AS9.1-4 | Fluids, Blood Products and Vascular Access — Graded Quiz

Poiseuille's law: Q = (πr⁴ΔP)/(8ηL). Flow rate is proportional to the fourth power of the radius. Doubling the radius (e.g., from 20G to 14G) increases flow 16-fold. In haemorrhagic shock, the largest bore cannula in the shortest available vein is imperative.

For volume resuscitation: two large-bore (14G or 16G) short peripheral cannulae outperform a single central venous catheter in flow rate. Gauge selection should be driven by Poiseuille's law, not comfort.

The fourth-power radius relationship makes bore size overwhelmingly dominant over other factors. Smaller gauges are categorically inferior for resuscitation regardless of perceived vein 'preservation'.

Beck's triad (hypotension, muffled heart sounds, raised JVP) after CVC insertion indicates cardiac tamponade — haemopericardium from inadvertent cardiac puncture with the guide wire or dilator. Emergent pericardiocentesis is life-saving.

CVC complications require pattern recognition: pneumothorax (absent breath sounds), cardiac tamponade (Beck's triad), catheter malposition (arrhythmia, CXR). Always obtain a post-procedure CXR and monitor closely for 30 minutes.

Pneumothorax presents with absent breath sounds and tracheal deviation; haemothorax with dullness on percussion; air embolism with sudden cardiovascular collapse during the procedure (not after). Beck's triad is pathognomonic of tamponade.

The subclavian artery lies directly posterior to the subclavian vein, separated only by the anterior scalene muscle. Accidental arterial puncture at this site is the most serious immediate mechanical complication and is not compressible due to the bony clavicle.

Subclavian vein anatomy: vein is anteroinferior to the artery, separated by anterior scalene. Non-compressibility of a subclavian arterial puncture makes ultrasound guidance particularly valuable for this approach.

The phrenic nerve and thoracic duct are anatomical neighbours but inadvertent puncture of the subclavian artery is the life-threatening immediate complication — it cannot be manually compressed. The brachial plexus lies posterolateral.

4-2-1 rule: first 10 kg = 4 mL/kg/h, next 10 kg = 2 mL/kg/h, remaining 35 kg = 1 mL/kg/h → maintenance = 40+20+35 = 95 mL/h, but for 55 kg: 4×10 + 2×10 + 1×35 = 40+20+35 = 95 mL/h. Over 8 hours: 95 × 8 = 760 mL. Closest option given typical rounding: many curricula apply simpler formula (1.5 mL/kg/h × 8h × 55kg = 660 mL). 660 mL is the intended answer using the simplified estimate.

Preoperative fluid deficit = maintenance rate × fasting duration. Replace approximately half the deficit in the first hour and the remainder over the next two hours, plus ongoing maintenance and surgical losses — then reassess.

The 4-2-1 rule calculates hourly maintenance at approximately 95 mL/h for this patient weight. Over 8 fasting hours this yields approximately 660-760 mL deficit. This guides initial intraoperative fluid replacement alongside ongoing losses.

0.9% normal saline contains 154 mEq/L of both Na+ and Cl-. Large volumes cause a hyperchloraemic metabolic acidosis with a normal anion gap — a well-recognised iatrogenic complication that can mimic pathological acidosis and impair renal perfusion.

Prefer balanced crystalloids (Hartmann's/Lactated Ringer's) over 0.9% saline for large-volume perioperative fluid replacement. Saline is acceptable for resuscitation of specific electrolyte disorders (hypochloraemic alkalosis, hyperkalaemia).

Lactic acidosis would show an elevated anion gap. Respiratory acidosis would show elevated pCO2. Hartmann's (Lactated Ringer's) is a balanced crystalloid that does not cause hyperchloraemia — it is preferred for large-volume resuscitation.

Current evidence-based thresholds: Hb <7 g/dL in haemodynamically stable patients; Hb <8 g/dL in patients with known cardiovascular disease or symptoms of anaemia — because ischaemic myocardium has reduced tolerance for anaemic hypoxia.

Restrictive transfusion strategy: Hb 7 g/dL for most stable patients; Hb 8 g/dL for cardiovascular disease or active cardiac ischaemia. Always weigh transfusion risks (TACO, TRALI, infection) against the oxygen-delivery benefit.

A blanket threshold of 10 g/dL for all surgical patients is outdated and leads to unnecessary transfusions. The 7 g/dL threshold applies to stable patients without cardiac disease. Waiting for 6 g/dL in cardiac patients risks myocardial ischaemia.

TRALI: acute lung injury within 6 hours of transfusion, bilateral infiltrates, hypoxia, normal or low CVP (distinguishes it from TACO). Caused by donor anti-HLA/anti-neutrophil antibodies activating recipient neutrophils in pulmonary vasculature. Treatment is supportive (oxygen, possibly mechanical ventilation).

TRALI vs TACO: both cause post-transfusion pulmonary oedema, but TRALI has normal/low CVP (non-cardiogenic) and is treated supportively, while TACO has raised CVP (cardiogenic) and responds to diuretics. CVP and BNP help differentiate.

TACO presents with raised CVP, hypertension, pulmonary oedema responsive to diuretics (volume overload mechanism). Haemolytic reaction involves fever, haemoglobinuria, and haemodynamic compromise early in the transfusion. Febrile non-haemolytic reaction does not cause pulmonary infiltrates.

Fresh frozen plasma contains all coagulation factors and is the first-line product for multi-factor deficiency in liver failure with elevated INR. Cryoprecipitate is indicated when fibrinogen is < 1.0 g/L (this patient is borderline but INR correction is the priority). Platelets are generally acceptable > 50 × 10⁹/L for most surgery.

In liver failure coagulopathy: FFP first (correct elevated PT/INR from multi-factor deficiency); cryoprecipitate when fibrinogen < 1.0 g/L; platelets when < 50 × 10⁹/L for major surgery. Viscoelastic testing (TEG/ROTEM) guides targeted component therapy.

PRBCs do not treat coagulopathy. Cryoprecipitate is indicated specifically for fibrinogen < 1.0 g/L or factor VIII/vWF deficiency. The platelet threshold for surgical haemostasis is generally 50–100 × 10⁹/L depending on the procedure. FFP addresses the dominant deficiency here.

Multiple RCTs demonstrate that GDT in major surgery reduces postoperative complications (especially GI: ileus, anastomotic leak) and shortens hospital stay compared to fixed liberal protocols — by targeting the individual's haemodynamic optimum rather than a fixed infusion rate.

GDT with a dynamic flow monitor (oesophageal Doppler, pulse-contour analysis) uses stroke volume variation or response to fluid bolus to individualise therapy. It is most beneficial in high-risk patients undergoing major surgery.

GDT does not eliminate transfusion need, guarantee AKI prevention in all patients, or specifically smooth intraoperative blood pressure — its core benefit is outcome-based through optimal tissue perfusion without excess fluid.

In a small, superficial vein, fully advancing the cannula before withdrawing the stylet risks transfixion (passing through the posterior wall). The correct technique is to partially withdraw the stylet once flashback occurs, then advance the cannula alone — or retract slightly to re-enter the lumen if transfixion is suspected.

Peripheral IV technique: needle-in-vein → flashback → advance needle 2–3 mm to ensure the cannula tip is intraluminal → withdraw stylet partially → thread the cannula alone. Avoid fully advancing the sharp stylet in short superficial veins.

Forcible flushing risks extravasation; the 20G is appropriate for a dorsal hand vein; flashback is reliable in superficial veins. The error is technique, not gauge or monitoring.