RAPID Response to questions from readers

(formerly Dear SIRS)

Considerations for Mechanical Support of Ventilation During Patient Transport

Supporting ventilation during transport is not a trivial exercise and is reported to be associated with some complication in 10% to 31% of cases.1,2 While patient safety concerns during transport of the intubated patient are similar to those in the operating room, the logistics of how we ventilate and monitor the intubated patient during transport are unique. As highlighted by the preceding report by Gerasimov and Toor, the devices used for ventilation during transport can lead to undesired consequences.3 In the operating room, anesthesia professionals have all of the resources needed to manage ventilation safely including both manual and mechanical ventilation, patient monitors and alarms, suction, and additional colleagues to help with emergencies. During transport, these resources are more limited and there is the added burden of pushing the bed through halls and into elevators.

Safer Transport through Device Selection and Monitoring

Drs. Gerasimov and Toor describe a case of significant expiratory airflow obstruction leading to pulseless electrical activity (PEA) arrest caused by secretions in a filter placed over the expiratory valve of a self-inflating resuscitation bag to protect the environment.3 Obstruction of a filter either directly connected to the endotracheal tube or anywhere downstream in the expiratory flow path is possible with any ventilation circuit and is always a consideration when there are elevated airway pressures. An obstruction may also occur within the endotracheal tube itself. In the reported case, the solution implemented to prevent a recurrence of the filter obstruction to exhalation scenario was to use a shield to deflect exhaled secretions instead of a filter that can become obstructed. This would certainly work to solve the ventilation circuit filter obstruction problem, but it still leaves the potential for environmental and personnel contamination.

Our informal sense is that when the resources are available, in-hospital transports of unstable patients between the operating room and the intensive care unit are increasingly being conducted with a transport ventilator of some type, and a respiratory therapist in attendance. This might be the safest option for transport as long as there is an adequate oxygen supply. In patients who remain intubated for airway control reasons but are otherwise clinically stable, the use of a self-inflating bag or a Mapleson is a matter of provider preference or institutional protocol. Both have advantages and disadvantages (Table 1). As transport ventilators become more available, there appears to be a trend towards more routine use of them.

Table 1: Comparison of Commonly Used Devices to Support Ventilation During Transport*

Transport Device Advantages Disadvantages
Self-Inflating (AMBU® type) Bag
  • Can ventilate even if gas supply fails
  • Lightweight, easy to use
  • Familiar apparatus
  • No visual indication of inspiration or exhalation—problems with gas delivery are more difficult to appreciate
  • Monitoring inspiration and expiration is not standard
  • Lower compliance of the bag can obscure detection of changes in patient compliance
  • Tidal volume is variable
  • Respiratory rate is variable
Mapleson-Type Circuit
  • Inspiration and exhalation can be appreciated manually
  • Visual indication of patient respiratory efforts
  • Requires a compressed gas supply
  • Delivered tidal volumes depend upon gas flow and APL setting
  • Monitoring inspiration and expiration is not standard
  • Tidal volume is variable
  • Respiratory rate is variable
Transport Ventilator
  • Ventilation is stable and reliable
  • Hands free
  • Monitoring patient-
    ventilator interaction is built into the device
  • Resource intensive, both device and trained personnel
  • Requires a compressed gas supply
*Use of capnography during transport mitigates many of the disadvantages of self-inflating and Mapleson transport ventilation devices

The lesson in the case report is that anything added to a breathing circuit that can obstruct exhalation can impair exhalation to the point of hemodynamic collapse and further4 that monitoring the manual ventilation process is useful to detect changes before they become significant. Perhaps with an “educated hand,” expiratory obstruction would be more readily detected with a Mapleson-type circuit, although that remains to be proven. With manual ventilation, continuous assessment of respiratory parameters with visual and tactile control of the circuit of choice is paramount. Some manual bags incorporate an airway pressure manometer to help monitor the ventilation process. Finally, use of capnography during transport is quite possible and verifies both inspiration and exhalation. If tidal volume is reliably achieved, the end-tidal carbon dioxide concentration can confirm adequate ventilation.

 

Dr. Algarra is an assistant professor of Anesthesiology and assistant program director, Clinical Operations, Department of Anesthesiology, University of Florida College of Medicine, Gainesville, FL.

Dr. Gravenstein is professor of Anesthesiology, Neurosurgery, and Periodontology, Department of Anesthesiology, University of Florida College of Medicine, Gainesville, FL.


Neither author has any conflict of interest pertaining to this article.


References

  1. Parmentier-Decrucq E, Poissy J, Favory R, et al. Adverse events during intrahospital transport of critically ill patients: incidence and risk factors. Ann Intensive Care. 2013;3:10.
  2. Winter MW. Intrahospital transfer of critically ill patients; a prospective audit within Flinders Medical Centre. Anaesth Intensive Care. 2010;38:545–549.
  3. Gerasimov M, Toor J. PEA arrest during transport of a ventilated patient due to a clogged respiratory filter on Ambu® Bag. APSF Newsletter. 2019;34:46.
  4. Espay AJ. Neurologic complications of electrolyte disturbances and acid-base balance. Handb Clinic Neurol. 2014;119:365–382.

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