From the Guidelines
To calculate the Pulmonary Embolism (PE) probability, I recommend using the Wells score, which is a widely validated and simple scoring system that classifies patients as having low, moderate, or high probability of PE. The Wells score consists of 7 variables, including clinical symptoms, signs, and risk factors, and has been prospectively validated in multiple studies, including a Class II investigation by Wells et al 1. The score ranges from 0 to 12, with higher scores indicating a higher probability of PE. A score of 0-1 indicates a low probability of PE (3.6%), a score of 2-6 indicates a moderate probability (20.5%), and a score of 6 or higher indicates a high probability (66.7%) 1.
When using the Wells score, it is essential to consider the patient's clinical presentation, medical history, and risk factors for PE. The score should be used in conjunction with D-dimer testing to further stratify patients and exclude PE in those with a low probability and a negative D-dimer result. The negative predictive value of the Wells score with D-dimer testing is high, with a study by Wells et al reporting a negative predictive value of 99.5% 1.
In addition to the Wells score, the Pulmonary Embolism Rule-out Criteria (PERC) can be used to exclude PE in patients with a low pretest probability, as shown in a study by Kline et al 1. The PERC consists of 8 clinical criteria, including age, pulse rate, oxygen saturation, and medical history, and has been validated in multiple studies. However, the PERC should only be used in patients with a low pretest probability of PE, as determined by clinical gestalt or the Wells score.
Overall, the Wells score is a widely validated and useful tool for calculating the probability of PE, and should be used in conjunction with D-dimer testing and clinical judgment to diagnose and manage patients with suspected PE. The use of the Wells score and PERC can help reduce unnecessary diagnostic testing and improve patient outcomes, while also reducing the risk of morbidity and mortality associated with PE.
From the Research
PEC Calculations
- PEC (Population Estimate of Clearance) calculations are not directly mentioned in the provided studies, but we can discuss the factors that influence vancomycin clearance:
- Renal function is a significant factor in vancomycin clearance, as it is primarily eliminated through glomerular filtration 2, 3.
- Creatinine clearance (CLCr) and age are covariates that influence vancomycin pharmacokinetics, with decreased renal function and older age resulting in lower clearance 3.
- The typical clearance value for vancomycin is around 2.829 L/h for a 75-year-old patient with a CLCr of 80 mL/min, and the rate constant of clearance with changing CLCr is 0.00842 3.
- Vancomycin dosing regimens can impact the risk of acute kidney injury (AKI) and mortality:
- High-dose vancomycin therapy may increase the risk of nephrotoxicity, particularly in patients with baseline deranged renal function or those receiving concomitant nephrotoxic agents 4.
- The use of vancomycin in combination with piperacillin/tazobactam or meropenem may also increase the risk of AKI, with some studies suggesting a higher risk with the vancomycin/piperacillin-tazobactam combination 5.
- Continuous infusion of vancomycin may be associated with a lower risk of AKI compared to intermittent infusion, as it minimizes peak concentrations and variability 6.
- To optimize vancomycin therapy and minimize the risk of AKI, it is essential to monitor renal function and adjust dosing regimens accordingly:
- Therapeutic drug monitoring is recommended for vancomycin, particularly in patients with altered kidney function or those receiving high-dose therapy 2, 3.
- Simulation studies can help determine the appropriate initial vancomycin dosage regimens to reach target steady-state trough concentrations and minimize the risk of AKI 3.