OLigaemic = Hypovolaemic= Haemorrhagic = 2ry = Surgical shock

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OLigaemic = Hypovolaemic= Haemorrhagic = 2ry = Surgical shock

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Thursday, 10 December 2009 09:57

O Causes: 1- Loss of blood either external or internal hge.
2- Loss of plasma as in burns.
3- Loss of fluid as in severe vomiting and diarrhea.
O Response of body towards oligaemic shock:
1- Stimulation of the barorecptors in the carotid sinus which leads to increase heart Rate "H.R."and vasoconstriction of peripheral vesselse.
This in turn leads to increase in blood pressure as:
Bl. pr = cardiac output (CO) X peripheral resistance
CO = Heart rate X stroke volume
2- Stimulation of adrenal medulla leads to floading of circulation with adrenaline which leads to:
a- more peripheral vasoconstriction.
b- contractility & heart rate.
3- Renal ischaemia ® oliguria if persist® renal failure.
Renal ischaemia ® release of Renin which convert angiotensin I to angiotensin II ® vasoconstriction of peripheral vessels.®
4- The accumulated fluid pass to blood vessels which lead to haemodilution and expansion of blood volume.
5- Contraction of splenic capsule only in animals but has minor or even no role in human being.
m Pathophysiology of shock:
Release of Aldosterone hormone which lead to salt and water retension.

1- Vasoconstriction of the capillary bed i.e. constriction of pre-and post - capillary sphincter® opening of arteriovenous shunt ® Blood passes directly from the arteries to the veins bypassing the tissues in trial to correct hypovolaemia®tissue anoxia.
2- If there is no interference by blood or fluid transfusion ; the persistant anoxia of the capillary bed leads to capillary damage which leads to loss of its selective permeability and the precapillary sphincters will be paralyzed.
3- The blood will rapidly enter to microcirculation and stagnate in it as the postcapillary sphincter is still constricted "accommodated to venous anoxic blood ". The stagnant blood will be lost in tissues through the damaged capillaries leads to more hypovolaemia ® vicious circle.

ì Hypovolaemia î

Fluid loss Tissue anoxia

ë Capillary damage í

"Death cycle of McDowal"

= Irreversible shock this cycle occurs if blood loss is more than 20% and neglected cases for more than 2 hours.
m Biochemical changes in shock:
1- Blood PH: acidosis due to accumulation of pyrovate and lactate.
2- Blood gases : ¯ arterial O2 tension (PO2)& arterial CO2 tension (PCO2).
3- Electrolytes : K blood level due to damage of cell membrane with disturbance of normal pump ® K leave the cells to intravascular space.
4- Blood components: If the cause of shock was fluid loss or plasma loss haemoconcentration will result.
Hemoconc. ® D.I.C. ® Consumption coagulopathy ® Bleeding tendency.
m Clinical Picture:
1- General expression : the patient is pale and irritable and afraid of death .
2- Hands ® Collapsed veins and cold sweaty skin.
3- Pulse ® rapid weak pulse.
4- Bl. pr ® low blood pressure.
5- Temperature ® subnormal.
6- Respiration ® Rapid and shallow .
7- Urine output ® oliguria < 1/2 cc / minute in adults.
The urine output is more important than pulse & bl. pr. why? as pulse may not increase in old age with sclerosed carotid body and bl . pr. may be fixed by compensatory mechanism.
m Investigations:
1- Urine output: < 1/2 cc / minute indicates low renal perfusion i.e. shock .
2- Blood chemistry:
- Low blood pH < 7.4 - ¯ PO2 < 100 & PCO2 > 40
- Blood K level .
3- Haematocrit : in cases of shock with plasma and fluid loss.
4- Central venous catheter:
Method:
mIt is 20 cm catheter. It can be passed through the internal jagular vein or subclavian vein to be positioned in the superior vena cava or the right atrium.
m Technique:
The patient lies supine with head down ( avoid air embolism and distend neck veins). The puncture is made lateral to the palpable carotid pulse in the middle of a line passing from the mastoid process to the corresponding sternoclavicular joint. Admit the catheter slowly with continuos aspiration of the connected syringe till blood comes freely, hence extract the trucker and admit the catheter to reach the target position. The correct position is confirmed radiologically in the first opportunity.
m Value of C.V. catheter :
1- Measurement of C.V.P. 2- Assessment of fluid therapy.
3- Swan Ganz catheter help in measuring cardiac output by thermodilution technique and also can differentiate by Rt. and Lt. heart failure by measuring pulmonary wedge pressure.
m Normal C.V.P. = 5:10 cm H20 not more than 20 cm H2O .
mC.V.P. variation with different types of shock:
1- In neurogenic shock ® within normal .
2- Hypovolaemic shock ®¯ "decrease".
3- Cardiogenic shock ® "increase" .
4- Septic shock ® early normal or ¯ late
m Clinical types of Shock :
1- Mild shock : less than 20% of bl. volume loss affect extremities.
2- Moderate shock : 20:40% bl. loss . kidney , Liver & are affected .
3- Severe (profound) shock: >40% bl . loss . Heart & brain are affected.
m Treatment :
(1) Maintain patent airway by:
· Suction of bronchial secretion.
· Oxygenation.
· Tracheostomy if needed.
(2) Maintain patent venous line:
By rapid cannulation of a vein for I.V.fluids and morphia
(3) I.V. Morphia: 10:20 mg
· Value: - Allay anxiety. - ¯O2 demand of the tissues.
· It is contraindicated in head injury " Resp. depression" .
· Not given I.M. in shock as it will not be absorbed and repeated injections will accumulate and absorbed rapidly when shock is corrected ® Morphine toxicity
(4) Restore blood volume :
We give ® - blood for blood loss.
- Plasma for plasma loss. - Fluid for fluid loss.
A- Blood : when the cause is blood loss
Disadvantages
· Time for grouping. · Expensive.
· Complications of bl. transfusion.
B- Plasma: When the cause is plasma loss or when blood is not immediately available
Disadvantages:® Expensive.
® Risk of transmission of diseases. as the bottle is collected from more than one donor.
C- Colloids:-
· Human albumin solution (4-4.5%) the best replacement when blood is not indicated. Reactions are rare but it is expensive.
· Plasma substitute :
Dextrans: Half life 4-24 hours. No more used for volume replacement as they impair coagulability and may cause anaphylaxis and nephrotoxicity.
Geltains: Half life 4-5 hours. Most commonly used plasma expanders. They are isotonic and reactions are rare (may impair function of reticuloendothelial system)
Hydroxyethy1 starches, Lowest risk of anaphylaxis. Half life is long (48 hours) but large volumes may cause bleeding tendency. Synthetic solutions with oxygen carrying capacity; still experimental.
d- Fluids "crystalloids:
× Preparations in common use:
1- Glucose 5% for water replacement.
2- Saline "0.9% NaCl.
3- Na HCO3 for III of acidosis.
4- Ringer lactate (kCl , NaCl, Ca Cl & Na lactate).
× Advantages : · Available · Cheep .
· Decrease blood viscosity (improve perfusion)
·Disadvantages: not maintain bl. volume for long time .
(5) V.C. or V.D. :
·Vasoconstrictors ( adrenaline ) is contraindicated . Why ?
· It gives false transient rise of blood pressure.
·¯ Capillary perfusion ® Tissue anoxia .
· It may even cause heart block .
·"Alpha blockers " e.g. phenoxybenzamine ® Vasodilatation of capillary bed in visceral and cutaeneous vessels ®¯ Work done by the heart .
(6) Corticosteroids:
· Action : Antistress, antiallergic, anti- in flammatory .
· Increase salt and water retention .
· Stabilize cell membrane against endotoxins.
·It is given in big single dose "esp. in septic shock " .
(7) Posture of the patient : No need for raising the foot of the bed as in cases of neurogenic shock as this position may cause respiratory embarrassment and dose not help tissue perfusion.
(8) Artificial Heating:
·Not recommended why ?
· It cause peripheral vasodilatation. · It increase metabolism and increase tissue needs for oxygen . · It increase sweating which ¯ Bl . pr. Only cover the patient by ordinary bed clothes.
SOURCE: Prof. AYMAN SALEM'S BOOK
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