Intraperitoneal drain placement and outcomes after elective colorectal surgery: international matched, prospective, cohort study

Despite current guidelines, intraperitoneal drain placement after elective colorectal surgery remains widespread. Drains were not associated with earlier detection of intraperitoneal collections, but were associated with prolonged hospital stay and increased risk of surgical-site infections.Background Many surgeons routinely place intraperitoneal drains after elective colorectal surgery. However, enhanced recovery after surgery guidelines recommend against their routine use owing to a lack of clear clinical benefit. This study aimed to describe international variation in intraperitoneal drain placement and the safety of this practice. Methods COMPASS (COMPlicAted intra-abdominal collectionS after colorectal Surgery) was a prospective, international, cohort study which enrolled consecutive adults undergoing elective colorectal surgery (February to March 2020). The primary outcome was the rate of intraperitoneal drain placement. Secondary outcomes included: rate and time to diagnosis of postoperative intraperitoneal collections; rate of surgical site infections (SSIs); time to discharge; and 30-day major postoperative complications (Clavien-Dindo grade at least III). After propensity score matching, multivariable logistic regression and Cox proportional hazards regression were used to estimate the independent association of the secondary outcomes with drain placement. Results Overall, 1805 patients from 22 countries were included (798 women, 44.2 per cent; median age 67.0 years). The drain insertion rate was 51.9 per cent (937 patients). After matching, drains were not associated with reduced rates (odds ratio (OR) 1.33, 95 per cent c.i. 0.79 to 2.23; P = 0.287) or earlier detection (hazard ratio (HR) 0.87, 0.33 to 2.31; P = 0.780) of collections. Although not associated with worse major postoperative complications (OR 1.09, 0.68 to 1.75; P = 0.709), drains were associated with delayed hospital discharge (HR 0.58, 0.52 to 0.66; P < 0.001) and an increased risk of SSIs (OR 2.47, 1.50 to 4.05; P < 0.001). Conclusion Intraperitoneal drain placement after elective colorectal surgery is not associated with earlier detection of postoperative collections, but prolongs hospital stay and increases SSI risk

Evaluation of prognostic risk models for postoperative pulmonary complications in adult patients undergoing major abdominal surgery: a systematic review and international external validation cohort study

Background Stratifying risk of postoperative pulmonary complications after major abdominal surgery allows clinicians to modify risk through targeted interventions and enhanced monitoring. In this study, we aimed to identify and validate prognostic models against a new consensus definition of postoperative pulmonary complications. Methods We did a systematic review and international external validation cohort study. The systematic review was done in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. We searched MEDLINE and Embase on March 1, 2020, for articles published in English that reported on risk prediction models for postoperative pulmonary complications following abdominal surgery. External validation of existing models was done within a prospective international cohort study of adult patients (≥18 years) undergoing major abdominal surgery. Data were collected between Jan 1, 2019, and April 30, 2019, in the UK, Ireland, and Australia. Discriminative ability and prognostic accuracy summary statistics were compared between models for the 30-day postoperative pulmonary complication rate as defined by the Standardised Endpoints in Perioperative Medicine Core Outcome Measures in Perioperative and Anaesthetic Care (StEP-COMPAC). Model performance was compared using the area under the receiver operating characteristic curve (AUROCC). Findings In total, we identified 2903 records from our literature search; of which, 2514 (86·6%) unique records were screened, 121 (4·8%) of 2514 full texts were assessed for eligibility, and 29 unique prognostic models were identified. Nine (31·0%) of 29 models had score development reported only, 19 (65·5%) had undergone internal validation, and only four (13·8%) had been externally validated. Data to validate six eligible models were collected in the international external validation cohort study. Data from 11 591 patients were available, with an overall postoperative pulmonary complication rate of 7·8% (n=903). None of the six models showed good discrimination (defined as AUROCC ≥0·70) for identifying postoperative pulmonary complications, with the Assess Respiratory Risk in Surgical Patients in Catalonia score showing the best discrimination (AUROCC 0·700 [95% CI 0·683–0·717]). Interpretation In the pre-COVID-19 pandemic data, variability in the risk of pulmonary complications (StEP-COMPAC definition) following major abdominal surgery was poorly described by existing prognostication tools. To improve surgical safety during the COVID-19 pandemic recovery and beyond, novel risk stratification tools are required. Funding British Journal of Surgery Society

New and accurate results on the performance of the Multitaper-based detector

In this paper an accurate analysis is provided for the Multitaper-based detector. We study the quadratic form representation of the Multitaper estimate (MTE), and we derive accurate expressions of the eigenvalues of the diagonalized representation of the quadratic form. It is found that in AWGN all the nonzero eigenvalues are identical, and the number of eigenvalues is identical to the number of the employed Slepian tapers. Using this information, closed forms are obtained for the probability of false alarm and the probability of detection. Furthermore, the case of propagation over fading channels is investigated and the corresponding eigenvalues are derived. The results demonstrate the accuracy of the obtained model. It is found that the performance of the Multitaper estimate is enhanced when the number of employed Slepian tapers is increased. In addition, at a given sensing threshold the conventional timedomain (TD) energy detector outperforms the MTE in terms of the probability of detection. However, the MTE outperforms the TD energy detector in terms of the probability of false alarm. © 2012 IEEE

An accurate model for periodogram-based energy detection over Nakagami fading

Spectrum sensing is a major function within a cognitive radio system, and it is recently shown that the frequency-domain implementation of the energy detector yields a lower probability of false alarm when compared with the timedomain model. In this paper, an accurate mathematical model is presented for spectrum sensing using the periodogram-based energy detector over for independent and identically distributed (i.i.d.) Nakagami fading channels. By exploiting the quadratic form representation of the periodogram, the eigenvalue of the product of the sample covariance matrix of the observed vector and the matrix of the quadratic form is investigated for the case of transmission over Nakagami fading. Hence accurate closed forms are derived for the average probability of missed detection as a function of the sensing threshold and the signal-to-noise ratio (SNR). The results show that the derived equations are accurate and the performance is enhanced with any increase of the eigenvalue or the SNR. However, it is also found that for a given signal and fading parameters, the detector is not affected with any change of the length of observations. © 2012 IEEE

Cooperative spectrum sensing for cognitive radio networks based on spectrum estimates

Spectrum sensing is a major function within the cognitive radio system. In this paper, spectrum sensing using energy detection is considered and an accurate performance analysis is provided for both cases of single and cooperative sensing. The performance of the periodogram-based energy detector is studied for random signals employing a complex envelope. The contribution of this paper is twofold. New and accurate closed forms are developed for the performance measures which are the probability of false alarm and the probability of miss. The obtained mathematical models are supported by Monte-Carlo simulations. In addition, the obtained derivations are extended to include the performance of centralized cooperative sensing using decision fusion. The considered decision rules are Logical OR (LO), Logical AND (LA) and Majority Rule (MR). The obtained numerical results reveal that the probability of detection tends to increase when using LO and MR. On the other hand, LA yields the same receiver operator characteristic (ROC) curve irrespective of the number of cooperative users. © 2011 IEEE

On the detection of unknown signals using welch overlapped segmented averaging method

In this paper, the problem of spectrum sensing for cognitive radios is investigated when the decision statistic is computed using Welch Overlapped Segmented Averaging (WOSA). A novel analysis is presented using the performance measures which are the probability of false alarm and the probability of detection. First, we present a novel investigation of the hermitian form of Welch's estimate. Using the theory of quadratic forms, we investigate the hermitian matrix of the hermitian form and exploit its characteristics to obtain the eigenvalues of the diagonalized representation of the hermitian form. Second, the obtained results are used to derive mathematical expressions for the probabilities of false alarm and detection over Rayleigh fading. The numerical results have revealed the high accuracy of the obtained mathematical models. © 2011 IEEE

A generalized system model and performance analysis for the periodogram-based energy detector

Spectrum sensing is an essential function for the operation of cognitive radios. This paper, considers the application of periodogram-based energy detection for spectrum sensing and presents a generalized mathematical model which includes the case of a complex non-zero mean primary signal. The model is then used to obtain accurate performance analysis of this technique. By defining and exploiting the noncentral quadratic form of the periodogram, the cumulative distribution function (CDF) is obtained directly through numerical inversion. The presented model is simplified through manipulating the characteristics of the hermitian matrix of the quadratic form along with the covariance matrix of the received signal. Using this, the non-zero eigenvalue of the corresponding product is obtained and the probabilities of false alarm and missed detection are derived. Furthermore, the performance of detecting multiple frequencies simultaneously is considered by investigating the independence requirements of the corresponding quadratic forms. The presented results are validated with the aid of Monti-Carlo simulations. © 2011 IEEE