Deliberate Hypotension (PART 1)

INTRODUCTION :
Deliberate(controlled)(induced) hypotension has been the special province of neuroanesthetist and has been used to decrease the likelihood of rupture by decreasing aneurysmal transmural pressure, mechanically improving the approach to, handling and actual clipping of the aneu
rysm and reducing bleeding should it occurs.(3)
This method is potentially dangerous therefore who 
intend to use it should be thoroughly conversant with  
the farmacology and physiology involved.
Before selecting this method one must be sure the advantages outweight. The disadvantages following a thorough review of all the facts. The preparation of the comprenhensive reviews of the entire case,including 
the patients age and physical and mental status,the surgical procedures, the skill and experience of the surgeon,anesthesiologist and operating room, recovery room and intensive care unit personnel should be considered (1).

However when indicated and carefully conducted,induced hypotension can be an effective safe tehnique that provide good operating condition for some operation.
Although the use of induced hypotension during surgical clipping of cerebral aneurysma is in decline 28% of North American Neurosurgical Centers continue to use it regularly. (3,4)


Advantages :
The method minimizes blood loss and need for transfusion of blood.(1)
Hypotension decreases bleeding from surrounding small vessels which allows better visualization of the anatomy of the aneurysm and the perforating vessels,for surgical clip ligation of intracranial aneurysms patients require precise intraoperative control blood pressure to prevent bleeding facilitate clip placement and counteract vasospasm(4,5).

Lowering the blood pressure during microscopic dissection of the aneurysm has been advocated to reduce the risk of rupture by dereasing aneurysmal wall tension and augment the malleability of the neck of the aneurysm.

The maneuver is effective because the wall of the aneurysm thins as the aneurysm increases in size.(4,5)
Less anesthetics are necessary.


INDICATION :
1.Neurosurgical operation ;(for aneurysm,meningioma and 
   excision of vascular tumors).
2.Vascular surgery,such as portcaval shunt.
3.Pelvic procedure,such as pelvic excentration with nodes  
   dissection.
4.Cancer operations which bleeding may be difficult to 
   control.
5.Orthopedic surgery;for disarticulation procedures and 
   surgery for scoliosis.


CONTRA INDICATION :
1.An Anesthesiologist who is not familiar with the techni-
   que,surgeon and post operative care personnel with 
   little or no experience.
2.Marked anaemia and/or decreased blood volume.
3.Hypertension;untreated hypertension however is 
   relative contra indication since the blood pressure may 
   be extremely labile and profound hypotension result.
4.Arteriosclerosis.
5.Cerebrovascular disease.
6.Heart failure and myocardial ischemia.
   This is made worse by an increase in the rate pressure 
   product.(2)
7.Respiratory insufficiency ;the increase in physiological 
  dead space due to ventilation/perfusion imbalance is 
  more important in patients in whom preoperative gas 
  exchange is limited.Under normal condition hypoxic 
  pulmonary vasoconstriction occuring in poorly ventilated 
  segments of the lung prevent gross disorders of ventila-
  tion/perfusion, although this effect is weakened by 
  anesthesia.Vasodilatation induced by direct acting drugs 
  such as sodium nitropruside(SNP) abolishes this response 
  and will therefore make shunting worse.
  Reversible airways obstruction and bronchospam may be 
  made worse by the use of ganglionic blocking drugs or 
  beta adrenoreceptors antagonist which are not 
  cardiospesific.
8.Impaired renal and hepatic function
9.Narrow angle glaucoma when ganglionic blocking drugs 
   are not used because of pupillary dilatation.


CONSIDERATION:(1,2)
1.An experienced anesthesiologist and skillful surgeon.
2.Advantages must outweigh risks.
3.Proper selection of patients.
4.Proper positioning of the patient.
5.Normal preoperative blood volume.

6.Careful monitoring :
a.Arterial blood pressure monitoring preferably with in 
  dwelling radial artery canula,to monitor the blood 
  pressure continuously provides the best method of 
  arterial pressure measurement. 
  It is important to remember that the position of 
  transducer is the level at which blood pressure is 
  measured.
  If one anticipating hypotension below a systolic presure 
  of 70mmHg direct arterial monitoring should be 
  considered essential.


b.Use of the electrocardioscope.
   ECG monitoring is essential to demonstrate two vital 
   signs of inadequate myocardial prefusion, the deve
   lopment of ectopic beats and ST segment depression.
   This myocardial response to relative hypoxia and 
   hypoperfusion is a sensitive indicator of clinically 
   excessive hypotension.


c.CVP monitoring related to blood volume.
d.Determination of arterial blood gases, haemoglobine 
   and hematocriet should be done as indicated during 
   procedure.
e.Temperature monitoring.
f. Gravimetric monitoring(weighing of sponges) and close 
    observation of the amount blood in the suction bottle 
    (be aware of fluids used for irrigation of the surgical 
    area).


7.Adequate ventilation and oxygenation.
8.Replacement of blood loss.
9.Minimal duration of hypotension period.
10.Excellent post operative care and supervision in the 
     recovery room or intensive care unit. 
    a.Ascertain that the blood has been replaced.
    b.The patient should be awake,responding and 
        ventilating well,and his color should be good.
    c.Oxygen must be administered by mask or nasal 
       cannula.

to be continued

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