Michelle Fulks, DVM

Small animal pediatric patients have several differences from their adult counterparts that make them unique patients in many regards. These differences are important to know as they can affect the diagnosis and treatment of many disease processes. The following is a review of the normal variations in pediatric patients as well as an overview of the most common pediatric emergencies.

Physical Exam

Neonatal puppies and kittens are "hypothermic" compared to adult patients. A normal temperature for a kitten is 98°F and a puppy is 96-97°F at birth. Their temperature increases to 100°F by one week in kittens and one month in puppies. This variation is important to remember so that pediatric patients are not warmed to an adult normal temperature, as this may cause over-heating.

Pediatric patients also have increased respiratory rates and heart rates compared to adults. A normal respiratory rate is approximately 2-3 times higher than that of adults due to increased airway resistance and higher oxygen demand. Their normal heart rate at birth is often greater than 200 beats per minute. Hypothermia is the major cause of bradycardia in pediatric patients, so a temperature should be evaluated in any patient with a low heart rate. Pediatric patients may also have a physiologic heart murmur for the first 3 months of life. Physiologic murmurs are generally low grade systolic murmurs. "Washing machine" and high grade murmurs over the aortic and pulmonary valves may indicate congenital abnormalities and should be evaluated.

Dehydration and hypovelemia can often be difficult to detect in pediatric patients. Skin turgor is an inaccurate assessment of hydration due to increased fat and decreased water content of the subcutaneous tissues. Their mucous membranes also often remain moist despite severe dehydration.   Pediatric patients also do not have the ability to compensate for dehydration and hypovolemia by increasing their heart rate or concentrating their urine. Due to immaturity of the sympathetic nerve fibers in the myocardium they cannot increase heart rate in response to hypovolemia until 8 weeks old. It is important to remember that a pediatric patient with a normal heart rate could still be in significant hypovolemic shock. Therefore, it should be assumed that pediatric patients with severe losses due to vomiting and diarrhea or inadequate intake are dehydrated and potentially hypovolemic and treatment should be initiated immediately.

Normal blood pressures are also different in pediatric patients. Normal mean arterial pressure is 49mmHg for the first 2 months in both puppies and kittens. This "hypotension" is believed to be due to an immature muscular component of the arterial wall at birth. The blood pressure normalizes to the adult level, with a mean arterial pressure of 94mmHg, by 9 months of age.

Neurologic evaluation can be difficult in pediatric patients as many reflexes tested take weeks to months to develop. Pain sensation is present in puppies and kittens at the time of birth. They have flexor tone present until day 5; meaning if they are scruffed they should curl into a ball. This progresses to extensor tone after day 5. If they are scruffed after this point all legs splay out. The withdrawal reflex is present by one week. Even though their eyes open by 2 weeks and vision normalizes by 1 month, a menace response is not present for 2-3 months.

Laboratory values

Pediatric patient have a normal decrease in hematocrit during the first month of life. This decrease is thought to be caused by the change from a relatively hypoxic environment to an oxygen rich environment. At birth, dogs have a hemotacrit of 47%, but it drops to 29% by 28 days. In cats, the at birth hematocrit of 35% drops to 27% by 28 days. By the end of the first month, the hematocrit starts to increase again to adult normal values. Knowledge of this decrease in hematocrit is essential in treatment of pediatric patients, as during this time an increase in hematocrit is generally indicative of significant dehydration.

Normal complete blood count values for pediatric patients are depicted below.

Pediatric patients also have unique reference ranges for biochemical values as well. There are dramatic increases in liver enzymes in puppies at birth with ALP and GGT greater than 20 times the adult value. Kittens also have an increased ALP, but it is only about 3 times that of adult values. Pediatric patients also have decreased levels of blood urea nitrogen, creatinine, cholesterol, albumin and globulin for the first 4-6 months of life.   Knowledge of these differences is crucial to prevent a misdiagnosis of liver disease in pediatric patients, as elevations in liver enzymes with low levels of BUN, cholesterol and albumin can mimic liver dysfunction. Bile acids are normal in puppies at birth and by 2 weeks in kittens. Bone growth in pediatric patients also cause increases in calcium and phosphorus. 

COMMON PEDIATRIC EMERGENCIES

Hypovolemia

Since pediatric fluid requirements are higher than adults, dehydration can rapidly progress to hypovolemia and shock in these patients if not adequately treated. The most common syndromes associated with hypovolemia in pediatric patients are diarrhea, vomiting and overfeeding. The most common cause of diarrhea is owner overfeeding with formula, however intestinal parasites, bacterial and viral infections are also common in pediatrics.

As discussed previously, dehydration is often difficult to accurately identify in these patients. However, early and aggressive treatment is essential. Pediatric kidneys are unable to concentrate urine in response to dehydration until 10 weeks of age. Immature kidneys also cannot auto-regulate renal perfusion pressure over a wide range of systemic arterial pressures, thus glomerular filtration rate decreases as systemic blood pressure decreases in these patients. Thus, restoration of fluid volume is critical in pediatric patients.

The treatment of hypovolemia includes fluid therapy, nutritional support, monitoring of electrolyte and glucose status and treating the underlying cause of vomiting, diarrhea or inappetance. Pediatric patients have higher fluid requirements due to higher percentage of total body water, greater surface area to body weight ratio, higher metabolic rate, decreased renal concentrating ability and decreased body fat. Their maintenance fluid requirements are 80-100 ml/kg/day. Fluid requirements normalize to adult requirements around 8 - 12 months of age. Fluid therapy should also account for any continued ongoing losses and dextrose should be supplemented with the lowest amount to maintain normoglycemia. Overhydration is also a concern in pediatric patients treated with fluid therapy due to the fact that the kidneys cannot dilute urine to rid the body of excess water. The best way to monitor for overhydration is with an accurate pediatric gram scale.

Venous access is necessary for fluid therapy but can be difficult in pediatric patients due to their size. The intravenous route is preferred and should always be attempted first. Small gauge catheters tend to burr easily so making a small skin puncture may facilitate placement. The jugular vein is often the best location for placement of intravenous catheters in these sick pediatric patients. If intravenous access cannot be obtained, an intraosseous catheter may be placed in the proximal femur or humerus. An intraosseous catheter may be placed using a 18-25 gauge hypodermic needle or a purpose made intraosseous catheter (such as the EZ IO catheter) in pediatrics. Complications correlate with duration of use, so intravenous access should be obtained as soon as possible. 

Hypoglycemia

Due to immature glucose feedback mechanisms, decreased ability of the liver to synthesize glucose, increased loss through the urine and increased demand by brain and myocardium, pediatric patients are highly susceptible to hypoglycemia. Urinary glucose reabsorption normalizes by 3 weeks of age. Clinical signs of hypoglycemia include lethargy and weakness, anorexia, hypothermia and tremors or seizures. Vomiting, diarrhea, infection and decreased intake all contribute to hypoglycemia in pediatric patients. Treatment of hypoglycemia focuses on boluses and constant rate infusion of dextrose. Over-supplementation should be avoided since osmotic diuresis can contribute to further dehydration. Treatment should also focus on nutritional support and treatment of the underlying cause.

Hypothermia

Pediatric patients are prone to hypothermia due to a decreased ability to thermoregulate. They have only brown fat, rather than insulating white fat. They also have an increased surface area to weight ratio and increased metabolic rate, which increases heat loss. Puppies and kittens do not have the ability to shiver or vasoconstrict until 6-8 days, which are normal responses to hypothermia. Clinical signs may include bradycardia, depressed respirations, ileus or coma. Treatment entails providing a constant source of exogenous heat with warm fluids, warm water blankets and bottles or forced heat. Again, it is important to remember that pediatric patients have lower temperatures than their adult counterparts and the optimal environment is 90°F and 55-65% humidity. It is important to reheat slowly (less than 2°F per hour) and avoid overheating.

Head trauma

Head trauma is an extremely common injury in pediatric veterinary patients who may be stepped on by owners, fall from arms and furniture or get heads slammed in refrigerators or cabinets. Human children have a higher percentage of diffuse brain injury due to greater head to torso ratio and characteristics of the neonatal brain, including higher water content and greater susceptibility to apoptosis and delayed cell death, lead to increased sensitivity to trauma. This may be true in our veterinary patients as well. Anisocoria is generally present in pediatric patients with head trauma. In adults, a decrease in cerebral perfusion pressure causes an increased systemic blood pressure and reflexive bradycardia, a physiologic phenomenon known as the Cushing's reflex. However, this sign is unreliable in pediatric patients due to immaturity of the autonomic nervous system until 8 - 10 weeks.

The goals of treatment for head trauma in pediatric patients, just like in adults, are to improve oxygen delivery, decrease intracranial pressure and maximize cerebral perfusion pressure. Since cerebral perfusion pressure is equal to mean arterial pressure minus intracranial pressure (CPP = MAP - ICP), the goal is to keep mean arterial pressure high and intracranial pressure low. Appropriate fluid therapy to maintain a systolic blood pressure above 90 mmHg is imperative. If a patient is well hydrated, hypertonic saline is a good fluid choice as it both increases intravascular volume to maintain blood pressure and decreases intracranial pressure. Once properly fluid resuscitated, if the patient is still hypotensive vasopressors should be used to maintain blood pressure. Mannitol may be considered to decrease intracranial pressure once the patient is fluid resuscitated. Maintaining adequate ventilation, while avoiding hyperventilation and hypoventilation, is also crucial to maximize cerebral perfusion pressure. Providing supplemental oxygen is also implemented to improve oxygen delivery.  In general, treatment for head trauma should focus on optimizing systemic blood pressure through fluid therapy and vasopressors, raising head 30° while avoiding jugular compression and optimizing oxygenation and ventilation.

Conclusions

Pediatric patients have unique physiologic characteristics that are crucial to be aware of when treating this unique subset of patients. Knowledge of physical exam and laboratory differences from adult patients is imperative for diagnoses of diseases, including something as simple as dehydration. Their differences also play a crucial role in tailoring treatment plans specific to meet their physiologic needs. Sick neonatal and pediatric patients require careful care and close observation. Many of these patients may need 24 hour care or referral for critical care and monitoring. 

References