Critical Care Flashcards
What is the first step in resuscitation of a drowning victim?
rescue breathing
How should CVLs placed under emergency conditions be managed?
replaced within 24 hours at a new site
Why is propofol infusion syndrome associated with lactic acidosis?
propofol prevents mitochondria from using fatty acids as an energy source, so after glucose and amino acids stores are used up, lactic acidosis develops
What is the equation for arterial oxygen content?
CaO2 = (1.34 x Hgb x SaO2) + (0.003 x PaO2)
What is the equation for oxygen delivery?
DO2 = CaO2 x CO
What is the equation for oxygen consumption?
VO2 = 1.34 x (SaO2 - SmvO2) x Hgb x CO
OR
SmvO2 = SaO2 - [VO2/(1.34 x Hgb x CO)]
What is the oxygen extraction ratio?
ER = VO2/DO2
What is the alveolar gas equation?
PAO2 = FiO2(Patm - PH2O) - PaCO2/RQ
Patm = 760 mmHg
PH2O = 47 mmHg
RQ = 0.8
What factors affect the Hgb dissociation curve?
What is a normal value for VO2?
250 mL/min
What is dysoxia?
When oxygen consumption (VO2) decreases because oxygen delivery (DO2) is so low (i.e., no more oxygen can be extracted from what is delivered)
What is the Bohr effect?
Increased CO2 binding to Hgb reduces its affinity for O2 (i.e., a right shift in the hgb dissociation curve)
What is the Haldane effect?
oxygenated Hgb has a lower affinity for CO2 (facilitating CO2 unloading in the lungs)
deoxygenated Hgb has a higher affinity for CO2 and can act as a buffer
What is the law of LaPlace?
pressure = 2 x wall tension x wall thickness/radius
How is the majority of CO2 carried in the blood?
as bicarbonate in the plasma and RBCs
Where does carbonic anhydrase act to store CO2 as bicarbonate in the blood?
in endothelium and RBCs
What is the P/F ratio in ARDS?
Berlin criteria for PaO2/FiO2*
200-300 = mild ARDS
100-200 = moderate ARDS
< 100 = severe ARDS
*with PEEP of at least 5
What are the components of ARDSnet ventilation?
low tidal volumes: 6 mL/kg and titrated down
keep plateau pressures < 30
PEEP for oxygenation and reduced atelectrauma
permissive hypercapnea
What is airway pressure release ventilation?
Two levels of CPAP with long periods spent at the high level (oxygenation) and brief periods spents at the low level (ventilation). Spontaneous respiration remains possible at both levels.
What is an RSBI? How is it used in the ICU?
rapid shallow breathing index = frequency*/TV**
*frequency in breaths/min
**tidal volume in liters
RSBI < 100 is predictive of successful extubation
What is the risk of ETTs left in place for more than 2-3 weeks?
subglottic stenosis
What are the SIRS criteria?
hypo/hyperthermia
tachypnea
tachycardia
high or low WBCs or left shift
What should be done if a patient aspirates on intubation?
- suction the oropharynx
- place the ETT
- suction the lungs (to prevent pushing particulate matter into smaller airways)
- begin ventilation
What is negative inspiratory force? What is the minimum value necessary for extubation?
a test of inspiratory force
-20 to -25 cm H2O is minimum for extubation
What are the independent risk factors for stress ulcers requiring H2 blocker prophylaxis?
mechanical ventilation for >48 h
coagulopathy (plt < 50, INR > 1.5, PTT > 2x control)
What is the most distinguishing receptor difference between norepinephrine and epinephrine?
only epinephrine is a clinically significant ß2 agonist
Which causes a greater increase in diastolic BP, norepinephrine or epinephrine?
norepinephrine
*ß2 agonist effects of epinephrine cause vasodilatation in some vascular beds, resulting in minimal change in diastolic BP*
What receptors do the enantiomers of dobutamine agonize?
one enantiomer is a ß1 >>> ß2 agonist
one enantiomer is an a1 agonist
What is increased dromotropy?
increased conduction speed within the heart (particularly the AV node)
What is lusitropy?
diastolic relaxation achieved by decreasing cytosolic Ca2+ levels via SERCA-mediate Ca2+ uptake into the sarcoplasmic reticulum
How do alpha adrenergic receptors and beta adrenergic recpetors differ in the way they increase cytosolic calcium?
alpha adrenergic receptors: activate Gaq going through PLC > DAG + IP3 > release of intracellular Ca2+ stores
beta adrenergic receptors: activate Gas going through adenylate cyclase > cAMP > PKA and increased intracellular Ca2+
How does inhaled NO result is smooth muscle relaxation?
NO > guanylate cyclase > cGMP > smooth muscle relaxation
*PDE-5 breaks down cGMP and is inhibited by sildenafil*
What is nesiritide, and how is it useful in treating decompensated heart failure?
recombinant BNP
activates guanylate cyclase > cGMP > vasodilatation, thus encouraging forward flow
How can nitroprusside affect hemoglobin?
oxidizes the the heme iron from the 2+ to 3+ state, creating met-hemoglobin
breaks down into CN-, which can bind met-hemoglobin and create cyan-met-hemoglobin
How does cyanide toxicity result in acidosis?
CN- binds to cytochrome oxidase, preventing ATP production through the electron transport chain, necessitating anaerobic metabolism a resultant lactic acidosis
What happens to mixed venous O2 during cyanide toxicity?
increases due to inability of tissues to utilize oxygen in the electron transport chain
How is cyanide toxicity treated?
Increasing the “sinks” for cyanide:
1) increasing methemoglobin with sodium nitrite
2) sodium thiosulfate, generating sodium thiocyanate which can be excreted by the kidneys
Which vasodilator is associated with improved subendocardial perfusion during periods of ischemia?
nitroglycerin
How is methemoglobinemia treated?
methylene blue
