Cardiology JC011: Low BP / Fast Pulse + No BP / No Pulse: Shock And Fluid Balance, Basic Life Support And Resuscitation Flashcards
Determinants of Oxygen delivery
- Oxygen content of blood —> CaO2
- Ability to deliver oxygenated blood around the body —> CO
CaO2:
[(Hb x SaO2 x 1.34) / 100] + (pO2 x 0.0027)
—> 1.34 ml of O2 can be carried by 1g of fully saturated Hb
—> only 0.0027 ml of O2 dissolved in plasma for each kPa of O2 partial pressure
—> Hb can carry O2 more efficiently
SaO2 vs CaO2 vs PaO2:
SaO2: % saturation of Hb with O2
CaO2: actual amount of O2
PaO2: indicator of lungs’ ability to exchange gases with atmosphere
Oxygen Delivery (DO2)
DO2 = CO x CaO2
CO = HR x SV
Shock
Inadequate oxygen delivery to meet cellular metabolic demands
—> ∵ low CaO2 / low CO
- may be caused by failure of >=1 factors
Pathophysiology
Impaired Oxygen delivery —> Hypoxia —> Anaerobic metabolism (inefficient energy production) —> Acidosis (***Lactate) —> Cell death
***Classification of Shock
- Hypovolaemic
- Haemorrhage
- Burns
- Dehydration - Cardiogenic (pump failure)
- MI - Distributive
- Vasodilatation
- Myocardial depression - Others
- Obstructive
- Adrenocortical insufficiency
- Neurogenic (spinal cord injury)
- Hypovolaemic shock
***Volume failure
Result of IV blood volume depletion
- haemorrhage
- vomiting
- diarrhoea
- dehydration
- evaporation during major operations
Effect:
1. **↓ Preload —> ↓ SV
2. ↓ CO, BP, LV filling pressure (usually after decompensation)
3. ↑ Systemic Vascular Resistance (from vasoconstriction), ↑ HR
—> **sympathetic compensatory response to ↓ BP
—> avoid analgesic / anaesthetics that ↓ sympathetic response!!!
- Cardiogenic shock
***Pump failure
↓ Blood flow due to intrinsic defect in cardiac function
- Muscles: HF
- Valves: Stenotic, Incompetent
Effect:
- ↓ Contractility —> ↓ SV
- ***↑ LV filling pressure (backward failure) —> with / without Pulmonary edema
- ↑ SVR, ↑ HR —> sympathetic compensatory response to ↓ BP
—> ↑ SVR can be detrimental ∵ ↑ afterload make heart work even harder
—> ↑ HR can ↓ perfusion time of myocardium during diastole
- Distributive shock
***Normal Heart, Normal Blood volume
Peripheral vascular dilation —> ↓ SVR —> ***Apparent hypovolaemia
- sepsis
- anaphylaxis
- adrenal insufficiency
- neurogenic (SNS damaged in spinal cord esp. neck)
Effect:
1. ↑ CO but perfusion of vital organs (e.g. brain, kidney) is compromised ∵ ↓ BP
—> body loses ability to ***distribute blood properly
- Low to Normal LV filling pressure
- Warm peripheries (later become cold), Bounding pulses (↑ SBP ∵ ↑ CO + ↓ DBP ∵ vasodilation)
—> Low BP
- Obstructive shock
Mechanical obstruction to ***cardiac filling
Consider ***Cardiac tamponade
- ***JVP / CVP high
- BP low
- ***Pulsus paradoxus
Other causes:
- Tension pneumothorax
- Massive pulmonary embolus
***Treatment of Shock
- Identify cause
- Treat appropriately
- Restore oxygen delivery
- Basic life support
Hypovolaemic:
- ***IV fluid / blood
- Vasopressors (only short term effect) —> will still eventually decompensate —> cardiac arrest
Cardiogenic:
- **Vasodilators / **Inotropes (more short term) —> ↓ backward failure —> ↓ Stretch of heart (Starling curve)
Sepsis:
- IV fluid + ***Vasopressors (Adrenaline: direct antagonist of histamine)
- Eradication of infective focus, Give antiobiotics
Basic life support
- Recognition of Cardiac arrest
- **unconscious
- **absent / abnormal breathing
- healthcare provider can check for pulse for ***<10s, no pulse —> assume cardiac arrest - Shout for help
- AED
- ∵ most cardiac arrest related to ***VF (definitive treatment: AED) - CPR
- 30 compressions + 2 breaths
- 2 finger breadths above Xiphisternum
- open up airway: ***Head tilt, Chin lift, Jaw thrust
- use AED as soon as available - Drug therapy
- IV / IO access
- **Epinephrine 1mg every 3-5 mins
- **Amiodarone / ***Lidocaine for refractory VF / pVT - Consider advanced airway
- Quantitative waveform capnography —> measure CO2 concentration in expired gas
Recognition of Cardiac arrest
Diagnosis: Clinical
- ***Loss of consciousness
- Absent major pulse
- assume cardiac arrest if patient suddenly **collapse / unresponsive + **breathing abnormally
- do not take >=10s to check for pulse —> start chest compressions immediately
Opening airway
- Head tilt
- Chin lift
- Jaw thrust
Beware suspected cervical spine injury
Breathing / Not breathing
If breathing:
- Recovery position
- allow patient to breathe more easily
- regurgitate gastric content less likely to obstruct airway - Call for help
If NOT breathing:
Start chest compression
- Press down sternum 5-6 cm, release fully
- ***100-120 / min
- compression and release should take equal amount of time
- compression only CPR: continuously give compressions —> stop ONLY if patient shows signs of regaining consciousness AND breathe normally
Expired air ventilation
- Occlude patient’s nose
- Maintain chin lift
- Normal full deep breath
- Ensure good mouth to mouth seal
- ***Compression : Ventilation = 30:2
- Blow steadily (1s) until ***visible chest rise + watch chest rise
- Allow chest to fall
Substitute:
- Laerdal mask
- Laryngeal mask
- Self-inflating bag
Post-cardiac arrest care
- Optimise **Cardiopulmonary function + **Vital organ perfusion after ROSC (Return of Spontaneous Circulation)
- Transport to appropriate hospital / ICU / CCU
- Identify + Treat ACS / other reversible causes
- Control temperature (***hypothermia) to optimise neurologic recovery
- Anticipate, treat, prevent ***multiple organ dysfunction
Case 1: motorcyclist hit lamppost
- unconscious (GCS 7/15)
- weak, rapid pulse
- stridor (supraglottic obstruction, occur on inspiration)
(Wheeze: Infraglottic obstruction, occur on expiration)
- Airway
- neck stabilisation + intubate - Breathing
- ventilate (ambu bag, high conc. O2) - Circulation
- 14G IV cannula x2 (L arm + L saphenous vein)
- draw 10 ml blood for cross-match
Reassess:
- BP 60/40
- Pulse 150
- GCS 7
- R femoral fracture
- Pelvic fracture
- R chest injury
Why still hypotensive + tachycardic?
- Cardiogenic problem?
- Preload problem?
—> Likely to be Hypovolaemia
Treatment:
- IV colloid solution
- 1000 ml (fluid warmer) immediately
—> ***leg raise alternative quick way to assess volume
—> after leg raise BP↑ and HR↓ —> indicative of Hypovolaemia - Assess + Repeat
Initial improvement then deterioration
- ↓ SaO2
- ↑ Airway pressure
- ↓ Air entry R side
DDx:
- Further bleeding
- Tension pneumothorax
- Cardiac tamponade
CXR shows Tension pneumothorax (mediastinum pushed to other side)
—> Chest drainage
Case 2: 69 male 48 hours after surgery for aortic aneurysectomy
- epidural local anaesthetic infusion —> good analgesia
Pre-op co-morbidities:
- stable angina
- hypertension: well controlled
- non-insulin dependent DM
- smoker: mild COPD
Presentation:
- pale
- sweaty
- conscious but slightly confused
- Pulse 130 but irregular
- BP 90/50 (low considering patient’s HT history)
- Airway
- clear - Breathing
- slightly tachypnea, O2 therapy given (nasal) - Circulation
- IV cannula inserted - Resuscitation trolley sent for
DDx:
- Arrhythmia
- ECG shows AF
- secondary to MI? (peak time for post-op incidence) / Ischaemia? - Hypotension
- could be secondary to arrhythmia / excessive sympathetic block from epidural (but usually not tachycardic) / surgical bleeding - LA toxicity
- causes bradyarrhythmia
CXR —> shows pulmonary edema, ↑ CTR —> HF
—> Can conclude Cardiogenic shock / Pump failure
Pathophysiology of Cardiogenic shock from AF:
- Loss of atrial contraction
—> ↓ LV filling
- Fast HR in presence of ischaemic heart disease —> myocardial supply demand imbalance —> exacerbation of ischaemia —> ↓ myocardial contractility —> ↑ LV pressure —> ↑ lung pressure —> pulmonary edema
Treatment:
- Cardioversion (if unstable haemodynamics)
- Antiarrhythmic drugs (if stable) —> Amiodarone
- May require inotropic support
* **Excessive IV fluids will exacerbate the condition!!!
