1/13/12 1 THE EMERGENCY CLINICIAN’S APPROACH TO THE FELINE RESPIRATORY DISTRESS PATIENT Gretchen Lee Schoeffler, DVM, DACVECC Emergency & Critical Care Overview ! Definitions ! The 5 causes of hypoxemia ! The 8 causes of respiratory distress ! The dyspneic cat ! Case examples ! Summary Definitions ! Symptom ! Subjective evidence of disease or physical disturbance observed by the patient ! Clinical sign ! An objective evidence of disease as observed and interpreted by the physician (or vet!) rather than by the patient or lay observer ! Dyspnea ! Symptom ! Patient’s perception of difficult or labored breathing ! Respiratory distress ! Clinical sign ! Our perception of difficult or labored breathing Medline Plus Medical Dictionary, Merriam-Webster Respiratory Function ! Ventilation - ability to move air into and out of the alveoli ! Reflected in the partial pressure of carbon dioxide dissolved in arterial blood (PaCO 2 ) as measured on a blood gas ! Oxygenation - ability to get oxygen into the blood ! Reflected in the partial pressure of oxygen dissolved in arterial blood (PaO 2 ) as measured on a blood gas ! Reflected in the percent saturation of arterial hemoglobin with oxygen SaO 2 (SpO 2 ) PaO 2 SaO 2 Implication 5 Causes of Hypoxemia ! Decreased FiO 2 ! Anesthesia ! Hypoventilation ! Neurologic ! Anesthesia/sedation ! Obstruction ! Airway disease ! Diffusion Impairment ! Pulmonary fibrosis ! Interstitial disease (edema/hemorrhage) ! V/Q Mismatch ! Alveolar disease ! Pulmonary hypertension ! Shunt (V/Q = ZERO) ! Atelectasis ! Severe alveolar disease ! No response to O 2 supplementation Respiratory Distress - Signs ! Increased respiratory rate and/or effort ! Abnormal posture (orthopnea) ! Pallor ! Vasoconstriction due to catecholamine ! Anemia ! Cyanosis ! 3-5 g/dl of deoxygenated hemoglobin ! With normal HCT, SpO 2 = 73-78%, PaO 2 = 39-44 mmHg ! With LOW HCT, SpO 2 is even LOWER ! If due to respiratory disease ! Hypoxemia: PaO 2 < 60 mmHg ! Hypercapnia: PaCO 2 > 50 mmHg
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THE EMERGENCY CLINICIAN’S APPROACH TO THE FELINE RESPIRATORY DISTRESS PATIENT
Gretchen Lee Schoeffler, DVM, DACVECC Emergency & Critical Care
Overview
! Definitions ! The 5 causes of hypoxemia ! The 8 causes of respiratory distress ! The dyspneic cat ! Case examples ! Summary
Definitions
! Symptom ! Subjective evidence of disease or physical disturbance
observed by the patient ! Clinical sign
! An objective evidence of disease as observed and interpreted by the physician (or vet!) rather than by the patient or lay observer
! Dyspnea ! Symptom ! Patient’s perception of difficult or labored breathing
! Respiratory distress ! Clinical sign ! Our perception of difficult or labored breathing
Medline Plus Medical Dictionary, Merriam-Webster
Respiratory Function
! Ventilation - ability to move air into and out of the alveoli ! Reflected in the partial pressure of carbon dioxide dissolved in
arterial blood (PaCO2) as measured on a blood gas
! Oxygenation - ability to get oxygen into the blood ! Reflected in the partial pressure of oxygen dissolved in arterial
blood (PaO2) as measured on a blood gas ! Reflected in the percent saturation of arterial hemoglobin with
! Flow by O2 and MINIMIZE STRESS! ! Thoracocentesis is a “twofer”
! Therapeutic ! Diagnostic
! Options ! Needle ! Catheter ! Butterfly
4. Pleural Space - Tx
! Indications for emergency thoracostomy tube ! Tension pneumothorax
" Disruption of lung " Tissue acting as “ball valve” " Air enters thorax on
each inspiration ! Continuous pneumothorax
" Hole in lung open to pleural space
" Hole in chest open to pleural space
! Pyothorax " Risk of sepsis " Evacuate abscess, just as if it were in some other location
! Once stable, place in O2
5. Chest Wall
! Characteristic Findings ! Palpation of chest wall defect ! Pain on palpation ! Identification of a flail segment
! Cause of Distress ! Hypoventilation ! Inability to expand lungs
! Blood Gas ! Hypercarbia ! ±Hypoxemia
5. Chest Wall - DDx
! Flail segment is the only chest wall disease that can cause respiratory distress ! Penetrating chest wound = pleural space ! Rib fracture = look alike (pain)
! Two fractures on same rib ! Compromises ventilation
5. Chest Wall - Diagnosis
! Radiographs ! Visualization
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5. Chest Wall - Tx
! Put in an O2 cage and MINIMIZE STRESS! ! Put affected side down
! Up lung ventilates better ! Fractures stabilized
! ANALGESIA!! ! Opiates
! Place bandage ! Consider surgical
stabilization
6. PTE
! Characteristic Findings ! Hypoxemia
" Often unresponsive to O2
! Cause of Distress ! Hypoxemia ! Presence of V/Q mismatch
and SHUNT ! Blood Gas
! Hypoxemia ! Hypocapnia
6. PTE - Pathophysiology
! A clot lodges in a pulmonary vessel ! This causes a high V/Q condition
! Blood is shunted to other areas of lung ! Proposed mechanisms of hypoxemia
1. Decreased surfactant production in affected area, alveoli collapse, leads to low V/Q when reperfused
2. Production of inflammatory mediators leads to lung injury and low V/Q
3. Increased PA pressure may increase intrapulmonary and intracardiac shunt
6. PTE - Diagnosis
! Diagnosis of exclusion ! Look for reason for hypercoagulability