Highlights of RSPT 2414 Mechanical Ventilation: Unit 1 By Elizabeth Kelley Buzbee AAS, RRT- NPS, RCP

Normal ventilation With normal compliance of 100 ml/cmH 2 0 pressure and normal R AW of.5 to 2.5 cm H 2 0/L/second the WOB is easy because the driving pressure is low.

Persons need help breathing when: The driving pressure might be excessive or the patient may lack the ventilatory muscles The patient may lack the ventilatory drive

Define respiratory failure Inability to oxygenate the tissues (Pa02 less than 60 mmHg) and /or to remove C0 2 (PaC0 2 more than 50 mmHg) in persons with chronic hypercapnia, the person is ok until his C02 rises to the point that he has partially compensated respiratory acidosis—he has de-compensated

Classify Respiratory failure Acute hypoxemic respiratory failure- if refractory hypoxemia 02 will not help – Decreased Pi0 2 such as with smoke inhalation or high altitude – Diffusion problems such as increased alveolar-capillary or decreased surface area due to atelectasis Acute hypercapnia respiratory failure- uncompensated respiratory acidosis – Associated with decreased ventilatory drive or decreased alveolar ventilation – Patient may be hypoxic only because the PA0 2 is decreased due to increased PaC0 2 —may or may not need increased Fi02 once ventilation starts Chronic hypercapnia respiratory failure- partially compensated respiratory acidosis – Exacerabation of existing problem such as COPD, neuromuscular disorder or morbid obesity

Differentiate between the V/Q mismatch and a shunt or shunt-like effect: V/Q mismatch : – Acute respiratory failure that will respond to supplementary 0 2 TX – When there is low V/Q, we have low ventilation with good perfusion – When there is high V/Q, we have good ventilation with poor perfusion Shunt: Acute respiratory failure with refractory hypoxemia – Supplementary 0 2 will not help – Physiological shunt of 10% in WLN—more is pathological shunt

02 indices to determine if patient is in refractory hypoxemia – Use the Pa0 2 :Fi0 2 as Pa0 2 :Fi0 2 to determine if we can correct hypoxemia – Use the a/A ratio to determine if patient is above.14 to.17 – Use rule of 50: Fi02 more than 50% with Pa02 less than 50 mmHg

02 indices to determine if patient’s hypercapnia is the only reason he is hypoxemic If the P[A-a]D02 is not elevated (10 mmHg for young and 25 mmHg for elderly), the hypoxemia may only be due to the rise in alveolar C0 2 replacing the alveolar 0 2. Once his alveolar ventilation is increased by our putting him on mechanical ventilation, his Pa02 is corrected

Conditions that result in increased WOB due to a need for driving pressures higher than they can handle increased R AW decreased lung compliance Persons at risk for muscle fatigue – Persons with severe muscle fatigue need to rest on mechanical ventilation for 24 – 48 hours

VC of less than 20 ml/kg IBW requires some ventilator support. VC of less than 25 ml/kg IBW is associated with decreased ability to cough effectively. [P I max ] inspiratory max pressure measures weakness of inspiratory chest wall muscles and diaphragm. a need for mechanical ventilation is seen with a[P I max ] of less -20 cmH20 [P E max ] expiratory max pressure measures weakness of the abdominal muscles. a need for mechanical ventilation is seen with a [P E max ] less than + 40 cmH20 be aware that facial weakness can result in false values for these two figures – if the patient cannot seal properly—needless to say, that alone tells us we have problems with patient being able to protect his airway Lung function studies that demonstrate situations that result in ineffective ventilator muscle action

Situations that result in increased V D ventilation will make a person need mechanical ventilation anatomical V D conducting airways. Comprises about 30% of the V T of the body. is equal to 1 ml / pound of IBW Is always present, but can be reduced by tracheostomy which bypasses upper airways V D /V T ratio will change, as the patient’s V T varies but the V D will stay the same alveolar V D when an alveoli gets ventilation but no perfusion, it is considered alveolar V D as CO drops or there are problems with pulmonary blood flow the alveolar V D will rise above baseline physiological V D is the sum of the anatomical V D + the alveolar V D

Problems with VD/VT physiological V D is the sum of the anatomical V D + the alveolar V D – the normal V D /V T is about.3 or 30%. It is not uncommon for mechanically ventilated persons to have V D /V T of.6 and higher. – if physiological V D is excessive, we can increase the V T to get the alveolar ventilation back to an effective level – Failure to get the V D /V T below.6 will prevent successful weaning of a patient from mechanical ventilation.

Clinical signs and symptoms of respiratory failure in the adult patient. – inadequate alveolar ventilation: hypercapnia above 55 torr & pH below 7.20 – inadequate lung expansion: V T less than 5 ml/kg IBW, VC less than 10 ml/kg IBW requires full ventilator support, and RR over 35 bpm – poor muscle strength: MIP less than -20 cmH20, VC less than 10 ml/kg and MVV less than 2x VE – increased WOB: V E more than 10 LPM & V D /V T more than.6 – hypoxemic respiratory failure: P(A-a)D0 2 on 100% more than 350 mmHg Pa0 2 /Fi0 2 less than 200.

ABG associated with respiratory failure. Acute respiratory acidosis with moderate/severe hypoxemia Partially compensated respiratory acidosis with moderate / severe hypoxemia. Chronic patient is no longer compensating effectively. Panic values on ABG: PaC0 2 above 55 torr & pH below 7.20 Serial ABG in which the PaC0 2 rises each time

Bedside measurements of increased WOB Calculation of the R AW – If R AW increased, WOB increased – High R AW – high driving pressure needed Calculation of the lung Compliance [C L ] – If C L decreased, WOB increased – Low C L high driving pressure needed

Mechanical ventilation: a machine that can perform bulk transfer of gas into the lung for a patient who cannot perform this task effectively enough to exchange gases. The ventilator works during inspiration, while exhalation is usually passive.

Phases of ventilation Inspiratory phase: inspiration in which gas enters the lung. – The T I is a function of the flow rate, the V T and the patient’s R AW Expiratory phase: the portion of the breath that is concerned with the passive flow of gas out of the lung. – The T E will be a function of the T I, and to a great part to the patient’s R AW

I:E ratio: comparisons of the T I to the T E. Normal I:E ratio during spontaneous breathing is 1:1.5, but to minimize some of the hazards of mechanical ventilation, with positive pressure ventilation, this ratio needs to be 1:2 or more. A patient with significant air-trapping may require much longer 1:E ratio such as 1:3 or 1:4.

Cycle time: cycle time = T I + T E cycle time = 60 seconds/BPM

Airway pressures PIP- highest pressure during the inspiratory phase– at the end of inspiration. – This is P1 of the R AW formula P plateau : during a breath hold, this is the second pressure during inspiration. – On a graphic, it looks like a flat plateau. – This pressure is the P 2 of the R AW formula and the Δ P of the static compliance formula Baseline pressure: After the positive pressure breath is given, the airway pressure returns to the baseline, which may be zero or a positive number if there is PEEP or CPAP.

Airway pressure P AW : the “mean airway pressure” is the average airway pressure. – It is a function of the inspiratory time (Ti), – the PIP, – the baseline pressure – and the I:E ratio. P AW = [PIP ( I )] + [PEEP (E)] [I + E]

Different types of ventilation Positive pressure ventilation Negative pressure ventilation Invasive mechanical ventilation Non-invasive mechanical ventilation:

Ventilator modes: Full-support mechanical ventilation: Most fatigued patients need to be rested for hours, but a serious complication of full- support is that after a few days, the patient’s respiratory muscles start to atrophy quickly. Partial-support mechanical ventilation: SIMV or IMV are examples of partial-support mechanical ventilation. Frequently patients are started on full support and are moved to partial support after the mandatory rest period. Spontaneous modes: When a patient is past the point of needing full or even partial support, we can challenge the patient with the machine acting only as a monitoring device with/without alarms and mechanical intervention in case of apnea or hypoventilation. – Patients on spontaneous modes of ventilation must have an intact ventilatory drive, and must be able to maintain their PaC0 2 with little or no help from the machine.

flow Wave forms/graphics: electronic devices convert airway pressures, volumes or flows into a graphic Peak flows /flow rates: All modern positive pressure ventilators have peak flow rates. If you select the flow/time wave form you can see the flow pattern: – Constant flow – Descending ramp – Sine wave

VT tidal volume To adjust the VE for the PaC02, we can alter the RR or the VT. Set VT: the VT the RCP selects that may or may not be the same as the delivered VT Return VT: the delivered VT that is measured at the exhalation point Corrected VT: the VT that is corrected for volume that is lost in the tubing as it swells during positive pressure