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Posts Tagged ‘balanced vasodilatation with inotropic support’

An elderly man  with past H/o CAD  was admitted with ischemic LVF and hypotension .Blood pressure was  90/60 mmhg  and pulse rate was 140 . Urine urine output  in the immediate past hour was 50 ml . Saturation was 95 % .He had fairly extensive  crackles in both lung fields.

A bed side echo showed  moderate LV dysfunction , with wall motion defect in LCX territory and  mild  MR .A dignosis of post  MI -ischemic LVF was made .

He  was  put on intensive anti failure protocol. I asked my  fellow to administer IV NTG  and left the ward .

On my next visit after few hours  . . . the patient was in much bad shape  , and when I enquired , I learnt  NTG was never administered . I was curious to know why the fellow  dis- obeyed my instruction .

He felt sorry  .  .  . But he earnestly told me  , he  could not comprehend the principle of administering NTG in a  patient  with shock ! . I was happy  to  note his  genuine concern  for   the patient  !  But  . . . I had to take a brief  lecture to convince the importance of NTG in some forms of shock !

What is the cause for hypotension in ischemic LVF ?

Lungs are flooded due to  very high LVEDP . Blood  not only struggles to  enter the LV  but also finds difficult to   leave the LV ,  former due to defective relaxation later due to poor pumping.

The extremely high pre-load actually stuns the left ventricle in diastole . (Primarily diastolic stunning  )  . Here is a hemodynamic paradox . Excess pre-load  occurs in  terms of pressure , but  in terms of volume there is miniscule amount  blood  that  traverses LV  .

This is pre-load mismatch  at play .Empty ventricles with high wall stress  and that is reflected in aortic afterword as well .

We have to some how reduce the  very high levels of LVEDP . IV NTG can  dramatically  reduce the pre load  ( and reduce the LVEDP .) The other major  benefit is ,  NTG   can reduce the MVO2 by improving sub endocardium coronary perfusion and de-stress the heart.

Once  LVEDP  is  lowered  , the ventricle will tend to recover and gain at least some  original elasticity ( Frank starling forces) . Of course it will be defective due to ongoing ischemia . Even slight fall of LVEDP (say from 25 to 18 mmhg  can have  significant benefits as the LV function curve labors on the steep shoulder region !) .

This is one situation where NTG can increase the blood pressure once the hemodynamics is favorably altered.

*Yes  . . . heavy doses  of  Frusemide injection can do the same job but it largely depends the kindey’s cooperation to flush out fluids  .In a shock like situation one can trust the kidney perfusion  !

Additional benefits of NTG

Mitral  regurgitation  is a serious destabilizer of LV function .NTG can reduce the regurgitant fraction in acute MR effectively .

Caution

NTG may worsen the hypotension of RV infarction . Make it very sure , you are not dealing with this unique  pre-load dependent circulation.

What happened to this patient ?

He  did show  improvement with IV NTG . Of course it was not dramatic as I have projected in this article .Still it was really helped him .He required simultaneous dobutamine infusion as well .The BP did not fall  further and lung congestion was relieved  .He went on to recover fully by 48 hours and was posted for elective cath study .

Final message

                                             We tend to  worry  more about falling blood pressure  when administering  NTG. . .It is a wonderfully effective drug especially in the setting of ischemia and cardiac failure  even if  the blood pressure is low !

Acute cardiac hemodynamics  is  complex phenomenon .No one has mastered it .Paradoxes are common . Hypotension in the back ground of  acute pulmonary edema  especially due to ischemic LVF  can be corrected by NTG . Of course physicians  need  some  courage to administer NTG in patients  with a systolic pressure of  80-90mmhg.

This should ideally be done with intra arterial line in place and a simultaneous inotropic line (Doubtamine /Nor-epinephrine ) back up in case of worsening perfusion pressure .

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