Say that three times fast.
We had a challenging case in our emergency department recently involving a patient with a self-inflicted stab wound to the anterior chest, which resulted in a pericardial effusion, prompting concern for the development of tamponade. A challenging element of the case involved thinking about the patient’s stability, and the urgent/emergent need for operative intervention v percutaneous intervention v observation — how could we determine whether this patient was, in fact, in cardiac tamponade or on their way towards developing this condition?
A classic teaching is to assess for a pulsus paradoxus, or an exaggerated decrease in the arterial blood pressure with inspiration. Traditionally this is done using a stethoscope and manual blood pressure cuff (I will not try to spell the S-word). If the difference in BP between the first expiratory Korotkoff sound and the first Korotkoff sound that no longer disappears with inspiration (the pulsus) is greater than 10 mmHg, a pulsus paradoxus is present.
Has anyone ever checked for one of these, or has this technique become like with many other physical exam findings, something that people are aware of but don’t really know how to check for? I’m not sure — I personally have never checked for one, and reach for the ultrasound when trying to risk stratify patients with pericardial effusions. Is there an easier way, or one that doesn’t require PoC echo?
These authors evaluate the utility of pulse oximetry, or plethysmography in the assessment of tamponade. They suggest that the difference between the inspiratory decrease in the magnitude of the waveform and the expiratory increase has been shown to correlate with intraarterially measured pulsus paradoxus. Unfortunately it turns out that this finding is not pathognomic for cardiac tamponade — it is linked to a number of other conditions (e.g. elevated intrathoracic pressures from asthma), and may be absent in patients who actually have tamponade physiology.
The most relevant article to this particular case is probably the study from Stone et al., “Respiratory changes in the pulse-oximetry waveform associated with pericardial tamponade.” from 2006, when they measured phasic respiratory variability in the pulse-oximetry waveform of patients undergoing aspiration of pericardial effusions. They found that the degree of respiratory variability in the pulse-oximetry waveform was significantly increased in these patients compared to effusion-less patients, and increased with the hemodynamic consequences of the tamponade. When the effusions were aspirated and drained, the variability disappeared.
So, is this something to hang your hat on? Probably not useful entirely for ruling OUT pericardial tamponade, but in a patient with an effusion if you’re asked by the consultant you wake up in the middle of the night whether you’ve checked for a pulsus yet, this might be an easier way than busting out your manual BP cuff and Googling how to check one the traditional way.