4/6/2013 Cardiac Blood Flow Beth Torres, PhD, RN, CCRN CJW Medical Center 1 2 Events during Diastole Events during Systole Remember: During systole the cardiac muscle has to overcome The cardiac muscle gets its perfusion during diastole. the pressures ahead of each chamber: Perfusion is determined by coronary perfusion pressure The right ventricle meets low to no pressure in the lungs. Coronary Perfusion Pressure = Diastolic BP – PCWP The left ventricle must overcome the diastolic pressure in the Normal: 60 -80 mmHg 3 aorta. 4 Compensation for Decreased Cardiac Output Hemodynamics cardiac output heart rate. Heart rate is controlled by stimulation of Cardiac Output = HR x Stroke Volume (SV) both the sympathetic and parasympathetic nervous system Normal Cardiac Output: Heart Rate 4-8liters / minute Preload Cardiac Output Afterload Stroke Volume Contractility Muscle Synchrony 5 6 1 4/6/2013 Stroke Volume (SV) Preload Stroke Volume- the amount of volume ejected The force on the ventricle during relaxation (diastole) by the ventricle with each systolic contraction Primary determinant is the volume of blood filling the ventricle OR, amount of blood ejected by the heart with Right Ventricle = RVEDP (Right heart preload): each beat Right Atrial Pressure (RAP); CVP Normal: 60-130ml Normal values: 2-6mmHg SV = (CO/HR) x 1000 Left Ventricle = LVEDP (Left heart preload): PCWP, PAWP, or PAOP Pulmonary Artery Diastolic (PAD) Left Atrial Pressure (LAP) Normal values: 8-12mmHg 7 8 Contractility Afterload Defined as the squeezing force generated by the Afterload—the ventricular force or pressure ventricles. required to overcome impedance to ejection. Refers to both the pressures of this ejection and the As impedance , ejection velocity and SV , amount of blood ejected. while ventricular workload & O2 consumption Manipulate with inotropic drugs Systemic vascular resistance (SVR): Left Normal SVR: 900-1400 dynes /sec/cm-5 Best global measure is CO Pulmonary vascular resistance (PVR): Right Normal ejection fraction is 50 – 70 % Normal PVR: 50-250 dynes /sec/cm-5 9 10 Cardiac Index Supply & Demand Cardiac Index—a more precise expression of CO, which takes into account the patient’s size Coronary artery patency Heart rate Normal CI = 2.5-4.2 L/min Diastolic filling time Preload Diastolic pressure Afterload CI < 2.0 is considered cardiogenic shock Hemoglobin Contractility 1.8-2.2 is low perfusion Arterial oxygen saturation Oxygen extraction by the Calculate: tissue Oxygen Demand Oxygen Supply CI = CO BSA 11 Heart 12 2 4/6/2013 Factors of SvO & ScvO SVO 2 2 2 SVO2 – amount of oxygen in the mixed SaO2 CO venous blood in the pulmonary artery Normal SVO: 70-75% (range 60-80%) 2 An estimate of the amount of oxygen returning to the cardiopulmonary circulation Reflects the patient’s ability to balance O 2 supply and demand at the tissue level Hgb O Tissue 2 Consumption 13 14 Oxygen Delivery Question SvO2 = 75% SaO2 = 100% Which of the following is a normal Venous compensatory response to a decrease in Return cardiac output? a. Increased oxygen delivery b. Decreased oxygen consumption Oxygen Arterial c. Increased oxygen extraction Oxygen Consumption 25% Delivery d. Decreased serum lactate The Cell 15 16 Cardiac Assessment Arterial Waveform Hemodynamic Monitoring Systolic Ejection (A) Peak of waveform ECG Interpretation Normal 90-140 Diastole (C) A Lowest portion of waveform B Heart Sounds Normal 60-90 Dicrotic Notch (B) Closure of Aortic valve C 17 18 3 4/6/2013 Peripheral Arterial Waveform Review: Right Atrial Waveform The PA catheter is threaded manually to the right atrium. A continuous pressure reading will demonstrate a CVP /RA waveform Normal RA: 2-6 mmHG 19 20 Preload CVP waveform What Decreases: What Increases: Pressure measurement is taken from Hypovolemia Vasoconstriction the a waveform (mean) at end- Position Change ↑ fluid volume expiration Vasodilation Right Heart Damage ↑ ventricular filling Normal RA/CVP: 2-6 mmHg time Atrial Arrhythmias Pericardial Effusion Bradycardia PEEP Tension Pneumothorax 21 22 Right Ventricular Waveform Pulmonary Artery Waveform As the PA catheter floats through the pulmonic valve and The RV is very irritable and ectopy is a potential into pulmonary circulation, the pulmonary systolic pressure complication during PA catheter insertion remains similar to RV systolic pressure Watch the monitor closely for Ventricular The catheter should stay here during continuous Tachycardia monitoring. Normal PA: Sys: 20-30 mmHg Normal RV: Sys: 15-30 Dia: 5-10 Dia: 2-6 mmHG Mean: 10-20 23 24 4 4/6/2013 Pulmonary Capillary Wedge Pressure Phlebostatic axis Apudlvmanocnea ruyn atirlt eitr yb escliogmhtelys lsomdagleledr iant a Normal PCWP: Head of the bed can range from flat to 60 degrees than the inflated balloon. 4 – 12 mmHG PA pressures may be significantly different in patients No blood flows distal to the catheter in a lateral position. tip. Allow 5 minutes for stabilization after changing the This pressure, the pulmonary artery patient’s position occlusion pressure (POAP), reflects LV pressure when the mitral valve is open. Resembles CVP waveform. The a wave falls later in the T-P cycle. The PCWP should be 1-4 mmHG lower than the PAD. IT SHOULD NEVER BE HIGHER! 25 26 Technical Factor: Technical Factors: Mechanical Ventilation Effect of Patient Respirations If the patient is on a mechanical ventilator, the positive pressure “pushes up” the PA tracing. “Ventilator Valleys” A PEEP > 10 will artificially elevate PA pressures If patient is breathing spontaneously, the negative pressure “pulls down” the PA tracing. “Spontaneous sky” The most accurate reading is obtained at respiratory end expiration. 27 28 Technical Factor: Spontaneous Respirations Afterload Normal SVR = 900-1400 dynes/sec/cm3 SVR = MAP-CVP x 80 CO MAP = systolic BP + (2) diastolic BP 3 Example: BP = 120/80 (93) CVP = 5 CO = 5 SVR = [(93 – 5) / 5] x 80 = 1406 29 30 5 4/6/2013 ECG Monitoring Pulmonary Vascular Resistance (PVR) Pulmonary Vascular Resistance (PVR) Treatment of Significant Arrhythmias reflects blood flow through the pulmonary circulation The resistance is influenced by the pulmonary capillaries & arteries Normal PVR = 50-250 dynes/sec/cm PVR = MPAP-PCWP x 80 CO 31 32 Conduction System Refractory Period KEY CONCEPT: An electrical stimulus landing on the T wave, may cause disorganized ventricular 33 contractions OR VENTRICULAR FIBRILLATION3 4 Question Premature Ventricular Contractions The cardiac monitor shows the rhythm below for your patient. Which of the following medications might the physician order? The complexes have a QRS > .12 seconds. Significance: • PVC’s can occur in healthy persons with normal hearts and no a. Atropine apparent cause. • Patients can be asymptomatic or feel “racing heart” / skipped b. Adenocard beats. • Frequent PVC’s increase risk of fatal arrhythmias x 5. c. Cardizem • Treat: More than 6/min, multi-focal, R on T configuration d. Amiodarone 35 36 6 4/6/2013 Amiodarone A patient with which of the following is at greatest risk for torsades de pointes? Dosage: Non-VT/V.fib: 150 mg IV over 10 min. Pulseless VT/V.fib: 300mg IV bolus a. Depressed ST segment b. Tall, tented T waves Adverse effects: c. Prolonged QT interval Hypotension and bradycardia are common during initial bolus. d. u-wave May be prevented by slowing the rate of infusion. 37 38 Second Line Drug: Lidocaine Too Fast Administration: Bolus: 1.0-1.5 mg/kg IVP; may repeat in 5-10 minutes to max of 3mg/kg Infusion: 1-4 mg/min Does not prolong QT Adverse effects: Confusion (most common), seizures, tremors. 39 40 Sinus Tachycardia Supraventricular Tachycardia Rate: 100-150 bpm Significance: If very fast, the heart cannot refill & results in ↓CO This tachycardia originates above the ventricles, but below the SA node. Characteristics: TREAT THE CAUSE! Rate: Rapid! Usually 160-250. May start / stop abruptly. QRS is normal looking. No bizarre, early, or late beats. Too fast to see a P wave. Significance: Must treat if prolonged 41 42 7 4/6/2013 SVT Treatment Atrial Flutter Try VAGAL maneuvers. Significance: If not effective, administer: Consider this a hazardous rhythm because it can suddenly change to a rapid ventricular response. ADENOSINE Indicated for stable SVT If patient is stable, no initial treatment. unresponsive to vagal maneuvers. Dose: 6 mg IV PUSH If ventricular rate is rapid, treatment is required. 12 mg IV PUSH 12 mg IV PUSH Adenosine depresses sinus & AV node activity. HALF LIFE: 10 seconds Not effective in ventricular rhythms. 43 44 Atrial Fibrillation R-R interval is always irregular Question Significance: A 69-year-old patient presents to the ED with If stable or chronic may be tolerated. complaints of palpitations and irregular heart If patient has symptoms, treatment will be beats for the last three of days. The cardiac required. monitor shows atrial fibrillation, a heart rate of 136 beats/min. His blood pressure is 124/76 mm Consider hazardous because ventricular rate Hg. Which of the following medications would can suddenly ↑. the physician likely order? Also lose atrial “kick”, which is 20% of the CO a. Lidocaine b. Cardizem c. Corvert d. Adenocard 45 46 To Control Rate, Irregular Narrow Complex Use Selective β- Blockers Tachycardia: Control of Rate Non-Selective: Propranolol (Inderal) Rate can be controlled by: Nadolol (Corgard) Selective agents: Beta Blockers Atenolol (Tenormin) Calcium Channel Blockers Betaxolol (Zebeta) Amiodarone * Metoprolol (Lopressor) Vasodilatory, Non-selective *Not considered a first line Labetalol (Normodyne) agent for narrow complex Carvedilol (Coreg) Shortest half-life: tachycardias Esmolol 47 48 8 4/6/2013 To Control Rate: Ventricular Tachycardia Use Calcium Channel Blockers Wide & bizarre QRS (> .12 sec) Significance: Slows AV node conduction & prolongs AV Treatment is REQUIRED nodal refractoriness Pulse or NO Pulse? Pulse & STABLE? Use AMIODARONE Example: Diltiazem Pulse & UNSTABLE ELECTRICAL CARDIOVERSION Do not use in: Drug-induced tachycardia Heart blocks Concurrent use of Beta blockers. 49 50 Question Electrical Cardioversion The nurse should perform which of the following interventions for a patient Immediate electrical cardioversion is indicated with chest pain, hypotension, and for a patient with serious signs & symptoms tachycardia at a rate of 180 beats/min? related to tachycardia. a. Administer amiodarone 150mg IV over 10 min b. Administer adenosine 6 mg rapid IVP c. Perform synchronized cardioversion d. Defibrillate with 300 joules 51 52 Synchronized Cardioversion: Synchronized Cardioversion: Energy Selection Energy Selection Start with 100 joules. If the rhythm does not change, recharge to 200 joules & repeat Repeat with 300 joules & 360 joules, if needed. Complications include: Deterioration into ventricular fibrillation Push the Synch button! Embolization of a thrombus 53 54 9 4/6/2013 Synchronized Cardioversion: Too Slow Pre-Medication For awake, alert patients who are hemodynamically stable, pre-medicate with both a sedative and a analgesic Sedatives Diazepam Watch for apnea & Midazolam hypoventilation after Etomidate sedation. Analgesics Frequent vital signs are Fentanyl required before Morphine & after cardioversion Merperidine 55 56 Sinus Bradycardia 3Heart Block Characteristics: Significance: PREPARE TO PACE! HR > 60 May be normal in All intervals within healthy, young New guidelines: normal limits patient. chronotropic drips except rate Treat symptomatic bradycardias! 57 58 Symptomatic Bradycardia Temporary Pacemakers Treat Bradycardia with BRADE Use an external generator. 3 types: Atropine: 0.5 mg IV push Transcutaneous Repeat every 3 – 5 min to total of 0.04 mg/kg (3 mg) Transvenous Dopamine: 2 to 10 mcg/kg/min Epinephrine gtt: Start at 1 mcg/ min and titrate Epicardial to patient response. 59 60 10
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