323 Mechanical Ventilatory Support Flashcards
The primary indication for initiation of mechanical ventilation is respiratory failure
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
Other indications for instituting mechanical ventilation
- 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
Group of patients who benefit from a trial of
NIV
Those with exacerbations of COPD and respiratory acidosis (pH <7.35)
Contraindications for Noninvasive Ventilation
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
It refers to the manner in which ventilator breaths are triggered, cycled, and limited
Mode
It can either be an inspiratory effort or a time- based signal, defines what the ventilator senses to initiate an assisted breath
Trigger
It refers to the factors that determine the end of inspiration
Cycle
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
Limiting factors
It is the most widely used mode of ventilation
Assist-Control Ventilation (ACMV)
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
Assist-Control Ventilation (ACMV)
In this mode, every breath delivered, whether patient- or timer-triggered, consists of the operator-specified tidal volume
Assist-Control Ventilation (ACMV)
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
Intermittent Mandatory Ventilation (IMV)
Disadvantages of this mode are potential hyperventilation
Barotrauma and volume trauma
Assist-Control Ventilation (ACMV)
Disadvantages of this mode are potential dysynchrony and potential hypoventilation
Intermittent Mandatory Ventilation (IMV)
Disadvantages of this mode are mask interface may cause discomfort and facial bruising,
leaks are common, and hypoventilation
NIV (noninvasive ventilation)
This form of ventilation is patient- triggered, flow-cycled, and pressure-limited
Pressure-Support Ventilation (PSV)
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
Pressure-Support Ventilation (PSV)
It is often used in combination with SIMV to ensure volume-cycled backup for patients whose respiratory drive is depressed
Pressure-Support Ventilation (PSV)
This form of ventilation is time- triggered, time-cycled, and pressure-limited
Pressure-control ventilation (PCV)
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
Pressure-control ventilation (PCV)
This mode is a variant of PCV that incorporates the use of a prolonged inspiratory time with the appropriate shortening of the expiratory time
Inverse-ratio ventilation (IRV)
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
Inverse-ratio ventilation (IRV)
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
Continuous Positive airway Pressure (CPAP)
Nonconventional Ventilatory Strategies
High-frequency oscillatory ventilation (HFOV)
Airway pressure release ventilation (APRV)
Extracorporeal membrane oxygenation (ECMO)
Partial liquid ventilation (PLV) using perfluorocarbons.
Protective Ventilatory Strategy
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
Medications commonly used for sedation and analgesia during ventilation
lorazepam, midazolam, diazepam, mor- phine, and fentanyl
DVT prophylaxis
subcutaneous heparin and/or pneumatic compression boots, fractionated low-molecular- weight heparin
Prevention of Decubitus Ulcer
Frequent changes in body position
Use of soft mattress overlays and air mattresses
Prophylaxis against diffuse gastrointestinal mucosal injury
Histamine-receptor (H2-receptor) antagonists, antacids, and cytoprotective agents such as sucralfate
Complications of mechanical ventilation
Pulmonary complications: Barotrauma, nosocomial pneumonia, oxygen toxicity, tracheal stenosis, and deconditioning of respiratory muscles
Hypotension
Gastrointestinal complications: stress ulceration and mild to moderate cholestasis
Criteria for Weaning
(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
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
Spontaneous Breathing Trial (SBP)
