Resuscitation of calves after dystocia (Proceedings)
Perinatal mortality (still births and deaths within the first 24 hours of life) should be 1-3% as a goal. The following are associated with an increased perinatal mortality rate: 1) increased fetal body weight relative to dam body weight and pelvic area; 2) twins or triplets; 3) primiparous dam; 4) increased duration of second stage labor; 5) poor abdominal press by dam; 6) meconium staining/aspiration; 7) premature placental separation; 8) placental abnormalities or placentitis; 9) immaturity or prematurity; 10) birth trauma, manifest as swollen head or tongue, fractured ribs, fractured vertebrae, femoral nerve paresis, limb fractures; 11) posterior presentation which places pressure on umbilicus and decreased placenta blood flow; and 12) prenatal administration of non steroidal anti-inflammatory drugs to the dam which causes narrowing of the fetal ductus venosus.
A practical definition of the duration of second stage labor is the time from rupture of the allantoic/amniotic sac to passage of the forehead or pelvis (if posterior presentation) through the vulva. Using this definition, a second stage labor of up to 120 minutes seems reasonable if fetal presentation and position is normal. However it should be remembered that if second stage labor is observed to be longer than 1 hour or assisted delivery is required, then the calf is at increased risk for postnatal acidosis and reduced absorption efficiency of colostrum. Elective cesarian section produces optimal calf viability if dexamethasone (20-25 mg) is administered 24 hours before the scheduled time of surgery in the last 2 weeks of gestation. Optimal calf viability is obtained when the cesearian section is performed at the start of stage 2 labor when the cervix is fully dilated.
Rib fractures are very common in calves delivered after a dystocia, being present in 21% (35/169) of calves delivered by extraction versus 0% (0/61) of calves delivered by cesarian section. Rib fractures are present in 5% calves born with assistance of 1 person, and 34% calves born with assistance of 2 people or a calving jack. Rib fractures are most easily detected by placing the calf in sternal recumbency and palpating for symmetry along both sides of the thorax. Rib fractures are frequently overlooked during the physical examination.Immediately after delivery (first 30 seconds of extrauterine life), each calf should have its upper respiratory passages cleared of any physical obstructions and external stimulation of the calf applied. A patent airway is ensured by cleaning the nostril/buccal cavity of amniotic remnants by suctioning, never by applying postural drainage via holding upside down or swinging the calf in a horizontal circle. The calf is externally stimulated by vigorous rubbing around head and neck, and placing a finger or straw in nostril and pharynx. A lack of response to stimuli suggests a poor prognosis. In particular, a high mortality rate results if a calf takes longer than 15 minutes to reach stable sternal recumbency. The calf must be placed in sternal recumbency to minimize ventilation perfusion inequalities. Positioning of the calf in any other manner facilitates the maintenance of ventilation perfusion inequalities and must be avoided at all costs.
The calf should make active respiratory movements within 30 seconds. Primary apnea is defined as no spontaneous breaths for 1-5 minutes; doxapram may be an effective treatment for these calves. Doxapram stimulates peripheral chemoreceptors and medullary respiratory neurons, and is an effective analeptic agent if given early. An analeptic agent is "a drug that stimulates depressed respiratory & cardiovascular centers". Doxapram at 2 mg/kg IV has a potent stimulating action on the respiratory center, with a wide margin of safety; abnormal clinical responses are convulsions and hypertension. If spontaneous breaths are not observed within one minute of expulsion, the calf needs to be intubated with an endotracheal tube: an internal diameter of 7 to 8 mm fits most calves, but 6 mm is needed for Jersey calves or twins. Intubation requires placing the neck and head in straight line, which is easiest with calf in sternal recumbency. A laryngoscope with an extension to depress the tongue is most helpful to visualize the larynx but may not be available. The presence of respiratory secretions can make visualization of the larynx extremely difficult, and suction is usually needed. Alternatively, the larynx can be palpated with one hand, and the endotracheal tube is manipulated with other hand. The cuff is inflated and the lungs expanded. Relatively high pressures may be needed initially but should be minimally applied to prevent barotrauma; -80 cm H2O pleural pressure is generated in the first few breaths by calf; this should be compared with -12 cm H20 pleural pressure generated by neonate when breathing normally at tidal volume. The endotracheal tube should be removed when calf is sufficiently strong enough to chew on the tube. Increased inspired oxygen tension can be obtained by suturing a plastic feeding cannula to one nares so that the end is in the nasopharynx; humidified oxygen is then delivered at 5 to 10 ml/min which will increase the inspired oxygen tension from 21% to approximately 30-35%.
Sodium bicarbonate has been used empirically at 1-2 mEq HCO3 / kg IV to resuscitate calves after a dystocia with no reported deleterious effects. The advantages of bicarbonate treatment is that a mixed respiratory/strong ion (metabolic) acidosis is present in all new born calves, and anaerobic glycolysis is a normal event in the fetus during parturition. The disadvantages of bicarbonate administration is increased production of CO2 (which may exacerbate respiratory acidosis), and hyperosmotic bicarbonate solutions have been associated with an increased incidence of cerebral vascular accidents in premature human infants. Sodium bicarbonate treatment therefore has some theoretical risks, and the current evidence suggests that sodium bicarbonate should not be routinely administered.
If the calf becomes profoundly bradycardic, 1 mL of epinephrine (1 mg/ml solution) IV, intracardiac, or into the base of the tongue can be administered to a 45 kg calf. This invariably induces a rapid tachycardia that may be helpful if the calf can be intubated and ventilation is assisted. If the calf fails to spontaneously breathe, mechanical ventilation is required. Mouth to nose resuscitation (by occluding one nostril of the calf and blowing into the other) or mask ventilation is ineffective in the neonate because it is much easier to inflate the abomasum than the lungs. Seizure activity may be difficult to recognize in calves, but is characterized by abnormal eye movement, paddling of limbs, and bawling. All are associated with central nervous system injury and constitute a poor prognosis. Corticosteroids (dexamethasone, 0.05 mg/kg BW IV or IM) should be administered to all premature calves with respiratory difficulties, because it helps to stimulate surfactant production after 24 hours. In other words, the calf has to live for at least 24 hours for this treatment to be of benefit.