Inverse ratio ventilation versus conventional ratio ventilation during one lung ventilation in neonatal open repair of esophageal atresia/tracheoesophageal fistula
A randomized clinical trial.
Pediatric Anesthesia
Submitted July 2024 by Dr K C Law
Read by 111 Journal Watch subscribers
Rationale
This study is based upon the practice of inverse ratio ventilation (IRV) used in ARDS (acute respiratory distress syndrome) to improve oxygenation and lung function. IRV can be used to prevent alveoli collapse through constant maintenance of lung inflation by increasing inspiratory time, reducing airway pressure and elevating mean airway pressure.
In neonates with oesophageal atresia/tracheooesophageal fistula, it is thought that a ventilation strategy that can maintain oxygenation during one lung ventilation phase of their open thoracotomy surgery can reduce hypoxemia, reduce surgery time and reduce the incidence of surgery being paused due to oxygenation issues. Potential IRV downsides include air entrapment (auto-PEEP), barotrauma, volutrauma, air leaks, decreased venous return and increased pulmonary vascular resistance.
Design
This is a single centre, prospective, blinded study comparing conventional ratio ventilation (CRV) using I:E (inspiratory : expiratory) ratio of 1:2, with inverse ratio ventilation (IRV) using I:E of 2:1 in a sample of 40 term neonates undergoing open right thoracotomy to repair oesophageal atresia / tracheoesophageal fistula in a paediatric hospital in Cairo, Egypt.
The study was approved by their local medical ethics committee and potential participants' parent / guardian was approached for consent. Exclusion criteria were:
- prematurity ≤36 weeks
- low weight <2.5 kg
- age >28 days
- significant congenital heart disease including cyanotic heart disease
- single ventricle pathology, large intracardiac defect with significant left to right shunt
- severe pulmonary hypertension more than 50 mmHg
- pneumonia or severe chest infection prior to the surgery and parent/guardian refusal
Of the 47 potential participants, 40 were successfully recruited and allocated using 1:1 ratio randomly using a computer-generated list sealed in opaque envelope. The sample size of 20 per arm of study gives 83% power to detect difference between group proportions of 0.4.
All participants were cared for in a comparable way at a neonatal intensive care unit preoperatively under neonatologist guidance; had standardised anaesthesia monitoring including preductal and postductal pulse oximetry; standardised anaesthesia medication and maintenance aims specifically keeping FiO2 at lower limit to keep preductal saturations >=92% with minimum FiO2 of 0.3; mechanically ventilated with SIMV-PCV (synchronised intermittent mandatory ventilation-pressure controlled ventilation) peak inspiratory pressure (PIP) 10–15 cmH2O above positive end-expiratory pressure (PEEP) of 5 cmH2O to achieve expired tidal volume (VTE) from 7 to 10 mL/kg, respiratory rate (RR) ranging from 30 to 50 breath/min to achieve end-tidal CO2 (EtCO2) from 30 to 40 mmHg, and pressure support (PS) 12 cmH2O; and operated on by the same paediatric surgical team.
Results
The IRV group experienced 13 desaturation episodes, needed lower FiO2 and had shorter operative time of 113 ± 18 min (range of 97–150 min); compared with the CRV group with 38 desaturation episodes and operative time 130 ± 29 min (range of 80–170 min). There were no significant differences in other complications between the two groups, and no major complications were noted. The authors concluded that IRV may have a role in decreasing incidences of hypoxemia for neonates undergoing open repair of oesophageal atresia/tracheoesophageal fistula.
Take Home Message
This small study adds on to the paucity of neonatal intraoperative literature surrounding IRV use, and is based upon acceptable ventilation strategy in intensive care setting. The authors discussed limitations of the study including potential inaccuracy of estimating PaO2 from SpO2 as arterial lines were not used, not confirming exact position of endotracheal tube using bronchoscopy, small sample size and lack of similar neonatal studies to compare result with.
Personally, I ponder whether IRV results would be affected by other variables such as type of ventilator used and surgical techniques (e.g. thoracoscopic rather than open approach), and whether use of cerebral oximetry to further inform on perfusion state of the patient will be more useful rather than hypoxemia as outcome measure. Although I would not convert to use IRV as a routine, in the neonate who is difficult to ventilate and oxygenate using CRV, I will be more likely to seek advice and help from my NICU colleagues to institute IRV/oscillator ventilation as an alternative strategy.
