Transport Ventilation

Ventilation is a complex series of interactions between the patient, RCPs’ knowledge and skills, transport environment, and ventilation equipment.

Several critical skills are required during the intra- or inter-facility transport of a ventilator patient. Maintaining an airway and adequate ventilation in the patient can be a challenge in the adverse environment of transport via ambulance, helicopter, or fixed-wing aircraft. Ventilation is a complex series of interactions between the patient, RCPs’ knowledge and skills, transport environment, and ventilation equipment. Patients who are hypoxic, hypercarbic, or hypoventilating are in need of immediate assistance. RCPs need options and alternatives for ventilation. They must be competent and validate individual performance with a variety of techniques of patient ventilation. The technical methods available to RCPs vary considerably.

Successful ventilation is critical to a positive outcome during transport of the critically ill patient. Proper patient management requires integration of cardiac care with adequate oxygenation and ventilation. Maximizing ventilation using available methods and maintaining the best possible homeostatic condition during interfacility transport is essential. This effort can also provide the patient with the precious edge that means the difference between success and failure in transport.

The equipment used, whether it is a simple bag-valve-mask (BVM), ventilator, or automatic resuscitator, is merely an adjunct to the skill and knowledge of the RCP. The equipment used for ventilation must not distract RCPs from a complete patient assessment and other interventions. The chaotic nature of a transport can also distract RCPs from the task at hand if the equipment being used is complicated or requires multiple decision-making processes in order to set up the ventilation parameters.

Changes in resistance and compliance during transport can dramatically alter the modes and parameters required to properly ventilate the patient. The cause of these alterations may be natural, such as the onset of bronchospasm or artificial, such as the insertion of an endotracheal tube or change in patient position. The patient may require higher airway pressures or a variation in the inspiratory flow rate in order to achieve adequate ventilation. Although ambulances and other modes of patient transport vehicles are well equipped with ventilation devices, RCPs may be called on to assess and care for a patient outside of their normal comfort zone.

Prior to departure from the discharging facility, confirm the proper functioning of all components of the ventilation system you plan to use. Verify that a simple backup system is immediately available in case of a problem requiring troubleshooting with the primary system. Check the oxygen tank pressure in the vehicle for transport and identify sources of additional oxygen if available.

The Bag-Valve-Mask
RCPs are familiar and comfortable with the most common form of short-term transport ventilation—the BVM. This is typically connected via supply tubing to a system capable of delivering nearly 100% oxygen with each inspiratory effort.3 The self-inflating device is a common method of patient ventilation and is widely accepted in the intrahospital and critical care interfacility transport environments.

• The BVM is connected to a facemask, an endotracheal tube, or other airway.

• The disposable BVM consists of the self-inflating silicone bag, two one-way valves, the connection port and reservoir for oxygen enrichment of the inspired gas, and a transparent facemask.

BVMs allow ventilation with room air or with oxygen concentrations nearing 100%. When used independently, the BVM provides for ventilation of the patient with room air, which may be inadequate to support the patient’s metabolic needs. This concentration can be increased to approximately 50% by attaching an oxygen supply at 5-6 lpm directly to the bag next to the air inlet valve. A reservoir bag should be attached, which, with oxygen flows of 8-10 lpm, will provide inspired oxygen concentrations nearing 100%.

A leak around the facemask may result in hypoventilation, and the delivery of high tidal volumes and airway pressures may result in gastric insufflation and increased risk of regurgitation. If ventilation must continue with a BVM and the face mask, the two-rescuer technique may be required.2,3

Transport Ventilators
Transport ventilators provide consistent ventilation to the patient, allowing RCPs to focus on other treatments. Transport ventilators provide controlled ventilation with low flow rates that minimize the risk of gastric distension, with the subsequent potential for aspiration. RCPs can determine the required tidal volumes and ventilation frequency, based on patient condition and local policies and procedures. Transport ventilators also allow the patient to breath spontaneously through the breathing circuit, delivering a high flow rate and 100% oxygen. These patient support capabilities make a transport ventilator a significant asset to RCPs during transport of the critical patient. Basic transport ventilator modes include:

• Pressure-support ventilation—augments the patient’s spontaneous inspiratory effort by providing a flow of oxygen during inspiration to a preset limit.

• Pressure-control ventilation—delivers volume until the target pressure is achieved during inspiration.

• Volume control and time limited ventilation—delivers volume within a certain period of inspiratory time.

Transport ventilators provide improved patient ventilation in many transport situations.4 They provide consistent ventilation5 while RCPs provide patient assessment, medication administration, intravenous access, and communication with the hospital.

Transport ventilators provide consistent and effective ventilation for a broad range of patient types and clinical needs, but do have limitations. Their initial purchase price exceeds that of all other transport ventilation methods, but the cost per patient is similar to that of the BVM. The transport ventilator requires additional training for RCPs and ongoing validation of clinical skills and knowledge. The automatic ventilators do require a constant oxygen supply for delivery of 100% oxygen and, with some models, for operation of the device.

Transport ventilators are relatively simple devices with easy to use controls. The ventilators have controls for both volume or pressure and respiratory rate based on normal physiological rates and volume requirements. The newer ventilators provide a variable I:E ratio, allowing time for the active process of inspiration and the passive process of exhalation. Some transport ventilators offer the capability for demand breathing of 100% oxygen for the spontaneously breathing patient. This allows the patient to breath spontaneously through the ventilator circuit while delivering 100% oxygen. Manual triggered breaths allow for the preoxygenation of patients before intubation or suctioning.

The modern, state-of-the-art devices now available offer functions that are normally seen only on critical care ventilators. Their small size and low weight and ease of using them allow common use in the transport environments.6 The controlled ventilation reduces the risks commonly associated with other forms of transport ventilation and optimizes oxygenation and ventilation. Many of the devices available today include a manual trigger for clinician-initiated patient ventilation, alarms, and demand valve type flow rates. Use of a transport ventilator allows the transport team to perform other tasks en route.

APRs in Transport Ventilation
The automated pulmonary resuscitator (APR) provides effective short-term, pressure cycled, and constant flow ventilatory support.7 The APR uses either pressure control or pressure support mode of ventilation. The primary working mechanism of an APR is the control unit that includes an exhalation valve that opens at one pressure (peak inspiratory pressure) and closes at another lower pressure (PEEP). This valve allows the unit to ventilate the patient with constant flow of gas, entrain additional room air, and provide a pop-off valve to minimize the risk of barotrauma.

Ventilation with an APR
Setup and use of the APR are simple—set the flow rate and adjust the pressure dial to obtain the necessary peak airway pressure. Under these circumstances, the APR is delivering pressure support ventilation and the patient must trigger the APR to begin subsequent full inhalations. In the pressure support mode, the patient initiates ventilation and the APR assists the patient with each breath.

If the patient is apneic or pressure control ventilation is desired, the transport team must restart automatic cycling of the APR by rotating the rate dial counterclockwise until cycling is initiated. If the APR stops cycling, always check the patient to confirm proper ventilation, then check the position of the rate dial to determine if the unit is in the pressure support mode. The APR is pressure cycled on inhalation and exhalation to minimize the possibility of breath stacking, the trapping of gases within the airway and lungs during exhalation.

The APR is equipped with an air entrainment valve that allows the unit to entrain additional air if the patient’s inspiratory flow rate exceeds the delivered oxygen flow rate. This entrainment will also result in a reduction of the Fio2. Although peak pressures are controlled through proper setting of the device, RCPs using the APR must use clinical judgment and patient assessment, and observe the patient with appropriate monitors to determine if inspiratory flow needs are met.

As with any ventilation device, only appropriately trained RCPs must use an APR. APRs are not independently functioning ventilators and should not be used during chest compressions. RCPs and other members of the transport team must continually assess the patient’s ventilation, vital signs, and operation of the device.

Demand Valves
Oxygen driven resuscitators, also known as demand valves, may be found on an ambulance. These devices provide RCPs with the ability to ventilate the patient with high flow rates and relatively high airway pressures, or deliver 100% oxygen to the spontaneously breathing patient. Demand valves can be used with a self-conforming facemask, endotracheal tube, or other artificial airway. The American Heart Association 1986 “Guidelines for CPR” reduced the recommended flow rates to 40 lpm in the ventilation mode in an attempt to reduce the high inspiratory pressures and resulting gastric distension. The guidelines also recommended a reduction in the maximum delivery pressure these devices can deliver to 60 cm H2O. This reduces the potential risks of barotrauma and associated complications.8 Control of respiratory rate, tidal volume, and airway pressure are the responsibility of the transport team when manually ventilating the patient with a demand valve.9 Demand ventilation is useful for spontaneously breathing patients in severe respiratory distress (such as the patient poisoned with carbon monoxide). The patient can truly inspire 100% oxygen with each breath.

Pressure Limited and Flow Triggered Ventilation Devices
Very aggressive delivery, including high respiratory rates and tidal volumes, often occurs at the beginning of a resuscitation effort with a BVM. In addition to the variability involved in manual ventilation, assessment of the adequacy of ventilation rate and volume may be difficult.10 A pressure limited and flow triggered (PLFT) type device may be used to ventilate the patient during cardiopulmonary resuscitation (CPR) and short transports.

The PLFT is not a ventilator, but an automatic resuscitator with applications in transport situations requiring an oxygen-driven resuscitation system. The PLFT is a small and simple system for patient ventilation with several methods available. The compact system offers advantages in the confined spaces of ambulances, helicopters, and fixed-wing transports. PLFT resuscitators do not consume oxygen to drive the device, thus limiting oxygen consumption during transport. One significant advantage compared to some other systems is that minute volume is maintained in automatic mode. During ventilation, the PLFT maintains positive pressure in the airway, unless a negative pressure is initiated by the patient’s own inspiratory flow. The unit would then deliver flow to satisfy the patient’s inspiratory effort. The PLFT system has two criteria that initiate the inspiratory and expiratory phases. The first criterion is the pressure limiting at the end of the inspiratory phase, initiating the expiratory phase. The second criterion is expiratory flow; in the expiratory phase, the PLFT does not initiate an inspiratory phase until the expiratory phase is complete. Termination of the expiratory phase initiates the next inspiratory phase. PLFT technology allows ventilation in conjunction with the patient’s own respiratory efforts. The PLFT device allows for the administration of near 100% oxygen and the manual or continuous ventilation of the patient.

Administration of near 100% oxygen is possible by achieving a good mask seal and allowing the patient to inspire normally with the control knob aligned accordingly. Inspiration is initiated for the apneic patient by pressing the oxygen release button until the PLFT releases at the end of the inspiratory phase. Passive exhalation follows the inspiratory phase. Continuous ventilation for the apneic patient cycles the PLFT device when the inspiratory preset pressure limit is achieved, followed by passive exhalation. The next inspiratory cycle is initiated when the expiratory pressure drops to a level of 2 to 4 cm H2O PEEP.

The Future of Transport Ventilation
The use of transport ventilators, BVMs, demand valves, and ventilation resuscitators must provide the patient with consistent tidal volume, respiratory rate, and controlled airway pressure. Responding to the changes in the patient’s ventilation and oxygenation status during transport is the primary role of RCPs.

Many of the devices reduce the time demands placed on RCPs and allow the clinician to concentrate on the patient rather than the equipment. The device used must provide adequate ventilation in situations involving high airway resistance and/or poor lung compliance. The various conditions that affect the patient’s ventilation require a variety of techniques and equipment for transport ventilation. The small size and light weight of many ventilation devices allow for easy transport.

Even a single patient may require multiple methods of oxygenation and ventilation. The patient may progress from shortness of breath through tachypnea and finally respiratory failure during an otherwise routine transport. As the patient’s condition worsens, the first signs of respiratory distress appear and the patient requires assistance with ventilation, including positive pressure ventilation using a BVM, transport ventilator, manually triggered, oxygen powered demand valve, or the pressure limited flow-triggered resuscitator. All of these adjuncts to ventilation require skilled and knowledgeable application for a successful outcome.

Dan Hatlestad is a clinical educator, author, and public speaker in Littleton, Colo; [email protected].

References:
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