A patient has a minute volume of 8.25 L/min and is breathing at a rate of 22 breaths/min. What is his average tidal volume?
- 182 mL
- 375 mL
- 275 mL
- 435 mL
VT = 8.25 ÷ 22 = 0.375 L or 375 mL.
At a normal venous blood PaO2 of 40 torr, what is the approximate percent saturation of hemoglobin with oxygen?
The affinity of Hb for O2 varies according to PO2, as described by the S-shaped oxyhemoglobin dissociation curve. At a venous PO2 of 40 torr, Hb saturation is about 73% (you can apply the "40-50-60/70-80-90" rule of thumb to this question, i.e., PO2s of 40, 50 and 60 torr correspond respectively to saturations of about 70%, 80% and 90%). Because the curve at this point is steep, a given drop in PO2 causes a large drop in saturation, indicating a weak affinity for O2. This decreased affinity for O2 at low PO2s helps release large amounts of O2 to the tissues in response to small drops in PO2.
What conclusions can you draw from the following data, obtained on a 47 year old 55 kg female patient admitted for pulmonary complications arising from kyphoscoliosis:
Actual Predicted % Predicted
TLC 3.13 4.10 76%
FRC 1.44 1.96 73%
RV 0.85 1.09 77%
VC 2.28 2.93 78%
FVC 2.28 2.92 78% FEF200-1200 4.32 4.48 97% FEF25-75 2.83 2.74 103%
- results indicate generalized airway obstruction
- results indicate a restrictive lung disorder
- results indicate normal pulmonary function
- results indicate poor patient effort during the test
With all lung volume less than predicted (including the FVC), but normal expiratory flows, this patient has a restrictive disorder, consistent with her history of kyphoscoliosis.
A patient with a history of nocturnal dyspnea has a FEV1 of 1.5 L before bronchodilator therapy and a FEV1 of 1.8 L fifteen minutes after treatment. These results indicate that the patient:
- has airway obstruction that is unresponsive to treatment
- is suffering from a combined obstructive and restrictive disorder
- has at least partially reversible airway obstruction
- is developing tolerance to the bronchodilator
The percent change in the FEV1 is +20% ([1.8 – 1.5]/1.5 = 0.3/1.5 = .20 = 20%). An increase in FEV1 of more than 12-15% between pre- and post-bronchodilator therapy indicates the presence of at least partially reversible airway obstruction.
A patient receiving 30% O2 has a PaO2 of 66 torr and PaCO2 of 32 torr. Which of the following best describes this patient’s oxygenation status?
- A mild disturbance of oxygenation consistent with hypoventilation
- A mild disturbance of oxygenation consistent with a V/Q imbalance
- A moderate disturbance of oxygenation consistent with acute lung injury
- A severe disturbance of oxygenation consistent with ARDS
The patient is hyperventilating so hypoventilation can be ruled out. The P/F ratio is 220 (66/.3). P/F ratios between 200 and 300 indicate mild disturbances of oxygenation, usually due to V/Q imbalances. Ratios between 100 and 200 indicate a moderate disturbance due to shunting, consistent with acute lung injury. A P/F < 100 indicates a severe disturbance of oxygenation/severe shunting consistent with ARDS.
You observe the following on the bedside capnograph display of a patient receiving ventilatory support. What is your interpretation of this display data?
- the capnogram indicates expiratory obstruction
- the capnogram indicates rebreathing
- the capnogram indicates a leak around the ET tube
- the capnogram indicates hypoventilation
This capnogram indicates a leak around the ET tube, revealed by the poorly formed (or missing) plateau and an irregular and less sharp than normal inspiratory downstroke.
On reviewing an ECG print-out you note widened QRS complexes. Which of the following is the most likely cause of this problem?
- atrial fibrillation
- 1st degree heart block
- sinus arrhythmia
- bundle branch block
The duration of a normal QRS complex is 0.12 seconds (3 small boxes) or less. Causes of a widened QRS complex include right or left bundle branch block (BBB), hyperkalemia, ventricular pre-excitation (e.g. Wolf-Parkinson-White pattern), and any ventricular rhythm, including those caused by a ventricular pacemaker.
Which of the following exercise test findings (as compared to normal) is MOST consistent with exercise intolerance due primarily to a ventilatory impairment?
- normal arterial PaO2
- increased max O2 consumption
- increased arterial PaCO2
- normal max heart rate
Exercise intolerance due to a ventilatory impairment usually manifests as a DECREASE in VO2max, maximum heart rate, maximum cardiac output, and PaO2 with an INCREASE in PaCO2 and the VE/VCO2 ratio during exercise evaluation. The O2 pulse, cardiac output/VO2 ratio and ventilatory (anaerobic) threshold may remain normal.
In performing a patient-ventilator check, you note that the expiratory portion of the flow-volume loop does not return to baseline. Which of the following is the most likely problem?
- decreased compliance
- air leak
The presence of auto-PEEP can be visualized on a ventilator's graphic display when flow does not return to the baseline before the start of next breath. Either a flow vs. volume loop or a flow vs. time scalar will reveal this pattern.
A patient has a body surface area (BSA) of 2.0 m2 and a cardiac output (CO) of 3.0 L/min. What conclusions can you draw regarding the patient's cardiac index?
- the patient's cardiac index is below normal
- the patient's cardiac index is normal
- the patient's cardiac index is above normal
- insufficient data to compute the cardiac index
Cardiac index (CI) = CO/BSA. In this case CI = 3.0/2.0 = 1.5 L/min/m2. Because a normal range for cardiac index is 2.5-5 L/min/m2, this patient's cardiac index is below normal.
The results of an arterial blood gas analysis for a patient who is breathing 100% oxygen are below:
pH7.24PaCO238 torrHCO323 mEq/LBE-1PaO2610 torrSaO2100%
Which of the following is the likely problem?
- respiratory acidosis
- large physiologic shunt
- metabolic acidosis
- laboratory error
In terms of oxygenation, a PaO2 of 610 torr on 100% O2 is not only possible, but near normal (based on the alveolar air equation). On the other hand, the acid-base values are not consistent with the underlying relationship that determines pH (the Henderson-Hasselbach equation). In this case, both the PaCO2 and HCO3 are normal. With both these values being within the normal range, the pH also would have to be close to normal, which it clearly is not (pH = 7.24). The only possibility here is a laboratory error.
After bedside measurement, you note that a patient's slow and forced vital capacity are approximately equal and both are less than 60% of the predicted values. Which of the following diagnoses is LEAST likely?
- lung resection
- interstitial fibrosis
- myasthenia gravis
If the slow vital capacity is low, a restrictive disorder is likely present, e.g., interstitial fibrosis, lung resection, consolidative processes, congestive heart failure, obesity, and neuromuscular disorders such as myasthenia gravis. In these patients the slow VC and FVC will not usually differ significantly. If the FVC is substantially less that the slow vital capacity, air trapping is likely present, signifying obstructive lung disease.
As compared to predicted normals, a patient has a normal FEV1%, normal FEF25-75, but a markedly reduced FVC. Test results are repeatable. Which of the following is the most likely underlying problem?
- poor patient effort during the test procedure
- a restrictive disorder of the lungs or chest wall
- combined restrictive and obstructive disease
- peripheral (small) airway obstruction
In the presence of normal expiratory flow parameters (such as the FEV1% and FEF25-75), a reduced FVC indicates a restrictive disorder of the lungs or chest wall.
A patient is receiving volume control A/C ventilation. The patient has become increasingly agitated and the end-tidal CO2 has decreased from 39 to 28 torr over the last 2 hours. Which of the following is the most likely cause?
- increased cardiac output
- mainstem intubation
- high body temperature
- increased ventilation
The most likely cause of this patient’s low end-tidal CO2 is hyperventilation caused by the patient’s agitation. Treating the cause of the agitation may restore normal ventilation and thus normalize end-tidal CO2. High body temperature (fever) increases metabolism and would tend to increase, not decrease expired CO2 levels. Mainstem intubation normally does not affect capnographic readings.
An unconscious patient admitted to the Emergency Department has a SpO2 of 94% but analysis of an arterial sample on a CO-oximeter reveals a SaO2 of 69%. Which of the following problems is most likely?
- carbon monoxide poisoning
- opiate drug overdose
- diabetic ketoacidosis
- acute pulmonary edema
The most likely problem is carbon monoxide poisoning. Most standard two wavelength pulse oximeters cannot detect HbCO. On the other hand, multi-wavelength CO-oximetry can detect the presence of abnormal hemoglobins, such as HbCO, and metHb and thus provide an accurate measure of the SaO2. A further clue in this case is that the patient is unconscious. HbCO levels over 20–25% (as likely in this case) often will cause a loss of consciousness.
A 48-year-old 180 lb male is orally intubated receiving mechanical ventilation with a 6.0 mm endotracheal tube secured in place, which requires a cuff pressure of 38 cm H2O to prevent significant volume loss. Which of the following actions would be appropriate in this case?
- replace the endotracheal tube with a smaller size
- accept the large volume loss during inspiration
- replace the endotracheal tube with a larger size
- deflate and reinflate the cuff with 20 mL air
The most common cause of high ET tube cuff pressures being needed to obtain a seal is that the tube is too small for the patient's airway. You should suggest reintubating the patient with a larger endotracheal tube in order to prevent excessive cuff pressures and mucosal damage.
A patient undergoing CPAP titration for sleep apnea exhibits prolonged periods of central sleep apnea during the procedure, even at a baseline pressure of 15 cm H2O. Which of the following would you recommend for this patient?
- titrate the CPAP pressure up to 20 cm H2O and reassess
- discontinue the titration and recommend a trial of a xanthine
- consider a trial of bi-level positive airway pressure (BiPAP)
- switch to an auto-CPAP unit and continue the titration
If during CPAP titration (1) the patient cannot tolerant high CPAP pressures, (2) there are continued obstructive respiratory events at higher levels of CPAP (> 15 cm H2O), or (3) the patient exhibits periods of central sleep apnea during titration, you should consider a trial of BiPAP, starting at EPAP = 4 cm H2O and IPAP = 8 cm H2O.
As measured by the single breath DLco method, the diffusing capacity of the lungs would be decreased in which one of the following cases?
- pulmonary hypertension
- secondary polycythemia
- strenuous exercise
- pulmonary emphysema
The DLco is low in conditions that actually impair membrane diffusion (as in pulmonary fibrosis) or decrease surface area (as in emphysema). The DLco can also be less than normal with reduced Hb (as in anemia), decreased pulmonary capillary blood flow, or decreased alveolar volume. Increases in DLco occur with increased Hb (as in secondary polycythemia), increased pulmonary blood flow, increased alveolar volume, and during exercise.
A patient's mixed venous PO2 has decreased from 41 mm Hg to 27 mm Hg over the last hour. What is the most likely explanation for this change?
- the blood sample was withdrawn too rapidly
- the patient's temperature has decreased
- a pulmonary diffusion defect is developing
- the patient's cardiac output has decreased
Venous oxygenation parameters indicate the adequacy of tissue oxygenation relative to blood flow. The drop in PvO2 from a normal value of 41 mm Hg to 27 mm Hg (abnormally low) indicates inadequate perfusion relative to tissue needs, as usually caused by a significant decrease in cardiac output. A diffusion defect would lower ARTERIAL oxygen parameters, while withdrawing blood too rapidly via a pulmonary artery catheter would result in falsely high levels of mixed venous oxygen.
A postoperative patient is receiving volume control A/C ventilation at the rate of 12/minute with 5 cm H2O PEEP. With the ventilator settings unchanged, you measure and record the following the data:
These changes indicate which of the following?
- increased airway resistance
- decreased airway resistance
- increased lung compliance
- decreased lung compliance
The PIP is steadily rising, while the plateau pressure (and plateau - PEEP) remains relatively constant. Thus it is the difference between PIP and plateau pressures that is increasing. Because the difference between PIP and plateau pressures is the pressure due to flow resistance, the patient airway resistance (Raw) must be increasing.
You obtain an SpO2 measurement on a patient of 80%. Assuming this is an accurate measure of hemoglobin saturation, what is the patient's approximate PaO2?
- 40 torr
- 50 torr
- 60 torr
- 70 torr
The rule of thumb used to equate hemoglobin saturation to PO2 is "40-50-60 (PO2) = 70-80-90 (SpO2)." With a SpO2 of 80%, this patient's PO2 would be approximately 50 torr (mm Hg)
A patient is receiving volume controlled A/C ventilation. Which of the following changes would occur if the patient's compliance were to decrease?
- the expiratory time will increase
- the flow rate will decrease
- the system pressure will increase
- the delivered volume will decrease
When faced with either a decrease in compliance and/or an increase in resistance, a ventilator operating in the volume control mode will deliver a constant volume, but at a higher system pressure. Delivered volume will decrease only if a preset pressure limit causes the ventilator to prematurely end inspiration.
Upon reviewing the patient's chart, results of a chest x-ray indicate: "Complete opacification of the left chest with a shift of the trachea and mediastinum to the left." These findings are most consistent with which of the following?
- pneumothorax of the right lung
- atelectasis of the left lung
- diffuse pulmonary emphysema
- right-sided pleural effusion
Opacification of lung tissue on x-ray occurs due to consolidation or atelectasis. Moreover, if the area affected is large the trachea and mediastinum tend to shift towards the area of collapse, as seen here. Pneumothorax would cause hyperlucency on the affected side, with emphysema also showing hyperlucency, but more generally throughout all lung fields. Effusion is generally visualized on upright or sitting x-ray as affective only the basal areas, obscuring the costophrenic angle.
Based on the following blood-gas report, what is the most likely acid-base diagnosis?
pH = 7.20 PCO2 = 51 torr HCO3 = 19.5 mEq/L
- acute (uncompensated) respiratory acidosis
- combined respiratory & metabolic acidosis
- partially compensated metabolic acidosis
- partially compensated respiratory acidosis
The pH is low, indicating acidosis. The PCO2 is high, indicating hypoventilation and a respiratory acidosis. The low HCO3 indicates a metabolic acidosis. Since both the high PCO2 and low HCO3 are contributing to the low pH, the problem is a combined respiratory and metabolic acidosis.
Prior to drawing an arterial blood sample, you note that a patient has significantly elevated prothrombin and partial thromboplastin times (PT and PTT). Which of the following actions would be appropriate in this situation?
- obtain a venous sample instead of an arterial one
- allow extra time after the procedure to assure hemostasis
- use extra heparin in preparing the sampling syringe
- switch to a larger bore (18g) needle to obtain the sample
High PTs or PTTs indicate abnormally slow clotting, in which case extra time should be provided after the procedure to assure hemostasis at the puncture site.
While performing a patient-ventilator check, you note the following settings and parameters:
Exhaled tidal volume 650 mL Peak inspiratory pressure 35 cm H2O High pressure limit 60 cm H2O Low pressure alarm 20 cm H2O Low tidal volume alarm 500 mL Which of the following change would you make?
- decrease the high pressure limit to 45-50 cm H2O
- increase the set tidal volume to 800 mL
- decrease the low pressure alarm to 5 cm H2O
- increase the low tidal volume alarm to 600 mL
All alarm/limit settings in this example are acceptable except the high pressure limit, which should be set 10-15 cm H2O above the peak inspiratory pressure, in this case to 45 or 50 cm H2O.
You observe a patient receiving control mode ventilation "bucking" the ventilator with accessory muscles use and ribcage–abdominal paradox clearly visible. This will result in:
- decreased ventilatory drive
- increased physiologic deadspace
- increased work of breathing
- acute respiratory alkalosis
Control mode ventilation is poorly tolerated by most patients, often resulting in asynchronous breathing efforts and other signs of respiratory distress. Patient-ventilator asynchrony increases the work of breathing, and with it, the oxygen consumption of the respiratory muscles. It is for this reason that sedation or paralysis is often required when controlled ventilation is necessary. If possible a different mode of ventilation should be considered.
Which of the following describes the correct procedure for performing a modified Allen's test?
- compress both the radial and ulnar arteries then release the radial artery
- compress both the radial and ulnar arteries then release the ulnar artery
- compress both the radial and ulnar arteries then release both arteries at once
- compress the brachial artery only and observe circulation to the hand
To perform the modified Allen's test, 1) the patient clenches his hand into a tight fist while you apply pressure to both the radial and ulnar arteries; 2) the patient then opens his hand without fully extending it (the palm and fingers are blanched); 3) you maintain pressure on the radial artery while removing pressure on the ulnar artery. At this point you should observe flushing of the entire hand, indicating the presence of collateral circulation.
Which of the following patients has the most serious problem with the adequacy of oxygenation?
Patient FIO2 PaO2
A 1.00 85
B 0.70 90
C 0.40 95
D 0.28 65
Patient A, with a PaO2 of 85 mm Hg breathing 100% O2, has the most serious oxygenation problem. This equates to a PaO2/FIO2 (P/F) ratio of about 85, well below the 200 threshold indicating a severe impairment in oxygenation. Patient B has a P/F ratio of about 130, also unacceptable but not quite so bad. Patients C and D all have P/F ratios greater than 200.
Which of the following can be used to assess a patient's response to oxygen therapy?
1. blood gases analysis
2. pulse oximetry
3. patient inspection
- 1, 2 and 3
- 2 and 3 only
- 1 and 3 only
- 1 and 2 only
Once the desired amount of O2 is being given, the patient's response should be assessed. Depending on the objectives, assessment may include observation, inspection, analysis of arterial blood gases or pulse oximetry. If the response indicates that the objectives are not being met, then the amount of O2 being given should be adjusted and the patient reevaluated.