A term infant is admitted to the intensive care nursery with severe respiratory distress. They are currently on CPAP 8cm H2O and FiO2 0.50 with no signs of improvement. You begin preparing for intubation. The nurse looking after the baby is setting up the ventilator. “What ventilator setting would you like, doctor”?Before listing off some ventilator settings, there are several decisions that we need to make. What type of ventilation should we be using for this baby? What settings will we start them on? What do we need to do post-ventilation? This post will begin to answer some of these questions, but as always, it is advisable to be guided by your unit policies and senior staff members.
Ventilation modesThis post will discuss the basics of conventional ventilation. High-frequency oscillatory ventilation (HFOV) is also commonly used in the nursery, particularly for extremely preterm infants or those with persistent pulmonary hypertension. Stay tuned for an upcoming post on HFOV.
Synchronized intermittent mandatory ventilation (SIMV)This type of ventilation administers a set amount of mechanical breaths that are synchronized with the patient’s own inspiration. When the infant breaths above the set ventilator respiratory rate, these additional breaths do not receive a ventilator breath. This mode can be useful when weaning ventilation.
Synchronized intermittent positive pressure ventilation (SIPPV) or patient triggered ventilation (PTV) or Assist Control (AC)This form of ventilation confusingly has many different names. It supports every breath the infant makes. The set ventilator respiratory rate is the backup number of breaths that will be mechanically administered if the infant makes no spontaneous breaths. Each mechanical breath is synchronized with the patient’s own inspiration.
Pressure support ventilation (PSV)Similar to SIPPV in that every breath is supported with mechanical ventilation. However, the inspiratory time is limited depending on the infant’s own inflation. The infant sets their own mechanical breath rate and inspiratory time.
Volume controlled (VC) or volume guaranteeThis mode of ventilation can be used with SIMV or SIPPV. The ventilator aims to deliver tidal volumes (VT) set by the clinician. A maximum peak inspiratory pressure (PIP) is set, the ventilator’s PIP will vary to reach the target volume.
So, which is better for our infant?There have been no large prospective trials that have determined if SIMV or SIPPV is the superior format of ventilation. The choice of ventilation will largely depend on unit preference. Studies have illustrated that volume-controlled ventilation reduces the duration of ventilation, the risk of pneumothorax, grade 3/4 intraventricular haemorrhage, and chronic neonatal lung disease.
So what’s on your ventilator screen?Peak end-expiratory pressure (PEEP): The maximum pressure that provides continuous distension of the lungs. Usually between 6-8cmH20 Peak inspiratory pressure (PIP): Maximum pressure used during inspiration. Consider the tidal volumes achieved to determine a suitable PIP. VT are usually around 4-5ml/kg. Respiratory rate (RR): Set number of mechanical breaths administered in a minute. Usually between 40-60. In SIMV the set RR is both the maximum and minimum rate while in SIPPV the RR is the minimum but not the maximum rate. Inspiratory time (Ti): Set time for inspiration during a breath. Usually between 0.3-0.5s Patient Circuit Flow Rate or Rise Time or Rise Slope: Depending on the manufacturer or the unit policy, one of these options will be available. If only the patient circuit flow rate is available then this is set 6 – 10 L/min. If rise time or slope is available then this is set to 30 – 50% of the Ti. Pmax: In the volume-controlled mode, this is the maximum peak inspiratory pressure you wish the ventilator to administer to reach target tidal volumes. Usually set 5 cmH2O higher than the average PIP used to achieve the set tidal volume. FiO2: The amount of supplementary oxygen. Target saturation will depend on the gestational age and the underlying condition affecting the infant. Your unit’s policy on SpO2 targets should guide the FiO2 setting.
What are the ventilator measurements we should be aware of?Minute volume (MV): Amount of gaseous exchange in one minute. MV= VT x RR Tidal volume (VT): The amount of gas in an expiration. Usually around 4-5ml/kg. Leak: Traditionally in neonates, uncuffed tubes are used for intubation due to concerns regarding subglottic stenosis and pressure necrosis. As a result, most infants will have a percentage of leak. It will change during an infant’s respiratory cycle, it is usually greater in inspiration.
What do we need to do next?After attaching our infant to the ventilator, clinical checks should once again be undertaken to ensure adequate ventilation. Review the infant, is there misting of ETT, equal air entry by auscultation, symmetrical chest rise, stable observations and adequate tidal volumes being achieved. A post-intubation chest x-ray should be taken as early as possible to check the placement of the endotracheal tube. The ideal placement is between T1-3, just above the carina. An arterial gas should be undertaken post-intubation to check for adequate ventilation, within an hour. The timing of the next gas will depend on the results, clinical condition and how old the patient is. Your boss will be able to give you some guidance.
- Avoiding mechanical ventilation using early continuous positive airway pressure (CPAP) with, or without, surfactant administration is the most effective way to reduce the risk of lung injury.
- Using volume-controlled ventilation reduces the risk of chronic neonatal lung disease.
- If you’re not sure where to start or how to alter ventilation, ask for your boss’ help.