Anesthetic considerations in a preterm: Extremely low birth weight neonate posted for exploratory laparotomy.

Preterm neonates present unique challenges to the anesthesiologist due to their immature physiology and anatomy. Many preterm neonates are critically ill and can develop necrotizing enterocolitis, respiratory distress syndrome, intra ventricular hemorrhage, and heart failure or retinopathy of prematurity. Anesthesiologists play a vital role in the management of preterm neonates requiring surgical interventions, by integrating their knowledge of the developmental physiology and pharmacology. The successful conduct of anesthesia in premature neonates requires an understanding of the basic principles of neonatal care.

INTRODUCTION

Babies born before 37 weeks of gestation are defined as premature.[1] Babies with a birth weight of less than 1000 g are classified as extremely low birth weight (ELBW) babies.[2] We report and discuss the key points in the anesthetic management of a preterm; ELBW neonate posted for exploratory laparotomy. During the search of the literature we did not come across any similar case reported earlier.

CASE REPORT

A preterm (born by cesarean section at 31 weeks + 4 days gestational age), ELBW (913 grams) neonate was posted for exploratory laparotomy at the age of 4 days. High risk consent was obtained in view of the risk of surgery and anesthesia and the need for postoperative mechanical ventilation. The clinical findings were suggestive of perforation peritonitis secondary to necrotizing enterocolitis (NEC) [Table 1, Figure 1].

Table 1

Clinical findings of the neonate on presentation for the surgery

Figure 1

X-ray showing air under the diaphragm, free air in the peritoneal cavity, grossly distended small bowel loops

Additional equipment was checked preoperatively, including an overhead radiant warming device (Infant warmer, Neotech, Mettukuppam, Chennai), fluid warming device (Hotline fluid warmer, Smiths medical ASD, inc., USA/Canada) and anesthesia machine capable of delivering air, O2 and N2O. The operation theatre (OT) was prewarmed to a temperature of 25°C. The patient's limbs were wrapped in cotton, covered with plastic. The neonate had a central venous catheter (Permacath 28G) in situ and a peripheral line was secured. Anesthesia was induced using O2 + air + inj atropine 0.016 mg + inj fentanyl 1 μg + sevoflurane. Trachea was intubated with size 2.5 uncuffed endotracheal tube that was secured at the 7 cm mark at the alveolar margin after confirming equal air entry bilaterally. Monitoring included ECG, SpO2; NIBP, temperature, ETCO2 and precordial stethoscope was placed.

The neonate was maintained on O2 + air + Sevoflurane along with intermittent doses of inj fentanyl and inj atracurium. Ventilation was controlled to maintain an ETCO2 of 40–45 mm Hg with Jackson Ree's apparatus. Intraoperative findings included perforation of the terminal ileum and gangrenous changes in the distal ileum. An ileostomy was fashioned after resection of the gangrenous segment. Postoperatively, the neonate was transferred to the nursery for elective mechanical ventilation. He was gradually weaned off ventilatory support and ileostomy closure was done at 12 days of age.

DISCUSSION

The incidence of preterm births is estimated at 9.6% of all births worldwide.[3] Premature infants are prone to morbidity including respiratory distress syndrome, intraventricular hemorrhage, periventricular leukomalacia (PVL), retinopathy of prematurity, necrotizing enterocolitis, and patent ductus arteriosus (PDA).[4] Extreme care should be taken if transporting the neonate to OT, in particular not to displace intravenous lines or the tracheal tube. The common indications for surgery in neonates are listed in Table 2.

Table 2

Common surgical conditions requiring anesthesia in the premature neonates

NEC occurs mainly in preterm infants, with an incidence of about 7% and a mortality of 15% to 30%.[5] Aetiology of NEC includes prematurity and poor mucosal integrity, hypoxia, and exchange transfusion, PDA with decreased blood supply to the gut, early feeding with formula milk and colonization with pathogenic bacteria. The classical presentation is of abdominal distension, bloody stool and bile-stained aspirates, but signs of sepsis may predominate, progressing to apnoea with shock, acidosis, and disseminated intravascular coagulation (DIC). Intestinal perforation may cause a localized mass. The abdominal wall may be reddened in the presence of peritonitis, as seen in our patient.

Radiographic findings of NEC include pneumatosis intestinalis (gas within the bowel wall), and a characteristic appearance on a radiograph of dilated thickened loops of bowel with intramural gas, portal vein air, pneumoperitoneum or the ‘football’ sign. Investigations may also reveal thrombocytopenia and metabolic acidosis, as in our case; and raised C-reactive protein.[5]

The patient had received vitamin K1, platelet transfusion and fresh frozen plasma preoperatively for correction of deranged bleeding parameters. Atropine was given during induction of anesthesia to preempt against bradycardia. We used fentanyl for pain relief as elective postoperative ventilation was planned.

A mixture of air and O2 was used for ventilation throughout the procedure and SpO2 was maintained between 88-95%, in view of the risk of ROP. The key points during ventilation include avoiding oxygen saturation greater than 95%, hyperventilation, high-peak inspiratory pressures, and barotrauma.

Special consideration was given to temperature monitoring as preterm neonates are prone to hypothermia and its deleterious consequences including, hypoglycaemia, apnoea, and metabolic acidosis.[6] Prewarming of the OT and availability of equipment including overhead radiant warmer, warming mattress and fluid warmers is useful as adjuncts to prevent hypothermia. Both surface and core temperature monitoring may be helpful in the preterm neonate.[7]

Pre-existing hypovolemia, bleeding and coagulopathy, significant third space losses, and metabolic acidosis, co-existing with NEC may require large volume replacement. Central venous access is important if large fluid shifts are expected or transfusion of blood products or inotropes is indicated. Although invasive arterial monitoring is useful in the septic patient on inotropes, we did not use invasive arterial monitoring as our patient had deranged coagulation profile.

Hypoglycaemia is common in preterm neonates and intraoperative monitoring of blood glucose is essential. Hyperglycemia should be avoided as it causes a hyperosmolar state and can lead to IVH and osmotic diuresis.[6] We used 5% dextrose with 0.45% saline as maintenance fluid. After surgery, the patient was transferred to the nursery for elective mechanical ventilation and complete hand over was given to the neonatologists about the intraoperative events.

Preterm neonates require mandatory monitoring of SpO2 postoperatively as they are prone to apnoeic spells for 48 to 72 h. Apnoea is cessation of respiration exceeding an arbitrary duration of 20 s, or less than 20 s but with bradycardia or oxygen desaturation. The incidence of apnoea varies from 25% in the LBW premature to 84% in the ELBW group[8] and is inversely related to gestational age. Risk of apnoeic spells is greater in former premature infants with anaemia, even up to a postconceptional age of 60 weeks. All general anesthetic agents, including ketamine, can cause postoperative apnoea.

In conclusion, ELBW, preterm neonates pose multiple problems to the team involved in their management and the anesthesiologist has to be prepared to handle these patients with extreme care and patience to ensure a successful outcome.