Neonatal survival

When puppies and kittens are born, they do not normally require assistance or resuscitation to survive. However, when neonates are stressed during parturition and the periparturient period, morbidity and mortality increase. Timely, effective intervention is required to successfully resuscitate a stressed neonate.

Puppy and kitten mortality rates vary from 9-26%. Neonates that fail to survive to weaning are most commonly stillborn or die within the first three days of life. Factors implicated in perinatal deaths include prematurity, in utero infection, anatomic birth defects, birth trauma/dystocia, low birth weight, inadequate nutrition, maternal neglect, and environmental stresses. Neonatal survival is optimized when breeders have good husbandry practices. Prospective planning includes genetic screening of the prospective dam and sire, ensuring that that dam is healthy at the time of breeding and throughout gestation, managing labor and delivery to reduce stillbirths, controlling parasitism and reducing infectious disease, preventing injury and environmental exposure, and optimizing nutrition of the dam and neonates.

Veterinarians often need to treat stressed and depressed neonates following dystocia and Caesarian section of the dam. In this situation, the primary causes of fetal depression are hypoxia and anesthesia.

Neonatal hypoxia

Neonates do not respond to hypoxia in the same manner as adults. In contrast to adults, hypoxic neonates respond with a decrease in heart and respiratory rates, presumably as a protective response to low pO². This compensatory response allows the neonate to survive a longer exposure to hypoxia than would an adult.

Baroreceptor reflexes are not present, nor is sympathetic innervation of the heart complete during the first 4 days of life. So bradycardia in the neonatal period is not vagally mediated. Bradycardia IS indicative of myocardial hypoxia and/or hypothermia. The heart rate in a neonate with a body temperature of 96°F is 200-250 bpm (beats per minute). Be aware that severely hypoxic puppies may have heart rates in the expected range for adults of their breed. If the rectal temperature drops to 70°F, the heart rate decreases to 40-50 bpm. However, the hypothermia protects neonates from ischemic brain injury that accompanies cardiovascular failure.

Administration of chronotropic agents is, at best controversial. Parasympatholytic agents such as atropine will only exacerbate cardiac hypoxemia via increasing oxygen consumption and demand. The more appropriate treatment for neonatal bradycardia is to supplement oxygen and assist ventilation, if necessary. Remember that atropine crosses the placenta while glycopyrrolate does not. This is important when considering choice of medications to be administered pre-or intra-operatively to a dam undergoing a caesarian section delivery.

Hypoxemia in the neonate may result in life threatening sequelae such as septic shock due to bacterial translocation despite a lack of mucosal lesions. It is vital that the environment be kept free of airway irritants and oxygenation is adequate.

If you choose to provide services that require resuscitation of neonates, you will need an oxygen source. If you do not have a second anesthesia machine that can be used for oxygen administration, an oxygen concentrator is an inexpensive oxygen delivery system. An oxygen concentrator concentrates room air to >95% oxygen.

Neonatal hypothermia

Unlike their homeothermic adult counterparts, neonates are poikilothermic and are unable to regulate their own body temperature. They can lose heat through evaporation, conduction, radiation and convection and they cool quickly. Shivering and vasoconstrictive reflexes are not yet functional. However, they have well developed behavioral heat seeking responses which enable them to maintain a stable rectal temperature providing sources of heat are available.

Prevention of hypothermia in neonates is extremely important. Without a heat source, hypothermia ensues and resuscitative measures lose their effectiveness. Due to incomplete maturity of the autonomic nervous system, the neonate is less able to respond to physiological stress. Physiological responses noted during hypothermia include bradycardia, cardiovascular failure, neuronal injury, and ileus. Body temperature is known to have a dramatic effect on gastrointestinal movement in the neonate. At rectal temperatures below 94°F, ileus develops. As ileus progresses, the willingness to nurse decreases and the necessity for tube feeding puppies increases. Inherent to the tube feeding process is the risk for aspiration and subsequent development of pneumonia.

Normal rectal temperatures in the puppy are 95 - 99°F (week 1), 97 - 100°F (weeks 2 and 3) and by weaning rectal temperatures approach that of the adult. The challenge is to maintain the body temperature of the neonates without overheating the dam.