Newsgroup: it.scienza.medicina
Titolo: Pulsion Picco (per anestesisti tosti)

Un saluto a tutti gli intensivisti.
Sto iniziando ad usare il Pulsion PiCCO. In un paziente mi č capitato di
ottenere una buona curva di pressione (quindi presumevo una buona
gittata cardiaca) ma per quanto riguarda la curva di termodiluizione un
Mtt cosě lungo che la macchina non č riuscita a fornirmi il C.O.(come se
il cuore avesse un bassissimo SV)
Domanda:
quali sono i fattori che influenzano la durata del Mtt?
Ciao a tutti
vostro affezionato                                   
I.C.U.er

vostro affezionato                                   
I.C.U.er
Non uso questo metodo anche se ne ho sentito parlare.
Mi sono quindi  documentato  in rete e fornisco questo contributo,
credo utile, per facilitare la discussione:
METODO DEL CONTORNO DEL POLSO
Il metodo del contorno del polso per la valutazione della gittata
cardiaca è stato originariamente descritto da Otto Frank nel 1899. Da
allora sono stati sviluppati una gran varietà di equazioni per la
stima dello stroke volume.
Il sistema PULSION PiCCO misura la gittata cardiaca per mezzo di un
algoritmo derivato dal metodo del contorno del polso opportunamente
corretto per garantire la massima affidabilità e precisione.
Come è noto l'area sottesa alla curva di pressione arteriosa durante
la fase sistolica è proporzionale allo stroke volume sinistro.
Gittata cardiaca valutata per mezzo del contorno del polso
Per ricavare lo stroke volume è necessario calcolare un fattore di
calibrazione che renda conto dell'impedenza aortica e del sistema
vascolare:
SV = Area sottesa x cal
Per ottenere il fattore di calibrazione "cal", è necessario disporre
di una misura di C.O. di riferimento. Il sistema PiCCO permette di
ricavare questa gittata di riferimento mediante una termodiluizione
arteriosa (COtd)dopo aver iniettato il bolo freddo in una via venosa
centrale senza richiedere il posizionamento di un catetere in arteria
polmonare. La curva di termodiluizione viene rilevata dallo stesso
catetere arterioso impiegato per il monitoraggio della pressione
arteriosa:
SV id = CO id/ HR
cal = SV id/ A
A questo punto è possibile misurare lo stroke volume ad ogni nuovo
battito e quindi la gittata cardiaca:
SV. = A x cal
CO = SV x HR
dove A è l'area sottesa alla curva di pressione, HR è la frequenza
cardiaca e "cal" è il fattore di calibrazione che rende conto
dell'impedenza aortica e del sistema vascolare.
Recentemente alcuni studi di valutazione hanno dimostrato che la
determinazione a minor invasività della gittata cardiaca per mezzo
dell'analisi del contorno del polso è affidabile, riproducibile ed è
una valida alternativa alla determinazione della gittata mediante
catetere in arteria polmonare.
Marco Nassini, Anestesista (poco tosto) a Merate (Lecco).

Ciao Marco,
ti ringrazio per la replica.
Se trovi qualche altra informazione fammelo sapere. Nel frattempo spero che
la discussione continui.
Ciao
I.C.U.er

Nel frattempo spero che la discussione continui.
Si', ma fate capire qualcosa pure a noi...
C.O., SV, Mtt... che d'e'??? Ho cominciato ad orizzontarmi un po' con la
risposta di Marco...
Ricordate che siamo pur sempre in un newsgroup NON dedicato agli
specialisti, quindi scendiamo pure nel tecnico, ma senza dimenticare di
fare un po' di divulgazione... Se no ci sono altre strade per
comunicare.
-- 
        ___
 /\/\/\/ _/  -Doctor Diabolicus
/     / /_   -Moderatore it.scienza.medicina
\/\/\/\__/   -e-mail: 
moderator...@doctor.com
charter: 
http://web.tiscalinet.it/ScienzaEmedicina/Manifesto.html

comunicare.
Sono sostanzialmente d'accordo, anche se trovo importante che il ng.
sia "anche" di servizio per quelle specialità che, nella medicina,
devono ma non sempre possono garantire nel giro di breve tempo (spesso
qualche ora..) di salvare la pelle ad un malato. La terapia intensiva
è una di queste ed il tempo è il nostro grande nemico. Per questo mi
permetto di fornire un secondo contributo informativo (in inglese
ahimè..) per tutti i colleghi più giovani sulla problematica della
misurazione della gettata cardiaca (cardiac output = C.O). E considero
personalmente esaurito ogni altro commento scientifico su questa
problematica.
Ringraziando tutti per la pazienza e tolleranza dimostrate
cordialmente vostro
Marco Nassini, Anestesista a Merate (Lecco)
******************************* inizio doc. **************************
Cardiac Output
What Is It?
Cardiac output is the volume of blood pumped by the heart per minute.
For an average size of adult (70 kg) at rest this would
be about 5 litres/min. During severe exercise it can increase to over
30 l/min, although not in the unfit! Miguel Indurain ("Big
Mig", who won the Tour de France in five successive years) had a
resting heart rate of 28 beats per minute and could
increase his cardiac output to 50 litres per minute and his heart rate
to 220 beats per minute. Cardiac output is often divided
by body surface area to take into account the size of the subject (see
- indexed values).
Why Measure It?
It is frequently necessary to assess the state of a patient's
circulation. The simplest measurements, such as heart rate and blood
pressure, may be adequate for many patients, but if there is a
cardiovascular abnormality then more detailed measurements
are needed. A common clinical problem is that of hypotension (low
blood pressure); this may occur because the cardiac
output is low and/or because of low systemic vascular resistance
(SVR). This problem can occur in a wide range of patients,
especially those in intensive care or postoperative high dependency
units. In these high risk patients more detailed monitoring
will usually be established and will often include measuring central
venous pressure via a central venous catheter and
continuous display of arterial blood pressure via a peripheral
arterial catheter. In addition, measurement of cardiac output
can be carried out and this, together with arterial pressure
measurements, allows SVR to be calculated. These measurements
are useful both in establishing a patient's initial cardiovascular
state and in measuring the response to various therapeutic
interventions such as transfusion, infusion of inotropic drugs,
infusion of vasoactive drugs (to increase or reduce SVR) or
altering heart rate either pharmacologically or by adjusting pacing
rate.
Methods of Measuring Cardiac Output.
Existing methods of measuring cardiac output are unsatisfactory for
various reasons.
The Fick Method
Cardiac
Output =   oxygen consumption / arteriovenous oxygen content
difference.
 
The original method described by Fick in 1870 is difficult to carry
out. Oxygen consumption is derived by measuring the
expired gas volume over a known time and the difference in oxygen
concentration between this expired gas and inspired gas.
Accurate collection of the gas is difficult unless the patient has an
endotracheal tube because of leaks around a facemask or
mouthpiece. Analysis of the gas is straightforward if the inspired gas
is air but if it is oxygen enriched air there are two
problems, (a) the addition of oxygen may fluctuate and produce an
error due to the non-constancy of the inspired oxygen
concentration, and (b) it is difficult to measure small changes in
oxygen concentration at the top end of the scale. The
denominator of the equation, the arteriovenous oxygen content
difference, presents a further problem in that the mixed venous
(i.e. pulmonary arterial) oxygen content has to be measured and
therefore a pulmonary artery catheter is needed to obtain the
sample. Complications may arise from these catheters. If carefully
carried out, the Fick method is accurate, but it is not
practicable in routine clinical practice. Several variants of the
basic method have been devised, but usually their accuracy is
less good. There are many other methods of measuring cardiac output
nowadays, but the most accurate are those which use
some form of
INDICATOR DILUTION
Other Methods
Bioimpedance - 
this method was described by Kubicek et al in 1966 and has recently
been reviewed by Critchley (1998). It
has the advantages of providing continuous cardiac output measurement
at no risk to the patient. A small high frequency
current is passed through the thorax from a pair of spot electrodes
stuck to the skin. Sensing electrodes are used to measure
the changes in impedance within the thorax; the normal value for an
adult is 20-48 ohms at a frequency of 50-100 Hz.
Contraction of the heart produces a cyclical change in transthoracic
impedance of about 0.5%, unfortunately giving a rather
low signal to noise ratio. Although the method has been reported to
give accurate results in normal subjects several studies
have shown it to be too inaccurate for use in critically ill patients
eg. Genoni et al (1998), Marik et al (1997) and Imhoff et al
(2000).
Echocardiography -
transoesophageal echocardiography (TOE) provides diagnosis and
monitoring of a variety of structural
and functional abnormalities of the heart (for review see Poelaert et
al. (1998). It can be used to derive cardiac output from
measurement of blood flow velocity by recording the Doppler shift of
ultrasound reflected form the red blood cells. The time
velocity integral, which is the integral of instantaneous blood flow
velocities during one cardiac cycle, is obtained for the
blood flow in the left ventricular outflow tract (other sites can be
used). This is multiplied by the cross-sectional area and the
heart rate to give cardiac output. In a study of patients having
coronary artery revascularisation (Krishnamurthy et al 1997)
the authors concluded that 'undue reliance placed on the absolute
values may be unwise'. Others have compared TOE with
thermodilution and reported agreements ranging from good (Perrino et
al 1998) to poor (Estagnasie et al 1997). The main
disadvantages of the method are that a skilled operator is needed
(Lefrant et al 1998), the probe is large and therefore heavy
sedation or anaesthesia is needed, the equipment is very expensive and
the probe cannot be fixed so as to give continous
cardiac output readings without an expert user being present.
Pulse Contour analysis
 In 1904 Erlanger and Hooker stated "Upon the amount of blood that is
thrown out by the heart during systole then, does the
magnitude of the pulse-pressure in the aorta depend". Although as
early as 1947 (Hamilton and Remington 1947) a good
correlation was found between stroke volume measured by dye injection
and by analysis of the arterial pressure waveform
the method has still not gained clinical acceptance. The method has
been developed further (eg Jansen, Wesseling et al 1990)
and a clinical device is now available (Pulsion PiCCO) which is
calibrated by arterial thermodilution . Several abstracts
have described promising results, but in a recent paper it was shown
that increasing systemic vascular resistance by infusion
of phenylephrine caused the PiCCO device to overread (Rödig et al.,
1999). 
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************************** fine doc. *********************************