Pocket Medicine

CARDIOLOGY

PA CATHETER AND TAILORED THERAPY

Rationale

•  Cardiac output (CO) = SV × HR; SV depends on LV end-diastolic volume (LVEDV)
∴ manipulate LVEDV to optimize CO while minimizing pulmonary edema

•  Balloon at tip of catheter inflated → floats into “wedge” position. Column of blood extends from tip of catheter, through pulmonary circulation, to a point just proximal to LA. Under conditions of no flow, PCWP  LA pressure  LVEDP, which is proportional to LVEDV.

•  Situations in which these basic assumptions fail:

(1) Catheter tip not in West lung zone 3 (and ∴ PCWP = alveolar pressure ≠ LA pressure); clues include lack of a & v waves and if PA diastolic pressure < PCWP

(2) PCWP > LA pressure (eg, mediastinal fibrosis, pulmonary VOD, PV stenosis)

(3) Mean LA pressure > LVEDP (eg, MR, MS)

(4) Δ LVEDP-LVEDV relationship (ie, abnl compliance, ∴ “nl” LVEDP may not be optimal)

Indications ( JACC 1998;32:840 & Circ 2009;119:e391)

•  Diagnosis and evaluation

Ddx of shock (cardiogenic vs. distributive; esp. if trial of IVF failed or is high risk) and of pulmonary edema (cardiogenic vs. not; esp. if trial of diuretic failed or is high risk)

Evaluation of CO, intracardiac shunt, pulmonary HTN, MR, tamponade

Evaluation of unexplained dyspnea (PAC during provocation w/ exercise, vasodilator)

•  Therapeutics (Circ 2006;113:1020)

Tailored therapy to optimize PCWP, SV, SvO2 in heart failure (incl end-stage) or shock

Guide to vasodilator therapy (eg, inhaled NO, nifedipine) in pulm HTN, RV infarction

Guide to perioperative management in some high-risk Pts, pretransplantation

•  Contraindications

Absolute: right-sided endocarditis, thrombus/mass or mechanical valve; PE

Relative: coagulopathy (reverse), recent PPM or ICD (place under fluoroscopy), LBBB (~5% risk of RBBB → CHB, place under fluoro), bioprosthetic R-sided valve

Efficacy concerns (NEJM 2006;354:2213; JAMA 2005;294:1664)

•  No benefit to routine PAC use in high-risk surgery, sepsis, ARDS

•  No benefit in decompensated HF ( JAMA 2005;294:1625); untested in cardiogenic shock

•  But: ~½ of CO & PCWP clinical estimates incorrect; CVP & PCWP not well correl.; ∴ use PAC to (a) answer hemodynamic ? and then remove, or (b) manage cardiogenic shock

Placement

•  Insertion site: R internal jugular or L subclavian veins for “anatomic” flotation into PA

•  Inflate balloon (max 1.5 mL) when advancing and to measure PCWP

•  Use resistance to inflation and pressure tracing to avoid overinflation & risk of PA rupture

•  Deflate the balloon when withdrawing and at all other times

•  CXR should be obtained after placement to assess for catheter position and PTX

•  If catheter cannot be successfully floated (typically if severe TR or RV dilatation) or if another relative contraindication exists, consider fluoroscopic guidance

Complications

•  Central venous access: pneumo/hemothorax (~1%), arterial puncture (if inadvertent cannulation w/ dilation → surgical/endovasc eval), air embolism, thoracic duct injury

•  Advancement: atrial or ventricular arrhythmias (3% VT; 20% NSVT and >50% PVC), RBBB (5%), catheter knotting, cardiac perforation/tamponade, PA rupture

•  Maintenance: infection (esp. if catheter >3 d old), thrombus, pulm infarction (≤1%), valve/chordae damage, PA rupture/pseudoaneurysm (esp. w/ PHT), balloon rupture

Intracardiac pressures

•  Transmural pressure ( preload) = measured intracardiac pressure – intrathoracic pressure

•  Intrathoracic pressure (usually slightly ) is transmitted to vessels and heart

•  Always measure intracardiac pressure at end-expiration, when intrathoracic pressure closest to 0 (“high point” in spont. breathing Pts; “low point” in Pts on  pressure vent.)

•  If ↑ intrathoracic pressure (eg, PEEP), measured PCWP overestimates true transmural pressures. Can approx by subtracting ~½ PEEP (× ¾ to convert cm H2O to mmHg).

•  PCWP: LV preload best estimated at a wave; risk of pulmonary edema from avg PCWP

Cardiac output

•  Thermodilution: saline injected in RA. Δ in temp over time measured at thermistor (in PA) is integrated and is  1/CO. Inaccurate if ↓ CO, sev TR or shunt.

•  Fick method: O2 consumption (O2) (L/min) = CO (L/min) × ∆ arteriovenous O2 content

∴ CO = O2 / C(a-v)O2

O2 ideally measured (esp. if ↑ metab demands), but freq estimated (125 mL/min/m2)

C(a-v)O2 = [10×1.36 mL O2/g of Hb × Hb g/dL × (SaO2–SvO2)]. SvO2 is key variable that Δs.

If SVO2 >80%, consider if the PAC is “wedged” (ie, pulm vein sat), L→R shunt, impaired O2 utilization (severe sepsis, cyanide, carbon monoxide), ↑↑ FiO2.

Tailored therapy in cardiogenic shock (Circ 2009;119:e391)

•  Goals: optimize both MAP and CO while ↓ risk of pulmonary edema

MAP = CO × SVR; CO = HR × SV (which depends on preload, afterload and contractility)

pulmonary edema when PCWP >20–25 (↑ levels may be tolerated in chronic HF)

•  Optimize preload = LVEDV  LVEDP  LAP  PCWP (NEJM 1973;289:1263)

goal PCWP ~14–18 in acute MI, ≤14 in acute decompensated HF

optimize in individual Pt by measuring SV w/ different PCWP to create Starling curve

↑ by giving NS (albumin w/o clinical benefit over NS; PRBC if significant anemia)

↓ by diuresis (qv), ultrafiltration or dialysis if refractory to diuretics

•  Optimize afterload  wall stress during LV ejection = [(~SBP × radius) / (2 × wall thick.)] and ∴ ∝ MAP and ∝ SVR = (MAP – CVP / CO); goals: MAP >60SVR 800–1200

MAP >60 & SVR ↑: vasodilators (eg, nitroprusside, NTG,  ACEI, hydral.) or wean pressors

MAP <60 & SVR ↑ (& ∴ CO ↓): temporize w/ pressors until can ↑ CO (see below)

MAP <60 & SVR low/nl (& ∴ inappropriate vasoplegia): vasopressors (eg, norepineph-rine [a, b], dopamine [D, a, b], phenylephrine [a] or vasopressin [V1] if refractory)

•  Optimize contractility ∝ CO for given preload & afterload; goal CI = (CO / BSA) >2.2

if too low despite optimal preload & vasodilators (as MAP permits):

 inotropes: eg, dobutamine (mod inotrope & mild vasodilator) or milrinone (strong inotrope & vasodilator, incl pulm), both proarrhythmic, or epi (strong inotrope & pressor)

mechanical support devices: eg, IABP, percutaneous or surgical VAD (left-sided, right-sided or both) or ECMO (Circ 2011;123:533)