Critical-Care Flashcards
Rx: ARDS
- Low volume
- Prone position
- NM blockade Exp: only interventions known to help
01-Critical-Care
- Acute organ failure
- Acute respiratory failure
- Shock
- Poisoning
Critical care medicine focuses on the management of acute organ failure and other life-threatening illnesses. Treatment of acute respiratory failure and its common causes, including pneumonia, chronic obstructive pulmonary disease (COPD), and the acute respiratory distress syndrome (ARDS), is an important component of critical care management. The timely diagnosis and rapid treatment of septic, cardiogenic, and hypovolemic shock are crucial to the survival of patients with these life-threatening conditions. Recent emphasis on minimizing and preventing the complications of critical care therapies is also highlighted here. Because toxin exposures often require acute management in a critical care setting, a review of the major types of toxin exposures is included.
Acute-respiratory-failure
Two pathophysiologic causes of acute respiratory failure
Meta: pathophysiologic cause
Failure to:
- Oxygenate
- Ventilate
Acute-respiratory-failure.Hypoxemic
Inadequate Pao2 despite high levels of supplemental inspired O2
Acute-respiratory-failure.Hypoxemic
Measures of oxygenation
- SaO2
- PaO2
- A-a gradient
- PaO2/FiO2
- A-a oxygen ratio
- Oxygenation index
The arterial oxygen saturation (SaO2), arterial oxygen tension (PaO2), alveolar to arterial (A-a) oxygen gradient, and the PaO2/fraction of inspired oxygen (FiO2) ratio are common measures. Alternatively, the A-a oxygen ratio and the oxygenation index can be used
Acute-respiratory-failure.Hypoxemic
Normal PaO2
Conventionally: PaO2 <80 mmHg
Similar to oxygen saturation, an abnormal PaO2 has not been precisely defined because a threshold below which tissue hypoxia predictably occurs has not been identified. However, it seems reasonable to consider a PaO2 <80 mmHg abnormal, although the value should not be considered in isolatio
Acute-Respiratory-Failure.Hypoxemic.AetioCauses
- RL shunt
- VQ mismatch
- Reduced diffusion capacity
- Alveolar hypoventilation
- Low FiO2
- Right-to-left shunt: (e.g., pulmonary AVMs, intracardiac right-to-left shunts), or space-filling pulmonary parenchymal lesions (e.g., atelectasis or pneumonia). Will not correct with supplemental oxygen.
- ▪Ventilation-perfusion () mismatch: Regional imbalances between blood flow and ventilation (e.g., pulmonary embolism or lung parenchymal disease); corrects, partially or completely, with the addition of supplemental oxygen
- Reduced diffusion capacity (e.g., interstitial lung disease, emphysema); may be minimal at rest; more pronounced with exercise
- Alveolar hypoventilation (e.g., from central nervous system [CNS] depression, neuromuscular disease, or chest wall abnormality); the only type of hypoxic failure with a normal alveolar-arterial (A-a) gradient
- Low fraction of inspired oxygen (Fio2) (e.g., high altitude)
Acute-Respiratory-Failure.Hypoxemic
The only type that has a normal A-a gradient
Alveolar hypoventilation
(e.g., from central nervous system [CNS] depression, neuromuscular disease, or chest wall abnormality); the only type of hypoxic failure with a normal alveolar-arterial (A-a) gradient
Acute-respiratory-Failure.Hypoxemic.VQ-Mismatch
Mechanism, examples and effect of oxygenation
Regional imbalances between blood flow and ventilation
Eg: PE or parenchymal disease;
Corrects: partially or completely, with the addition of supplemental oxygen
Acute-Respiratory-Failure.Hypoxemic.RL-shunt
Mechanism, example, effect of O2
- Pathologic vascular communications. Eg: pulmonary AVMs, intracardiac right-to-left shunts
- Space-filling parenchymal lesions. Eg: atelectasis or pneumonia.
Will not correct with supplemental oxygen.
I think the reason is that in this situation the blood never gets a chance to be oxygenated. Raising alveolar O2 in other parts of the lung does not help. In the case of a P
Acute-Respiratory-Failure.Ventilatory.EtioCauses
Meta: EtioCause
High Paco2 +decreased pH
- Increased CO2 production. Eg: sepsis, overfeeding, thyrotoxicosis
- Decreased CO2 elimination
- Decreased minute ventilation. Eg: CNS depression
- Decreased alveolar ventilation. Eg: COPD, increase in dead space from pneumonia or large PE
Acute-Respiratory-Failure.Cyanosis
Cyanosis occurs when deoxyhemoglobin level is greater than 5 g/dL, Sao2 around _%
Cyanosis occurs when deoxyhemoglobin level is greater than 5 g/dL, Sao2 around 67%
Pulse-oximeter is unreliable when:
- Steep part of O2-dissociation curve: ie < 90%
- Carboxyhemoglobin or methemoglobin
- Shock
- Nail polish
- Pigmented skin
Mechanical-ventilation.Indications
- PaO2 < 60 to 70 mm Hg and FiO2 > 80%
- PaCO2 ≥45 mm Hg and pH <7.35
Other indications:
- high respiratory rate with use of accessory muscles
- Inability to protect airway
Measures-of-oxygenation
- Arterial oxygen saturation (SaO2)
- Arterial oxygen tension (PaO2)
- A-a oxygen gradient
- PaO2/FiO2 ratio
- a-A oxygen ratio
- Oxygenation index
Acute-respiratory-failure.Hypoxemic
Goal of O2 therapy
SaO2 > 88%
or
PaO2 >55 mm Hg
Acute-Respiratory-Failure.Mechanical-Ventilation
Modes
- Volume cycled
- AC
- SIMV
- Pressure cycled
- PRVC
- PS
Acute-Respiratory-Failure.Mechanical-Ventilation
AC
Assist control: Patient receives a set tidal volume for every initiated breath. A preset number of breaths per minute prevents hypoventilation
SIMV
Synchronized intermittent mandatory ventilation (SIMV): Patient receives a set tidal volume for only a designated number of breaths per minute. Additional patient-initiated breaths have no support
PRVC
Pressure-regulated volume control (PRVC): Patient receives set tidal volume for every initiated breath as long as the pressure required to deliver remains below a preset value.