Discrepancies between NIBP and Arterial Pressure
Discrepancies between NIBP and Arterial Lines Pressures
- many reasons
Error in Intra-arterial measurement
- zero error (poor calibration, drift, wrong height)
- poor system (long tubing, soft wall, narrow bore)
- catheter kinked
- no pressure in the pressure bag
- local arterial stenosis
- spasm
- hypothermia
- intense vasoconstriction
- subclavian stenosis
Error in the NIBP measurement
- wrong cuff size
- irregular pulse (AF)
- subclavian stenosis
Lack of correlation because measures are from different sites and use different principles
Intra-arterial line
- fluctuations of vascular pressure cause a pulsation of the saline column
- displaces electomanometer’s diaphragm
- sensed electrically
- wave form built up by Fourier analysis from sinusoids or simple wave forms.
- wave forms differ depending on where the cannula is inserted.
NIBP
- single cuff inflated above systolic and then incrementally deflated while the amplitudes of cuff pressure oscillations measured by pressure transducer.
- cuff should be near level of heart.
- cuff pressure at which the amplitudes start to increase to 25-50% of maximum = systolic.
- the point of maximum oscillation = MAP (most reliable measurement)
- cuff pressure at which the amplitudes decrease by 80% or disappear = diastolic.
- time vs pressure graph constructed with above variables derived
Which reading do you believe?
- depends on the above factors and which recording you determine to be the most accurate
- MAP from the intra-arterial line is the most reliable
- if there is doubt may require a more proximal reading (femoral or long brachial catheter)
- in the vasculopath it would seem wise to trust the higher pressure
References and Links
Introduction to ICU Series
Introduction to ICU Series Landing Page
DAY TO DAY ICU: FASTHUG, ICU Ward Round, Clinical Examination, Communication in a Crisis, Documenting the ward round in ICU, Human Factors
AIRWAY: Bag Valve Mask Ventilation, Oropharyngeal Airway, Nasopharyngeal Airway, Endotracheal Tube (ETT), Tracheostomy Tubes
BREATHING: Positive End Expiratory Pressure (PEEP), High Flow Nasal Prongs (HFNP), Intubation and Mechanical Ventilation, Mechanical Ventilation Overview, Non-invasive Ventilation (NIV)
CIRCULATION: Arrhythmias, Atrial Fibrillation, ICU after Cardiac Surgery, Pacing Modes, ECMO, Shock
CNS: Brain Death, Delirium in the ICU, Examination of the Unconscious Patient, External-ventricular Drain (EVD), Sedation in the ICU
GASTROINTESTINAL: Enteral Nutrition vs Parenteral Nutrition, Intolerance to EN, Prokinetics, Stress Ulcer Prophylaxis (SUP), Ileus
GENITOURINARY: Acute Kidney Injury (AKI), CRRT Indications
HAEMATOLOGICAL: Anaemia, Blood Products, Massive Transfusion Protocol (MTP)
INFECTIOUS DISEASE: Antimicrobial Stewardship, Antimicrobial Quick Reference, Central Line Associated Bacterial Infection (CLABSI), Handwashing in ICU, Neutropenic Sepsis, Nosocomial Infections, Sepsis Overview
SPECIAL GROUPS IN ICU: Early Management of the Critically Ill Child, Paediatric Formulas, Paediatric Vital Signs, Pregnancy and ICU, Obesity, Elderly
FLUIDS AND ELECTROLYTES: Albumin vs 0.9% Saline, Assessing Fluid Status, Electrolyte Abnormalities, Hypertonic Saline
PHARMACOLOGY: Drug Infusion Doses, Summary of Vasopressors, Prokinetics, Steroid Conversion, GI Drug Absorption in Critical Illness
PROCEDURES: Arterial line, CVC, Intercostal Catheter (ICC), Intraosseous Needle, Underwater seal drain, Naso- and Orogastric Tubes (NGT/OGT), Rapid Infusion Catheter (RIC)
INVESTIGATIONS: ABG Interpretation, Echo in ICU, CXR in ICU, Routine daily CXR, FBC, TEG/ROTEM, US in Critical Care
ICU MONITORING: NIBP vs Arterial line, Arterial Line Pressure Transduction, Cardiac Output, Central Venous Pressure (CVP), CO2 / Capnography, Pulmonary Artery Catheter (PAC / Swan-Ganz), Pulse Oximeter
Critical Care
Compendium
Chris is an Intensivist and ECMO specialist at The Alfred ICU, where he is Deputy Director (Education). He is a Clinical Adjunct Associate Professor at Monash University, the Lead for the Clinician Educator Incubator programme, and a CICM First Part Examiner.
He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives. He was one of the founders of the FOAM movement (Free Open-Access Medical education) has been recognised for his contributions to education with awards from ANZICS, ANZAHPE, and ACEM.
His one great achievement is being the father of three amazing children.
On Bluesky, he is @precordialthump.bsky.social and on the site that Elon has screwed up, he is @precordialthump.
| INTENSIVE | RAGE | Resuscitology | SMACC