New Deck Flashcards
When is mechanical ventilation indicated?
Inadequate spontaneous hypoxia even with 100% O2, Acute Lung Injury: PaO2/FiO2 <300 or arterial blood gas indicating respiratory failure.
Inadequate lung expansion
Respiratory muscle fatigue
Excessive work of breathing (WOB)
Postoperative prophylaxis
Closed head injury
need to reduce PaCO2
Flail chest
Apnea
Conditions that reduce the patient’s drive to breathe
Drug overdose or over sedation
CVA, subarachnoid hemorrhage
Neuromuscular disease
(ALS, myasthenia gravis, polio, spinal cord injury, MS)
Musculoskeletal/pleural conditions
(kyphoscoliosis, pneumothorax, pleural effusion)
Upper airway obstruction
Respiratory and Gas exchange indicators for mechanical ventilation
Respiratory assessment
Respiratory rate > 35 bpm
Negative inspiratory force < -25 cm H2O
Vital capacity < 10 ml/kg
Minute ventilation < 3 lpm or > 20 lpm
Gas exchange
PaO2 < 60 mm Hg with FiO2 > 50%
PaCO2 > 50 mm Hg (acute) and pH < 7.25
How does positive pressure ventilation work?
In positive-pressure ventilation, intrathoracic pressure remains positive throughout respiration. Gas flow takes the path of least resistance, and is distributed to the non-dependent, less perfused lung regions bc patient is supine. V/Q or ventilation/perfusion mismatch is more likely to occur.
Assume 2.5cc/kilo (but depends on demand)
Basic ventilatory parameters
FIO2 - fraction of inspired oxygen
Rate - number of breaths per minute
Tidal Volume - volume of each breath
Sensitivity - how responsive the ventilator is to the patient’s efforts
Peak Flow - the maximum flow rate used to deliver each breath to the patient
Inspiratory Time - the time spent in the inspiratory phase of the ventilatory cycle
I:E Ratio - the inspiratory time compared to the expiratory time; I + E = total cycle time
What are the modes of action of ventilators?
Mandatory:
Assist/Control (only when patient’s breath is inadequate but all at same volume so problematic if hyperventilation-hypocapnea, time cycled and pressure limited), Synchronized Intermittent Mandatory Ventilation (SIMV or IMV-patient friendly control, opening and closing of exhalation valve, only machine initiated beraths are time cycled and pressure limited), Pressure Control (clinician determines inspiratory time, patient controls flow-not used anymore)
Spontaneous:
Pressure Support (backup, follows spontaneous breathing. Low level: with SIMV, High level: good ventilation but low tidal volume), and CPAP.
What type of ventilator is usually used for small children? For adults?
SIMV for both.
Time sensitive because tidal volumes are very low and volume sensitivity is delicate.
Volume control: set volume guarantees Vt.
Volume Controlled Ventilation vs Pressure Controlled Ventilation
Volume Ventilation
Volume delivery constant
Inspiratory pressure varies
Inspiratory flow constant
Inspiratory time determined by set flow and VT
Pressure Ventilation (control no longer used)
Volume delivery varies
Inspiratory pressure constant
Inspiratory flow varies
Inspiratory time set by clinician
PEEP definition
Positive end expiratory pressure
Application of a constant, positive pressure such that at end exhalation, airway pressure does not return to a 0 baseline
Used with other mechanical ventilation modes such as A/C, SIMV, or PCV
Referred to as CPAP when applied to physiological breaths
Increases functional residual capacity (FRC) and improves oxygenation
Recruits collapsed alveoli
Splints and distends patent alveoli
Redistributes lung fluid from alveoli to perivascular space
CPAP Definition
Continuous positive airway pressure
Application of constant positive pressure throughout the spontaneous ventilatory cycle
No mechanical inspiratory assistance is provided
Requires active spontaneous respiratory drive
Same physiologic effects as PEEP
Tidal volume and rate determined by patient.
May need to provide volume support in heard disease patients because of decreased venous return.
What are the types of ventilator alarms?
High airway pressure (usually 10 mm H20 above PIP)
Low airway pressure
High respiratory rate
High minute volume
Low minute volume
Low exhaled tidal volume
Apnea (backup-some default to autoventilation)
