Measuring blood pressure from Korotkoff sounds as the brachial cuff inflates on average provides higher values than when the cuff deflates

OBJECTIVES

In this study, we test the hypothesis that if, as demonstrated in a previous study, brachial arteries exhibit hysteresis as the occluding cuff is deflated and fail to open until cuff pressure (CP) is well below true intra-arterial blood pressure (IAPB), estimating systolic (SBP) and diastolic blood pressure (DBP) from the presence of Korotkoff sounds as CP increases may eliminate these errors and give more accurate estimates of SBP and DBP relative to IABP readings. Approach. In 62 subjects of varying ages (45.1±19.8, range 20-6 - 75.8 years), including 44 men (45.3±19.4, range 20.6 - 75.8 years) and 18 women (44.4±21.4, range 20.9 - 75.3 years), we sequentially recorded SBP and DBP both during cuff inflation and cuff deflation using Korotkoff sounds. Results. There was a significant (p<0.0001) increase in SBP from 122.8±13.2 to 127.6±13.0 mmHg and a significant (p=0.0001) increase in DBP from 70.0±9.0 to 77.5±9.7 mmHg. Of the 62 subjects, 51 showed a positive increase in SBP (0 to 14 mmHg) and 11 subjects showed a reduction (-0.3 to -7 mmHg). The average differences for SBP and DBP estimates derived as the cuff inflates and those derived as the cuff deflates were 4.8±4.6 mmHg and 2.5±4.6mmHg, not dissimilar to the differences reported between IABP and NIBP measurements. Although we could not develop multiparameter linear or non-linear models to explain this phenomenon we have clearly demonstrated through ANOVA tests that both body mass index (BMI) and pulse wave velocity (PWV) are implicated, supporting the hypothesis that the phenomenon is associated with age, higher BMI and stiffer arteries. Significance. The implications of this study are that brachial sphygmomanometry carried out during cuff inflation could be more accurate than measurements carried out as the cuff deflates. Further research is required to validate these results with intra-arterial blood pressure measurements. .

Tracheal airway pressure in tracheostomy tube capping trials: an experimental study

BACKGROUND

Tracheostomy tube capping is a commonly used test to determine if the tracheostomy tube can be removed. The success of the capping trial depends on the patient's ability to maintain sufficient spontaneous breathing with an occluded tracheostomy tube. The impact of an occluded tracheotomy tube on airway resistance is currently unknown. The aim of this study was to investigate tracheal pressure during capping or stoma button insertion and potential determinants concerning cuff.

METHODS

Eight cuffed and uncuffed tracheostomy tubes and three stoma buttons of various manufacturers and sizes were inserted into the trachea model. Cuffs were completely deflated or contained atmospheric pressure. The trachea was ventilated bidirectional with a respirator in volume-controlled mode and volume flows 15-60 L/min. Tracheal pressure drop during inspiration as a parameter of pressure required to move gas through the airway was measured.

RESULTS

Tracheal pressure drops occurred linearly or irregularly during capping trials to a maximum of 4.2 kPa at flow rates of 60 L/min for atmospheric pressure cuffs. In tracheostomy tubes with completely deflated cuffs, pressure drop in the trachea reaches a maximum of 3.4 kPa at a flow rate of 60 L/min. For tracheostomy tubes with cuff smaller inner or outer diameters do not regularly result in lower tracheal pressure drop. The pressure drop varies between different tracheostomy tubes depending on the manufacturer. In cuffed tracheostomy tubes, we observed three phenomena: sail-like positioning, folding over, and tightening of the cuff during flow. The maximum tracheal pressure drop during stoma button insertion reaches 0.014 kPa.

CONCLUSIONS

The cuff is a central element for the pressure drop in the airway and thus airway resistance during spontaneous translaryngeal breathing with a capped TT. Complete deflation reduces the pressure drop in the trachea. Due to deformation of the cuff, measured pressures are irregular as the volume flow is increased. Incomplete deflated cuffs and material characteristics of tracheostomy tubes and cuffs in addition to anatomical and clinical variables may cause unsuccessful capping trials due to increased airway resistance. All stoma buttons showed that pressure drop and thus airway resistance due to stoma buttons has no clinical relevance.

Clinical indicators associated with successful tracheostomy cuff deflation

BACKGROUND

Tracheostomy cuff deflation is a necessary stage of the decannulation pathway, yet the optimal clinical indicators to guide successful cuff deflation are unknown.

OBJECTIVES

The study aims were to identify (1) the proportion of patients tolerating continuous cuff deflation at first attempt; (2) the clinical observations associated with cuff deflation success or failure, including volume of above cuff secretions and (3) the predictive capacity of these observations within a heterogeneous cohort.

METHODS

A retrospective review of 113 acutely tracheostomised patients with a subglottic suction tube in situ was conducted.

RESULTS

Ninety-five percent of patients (n=107) achieved continuous cuff deflation on the first attempt. The clinical observations recorded as present in the 24h preceding cuff deflation included: (1) medical stability, (2) respiratory stability, (3) fraction of inspired oxygen ≤0.4, (4) tracheal suction ≤1-2 hourly, (5) sputum thin and easy to suction, (6) sputum clear or white, (7) ≥moderate cough strength, (8) above cuff secretions ≤1ml per hour and (9) alertness≥eyes open to voice. Using the presence of all 9 indicators as predictors of successful cuff deflation tolerance, specificity and positive predictive value were 100%, although sensitivity was only 77% and negative predictive value 19%. Refinement to a set of 3 clinically driven criteria (medical and respiratory stability, above cuff secretions ≤1ml/h) provided high specificity (100%), sensitivity (95%), positive predictive value (100%) and an improved negative predictive value (55%).

CONCLUSIONS

Key criteria can help guide clinical decision-making on patient readiness for cuff deflation.