It is important to establish the presence or absence of utility of invasive blood pressure monitoring as arterial lines are not a benign intervention. Potential issues include pain for patients, limiting movement/participation with physical therapy, bacteremia, and potentially can risk digital ischemia.
Paper: Haber, EN et al. Accuracy of Noninvasive Blood Pressure Monitoring in Critically Ill Adults. J Intensive Care Med 2024. PMID: 38215002
Clinical Question: In critically ill adults in the ICU is noninvasive blood pressure (NIBP) monitoring similar (≤10% difference) to invasive arterial blood pressure (IABP) monitoring?
What They Did:
- Single center, retrospective, observational study of critically ill adults
- Authors were evaluating agreement (≤10%) difference between simultaneously measured invasive arterial blood pressure (IABP) and noninvasive blood pressure (NIBP)
Outcomes:
- Primary: Agreement of MAP between IABP and NIBP
- Defined as a difference of ≤10% in simultaneously recorded IABP and NIBP
Inclusion:
- All consecutive patients admitted to the MICU from April 2019 to July 2021
- Arterial line in place
- At least one BP measurement taken from arterial line along with a simultaneous measurement made noninvasively
Exclusion:
- Non-simultaneous BP meaurements
Results:
- 1852 critically ill adults with simultaneous IABP and NIBP readings
- BMI 27 (Range 23 to 32)
- Morbidly Obese (BMI >40): 8%
- A-Line Location: Radial 81% > Femoral 11% > Other 8%
- Mechanical Ventilation: 58%
- Renal Replacement Therapy: 19%
- Most Common Admission Diagnoses: Respiratory Failure 34% > Sepsis 23% > Primary CNS Disease (i.e Stroke) 18%
- 52,717 simultaneous IABP and NIBP measurements (Median of 13 measurements per patient)
- 42,184 of the comparisons were made between a radial line and a cuff
- 6,768 comparisons were made between a femoral line and a cuff
- 3,765 comparisons were made between brachial/axillary, or dorsalis pedis line and a cuff
- Median Difference in MAP (Primary Outcome):
- IABP MAP: 77mmHg (Range 68 to 90)
- NIBP MAP: 84mmHg (Range 76 to 95)
- Mean Difference in MAP: 6mmHg; Range 1 to 12mmHg; P < 0.01
- 67% of measurements were in agreement
- Measurement Discrepancy seemed to be Associated with Parameters that Suggested Greater Severity of Illness:
- Median NE Dose: 9 vs 6ug/min
- Mechanical Ventilation: 61% vs 56%
- Continuous Renal Replacement Therapy: 22% vs 15%
- Logistic regression analysis identified 5 independent predictors of measurement discrepancy:
- Increasing Dose of Norepinephrine: aOR 1.10; 95% CI 1.08 to 1.12; p = 0.03 for every change in 5ug/min
- Lower MAP Value: aOR 0.98; 95% CI 0.98 to 0.99; p <0.01 for every change in 1mmHg
- Higher BMI: aOR 1.04; 95% CI 1.01 to 1.09; p = 0.01 for an increase in 1
- Increased Patient Age: aOR 1.31; 95% CI 1.30 to 1.37; p <0.01 for every 10 years
- Radial Arterial Line Location: aOR 1.74; 95% CI 1.16 to 2.47; p – 0.04
- IABP vs NIBP Concordance & MAP Cutoffs
- ≤55mmHg: 62%
- 65 to 75mmHg: 67%
- >75mmHg: 71%
Strengths:
- Largest evaluation of agreement between NIBP and IABP in critically ill patients
- Included patients were typical of an ICU population (i.e. on mechanical ventilation, on vasopressors, on continuous renal replacement therapy, etc…)
- Racially diverse population with a wide range of illnesses
Limitations:
- Single center, retrospective study
- Limited number of cardiac patients limits generalizability to this population of patients
- Unclear how long patients had been in ICU for when info was gathered (i.e. were they in the resuscitative phase? Was norepinephrine being titrated? Were patients still hypoperfused?)
- Mean blood pressures in this study suggest this group of patients was not that sick
- Simultaneous measurement of NIBP and IABP was clinician or nursing preference without a protocol (i.e. patients with more discrepant readings had NIBP checked more frequently)
- Some patients were on multiple vasopressors, but for an unclear reason the authors decided to only evaluate the dose of norepinephrine
- MAP discrepancy is not a patient oriented outcome (i.e. how did this impact morbidity/mortality?)
- While predictors of discrepancy between IABP and NIBP were statistically significant, many of them had a very low odds ratio (very close to crossing 1) indicating a modest ability of these factors to predict measurement disagreements (i.e. the statistical significance is due to the large sample size)
Discussion:
- In this single center observational retrospective trial there was significant agreement in almost 2/3rds of simultaneous NIBP and IABP measurements across a range of blood pressures and severity of illness. The median difference between IABP and NIBP was 6mmHg in MAP.
- There were 5 predictors were IABP and NIBP measurements were discrepant (All associated with compromise in the accuracy of cuff BP measurements):
- Higher doses of norepinephrine
- Lower MAPs
- Higher BMI
- Increased patient age
- Radial arterial line location
- The premise of this study is to look at blood pressure monitoring. However ,arterial lines are used for other reasons:
- Arterial blood gases
- Frequent blood tests
- Continuous BP monitoring during procedures
- Monitoring rapid changes in clinical status
- Study was performed in ICU patients who appeared to be rather stable. This study does not address the utility of arterial lines vs NIBP in the acute resuscitative phase
Author Conclusion: “There was broad agreement between IABP and NIBP in critically ill patients over a range of BPs and severity of illness. Several variables are associated with measurement discrepancy; However, their predictive capacity is modest. This may guide future study into which patients may specifically benefit from an arterial catheter.”
Clinical Take Home Point: While this single center observational trial suggests that invasive blood pressure monitoring is not superior to non-invasive blood pressure monitoring, this study does not inform clinical practice during the acute resuscitation phase or take into account the other important uses of an arterial line.
References:
- Haber, EN et al. Accuracy of Noninvasive Blood Pressure Monitoring in Critically Ill Adults. J Intensive Care Med 2024. PMID: 38215002
- Kaufmann T et al. Non-Invasive Osicllometric Versus Invasive Arterial Blood Pressure Measurements in Critically Ill Patients A Post Hoc Analysis of a Prospective Observational Study. J Crit Care 2020. PMID: 32109843
For More Thoughts on This Topic Checkout:
Post Peer Reviewed By: Anand Swaminathan, MD (Twitter/X: @EMSwami)
