🩺 Peripheral IV Cannulation

Blood pressure measurement is a fundamental clinical skill used to assess cardiovascular status and screen for hypertension. It involves the use of a sphygmomanometer and stethoscope (manual) or an automated device to determine the pressure exerted by the blood against arterial walls during systole and diastole. Accurate technique is crucial to avoid misdiagnosis, as factors like cuff size, patient position, and rest period significantly impact readings. In the UK, NICE guidelines mandate specific thresholds for the diagnosis of hypertension, often requiring ambulatory monitoring for confirmation. Proper performance of this skill is essential for calculating the National Early Warning Score (NEWS2) and managing chronic cardiovascular risk.

Measurement of blood pressure is a core vital sign required for the assessment of cardiovascular health and hemodynamic stability in almost all clinical encounters. It is indicated for the screening and diagnosis of hypertension, as well as the monitoring of known hypertensive patients undergoing treatment. It is essential in acute settings to screen for shock, sepsis, or hypertensive emergencies. Furthermore, it is a routine component of pre-operative assessments and the longitudinal monitoring of chronic diseases such as diabetes and chronic kidney disease. Standardized measurements are also required for calculating the National Early Warning Score (NEWS2) in unwell patients.

Blood pressure should not be measured on an arm with an arteriovenous fistula (commonly found in renal dialysis patients) or on the side of a previous lymphedema-associated axillary node clearance (e.g., post-mastectomy). It should be avoided in limbs with acute trauma, extensive burns, or an existing intravenous infusion if an alternative site is available. If a patient has a peripherally inserted central catheter (PICC line), the contralateral arm must be used. In cases of suspected aortic dissection, blood pressure should be measured in both arms to identify a significant discrepancy. Severe skin conditions or fragile skin may also necessitate alternative sites or cautious technique.

A manual sphygmomanometer (mercury, aneroid, or validated digital) and a stethoscope are the primary tools required. An appropriately sized blood pressure cuff is essential; the bladder should encircle at least 80% of the arm circumference and 40% of the width. Alcohol wipes for cleaning the stethoscope diaphragm and earpieces between patients are necessary for infection control. A hard surface or pillow may be needed to support the patient's arm at the level of the heart. Documentation materials, such as a physical observation chart or an electronic patient record (EPR) system, are required to note the result, arm used, and patient position.

Begin by introducing yourself, confirming the patient's identity, and explaining the procedure. Ensure the patient has rested for at least five minutes in a quiet environment. Position the patient's arm so the antecubital fossa is at the level of the heart and remove restrictive clothing. Apply the cuff 2-3 cm above the antecubital fossa, aligning the arrow with the brachial artery. Palpate the radial pulse and inflate the cuff until the pulse disappears to estimate systolic pressure, then deflate. Place the stethoscope over the brachial artery, reinflate the cuff to 20-30 mmHg above the estimated systolic, and slowly deflate at 2-3 mmHg per second. The first sound (Korotkoff I) is the systolic pressure, and the point where sounds disappear (Korotkoff V) is the diastolic pressure. Record the results accurately.

Results should be interpreted according to NICE guidelines (NG136), where a clinic reading of 140/90 mmHg or higher suggests Stage 1 hypertension, requiring confirmation via ambulatory (ABPM) or home (HBPM) monitoring. Stage 2 hypertension is defined as a clinic reading of 160/100 mmHg or higher. A systolic reading below 90 mmHg, if symptomatic or significantly below the patient's baseline, may indicate hypotension or shock. Postural (orthostatic) hypotension is diagnosed if there is a drop in systolic blood pressure of 20 mmHg or more (or diastolic 10 mmHg) upon standing. Significant differences between arms (e.g., >15-20 mmHg) warrant further investigation for peripheral arterial disease or aortic pathology.

A frequent mistake is using a cuff that is too small for the patient's arm circumference, which provides a falsely elevated reading; conversely, a cuff that is too large can underestimate pressure. Failing to allow the patient to rest for 5 minutes before measurement or allowing them to talk during the procedure often results in transiently high readings. Positioning the arm significantly above or below the level of the heart will affect the hydrostatic pressure and lead to inaccurate results. Not inflating the cuff high enough to occlude the pulse initially can lead to missing the auscultatory gap, resulting in an underestimated systolic pressure. Finally, deflating the cuff too rapidly (faster than 2-3 mmHg per second) prevents accurate identification of Korotkoff sounds.

Always ensure the patient's feet are flat on the floor and their legs are uncrossed, as crossing legs can increase blood pressure. Palpate the radial pulse while inflating the cuff to estimate the systolic pressure first; this ensures you inflate the cuff 20-30 mmHg above the point the pulse disappears. Ensure the stethoscope diaphragm is placed over the brachial artery but not tucked under the cuff, as this creates noise interference. Maintain eye level with the manometer scale to avoid parallax error. Always clean your stethoscope before and after use to demonstrate good infection control practice.

Students must be aware of the 'white coat effect' and the importance of repeated readings; if the first reading is high, a second should be taken later in the consultation. Understanding the Korotkoff sounds (Phase I for systolic, Phase V for diastolic) is essential for manual measurements. Familiarity with the British and Irish Hypertension Society (BIHS) list of validated monitors is expected. Documentation should always include the arm used and the patient's posture (e.g., sitting or standing). Accuracy is paramount as hypertension is a major modifiable risk factor for stroke and myocardial infarction.