EMCrit.org | Emergency Critical Care

PvCO2 less than 45 on room air rules out hypercarbia (Journal of Emergency Medicine
Volume 28, Issue 4 , May 2005, Pages 377-379)

Central (SVC) pH, bicarb, BE, and lactate agrees with arterial (Emerg Med J 2006;23:622)

Lactate

A normal venous lactate rules out an elevated arterial, an elevated venous does not necessarily correlate with an elevated arterial. Tourniquet time may contribute to this inaccuracy. If you do venous lactate, draw as first tube and put on ice immediately. (Annals EM 1997. Vol 29. Number 4)

Relative hyperlactatemia is still associated with mortality (>0.75 mmol/L) Crit Care 2010;14:R25

reanaylyzed in healthy subjects. no effect from tourniquet time or room temp holding if analyzed in 15 min or less (Acad Emerg Med 2007;14:587)

both arterial and venous lactates performed within 10 minutes.
Collected data included injury mechanism, demographics,
admission vital signs, disposition, length of stay, hospital
outcomes and injury severity score. The mean arterial lactate
concentration was 3.11 mmol/L (SD 3.45, 95% CI 2.67-3.55)
and the mean venous lactate concentration was 3.43 mmol/L
(SD 3.41, 95% CI 2.96-3.90) demonstrating no significant
differences between the two sources of blood lactate. The
correlation between venous and arterial lactate levels was 0.94 (Lavery RF, Livingston DH, Tortella BJ, Sambol JT, Slomovitz BM, Siegel JH. The utility
of venous lactate to triage injured patients in the trauma center. J Am Coll Surg.
2000;190(6):656-664.)

Adams et al. included all ED
patients over a seven month time period in whom a lactate
level was measured for any reason. They considered an AG
>12 abnormal and conducted sensitivity analyses of the AG
for detecting the presence of a lactate >2.5 mmol/L. The AG
was 52.8% sensitive, 81.0% specific with a negative predictive
value of 89.7% for the prediction of lactic acidosis.(

Nguyen HB, Rivers EP, Knoblich BP, et al. Early lactate clearance is associated
with improved outcome in severe sepsis and septic shock. Crit Care Med.
2004;32(8):1637-1642.

In ARDS, the lung may be the major source of lactate Intens Care Med 2004;30:817

Whole blood venous point-of-care lactate concentrations in healthy subjects do not change significantly
over 15 minutes at either 18C or 238C, and the use of a tourniquet has no appreciable effect on
lactate concentrations. (Acad Emerg Med 2007; 14:587–591)

the utility of venous lactate to triage pts in trauma (J Am Coll Surg 2000;190(6):656)
VLAC equiv to ALAC; >=2 predicts need for ICU, etc.

another study correlating lactates with mortality (Inten Care Med 2007;33:1892)

PECO2 is the CO2 in expired gas, but not same as ETCO2, it must be measured by resp therapy

Normal Aa gradient increases 5-7 mmHG for every 10% increase in FiO2 due to the overcoming of hypoxic vasoconstriction opening blood flow to poorly ventilated lung areas.

In disorders with intrapulmonary shunt (pneumonia, ards), the mixed venous O2 will be a larger determinant of PaO2 and should be evaluated.

Increased-V/Q Abnormality and/or systemic supply/demand imbalance (DO2/VO2). Obtain a SvO2 or CvO2.

Low-Systemic DO2/VO2 imbalance. Either decreased oxygen delivery (anemia, Low CO) or increased consumption (hypermetabolic state)

.
In such cases, there is a dissociation between
the condition of central venous blood, with a
high partial pressure of arterial carbon dioxide and a
low pH, and that of the systemic arterial blood, with
a low carbon dioxide tension and an alkalemic pH;
this dissociation is due to the combination of low pulmonary
perfusion and normal ventilation, and this
condition is called pseudorespiratory alkalosis.
16

Hypocapnia may cause
or aggravate cellular or tissue ischemia by both decreasing
the cellular oxygen supply and increasing the
cellular oxygen demand (Fig. 3). Although hypocapnia
induced by hyperventilation may increase alveolar
oxygen tension, multiple important pulmonary effects
of hypocapnic alkalosis (e.g., bronchoconstriction,
48
attenuation of hypoxic pulmonary vasoconstriction,
49
and increased intrapulmonary shunting
49
) result in a
net decrease in the partial pressure of arterial oxygen.

Because both hypocapnia and alkalosis cause a leftward
shift of the oxyhemoglobin dissociation curve,
off-loading of oxygen at the tissue level is restricted.
50
In addition, hypocapnia causes systemic arterial
vasoconstriction, decreasing the global and regional
oxygen supply and compounding the reduction in
the delivery of oxygen to tissue

the time required for equillibration of PaO2 after PEEP adjustment is 20 minutes (Crit Care Med 2005;33(5):995)

PECO2 is the CO2 in expired gas, but not same as ETCO2, it must be measured by resp therapy

Shunt Fraction

Place pt on 100% O2 for 5-15 minutes. The Aa Gradient is entirely from shunt. Dive Aa by 20 to get the shunt fraction

Normal Aa gradient increases 5-7 mmHG for every 10% increase in FiO2 due to the overcoming of hypoxic vasoconstriction opening blood flow to poorly ventilated lung areas.

In disorders with intrapulmonary shunt (pneumonia, ards), the mixed venous O2 will be a larger determinant of PaO2 and should be evaluated.

Increased-V/Q Abnormality and/or systemic supply/demand imbalance (DO2/VO2). Obtain a SvO2 or CvO2.

Low-Systemic DO2/VO2 imbalance. Either decreased oxygen delivery (anemia, Low CO) or increased consumption (hypermetabolic state)

the time required for equilibration of PaO2 after PEEP adjustment is 20 minutes (Crit Care Med 2005;33(5):995)

Lab Tubes

What's in those vacuum-filled blood sample tubes?

Worth knowing:

Red-top: Nothing. The blood will clot, and we'll extract the serum. Used for most routine chemistries. Nowadays most "red top" tubes are red-and-gray top tubes, with a silicone separator

Purple-top: EDTA (calcium-chelating anticoagulant). Best for blood cell counting.

Blue-top: Citrate (calcium-chelating anticoagulant, readily neutralized). Best for routine coagulation studies.

Gray-top: Fluoride-oxalate. Inhibits glycolytic enzymes. Best for glucose and routine toxicology.

Green-top: Heparin anticoagulant. Less popular than the others.

*Navy-blue top: Trace-metal-free

*Yellow top: Acid citrate dextrose. Tests that must be kept at room temperature and shipped to a reference lab. PCR's and reference-immunology especially. (NOTE: Some yellow-top tubes are silicone-barrier-gel only).

Healthy serum lacks clotting factors I, II, V, VII, and XIII

"Routine Screening"

Contents of tubes

A large SST vacutainer.

The tubes may contain additional substances that preserve the blood for processing in the medical laboratory. Using the wrong tube may therefore make the blood sample unuseable.

The substances may include anticoagulants (EDTA, lithium citrate , heparin) or a gel with intermediate density between blood cells and blood plasma. When the tube is centrifuged, the blood cells sink to the bottom of the tube, are covered by a layer of the gel, and the plasma (or serum) is left on top. The gel enables the tube to be tipped upside-down, and transported without the blood cells remixing with the plasma.

The meaning of the different colors are standardized across manufacturers. For more details on the meaning of these different colors, see ^[1], ^[2], or the bottom of ^[3].

The Order of Draw refers to the sequence in which these tubes should be filled. The needle which pierces the tubes can carry additives from one tube into the next, and so the sequence is standardized so that any cross-contamination of additives will not affect laboratory results ^[3].

[edit ]

Containers containing coagulants

Gold - A serum-separating tube (SST). These contain particles that cause blood to clot quickly, as well as a gel to separate blood cells from serum. (Because the blood has clotted before it has been centrifuged, the liquid part is called serum not plasma.)
Orange - These tubes contain thrombin which makes the blot clot extremely rapid. This allows the serum to be analysed in a shorter time.

[edit ]

Containers containing anticoagulants

Green - Contains the lithium salt of heparin, an anticoagulant. Also may contain ammonium or sodium salts of heparin.
Purple or lavender - contains EDTA. This is a strong anticoagulant and these tubes are usually used for full blood counts and blood films. Can also be used for blood bank.
Grey - These tubes contain fluoride and oxalate. Fluoride prevents enzymes in the blood from working, so a substrate such as glucose will not be gradually used up during storage. Oxalate is an anticoagulant.
Light blue - Contain a measured amount of citrate. Citrate is a reversible anticoagulant, and these tubes are used for coagulation assays. Because the liquid citrate dilutes the blood, it is important the tube is full so the dilution is properly accounted for.
Dark Blue - Contains the sodium salt of heparin, an anticoagulant. Also can contain EDTA as an additive or have no additive. These tubes are used for trace metal analysis.
Pink - Similar to purple tubes (both contain EDTA) these are used for ABO grouping and cross-matching.

[edit]

Other

Red - Contains no additives. Tests for antibodies and drugs often require these.
Light yellow - Used in HLA phenotyping. Also contains SPS, used for blood cultures.
Speckled top -- no anticoagulant. Also called a "tiger top" tube. Contains clot activator.

[edit]

Miscellaneous

The purple top tube became an issue in the O. J. Simpson murder trial when the defense alleged that small droplets of blood found at the crime scene contained the preservative EDTA; had this been true, it would have meant that the droplet might have been taken from the purple top tube used to collect Simpson's blood and planted at the crime scene. ^[4]

Table 1. Massachusetts General Hospital Critical Value List

Test Critical Values

Chemistry (blood gas)

   Bilirubin, total, 0-3 mo old, mg/dL (µmol/L) >20 (>342)

   Calcium, ionized, mg/dL (mmol/L) <3.20 or >6.16 (<0.8 or >1.54)

   Hemoglobin, g/dL (g/L) <6.5 (<65)

   pco₂, mm Hg <20 or >75

   pH <7.10 or >7.59

   po₂, mm Hg <40

Chemistry (main laboratory)

   Calcium, mg/dL (mmol/L) <6.5 or >14.0 (<1.63 or >3.53)

   Carbon dioxide, total, mEq/L (mmol/L) <11 (<11)

   Glucose, CSF, mg/dL (mmol/L) <40 (<2.2)

   Glucose, plasma, mg/dL (mmol/L) <45 or >500 (<2.5 or >27.8)

   Magnesium, mEq/L (mmol/L) <1.0 or >4.9 (<0.50 or >2.45)

   Osmolality, plasma or serum, mOsm/kg H₂O (mmol/kg H₂O) <250 or >335 (<250 or >335)

   Phosphorus, mg/dL (mmol/L) <1.1 (<0.36)

   Potassium, mEq/L (mmol/L) <2.8 or >6.0 (<2.8 or >6.0)

   Sodium, mEq/L (mmol/L) <120 or >160 (<120 or >160)

Hematology

   All hematocrit values, % >56% (>0.56)

   δ values Various δ checks for platelet and hematocrit values

   Differential Presence of blasts on initial smear

   Initial hematocrit, % <20 (<0.20)

   Initial platelet count, × 10³/µL (× 10⁹/L) <50 or >999 (<50 or >999)

   Initial WBC count, /µL (× 10⁹/L) <2,000 or >50,000 (<2.0 or >50.0)

   Partial thromboplastin time, s >100

   Prothrombin time, s >30

CSF, cerebrospinal fluid.

Lab and Arterial Blood Gas Interpretation

Venous Blood Gas