Figure 11-1 illustrates the location of various pulmonary and cardiac structures seen on a CXR (PA view). The following is a short guide to reading a CXR.1. Check exposure technique for lightness or darkness.
2. Verify left and right by looking at the heart shape and stomach bubble, respectively.
3. Check for rotation. Does the thoracic spine shadow align in the center of the sternum between the clavicles?
4. Make sure the CXR is taken in full inspiration (10 posterior or 6 anterior ribs should be visible).
5. Is the film a portable, AP, or PA film? (The heart size cannot be accurately judged from an AP film.)
6. Check the soft tissues for foreign bodies or SC emphysema.
7. Check all visible bones and joints for osteoporosis, old fxs, metastatic lesions, rib notching, or presence of cervical ribs.
8. Look at the diaphragm for tenting, free air, and position.
9. Check hilar and mediastinal areas for the following: size and shape of the aorta, presence of hilar nodes, prominence of hilar blood vessels, elevation of vessels (left slightly higher), and elevation of the left main stem bronchus indicating left atrial enlargement.
10. Look at the heart for size, shape, calcified valves, and enlarged atria.
11. Check the costophrenic angles for fluid or pleural scarring.
12. Check the pulmonary parenchyma for infiltrates, ↑ interstitial markings, masses, absence of nl margins, air bronchograms, or ↑ vascularity and “silhouette” signs.
13. Look at the lateral film for the following: confirmation and position of questionable masses or infiltrates, size of retrosternal air space, AP chest diameter, vertebral bodies for bony lesions or overlying infiltrates, and posterior costophrenic angle for small effusion.
2. Calcifications on Chest X-Ray
Lung neoplasm (primary or metastatic)
Silicosis
Idiopathic pulmonary fibrosis (IPF)
Tuberculosis
Histoplasmosis
Disseminated varicella infection
Mitral stenosis (end-stage)
Secondary hyperparathyroidism3. Cardiac Enlargement
Cardiac Chamber Enlargement
Chronic volume overload
Mitral or aortic regurgitation
Left-to-right shunt (PDA, VSD, AV fistula)
Cardiomyopathy
Ischemic
Nonischemic
Decompensated pressure overload
AS
HTN
High-output states
Severe anemia
Thyrotoxicosis
Bradycardia
Severe sinus bradycardia
FIGURE 11-1 Normal anatomy on the female chest radiograph in the upright posteroanterior projection (A) and in the lateral projection (B). (From Mettler FA: Primary Care Radiology. Philadelphia, Saunders, 2000.)
Left Atrium
LV failure of any cause
Mitral valve disease
MyxomaRight Ventricle
Chronic LV failure of any cause
Chronic volume overload
Tricuspid or pulmonic regurgitation
Left-to-right shunt (ASD)
Decompensated pressure overload
Pulmonic stenosis
Pulmonary HTN
Primary
Secondary (PE, COPD)
Pulmonary veno-occlusive diseaseRight Atrium
Multichamber Enlargement
Hypertrophic cardiomyopathy
Acromegaly
Severe obesityPericardial Disease
Pericardial effusion w/ or w/o tamponade
Effusive constrictive disease
Pericardial cyst, loculated effusionPseudocardiomegaly
Epicardial fat
Chest wall deformity (pectus excavatum, straight back syndrome)
Low lung volumes
AP CXR4. Cavitary Lesion on Chest X-Ray
Necrotizing Infections
Bacteria: anaerobes, Staphylococcus aureus, enteric gram(−) bacteria, Pseudomonas aeruginosa, Legionella species, Haemophilus influenzae, Streptococcus pyogenes, Streptococcus pneumoniae, Rhodococcus, Actinomyces
Mycobacteria: Mycobacterium tuberculosis, Mycobacterium kansasii, Mycobacterium avium-intracellulare
Bacteria-like: Nocardia species
Fungi: Coccidioides immitis, Histoplasma capsulatum, Blastomyces hominis, Aspergillus species, Mucor species
Parasitic: Entamoeba histolytica, Echinococcus, Paragonimus westermaniCavitary Infarction
Bland infarction (w/ or w/o superimposed infection)
Lung contusionSeptic Embolism
Staphylococcus aureus
Anaerobes
OthersVasculitis
Wegener’s granulomatosis
PeriarteritisNeoplasms
Bronchogenic carcinoma
Metastatic carcinoma
LymphomaMiscellaneous Lesions
Cysts, blebs, bullae, or pneumatocele w/ or w/o fluid collections
Sequestration
Empyema w/air-fluid level
Bronchiectasis5. Mediastinal Masses or Widening on Chest X-Ray
Lymphoma: Hodgkin’s disease and non-Hodgkin’s lymphoma
Sarcoidosis
Vascular: aortic aneurysm, ectasia or tortuosity of aorta or bronchocephalic vessels
Carcinoma: lungs, esophagus
Esophageal diverticula
Hiatal hernia
Achalasia
Prominent pulmonary outflow tract: pulmonary HTN, PE, right-to-left shunts
Trauma: mediastinal hemorrhage
Pneumomediastinum
Lymphadenopathy caused by silicosis and other pneumoconioses
Leukemias
Infections: TB, viral (rare), mycoplasmal (rare), fungal, tularemia
Thymoma
Teratoma
Bronchogenic cyst
Pericardial cyst
Neurofibroma, neurosarcoma, ganglioneuromaB. Use and Interpretation of Pulmonary Function Tests
Basic spirometry: Figure 11-2
PFTs in common lung diseases: Table 11-1
Flow volume curves: Figure 11-3
FIGURE 11-2 Basic spirometry. Long volumes obtained with a bell spirometer. (From Kiss GT: Diagnosis and Management of Pulmonary Disease in Primary Practice. Menlo Park, Calif, Addison-Wesley, 1982.)
TABLE 11-1
Pulmonary Function Test Patterns in Common Lung Diseases
| Disorder | Parameter | Bronchodilator Response | |||||
| FVC | FEV1 | FEV1/FVC | RV | TLC | Diffusion (DLCO) | ||
| Asthma | ↓ | ↓ | ↓ | Nl, ↑ | Nl, ↑ | Nl | + |
| Chronic obstructive bronchitis | ↓ | ↓ | ↓ | Nl, ↑ | Nl, ↑ | Nl | − |
| Chronic obstructive bronchitis w/ bronchospasm | ↓ | ↓ | ↓ | Nl, ↑ | Nl, ↑ | Nl | + |
| Emphysema | ↓ | ↓ | ↓ | Nl, ↑ | Nl, ↑ | Nl, ↓ | − |
| Interstitial fibrosis | ↓ | Nl, ↓ | Nl, ↑ | Nl, ↓ | ↓ | ↓ | − |
| Obesity, kyphosis | ↓ | Nl, ↓ | Nl, ↑ | Nl, ↑ | ↓ | Nl | − |
↑, greater than predicted; ↓, less than predicted.
FIGURE 11-3 Flow-volume curves of restrictive disease and various types of obstructive diseases compared with normal curves.
C. Pulmonary Formulas
Lung volumes: Box 11-1
Alveolar-arterial O2 gradient (A-a gradient): Box 11-2
Evaluation of pt in respiratory failure: Box 11-3Box 11-1 Lung Volumes: Normal Volumes in Upright Subjects
| Volume or Capacity | Approximate Value in Upright Subjects |
| Total lung capacity (TLC) | 6 L |
| Vital capacity (VC) | 4.5 L |
| Residual volume (RV) | 1.5 L |
| Inspiratory capacity (IC) | 3 L |
| Functional residual capacity (FRC) | 3 L |
| Inspiratory reserve volume (IRV) | 2.5 L |
| Expiratory reserve volume (ERV) | 1.5 L |
| Tidal volume (VT) | 0.5 L |
| The VC is calculated as:
The RV is calculated as the difference between the FRC and the ERV:
Alternatively, if the TLC and VC are known, the following formula can be used:
|
|
Box 11-2 Alveolar-Arterial Oxygen Gradient (A-a Gradient)
Normal A-a gradient = 5-15 mm
FIO2, fraction of inspired oxygen (normal = 0.21-1.0)
PaCO2, arterial carbon dioxide tension (normal = 35-45 mm Hg)
PaO2, arterial partial pressure of oxygen (normal = 70-100 mm Hg)
Ddx of A-a gradient:
| Abnormality | 15% O2 | 100% O2 |
| Diffusion defect | Increased gradient | Correction of gradient |
| V/Q mismatch | Increased gradient | Partial or complete correction of gradient |
| Right-to-left shunt (intracardiac or pulmonary) | Increased gradient | Increased gradient (no correction) |
Box 11-3 Formulas for Evaluation of Patients in Respiratory Failure
Age-predicted PaO2 = Expected PaO2 − 0.3(age − 25) [expected Pao2 at sea level is 100 mg/Hg]
As a rough rule of thumb: Expected PaO2 ≈ FIO2 (%) × 5
AaDO2 = (FIO2 × [BP∗− 47]) − (PaO2 + PaCO2), where BP = barometric pressure
Pao2/Fio2 ratio
AaDO2, Alveolar-arterial gradient; VD, dead space.
From Vincent JL, Abraham E, Moore FA, et al (eds): Textbook of Critical Care, 6th ed. Philadelphia, Saunders, 2011.
D. Mechanical Ventilation
Indications (Please see section “M” for Respiratory Failure Classification)
1. Clinical assessment: presence of apnea, tachypnea (>40 bpm), or respiratory failure that cannot be adequately corrected by any other means
2. Clinical instability, failure to protect the airway—usually from declining mental status
3. ABGs: severe hypoxemia despite high-flow O2 or significant CO2 retention (e.g., PO2 <50, PCO2 >50)
4. Physiologic parameters are of limited use because many pts w/respiratory insufficiency are unable to perform PFTs, and their respiratory failure mandates immediate intervention. Some of the commonly accepted physiologic parameters for intubation and respiratory support are as follows:
a. VC <10 mL/kg
b. Inspiratory force ≤25 cm H2O
c. FEV1 <10 mL/kg
d. VT <5 mL/kg BW
e. 
E >10 L/min
E >10 L/minf. Ratio of RR (breaths/min) to VT (L) >105
Note: The clinical assessment is the most important determinant of the need for mechanical ventilation because neither physiologic parameters nor ABGs distinguish between acute and chronic respiratory insufficiency (e.g., a PCO2 >60 mm Hg and an RR >30/min may be the “norm” for a pt w/COPD, whereas the same values in a young, otherwise healthy adult are indications for intubation and mechanical ventilation).
ICU Sedation
Commonly used agents are GABA agonists such as propofol and benzos. These agents can cause respiratory depression and delirium. The α-adrenoreceptor agonist dexmedetomidine is as effective for sedation but significantly better in pts at risk for delirium.
Common Modes of Mechanical Ventilation
Invasive mechanical ventilation is defined as ventilatory support supplied through endotracheal intubation. The use of devices that apply intermittent (−) extrathoracic pressure or furnish intermittent positive pressure through a tight-fitting nasal or face mask w/o an artificial airway in place is known as noninvasive ventilation. The delivery of gas under positive pressure into the airways and the lungs is known as positive-pressure ventilation (Table 11-2).
1. IMV: The pt is allowed to breathe spontaneously, and the ventilator delivers a number of machine breaths at a preset rate and volume.
a. Advantages and indications
i. IMV is indicated in the majority of spontaneously breathing pts because it maintains respiratory muscle tone and results in less depression of cardiac output than with ACV.
ii. It is useful for weaning because as the IMV rate is ↓, the pt gradually assumes the bulk of the breathing work.
b. Disadvantages
i. The ↑ work of breathing results in ↑ O2 consumption (deleterious to pts w/myocardial insufficiency).
ii. IMV is not useful in pts w/depressed respiratory drive or impaired neurologic status.
TABLE 11-2
Modes of Positive-Pressure Ventilation
| Mode | Description | Advantages and Disadvantages |
| Controlled mechanical ventilation (CMV) | Ventilator f, inspiratory time, and VT (and thus  E) preset |
Can be used in patients w/sedation or paralysis; ventilator cannot respond to ventilatory needs |
| Assisted mechanical ventilation (AMV) or assist-control ventilation (ACV) | Ventilator VT and inspiratory time preset, but patient can f (and thus  E) |
Ventilator may respond to ventilatory needs; ventilator may undertrigger or overtrigger, depending on sensitivity |
| Intermittent mandatory ventilation (IMV) | Ventilator delivers preset VT, f, and inspiratory time, but patient also can breathe spontaneously | May ↓ asynchronous breathing and sedation requirements; ventilator cannot respond to ventilatory needs |
| Synchronized intermittent mandatory ventilation (SIMV) | Same as IMV, but ventilator breaths delivered only after patient finishes inspiration | Same as IMV, and patient not overinflated by receiving spontaneous and ventilator breaths at same time |
| High-frequency ventilation (HFV) | Ventilator f is and VT may be smaller than VD | May reduce peak airway pressure; may cause auto-PEEP |
| Pressure support ventilation (PSV) | Patient breathes at own f; VT determined by inspiratory pressure and CRS | ↑ comfort and ↓ work of breathing; ventilator cannot respond to ventilatory needs |
| Pressure control ventilation (PCV) | Ventilator peak pressure, f, and respiratory time preset | Peak inspiratory pressures may be ↓; hypoventilation may occur |
| Inverse ratio ventilation (IRV) | Inspiratory time exceeds expiratory time to facilitate inspiration | May improve gas exchange by ↑ time spent on inspiration; may cause auto-PEEP |
| Airway pressure release ventilation (APRV) | Patient receives CPAP at high and low levels to simulate VT | May improve oxygenation at lower airway pressure; hypoventilation may occur |
| Proportional assist ventilation (PAV) | Patient determines own f, VT, pressures, and flows | May amplify spontaneous breathing; depends entirely on patient’s respiratory drive |
CRS, Respiratory system compliance; f, respiratory rate; VD, dead space.
Modified from Goldman L, Schafer AI (eds): Goldman’s Cecil Medicine, 22nd ed. Philadelphia, Saunders, 2004.
iii. It was previously assumed that the degree of respiratory muscle rest was proportional to the level of machine assistance. However, more recent evidence indicates that respiratory-sensor output does not adjust to breath-to-breath changes in respiratory load, and IMV may therefore contribute to the development of respiratory muscle fatigue or prevent recovery from it.
2. ACV: The pt breathes at his or her own rate, and the ventilator senses the inspiratory effort and delivers a preset VT w/each pt effort; if the pt’s RR ↓ past a preset rate, the ventilator delivers tidal breaths at the preset rate.
a. Advantages and indications: ACV is useful in pts w/neuromuscular weakness or CNS disturbances.
b. Disadvantages
i. Tachypnea may result in significant hypocapnia and respiratory alkalosis.
ii. Improper setting of sensitivity to the (−) pressure necessary to trigger the ventilator may result in “fighting the ventilator” when the sensitivity is set too low.
iii. ↑ Sensitivity may result in hyperventilation; sensitivity is generally set so that an inspiratory effort of 2 to 3 cm will trigger ventilation.
iv. The respiratory muscle tone is not well maintained in pts on ACV, and this may result in difficulty w/weaning.
3. CMV: The pt does not breathe spontaneously; the RR is determined by the physician; the ventilator assumes all respiratory work by delivering a preset volume of gas at a preset rate.
a. Advantages and indications
i. CMV is useful in pts who are unable to make an inspiratory effort (e.g., severe CNS dysfunction) and in pts w/excessive agitation or breathing effort.
ii. Pts w/excessive agitation are often sedated w/morphine or benzos and paralyzed w/pancuronium bromide; adequate sedation is necessary to eliminate awareness of paralysis.
iii. Initial pancuronium dose is 0.08 mg/kg IV in adults.
iv. Later incremental doses starting at 0.01 mg/kg may be used as necessary to maintain paralysis; pancuronium should be administered only by or under the supervision of experienced clinicians; a combination of neostigmine and atropine may be used to reverse the action of the pancuronium.
b. Disadvantages: Paralyzed pts on CMV must be closely monitored because ventilator malfunction or disconnection is rapidly fatal.
4. SIMV: A hybrid of ACV and IMV, the ventilator delivers a number of specified breaths/min (as w/IMV). However, at the appropriate interval (e.g., q6sec if machine rate is 10 breaths/min), the machine waits for an ETT pressure deflection to signal pt effort and then delivers a positive-pressure breath; ventilator breaths are thus synchronized w/pt respiratory efforts, as w/assist features of ACV.
5. Other useful ventilation modes are as follows:
a. Pressure control ventilation (PCV): A ventilatory mode in which inspiratory pressure, RR, and inspiratory time (TI) are determined by the ventilator settings. Because inspiratory pressure is the controlled variable, VT during PCV is influenced by the mechanical properties of the respiratory system (resistance and compliance).
b. Pressure support ventilation (PSV): A ventilatory mode in which the pt’s inspiratory effort is supported by a set level of inspiratory pressure. This pressure is maintained until respiratory flow falls below a threshold value, signaling the onset of expiration. VT during PSV is determined by pt effort and the mechanical properties of the lung. PSV differs from PCV in that the RR and the TI are determined by the pt.
c. Inverse ratio ventilation (IRV): A ventilatory strategy in which the inspiratory-to-expiratory ratio is prolonged to 1:1 or greater. In pts w/ARDS, IRV is used to improve oxygenation by increasing mean airway pressure. This modality is used as a salvage Rx when adequate oxygenation cannot be achieved w/conventional ventilation in ARDS. When used, pressure cycled IRV is preferred because of ↓ barotrauma risk.
d. Noninvasive positive-pressure ventilation (NPPV), Continuos positive airway pressure (CPAP), Bi-level positive airway pressure (BiPAP): In NPPV, ventilatory support is delivered by use of a mechanical ventilator connected to a mouthpiece or mask instead of an ETT. It is very useful in pts w/chronic respiratory failure caused by neuromuscular disease or thoracic deformities and in pts w/idiopathic hypoventilation. It improves the pt’s well-being and may eliminate the need for tracheostomies. It is also used in pts as a short-term bridge to avoid intubation and mechanical ventilation, when possible, in conditions that are rapidly reversible, such as hypercarbic respiratory failure in COPD and, importantly, acute pulmonary edema in heart failure. It is also sometimes used as salvage Rx in pts w/any of the indications for intubation who do not want to be intubated. CPAP is applied with an oxygen source connected to either a tight-fitting nasal or full-face mask or via nasal prones. It delivers high concentration of oxygen and maintains (+) airway pressure in the spontaneously breathing patient. It offers the benefit of maintaining alveolar expansion and decreases work of breathing. BiPAP, like CPAP can be provided by mask, but it requires a ventilator to assist with flow delivery. The patients inspiratory effort triggers the BiPAP machine to deliver decelerating flow in order to reach a preset pressure, defined as inspiratory positive airway pressure. When a pt’s own inspiratory flow falls below a preset amount, ventilatory assistance ceases and maintains airway pressure at a predetermined value (usually 5-10 mmHg).
Selection of Ventilator Settings
1. VT IS 10 to 15 mL/kg of ideal BW. Low volume ventilation = 6-8 ml/kg w/ARDS
2. Rate (number of tidal breaths delivered per minute) is 8 to 16, depending on the desired PaCO2 or pH (↑ rate = ↓ PaCO2).
3. Mode is IMV, ACV, CMV (or PCV or PSV, depending on what is available at one’s institution).
4. O2 concentration (FIO2): The initial FIO2 should be 100% unless it is evident that a lower FIO2 will provide adequate oxygenation. The FIO2 should be calibrated down as quickly as possible to prevent O2 toxicity.
5. Obtain ABGs 15 to 30 minutes after initiation of mechanical ventilation.
6. Immediate CXR is indicated after intubation to evaluate for correct placement of ETT.
7. Sedation orders (e.g., morphine, diazepam) are necessary in most pts.
8. PEEP:
a. The application of PEEP may prevent the closure of edematous small airways; it is indicated when arterial oxygenation is inadequate (saturation <90%) despite an FIO2 >50%; it is useful in pts w/diffuse lung edema and refractory hypoxemia caused by intrapulmonary shunting (e.g., ARDS). It is also useful to ↓ the needed FIO2 to ↓ O2 toxicity. In reality, ≥5 mm PEEP is used on virtually everyone, but it can be ↓ if oxygenation is not a problem but intubation-associated hypotension is.
TABLE 11-3
Effects of Ventilator Setting Changes
| Typical Effects on Blood Gases | ||
| Ventilator Setting Changes | PaCO2 | PaO2 |
| ↑ PIP | ↓ | ↑ |
| ↑ PEEP | ↑ | ↑ |
| ↑ Rate (IMV) | ↓ | Minimal ↑ |
| ↑ I/E ratio | No change | ↑ |
| ↑ FIO2 | No change | ↑ |
| ↑ Flow | Minimal ↓ | Minimal ↑ |
| ↑ Power (in HFOV) | ↓ | No change |
↑  (in HFOV) |
Minimal ↓ | ↑ |
HFOV, High-frequency oscillatory ventilation; I/E, inspiratory/expiratory ratio; 
, mean airway pressure; PIP, peak inspiratory pressure.
From Tschudy MM, Arcara KM: The Harriet Lane Handbook, 19th ed. Philadelphia, Mosby, 2012.
TABLE 11-4
Common Ventilator Machine Settings for Various Disorders
| Condition | Mode | Vt,  E |
PEEP (cm H2O) | Pressure Targets | FIO2 |
| Depressed CNS drive | Mandatory ACV, SIMV | Vt = 10 mL/kg E = 6-8 L/min |
0-5 | Peak usually <35 cm H2O | Minimum for Sao2 >90% |
| Neuromuscular insufficiency | Acute: mandatory ACV, SIMV | Vt = 8-10 mL/kg E = 6-8 L/min |
0-5 | Peak usually <35 cm H2O | As above |
| Mild, recovering: SIMV and PSV, PSV alone | Guarantee VT >350 mL w/PSV breaths | 0-5 | |||
| COPD | Early: ACV, SIMV Late: see text |
Vt = 8 mL/kg E: minimize, usually 8-10 L/minPeak flow ≥60 L/min |
0∗ | Plateau <30 cm H2O; monitor for intrinsic PEEP (auto-PEEP) | As above |
∗ PEEP added to obstructive disease only in special circumstances.
From Noble J (ed): Textbook of Primary Care Medicine, 2nd ed. St. Louis, Mosby, 1996.
b. PEEP is generally started at 5 cm H2O and by increments of 2 to 5 cm to maintain the PaO2 at 60 mm Hg or greater.
c. The use of PEEP can result in pulmonary barotrauma and hemodynamic compromise (secondary to ↓ right ventricular filling).
d. Pts receiving PEEP should have their cardiac output frequently monitored; the measurement of mixed venous O2 sat is useful to evaluate the effect of PEEP on cardiac output. The surrogate of cardiac output (BP) is fine in most pts.
9. Adjust the initial ventilator setting according to results of the ABGs and clinical response.
a. Use the lowest FIO2 necessary to maintain a PaO2 >60 mm Hg (90% Hgb saturation in pts w/nl pH).
b. Adjust 
E (VT time rate) to nlize the pH and the PaCO2.
E (VT time rate) to nlize the pH and the PaCO2.i. The VT or the rate will ↓ PaCO2 and ↑ pH.
ii. Do not lower the PaCO2 below the “norm” for that pt (e.g., some pts w/COPD should be allowed to maintain their usual mildly ↑ PaCO2 to avoid alkalosis and to provide stimulus for breathing).
10. Effects of ventilator setting changes are described in Table 11-3. Common ventilator machine settings for various disorders are described in Table 11-4 and Box 11-4.
1. Ventilatory mode
Unintubated patients:
NIV for patients with COPD and acute hypercapnic respiratory failure if alert, cooperative, and hemodynamically stable
NIV not routinely recommended for acute hypoxemic respiratory failureIntubated patients:
Assist/control with volume-limited ventilation as initial mode
Consider specific indications for PCV or HFOV (see text) in acute lung injury
SIMV: consider if some respiratory effort, dyssynchrony
PSV: consider if patient’s effort good, ventilatory needs moderate to low, and patient more comfortable during PSV trial2. Oxygenation
If infiltrates on chest radiograph, then
FIO2: begin with 0.8-1.0, reduce according to Spo2
PEEP: begin with 5 cm H2O, increase according to Pao2 or Spo2, FIO2 requirements, and hemodynamic effects; consider PEEP/FIO2 “ladder”; goal of Spo2 >90%, FIO2 ≤0.6
No infiltrates on chest radiograph (COPD, asthma, PTE), FIO2: start at 0.4 and adjust according to Spo2 (consider starting higher if PE is strongly suspected)3. Ventilation
VT: begin with 8 mL/kg PBW; decrease to 6 mL/kg PBW over a few hours if acute lung injury present
Rate: begin with 10-20 breaths/min (10-15 if not acidotic; 15-20 if acidotic); adjust for pH; goal pH >7.3 with maximal rate of 35; may accept lower goal if 
E high4. Secondary modifications
Triggering: in spontaneous modes, adjustment of sensitivity levels to minimize effort
Inspiratory flow rate of 40-80 L/min; higher if tachypneic with respiratory distress or if auto-PEEP present, lower if high pressure in ventilator circuit leads to a high-pressure alarm
Assessment of auto-PEEP, especially in patients with increased airways obstruction (e.g., asthma, COPD)
I/E ratio: 1:2, either set or as function of flow rate; higher (1:3 or more) if auto-PEEP present
Flow pattern: decelerating ramp reduces peak pressure5. Monitoring
Clinical: blood pressure, ECG, observation of ventilatory pattern including assessment of dyssynchrony, effort or work by the patient; assessment of airflow throughout expiratory cycle
Ventilator: VT, 
E, airway pressures (including auto-PEEP), total complianceBuy Membership for Internal Medicine Category to continue reading. Learn more here
