Don’t ignore the diastolic

August 12, 2012 by  
Filed under Acute Med, All Updates, EMS, ICU, Kids, Resus

Most of us are pretty good at spotting hypotension and activating help or initiating therapy.

But ‘hypotension’ in many practitioners’ minds refers to a low systolic blood pressure. Who pays serious attention to the diastolic blood pressure? A low diastolic in a sick patient to me is a warning sign that their mean arterial pressure (MAP) is – or will be – low. After all, we spend about twice as long in diastole as in systole, so the diastolic pressure contributes more to the MAP than does the systolic.

A recent study showed that a low diastolic BP was one of several factors predictive of cardiac arrest on hospital wards: the most accurate predictors were maximum respiratory rate, heart rate, pulse pressure index, and minimum diastolic BP. These factors were more predictive than some of the variables included in the commonly used Early Warning Scores that trigger an emergency review.

The ‘pulse pressure index’ examined in the study is the pulse pressure divided by the systolic blood pressure (ie. [SBP-DBP]/SBP) which of course will be higher with lower diastolic blood pressures.

Importantly, the authors point out:


“In addition, our findings suggest that for many patients there is ample time prior to cardiac arrest to provide potentially life-saving interventions.”

…suggesting that there is still room for improvement in the identification and management of patients at risk for cardiac arrest, as the NCEPOD report ‘Cardiac Arrest Procedures: Time to Intervene?’ also showed.

They also recommend:


“…although systolic BP is commonly used in rapid response team activation criteria, incorporation of pulse pressure, pulse pressure index, or diastolic BP in place of systolic BP into the predictive model may be superior.”

Perhaps this may remind all of us to keep an eye on the diastolic as well as systolic BP when patients first present to us, and to include the importance of recognising diastolic hypotension in the teaching we provide our medical, paramedical and nursing students.

Predicting Cardiac Arrest on the Wards: A Nested Case-Control Study
Chest. 2012 May;141(5):1170-6 Free Full Text here


Background: Current rapid response team activation criteria were not statistically derived using ward vital signs, and the best vital sign predictors of cardiac arrest (CA) have not been determined. In addition, it is unknown when vital signs begin to accurately detect this event prior to CA.

Methods: We conducted a nested case-control study of 88 patients experiencing CA on the wards of a university hospital between November 2008 and January 2011, matched 1:4 to 352 control subjects residing on the same ward at the same time as the case CA. Vital signs and Modified Early Warning Scores (MEWS) were compared on admission and during the 48 h preceding CA.

Results: Case patients were older (64 ± 16 years vs 58 ± 18 years; P = .002) and more likely to have had a prior ICU admission than control subjects (41% vs 24%; P = .001), but had similar admission MEWS (2.2 ± 1.3 vs 2.0 ± 1.3; P = .28). In the 48 h preceding CA, maximum MEWS was the best predictor (area under the receiver operating characteristic curve [AUC] 0.77; 95% CI, 0.71-0.82), followed by maximum respiratory rate (AUC 0.72; 95% CI, 0.65-0.78), maximum heart rate (AUC 0.68; 95% CI, 0.61-0.74), maximum pulse pressure index (AUC 0.61; 95% CI, 0.54-0.68), and minimum diastolic BP (AUC 0.60; 95% CI, 0.53-0.67). By 48 h prior to CA, the MEWS was higher in cases (P = .005), with increasing disparity leading up to the event.

Conclusions: The MEWS was significantly different between patients experiencing CA and control patients by 48 h prior to the event, but includes poor predictors of CA such as temperature and omits significant predictors such as diastolic BP and pulse pressure index.

Comments

3 Responses to “Don’t ignore the diastolic”

  1. Matthew Mac Partlin on August 13th, 2012 17:02

    Hi Cliff,

    I routinely look at dBP when assessing a patient’s vitals. When low, I think about peripheral vasodilation and aortic regurgitation. When high, it becomes a threshold for diagnosing a hypertensive emergency (>110mmHg).

    This study backs up previous similar trials that have shown that vital signs like RR are underrated and often ignored in preference for starlet vitals like sBP.

    Matthew

  2. Robert Simpson on August 16th, 2012 00:55

    Thanks Cliff, an excellent post.
    I spend far too much of my time as an intensive care paramedic trying to explain the importance of diastolic pressure to students and junior staff. There is an unfortunate habit of accepting a systolic BP as the sole indicator of pressure and perfusion. This article will be getting printed off for the all to frequent “why does it matter” responses I get!

  3. Cliff on August 16th, 2012 16:44

    Great thanks for the feedback. I’m really chuffed prehospital professionals are finding it useful – that’s where we start making some of the biggest differences

    Cliff