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9 Cards in this Set

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Why obtain blood gases?
Assess the oxygenation capacity of the cardiopulmonary system
Assessment of oxygen pressure to guide therapy
Assessment of adequacy of ventilation
Assessment of acid-base status
Assessment of Hb concentration, electrolytes and glucose
Oxygen Content in the Blood
You determine this via summing the diffused oxygen in the blood and the oxygen bound to Hb;
diffused blood is low
Weakness of Oxyhemoglobin dissociation curve?
It assumes that Hb is functioning properly.
Oxygen delivery to tissues
Your blood delivers almost 1L/min but tissues only use 270mL/min
Ways to measure Hg saturation?
Co oximeter - gold standard, but not practical to be in each OR, measures fractional Hb; limited by # of wavelengths of light, can't detect SulfHb

Pulse oximeter - simple, recorded every 5 minutes, although does not record if Hb is afunctional; measure functional Hb; false high reading w/ pts with CO poisoning and methemoglobin





Intravascular - measures functional Hb,

Blood Gas machine
Carboxyhemoglobin
CO competes with O2 for binding site
Decreased oxygen delivery

Clinical signs:
5% COHb - Impaired visual and temporal discrimination
8% COHb - Alterations in mood and sleep
loss of short term memory, mild hypotension, sinus tachacardia, pvc’s
20% COHb - Headache and weakness
atrial flutter/fibrillation, T-wave inversion,
40% to 60% COHb - unconsciousness and death

(Smokers normal have 2-4%)
Methemoglobin
Fe++ is oxidized to Fe+++
Fe+++ cannot bind O2
One Fe+++ molecule causes the affinity of the other 3 molecules of Fe++ to increase their binding affinity for oxygen - not releasing it to tissue.
Oxygen content is reduced
Oxygen delivery may be reduced without compensatory increase in cardiac output

sources of methhemoglobin

Local Anesthetics
benzocaines (topical anesthetics)
Drugs
primaquine (anti-malarial)
dapsone (treating Pneumocystis Carinii)
nitrites and nitrates (diet or drugs)
nitroglycerine
sodium nitroprusside
Smoke inhalation
Clinical signs and symptoms of MethHb
0.6% - 1.5% MetHb - normal
10% - 15% MetHb - cyanosis is obvious
blood is chocolate brown in color
20% - 45% MetHb - dizziness, shortness of breath, fatigue, lethargy, headache and syncope
45% - 55% MetHb - depressed consciousness
55% - 70% MetHb - seizures, coma, dysrhythmias
> 70% MetHb - results in Death

Blood is chocolate brown

Treated w/ Methylene Blue
Sulfhemoglobin
Sulfur atom incorporated into the porphyrin ring
incapable of binding oxygen at that site
green pigmentation
favors sickling in HbS
Decreased oxygen content
Decreased oxygen delivery without cardiovascular compensation

Mainly found in industrial compounds and some drugs

Sign = cyanosis

No treatment except transfusion