Skip to main content

Which blood pressure is the baseline for the one-third drop after nitroglycerin?

Question #87

The Cardiac Ischemia Medical Directive contraindicates further nitroglycerin if systolic blood pressure drops by one-third or more of its initial value. If several blood pressures were obtained before treatment, which reading should be used?

Answer:

Use the first blood pressure obtained before nitroglycerin was administered as the initial value for this comparison.

Keep that baseline throughout the nitroglycerin treatment sequence; do not reset it to each newer reading. Continue to use the current blood pressure and clinical assessment to determine whether the patient meets all other treatment conditions and contraindications (Ontario Ministry of Health, 2025).

Example: An initial systolic BP of 150 mmHg has a one-third drop of 50 mmHg. A subsequent systolic BP of 100 mmHg or lower meets this stopping criterion, even if the immediately preceding reading was higher.

References

Ontario Ministry of Health. (2025). Advanced life support patient care standards (Version 5.4), Cardiac Ischemia Medical Directive. https://www.ontario.ca/files/2025-04/moh-advanced-life-support-als-patient-care-standards-pcs-5.4-en-2025-04-23.pdf

Back to the questions

Medical Directive Category

Cardiac Ischemia

Published

24 October 2026

ALSPCS Version

5.4

Views

7

Please reference the MOST RECENT ALS PCS for updates and changes to these directives.