Effect of compression waveform and resuscitation duration on blood flow and pressure in swine: One waveform does not optimally serve.

BACKGROUND: Chest compression (CC) research primarily focuses on finding the 'optimum' compression waveform using a variety of compression efficacy metrics. Blood flow is rarely measured systematically with high fidelity. Using a programmable mechanical chest compression device, we studied the effect of inter-compression pauses in a swine model of cardiac arrest, testing the hypothesis that a single 'optimal' CC waveform exists based on measurements of resulting blood flow. METHODS: Hemodynamics were studied in 9 domestic swine (∼30 kg) using multiple flow probes and standard physiological monitoring. After 10 min of ventricular fibrillation, five mechanical chest compression waveforms (5.1 cm, varying inter-compression pauses) were delivered for 2 min each in a semi-random pattern, totaling 50 compression minutes. Linear Mixed Models were used to estimate the effect of compression waveform on hemodynamics. RESULTS: Blood flow and pressure decayed significantly with time in both arteries and veins. No waveform maximized blood flow in all vessels simultaneously and the waveform generating maximal blood flow in a specific vessel changed over time in all vessels. A flow mismatch between paired arteries and veins, e.g. abdominal aorta and inferior vena cava, also developed over time. The waveform with the slowest rate and shortest duty cycle had the smallest mismatch between flows after about 30 min of CPR. CONCLUSIONS: This data challenges the concept of a single optimal CC waveform. Time dependent physiological response to compressions and no single compression waveform optimizing flow in all vessels indicate that current descriptions of CPR don't reflect patient physiology.

The involvement of physician assistants in inpatient care in hospitals in the Netherlands: a cost-effectiveness analysis.

OBJECTIVE: To investigate the cost-effectiveness of substitution of inpatient care from medical doctors (MDs) to physician assistants (PAs). DESIGN: Cost-effectiveness analysis embedded within a multicentre, matched-controlled study. The traditional model in which only MDs are employed for inpatient care (MD model) was compared with a mixed model in which, besides MDs, PAs are also employed (PA/MD model). SETTING: 34 hospital wards across the Netherlands. PARTICIPANTS: 2292 patients were followed from admission until 1 month after discharge. Patients receiving daycare, terminally ill patients and children were excluded. PRIMARY AND SECONDARY OUTCOME MEASURES: All direct healthcare costs from day of admission until 1 month after discharge. Health outcome concerned quality-adjusted life years (QALYs), which was measured with the EuroQol five dimensions questionnaire (EQ-5D). RESULTS: We found no significant difference for QALY gain (+0.02, 95% CI -0.01 to 0.05) when comparing the PA/MD model with the MD model. Total costs per patient did not significantly differ between the groups (+€568, 95% CI -€254 to €1391, p=0.175). Regarding the costs per item, a difference of €309 per patient (95% CI €29 to €588, p=0.030) was found in favour of the MD model regarding length of stay. Personnel costs per patient for the provider who is primarily responsible for medical care on the ward were lower on the wards in the PA/MD model (-€11, 95% CI -€16 to -€6, p<0.01). CONCLUSIONS: This study suggests that the cost-effectiveness on wards managed by PAs, in collaboration with MDs, is similar to the care on wards with traditional house staffing. The involvement of PAs may reduce personnel costs, but not overall healthcare costs. TRIAL REGISTRATION NUMBER: NCT01835444.

Detection of a spontaneous pulse in photoplethysmograms during automated cardiopulmonary resuscitation in a porcine model.

INTRODUCTION: Reliable, non-invasive detection of return of spontaneous circulation (ROSC) with minimal interruptions to chest compressions would be valuable for high-quality cardiopulmonary resuscitation (CPR). We investigated the potential of photoplethysmography (PPG) to detect the presence of a spontaneous pulse during automated CPR in an animal study. METHODS: Twelve anesthetized pigs were instrumented to monitor circulatory and respiratory parameters. Here we present the simultaneously recorded PPG and arterial blood pressure (ABP) signals. Ventricular fibrillation was induced, followed by 20 min of automated CPR and subsequent defibrillation. After defibrillation, pediatric-guidelines-style life support was given in cycles of 2 min. PPG and ABP waveforms were recorded during all stages of the protocol. Raw PPG waveforms were acquired with a custom-built photoplethysmograph controlling a commercial reflectance pulse oximetry probe attached to the nose. ABP was measured in the aorta. RESULTS: In nine animals ROSC was achieved. Throughout the protocol, PPG and ABP frequency content showed strong resemblance. We demonstrate that (1) the PPG waveform allows for the detection of a spontaneous pulse during ventilation pauses, and that (2) frequency analysis of the PPG waveform allows for the detection of a spontaneous pulse and the determination of the pulse rate, even during ongoing chest compressions, if the pulse and compression rates are sufficiently distinct. CONCLUSIONS: These results demonstrate the potential of PPG as a non-invasive means to detect pulse presence or absence, as well as pulse rate during CPR.

The impact of compliant surfaces on in-hospital chest compressions: effects of common mattresses and a backboard.

PURPOSE: To evaluate, in a hospital setting, the influence of different, common mattresses, with and without a backboard, on chest movement during CPR. DESIGN AND SETTING: Sixty CPR sessions (140s each, 30:2, C:R ratio 1:1) were performed using a manikin on standard hospital mattresses, with or without a backboard in combination with variable weights. Sternum-to-spine compression distance was controlled (range 30-60mm) allowing evaluation of the underlying compliant surface on total hand travel. RESULTS: Movement of the caregiver's hands was significantly larger (up to 111mm at 50mm compression depth, p<0.0001) when sternum-to-spine compressions were performed without a backboard than with one. The extent of this variable extra travel effect depended on the type of mattress as well as the force of compression. Foam mattresses and air chamber systems act as springs and follow hand movement, while 'slow foam' mattresses incorporate time delays, making depth and force sensing harder. A backboard decreases the extra hand movement due to mattress effects by more than 50%, strongly reducing caregiver work. CONCLUSIONS: Total vertical hand movement is significantly, and clinically relevantly much, larger than sternum-to-spine compression depth when CPR is performed on a mattress. Additional movement depends on the type of mattress and can be strongly reduced, but not eliminated, when a backboard is applied. The additional motion and increased work load adds extra complexity to in-hospital CPR. We propose that this should be taken into account during training by in-hospital caregivers.

The quality of chest compressions by trained personnel: the effect of feedback, via the CPREzy, in a randomized controlled trial using a manikin model.

Even after training, the ability to perform effective cardiac compressions has been found to be poor and to decrease rapidly. We assessed this ability with and without a non-invasive feedback device, the CPREzy, during a 270s CPR session in an unannounced, single-blinded manikin study using 224 hospital employees and staff chosen at random and using a non-cross over design. The two groups self-assessed their knowledge and skills as adequate. However, the control group (N=111) had significantly more difficulty in delivering chest compressions deeper than 4 cm (25 versus 1 candidate in the CPREzy group), P=0.0001. The control group compressed ineffectively in 36% (+/-41%) of all compressions as opposed to 6+/-13% in the CPREzy group (N=112, P=0.0001). If compressions were effective initially, the time until >50% of compressions were less than 4 cm deep was 75+/-81s in the control group versus 194+/-87 s in the CPREzy group (P=0.0001 [-180 to -57.5]). After a few seconds of training in its use, our candidates used the CPREzy effectively. Against the background knowledge that estimation of compression depth by the rescuer or other team members is difficult, and that performing effective compressions is the cornerstone of any resuscitation attempt, our data suggests that a feedback device such as the CPREzy should be used consistently during resuscitation.