323 Mechanical Ventilatory Support

Question 1

The primary indication for initiation of mechanical ventilation is respiratory failure

Answer 1

Hypoxemic- when arterial O2 saturation (Sao2) <90% occurs despite an increased inspired O2 fraction and usually results from ventilation-perfusion mismatch or shunt

Hypercarbic- elevated arterial carbon dioxide partial pressure (PCO2) values (usually >50 mmHg) resulting from conditions that decrease minute ventilation or increase physiologic dead space such that alveolar ventilation is inadequate to meet metabolic demands

Question 2

Other indications for instituting mechanical ventilation

Answer 2

• To reduce cerebral blood flow in patients with increased intracranial pressure
• For airway protection to prevent aspiration of gastric contents in otherwise unstable patients during gastric lavage for suspected drug overdose or during gastrointestinal endoscopy
• Critically ill patients: before the performance of essential diagnostic or therapeutic studies

Question 3

Group of patients who benefit from a trial of

NIV

Answer 3

Those with exacerbations of COPD and respiratory acidosis (pH <7.35)

Question 4

Contraindications for Noninvasive Ventilation

Answer 4

Cardiac or respiratory arrest
Severe encephalopathy
Severe gastrointestinal bleed
Hemodynamic instability
Unstable angina and myocardial infarction
Facial surgery or trauma
Upper airway obstruction
High-risk aspiration and/or inability to protect airways
Inability to clear secretions

Question 5

It refers to the manner in which ventilator breaths are triggered, cycled, and limited

Answer 5

Mode

Question 6

It can either be an inspiratory effort or a time- based signal, defines what the ventilator senses to initiate an assisted breath

Answer 6

Trigger

Question 7

It refers to the factors that determine the end of inspiration

Answer 7

Cycle

Question 8

These are operator-specified values, such as airway pressure, that are monitored by transducers internal to the ventilator circuit throughout the respiratory cycle; if the specified values are exceeded, inspiratory flow is terminated, and the ventilator circuit is vented to atmospheric pressure or the specified pressure at the end of expiration

Answer 8

Limiting factors

Question 9

It is the most widely used mode of ventilation

Answer 9

Assist-Control Ventilation (ACMV)

Question 10

In this mode, an inspiratory cycle is initiated either by the patient’s inspiratory effort or, if none is detected within a specified time window, by a timer signal within the ventilator

Answer 10

Assist-Control Ventilation (ACMV)

Question 11

In this mode, every breath delivered, whether patient- or timer-triggered, consists of the operator-specified tidal volume

Answer 11

Assist-Control Ventilation (ACMV)

Question 12

In this mode, the operator sets the number of mandatory breaths of fixed volume to be delivered by the ventilator; between those breaths, the patient can breathe spontaneously

Answer 12

Intermittent Mandatory Ventilation (IMV)

Question 13

Disadvantages of this mode are potential hyperventilation

Barotrauma and volume trauma

Answer 13

Assist-Control Ventilation (ACMV)

Question 14

Disadvantages of this mode are potential dysynchrony and potential hypoventilation

Answer 14

Intermittent Mandatory Ventilation (IMV)

Question 15

Disadvantages of this mode are mask interface may cause discomfort and facial bruising,
leaks are common, and hypoventilation

Answer 15

NIV (noninvasive ventilation)

Question 16

This form of ventilation is patient- triggered, flow-cycled, and pressure-limited

Answer 16

Pressure-Support Ventilation (PSV)

Question 17

It provides graded assis- tance and differs in that the operator sets the pressure level (rather than the volume) to augment every spontaneous respiratory effort

Answer 17

Pressure-Support Ventilation (PSV)

Question 18

It is often used in combination with SIMV to ensure volume-cycled backup for patients whose respiratory drive is depressed

Answer 18

Pressure-Support Ventilation (PSV)

Question 19

This form of ventilation is time- triggered, time-cycled, and pressure-limited

Answer 19

Pressure-control ventilation (PCV)

Question 20

It is the preferred mode of ventilation for patients in whom it is desirable to regulate peak airway pressures, such as those with preexisting barotrauma, and for post– thoracic surgery patients, in whom the shear forces across a fresh suture line should be limited

Answer 20

Pressure-control ventilation (PCV)

Question 21

This mode is a variant of PCV that incorporates the use of a prolonged inspiratory time with the appropriate shortening of the expiratory time

Answer 21

Inverse-ratio ventilation (IRV)

Question 22

This approach increases mean distending pressures without increasing peak airway pressures. It is thought to work in conjunction with PEEP to open collapsed alveoli and improve oxygenation

Answer 22

Inverse-ratio ventilation (IRV)

Question 23

It is used to assess extubation potential in patients who have been effectively weaned and who require little ventilatory support and in patients with intact respiratory system function who require an endotracheal tube for airway protection

Answer 23

Continuous Positive airway Pressure (CPAP)

Question 24

Nonconventional Ventilatory Strategies

Answer 24

High-frequency oscillatory ventilation (HFOV)

Airway pressure release ventilation (APRV)

Extracorporeal membrane oxygenation (ECMO)

Partial liquid ventilation (PLV) using perfluorocarbons.

Question 25

Protective Ventilatory Strategy

Answer 25

Set a target tidal volume close to 6 mL/kg of ideal body weight

Prevent plateau pressure (static pressure in the airway at the end of inspiration) exceeding 30 cm H2O

Use the lowest possible fraction of inspired oxygen (Fio2) to keep the Sao2 at ≥90%

Adjust the PEEP to maintain alveolar patency while preventing overdistention and closure/reopening

Question 26

Medications commonly used for sedation and analgesia during ventilation

Answer 26

lorazepam, midazolam, diazepam, mor- phine, and fentanyl

Question 27

DVT prophylaxis

Answer 27

subcutaneous heparin and/or pneumatic compression boots, fractionated low-molecular- weight heparin

Question 28

Prevention of Decubitus Ulcer

Answer 28

Frequent changes in body position

Use of soft mattress overlays and air mattresses

Question 29

Prophylaxis against diffuse gastrointestinal mucosal injury

Answer 29

Histamine-receptor (H2-receptor) antagonists, antacids, and cytoprotective agents such as sucralfate

Question 30

Complications of mechanical ventilation

Answer 30

Pulmonary complications: Barotrauma, nosocomial pneumonia, oxygen toxicity, tracheal stenosis, and deconditioning of respiratory muscles

Hypotension

Gastrointestinal complications: stress ulceration and mild to moderate cholestasis

Question 31

Criteria for Weaning

Answer 31

(1) Lung injury is stable or resolving
(2) Gas exchange is adequate, with low PEEP/Fio2 (<8 cmH2O) and Fio2(<0.5)
(3) Hemodynamic variables are stable, and the patient is no longer receiving vasopressors
(4) The patient is capable of initiating spontaneous breaths

Question 32

It is usually implemented with a T-piece using 1–5 cmH2O CPAP with 5–7 cmH2O or PSV from the ventilator to offset resistance from the endo- tracheal tube

Answer 32

Spontaneous Breathing Trial (SBP)