There are over 320 million inpatient surgical procedures worldwide [1]. We learn from the recent International Surgical Outcome Study [2] that around 17% of these patients develop one or more complications, and among them, that 2.8% die from their complications. One can therefore estimate that around 1.5 million patients/yr (or 3 patients/min!) die of postoperative complications. In the United States (US), if postoperative mortality was part of the official statistics from the Centers for Disease Control and Prevention, it would represent the third leading cause of death, right after cancer [3]. Postoperative complications are not only a human burden. They also dramatically increase hospital costs [4].

Several initiatives have been developed to improve quality of surgical care, from the WHO surgical safety checklist, to minimally invasive surgery, protective mechanical ventilation, and enhanced recovery programs. Smartphones and electronic tablets (e-tablets) are now ubiquitous devices. Their ease of use, smartness, accessibility, mobility and connectivity create unique opportunities to transform medicine and improve quality of care [5]. Potential clinical applications of smartphones and e-tablets in surgical patients will be described and discussed in this manuscript, from prehabilitation to rehabilitation.

Prehabilitation is known to have an impact on postoperative outcome. Preoperative change in physical status and a better control of risk factors can be facilitated by digital tools and applications (Apps) downloaded on smartphones or e-tablets. Connected devices such as wireless brachial cuffs and electronic scales can be used for self-monitoring of blood pressure and weight, and the visualization of trends over time. Apps, text messaging and serious games (video games designed for training and education) have been shown to help for a better control of hypertension, to reduce overweight, as well as for smoking cessation [6,7]. Multiple activity trackers and Apps now exist to invite patients monitor and increase their physical activity. These digital tools seem to be effective only for a short period of time [8], which is clearly an issue when dealing with chronic conditions and diseases, but less of a problem if used during the weeks preceding surgery (Fig. 1). Electronic checklists are Apps developed to optimize communication between patients and healthcare professionals during the entire surgical journey. Before surgery they can be used to ensure patients follow preoperative recommendations, in particular regarding medications (Fig. 2).

Recent studies have shown that around one third of deaths after surgery occur in the wards [2]. This situation has been called « failure to rescue » and has been proposed to explain why hospitals with comparable postoperative morbidity rates may have very different mortality rates: outcome depends more on the ability to detect early and treat properly postoperative complications than in the occurrence of complications [17]. Importantly, studies have also shown that most patients start deteriorating hours before medical teams are called for rescue or intensive care unit (ICU) transfer. In this regard, several studies have logically demonstrated the value of continuous monitoring systems for the early detection of deteriorating patients. For instance, the use of pulse oximeters to continuously monitor arterial oxygen saturation (SpO₂) and heart rate in 2,841 orthopedic patients (many of them receiving opioids) was associated with a significant decrease in the number of rescue events and ICU transfers [18]. The use of a piezoelectric contact-free sensor (placed under the mattress) to continuously monitor heart rate and respiratory rate in 2,314 medico-surgical patients was associated with a significant decrease in the number of calls for cardiac arrest and hospital length of stay [19]. More recently, the use of wireless sensors to monitor vital signs (SpO₂, heart rate, blood pressure, respiratory rate), automatically calculate an early warning score, and alert nurses in case of deterioration, was associated with a significant decrease in the number of cardiac arrests and in mortality [20].

Multiple sensors are becoming available for proactive and wireless monitoring in ambulatory patients [21,22]. Thanks to stretchable and flexible electronics, electronic tattoos will soon be available [23]. Technically speaking, physiologic signals can be transmitted to, processed by, and displayed on smartphones or e-tablets (Fig. 6). Smart algorithms and software are currently under development to filter artifacts in ambulatory patients and prevent alarm fatigue, as well as to fuse multiple vital signs into a single wellness index or warning score. Such indexes or scores are susceptible to improve the detection of clinical deterioration at an early stage and should help to tackle failure to rescue [21,23]. Once health care professionals have been alerted, pocket echo devices or probes (Fig. 3) can be useful to provide information about cardiac function and clarify the underlying mechanisms of clinical deterioration.

Multiple Apps and connected devices have become available over the last few years and, given their ease of use and low cost, the temptation is to integrate them into clinical practice before they have been validated and/or have demonstrated clinical value. In other words, the main risk associated with the use of digital innovations and wearable devices is novelty blindness.

The “Instant Blood Pressure” App was developed to measure blood pressure with a smartphone, from the simultaneous recording of a balistogram (smartphone on the chest detecting heart contraction from built-in accelerometers) and a peripheral pulse (finger on the camera). The time difference between the heart beat and the arrival of the corresponding peripheral pulse is the pulse wave transit time (PWTT). It is known to be inversely proportional to blood pressure. However, the relationship between PWTT and blood pressure is different from one patient to the other, and for a given patient, it is dependent on cardiac output, which may vary with physical activity and underlying diseases (e.g. cirrhosis, heart failure). In other words, it is unlikely that this method may be useful to measure accurate absolute blood pressure values without regular calibrations. Nevertheless, over 140,000 people had downloaded the App on their smartphone before it was removed from market after a publication from the Johns Hopkins hospital. This study showed it was not accurate and missed most hypertension cases [34]. The Scout device from Scanadu is another gadget that was supposed to measure blood pressure from a similar principle, by quantifying the time difference between a forehead pulse (device on the forehead) and a finger pulse (index on the device). Scanadu had been able to raise first $1.5M from crowdfunding, then $35M in series B funding, bringing a lot of attention around this new product. Recently, following the disappointing (but expected) results of a clinical evaluation, the company was forced by the FDA to withdraw the product and its App from the market [35]. These examples illustrate well the risk of gizmo idolatry [36]. If some new connected devices and Apps have value, many lack of reliability. Serious clinical evaluations are therefore needed before clinical implementation. Given their expertise in physiologic monitoring and clinical research, anesthesiologists are well positioned to lead this endeavor.

Postoperative complications are a major clinical and economic burden. Each year, they are responsible for over 1 million deaths. Many complications and deaths could be prevented with a better perioperative management. Smartphones and e-tablets are ubiquitous devices that can help both healthcare professionals and patients to better prepare for surgery, to improve intraoperative management and postoperative monitoring in the hospital and beyond. These tools may be especially useful in developing countries and small hospitals where expensive medical technologies are not always readily available.