Cardiogenic Shock

Nail the shock category first - A 12-lead ECG, serum lactate, cardiac biomarkers, coagulation profile, renal and liver function, blood gas, and a chest radiograph separate this from the hypovolemic, obstructive, and distributive shock that look identical at the bedside. Echocardiography is what tells you the mechanism — systolic versus diastolic dysfunction versus a valvular lesion.

Physical findings that point cardiogenic - Narrow pulse pressure, elevated jugular venous pulsations, lung crackles, cold clammy skin, oliguria, altered mental status, and significant arrhythmias on telemetry or ECG in a patient with cardiac-sounding chest pain.

Revascularization is the treatment - Early restoration of coronary blood flow is the single most important intervention when MI is the cause; SHOCK trial data support early revascularization combined with medical management. If they are going to the cath lab, your job is to hold perfusion pressure and get them there.

Inotrope first, then pressor - Dobutamine is the most commonly used inotrope; add norepinephrine when perfusion pressure is still inadequate. Fluids only in the absence of pulmonary edema, and then judiciously — this ventricle does not reward volume.

Fix the rhythm rather than out-titrate it - Unstable tachyarrhythmia or bradyarrhythmia gets ACLS and cardioversion. The arrhythmia is frequently what tipped a marginal ventricle into shock.

Stop the myocardial depressants - Beta-blockers and anything else that depresses heart function come off. Every further hit to contractility feeds the spiral.

Induction is the moment of maximum risk - Any agent that drops SVR or contractility removes the compensation holding up a cardiac index already at or below 2.2. Have the vasopressor and inotrope running and an arterial line in before you push induction drug.

Know what mechanical support is in place - An intra-aortic balloon pump inflates in diastole to displace blood into the proximal aorta and deflates rapidly in systole to cut afterload. It is contraindicated in severe aortic regurgitation, aortic dissection, uncontrolled sepsis, and uncontrolled bleeding disorders, and it requires therapeutic anticoagulation, usually heparin, with daily creatinine, platelet count, and hemoglobin. Percutaneous LVADs and VA-ECMO are the next escalation — know what is in the groin before you position.

Monitor for the sequelae, not just the pressure - Oliguria, coagulopathy, poor oxygenation, loss of pulses, abdominal pain suggesting mesenteric ischemia, and stroke. Multiorgan failure is common even after successful revascularization, so a good number on the monitor is not the endpoint.

It is the pump, not a sac - prove it - Tamponade and pump failure both run high filling pressures, so a high central venous pressure will not sort them out. On right heart catheterization, advanced tamponade equalizes central venous, pulmonary artery, and pulmonary capillary wedge pressures across all chambers and blunts the Y-descent on the right atrial waveform. In left ventricular failure the wedge sits well above the central venous pressure. Neither the equalization nor the attenuated Y-descent belongs to a failing ventricle.

Rule out pharmacologic shock before you commit - Benzodiazepines, beta blockers, calcium channel blockers, opioids, anticholinergics, and sildenafil all produce vasodilation or myocardial depression that reads as cardiogenic shock. Check the medication administration record and the prehospital drugs before the diagnosis is locked in, because the treatment diverges completely.

The septic patient with a failing ventricle - The categories are not mutually exclusive, and sepsis on top of a marginal ventricle is the common version. The treatments pull against each other: septic shock wants 30 mL/kg of isotonic crystalloid inside the first 3 hours, and a ventricle at a cardiac index of 2.2 will not take it. Echo settles which problem is in front of you, and the answer changes - the same patient can need volume early and inotrope with restriction an hour later.

Subjective and objective perfusion move at different speeds - Capillary refill, mental status on the Glasgow Coma Scale, and urine output are the subjective read on oxygen delivery; lactate, mixed venous saturation, heart rate, and blood pressure are the objective one. Notice that the diagnostic criteria for cardiogenic shock are built out of late findings - urine output at or below 30 mL/hr, cool extremities - so meeting the definition means you are already well down the spiral rather than early in it.

Agent choice for a ventricle that cannot compensate - Etomidate's hemodynamic stability is why it is the usual pick for a poor ejection fraction, coronary disease, or a severe valvular lesion: heart rate and cardiac output stay put, and myocardial oxygen supply and demand stay proportional. Know its one hemodynamic cost - the modest pressure drop it does cause comes from a fall in systemic vascular resistance, which is exactly the compensation a fixed-output ventricle cannot make up, so have the pressor running before you push it. Ketamine raises heart rate and blood pressure by sympathetic stimulation, the wrong direction for an ischemic myocardium's oxygen balance, and its direct negative inotropy shows through once catecholamine reserve is spent.

Cardiogenic shock is circulatory failure from a primary cardiac disorder — cardiac output falls far enough that end organs are hypoperfused and tissue goes hypoxic. The clinical definition is a systolic pressure at or below 90 mmHg for 30 minutes or more (or support needed to hold it there) with urine output at or below 30 mL/hr or cool extremities; hemodynamically, a cardiac index at or below 2.2 L/min/m2 with a pulmonary capillary wedge pressure above 15 mmHg.

Acute MI is the most common cause — roughly 5% to 8% of STEMIs and 2% to 3% of NSTEMIs. Ischemia depresses both systolic and diastolic LV function, and the resulting low output and low perfusion pressure worsen the coronary ischemia that started it. Compensatory vasoconstriction is then undercut by inflammatory mediators — IL-1, TNF-alpha, IL-6, nitric oxide, peroxynitrite — that vasodilate and are directly cardiotoxic. Mortality exceeds 30%.

Cardiogenic shock is one of four shock categories - distributive, hypovolemic, cardiogenic, and obstructive. It shares low cardiac output and reduced oxygen transport with hypovolemic and obstructive shock, while distributive shock is the outlier, running a low peripheral vascular resistance with abnormal oxygen extraction. What separates cardiogenic from hypovolemic shock is filling: cardiogenic shock runs an elevated central venous pressure alongside a raised peripheral vascular resistance, where hypovolemic shock runs a reduced central venous pressure with that same raised resistance.

Mixed venous oxygen saturation completes the picture. Normal is 65% to 75%, meaning tissues extract 25% to 35% of what you deliver, and when cardiac output falls extraction climbs and the saturation drops. The relationship behind it is worth holding onto - saturation varies directly with arterial saturation, hemoglobin, and cardiac output, and inversely with oxygen consumption - because it means the number also rises when you transfuse, when you oxygenate, and when you sedate or cool the patient. A climbing mixed venous saturation is not by itself evidence that the ventricle got better.