Anaesthesia and Chronic Pain

Anaesthetic Management of Retinopathy of Prematurity (ROP)

Pratima Kothare 

Introduction
Progress in medical field and advances in
neonatology have increased the survival rate of preterm infants (< 37 week gestation). Nevertheless they may develop ROP and may require surgical intervention according to the stage of ROP. Hence a complete understanding of neonatal and infant physiology along with the impact of anaesthetics on the infant is essential to deal with the surgeries of ROP.1,2
Conceptual age = gestational age + postnatal age
This means that an infant < 44 weeks is at risk of retrolental fibroplasias3 and < 46 weeks age is at risk of postoperative apnoea.4
ROP is the major cause of blindness in infants. It is characterised by a fibrous gliovascular proliferation arising from the inner retina. This gliovascular proliferation is unique to the premature developing retina and is associated with very low birth weight (< 1000 grams) and with gestational age under 32 week.5

Stages of ROP
There are five stages of ROP and the treatment approach to each of them varies

These are done under GA in the operation theatre.
Laser surgery and cryotherapy can be done under local and topical anaesthesia.

Preanaesthtic Evalutation
This includes history taking, examination, consent and preoperative advise. Direct communication with the parent by the anaesthesiologist is important and human as your patient is their precious child. Explain the risks involved to a preterm infant during anaesthesia and the potential intraoperative and postoperative complications and the necessity of postoperative intensive care treatment with or without artificial ventilation, after establishing the apnoea protocol1.

History
Birth age : Birth weight; H/0 jaundice, convulsions, apnoeic spells; present age
Physical examination : Exact weight; look for congenital anomalies
Investigations : CBC; Chest X-ray; CT scan of the brain
This is done to look for intraventricular haemorrhage Infants < 1500 grams are susceptible to IVH, hydrocephalus and seizures.
All the additional risk factors that emerge after investigations are explained to the parents in common language.

Preoperative instructions and advise
1. Nil orally for 4 hours preoperatively
2. Continue all medications on the day of surgery.
3. Secure an intravenous access and start ringer lactate @ 2 ml/kg/hr
4. Neonatal ICU personnel informed for necessary pre and post operative care.

Intraoperative Management
The important aspects of intra operative care are
Transportation
As a policy decision at our Institute we shift the infant in a temperature controlled incubator with oxygen source, ECG and pulse oximeter monitoring, and an ambu bag accompanied by the anaesthesiologist, neonatologist and a nurse along with a tray of emergency drugs and necessary equipment as the infant is most vulnerable to environmental stresses during transportation.

Temperature Management
Increasing environmental temperature of the theatre is the best way to maintain the infant’s core temperature, also wrap the child in gamgee, give intravenous fluids through a warmer, give humidified anaesthetics gases and cover the infant with an electric warmer blanket. By taking these precautions we avoid hypothermia and its undesirable physiological changes.

Theatre Preparation
Fully equipped and functional intubation trolley is prepared. Anaesthetic drugs loaded in required doses in 1 ml and 2 ml syringes. Emergency drugs are kept ready. Infusion pump for the fluids set at calculated dose of 2 ml/kg/hr. Ventilator is set at Tidal volume of 15 ml/kg and respiratory rate at 25. Laryngeal mask airway is always kept as a standby.
Anaesthesia Technique
On arrival in the warm theatre standard monitors are applied i.e. ECG, Pulse oximeter, temperature probe, NIBP cuff, warmer blanket to cover the infant. The I V access is connected to the infusion pump to prevent overinfusion.

Premedication
Preoxygenation with 100% oxygen
Atropine or Glycopyrrolate

Induction
I V  Ketamine- It is the safest drug to use in these very small children. Propofol may also be used. One of the basic principle is to mask, ventilate and judge that the infant can be safely ventilated. Only then a muscle relaxant is given. The choices are vecuronium or atracurium.
After adequate IPPV Laryngoscopy performed with a straight blade laryngoscope with a head ring under the infants head then an adequate size.
Plain Endotracheal tube passed (ETT size =Age in years/3 +3.5)
Tube placement is confirmed by conventional auscultation and by connecting the End Tidal Carbon dioxide monitor and to the ventilator which further confirms the expiratory tidal volume

Maintenance
Oxygen 50% + Nitrous oxide 50% + Isofluorane in minimal concentrations. Muscle relaxants are supplemented only when needed.

Reversal
Oxygen 100% is given for five minutes to saturate the infant with oxygen. On evidence of some spontaneous effort or breathing the muscle relaxant is reversed. The reversal drug is neostigmine and is combined with atropine to balance the muscarinic effects of neostigmine i.e. bradycardia and excessive secretions.
“ Wake up” of the infant is confirmed with spontaneous eye opening, flexion of knees, good power in both limbs, crying on the endotracheal tube and return of respiration.

Criteria for extubation
All evidence of having “woken up”
Spontaneously and adequately maintaining SaO2 of 96%
Core temperature of .35 degrees Celsius,
In occasional cases if it is risky to extubate it is preferable to shift the child to the NICU where the child can either be ventilated or observed on T piece with oxygen. And the extubation can be done in the NICU.

Post Operative Care
After adequate observation with full monitoring the child is shifted to the NICU.
For postoperative pain relief local infiltration of conjunctiva with 1 -2 ml of plain Xylocaine is preferred over narcotic analgesics.
It is the duty and responsibility of the anaesthetist to ensure safe transportation of the patient to the NICU.

Discussion
The expected difficulties and complications deserves a mention in the management of ROP infants

Difficult intravenous approach

• Difficulty in handling infants head and neck
• Difficult Intubation
• Hypothermia.
• Laryngospasm during intubation and emergence.
• Hypoxaemia and Bradycardia during intubation and emergence.
• Inadequate reversal of nondepolarising muscle relaxant due to various reasons and hence not extubated infant
  
• Post operative apnoea
• Metabolic complications like hypoglycaemia hypocalcaemia acidosis
• Transportation complications