Bucket thinking treats each shock as a pure type: sepsis gets fluids and antibiotics, cardiogenic gets pressors, arrhythmia is a separate issue, and the ventilator is only a lung tool. In reality shock is usually mixed — sepsis with poor intake and an underlying cardiomyopathy, AF or flutter driving low output, a post-intubation preload drop or auto-PEEP masquerading as “worsening shock,” or RV failure layered on vasoplegia and hypoxemia. Don’t stop thinking after the label.

Recognize perfusion failure, then move quickly: oxygen and airway support, IV or central access, cultures (blood, sputum, urine) with antibiotics when indicated, ABG/VBG, lactate, CBC/CMP, and troponin, plus EKG, CXR, bedside POCUS or formal echo, and CTA chest where the story fits. Treat and reassess rather than waiting for a complete picture.

No single marker rules shock in or out — trajectory matters. Skin temperature reflects peripheral perfusion, but warm does not exclude shock. Lactate reflects stress and hypoperfusion, but can stay elevated after flow improves or rise for non-hypoperfusion reasons. Pulse pressure tracks stroke volume and arterial tone. Urine output is a late, confounded signal (CKD, diuretics). Mentation is multifactorial. Read them together.

A low ScvO₂ suggests low cardiac output, anemia, hypoxemia, or high demand (fever, shivering, sepsis). A normal or high ScvO₂ means oxygen is being delivered but not extracted — high-output states, shunting, or maldistribution, as in sepsis or cirrhosis. A reassuring number can mislead when extraction is impaired.

Anchor on the ranges: CVP 2–6, RV systolic 15–30, PA systolic 15–30, PA diastolic 4–12, mPAP 8–20 (>20 = pulmonary hypertension), PCWP roughly 6–15, CO 4–8 L/min, CI 2.5–4, SVR 800–1200, PVR 0.3–2.0 Wood units. Basic patterns: LV failure = high wedge, low CI; RV failure = high CVP, lower wedge, low CI; distributive = low SVR; mixed septic-cardiogenic = low CI with variable filling pressures.

PAPi = (PA systolic − PA diastolic) / CVP — RV squeeze divided by RV congestion, or push versus traffic jam. Normal is above 2; in many of our ICU cases the working threshold is 0.9, and a PAPi below 0.9 is very specific for RV dysfunction.

SVR = (MAP − CVP)/CO × 80 (normal 800–1200). Beware the normalization fallacy: elevated SVR with a normal or low MAP may simply be compensatory. Elevated SVR with an adequate MAP and CVP may benefit from afterload reduction; elevated SVR with low CO and poor perfusion may need an inotrope; sometimes the move is to start weaning pressors. PVR = (mPAP − PCWP)/CO (normal 0.3–2.0 Wood) — optimize the ventilator first (oxygenation, ventilation, pH, PEEP) before reaching for pulmonary vasodilators.

A CVP above 15 is more specific for RV failure, but elevation can also come from severe hypervolemia, a PEEP up-titration, tamponade, pneumothorax, or abdominal compartment syndrome. CVP does not equal volume status — for a low CVP, pulse-pressure variation (PPV >13% suggests fluid responsiveness) is more useful than CVP alone. Wedge approximates left-sided filling: a high wedge with low CI points to LV failure.

Sedation and positive pressure routinely drop the pressure: propofol vasodilates and depresses the heart, PEEP reduces venous return, and auto-PEEP can look like “worsening shock.” Anticipate the preload drop around intubation, and when a patient deteriorates in that window, look at the ventilator and sedation before adding fluid or pressor.

Check it with an end-expiratory hold. Consequences: hypotension from reduced venous return, and alveolar overdistention. Risk factors: asthma, COPD, or CF; a high respiratory rate; an increased I:E ratio. Management: lower the rate or I:E ratio, and for severe hemodynamic compromise, disconnect from the ventilator and bag (running it by the attending).

Know the basics and the common alarms. IABP: position at the level of the carina, and watch augmentation timing and limb ischemia. Impella: the P-level sets support; suction alarms usually signal too little LV filling (low preload, RV failure, tamponade, high PEEP, or too high a P-level) — lower the P-level first, try albumin, then check a plasma-free hemoglobin. Recurrent suction, hemolysis, bleeding, purge-pressure problems, or a sudden drop in flow are reasons to call the intensivist.

Match the intervention to the dominant physiology: an inotrope for a low pump; diuresis or CRRT and lower PEEP for congestion; norepinephrine, vasopressin, steroids, and source control for low SVR; a small bolus (if responsive) or blood for low preload; ventilation and pH optimization plus afterload reduction for high PVR or RV failure; cardioversion or pacing for rhythm; and fixing the tube, bronchospasm, or PEEP for ventilator problems. Then reassess — and avoid the trap of “the next liter” or “the next pressor” before naming what changed and whether your last move did what you predicted.