Acute Respiratory Distress Syndrome
Case Studies 2024-2025. Questions &
Correct Verified Answers. Graded A
A-a Gradient – ANS 1. *A = alveolar* pO2. -Obtained from
*alveolar gas equation:* *pAO2 = FiO2 (Patm - pH2O) -
paCO2/RER* 2. *a = arterial* pO2. -Measured from ABG. -*A
normal A-a gradient should be ~1/3 of a person's age*. -If much
*higher* than this, *indicates bad respiratory impairment*.
Acute Respiratory Distress Syndrome (ARDS) – ANS Condition in
which *fluid* collects *in the lungs' air sacs*, depriving organs
of oxygen. ARDS vs. Cardiogenic (Heart-Failure Induced)
Pulmonary Edema – ANS In *ARDS*, there will be *no elevated
left atrial pressure or elevated pulmonary capillary pressure*
<18 mmHg. -ECHO will also show no evidence of CHF.
PG 1
, Common Physiologic Changes in ARDS – ANS
1. *Stiff (non-compliant) lungs* that are hard to inflate. -This
increases the work of breathing, which requires more energy
and thus increases the need for more oxygen.
2. Damaged *alveoli filled with proteinaceous fluid, cellular
debris, and hyaline membranes*. -These all lower the V/Q ratio
(less ventilation).
3. *Increased shunting* of blood through the lungs without
oxygenation or ventilation (right -> left shunt).
4. *Increased* pulmonary vascular *resistance due to hypoxic
pulmonary vasoconstriction*.
5. *Increased dead space*:tidal volume ratio.
6. Reduced functional residual capacity, leading to *atelectasis*
(collapse of alveoli): a. Edema in the lungs further compresses
the alveoli -> collapse. b. *CPAP (continous positive airway
pressure) or PEEP (positive end-expiratory pressure) are both
used to keep the alveoli open and prevent collapse with each
PG 2
Case Studies 2024-2025. Questions &
Correct Verified Answers. Graded A
A-a Gradient – ANS 1. *A = alveolar* pO2. -Obtained from
*alveolar gas equation:* *pAO2 = FiO2 (Patm - pH2O) -
paCO2/RER* 2. *a = arterial* pO2. -Measured from ABG. -*A
normal A-a gradient should be ~1/3 of a person's age*. -If much
*higher* than this, *indicates bad respiratory impairment*.
Acute Respiratory Distress Syndrome (ARDS) – ANS Condition in
which *fluid* collects *in the lungs' air sacs*, depriving organs
of oxygen. ARDS vs. Cardiogenic (Heart-Failure Induced)
Pulmonary Edema – ANS In *ARDS*, there will be *no elevated
left atrial pressure or elevated pulmonary capillary pressure*
<18 mmHg. -ECHO will also show no evidence of CHF.
PG 1
, Common Physiologic Changes in ARDS – ANS
1. *Stiff (non-compliant) lungs* that are hard to inflate. -This
increases the work of breathing, which requires more energy
and thus increases the need for more oxygen.
2. Damaged *alveoli filled with proteinaceous fluid, cellular
debris, and hyaline membranes*. -These all lower the V/Q ratio
(less ventilation).
3. *Increased shunting* of blood through the lungs without
oxygenation or ventilation (right -> left shunt).
4. *Increased* pulmonary vascular *resistance due to hypoxic
pulmonary vasoconstriction*.
5. *Increased dead space*:tidal volume ratio.
6. Reduced functional residual capacity, leading to *atelectasis*
(collapse of alveoli): a. Edema in the lungs further compresses
the alveoli -> collapse. b. *CPAP (continous positive airway
pressure) or PEEP (positive end-expiratory pressure) are both
used to keep the alveoli open and prevent collapse with each
PG 2
