Resuscitation and critical care of neonatal calves (Proceedings)

August 1, 2009

Article

Adequate resuscitation of the newborn is critical to decreasing calf losses in both beef and dairy herds.

Adequate resuscitation of the newborn is critical to decreasing calf losses in both beef and dairy herds. Despite the importance, there is little critically evaluated data available to aid in protocol development. Establishing a patent airway, initiating breathing, and establishing adequate circulation are the cornerstones to resuscitation in any species. In cattle post-dystocia resuscitation of the neonate focuses on establishing breathing and correction of acid base abnormalities. Additional attention may be required to address specific ailments that occur during calving, maintaining appropriate body temperature, and ensuring adequate colostral intake.

Rupture of the umbilical cord initiates hypoxia. Decreased oxygen tension and increased carbon dioxide concentrations stimulate gasping reflexes with subsequent aeration of the lungs. Increased oxygen tension in the blood and increased peripheral vascular resistance initiates closure of the ductus arteriosus, foramen ovale, and ductus venosus preparing the neonatal cardiovascular system for extra uterine life. If dystocia is prolonged and a substantial hypercarbia or acidosis develops prior to expulsion of the fetus, central nervous system depression may be severe enough to impair the reflexes that initiate respiration.

Removal of fluid from the pulmonary system is critical for normal aeration and oxygenation of blood. Some fluid is eliminated from the body during the birthing process. However, the vast majority is reabsorbed across the alveolar walls into the interstitium rapidly upon the initiation of respiration. Complete absorption of pulmonary interstitial generally occurs within several hours postpartum. After delivery a clear airway should be ensured. Recent data suggests that the practice of hanging calves to expel fetal fluids is unnecessary and placing them in sternal recumbency should allow for normal oxygen exchange and fetal fluid resorption.

There are many methods that have been advocated for establishing respiration and airway patency in calves. Rubbing calves with bedding or towels is an attempt to stimulate the phrenic nerve. Placing a finger, piece of straw, or other implement in the nose will initiate a gasping reflex and help aerate the lungs. The use of acupuncture points on the muzzle has been advocated. Pouring cold water over the calf's head or ear has been advocated for stimulation of hypothermal respiratory stimulation. In addition to these methods positive pressure ventilation can be used to establish respiration. Many of these methods are practiced on a regular basis. However, very little information is available as to their efficacy in calves. Pharmacologic initiation of respiration is often attempted with the use of doxapram hydrochloride. This may have efficacy in mildly hypercarbic animals, but it is unlikely that severely affected animals will have a response. Reversal agents may be used if the dam was sedated during parturition with xylazine.

Cardiac resuscitation is rarely undertaken in ruminants as the likelihood of survival is less than 50% if resuscitation is begun prior to the start of a nonperfusing rhythm and less than 10% is started after asystole.

In addition to basic life support, care should be addressed to any trauma sustained to the calf during calving or as a result of prolonged dystocia. Fractures and crush injuries may be sustained during hard pulls using implements such as chains and fetal extractors. Calves with prolonged time in the pelvic canal may suffer from regional swelling secondary to poor venous return. Extraction of the fetus will reestablish venous drainage and subsequent reduction in the swelling over the next few days. Furosemide or mannitol may speed the removal of edema in severely affected individuals. Fractures and luxations may be treatable with reduction ad casting or splinting techniques.

In particularly harsh environments or after prolonged dystocia care should be taken to ensure normal thermal adaptation to extra uterine life. Rapid declines in body temperature and a failure of thermostatic regulatory mechanisms to completely restore normal rectal temperatures are characteristic of calves born to severe dystocia. Moderate to severe metabolic disturbances also mirror the changes seen in body temperature. This highlights the need to ensure that adequate body temperature is maintained in neonates. A recent study revealed that calves exposed to an infrared heater for 24 hours postpartum had significantly improved rectal temperature, arterial hemoglobin oxygen saturation, tidal volume, dynamic lung compliance, and respiratory rates that control calves. The authors postulated that the lower energy expenditures required for thermogenesis in these calves allowed for the increased energy demands required for the increased respiratory work needed to generate the changes in the respiratory parameters.

In addition to these vital parameters, ensuring adequate colostrum intake is critical to the long term health and immunologic stability of the calf. The ingestion and absorption of maternally derived colostral components plays a large role in the immunologic capability of the neonate. Bovine colostrum contains many substances that support immune function in the neonatal calf. Immunoglobulins are the most commonly studied molecules, but maternal derived immune cells, complement factors, lactoferrin, insulin like growth factor – 1, transforming growth factor, interleukin 2, and other soluble factors are present. In addition to immune support colostrum is an excellent source of nutrients vital to the survival of the newborn including sugars and fat soluble vitamins.

It is critical that a complete physical examination be performed on sick calves. Some diseases of the neonate are relatively easy to correct in an economical fashion, while others are not. Adequate patient evaluation is critical to determining an appropriate course of therapy. Hypothermia, hypoglycemia, dehydration, and acidosis are common causes of poorly responsive calves that are easy to correct as long as the underlying cause is addressed. Unlike these the treatment of sepsis is often prolonged and unrewarding. Routine diagnostic examinations such as auscultation of the thorax can and should be performed. Pneumonia is a common finding in septicemic calves. However, the heart and respiratory rates are poor predictors of sepsis in the bovine neonate. Rectal temperature should also be determined, but the absence of fever does not preclude the possibility of septicemia. Neonates seem less prone to demonstrate fever than adult cattle, particularly in environments with cool ambient temperatures. The most consistent signs of septicemia are scleral injection, swollen joints, an enlarged, inflamed umbilicus, hypopyon, and evidence of meningitis – opisthotonus, teeth grinding, and seizures. Normal physical examination parameters in calves will vary somewhat based on age and environmental parameters.

Establishing vascular access will allow for the administration of intravenous fluids and drug administration in neonates in septic or hypovolemic shock. Intravenous fluid therapy is contraindicated in animals during a cardiac arrest due to the decrease in cardiac output caused by the non perfusing rhythm. Increased fluid administration at this time will serve to increase venous pressure and impair coronary perfusion. The jugular vein is the vessel of choice in calves that require large volumes of fluids or the administration of caustic drugs. A 16 gauge 3.5 inch catheter should provide adequate access in any size calf. In animals with profound hypovolemia, dropping the head below the level of the heart may help facilitate jugular filling for catheter placement. Administration of hypertonic (7%) saline (4 ml/kg IV slowly) will temporarily increase intravascular volume and aid in IV catheter placement. Electrolyte derangements and acid base abnormalities should be corrected.

In addition to electrolyte and acid base correction, adequate nutritional and thermal support should be addressed. Unlike adults, young calves do not have minimal energy reserves to combat prolonged anorexia. The use of dextrose in intravenous fluids can not be viewed as a replacement to adequate enteral nutrition in the sick calf. High quality milk replacer or cow's milk should be provided at approximately 10-15% of body weight per day. Lower ends of this estimate will not support growth and may not be adequate if increased energy demands are present due to pathologic processes. The higher end of the range may promote diarrhea in some calves. This author prefers to provide multiple small meals per day (½ - 1 L feedings depending on calf size) to avoid engorgement and minimize the potential for osmotic diarrhea. If calves will not suckle an oroesophageal feeder can be used. If prolonged feeding is expected a nasoesophageal tube can be placed in lieu of multiple passages of an oroesophageal feeder. Care must be taken to ensure that calves are in sternal recumbency or standing to limit the potential for regurgitation and overflow into the lungs. In addition, overfeeding should be avoided as milk may sit for prolonged periods of time and putrefy in the rumen.

Newborn calves often thermoregulate poorly, particularly if neurologic disease is present. Rectal temperature should be routinely monitored especially when heating devices are being applied. Circulating water heating pads can be used, but these often warm slowly and animals that are struggling may puncture the pad. Electric heating pads should be monitored closely if they are used because they can get hot enough to induce local burns particularly in animals that can not move from the pad when they get too hot. Care should also be taken when using heat lights as burning is possible. Calves will often continue to warm after heating devices are removed so consider removing heating devices or decreasing the intensity of the applied heat when calves attain a rectal temperature of 98°F – 99°F.

In calves, cardiopulmonary failure is generally due systemic disease as opposed to disease inherent to the organ system. The on-farm nature of cattle practice makes aggressive treatment of arrest unlikely unless the veterinarian is present at the time of arrest. The economic feasibility and likelihood of successful treatment of the underlying cause also needs to be considered. There is no evaluation of cardiopulmonary resuscitation techniques in calves and as a result most information presented here is extrapolated from techniques described for humans and foals.

In humans establishing an airway is considered of secondary importance to cardiac compressions when initiating CPR because blood flow as opposed to hypoxia is typically the limiting factor in oxygen delivery during early arrest. In cattle, this is unlikely to be true as primary cardiac disease is not commonly the cause of arrest. If a patient is hypoxic at the time of cardiac arrest, establishing an adequate airway and oxygenation becomes much more important for positive outcomes. No information exists on adequate parameters for respiratory rate, tidal volume, oxygenation, or cardiac compression rate in calves. In humans a compression rate of 100/minute with respirations provided at 8-10/minute making no attempt to coordinate respirations to cardiac compressions is recommended. This is a reasonable goal for calves.

Many medications have been used historically in cardiopulmonary resuscitation. It is important to recognize that the data surrounding many of the medications administered during CPR is contradictory. Prospective and retrospective studies, as well as meta-analyses have found disagreeing information regarding the immediate and long term outcomes associated with the administration of most commonly used drugs. Furthermore, some drugs are incorporated into protocols based on sound physiologic principles as opposed to hard data. Drugs can be administered IV or endotracheally if venous access has not been established. Endotracheal administration requires an increased dosage of drugs. In general 2-2½ times the intravenous does is administered endotracheally, although no data exists to substantiate this practice.

Epinephrine hydrochloride is commonly used (1 mg IV every 3-5 minutes) during cardiopulmonary arrest in people. The vasoconstrictive α–adrenergic effects are able to increase coronary blood and cerebral blood flow during CPR. Administration of epinephrine is commonplace and various low dose and high dose regimens exist in the human literature. Despite this, there is very little data available that demonstrates improved rates of hospital discharge in patients that have been administered epinephrine at the time of resuscitation.

The on farm nature of most cattle practice, make the use of advanced CPR uncommon. It is important to remember that even with the rapid, well equipped responses in human medicine; the single biggest predictor of positive outcome is the time to the initiation of cardiac compressions. When considering cardiopulmonary resuscitation in calves, initiating an appropriate compression rate and establishing an airway and are the two most critical procedures. Medication administration should be considered secondary to cardiac compressions and breathing. It is important to recognize that eliminating breaks in compressions is vital to maintaining blood pressure and perfusion. This requires that all equipment and medications be in a single place, ready for use. It is also critical to remember that reestablishing a perfusing heart rhythm and voluntary breathing us not the end. Animals will often have electrolyte and acid base abnormalities that require correction. In addition, if the underlying cause of arrest is not addressed it is likely that the animal will rearrest.

Resuscitation and critical care of neonatal calves (Proceedings)

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