Mechanical Ventilation Chapter 17
lung damage caused by excessive volume in the lungs
Overdistention causing the release of inflammatory mediators from the lungs that can lead to multi-organ failure
Shear stress injury and loss of surfactant in the lungs
Describe the difference between ventilator-induced lung injury and ventilator-associated lung injury
VILI is a form of lung injury that occurs at the alveolar level and resembles ARDS. VALI includes injury caused by extra-alveolar gas, patient-ventilator dyssynchrony, air trapping, and ventilator-associated pneumonia
List five conditions that can predispose a patient to barotrauma while he or she is being mechanically ventilated?
High PIP, with low end-expiratory pressures
Presence of bullae
High levels of peep with high VT
Aspiration of gastric acid
Necrotizing pneumonias, and ALI/ARDS
During a patient ventilator system check the RT notes right lateral side of the patients neck and face appear puffy. The areas feel crepitant to the touch; however, no distress is observed what is the most likely cause of this problem?
What is likely the cause of a sudden onset of increased peak airway pressures and hyper-resonance in a patient receiving mechanical ventilation?
What is the treatment for a tension pneumothorax?
A 14 gauge needle into the anterior second to third intercostal space on the affected side
When a mechanically ventilated patient develops a tension pneumothorax, how should they be ventilated?
Manual ventilation (Ambu Bag) with high FiO2
List four clinical signs of a tension pneumothorax:
Mediastinal structures and possible tracheal deviation shift away from the affected side
Absent breath sounds on the affected side
Neck vein distention (JVD)
Tympanic percussion note over the affected side
How would a chest radiograph of a patient with a tension pneumothorax look?
One diaphragm will be more depressed than the other and possibly a deep sulcus sign with air appearing adjacent to the depressed diaphragm
Air dissecting into the retroperitoneal space is known as?
What is the minimum transpulmonary pressure that has been associated with lung injury in animals?
30 to 35 cmH2O
List three examples of clinical situations where lung injury can occur from high transpulmonary pressure:
Very stiff lungs with the pleural space near normal
Normal lungs, but there is a right main stem intubation with a large VT
Lungs and chest wall are normal, but the pressure around the chest is high (with n obese patient)
Describe how volutrauma occurs:
Overdistention that occurs at the alveolar level and involves alveolar and interstitial edema formation
What are three primary types of lung injury that can occur with repeated opening and closing of the lung units?
Shear stress (atelectrauma)
Alterations and washout of surfactant
Explain shear stress and how it can lead to edema formation:
It causes intense strain and rupture of lung tissue, which may lead to an inflammatory response and edema formation
Define atelectrauma and give a clinical situation that puts a ventilator patient at risk of developing it?
injuries to the lung that occurs because of repeated opening and closing of lung units at lower lung volumes. Managing a patient with ARDS using low tidal volumes and inadequate levels of peep.
What two chemical mediators are released when the alveolar epithelial cells are overstretched?
Cytokines and tumor necrosis factor
Platelet-activating factor, thromboxane-B2, interleukin-1B
How does multiorgan dysfunction syndrome develop in a patient receiving mechanical ventilation?
Chemical mediators leak out into the pulmonary blood vessels. Circulation carries them to other areas of the body and sets up on inflammatory reaction in other organs, such as kidneys, gut and liver.
How can multiorgan dysfunction be avoided during mechanical ventilation?
Low VT and therapeutic peep (>15 cmH2O) and hypercapnia may be beneficial in ARDS patients
In what areas of the lungs are ventilation and perfusion best matched during spontaneous ventilation in the supine position?
Dependent lung areas (near the back)
How is ventilation and perfusion altered during PPV in a patient who is sedated and paralyzed?
Contraction of the diaphragm is blocked. When PPV is provided the diaphragm is most displaced in the nondependent regions of the lungs; therefore gas flows easily to this area, whereas blood flow to this area is decreased. Alveolar collapse is most likely to occur in the dependent areas of the lungs, where perfusion is the greatest.
How can the changes in gas distribution during mechanical ventilation be minimized?
ventilator modes that preserve spontaneous breathing (PSV)
How can PPV increase dead space?
it increases the size of the conductive airways, which in turn increases dead space. Also, if normal alveoli are overexpanded and compression of pulmonary vessels results, alveolar dead space also increases.
Why would the use of high volumes during PPV and PEEP cause an increase in pulmonary shunting?
Increased volume during PPV + peep squeezes blood out of non-dependent zones, further contributes to V/Q mismatching and dead space by sending more blood into the dependent areas where ventilation is now lower, leading to increased shunting and decreased PaO2
How can mechanical ventilation cause an increase in pulmonary vascular resistance?
increased airway and alveolar pressures can lead to thining and compression of the pulmonary capillaries, decreased perfusion and an increased PVR.
How does hypoventilation lead to cardiac dysrhythmias?
hypoventilation causes an increase in plasma hydrogen ion levels contributing to high potassium levels (hyperkalemia) which leads to cardiac dysrhythmias
What type of patient may benefit from permissive hypercapnia?
List four reasons for patient-induced hyperventilation:
Pain and anxiety syndromes
What acid-base disturbances can cause a right shift in the oxygen dissociation curve?
Respiratory acidosis (hypoventilation, hypercapnia)
Describe two clinical implications of prolonged ventilator-induced hyperventilation:
Hypokalemia, which can lead to cardiac arrhythmias, other problems include tetany and reduced cerebral perfusion, which contributes to increased cerebral hypoxia
Respiratory Alkalosis also reduces the patients drive to breathe, making weaning difficult
What happens to the cerebral spinal fluid during prolonged hyperventilation during mechanical ventilation?
Hyperventilation causes respiratory alkalosis, which leads to the diffusion of CO2 out of the cerebral spinal fluid (CSF) because of the low blood CO2 levels. The hydrogen ion concentration in the CSF decreases, and respirations are not stimulated
When is the administration of bicarbonate indicated?
Life-threatening hyperkalemia caused by metabolic acidosis or salicylate toxicity
List four causes of metabolic alkalosis in the clinical setting
Gastrointestinal vomiting or suctioning
Administration of diuretic
Administration of lactate, acetate, or citrate
What can cause auto-peep without dynamic hyperinflation?
When the expiratory muscles are actively contracting during exhalation. This raises the alveolar pressure at end-exhalation (auto-peep without lung distention)
Describe how ventilator-induced auto-peep can be created?
High minute ventilation (high RR, increased VT), short expiratory times, mechanical devices that increase expiratory resistance ( small ETs, High-resistance expiratory valves, and certain peep devices) and low inspiratory flow rates
What patient factors increase the risk of auto peep?
COPD, high Ve (10 to 20L/min), age (>60), increased Raw (small ETs, bronchospasm, increased secretions, mucosal edema), increased lung compliance (longer time constants) High respiratory frequency, High I:E ratios ( 1:1, 2:1), increased tidal volumes, particularly with airway obstructions
What technique is used to detect the presence of auto-peep?
How many time constants are necessary for the lungs to empty 98% of the inspired volume?
3 to 4
Define dynamic hyperinflation?
Failure of lung volume to return to passive FRC during exhalation by the time the next inspiration begins
What effects can the presence of auto-peep have on ventilator function?
It slows the beginning of gas flow during inspiration because flow delivery does not start until mouth pressure exceeds alveolar pressure, which is now higher than the ambient pressure at the end of exhalation. Auto-peep also makes it more difficult for the spontaneous breathing patient to trigger a ventilator breath, even when the sensitivity settings are appropriate
How do you calculate static compliance?
VT / (plateau-peep)
Note: if there is auto-peep you must add it to your peep
List four strategies that can be used to decrease auto-peep when the patient is receiving full ventilatory support?
Shorten inspiratory time and allow for a longer expiratory by increasing inspiratory flow rate
Use smaller tidal volumes and low respiratory rates to increase expiratory time
Use low-resistance exhalation valves
Use large ET tubes to reduce air trapping
What four modes of ventilation may be used to decrease auto-peep in a patient who is intubated and has spontaneous breathing efforts?
When does pulmonary oxygen toxicity become a problem in adults and premature infants?
FiO2 > .60 prolonged periods >48 hrs or maintaining PaO2 > 80 mmHg in a new born or premature infant
If a FiO2 of greater than _____ is required, PEEP should be used. List four ways to assess pulmonary changes associated with oxygen toxicity?
1. decreased vital capacity
2. decreased compliance
3. decreased diffusing capacity
4. alveolar to arterial PO2 difference
What are the lower limit targets for oxygenation for patients receiving mechanical ventilation?
PaO2 of 60 mmHg, SpO2 90%
The use of low tidal volumes with oxygen concentrations greater than 70% may lead to what?
What is the normal inspiratory WOB?
0.5J/L or 0.05kg/mL
What are some signs a patient has an increased WOB?
High spontaneous rate and accessory muscle use
When is inspiratory WOB considered high?
>1.5 J/L or 15J/L/min
How would you calculate WOB?
( PIP - 0.5 x plateau) / 100 x VT (L)
List four strategies for minimizing a patients WOB?
Largest possible ET tube
Appropriate senstivity setting
Ensure no asynchrony
Reduce patients Raw
List four signs of patient-ventilator dyssynchrony:
Tachypnea, chest wall retractions, chest abdominal paradox, and use of accessory muscles
Define trigger asynchrony
Occurs when the vent sensitivity setting is not appropriate for the patient.
Note: you can resolve this issue by changing to a flow trigger
How can auto-peep cause trigger asynchrony?
When auto-peep is present, the patients effort may not be transmitted to the sensing mechanism and the vent does not provide inspiratory gas flow.
What should the initial flow be set at when using volume ventilation with a constant flow?
What type of breaths may provide more synchrony for a patient with high flow demands?
Pressure-targeted breaths such as PC-CMV and PSV
Note: As long as the set pressure is adequate, flow to the patient will be adequate
What adjustment can be made during pressure target ventilation to lessen the rapid rise of flow when a breath begins?
Adjust the rise time or slope
What is cycle dyssynchrony and under what conditions can it occur?
Occurs when the patient begins to exhale before completion of ventilator breath (inspiration). This may occur when the inspiratory time is set too long by a control itself or result of a combination of rate, flow, and volume settings
What strategies may be used to eliminate cycle dyssynchrony during mechanical ventilation with full support and spontaneous ventilation?
During full ventilatory support, either flow rate can be increased to shorten TI or the set TI may be reduced.
During spontaneous ventilation, the flow cycle percentage can be changed
What mode of ventilation delivers varying breath types, which may result in mode dyssynchrony?
When does peep asynchrony occur?
occurs either when peep is set too low and atelectasis forms or when peep levels are too high and overdistention occurs
How can closed-loop ventilation lead to asynchrony?
Two forms can occur one that depends on the equipment used, and the other that depends on the patient
What are five potential mechanical failures that can occur during mechanical ventilation?
Disconnection from power source
Leak in system
Failure of expiratory valve to function
Disconnection of the patient from the Y connector