6. Strategies for Mechanical Ventilation Hypercapnia allowed, pH 7.2-7.4 Normal, pH 7.36-7.44 ABG 5-15 cm of water PRN to keep FiO2<0.6 PEEP Plateau Pr<35 Peak Pr<50cm water End-insp. pressure 5-10 ml/kg 10-15 ml/kg Inflation Volume Lung-Protective Traditional Ventilatory Parameter
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32. Bedside Weaning Parameters 10ml/kg 65-75ml/kg Vital capacity <10L/min 5-7L/min Minute Ventl. <40/min 14-18/min Resp. Rate 5ml/kg 5-7ml/kg Tidal Volume 200 >400 PaO2/FiO2 Threshold for weaning Normal Adult range Parameter
33. Bedside Weaning Parameters <100/min/L <50/min/L Rate/Tidal Volume -25cm of water >-90 cm Water (F) >-120 cm water (M) Maximal Inspiratory Pressure
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
Notas do Editor
Instead of the usual list, follow these rules: There is a tendency to delay intubation as long as possible in the hopes that it will be unnecessary. Elective intubation carries fewer dangers than emergent intubation. So, if the patient’s condition is severe enough that intubation is considered, then proceed without delay Remember you will never be faulted for establishing the control of airways ETT and ventilators do not create the need for mechanical ventilation: cardiopulmonary and neuromuscular disease do
At constant inflation volume the peak pressure is directly related to the airflow resistance and to the elastic recoil force of the lungs and the chest wall. Plateau pressure is measured by occluding the expiratory tubing at the end of inspiration. Because no airflow is present when the plateau pressure is created, the pressure is not a function of flow resistance. Instead Plateau pressure is proportional directly to the elastance of the lungs and the chest walls.
Very useful for determining the cause of sudden deterioration of a patient on a ventilator.
Connector tubing between the ventilator and the patient expands during lung inflations, some of the TV is lost in this tubing. Connector tubing compliance is 3ml/cm of water Meaning that 3ml of volume is lost for every 1cm increase in inflation pressure. Example: Inflation vol from vent is 700cc at Pk of 40cm water, then volume lost to expansion of ventilator tubing is 40X3=120ml. Therefor actually only 700-120=580ml reaches the patient, and this should be used as the Vt for compliance measurement.
Volume cycled means that each machine breath delivers a preselected lung inflation volume
IMV delivers periodic volume cycled breaths at a preselected rate but allows spontaneous breathing between machine breaths. Because each spontaneous breath does not trigger a machine breath, there is a reduced risk of respiratory alkalosis and hyperinflation Synchronized IMV: Machine breaths are synchronized to coincide with spontaneous lung inflations.
Increased work of breathing could lead to respiratory muscle fatigue and ventilator dependency
At the onset of each spontaneous breath, the negative pressure generated by the patient opens a valve that delivers the inspired gas at a preselected pressure (5-15cm water) The patient’s inspiratory flow rate is adjusted by ventilator as needed to keep inflation pressure constant. When inspiratory flow rate falls below 25% of the peak inspiratory flow, the augmented breath is terminated
Normally the alveolar pressure at the end of expiration is equal to the atmospheric pressure, called the zero reference point.
Valve exerts back pressure and exhalation proceeds until this back pressure is reached where upon, flow ceases. Something like placing the distal end of the expiratory tubing under water. Back pressure would be equal to the distance the tube is submerged.
Low levels of PEEP are as deleterious for cardiac output if the mean intrathoracic pressure is high Effects of PEEP on systemic oxygenation are determined by the change in cardiac output not by change in the arterial oxygenation Best PEEP curve?
In localized lobar pneumonia, PEEP may overdistend the normal alveoli and redirect blood back to the diseased areas Prevents the repeated opening and closing of small airways which is a source of further lung injury Small airways collapse in obstructive lung disease, PEEP can keep these open at the end of expiration. Level of peep should be enough to counterbalance the closing pressure of the small airways, but not be more than the intrinsic-PEEP, so as to not impair the inspiratory flow. The level of Extrinsic peep which first causes an increase in peak pressures is taken as the level of occult PEEP.
PEEP does not reduce lung edema in ARDS, but can increase water accumulation in the lungs by impaired lymphatic drainage from lungs Glottic closure at end exp causes low level of physiologic PEEP. No documented benefit in intubated patients PEEP is transmitted across the walls of the blood vessels, it may not reduce transmural pressure. No benefit.
In spontaneous PEEP, a negative pressure is required for inhalation. CPAP thus reduces work of breathing
Factors predisposing to auto peep fall in 2 categories. Occult peep increases work of breathing: hyperinflation places lungs in the flatter portion of the pressure volume curve. Take a deep breath and then try to breathe in further, higher pressures are needed to inhale the tidal volume. Level of Extrinsic peep that first causes a rise in peak inspiratory airway pressures is a quantitative measure of occult PEEP.
Excluding the complications if intubation, sedation etc. One liter of saliva a day with a billion bugs per microliter.
These two have a greater predictive value than the ones mentioned before which have a very poor predictive value.
Show figure
PSV to overcome resistance of the circuit and valve
False sense of security, patient often left unattended more than those with T-piece weaning
ELECTROLYTES:phosphorus, K, Mg OVERFEEDING: Excess calories causes excess CO2 production, can impair ability to wean
Rapid breathing could be the result of anxiety, which leads to hyperventilation and high tidal volume. Where as wean failure muscle fatigue and cardiopulmonary disease usually causes rapid shallow breathing.
CSA of tracheal tube is 50 cu. mm and that of the glottis is 66 cu. mm