11 The skin tent test for dehydration assessment is not reliable in neonates because of increased water content and decreased fat content of the skin.11 However, dehydration can be judged most reliably by evaluating the mucous membranes (they should be moist and hyperemic, not tacky or pale) and assessing ability to urinate. If you use a moist cotton swab to stimulate the perineal region of a neonate that has not recently urinated and no urine is produced, the neonate is likely dehydrated.
The fluid rate and route of administration depends on the degree of dehydration, which is determined subjectively by the degree of mucous membrane dryness, urine production, and overall patient status. Fluids should be warmed to 95 to 99 F (35 to 37.2 C)13 before they are given by any route to prevent iatrogenic hypothermia. Possible fluid administration routes include oral, subcutaneous, intraperitoneal, intravenous, and intraosseous.
And keep in mind that a neonate's renal system is immature and incapable of concentrating urine. It is not difficult to fluid-overload a neonate. Weight must be monitored hourly and signs of fluid overload (e.g. increased lung sounds) are cause for reevaluation of the fluid therapy plan.
Oral fluids in the form of a commercial milk replacer or a replacement fluid such as lactated Ringer's solution with added dextrose can be given through a stomach tube only to normothermic, hydrated neonates with normal blood glucose. Oral fluids are a favorable consideration when a neonate is conscious and normothermic but not able to nurse from the dam.
At a core body temperature of < 94 F (34.4 C), bradycardia and gastrointestinal ileus occur,3,12,13,19 and fluids given orally cannot be properly absorbed. In addition to not receiving the nutrition and hydration that the neonate needs, this also places the puppy or kitten at risk for aspirating stomach contents and acquiring bacterial pneumonia or developing sepsis due to gastrointestinal stasis.
To administer oral fluids, measure a 5- to 8-Fr feeding tube from the tip of the nose to the last rib, and mark where it exits the mouth.11 Passing the tube down the left side of the throat will help ensure that the tube is placed in the esophagus rather than the trachea. Puppies and kittens do not develop a gag reflex until about 10 days of age,1 so this cannot be used to assess whether the tube has entered the esophagus. Confirm proper placement of the feeding tube radiographically or by instilling a small amount of saline solution; if the saline exits the neonate's nose, the tube is in the trachea.
When administering milk replacer, remember that the stomach capacity of a neonate is about 50 ml/kg1 and the energy requirement is about 20 to 26 kcal/100 g body weight/day.3 Avoid filling the stomach to capacity to help prevent aspiration pneumonia. Feeding every two to four hours while the neonate is awake is ideal.11 Kink the tube during removal to avoid aspiration pneumonia.
Subcutaneous fluids are a desirable option if a neonate is only mildly or moderately dehydrated and has normal tissue perfusion. Fluids can be delivered in the interscapular space, as in adults. The maintenance fluid dose can be calculated and given subcutaneously in several divided doses over the day.
Balanced electrolyte solutions such as lactated Ringer's solution and Normosol-R (Hospira) are appropriate for correcting mild dehydration.11 Treat mild hypoglycemia by adding 2.5% dextrose solution to 0.45% sodium chloride solution and administer it subcutaneously (adding dextrose to isotonic fluids will result in fluids being drawn out of the intravascular space).11
Serum can be delivered subcutaneously in neonates that did not nurse for the first 24 hours and have failure of passive transfer. Pooled serum from well-vaccinated adult dogs or cats can be administered subcutaneously at a dose of 22 ml/kg for puppies20,21 and 150 ml/kg for kittens22 to raise serum IgG concentrations. Perform blood typing and crossmatching to prevent neonatal isoerythrolysis, especially in kittens.
Warmed crystalloid fluids can be given directly into the peritoneum.11 As with subcutaneous fluids, this route is not advised if the patient is severely dehydrated, as fluid will be absorbed more slowly from the peritoneum than with direct venous access. It is important not to give hypertonic fluids intraperitoneally to a dehydrated animal to keep fluids from being pulled from the intravascular space. Also, if this route is used, strict asepsis must be followed to prevent peritonitis.12
The jugular vein is the best site for intravenous fluid administration.11 It is highly desirable to place a 20- to 22-ga catheter to prevent repeated venipuncture. Give fluid boluses at 1 ml/30 g body weight over five to 10 minutes2 until mucous membrane color and capillary refill time are normal. Fluid therapy can then be continued at the maintenance rate.
Intraosseous fluids are often the veterinarian's choice for providing fluid therapy to neonates because of ease of access and efficacy. All fluids that can be given intravenously can also be given intraosseously at the same dose and rate.11 Sites that can be used include the greater trochanter of the femur, the tibial tuberosity, the medial process of the proximal tibia, and the greater tubercle of the proximal humerus.14
Clip and aseptically prepare the site to be injected. For pain control, inject a minimal amount of lidocaine (no more than 4 mg/kg) diluted with 50% saline solution or of bupivacaine14 into the skin and periosteum around the planned injection site. A 1- or 2-in, 18- to 22-ga spinal needle is ideal for intraosseous fluid administration. The needle should feel firmly seated and must be removed within 24 hours.11 Proper placement of the intraosseous catheter can be confirmed radiographically.
FADING PUPPIES AND KITTENS
In many instances, the cause of neonatal death remains unknown. The term fading syndrome refers to a previously healthy full-term puppy or kitten that suddenly deteriorates for no apparent reason, frequently ending in death. Often hypothermia, dehydration, hypoglycemia, and hypoxia are present and lead to the patient's decline, and these may be the only findings of diagnostic tests. Viral or bacterial disease may be the cause, but the animal's deterioration can be so rapid that care must be instituted before test results are available. Multiple causes of disease may be present in a single animal, further complicating the issue.3 Common lesions found in neonates that do not survive involve combinations of pulmonary congestion, edema, hemorrhage, and atalectasis.23 Since the causes can be many and the inciting cause may not be determined before death occurs, supportive care is key for neonates that suddenly show weakness, a slow rate of weight gain, are isolated from the rest of the litter, or otherwise deteriorate in health status.
To ensure the best care of the neonate, a complete physical examination is imperative to identify congenital abnormalities such as cleft palates, atresia ani, open fontanelles, pectus excavatum, and heart murmurs. It is also important to obtain a complete history, including the environment at home, normal feeding patterns for the patient, and if the dam has successfully reared healthy litters. Seemingly healthy and robust puppies and kittens should be separated from those that seem ill.
If blood can be collected from a peripheral vein, first measure blood glucose concentration, then measure packed cell volume and total protein concentration. Puppies 1 to 4 weeks old have a PCV of 32% to 48% and a total protein concentration of 3.4 to 5.2 g/dl. Kittens 1 to 4 weeks old have a PCV of 27% to 35% and a total protein concentration of 4 to 5.2 g/dl.8 Then perform cytologic examination of a blood smear and a white blood cell count. After that perform a complete blood count and serum chemistry profile4 if a sufficient sample remains. Keep in mind the small sample availability; a neonatal kitten has 15 ml of circulating blood, less than 1.5 ml of which can be safely removed for collection.3 A blood bacterial culture can be performed, but treatment should be instituted before results are available.
Urine and fecal samples can also be analyzed. Because renal function is immature, a low specific gravity (1.006 to 1.017), proteinuria, and glucosuria are normal findings in neonatal urine.8
Rewarming the neonate is an important first step in care, as hypothermia inhibits gastric motility and causes bradycardia, which may eventually result in a decreased respiratory rate and cardiovascular collapse.12 Normal neonatal temperatures range from 95 to 99 F (35 to 37.2 C).9,15 Hypothermic neonates need to be slowly warmed to a rectal temperature of 97 to 98 F (36.1 to 36.6 C) over a period of one to three hours. Rewarming too rapidly increases the neonate's metabolic demand, which can cause pulmonary and circulatory collapse.3
You can use several methods to warm a hypothermic neonate, but an infant incubator is ideal.15 The ideal ambient temperature is 85 to 90 F (29.4 to 32.3 C).15 Other sources such as warm-water circulating pads, microwaved rice bags, warm-water bottles, warm towels, and infrared heat lamps can be used, but take extreme care to ensure that the neonate is not overheated or burned. It has been suggested to place a warm-water circulating pad on the ceiling of the cage to create a warmer environment.14 Establish a temperature gradient, allowing neonates to be able to move away from the heat source14 to prevent hyperthermia.
Normal blood glucose concentrations in neonatal animals are 90 to 140 mg/dl.13 Hypoglycemia usually results from inadequate or infrequent feedings. A puppy can survive 24 hours and maintain normal blood glucose concentrations through glycogenolysis and gluconeogenesis,24 but has used most of the substrates for gluconeogenesis by this point and the blood glucose concentration can drop precipitously. Disease processes such as sepsis can also result in hypoglycemia.
Clinical signs of hypoglycemia, which can also be the result of processes other than hypoglycemia, include muscle tremors, seizures, lethargy, depression, collapse, and coma; death may also occur.13 Intravenous or intraosseous dextrose is the ideal treatment until the neonate is capable of feeding (normothermic and well-hydrated). Examples of intravenous doses include 10% dextrose solution at 1 to 2 ml/kg intravenously or intraosseously13 and 10% dextrose solution at 2 to 4 ml/kg intravenously or intraosseously as a slow bolus.15 The dose depends on the severity of hypoglycemia. The goal is to maintain the animal's blood glucose concentration in the normal range.
Antibiotics are often administered empirically to neonates that may have sepsis. Consider these drugs when a neonate is as stable as possible. Antibiotics that are safer to administer to neonates include cephalosporins, penicillins, clavulanic acid, macrolides, and trimethoprim-sulfonamide.19 Penicillins are recognized as one of the safer antibiotics because of their broad dose range and are often used as a first choice.12
Antibiotics to avoid in neonates are aminoglycosides (renal damage and ototoxicosis), tetracyclines (dental damage), chloramphenicol (bone marrow suppression), and quinolones (cartilage damage).12
If a puppy or kitten does not survive, perform a necropsy or have one performed by a veterinary pathologist. A bacterial (e.g. streptococcus) or viral (e.g. herpesvirus) cause may be found. A necropsy does not always provide the answer, but the results may direct a more specific treatment plan for surviving littermates.
Neonates that need critical care can be treated successfully, but the physiologic differences between adults and neonates must be recognized in order to institute the most successful therapy. Once the emergency stage has passed, careful monitoring for hypoxia, hypothermia, hypoglycemia, and dehydration must continue to ensure the best chance of survival for the neonate. Additional treatments should begin after the animal is as stable as possible. Although not every puppy and kitten will be saved, a higher percentage of survival can be ensured when an intensive treatment effort is made.
Olivia Wilson, DVM
Tigard Animal Hospital
13599 Southwest Pacific Highway, Suite C
Tigard, OR 97223
Mushtaq A. Memon, BVSc, PhD, DACT
Department of Veterinary Clinical Sciences
College of Veterinary Medicine
Washington State University
Pullman, WA 99164
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