Initiation of Mechanical Ventilation-6-1_٠١٥٣٢٦.pptx

Beginning for mechanical ventilation

1. Initiation of Mechanical Ventilation- RT/ SADIQ ALMAKTARI Sup. Of R.T.U.IN MEH

2. When it becomes necessary to provide mechanical ventilatory support for a patient, the following basic ventilator settings must be determined: mode , frequency, tidal volume, FIO2 , inspiratory:expiratory ratio , inspiratory flow pattern , and various alarm limits .

3. These initial ventilator settings are mainly based on: a patient’s body size, diagnosis, pathophysiology, and laboratory results . These settings only serve as a starting point and they should be adjusted according to changes in the patient’s condition and requirements.

4. Mode The first step in selecting the ventilator mode is to decide whether the patient should receive full ventilatory support (FVS) partial ventilatory support (PVS).

5. FVS Full ventilatory support is achieved by any mode that assumes essentially all of the work of breathing. The majority of ventilator patients initially require full support, with the control mode or the assist/control mode. (SIMV) mode also provides full ventilatory support if the patient is not breathing spontaneously between mechanical breaths, and the mandatory frequency is set at 12/min or higher

6. PVS Partial ventilatory support is achieved by any mode that provides less than the total amount of the work of breathing. Partial support would be inappropriate initially for patients with ventilatory failure, and it is more commonly used during the weaning process. Some examples are ( BiPAP ), and (PSV)

7. Frequency The initial ventilator frequency is the number of breaths per minute that is intended to provide eucapneic ventilation (PaCO2 at patient’s normal). The initial frequency is usually set between 10 and 12/min . Frequencies of 20/min or higher are associated with auto-PEEP and should be avoided . In addition to high ventilator frequency, inadequate inspiratory flow and air trapping contribute to the development of auto-PEEP.

8. An alternative method of selecting the initial frequency is to estimate the patient’s minute volume requirement and divide the estimated minute volume by the tidal volume. Frequency = Estimated minute volume Tidal volume

9. Adjusting the Frequency The initial frequency setting of 10 to 12/min and the calculation shown above are based on the assumption that both CO2 production and physiologic dead space are normal. Ventilator frequency is the primary control to regulate the PaCO2. frequency if the PaCO2 is too high. frequency if the PaCO2 is too low. After placing the patient on a ventilator, ABG should be obtained within 15 to 30 min after the patient has stabilized, to assess both ventilation and oxygenation

10. Ventilator circuits are compliant and expand during a positive pressure breath. The amount of circuit expansion results in a volume that does not reach the patient but is recorded as part of the expired tidal volume. This volume “lost” in the ventilator circuit is called the circuit compressible volume

11. circuit compressible volume may be calculated by following the steps in Table. Once the circuit compressible volume is known, the patient’s corrected tidal volume can be calculated by: Corrected Tidal Volume = Expired Tidal Volume -Circuit Compressible Volume

12. Pressure Support (PSV) is used to augment a patient’s breathing effort by reducing the airflow resistance during spontaneous breathing. The contributing factors of airflow resistance during mechanical ventilation may include : the artificial airway ventilator circuit secretions

13. Pressure support (PS) is available in modes of ventilation that allows spontaneous breathing (e.g., SIMV). The patient must also be able to breathe spontaneously.

14. The initial pressure support level can be calculated as follows.

15. FI O2 For patients with severe hypoxemia or abnormal cardiopulmonary functions (e.g., post-resuscitation, smoke inhalation, ARDS), the initial FIO2 may be set at 100%. The FIO2 should be evaluated by means of arterial blood gas analyses after stabilization of the patient. It should be adjusted accordingly to maintain a PaO2 between 80 and 100 mm Hg (lower for patients with chronic CO2 retention).

16. After stabilization of the patient , the FIO2 is best kept below 50% to avoid oxygeninduced lung injuries . patients with mild hypoxemia or patients with normal cardiopulmonary functions the initial FIO2 may be set at 40%

17. PEEP Positive end-expiratory pressure (PEEP) increases the functional residual capacity and is useful to treat refractory hypoxemia (low PaO2 not responding to high FIO2). The initial PEEP level may be set at 5 cm H2O.

18. 5 cm H2O in most patients ventilated without acute lung injury 10 cm H2O in patients with mild ARDS 15–20 cm H2O in most patients with moderate to severe ARDS 5 cm H2O in patients with COPD, adjust as indicated to offset effect of auto-PEEP on ventilator triggering

19. Subsequent changes of PEEP should be based on : the patient’s blood gas results. FIO2 requirement. tolerance of PEEP. cardiovascular responses.

20. I:E Ratio The I:E ratio is the ratio of inspiratory time to expiratory time. It is usually kept in the range between 1:2 and 1:4. A larger I:E ratio (longer E ratio) may be used on patients needing additional time for exhalation because of the possibility of air trapping and auto-PEEP

21. Auto-PEEP :is present when the end-expiratory pressure does not return to baseline pressure at the end of expiration.

22. Inverse I:E ratios have been used to correct refractory hypoxemia in ARDS patients with very low compliance. Inverse I:E ratio should be tried only after traditional strategies have failed to improve a patient’s ventilation and oxygenation status

23. Depending on the features available on the ventilator, the I:E ratio may be altered by manipulating any one or a combination of the following controls: (1) flow rate (2) inspiratory time. (3) inspiratory time %. (4) frequency (5) minute volume.

24. Effects of Flow Rate on I:E Ratio Adjusting the flow rate is the most common method to change an I:E ratio because the flow rate control is a feature available on almost all ventilators.

25. Changing the I:E Ratio Since the I:E ratio may be changed by altering different settings available on selected ventilators, different methods to obtain a desired I:E ratio are provided as follows

26. Using I Time % to Set the I:E Ratio

27. Flow Pattern Most modern ventilators offer different inspiratory flow patterns. there are subtle variations, the principal flow patterns are (1) square (constant) flow pattern, (2) accelerating (ascending) flow pattern, (3) decelerating (descending) flow pattern, (4) sine wave flow pattern . The waveforms for each of these flow patterns are shown in Figure 8-1