Trigger - the factor that initiates inspiration. A breath can be pressure-triggered, flow-triggered, or time-triggered.
Cycle - the determination of the end of inspiration, and the beginning of exhalation. For example, the mechanical ventilator can be volume, pressure, or time cycled.
Initiation phase is the start of the mechanical breath, whether triggered by the patient or the machine. With a patient initiated breath, you will notice a ?
Inspiratory phase is the portion of mechanical breathing during which there is a flow of air into the patient's lungs to achieve a ?
Plateau phase does not routinely occur in ?, but may be checked as an important diagnostic maneuver to assess the plateau pressure (Pplat). With cessation of air flow, the plateau pressure and the tidal volume (TV or VT) are briefly held constant.
Exhalation is a passive process in mechanical breathing. The start of the exhalation process can be either ?
Peak Inspiratory Pressure (PIP or Ppeak) is the maximum pressure in the airways at the end of the inspiratory phase. This value is often displayed on the ventilator screen. Since this value is generated during a time of airflow, the PIP is a determined by both ?. By convention, all pressures in mechanical ventilation are reported in "cm H2O." It is best to target a PIP ?
-Plateau Pressure (Pplat) is the pressure that remains in the alveoli during the plateau phase, during which there is a cessation of air flow, or with a breath-hold. To calculate this value, the clinician can push the "?" button on the ventilator. The plateau pressure is effectively the pressure at the ?, and reflects the ? in the airways. To prevent lung injury, the Pplat should be maintained at ?
Positive End Expiratory Pressure (PEEP) is the positive pressure that remains at the end of ?. This additional applied positive pressure helps prevent atelectasis by preventing the end-expiratory alveolar collapse. PEEP is usually set at ? cm H2O or greater, as part of the initial ventilator settings. PEEP set by the clinician is also known as extrinsic PEEP, or ePEEP, to distinguish it from the pressure than can arise with ?. By convention, if not otherwise specified, "PEEP" refers to ePEEP.
Intrinsic PEEP (iPEEP), or auto-PEEP, is the pressure that remains in the lungs due to incomplete exhalation, as can occur in patients with obstructive lung diseases. This value can be measured by holding the ? button on the mechanical ventilator.
Driving pressure (∆P) is the term that describes the pressure changes that occurs during inspiration, and is equal to the difference between the ? For example, a patient with a Pplat of 30 cm H2O and a PEEP of 10 cm H20 would have a driving pressure of 20 cm H2O. In other words, 20 cm H2O would be the pressure that ?
Inspiratory time (iTime) is the time allotted to deliver the set tidal volume (in volume control settings) or set pressure (in pressure control settings).
Expiratory Time (eTime) is the time allotted to fully exhale the delivered mechanical breath.
I:E ratio, or the inspiratory to expiratory ratio, is usually expressed as 1:2, 1:3, etc. The I:E ratio can be set directly, or indirectly on the ventilator by changing the ? By convention, decreasing the ratio means increasing the ?. For example, 1:3 is a decrease from 1:2, just like 1/3 is less than 1/2.
Peak inspiratory flow is the ? at which the breath is delivered, expressed in L/min. A common rate is ? L/min. Increasing and decreasing the inspiratory flow is a means of indirectly affecting the I:E ratio. A patient with a respiratory rate set at 20, who is not overbreathing, has 3 seconds for each complete cycle of breath. If you increase the inspiratory flow, the breath is given faster, and that leaves more time for exhalation. Thus, inspiratory flow indirectly changes the I:E ratio.
Tidal volume (TV or VT) is the volume of gas delivered to the patient with each breath. The tidal volume is best expressed in both milliliters (ex: 450mL) and milliliters/kilogram (ex: 6 mL/kg) of predicted body weight, much as one might describe a drug dosage in pediatrics. Clinicians can choose to set the ventilator in a volume control mode, where the tidal volume will be constant for each breath. In pressure control modes, the pressure is constant, and the tidal volume will vary slightly with each breath. Regardless, every mode of ventilation delivers a tidal volume.
Respiratory rate (RR or f, for "frequency") is the mandatory number of breaths delivered by the ventilator per minute. However, it is important to be mindful that the patient can breathe over this set rate, and therefore one must report both ?; both of these values can found on the ventilator screen. In addition, it is important to remember that the RR is a key factor in determining time for ?. For example, if a patient has a RR of 10 breaths per minute (bpm), he will have 6 seconds per breath; ((60 seconds/min) / 10 bpm = 6 sec/breath). A RR of 20 bpm, only allows 3 seconds for the entire respiratory cycle.
Minute ventilation (VĖ, Vė, or MV ) is the ventilation the patient receives in one minute, calculated as the tidal volume multiplied by the respiratory rate (TV x RR), and expressed in liters per minute (L/min). Most healthy adults have a baseline minute ventilation of ?L/min, but critically ill patients, such as those attempting to compensate for a metabolic acidosis, may require a minute ventilation of ? L/min, or even higher, to meet their demands.
Fraction of inspired oxygen (FiO2) is a measure of the oxygen delivered by the ventilator during inspiration, expressed at a percentage. Room air contains ?% oxygen. A mechanical ventilator can deliver varying amounts of oxygen, up to 100%.
Assist Control (AC) is a commonly used mode of ventilation, and one of the safest modes of ventilation in the Emergency Department. Patients receive the same breath, with the same parameters as set by the clinician, with every breath. They may take additional breaths, or over-breathe, but ?. Assist control can be ?
? (SIMV) is a type of intermittent mandatory ventilation, or IMV. The set parameters are similar to those in AC, and the settings can be ?Similar to AC, each mandatory breath in SIMV will deliver the identical set parameters. However, with additional spontaneous breaths, the patient will only receive ?. For example, in SIMV-VC we can set a TV, and as long as the patient is not breathing spontaneously, each delivered mechanical breath will achieve this tidal volume. However, spontaneous breaths in this mode of ventilation will have more variable tidal volumes, based on patient and airway factors.
Pressure Regulated Volume Control (PRVC) is a type of assist-control that combines the best attributes of volume control and pressure control. The clinician selects a desired tidal volume, and the ventilator gives that tidal volume with each breath, at the lowest possible pressure. If the pressure gets too high and reaches a predefined maximum level, ?. In this mode of ventilation, the pressure target is adjusted based on ?, to help achieve the set tidal volume.
? is a partial support mode of ventilation in which the patient receives a constant pressure (the PEEP) as well as a supplemental, "supporting" pressure when the ventilator breath is triggered. In this mode, the clinicians can set the PEEP and the additional desired pressure over the PEEP. However, the ? are all dependent variables, and determined by the patient's effort. The patient triggers every breath, and when the patient stops exerting effort, the ventilator stops administering the driving pressure, or the desired pressure over PEEP. Therefore, patients placed on this mode of ventilation must be able to take spontaneous breaths.
Non-invasive positive pressure ventilation (NIPPV): refers to two non-invasive modes of ventilation, in which the patient's airway is not secured with an endotracheal tube. Rather, these modes of ventilation are delivered through a ?. There are several indications, and clear contraindications to these modes of ventilation, as discussed in the text. Both CPAP and BPAP are non-invasive modes of ventilation.
Continuous Positive Airway Pressure (CPAP) is a partial support mode of ventilation, in which the patient received a constant airway pressure throughout the respiratory cycle. The ? are all dependent variables and determined by the patient's effort. Therefore, the patient must be awake, minimally sedated, and able to take spontaneous breaths during this mode of ventilation.
Bilevel Positive Airway Pressure (BPAP or BiPAP) is a partial support mode of ventilation, in which the patient receives two levels of airway pressure throughout the respiratory cycle. A high inspiratory pressure (iPAP), is similar to the ? setting. The lower expiratory pressure (ePAP), similar to ?, is clinically apparent at the end of expiration and helps maintain alveolar distention. The patient must be awake, minimally sedated, and able to take spontaneous breaths during this mode of ventilation.
Unconventional Modes of Ventilation: There are other modes of ventilation occasionally used in specific circumstances in ICUs, including Airway Pressure Release Ventilation (APRV), also referred to as Bi-Level or Bi-vent, High-frequency Oscillatory Ventilation, Proportional Assist Ventilation (PAV), and Neurally Adjusted Ventilator Assist (NAVA), but these modes are not appropriate in the ED without expert consultation.
Delivery of Oxygen = ?
There are five broad physiologic causes of hypoxemia: ?
There are several different causes of intra-pulmonary shunts, including ?
When an area has ventilation, but no perfusion, this is dead space. In other words, the airways are functioning normally, but there is a disease process in the vasculature. The best example would be a patient in cardiac arrest who is intubated and ventilated, but there is an interruption of chest compressions. Dead space can be anatomic and physiologic, such as oxygenation but lack of gas exchange that occurs in the upper airways, like the trachea. There can also be pathological causes of dead space, such as this diagram of microthrombi blocking a capillary. Other examples of dead space include low cardiac output and hyperinflation, as occurs in obstructive lung disease. In diseases such as chronic obstructive lung disease (COPD), there can be a significant level of hyperinflation or auto-PEEP, which can lead to vasoconstriction of the capillaries involved in gas exchanged, thereby leading to impaired gas exchanged. Dead space ventilation can lead to both hypoxia and hypercapnia, due to CO2 retention.
Maximizing V/Q matching, by preventing atelectasis, is a key principle in the management of respiratory failure. Alveolar derecruitment, or atelectasis, leads to the creation of shunts. Atelectasis has multiple detrimental effects in ventilated patients. First, atelectasis decreases the surface area for gas exchange. Atelectasis on a large scale is derecruitment.
Derecruitment is compounded by ?. The addition of sedation and paralysis to positive pressure ventilation can further augment this derecruitment. This diagram reflects the pressures leading to compression of the lungs when lying a patient supine - the weight of the heart, the weight of the chest wall, the weight of the abdominal contents, and the weight of the lungs themselves.
Cardiac Output x (Hgb x 1.39 x Oxygen Saturation) + (PaO2 x 0.003)
shunting, VQ mismatch, alveolar hypoventilation, diffusion defect, and decreased partial pressure of oxygen.
atelectasis, pneumonia, pulmonary edema, acute respiratory distress syndrome (ARDS), hemothorax or pneumothorax, hyperinflation or auto-PEEPing
excessive lung weight (such as with pulmonary edema), chest wall weight (as with morbid obesity), abdominal contents and distention (as with small bowel obstructions), and even cardiac compresses (as with pericardial effusion)
Resistance (R) = ?
R = ?
R = (PIP- Pplat) / (TV)
Assuming a constant tidal volume, the resistance equation can be simplified to:?
Normal airway resistance should be ≤ 5 cmH20. Resistance is a factor in ventilating all patients but can become particularly important when ventilating patients with COPD or asthma.While common examples include a very small endotracheal tube (ETT) or bronchospasm leading to narrowing of the airways, recall that a "decrease in the diameter" can also occur at just one point, such as with kinking or biting of the ETT, or a mucous plug in a large airway.
Although compliance commonly is used to describe the lung parenchyma, remember that compliance actually involves all components of the system. In other words, a patient with pulmonary edema may have low compliance due to an issue with the lung parenchyma, but another patient may have similarly low compliance due to severe chest wall stiffness after a third-degree burn. Clinically, knowing the exact cause of decreased compliance in a given patient can be challenging. Physicians should not, therefore, always assume that it is always related to "stiff lungs."
In the schematic below, the top "lungs" are healthy. The lungs on the left have a resistance problem or impairment in airflow. The lungs on the right have a compliance problem or impairment in stretch and recoil. In this diagram, both figures could have elevated peak inspiratory pressures (PIP), due to the excess pressure generated in the system. However, only the right-hand figure would have an elevate plateau pressure (Pplat), since this process occurs when there is an absence of airflow.
Compliance (C) = ?
C = ?
C = (TV) / (Pplat - PEEP)
An elevated PIP and normal Pplat is indicative of increased airway resistance. An elevated PIP and elevated Pplat is indicative of abnormal compliance.
High PIP, Low/Normal Pplat:
causes - 6?
High PIP/ High Pplat
causes - 13?
Auto PEEP is most common in patients with prolonged expiratory phases, such as ?, it can also occur in patients who have a ?
Auto-PEEP (iPEEP) = ?
The increased intrathoracic pressure from autoPEEP can decrease venous return and lead to hemodynamic instability, even cardiac arrest in severe cases. The increased pressures may also result in a ?
Additionally, air trapping can lead to ineffective ventilation due to ?, with worsening hypercarbia and hypoxemia. While this may seem like a paradox, as one may assume that increasing the minute ventilation, or moving more air, will improve ventilation, there is a limit to the beneficial effects. Once the lungs are overdistended, gas exchange is ineffective. In these circumstances, allowing the patient sufficient time to exhale can decrease CO2 retention.
Kinked tube, bronchospasm, too small ET tube, mucus plug, coughing
mainstem intubation, pulmonary edema, atelectasis, pneumonia, pneumo/hemothorax, ARDS, restrctive lung disease, circumferential chest wall burns, air trapping with autoPEEP, obesity, abdominal compartment syndrome, scoliosis, supine position
-asthma or COPD
-fast respiratory rate or those who are being ventilated with large tidal volumes.
-Total PEEP - ePEEP
-pneumothorax or pneumomediastium.
-collapse of the capillaries responsible for gas exchange
Critically ill patients are at high risk of deterioration with intubation and initiation of mechanical ventilation.Specifically, PPV leads to an increase in the intrathoracic pressure, which has different effects on the right and left ventricles. For the right ventricle, the PPV will lead to decreased preload via decreased venous return. The distention of the alveoli can also lead to increased afterload on the right ventricle.
PPV also decreases the left ventricular preload, given the impact on the right ventricle. However, the increased intrathoracic pressure also decreases the transmural pressure, or the afterload, on the left ventricle. While we use this principle to care for those with congestive heart failure (CHF), it can lead to an increase in stroke volume and cardiac output.
However, in excess, these impacts on the cardiovascular system can lead to a decrease in the cardiac output and hypotension, especially in the intravascularly depleted patient, those with shock physiology, or with air trapping.
A volume-depleted patient, such as a patient with a GI bleed, may have ?
When initiating mechanical ventilation, the practitioner must be conscientious to ensure adequate gas exchange to meet the metabolic demands of the patient. For example, a patient in severe metabolic acidosis with respiratory compensation might be very tachypneic. One must be cognizant to increase the respiratory rate on the ventilator to help meet the patient's metabolic demands. Failure to do so can be detrimental for the patient, and lead to rapid decompensation.
Along the same lines, the practitioner must be careful to set and then adjust the ventilator settings to prevent further decompensation or injury. For example, excessive volumes on the ventilator can lead to volutrauma and impaired gas exchange. Excess pressure can lead to hemodynamic instability or barotrauma.
check breath sounds, check ETT tube position and compare to prior, check suction catheter (change if needed), check heat-moisture exchanger (change if needed- secretions are present0 usually a few days), everything is secure, check humidifier chamber is filled with water
always check arterial blood gas for adjustments to ventilation - can use venous blood gas for pH and PCO2, check Sp02 for oxygenation
-volume control ventilation: checking PIP and Pplat because changes to respiratory mechanics will be regarding pressure since volume is fixed
-Pressure control or pressure support: check tidal volume and minute ventilation since pressure is fixed
-respiratory rate, minute ventilation, tidal volume, PIP, apnea -- curcuit disconnect or occlusion
-blood pH and oxygenation is used for adjustments, if Pplat > 27 you need to adjust, if PEEP is high eveeryday you should be trying to aggressively ween this, patient interaction -- are they triggering the ventilator on assist control mode, the sooner you can have the patient breathing spontaneously the better
patient is improving medically, Fi02 is 0.5 or less, PEEP is <10, and patient is making spontaneous efforts
if patient is in AC you can put them on pressure support and turn everythign to 0 -- you do this for 2 minutes and calculate RSBI = freq (bpm)/ TV (L) -- anything <105 is successful and patient can be continued to a spontaneous breathing trial
-T-piece = patient is removed from the ventialtor but T-piece is used to allow for oxygen supplied via ETT
-0/0= patient is taken off AC and placed on pressure support but everythign is turned to 0 -- adv is you can still monitor RR, TV, and MV
-pressure support -- patient has low amount of PS to augment inspiratory effort that may be effected due to presence of ETT tube
minumum of 30 minutes up to 1 hour but never more than 2 hours
-patient has high oxygyen needs, patient has high occulusion pressure P0.1 -- pressure drop in the first 100 millisec of triggered breath (>4 or -4) is example of excessive effort-- in these cases NMB may be needed to help protect the lungs from barotrauma/aerotrauma
In general, while a patient continues to have moderate-to-severe ARDS requiring controlled ventilation, most patients will require fairly deep sedation. However, as soon as the patient is demonstrating pulmonary improvement, ?
4 ways to help alleviate delerium severity when patient is in the ICU or anywhere?
Hypotension is common with COVID-19, due in large part to use of high doses of sedatives and analgesics to maintain ventilator synchrony, relative volume depletion in an effort to optimize the lungs, and vasoplegia from sepsis. In patients with chronic hypertension, a study found that maintaining a mean arterial pressure greater than 75 mmHg was associated with a reduced risk of need for renal replacement therapy.
The basic vital signs that should be reviewed every day include the mode of ventilation, tidal volume, pressure, plateau pressure, driving pressure, PEEP, respiratory rate, and FiO2. Additionally, the milliliters per kilogram of predicted body weight, and PaO2/FiO2 ratio (ARDS classification) should be assessed every day.
In volume assist control, check ?
In pressure assist control and pressure support, check ?
When patients are breathing spontaneously, it is important to monitor changes in ?
In addition, make sure that plateau pressure is < ? and consider if higher PEEP is appropriate. Aggressive action should be taken to decrease PEEP and wean the patient off.
If the patient is doing worse, indicated by increasing FiO2, the need to increase the PEEP, or decreased compliance, the clinician should assess for the underlying issue. Issues can include ? and others. Additionally, specifically in COVID-19, patients require prolonged weaning from the ventilator. Attempting to make rapid ventilator changes may result in some deterioration. The clinicians should decide what the next best step is, often including ?
If the patient is doing better, defined as requiring less FiO2, lower PEEP, or improved compliance, the clinician may consider liberalizing the ventilator settings. Many will use a PaO2/FiO2 ratio greater than ? as a cut-off for changing the patient to pressure support ventilation.
Patients should be evaluated every day for readiness for a spontaneous breathing trial (SBT). To determine, consider if:
After changes to ventilator settings, be sure to monitor:
lightning sedation and especially allowing for daily awakening trials, is one of the most important things one can do to reduce ventilator days.
minimize agitation (ventiltor dyssynchrony, reorient), minimal sedation, allow for sleep, early mobilization
peak pressure and plateau pressure.
-peak tidal volume and minute ventilation.
-27 cm H2O (or 30 in patients with ARDS)
-derecruitment, pulmonary edema, or the development of pneumonia,
-deepening sedation, ensuring ventilator synchrony, increasing the PEEP, performing a recruitment maneuver, or proning.
-The patient is stable and/or improving medically.
The FiO2 requirements are 0.5 or less.
The PEEP requirements are 10 cm H2O or less.
The patient can make spontaneous efforts
Arterial blood gas for sufficient oxygenation and acid-base balance
When using venous blood gases consider pH and use SpO2 for oxygenation
Approximately 35% of patients with ARDS well developed acute kidney injury at some point during their critical illness. Acute kidney injury has a high attributable mortality. However, simply providing more fluids does not necessarily improve renal outcomes. A large study published in 2006 found that keeping a negative fluid balance in patients who were not in shock was associated not only with better pulmonary outcomes, but also renal outcomes. The hourly urine output, total body balance for the last 24 hours, BUN, creatinine, as well as other electrolytes should be assessed daily.
For patients with worsening renal failure, determined by ?, the next step is to evaluate when the patient might need dialysis. The indications for emergency dialysis are ?.
GI/Nutrition: Nutrition is essential for healing in any critically ill patient. The patient should be assessed for an appropriate nutrition plan including tolerance of tube feeds. Liver injury is common and critically ill patients, often due to shock liver. Bowel regimens are essential in patients who are receiving Opioids as this can cause substantial constipation.
The hemoglobin, platelets, coagulation factors should be assessed as indicated. In patients with COVID-19, Ddimers are frequently elevated, and higher levels correspond to worse outcomes. Patients with unexplained drops in hemoglobin should be evaluated for bleeding or hemolysis. Please note that the average critically ill patient loses ? mL of blood a day simply from ?. Most patients should be transfused if there are signs of hemodynamically significant, active bleeding or a hemoglobin of less than 7.
The white blood cell count, maximum temperature for the last 24 hours, current temperature, and culture data should all be reviewed. If the patient is on antibiotics, they should be reviewed as well as the day of antibiotics noted. For patients with isolated COVID-19, ?levels are often low, but they can be used to evaluate the patient for a superimposed bacterial pneumonia. Imaging should be reviewed for evidence of ongoing infection. If the patient has a known infection, it should be assessed as to whether it is improving for worsening. The patient should also be assessed for any evidence of new infections. If the patient is showing clinical improvement on antibiotics, but does not have any clear evidence of infection and negative cultures, stopping antibiotics should be considered. All antibiotics in the ICU should have a ?
Ppx: Reduce risk for ventilator-associated pneumonia (VAP):
Raise head of bed to 30-45 degrees (if permissible given patient's specific situation)
Use aseptic technique while suctioningSuction as minimally as possible using the lowest pressure possibleHyperoxygenate the patient pre and post suctioningDo not add normal saline to the ET tube
surgical procedure ?
Respiratory distress? = Sp02 = <90%, hypercapnia (pH < 7.3), Pplat > 30
-hemodynamically unstable w/ prssors?
-Depressed mental status?
RR < 10?
-PEEP > 10
-FiO2 > 0.5
T-piece, 0/0 (also gives you info on post-extubation work of breathing), CPAP, pressure supports with little support (just to overcome ET tube), automatic tube compensation (insp support proportional to ET tube size)
-RR > 35 or 20% incr from baseline WITH signs of resp distress; SpO2 <90%; HR >140 or 20% incr from baseline WITH signs of resp distress; systolic BP changes >180 or <90; somnolence, agitation, diaphoresis, anxiety; incr in pressure requirements; chest pain or any undue pain preventing continuation
back on support prior -- if this was AC you can try pressure support that is close to extubation parameters
assess for extubation parameters -- are they sating >90%; are the neurologically intact; can they cough/did they require frequent suctioning; are they hemodynamically stable; is there a cuff leak (only if you are worried about laryngeal edema)
pneumonia, weak cough, frequent suctioning, RSBI >58, positive fluid balance in the 24 hrs before extubation