25%

Approximate percentage of CO that goes to the brain:

15%

Approximate percentage of CO that goes to the heart:

5%

INVASIVE MONITORING

What complications can occur during central venous catheter placement?

Arterial puncture, air or catheter embolism, dysrhythmias, hemorrhage or arteriovenous fistulization, pneumothorax, pseudoaneurysm formation

What should you immediately do if a patient receives an air embolus?

Roll the patient to the left and place head down to keep air in right atrium/ventricle; attempt to aspirate air with central catheter/pulmonary artery catheter

Relative contraindications for pulmonary artery catheter placement:

Left bundle branch block, previous pneumonectomy

Treatment for hemoptysis after pulmonary artery catheter placement:

Immediately pull the pulmonary artery catheter slightly back and reinflate balloon, increase positive end expiratory pressure (PEEP) to help tamponade the bleeding, mainstem intubate the nonaffected side; attempt can be made to place a fogarty catheter down the affected side; if recalcitrant, may need thoracotomy and lobectomy

What West zone of the lung is the desired location for a pulmonary artery catheter?

Zone III (Pa > Pv > PA); pressure in the arteries (Pa), pressure in the veins (Pv), pressure in the alveoli (PA)

Which portion of the lung has the highest V/Q ratio and which portion has the lowest V/Q ratio?

V/Q ratio highest in upper lobes

V/Q ratio lowest in lower lobes

At what point in the respiratory cycle is the PCWP most accurate in a ventilated patient?

End expiration

At what point in the respiratory cycle is the PCWP most accurate in a nonventilated patient?

Peak inspiration

What conditions may make the wedge pressure unreliable?

Aortic regurgitation, high PEEP, mitral stenosis, mitral regurgitation, poor left ventricular compliance, pulmonary hypertension, pulmonary disease (acute respiratory distress syndrome [ARDS]), tamponade, pneumothorax

Pulmonary artery catheters allow the direct measurement of which physiologic parameters?

CVP, right atrial pressure, pulmonary arterial pressure, right ventricular end-diastolic pressure, pulmonary artery wedge pressure, SVO₂

Arrhythmias and conduction defects, knotting or catheter entrapment, pulmonary infarction, pulmonary artery rupture, valvular damage.

What is an intra-aortic balloon pump?

A mechanical device that consists of a cylindrical balloon that actively deflates in systole increasing forward blood flow by reducing afterload, and actively inflates in diastole increasing blood flow to the coronary arteries resulting in decreased myocardial oxygen demand and increased CO

When does the balloon from an intra-aortic balloon pump inflate on ECG?

T wave (diastole)

When does the balloon from an intra-aortic balloon pump deflate on ECG?

P wave or start of Q wave (systole)

Indications for intra-aortic balloon pump placement:

Bridge to heart transplant for patients with left ventricular failure; cardiogenic shock, percutaneous coronary angioplasty, post cardiothoracic surgery, preoperative use for high-risk patients (unstable angina with stenosis >70% main coronary artery), reversible intracardial mechanical defects complicating infarction, unstable angina pectoris, ventricular dysfunction with ejection fraction <35%

Absolute contraindications to intra-aortic balloon pump placement:

Aortic regurgitation, aortic dissection, severe aortoiliac occlusive disease

Relative contraindications to intra-aortic balloon pump placement:

Prosthetic vascular grafts in the aorta, aortic aneurysm, aortofemoral grafts

Desired location for the tip of the intra-aortic balloon pump catheter?

1 to 2 cm below the top of the aortic arch just distal to the left subclavian

CARDIAC PHYSIOLOGY

What is preload?

End diastolic length of cardiac myocytes, which is linearly related to end-diastolic volume (EDV) and filling pressure

What is afterload?

Resistance against ventricular contraction (SVR)

What is contractility?

The force of myocardial contraction

What 3 things determine stroke volume?

Left ventricular EDV (LVEDV) (preload), contractility, afterload

How is stroke volume calculated?

LVEDV – left ventricular end-systolic volume

How is the ejection fraction calculated?

Stroke volume/EDV

What is the normal O₂ delivery to consumption ratio?

5 to 1

Heart rate (HR), increased ventricular wall tension

What is the normal range for the alveolar:arterial gradient?

10 to 15 mm Hg

What shifts the oxygen-hemoglobin dissociation curve to the left?

Decrease temperature

Decrease 2,3-diphosphoglycerate (DPG)

Decrease pCO₂

Increase pH

What shifts the oxygen-hemoglobin dissociation curve to the right?

Increase temperature

Increase 2,3-DPG

Increase pCO₂

Decrease pH

SHOCK

What is the definition of shock?

Inadequate perfusion to meet the body’s metabolic needs

What are the 5 broad categories of shock?

Hypovolemic, obstructive, neurogenic, septic, cardiogenic

Table 22-1 Signs and Symptoms of Advancing Stages of Hemorrhagic Shock

What is the formula for the O₂ content of blood (CaO₂)?

CaO₂ = [Hb × SaO₂ × 1.34] + [0.003 × PaO₂]; Hb is hemoglobin in g/dL, SaO₂ is arterial O₂ saturation (%), PaO₂ is partial pressure of O₂ (mm Hg) in arterial blood

What is the formula for O₂ delivery (DO₂)?

DO₂ = Cao₂ × CO; [(Hb × Sao₂ × 1.34) + (0.003 × PaO₂)] × (HR × SV); Hb is hemoglobin in g/dL, SaO₂ is arterial O₂ saturation (%), PaO₂ is partial pressure of O₂ (mm Hg) in arterial blood, HR is heart rate (beats/min [bpm]), SV stroke volume (mL)

VO₂ = CO × (CaO₂ – CVO₂) × 10

(This can be rearranged to estimate the mixed venous saturation; the Fick equation)

How many milliliters of oxygen will a gram of hemoglobin bind when hemoglobin is fully saturated with oxygen?

1.34 mL of oxygen is bound to each gram of hemoglobin. (1.39 mL of oxygen is normally bound to hemoglobin, but you subtract the 3%–5% of circulating hemoglobin present as methemoglobin and carboxyhemoglobin.)

What does the solubility coefficient of 0.03 mL/L/mm Hg in the oxygen delivery equation signify?

0.03 mL of O₂ dissolves in 1 L of water when the PO₂ is 1 mm Hg at normal body temperature (37°C)

Manipulation of what factors can increase oxygen delivery?

Greatest increase of oxygen delivery with increasing hemoglobin content and SaO₂; can also increase oxygen delivery by raising CO by increasing either HR or stroke volume

What is the equation for oxygen extraction ratio?

O₂ ER = VO₂/DO₂

Usually expressed as a percentage; the normal value is 0.25 to 0.3 or 25% to 30%

ARRHYTHMIAS

Treatment for ventricular fibrillation/pulseless ventricular tachycardia:

1 shock (monophasic 360 J; biphasic, 100–200 J); cardiopulmonary resuscitation with additional countershocks if shockable rhythm obtained; epinephrine 1 mg IV and repeat every 3 to 5 minutes, or vasopressin, 40 units IV (to replace the first or second dose of epinephrine); consider amiodarone (300 mg IV), lidocaine (1–1.5 mg/kg), magnesium (1–2 g IV); if no shockable rhythm, revert to asystole/pulseless electrical activity algorithm

Treatment for asystole/pulseless electrical activity:

Verify with lead rotation; epinephrine 1 mg IV and repeat every 3 to 5 minutes, or vasopressin 40 units IV (to replace the first or second dose of epinephrine); consider atropine 1 mg IV every 3 to 5 minutes, up to 3 doses; if shockable rhythm, revert to ventricular fibrillation/ventricular tachycardia algorithm

Treatment for an unstable patient with bradycardia (HR <60 bpm):

Transcutaneous pacing; if transcutaneous pacing not immediately available, give atropine 1 mg and epinephrine 2 to 10 mg/min

In which patients with atrial fibrillation is anticoagulation unnecessary?