Segni di Intolleranza SBT
Grafico 7 Andamento Pressione Arteriosa Diastolica: Media
(Basale) T0 (PSV) T1 (15' ) T2 (30' -T ) T3 (45' ) T4 (60' ) T5 (75' ) T6 (90' ) T7 (105' ) T8 (Estub) T9 (15' ) T1 0 S1 60,0 62,0 64,0 66,0 68,0 70,0 72,0 PAD
A dimostrazione del fatto che esiste una discrepanza almeno iniziale tra disponibilità e consumo di ossigeno abbiamo inoltre rilevato, su analisi ematiche effettuate a T0 e a T4, un incremento dei lattati nei pazienti sottoposti a svezzamento (Tabella XI e XII).
Questo potrebbe essere legato in parte all’aumento del consumo di ossigeno dovuto all’utilizzo di gruppi muscolari rimasti a riposo per effetto di sedativi e talvolta curari utilizzati nei giorni precedenti. Si conferma così il dato già riportato in letteratura da Pinsky, in cui lo svezzamento del paziente dal ventilatore viene assimilato ad un esercizio fisico, in cui si ha un aumento delle richieste di ossigeno, solo in parte seguite da un aumento della sua disponibilità. [51]
Tabella XI Valori Ematici Pre-Test (T0)
Pz 1 Pz 2 Pz 3 Pz 4 Pz 5 Pz 6 Pz 7 Pz 8 Pz 9 Ph 7,44 7,39 7,38 7,43 7,41 7,42 7,52 7,35 7,49 PaO2 81,6 110 126,5 180 170 105 137 175 108,3 PaCO2 36,4 56 42,9 38 35 37 32,3 37,5 37,3 Lattati 22 62 13 23 13 15 16 14 18 HCO3 24,5 29 24,4 24,6 24,4 25,3 25,8 20,3 28,1 BE O,5 2,9 -0,2 1,2 1,5 1,9 2,8 -4,7 4,6
Tabella XII Valori Ematici durante Weaning (T4)
Pz 1 Pz 2 Pz 3 Pz 4 Pz 5 Pz 6 Pz 7 Pz 8 Pz 9 Ph 7,46 7,34 7,37 7,44 7,40 7,32 7,42 7,34 7,53 PaO2 74 107,7 94 74,7 98 120 92,4 189 67,6 PaCO2 37,5 62,6 42,7 39,3 41 38 41,8 35,7 35,5 Lattati 31 42 16 24 16 18 16 25 17 HCO3 26,5 33,1 24 26,3 26,3 26,1 26,6 18,9 29 BE 2,7 6,1 -1 2,2 2,4 2,7 2,9 -6,2 5,9
L’analisi dei valori di NT-pro-BNP mostra una discreta variabilità dei valori che risultano compresi tra 109-444 pg/L (Tabella XIII).
Nonostante in letteratura siano riportati valori di cutoff di 275 pg/L, [69] nel nostro studio anche livelli al di sopra di tale soglia non hanno influito sulla svezzabilità dal ventilatore; dati più accurati possono però essere disponibili solo incrementando il numero di pazienti e soprattutto documentando anche casi di insuccesso, che nel nostro studio non si sono verificati, forse anche per le piccole dimensioni del gruppo studiato. Da ricordare inoltre che anche i dati presenti in letteratura sulla accuratezza diagnostica del pro-BNP nell’insufficienza cardiaca sono tutt’oggi contrastanti [77] [78] [79] e che, come sottolineato in un recente studio del CNR di Pisa, eventuali concentrazioni cutoff variano molto in base ai metodi di laboratorio utilizzati per la rilevazione ed alla popolazione studiata. [80]
Tabella XIII Valori Ematici di NT-proBNP
Pz 1 Pz 2 Pz 3 Pz 4 Pz 5 Pz 6 Pz 7 Pz 8 Pz 9 NT-
4. CONCLUSIONI
Lo svezzamento dalla ventilazione meccanica è associato ad un incremento della richiesta di ossigeno per aumento sia del lavoro respiratorio che della secrezione endogena di catecolamine.
L’aumento del Cardiac Index che ne deriva rappresenta uno stress cardiaco importante che può esacerbare, in pazienti a rischio, sofferenza ischemica miocardica, facilitare lo sviluppo di un metabolismo miocardico anaerobio, precipitare una disfunzione ventricolare sinistra e/o destra.
La riduzione del rendimento del sistema cardio-circolatorio, che abbiamo registrato in corso di svezzamento dal ventilatore tramite variazioni del CCE, potrebbe esser legata non solo ad un aumento del CI, ma anche ad un aumento delle resistenze vascolari periferiche, che mostrano un andamento in crescendo nei primi 30 minuti dall’inizio del trial.
La discrepanza fra disponibilità e consumo di ossigeno è confermata dall’incremento dei lattati in questo intervallo di tempo.
I dati preliminari emersi dal nostro studio tendono a confermare quanto riportato in letteratura [28], evidenziando come una insufficienza cardiaca occulta instaurata in corso di svezzamento in pazienti critici possa essere la causa primaria di fallimento di weaning.
A tal proposito alterazioni dei livelli basali del NT-proBNP come indice di disfunzione miocardica potrebbero spiegare l’insuccesso nello svezzamento di alcune tipologie di pazienti, affiancandolo ad altri parametri, quale indice di predittività di successo di distacco dal ventilatore.
In letteratura non si trovano ancora lavori in cui è stato studiato questo nuovo parametro clinico in correlazione ai parametri ventilatori.
Nel nostro studio le variazioni medie dei valori del CCE (parametro che esprime la performance cardiaca in termini di dispendio energetico del sistema cardiocircolatorio) in corso di svezzamento si sono mostrate
statisticamente significative, ma, data l’esiguità della popolazione dei pazienti da noi considerata, sono necessari ulteriori approfondimenti per la conferma della sua validità diagnostica in corso di weaning.
Infine, il protocollo di svezzamento utilizzato nel nostro studio, ha presentato una percentuale di successo inaspettatamente molto alta, anch’essa però da confermare su numeri più vasti.
Inoltre questo studio conferma quanto già riportato in letteratura circa la necessità della applicazione di protocolli standardizzati di svezzamento, quali strumenti efficaci per diminuire la durata della dipendenza dal ventilatore, l’incidenza di reintubazione, l’insorgenza di complicanze ventilatore-dipendenti, ed i costi legati ad un aumento della degenza in Terapia Intensiva. [18] [19] [20] [21]
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