Bear Cub 750vs Katherine Fedor




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Bear Cub 750vs

Katherine Fedor
The Bear Cub 750vs (Cardinal Health [previously VIASYS Healthcare—Critical Care Division] Palm Springs, CA) is electronically (microprocessor) and pneumatically controlled and functions as a pressure or flow controller (Figure1). Mandatory breaths are time or flow triggered, pressure or flow limited, and time cycled. A continuous gas flow is available for spontaneous breathing.1 An enhanced Bear Cub, 750psv, is also available which allows for spontaneous enhanced pressure support ventilation.


Figure 1 Bear Cub 750vs Infant Ventilator. (Courtesy Cardinal Health [previously VIASYS Healthcare—Critical Care Division] Palm Springs, CA)

Power Conversion and Transmission

The Bear Cub 750vs utilizes compressed air and oxygen in a range of 30 to 80 psig. Air and oxygen pressures are reduced by separate pressure regulators, and the balanced gases are mixed at the air-oxygen blender, a mechanical proportioning valve. Gas flow is regulated by dual mechanical needle valves (flowmeters): the inspiratory flow control valve and the base flow control valve. The inspiratory solenoid switches the gas flows, providing the inspiratory flow rate during the inspiratory phase of mandatory breaths and base flow during the expiratory phase. Blended gas flows past a subambient/overpressure relief valve, dump valve, and pressure transducer before entering the inspiratory limb of the patient circuit.


Peak inspiratory pressures and PEEP pressures function independent of each other and each parameter is set separate from the other.
A jet Venturi is used to decrease flow resistance in the expiratory limb and eliminates inadvertent PEEP.

Control

The Bear Cub 750vs can be operated in the assist-control (A/C), SIMV/intermittent mandatory ventilation (IMV), and CPAP modes. When placed in the standby mode, the ventilator discontinues all electronic function except the charging system for the internal battery. Pressure support and a backup ventilation mode are available on the Bear Cub 750psv.


Mandatory breaths are pressure or flow controlled. Inspiration is pressure limited if airway pressure reaches set inspiratory pressure (0 to 72 cm H2O) and time cycled at the end of the set inspiratory time interval (0.1 to 3.0 seconds). The inspiratory flow setting (1 to 30 L/min) determines inspiratory flow rate. The ventilator effectively becomes a flow controller if the pressure limit is set higher than the actual pressure reached during the inspiratory time interval. In this case, mandatory breaths are flow limited. With the flow sensor in line and functional, mandatory breaths are volume cycled to expiration if measured inspiratory volume reaches the set volume limit (5 to 300 ml). Alternately, the inspiratory phase is pressure cycled if airway pressure reaches the high-pressure alarm limit.
In the A/C mode all breaths are mandatory and are either time triggered at the set ventilator rate (1 to 150 breaths per minute) or flow triggered if the patient’s spontaneous inspiratory effort is sufficient to meet the set trigger sensitivity criteria. The Bear Cub 750vs uses a double hot wire anemometer type sensor to measure flow rate bidirectionally at the patient airway. Assist (trigger) sensitivity is set in a range of 0.2 to 5.0 L/min. In SIMV/IMV, mandatory breaths are time or flow triggered at the set ventilator rate. Depressing the manual breath button triggers a single mandatory breath. Mandatory breaths can be manually triggered in all modes.
The set base flow rate (1 to 30 L/min) determines the rate of continuous gas flow available for spontaneous breathing in the CPAP mode or between mandatory breaths in the SIMV/IMV mode. Baseline pressure is set in a range of 0 to 30 cm H2O with the PEEP/CPAP control. The oxygen percentage control regulates the blender proportioning valve to produce oxygen concentrations in a range of 21% to 100%. The mechanical over pressure relief valve is an additional safety mechanism set to relieve circuit pressure in a range of 15 to 75 cm H2O.
With the Bear Cub 750PSV, base gas flow and inspiratory gas flow rates are set separately. Pressure support breaths are patient (flow) triggered, pressure limited at the set pressure support level, and cycled to expiration when inspiratory flow falls to 10% of the peak flow rate. Alternately, inspiration is terminated if either a set volume or time limit is reached before the flow-cycling threshold. Flow cycling can also be applied to non-pressure support breaths in the A/C and SIMV modes.
Table 1 summarizes the control and phase variables for mandatory and spontaneous breaths in the operational modes available on the Bear Cub 750vs ventilator.

Table 1

Control and Phase Variables for Mandatory and Spontaneous Breaths in the Operational Modes Available on the Bear Cub 750vs Infant Ventilator





Mandatory

Spontaneous

Mode

Control

Trigger*

Limit

Cycle

Control

Trigger

Limit

Cycle

SIMV/IMV

Pressure, flow†

Time, flow

Pressure, flow†

Time, volume,‡ pressure‡












Pressure, flow†

Time, flow

Pressure, flow†

Time, volume,‡ pressure‡

NA

NA

NA

NA

CPAP

















Modified from Chatburn RL, Lough MD, Primiano FP Jr: Mechanical ventilation. In Chatburn RL, Lough MD, editors: Handbook of respiratory care, ed 2. St Louis. Mosby, 1990; pp 159-223.

A/C, Assist/control; CPAP, continuous positive airway pressure; IMV, intermittent mandatory ventilation; N/A, not applicable; SIMV, synchronized intermittent mandatory ventilation; —, ventilator does not respond.

*Mandatory breaths can be manually triggered in all modes.

†Applies if airway pressure does not reach the set pressure limit.

‡Secondary or safety cycle variable.


Output

Waveforms

If mandatory breaths are pressure controlled, the inspiratory pressure waveform can be nearly rectangular or exponential, depending on specific control settings. The resulting flow and volume waveforms are exponential. When used as a flow controller, the ventilator produces an approximately rectangular inspiratory flow waveform. In this case, the pressure and volume waveforms are shaped like an ascending ramp.


Monitoring

Airway pressure is measured at the patient Y-connector and displayed throughout the ventilatory cycle on the ventilator’s analog manometer. Peak inspiratory pressure and mean airway pressure are derived from measurements made by an electronic proximal pressure transducer and are displayed digitally.


Expiratory tidal volume, expiratory minute volume, breath rate, and a patient-trigger indicator are derived from the flow measurements made by the flow sensor at the patient airway. The flow sensor has a range of 0.2 to 40 L/min. Tube leak is calculated as the difference between the inspiratory and expiratory tidal volume expressed as a percentage of inspiratory volume. The inspiratory time for both mandatory and spontaneous breaths, as well as expiratory time and I:E ratio for mandatory breaths, is also displayed.
The Bear Cub 750vs is equipped with both analog and digital connections. A Bear Graphics Display is an option.
Alarms

Input Power Alarms

The low gas supply alarm activates if either the air or oxygen pressure falls below 24 ± 2 psig. With the loss of one gas supply, the ventilator continues to operate using the remaining available gas supply. In the event of complete pneumatic power loss, a fail-to-cycle alarm activates and spontaneous breathing can be accomplished through the subambient valve if the patient generates an inspiratory pressure of approximately 3 cm H2O. The ventilator’s line power indicator changes from green to red if AC power is lost and the ventilator switches to battery power. If all electric power is lost, the indicator is extinguished. The low battery alarm signals that the internal battery has approximately 5 minutes of power remaining. A fully charged battery will power the ventilator for approximately 30 minutes.


Control Circuit Alarms

The fail to cycle alarm activates if the ventilator detects an internal or external malfunction. An incompatible settings alarm indicates an inappropriately set inspiratory pressure (relative to set PEEP), inspiratory time, flow rate, or volume limit. If the ventilator detects a flow sensor malfunction or disconnect, the flow sensor alarm activates and volume monitoring and patient-triggering functions are lost.


Output Alarms

The Bear Cub 750vs is equipped with operator-adjustable alarms for low inspiratory pressure, high inspiratory pressure, low PEEP/ CPAP, and high breath rate. The apnea alarm interval can be set at 5, 10, 20, or 30 seconds. The patient circuit and prolonged pressure alarms activate for conditions resulting in sustained increased pressure in the ventilator or patient circuit. The volume limit alarm is used to avoid excessive volume expansion as lung compliance improves during pressure controlled or pressure support ventilation as might be experienced following surfactant replacement therapy.


The Bear Cub 750vs is equipped with a remote nurse call connection to signal alarm conditions.
Reference

1. Instruction manual: Bear Cub 750vs Infant Ventilator. Riverside, Calif. Bear Medical Systems, 1996.






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