Effect of tidal volume on gas exchange during rescue ventilation.

Tidal volume VT required for mouth-to-mouth (MTM) and bag-valve-mask (BVM) rescue ventilation remains debatable owing to differences in physiology and end-point objectives. Analysis of gas transport may clarify minimum necessary VT and its determinants. Alveolar and arterial O2 and CO2 responses to MTM and air BVM ventilation for VT between 0.4 and 1.2 liters were computed using a model of gas exchange that incorporates inspired gas concentrations, airway dead space, cardiac output, pulmonary shunt, blood gas dissociation curves, tissue compartments, and metabolic rate. Parameters were adjusted to match published human data. Steady state arterial oxygen saturation reached plateaus at VT above 0.7 liters with MTM and 0.6 liters with air ventilation at 12 breaths per minute. Increasing shunt shifted oxygenation plateaus downward, but larger tidal volumes did not improve oxygen saturation. Carbon dioxide retention occurred at VT below 2.3 liters for MTM ventilation and 0.6 liters for air ventilation. Results establish a physiological foundation for tidal volume requirements during resuscitation.

Patient-specific predictors of failure to rescue after pancreaticoduodenectomy.

BACKGROUND: Failure to rescue (FTR) is a recently described outcome metric for quality of care. However, predictors of FTR have not been adequately investigated, particularly after pancreaticoduodenectomy. We aim to identify predictors of FTR after pancreaticoduodenectomy. METHODS: We reviewed all patients who developed serious morbidity after pancreaticoduodenectomy from 2005 to 2012 in the ACS-NSQIP database. Logistic regression was used to identify preoperative and postoperative risks for 30-day mortality within a development cohort (randomly selected 80%). A score was created using weighted beta coefficients. Predictive accuracy was assessed on the validation cohort (remaining 20%) using a receiver operator characteristic curve and calculating the area under the curve (AUC). RESULTS: The FTR rate was 7.2% after pancreaticoduodenectomy (n = 5,027). We identified 5 independent risk factors: age ≥65 and albumin ≤3.5 g/dL, preoperatively; and development of shock, renal failure, and reintubation, postoperatively. The generated score had an AUC = 0.83 (95% CI, 0.77-0.89) in the validation cohort. Using the score: 1*Albumin ≤3.5 g/dL + 2*Age ≥ 65 + 2*Shock + 5*Renal failure + 5*Reintubation, FTR rates increased with increasing score (p < 0.001). CONCLUSION: FTR rates have previously been shown to be associated with hospital factors. We show that FTR is also associated with preoperative and postoperative patient-specific factors.

Fast or Slow Rescue Ventilations: A Predictive Model of Gastric Inflation.

BACKGROUND: Rescue ventilations are given during respiratory and cardiac arrest. Tidal volume must assure oxygen delivery; however, excessive pressure applied to an unprotected airway can cause gastric inflation, regurgitation, and pulmonary aspiration. The optimal technique provides mouth pressure and breath duration that minimize gastric inflation. It remains unclear if breath delivery should be fast or slow, and how inflation time affects the division of gas flow between the lungs and esophagus. METHODS: A physiological model was used to predict and compare rates of gastric inflation and to determine ideal ventilation duration. Gas flow equations were based on standard pulmonary physiology. Gastric inflation was assumed to occur whenever mouth pressure exceeded lower esophageal sphincter pressure. Mouth pressure profiles that approximated mouth-to-mouth ventilation and bag-valve-mask ventilation were investigated. Target tidal volumes were set to 0.6 and 1.0 L. Compliance and airway resistance were varied. RESULTS: Rapid breaths shorter than 1 s required high mouth pressures, up to 25 cm H2O to achieve the target lung volume, which thus promotes gastric inflation. Slow breaths longer than 1 s permitted lower mouth pressures but increased time over which airway pressure exceeded lower esophageal sphincter pressure. The gastric volume increased with breath durations that exceeded 1 s for both mouth pressure profiles. Breath duration of ∼1.0 s caused the least gastric inflation in most scenarios. Very low esophageal sphincter pressure favored a shift toward 0.5 s. High resistance and low compliance each increased gastric inflation and altered ideal breath times. CONCLUSIONS: The model illustrated a general theory of optimal rescue ventilation. Breath duration with an unprotected airway should be 1 s to minimize gastric inflation. Short pressure-driven and long duration-driven gastric inflation regimens provide a unifying explanation for results in past studies.

Breath-Hold Diving.

Breath-hold diving is practiced by recreational divers, seafood divers, military divers, and competitive athletes. It involves highly integrated physiology and extreme responses. This article reviews human breath-hold diving physiology beginning with an historical overview followed by a summary of foundational research and a survey of some contemporary issues. Immersion and cardiovascular adjustments promote a blood shift into the heart and chest vasculature. Autonomic responses include diving bradycardia, peripheral vasoconstriction, and splenic contraction, which help conserve oxygen. Competitive divers use a technique of lung hyperinflation that raises initial volume and airway pressure to facilitate longer apnea times and greater depths. Gas compression at depth leads to sequential alveolar collapse. Airway pressure decreases with depth and becomes negative relative to ambient due to limited chest compliance at low lung volumes, raising the risk of pulmonary injury called "squeeze," characterized by postdive coughing, wheezing, and hemoptysis. Hypoxia and hypercapnia influence the terminal breakpoint beyond which voluntary apnea cannot be sustained. Ascent blackout due to hypoxia is a danger during long breath-holds, and has become common amongst high-level competitors who can suppress their urge to breathe. Decompression sickness due to nitrogen accumulation causing bubble formation can occur after multiple repetitive dives, or after single deep dives during depth record attempts. Humans experience responses similar to those seen in diving mammals, but to a lesser degree. The deepest sled-assisted breath-hold dive was to 214 m. Factors that might determine ultimate human depth capabilities are discussed. © 2018 American Physiological Society. Compr Physiol 8:585-630, 2018.

Performance of life support breathing apparatus for under-ice diving operations.

INTRODUCTION: Single-hose scuba regulators dived in very cold water may suffer first- or second-stage malfunction, yielding complete occlusion of air flow or massive freeflow that rapidly expends a diver's air supply. PURPOSE: This study, conducted in Antarctica, evaluated the under-ice performance of a sampling of commercially available regulators. METHODS: Seventeen science divers logged a total of 305 dives in -1.86°C seawater under 6-meter-thick Antarctic fast-ice over two field seasons in 2008 and 2009. Dive profiles had an average depth of 30 msw and dive time of 29 minutes, including a mandatory three-minute safety stop at 6 msw. Sixty-nine unmodified regulator units (17 models) from 12 different manufacturers underwent standardized pre-dive regulator care and were randomly assigned to divers. Depths and times of onset of second-stage regulator freeflow were recorded. RESULTS: In 305 dives, there were 65 freeflows. The freeflows were not evenly distributed across the regulator brands. Regulator failure rates fell into two categories (⟨ 11% and ⟩ 26%). The regulators classified for the purpose of the test as "acceptable" (⟨ 11% failure rate: Dive-Rite Jetstream, Sherwood Maximus SRB3600, Poseidon Xstream Deep, Poseidon Jetstream, Sherwood Maximus SRB7600, Poseidon Cyklon, Mares USN22 Abyss) experienced only nine freeflows out of 146 exposures for a 6% overall freeflow incidence. Those classified as "unacceptable" (⟨ 26% failure rate) suffered 56 freeflows out of 159 exposures (35% freeflow incidence.). CONCLUSIONS: Contrary to expectations, the pooled incidences for the seven best performing regulators was significantly different by Chi-square test from the 10 remaining regulators (P ⟨ 0.001).

WHipple-ABACUS, a simple, validated risk score for 30-day mortality after pancreaticoduodenectomy developed using the ACS-NSQIP database.

BACKGROUND: Pancreaticoduodenectomy needs simple, validated risk models to better identify 30-day mortality. The goal of this study is to develop a simple risk score to predict 30-day mortality after pancreaticoduodenectomy. METHODS: We reviewed cases of pancreaticoduodenectomy from 2005-2012 in the American College of Surgeons-National Surgical Quality Improvement Program databases. Logistic regression was used to identify preoperative risk factors for morbidity and mortality from a development cohort. Scores were created using weighted beta coefficients, and predictive accuracy was assessed on the validation cohort using receiver operator characteristic curves and measuring area under the curve. RESULTS: The 30-day mortality rate was 2.7% for patients who underwent pancreaticoduodenectomy (n = 14,993). We identified 8 independent risk factors. The score created from weighted beta coefficients had an area under the curve of 0.71 (95% confidence interval, 0.66-0.77) on the validation cohort. Using the score WHipple-ABACUS (hypertension With medication + History of cardiac surgery + Age >62 + 2 × Bleeding disorder + Albumin <3.5 g/dL + 2 × disseminated Cancer + 2 × Use of steroids + 2 × Systemic inflammatory response syndrome), mortality rates increase with increasing score (P < .001). CONCLUSION: While other risk scores exist for 30-day mortality after pancreaticoduodenectomy, we present a simple, validated score developed using exclusively preoperative predictors surgeons could use to identify patients at risk for this procedure.

The use of collaboration to implement evidence-based safe practices.

The Pennsylvania Patient Safety Authority receives over 235,000 reports of medical error per year. Near miss and serious event reports of common and interesting problems are analysed to identify best practices for preventing harmful errors. Dissemination of this evidence-based information in the peer-reviewed Pennsylvania Patient Safety Advisory and presentations to medical staffs are not sufficient for adoption of best practices. Adoption of best practices has required working with institutions to identify local barriers to and incentives for adopting best practices and redesigning the delivery system to make desired behaviour easy and undesirable behaviour more difficult. Collaborations, where institutions can learn from the experiences of others, have show decreases in harmful events. The Pennsylvania Program to Prevent Wrong-Site Surgery is used as an example. Two collaborations to prevent wrong-site surgery have been completed, one with 30 institutions in eastern Pennsylvania and one with 19 in western Pennsylvania. The first collaboration achieved a 73% decrease in the rolling average of wrong-site events over 18 months. The second collaboration experienced no wrong-site operating room procedures over more than one year. Significance for public healthSince the Institute of Medicine's To Err is Human identified medical errors as a major cause of death, the public has been interested in the recommendations for reporting of medical errors and implementing safe systems for the delivery of healthcare. The Commonwealth of Pennsylvania has followed those recommendations and found that an essential intermediate step between analysing reports and implementing safe systems is collaborative learning among healthcare institutions. The experience in Pennsylvania should be useful to other public organizations wishing to improve safety.

Establishing a global learning community for incident-reporting systems.

BACKGROUND: Incident-reporting systems (IRS) collect snapshots of hazards, mistakes and system failures occurring in healthcare. These data repositories are a cornerstone of patient safety improvement. Compared with systems in other high-risk industries, healthcare IRS are fragmented and isolated, and have not established best practices for implementation and utilisation. DISCUSSION: Patient safety experts from eight countries convened in 2008 to establish a global community to advance the science of learning from mistakes. This convenience sample of experts all had experience managing large incident-reporting systems. This article offers guidance through a presentation of expert discussions about methods to identify, analyse and prioritise incidents, mitigate hazards and evaluate risk reduction.

Wrong site surgery near misses and actual occurrences.

Under coordination by the Patient Safety Authority, staff members in facilities across Pennsylvania analyzed 97 wrong site surgery near misses and 44 actual occurrences using a common analysis form from August 2007 to August 2008. These assessments were aggregated and compared by the Patient Safety Authority. Assessments in which near misses were identified that did not advance to actual wrong site occurrences were significantly more likely to report compliance with patient identification and preoperative reconciliation protocols, accurate scheduling, notation of the surgical site on the consent form, participation of the surgeon in preoperative verification, participation of all surgical team members in the time out, time outs performed with the site marking visible after draping, and the surgeon explicitly empowering team members to speak up if concerned and acknowledging concerns when expressed.

Lung compression effects on gas exchange in human breath-hold diving.

Lung compression during breath-hold diving reduces gas exchanging surface area. Beyond a critical depth, collapse of all alveoli should result in total pulmonary shunt and a drop in arterial oxygen partial pressure toward the mixed-venous level. The effect of lung collapse on human breath-hold diving capability is analysed using a computational model of the lungs and circulation that simulates oxygen, carbon dioxide, and nitrogen exchange between alveoli, blood, and tissues. Gas uptake during descent becomes limited by lung compression when the ratio of diffusing capacity to the product of perfusion and gas solubility in blood drops below one. An equation is derived for estimating collapse depth due to direct alveolar compression and time-dependent absorption atelectasis. Oxygen dissolved in blood during descent builds a limited capacitive store for supporting metabolism during the period of lung collapse. Hypoxemia with loss of consciousness prior to alveolar re-opening on ascent is predicted to occur on dives beyond 300 m, depending on initial lung volume.

Designing safety into the minimally invasive surgical revolution: a commentary based on the Jacques Perissat Lecture of the International Congress of the European Association for Endoscopic Surgery.

Surgical errors with minimally invasive surgery differ from those in open surgery. Perforations are typically the result of trocar introduction or electrosurgery. Infections include bioburdens, notably enteric viruses, on complex instruments. Retained foreign objects are primarily unretrieved device fragments and lost gallstones or other specimens. Fires and burns come from illuminated ends of fiber-optic cables and from electrosurgery. Pressure ischemia is more likely with longer endoscopic surgical procedures. Gas emboli can occur. Minimally invasive surgery is more dependent on complex equipment, with high likelihood of failures. Standardization, checklists, and problem reporting are solutions for minimizing failures. The necessity of electrosurgery makes education about best electrosurgical practices important. The recording of minimally invasive surgical procedures is an opportunity to debrief in a way that improves the reliability of future procedures. Safety depends on reliability, designing systems to withstand inevitable human errors. Safe systems are characterized by a commitment to safety, formal protocols for communications, teamwork, standardization around best practice, and reporting of problems for improvement of the system. Teamwork requires shared goals, mental models, and situational awareness in order to facilitate mutual monitoring and backup. An effective team has a flat hierarchy; team members are empowered to speak up if they are concerned about problems. Effective teams plan, rehearse, distribute the workload, and debrief. Surgeons doing minimally invasive surgery have a unique opportunity to incorporate the principles of safety into the development of their discipline.

A comparison of methods for assessing penetrating trauma on retrospective multi-center data.

OBJECTIVE: TraumaSCAN-Web (TSW) is a computerized decision support system for assessing chest and abdominal penetrating trauma which utilizes 3D geometric reasoning and a Bayesian network with subjective probabilities obtained from an expert. The goal of the present study is to determine whether a trauma risk prediction approach using a Bayesian network with a predefined structure and probabilities learned from penetrating trauma data is comparable in diagnostic accuracy to TSW. METHODS: Parameters for two Bayesian networks with expert-defined structures were learned from 637 gunshot and stab wound cases from three hospitals, and diagnostic accuracy was assessed using 10-fold cross-validation. The first network included information on external wound locations, while the second network did not. Diagnostic accuracy of learned networks was compared to that of TSW on 194 previously evaluated cases. RESULTS: For 23 of the 24 conditions modeled by TraumaSCAN-Web, 16 conditions had Areas Under the ROC Curve (AUCs) greater than 0.90 while 21 conditions had AUCs greater than 0.75 for the first network. For the second network, 16 and 20 conditions had AUCs greater than 0.90 and 0.75, respectively. AUC results for learned networks on 194 previously evaluated cases were better than or equal to AUC results for TSW for all diagnoses evaluated except diaphragm and heart injuries. CONCLUSIONS: For 23 of the 24 penetrating trauma conditions studied, a trauma diagnosis approach using Bayesian networks with predefined structure and probabilities learned from penetrating trauma data was better than or equal in diagnostic accuracy to TSW. In many cases, information on wound location in the first network did not significantly add to predictive accuracy. The study suggests that a decision support approach that uses parameter-learned Bayesian networks may be sufficient for assessing some penetrating trauma conditions.

Wrong-site surgery: can we prevent it?

Wrong-site surgery happens frequently enough that it is a significant risk for many surgeons during their professional careers. But it is an event that should never happen. Most wrong-site surgery is wrong-side surgery, followed by wrong-digit and wrong-vertebral-level surgery. Wrong-site surgery results from misinformation or misperception of the patient's orientation. The key to preventing wrong-site surgery is to have multiple independent checks of critical information. Discrepancies among the operative record, consent, and the surgeon's record of the history and physical examination should ideally be resolved prior to the day of surgery to avoid time-consuming reconciliations. We noted that the preoperative verification was the most effective of the three steps of the Universal Protocol and that the patient was a more reliable source of accurate information than the documents. Marking the operative site gives patients a voice after they are sedated or anesthesia is induced. Wrong-site surgery has involved local or regional anesthesia at the wrong site when anesthesiologists did not adhere to formal time-outs for their procedures. Surgeons need to have access to all relevant information and to be engaged in the processes to prevent wrong-site surgery, particularly in the final time-out. Junior members of the operating room team must be made comfortable about speaking up if concerned. During spinal surgery, the vertebral level needs to be confirmed radiographically. Wrong-site surgical problems can occur after an operation if accurate information is not provided to accompany the specimen or if leftover labels from a previous patient are used to identify the specimen.

A roadmap to safe surgical care: a view from Pennsylvania.

An effort to make operations safe is realistic if surgeons are committed. Such an effort involves educating surgeons about safe practices based on current knowledge of best practices, including team training and talking to patients. It involves identifying leaders and developing appropriate infrastructure for academic activities. It also involves the collection of information needed to identify safe and unsafe situations. The potential advantages of a drive for safe surgery should be fewer complications, less care per patient, lower costs, and less liability.

The role for leaders of health care organizations in patient safety.

We review what leaders of health care systems, including chief executive officers and board members, need to know to have "patient safety literacy" and do to make their systems safe. High reliability organizations produce reliable results that are not dependent on providers being perfect. Their characteristics include the commitment of leadership to safety as a system responsibility, with a culture of safety that decreases variability with standardized care and does not condone "at-risk behavior." A business case can be made for investing resources into systems that produce good outcomes reliably. Leaders must see patient safety problems as problems with their system, not with their employees. Leaders need to give providers information to make and monitor system progress. All medical errors, including near misses, and processes associated with all adverse events may provide information for system improvement. Improving systems should produce better long-term results than educating workers to be more careful.