Respiratory and Cardiovascular Physiology

Respiratory and Cardiovascular Physiology

Anne Warner, MD, Harsh Desai, MD, and Frederick Giberson, MD

Department of Surgery, Christiana Care Health Care System, Newark, DE, USA

  1. In a patient who develops ARDS, the addition of PEEP in optimizing ventilatory support has which of the following effects?

    1. Maximal alveolar recruitment with inspiration.
    2. Decreasing mean airway pressure.
    3. Decreased right ventricular afterload.
    4. Improvement of functional residual capacity (FRC).
    5. Increasing left ventricular afterload.

    The use of positive end‐expiratory pressure (PEEP) as part of the ARDS ventilatory strategy has been shown to improve the functional residual capacity (FRC) above the closing pressure of alveoli, thereby preventing alveolar collapse. PEEP maximizes alveolar recruitment at end expiration, not inspiration. The addition of PEEP increases inflation pressure, thereby increasing peak alveolar pressure and ultimately mean airway pressure. Increased PEEP increases pulmonary vascular resistance impeding right vascular stroke volume and thereby left ventricular filling. It also decreases the transmural pressure – the pressure needed to be overcome in order to eject stroke volume – thereby decreasing left ventricular afterload.

    Answer: D

    Briel M, Meade M, Mercat A, et al. Higher vs lower positive end‐expiratory pressure in patients with acute lung injury and acute respiratory distress syndrome. JAMA. 2010; 303 (9): 865–873.

    Schmitt JM, Viellard‐Baron A, Augarde R, et al. Positive end‐expiratory pressure titration in acute respiratory distress syndrome patients: impact on right ventricular outflow impedance evaluated by pulmonary artery Doppler flow velocity measurements. Crit Care Med. 2001; 29: 1154–1158.

  2. Which of the following is NOT a component of the inflammatory cascade leading to lung injury in ARDS?

    1. Injury to type I and type II epithelial cells within the alveoli.
    2. Capillary endothelial dysregulation resulting in recruitment of neutrophils.
    3. Sequestration of predominantly lymphocytes within the pulmonary microcirculation.
    4. Release of cytoplasmic granules from neutrophil degranulation.
    5. Exudation of protein‐rich fluid into the distal airspaces.

    The inflammatory cascade in ARDS is thought to be initiated by activation of circulating neutrophils by the release of IL‐1 and TNF by macrophages and monocytes. Endothelial dysregulation attracts and retains neutrophils with subsequent sequestration within the pulmonary microcirculation. This occurs through adhesion of neutrophils to endothelial cells and neutrophil stiffening. Neutrophils then move into lung parenchyma and degranulate propagating injury to the type I and II epithelial cells within the alveoli allowing for exudation of protein‐rich fluid, erythrocytes, and platelets into the distal airspaces.

    Answer: C

    Abraham E. Neutrophils and acute lung injury. Crit Care Med. 2003; 31(supp): S195–S199.

  3. A 27‐year‐old man is undergoing exploratory laparotomy after presenting with a gunshot wound to the left flank. He is currently hemodynamically stable. The operative team has concern for possible ureteral injury and asks that methylene blue be administered for identification of possible urine leak. Shortly after administration, the patient desaturates to SpO2 of 82% with remaining hemodynamics remaining appropriate. What is the management for the etiology of this patient’s desaturation event?

    1. Perform a left tube thoracostomy.
    2. Immediate bronchoscopy.
    3. Abort the procedure.
    4. Manual bag mask ventilation.
    5. Watch and wait without immediate intervention.

    The multiple uses of methylene blue have been established including use in methemoglobinemia treatment as well as potential use in vasoplegic syndrome. In the operating room, methylene blue is often used to evaluate renal function and for potential leak in urologic procedures. However, one of the adverse effects of methylene blue is to decrease pulse oximetry readings.

    Pulse oximeters are made up of a side containing two light emitting diodes that emit at 660nm and 940nm detecting deoxygenated and oxygenated hemoglobin, respectively. The light is captured after passing through the arteries in the finger by a probe on the other side of the oximeter. This is then passed through and alternating current amplifier to block nonpulsatile wave forms from veins. The ratio of oxygenated to total hemoglobin is used to calculate SpO2. When administered, methylene blue transiently decreases the detected oxygenated hemoglobin as the methemoglobin fraction, usually a small percentage of total circulating hemoglobin, increases until processed out through the renal system. Therefore, for this patient, aborting the procedure is not necessary. The desaturation is transient and not caused by mucus plugging, which may require bronchoscopy, pneumothorax, which would require tube thoracostomy, or significant atelectasis, which may require bag mask ventilation.

    Answer: E

    Clifton J and Leikin JB . Methylene blue. Am J Ther. 2003; 10(4): 289–291.

    Rong LQ, Mauer E, Mustapich TL, et al. Characterization of the rapid drop in pulse oximetry reading after intraoperative administration of methylene blue in open thoracoabdominal aortic repairs. Anesth Analg. 2019; 129(5): 142–145.

  4. A 65‐year‐old woman is in the post‐anesthesia care unit following elective inguinal hernia surgery. Shortly after arriving, she is noted to have increasing shortness of breath and wheezing requiring administration of a nebulized beta agonist. The patient has a known history of COPD. Which of the following pulmonary function test patterns would be expected in a patient with COPD?

    1. FEV1 decreased; FVC decreased/normal; FEV1/FVC ratio decreased.
    2. FEV1 increased; FVC decreased; FEV1/FVC ratio increased.
    3. FEV1 decreased/normal; FVC decreased; FEV1/FVC ratio normal.
    4. FEV1 increased; FVC increased; FEV1/FVC ratio increased.
    5. FEV1 decreased; FVC decreased; FEV1/FVC ratio decreased.

    Pulmonary function testing is often used in preoperative evaluation, particularly prior to thoracic procedures. These can be used, in addition to history and exam, to identify obstructive versus restrictive lung processes. Three of the important measures are the forced vital capacity (FVC) – the total volume forcefully expired after maximal inspiratory effort; forced expiratory volume in 1 second (FEV1) – the volume of air forcefully expired after maximal inspiratory effort in 1 second; the FEV1/FVC ratio. In evaluating spirometry results, first step is to interpret the FEV1/FVC ratio. If less than the lower limit of normal, an obstructive pattern is suspected. If greater than lower limit of normal, the FVC is evaluated and if less than lower limit of normal, a restrictive process is considered. Obstructive diseases include COPD, asthma, and emphysema while restrictive lung diseases include neuromuscular disorders and interstitial lung diseases.

    Answer: A

    Barreiro TJ and Perillo I . An approach to interpreting spirometry. Am Fam Physician. 2004; 69(5): 1107–1115.

    Pellegrino R, Viegi G, Brurasco V, et al. Interpretative strategies for lung function tests. Eur Respir J. 2005; 26:948–968.

  5. You are caring for a patient in your SICU who is post total abdominal colectomy and end ileostomy. Ileostomy output has been in excess of 1.5L daily with concomitant acute kidney injury noted on basic metabolic panel with continued required resuscitation. Which of the following represents the primary relationships between alveolar pressure (PA), pulmonary arterial pressure (Pa), and pulmonary venous pressure (Pv) within the lung in a state of hypovolemia?

    1. Pa > Pv > PA and PA > Pv > Pa
    2. PA > Pv > Pa and Pa > PA > Pv
    3. Pa > PA > Pv and PA > Pa > Pv
    4. PA > Pa > Pv and Pv > Pa > PA
    5. Pa > PA > Pv and Pa > Pv > PA

    The relationship between alveolar pressure, pulmonary arterial pressure, and pulmonary venous pressure represents the West zones of the lung. Zone 1, not seen in normal physiology, signifies alveolar dead space secondary to increased alveolar pressure causing arterial collapse (PA > Pa > Pv). Zone 2 represents pulsatile perfusion (Pa > PA > Pv) typically the upper portions of lung in a typical, upright person. Zone 3 represents the bulk of healthy lung tissue with continuous blood flow without extrinsic compression (Pa > Pv > PA). In a hypovolemic individual, as in this patient, decreased circulating volume converts Zone 3 tissue to Zone 1 and 2, increasing dead space.

    Answer: C

    West JB and Dollery CT . Distribution of blood flow and the pressure‐flow relations of the whole lung. J Appl Physiol. 1965; 20(2): 175–183.

    For questions 7–10, use the following figure to match the clinical scenario to the appropriate flow volume loop:

    Schematic illustration of a graph showing the ploto f volume versus flow.

  6. A 42‐year‐old man presents to the ICU following intubation for COPD exacerbation.
  7. An 18‐year‐old woman diagnosed on bronchoscopy with intratracheal lipoma.
  8. A recovered COVID‐19 patient who develops tracheal stenosis following a 2 week intubation.
  9. A 75‐year‐old male who undergoes emergent intubation following development of angioedema found to have R vocal cord paralysis.

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Dec 15, 2022 | Posted by in CRITICAL CARE | Comments Off on Respiratory and Cardiovascular Physiology

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