Mechanical ventilation is becoming more prevalent in the prehospital and interfacility transport arenas.
Healthcare providers use mechanical ventilation to manage many patient conditions, including:
- Respiratory insufficiency
- Refractory hypoxia
- Elevated carbon dioxide levels
- Other therapeutic modalities
Mechanical ventilation differs from spontaneous ventilation in that it uses positive pressure rather than negative pressure ventilation. This can often cause patient discomfort and increase the risk of barotrauma and/or perfusion issues because of increased intrathoracic pressures.
When managing a patient on mechanical ventilation, it is imperative to use only the minimum level of oxygenation required to attempt to prevent hyperoxygenation-negative consequences. These include absorptive atelectasis, and to decrease perfusion because of vasoconstriction and/or lung tissue damage.
Close monitoring of arterial blood gasses, end tidal capnography and oxygen saturation levels are an integral part of managing the mechanically ventilated patient appropriately.
Some of the goals of mechanical ventilation include ensuring adequate minute ventilation, ensuring adequate oxygenation, preventing or worsening lung barotrauma and preventing atelectasis or alveolar collapse. By setting adequate and easily changed ventilation parameters, the provider can achieve these goals in a safe and clinically advantageous approach.
Many ventilators allow the practitioner to set not only breath types but also:
- Tidal volumes
- Pressure settings
- Respiratory rate
- PEEP settings
- FiO2 levels
- Inspiratory and expiratory time settings
Tidal volume is one parameter that is frequently set incorrectly. Many providers set tidal volume based on the patient’s actual weight rather than the ideal body weight.
Over the past decade, total tidal volume settings have decreased from approximately 8-10 ml/kg of ideal body weight to a more realistic 4-7 ml/kg of ideal body weight.
Checks and balances matter
Whether using pressure or volume ventilation strategies, it is important to employ a strategy of checks and balances to prevent overinflation and ensure adequate ventilation of the distal alveoli.
When in volume control mode, it is important to measure and monitor the airway pressures. You can do this by tracking the peak inspiratory pressure and the plateau airway pressure regularly during transport.
Conversely, with in pressure-controlled ventilation strategies, it is useful and advisable to frequently check the exhaled tidal volume.
Pressure ventilation strategies are frequently employed for the pediatric population and adults with Acute Respiratory Distress Syndrome as well as other respiratory conditions.
Preset by the operator, pressure-regulated volume control allows the provider to monitor both pressure and volume parameters.
When transporting a mechanically ventilated patient, it’s important to measure physiologic parameters and monitor quantitative and qualitative parameters.
Relying on monitors and vital sign measurement alone is not enough. It is important to use all available tools to monitor the patient’s condition. Consider each tool as a piece of the puzzle to ensure safe and effective patient care.
Oxygen saturation and end tidal capnography are two such pieces of the puzzle.
- End tidal capnography allows for a real-time measurement of the exhaled carbon dioxide that frequently correlates with the patient’s PaCO2 in healthy people.
- Oxygen saturation, while being the gold standard for years, is gradually becoming a less reliable method to measure oxygenation levels. This is due to a delay in obtaining readings, and there are extraneous factors that can affect its accuracy.
Mechanical ventilation conclusions
No one piece of the puzzle is 100% reliable, so the practitioner must use all pieces in unison to arrive at an informed decision as to whether the patient is benefiting from interventions.
While mechanical ventilators have come a long way over the past 40 years in ease of use and adjustability, there is still no substitute for provider judgement and intellect. The premise of setting the mechanical ventilator and forgetting it is a potentially detrimental approach to ventilator management.
Consistent oversight and a series of checks and balances are needed to ensure no harm is imparted on the patient under our care and being mechanically ventilated. It is important to remember patients are dynamic and unique, and that one size does not fit all.
Changes for the good and bad can occur during transport of these patients. It is up to us to provide the best, most up-to-date care to our patients.