Meaning of Shock....

• Background

  Definition

  • Circulatory failure leading to ↓perfusion and thus tissue dysfunction due to ↓O2.
  • Due to pump failure – cardiogenic or obstructive shock – or peripheral circulation failure – hypovolaemic or distributive shock.

  Stages

  1. Initial:↓O2 and ↑lactate.
  2. Compensatory:
  • ↑RR
  • Sympathetic response: ↑HR, fluid retention.
  • ↑Renin, ↑ADH.
  3. Progressive. If compensatory mechanisms and treatment are unsuccessful:
  • Worsening hypotension due to vasodilation, blood pooling in capillaries, and fluid leak from vessels.
  • Metabolic acidosis.
  • Altered mental status.
  • Electrolyte imbalances.
  4. Refractory: irreversible.

  Types and causes

  Hypovolaemic shock

  Haemorrhage:
  • Trauma
  • Ruptured AAA.
  • Aortic dissection.
  • Upper GI bleed.
  • Ruptured ectopic pregnancy.
  Gastrointestinal:
  • Diarrhoea and vomiting.
  • Fluid sequestration e.g. in acute pancreatitis.
  Others:
  • Burns
  • Heat exhaustion.

  Distributive shock

  Vasodilation leads to a relative (though not absolute) deficiency in volume.
  Neurogenic shock:
  • CNS injury → ↓sympathetic tone → ↓BP and ↓HR.
  • Not to be confused with 'spinal shock', which is the immediate, complete loss of sensation, movement, and reflexes below the level of a spinal injury. Recovers over days to weeks. Not actually a type of shock.
  Sepsis and anaphylaxis are types of distributive shock, though may also include an element of hypovolaemic shock as altered capillary permeability leads to volume loss from the vasculature.

  Cardiogenic shock

  Primary pump failure due to:
  • MI or its complications e.g. ventricular septal rupture.
  • Myocarditis
  • Severe valve disease.
  • Trauma

  Obstructive shock

  Secondary pump failure due to:
  • Impaired ventricular emptying: pulmonary embolus.
  • Impaired ventricular filling: tension pneumothorax, cardiac tamponade.
  Often considered part of cardiogenic shock.

• Signs and symptoms

  General signs of hypoperfusion:
  • ↓BP: SBP <90 or 60 below normal.
  • Oliguria: <30 ml/hr
  • ↑HR. Pulse may be 'thready' (barely perceptible).
  • Capillary refill >2 seconds. Ideally check central cap refill.
  Specific signs:
  • Distributive shock (septic, anaphylactic, neurogenic) is characterised by vasodilation. Patient is warm and sweaty (though may become cold later) and pulse pressure may be wide, with a low DBP.
  • Cardiogenic, obstructive, or hypovolaemic shock often leads to vasoconstriction. Patient is cold and clammy and pulse pressure may be narrow.
  • Cardiogenic/obstructive shock: ↑JVP, ↓HR.
  Signs of hypovolaemic shock:
  • Orthostatic ↓BP can be an early sign of hypovolaemia.
  • In haemorrhagic shock, trauma or signs of GI bleed (melaena, abdo pain).
  • In later stages, ↓HR.

• Investigations

  Bloods:
  • Basics: FBC, U+E, LFT, glucose.
  • ABG: lactate >2 suggests hypoperfusion.
  • Coagulation screen.
  • Cross-match in haemorrhagic shock.
  Look for cause:
  • Blood and urine culture.
  • CRP
  • Cardiorespiratory: ECG, CXR, and echo.
  • Other imaging: abdo CT or US.

  Measures of circulatory function

  Mean arterial pressure (MAP)

  • MAP = {Diastolic} + {(Systolic-Diastolic)/3}

  Cardiac index (CI)

  • CI = Cardiac output ÷ Body surface area
  • ↓ in cardiogenic and hypovolemic shock.
  • ↑ in septic shock.

  Systemic vascular resistance (SVR)

  • ↑ in hypovolemic shock.
  • ↓ in septic shock.

  Pulmonary capillary wedge pressure (PCWP)

  • Measure of pulmonary artery pressure, an indirect measure of left atrial pressure.
  • ↓ in hypovolemic and septic shock.

• Management

  • Most patients with hypotension respond to IV fluids or, in heamorrhage, blood products.
  • Those with refractory hypotension may need inotropes and/or vasopressors.

• Intravenous fluid therapy

  Fluid physiology

  60% of the body is fluid, or roughly 40 L in an average (67 kg) man. It is distributed in 3 compartments:
  • ⅔ is intracellular fluid (ICF) (25 L).
  • ⅓ is extracellular fluid (ECF). 80% of ECF is in the interstitium (12 L), and 20% is intravascular (3 L).
  Colloids and crystalloids:
  • Colloids contain large insoluble molecules, increasing oncotic pressure and in theory keeping the fluid in the intravascular compartment for longer. In clinical trials, however, colloids have shown no benefit (and sometimes harm) relative to crystalloids.
  • Crystalloids contain water-soluble molecules, and are freely distributed across the extracellular compartments. Dextrose is also freely distributed into the intracellular space, but unlike water it is isotonic so doesn't risk causing cell swelling and rupture. Saline doesn't freely distribute into cells because of Na+-K+ ATPase
  • Physiological crystalloids such as Hartmann's and PlasmaLyte reduce the risk of electrolyte imbalances that can occur with unbalanced solutions such as normal saline. They are preferred by some in resuscitation and fluid replacement, though there is little evidence of superiority from clinical trials.

  Resusciation

  • 500 ml crystalloid bolus over <15 minutes. 250 ml if old or heart failure.
  • Reassess and re-give up to 2 L, then get expert help (if not sooner).
  • Don't wait until SBP is under 90. An SBP of 110 in the presence of ↑HR suggests impaired output.

  Replacement

  Estimate fluid losses, and replace gradually over 2-3 days i.e. in addition to maintenance fluids.

  Maintenance

  Basic needs:
  1. 25-30 ml/kg/day H2O. 20-25 ml/kg/day if old, kidney or heart failure, or malnourished. So just over 1 ml/kg/hr.
  2. 1 mmol/kg/day of Na+, K+, and Cl-. In general, don't give >10 mmol/hr.
  3. 50-100 g/day of glucose.
  Management:
  • Usually need around 2-3 litres per day, so around 100 ml/hr is typical e.g. 1 L over 8-10 hours. 500 ml over 8 hours if old or heart failure.
  • 1 L of normal saline contains 154 mmol of both Na+ and Cl-, and 1 L of Hartmann's contains 131 mmol of Na+ and 111 mmol of Cl- (plus 5 mmol of K+). So 500 ml of each roughly covers daily needs.
  • Typical daily regimen may be 1 L 5% dextrose with 20 mmol K+, then 500 ml normal saline with 20 mmol K+, then 1 L 5% dextrose with 20 mmol K+.
  • Monitor K+ to determine needs.
  • Monitor ↑Cl- daily if on normal saline due to risk of ↑Cl-.

• Transfusion

  Blood group testing

  • Crossmatch: blood group is determined, matching blood is retrieved, and a sample of the patient's blood is mixed with it to ensure there are no adverse reactions.
  • Group and save: blood group is determined, then the sample retained for around a week so that if blood is asked for, the mixing test can be done – but it does not mean that any blood is set aside or necessarily on site.

  Blood products and their indications

  Red blood cells (RBCs)

  • Indications: symptomatic ↓Hb, Hb <70 g/L, Hb <80 g/L in patients with ACS. In major haemorrhage, a combination of RBCs, FFP, and platelets are given.
  • 1 unit of blood increases Hb by around 10 g/L.
  • 1 unit of whole blood is around 450 ml, while 1 unit of packed RBCs (commoner) is 250-300 ml.
  • Prescribe one unit at a time, checking response (symptoms and/or Hb) after each.
  • If unused, must return to fridge within 30 minutes for reuse.

  Fresh frozen plasma (FFP)

  • Human plasma, which contains clotting factors.
  • Indications: major haemorrhage, warfarin reversal.
  • Prothrombin complex concentrates (e.g. Beriplex) are concentrated clotting factors from human plasma, and are preferred to FFP in contexts such as warfarin reversal. Contains factors 2, 7, 9, 10 (mnemonic 1927), plus protein C and S.
  • Cryoprecipitate is another alternative to FFP, though less used now. It is the precipitate from human plasma, and contains fibrinogen, f8, vWF, and f13.

  Platelets

  • Indications: PLT <50 K/μL and bleeding, PLT <20 K/μL and septic, PLT <10 K/μL otherwise.
  • Stop any anti-platelets if giving.

  Special considerations

  • CMV -ve: needed if pregnant or <1 years old.
  • Irradiated: needed in various haematological conditions – e.g. Hodgkin's lymphoma, planned bone marrow transplant – or if patient is on chemotherapy. Ask patient if they see a haematologist for anything.

  Administration

  • RBCs typically given over 2-3 hours, but can be up to 4. Most other products are given over 30 minutes.
  • Check obs at baseline, 15 minutes, and at end of transfusion.

  Adverse transfusion reactions

  Mild

  Signs:
  • <2°C rise in temperature.
  • Rash/urticaria.
  Management:
  • Pause transfusion and assess patient.
  • Consider paracetamol or chlorphenamine.
  • Re-start transfusion with close observation.

  Severe

  Signs:
  • >2°C rise in temperature.
  • Rigors
  • Loin or back pain.
  • Anxiety or angor animi.
  • Unexpected ↑HR.
  • Infusion site pain.
  Management:
  • Stop transfusion and replace any fluid needs with saline.
  • Call haematology, contact lab to return product, and complete incident report.
  • For some reactions e.g. infection, might need to contact blood service.
  Transfusion associated circulatory overload (TACO):
  • Commonest cause of transfusion-associated death.
  • Presents within 6 hours of transfusion with acute respiratory distress, pulmonary oedema, ↑HR, and ↑BP.
  • Risk factors: age <3 or >60, low birth weight, heart failure, kidney failure.
  • Bloods products are prescribed in mls in neonates to reduce the risk of TACO.
  Transfusion-related acute lung injury (TRALI):
  • Very uncommon.
  • Respiratory distress, ↓BP.
  • Usually due to FFP or platelets
  Other complications:
  • Anaphylaxis
  • Haemolytic anaemia.
  • ↑K+
  • Infection

• Inotropes and vasopressors

  Overview

  • Drugs that increase BP by increasing cardiac contractility (inotropes) and/or vasoconstriction (vasopressors). Many also increase HR (+ve chronotropy).
  • Indicated in shock for which IV fluids are insufficient or inappropriate.
  • Delivery is typically as an infusion through a central line.
  • Many commonly used agents are synthetic versions of endogenous catecholamines.

  Drugs, mechanisms, and indications

  For most outcomes, no clear evidence of superiority of any specific agent in RCTs, thus choice of agent is often guided by physiological reasoning and clinical familiarity.

  Noradrenaline

  • Aka norepinephrine
  • Primarily a vasopressor, via α1 agonism, but also inotropy via β1 agonism at higher doses. Reflex bradycardia from ↑BP typically cancels out chronotropic effects.
  • First line agent for shock in many ICUs.

  Adrenaline

  • Aka epinephrine.
  • Acts on all adrenergic receptors. At lower doses works primarily via β1, providing inotropy and chronotropy, and β2, causing airway and vessel dilation. α1 effects (vasoconstriction) at higher doses (inc. cardiac arrest dose).
  • Most commonly used for anaphylaxis and cardiac arrest. Price and availability also make it a popular alternative for shock in the developing world.

  Other agents

  Adrenergic:
  • Dobutamine: inodilator, with inotropy via β1 agonism and vasodilation via β2. Used in acute HF.
  • Dopamine: DA agonist at lower doses, alpha and Beta effects at higher doses. Risk of tachyarrhythmias.
  • Isoprenaline: non-selective β-agonist used for bradycardia.
  • Metaraminol: vasoconstriction via α1.
  • Phenylephrine: vasoconstriction via α1.
  Non-adrenergic:
  • Vasopressin: vasoconstriction via V1 receptor, as well as renal and endocrine effects inc. antidiuresis.
  • Milrinone: inodilator via PDE inhibition.
  • Levosimendan: inodilator, by increasing cardiac calcium sensitivity.

  Side effects

  • Peripheral administration carries a risk of extravasation and hence tissue necrosis via vasoconstriction. However, short-term delivery via a large, proximal peripheral line is sometimes acceptable.
  • Ischaemia, especially GI tract, kidneys, and extremities.
  • Arrhythmias, atrial and ventricular.

• Central lines

  Aka central venous catheters.

  Definition and use

  • An intravenous catheter in a major vein i.e. jugular (usually internal [IJ]), subclavian (SC), or femoral.
  • Allows administration of drugs and fluids, withdrawal of venous blood samples, and measurement of central venous pressure.
  • When used in isolation, the term 'central line' typically refers to a short-term (<2 weeks) line that is inserted directly into a major vein (i.e. nontunneled).

  Line placement

  • Asceptic technique.
  • Seldinger technique i.e. guidewire-directed.
  • Local anaesthesia ± sedation.
  • Should be ultrasound-guided, in preference to anatomical landmarks alone.
  • Confirm IJ and SC line placement with CXR. The tip should be in the SVC, though the right atrium and major veins themselves are also acceptable. Femoral line tips should be in the IVC, but a confirmatory XR is generally not needed.

  Indications

  • Drugs whose peripheral administration risks phlebitis or toxicity from extravasation e.g. vasopressors, chemotherapy, parenteral nutrition, potassium, amiodarone.
  • Long-term IV drugs e.g. chemotherapy, antibiotics, parenteral nutrition.
  • Inadequate peripheral venous access.
  • Bone marrow transplant.
  • Extracorporeal therapy: haemodilaysis/filtration, plasmapharesis.

  Complications

  • Bloodstream infection.
  • Vascular injury, bleeding, haematoma.
  • Pneumothorax, haemothorax.
  • Thrombosis
  • Arrhythmias due to guidewire or catheter stimulation of right heart.

  Long-term central lines

  The following central lines have a lower infection risk and less visible access sites, thus can be left in for several months.

  Tunnelled line

  • Line which is tunnelled under skin from a chest wall 'exit site', where it can be accesssed, to an 'entrance site', typically the IJV. Tip of line then advanced into SVC.
  • Typically inserted in theatre under fluoroscopy. Local anaesthesia ± sedation is usually sufficient.
  • Hickman catheter: dual-lumen line, usually for chemotherapy.
  • Broviac cather: single-lumen line, usually for antibiotics or parenteral nutrition.
  • Groshong catheter: unlike other catheters, tunneled after line is placed.
  • Dialysis and apharesis lines are both dual lumen lines specific to the needs of those indications.

  Venous access port

  • Aka implanted/subcutaenous port, Port-a-Cath.
  • Essentially a tunnelled line in which the access site is a port implanted entirely under the skin, typically upper chest. Tip may sit in SVC or right atrium.
  • Typically inserted in theatre under fluoroscopy. Local anaesthesia ± sedation is usually sufficient.
  • The ports itself contains a reservoir, with a silicone septum through which drugs are administered via a needle through the skin.
  • Cosmetically better than other forms of central access.

  PICC line (peripherally-inserted central catheter)

  • Inserted peripherally, but tip sits in a major vein: basilic/brachial/cephalic vein insertion → tip in SVC.
  • Can be inserted on wards and placement confirmed with CXR.
  • Typically used for intermediate to long-term access, around 1-6 months.
  • A midline catheter is an alternative for shorter-term access e.g. 2-4 weeks. Although inserted in an upper arm vein like a PICC, the midline is not a central line as its tip remains in that vein.