Flinders Medical Centre’s preset mode for mechanical ventilation is Synchronised intermittent mandatory ventilation (SIMV).
SIMV achieves a mandatory minute ventilation by,
Mandatory controlled breathing
Assisted breaths which are synchronised with a patient trigger
Spontaneously triggered and patient controlled breaths often with assistance (Tol & Palmer 2010).
Mandatory breaths deliver a preset volume over a set time, Synchronised breaths still give mandatory breaths which are preset but are synchronised with respiratory effort reducing the danger of breath stacking causing barotruama, and spontaneous breaths are initiated and controlled by the patient including respiratory ...view middle of the document...
Therefore the current tidal volumes delivered for Mr J seems appropriate (Gattinoni et al, 2006).
Mr J also has a high PaC02 of 53, so a volume controlled mode is appropriate to help clear his C02. Mr J also has a history of Chronic heart failure, previous MI, and Hypertension, so close haemodynamic monitoring would be important due to potential issues created by increasing airway pressures.
In flinders medical centre the standard setting for the respiratory rate is 14.
The respiratory rate of 14 is often set as a minimum backup in SIMV enabling the patient to start taking spontaneous breaths, and control minute ventilation in accordance with their needs (Hasan 2010).
12-20 breaths per minute is within normal range for a self-ventilating patient so 14 would be on the lower side (Aitken, Elliott & Chaboyer 2012).
Respiratory rate can affect the tidal volume and consequently minute volume having a direct impact upon CO2 retention or evacuation (Hasan 2010).
The set respiratory rate must take into consideration inspiration and expiration requirements for adequate ventilation, and the contributing effort of the patient (Aitken, Elliott & Chaboyer 2012).
In relation to Mr J, he is not making any respiratory effort, and his PaCO2 level is 53 with a pH of 7.32. So a rate of 14 would not be adequate ventilation. Later on we see that Mr J has his respiratory rate turned up to 16 with a good result of a PaCO2 level of 38 and a pH of 7.38.
Flinders Medical Centre sets its tidal volume at 500mls,
500mls is based on an average ideal body weight of 70kg and uses the equation of 6-8mls/kg which is an advised ratio in all ventilated patients (Determann et al, 2010).
Mr J has a weight of 74 kg and a height of 176cm, which would give him a predicted body weight of 70.7kg which is close to Mr J’s current weight (Aitken, Elliott & Chaboyer 2012). According to the predicted body weight chart supplied by ARDSnet, Mr J should have a tidal volume between 424-566mls . Giving Mr J a tidal volume of 500mls in a normal situation would seem appropriate, however since the tidal volume directly impacts ventilation and Mr J’s CO2 levels are high, a higher tidal volume up to 550mls (as he is actually being given) would seem appropriate (Orlando Health 2010).
Flow pattern waveform:
A square wave form is used at Flinders Medical Centre which represents a constant inspiratory flow rate during the inspiration time (Orlando Health 2010). Flow is the speed at which air moves through the circuit, and this is set at 30L/min on admission.
When giving a set tidal volume of 500mls, a square waveform with a flow of 30L/min minimises inspiratory time to 1 second, and allows for a longer exhalation but consequently has a higher peak inspiratory pressures which may not be good with compliance issues (Hasan 2010). For decelerating waveform see appendix no 1.
In relation to Mr J, his peak pressure and compliance are...