Prematurity

Postoperative apnea is the headline - Preterm infants under 44 weeks postconceptual age (PCA) are at higher apnea risk after sedation or general anesthesia. Pooled herniorrhaphy data: apnea incidence does not fall below 5% until 48 weeks PCA in infants born at 35 weeks gestational age, or 50 weeks PCA in those born before 32 weeks; it falls below 1% at 54 weeks PCA (35-week GA) or 56 weeks PCA (32-week GA). Risk is inversely proportional to both gestational age and PCA.

Decide admission by PCA and hematocrit - Premature infants under 55 weeks PCA, anyone with a hematocrit under 30%, and anyone with apnea are admitted for monitoring. Between 55 and 60 weeks PCA, not anemic and not apneic, an extended PACU observation is reasonable. Apnea beyond 60 weeks PCA has not been reported, so many institutions simply admit every premature infant under 60 weeks. Elective and nonurgent cases under 50 weeks PCA are better postponed.

Monitor at least 12 hours - Apnea and bradycardia are most frequent in the first 4 to 6 hours after surgery but are reported out to 12 hours.

Regional does not buy you out of monitoring - The GAS trial found no difference in overall postoperative apnea between spinal and general anesthesia (about 6% in preterm infants), though severity and apnea in the first 30 PACU minutes were lower with spinal. Block adjuncts such as clonidine and sedatives such as midazolam and dexmedetomidine are themselves linked to postoperative apnea.

Caffeine is the prophylaxis - Methylxanthines remain the main pharmacologic treatment. Caffeine is preferred over theophylline for its longer half-life and wider therapeutic index; a standard regimen is 20 mg/kg loading then 5 to 10 mg/kg/day. Expect tachycardia, emesis, and jitteriness. Theophylline requires serum levels.

Treat an apneic episode in steps - Stimulation and airway maneuvers first, bag-mask ventilation reserved for prolonged or profound episodes. Nasal CPAP at 4 to 6 cm H2O reduces frequency and severity, and works best alongside a methylxanthine.

PACU bradycardia is hypoxemia until proven otherwise - It is the most common dysrhythmia in these infants. Other causes are vagal stimulation (NG tube, laryngoscopy), drugs (neostigmine, beta blockade, alpha-2 agonists, fentanyl), raised ICP, and a high neuraxial block. Continuous pulse oximetry is mandatory — upper airway obstruction is the most common postoperative complication and desaturation follows fast.

Know the apnea risk factors before you start - Anemia, glucose or electrolyte imbalance, a large-shunt PDA, opioid analgesics and magnesium sulfate, gastroesophageal reflux, elevated body temperature, chronic lung disease, and multiple congenital anomalies all raise the odds.

Heat leaves fast - Preterm infants have less brown fat and less thermogenesis, a large exposed surface area, and general anesthesia blocks hypothalamic thermoregulation; core temperature commonly drops 1°C to 2°C in the first hour. Warm the room to 78°F to 80°F before arrival, use an underbody forced-air warmer, transwarmer, warming lights, and a hat, warm all field fluids to body temperature, and run blood through a fluid warmer. Keep the isolette plugged in for transport.

Glucose runs out quickly - Preterm neonates have low glycogen stores and impaired glycogenolysis and gluconeogenesis, and go hypoglycemic after even short NPO periods. They need 5 to 6 mg/kg/min of glucose against 3 to 5 for term neonates. Never stop a running TPN or PPN — that alone causes acute hypoglycemia. D5LR at maintenance is standard under 6 months; give boluses as glucose-free NS or LR, 10 mL/kg.

There is not much blood to lose - Circulating volume is 100 mL/kg in the preterm neonate against 90 mL/kg at term. Twenty percent of that is roughly 50 to 75 mL. Calculate allowable blood loss before incision using estimated blood volume and starting hemoglobin, and watch the field rather than the canister — it takes about 50 mL just to fill the suction tubing.

Cardiac output rides on heart rate - Neonatal myocardium is less compliant than adult myocardium, so output is rate-dependent. Vasoconstriction also responds poorly to hemorrhage: a 10% drop in blood volume produces a 15% to 30% fall in mean arterial pressure.

Plan the airway around neonatal anatomy - Larger head, floppy epiglottis, more cephalad larynx; a neutral or slightly flexed position may be easier than a shoulder-roll sniffing position. Up to 20% of babies under 6 months need more than one intubation attempt, so video laryngoscopy is reasonable for the first look under 10 kg and 1 year. Uncuffed 3.0 tube for neonates over 1 kg, 2.5 under 1 kg. Tochen's 7-8-9 rule sets depth at the gums — 7 cm at 1 kg, 8 cm at 2 kg, 9 cm at 3 kg — or weight in kilograms plus 6 cm, then confirm with auscultation, chest rise, ETCO2, and chest x-ray.

They desaturate fast and recover slowly - Alveolar maturation is incomplete at birth, airway closing pressure is low so alveoli collapse quickly with loss of ventilation, and neonatal oxygen consumption is 6 mL/kg/min against 3 mL/kg/min in an adult.

But do not over-oxygenate - Retinopathy of prematurity is retinal vascular and capillary proliferation driven by supplemental oxygen against an incompletely vascularized retina; the nasal and temporal retina do not finish vascularizing until 32 and 40 weeks. Oxygen concentration is an independent risk factor, and every 12-hour period with transcutaneous PO2 at or above 80 mmHg doubles the risk. Titrate FiO2 to the lowest that works.

Positioning and skin need real attention - Thin skin, minimal fat, and a soft moldable skull. Gel headrests can cause pressure necrosis and hair loss as well as head molding. Pad every line, monitor, tubing, and the cautery pad before drapes go on, and know exactly where they are — once the baby is draped you cannot reach under without breaking the field.

Drug handling is immature - Renal and hepatic maturation generally reaches adult levels around 6 months. Most drugs used in neonates, including acetaminophen, are off-label, and pharmacokinetic data are thin.

Prematurity is birth before 37 completed weeks — about 11% of US deliveries. Every organ system is unfinished, and the four that drive an anesthetic are respiratory control, thermoregulation, glucose handling, and the retina. Immature neurons in the medullary respiratory centers and immature peripheral chemoreceptors produce apnea of prematurity: a pause of 20 seconds or more, or a shorter pause with bradycardia under 100 or desaturation. Because the newborn parasympathetic system is mature while the sympathetic is not, hypoxemia produces bradycardia rather than tachycardia. Virtually all infants born under 28 weeks have apnea of prematurity; incidence falls to about 85% at 30 weeks and 20% at 34 weeks, and episodes typically resolve by 52 weeks postconceptual age. Anesthesia and sedation reopen that window long after the nursery has closed it.