Patent Publication Number: US-2016243304-A9

Title: Infusion pressure control using blood pressure

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of prior application Ser. No. 13/112,504, filed May 20, 2011, which claims the benefit of U.S. Provisional Application No. 61/346,746 filed May 20, 2010, the contents of both being incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to controlling fluid infusion pressure, such as during an intraocular surgical procedure, utilizing systemic blood pressure. Particularly, the present disclosure describes systems and methods for controlling, and in some instances preventing interruption of, blood flow through the central retinal artery using both systemic blood pressure and fluid infusion pressure. 
     BACKGROUND 
     Low systemic blood pressure may be routine when operating on children and often occurs with adults undergoing general anesthesia or deep sedation. Intraocular pressure levels produced by an infusion system, such as during vitreoretinal surgery, may result in occlusion of the central retinal artery if the blood pressure is low. Prolonged vascular occlusion can result in blindness. Such procedures may involve a vitreous hemorrhage, a dense cataract, or some other obstruction that may prevent a medical practitioner from being able to observe circulation in the retinal vessels. Therefore, the retinal vessels are not visible and cannot be monitored for effective blood flow. 
     SUMMARY 
     According to one aspect, the disclosure describes a method for controlling infusion pressure, such as during an intraocular surgical procedure. The method may include determining an infusion pressure of a patient&#39;s eye with a first pressure determining device, determining a blood pressure indicative of a patient&#39;s central retinal artery blood pressure with a second pressure determining device, and determining, with a processor, an estimated critical closing pressure of the central retinal artery of the eye based on the systemic blood pressure. 
     Another aspect encompasses a computer program product for controlling an infusion pressure. The computer program product may include machine-readable instructions embodied on tangible media and operable when executed to read an infusion pressure of a patient&#39;s eye, determine an estimate of a patient&#39;s central retinal artery blood pressure, and determine an estimated critical closing pressure of the central retinal artery of the eye based on the estimated central retinal artery blood pressure. 
     A further aspect relates to a system for controlling infusion pressure during an intraocular surgical procedure. The system may include a data receival unit adapted to receive systemic blood pressure and infusion pressure. The system may also include a computational unit adapted to determine an estimated retinal artery blood pressure based on the received systemic blood pressure and determine an estimated critical closing pressure based on the estimated retinal artery blood pressure. The system may additionally include a logic unit adapted to compare infusion pressure with the estimated critical closure pressure and trigger an alarm when the infusion pressure reaches a selected pressure relative to the estimated critical closing pressure. 
     Another aspect relates to a computer-implemented method for controlling infusion pressure performed by a processor. The method may include determining an infusion pressure of a patient&#39;s eye, determining an estimate of a patient&#39;s central retinal artery blood pressure, and determining an estimated critical closing pressure of a central retinal artery of the eye based on the estimated central retinal artery blood pressure. 
     Another aspect relates to a system including memory for storing at least one of systemic blood pressure data, estimated central retinal artery blood pressure data, infusion pressure data, and estimated critical closing pressure data and one or more processors. The one or more processors may be operable to determine an infusion pressure of a patient&#39;s eye, determine an estimate of a patient&#39;s central retinal artery blood pressure, and determine an estimated critical closing pressure of a central retinal artery of the eye based on the estimated central retinal artery blood pressure. 
     The various aspects may include one or more of the following features. A blood pressure indicative of a patient&#39;s central retinal artery blood pressure may be determined by determining a patient&#39;s systemic blood pressure with a pressure determining device and converting the systemic blood pressure into the estimated central retinal artery blood pressure with a processor. Determining the patient&#39;s systemic blood pressure may include determining at least one of the patient&#39;s brachial artery blood pressure or radial artery blood pressure with a pressure determining device. The systemic blood pressure may be converted into the estimated central retinal artery blood pressure with an ophthalmodynamometry offset with a processor. The infusion pressure may be compared to the estimated critical closing pressure with a processor. An alarm may be triggered when the infusion pressure reaches a selected pressure relative to the estimated critical closing pressure. An alarm may be at least one of a visual or audible alarm. A patient&#39;s systemic blood pressure may be at least one of the patient&#39;s brachial artery blood pressure or radial artery blood pressure. Infusion pressure may be increased above the estimated critical closing pressure with a fluid flow device to stop intraocular bleeding. The infusion pressure may be increased above the estimated critical closing pressure for a selected period of time to stop intraocular bleeding at a site of the eye. A procedure may be performed at the site of the eye to prevent continued bleeding after lowering of the infusion pressure below the estimated critical closing pressure. Infusion pressure may be automatically adjusted when the infusion pressure is at a selected value relative to the estimated critical closing pressure. For example, infusion pressure may be reduced when the infusion pressure is equal to or greater than the estimated critical closing pressure. 
     The various aspects may also include one or more of the following features. Machine-readable instructions operable when executed to read a patient&#39;s systemic blood pressure may include machine-readable instructions operable when executed to read at least one of the patient&#39;s brachial artery blood pressure or radial artery blood pressure. Machine-readable instructions operable when executed to determine an estimate of a patient&#39;s central retinal artery blood pressure may include machine-readable instructions operable when executed to read a patient&#39;s systemic blood pressure and convert the systemic blood pressure into the estimated central retinal artery blood pressure. Machine-readable instructions operable when executed to convert the systemic blood pressure into the estimated central retinal artery blood pressure may include machine-readable instructions operable when executed to convert the systemic blood pressure into the estimated central retinal artery blood pressure with an ophthalmodynamometry offset. Machine-readable instructions may also be included that, when executed, trigger an alarm when the infusion pressure reaches a selected pressure relative to the estimated critical closing pressure. The machine-readable instructions operable when executed to trigger an alarm when the infusion pressure reaches a selected pressure relative to the estimated critical closing pressure may include machine-readable instructions operable when executed to trigger at least one of a visual or audible alarm. The machine readable instruction may be operable when to automatically adjusted infusion pressure when the infusion pressure is at a selected value relative to the estimated critical closing pressure. For example, infusion pressure may be reduced when the infusion pressure is equal to or greater than the estimated critical closing pressure. 
     The various aspects may further include one or more of the following features. A data receival unit adapted to receive systemic blood pressure may be adapted to receive at least one of brachial artery blood pressure or radial artery blood pressure. A computational unit adapted to determine an estimated retinal artery blood pressure based on the received systemic blood pressure may be adapted to convert the systemic blood pressure into the estimated retinal artery blood pressure using an ophthalmodynamometry offset. A logic unit adapted to trigger an alarm when the infusion pressure reaches a selected pressure relative to the estimated critical closing pressure may be adapted to trigger at least one of a visual or audible alarm. 
     The various aspects may also include one or more of the following features. An estimate of a patient&#39;s central retinal artery blood pressure may be determined by determining a patient&#39;s systemic blood pressure and converting the systemic blood pressure into the estimated central retinal artery blood pressure. The systemic blood pressure may be converted into the estimated central retinal artery blood pressure with an ophthalmodynamometry offset. An alarm may be triggered when the infusion pressure reaches a selected pressure relative to the estimated critical closing pressure. Triggering an alarm when the infusion pressure reaches a selected pressure relative to the estimated critical closing pressure may include triggering at least one of a visual or audible alarm. A patient&#39;s systemic blood pressure may be determined by determining at least one of the patient&#39;s brachial artery blood pressure or radial artery blood pressure. The infusion pressure may be increased above the estimated critical closing pressure to stop intraocular bleeding. Increasing the infusion pressure above the estimated critical closing pressure to stop intraocular bleeding may include increasing the infusion pressure above the estimated critical closing pressure for a selected period of time to stop intraocular bleeding at a site of the eye and performing a procedure, during application of the increased infusion pressure, at the site of the eye to prevent continued bleeding after lowering of the infusion pressure below the estimated critical closing pressure. Infusion pressure may be automatically adjusted when the infusion pressure is at a selected value relative to the estimated critical closing pressure. For example, the infusion pressure may be reduced when the infusion pressure is equal to or greater than the estimated critical closing pressure. 
     The various aspects may include one or more of the following features. One or more processors operable to determine an estimate of a patient&#39;s central retinal artery blood pressure may include one or more processors operable to receive a patient&#39;s systemic blood pressure and convert the systemic blood pressure into the estimated central retinal artery blood pressure. One or more processors operable to convert the systemic blood pressure into the estimated central retinal artery blood pressure may include one or more processors operable to convert the systemic blood pressure into the estimated central retinal artery blood pressure with an ophthalmodynamometry offset. The one or more processors may be further operable to trigger an alarm when the infusion pressure reaches a selected pressure relative to the estimated critical closing pressure. The triggered alarm may be at least one of a visual or audible alarm. One or more processors operable to receive a patient&#39;s systemic blood pressure may include one or more processors operable to receive at least one of the patient&#39;s brachial artery blood pressure or radial artery blood pressure. One or more processors may be further operable to automatically adjust infusion pressure when the infusion pressure is at a selected value relative to the estimated critical closing pressure. the one or more processors is further operable to automatically adjust infusion pressure when the infusion pressure is at a selected value relative to the estimated critical closing pressure comprises one or more processors operable to automatically reduce infusion pressure when the infusion pressure is equal to or greater than the estimated critical closing pressure. 
     The details of one or more implementations of the present disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIGS. 1-3  are example systems for controlling fluid infusion pressure into an eye. 
         FIG. 4  is a cross sectional view of an eye undergoing an intraocular surgical procedure. 
         FIGS. 5-6  show example outputs of central retinal artery blood pressure and critical closing pressure. 
         FIG. 7  is an example method for controlling fluid infusion pressure to which an eye is subjected during an intraocular surgical procedure. 
     
    
    
     DETAILED DISCLOSURE 
     The present disclosure describes methods, systems, and computer software for controlling fluid infusion pressure (i.e., the pressure at which fluid is infused into an eye during an intraocular surgical procedure) (hereinafter referred to as “infusion pressure”) using systemic blood pressure. For example, surgical procedures on an eye may include aspiration of a portion of vitreous humor (interchangeably referred to as “vitreous material”) from the posterior segment as well as infusion of a fluid into the eye, such as artificial aqueous humor or other fluid (collectively referred to as “infusion fluid”). Aspirating vitreous humor from and infusing infusion fluid into the eye may cause a change in the intraocular pressure (“IOP”). IOP may be particularly affected by the infusion pressure. For example, infusion pressure may be representative of IOP when little or no aspiration from the eye is occurring. However, infusion pressure may be used as an adequate representative of IOP under other conditions during intraocular surgical procedures. The present disclosure describes methods and systems for controlling infusion pressure and, thereby, controlling IOP, during medical procedures as well as providing notification to a medical services provider that infusion pressure has reached a selected pressure. 
     In an example implementation, an infusion pressure application for controlling infusion pressure (“infusion services”) is described. In some instances, the infusion pressure application may be implemented via a system (interchangeably referred to as an “ocular system”) that is at least partially electronically implemented. For example, the ocular system may be incorporated into one or more devices. In some instances, the ocular system may form part of a medical apparatus, such as an intraocular medical apparatus. Further, the ocular system may be at least partially implemented over a computer network to one or more remote devices. The present disclosure also describes computer networks that may be utilized for implementing the infusion services in some implementations. 
       FIG. 1  illustrates an example system  100  for dynamically implementing the infusion services. System  100  may encompass an example ocular system that may be operable to transmit information to one or more clients  102 , receive information from one or more of the clients  102 , and otherwise administer and control various aspects of the infusion services. 
     System  100  may be a distributed client/server system that spans one or more networks, such as network  104 . In such implementations, data may be communicated or stored in an encrypted format using any standard or proprietary encryption algorithm. In other instances, the data may be stored at least partially in an unencrypted format. System  100  may be in a dedicated environment, implemented across a local area network or subnet, or implemented in any other suitable environment without departing from the scope of this disclosure. In some instances, the system  100  may include or be communicably coupled with a server  106 , one or more clients  102 , network  104 , and one or more medical devices  110 . Additionally, one or more of the clients  102  may be communicably coupled to a repository  112 . In some implementations, the one or more clients  102  may be consoles utilized by medical practitioners to control the infusion services, either alone or in addition to other aspects associated with the system  100 . Further, system  100  may include additional or different features and components than those described. 
     Server  106  may include an electronic computing device operable to receive, transmit, process, and store data associated with system  100 . Generally,  FIG. 1  provides merely one example of computers that may be used with the disclosure. Each computer is generally intended to encompass any suitable processing device. For example, although  FIG. 1  illustrates one server  106  that may be used with the disclosure, system  100  can be implemented using computers other than servers, as well as a server pool. Indeed, server  106  may be any computer or processing device such as, for example, a blade server, general-purpose personal computer (PC), Macintosh, workstation, Unix-based computer, or any other suitable device. In other words, the present disclosure contemplates computers other than general purpose computers as well as computers without conventional operating systems. Server  106  may be adapted to execute any operating system including Linux, UNIX, Windows Server, or any other suitable operating system. According to one embodiment, server  106  may also include or be communicably coupled with a web server and/or a mail server. 
     The server  106  may include local memory  108 . Memory  108  may include any memory or database module and may take the form of volatile or non-volatile memory including, without limitation, magnetic media, optical media, random access memory (RAM), read-only memory (ROM), removable media, or any other suitable local or remote memory component. Illustrated memory  108  may include, among other items, an infusion pressure application  114 . For example, medical practitioners may use the clients  102  to interact with activities associated with operation of the medical device  110 , including the infusion services at least partially provided by the infusion pressure application  114 . For example, in some instances, the infusion services may be conducted entirely on the server  102  with information sent to and from each client  104  and/or medical device  110  to interact with the infusion pressure application  114 . 
     In other instances, infusion services of the infusion pressure application  114  may be performed partially on the server  106  and partially at one or more locations remote from the server  106 . For example, in some implementations, the infusion services of the infusion pressure application  114  may be partially or fully performed on the medical device  110 . 
     Memory  108  may store classes, frameworks, applications, backup data, jobs, or other information that includes any parameters, variables, algorithms, instructions, rules, or references thereto. Memory  108  may also include other types of data, such as environment and/or application description data, application data for one or more applications, as well as data involving virtual private network (VPN) applications or services, firewall policies, a security or access log, print or other reporting files, HyperText Markup Language (HTML) files or templates, related or unrelated software applications or sub-systems, and others. Consequently, memory  108  may also be considered a repository of data, such as a local data repository from one or more applications. Memory  108  may also include data that can be utilized by the infusion pressure application  114 . 
     Server  106  may also include processor  118 . Processor  118  executes instructions and manipulates data to perform the operations of the server  106 , e.g., computational and logic operations, and may be, for example, a central processing unit (CPU), a blade, an application specific integrated circuit (ASIC), or a field-programmable gate array (FPGA). Although  FIG. 1  illustrates a single processor  118  in server  106 , multiple processors  118  may be used according to particular needs and reference to processor  118  is meant to include multiple processors  118  where applicable. In the illustrated embodiment, processor  118  executes infusion pressure application  114 . 
     Server  106  may also include interface  120  for communicating with other computer systems, such as clients  102 , over network  104  in a client-server or other distributed environment. For example, the interface  120  may receive data from different parts of the system  100  or from sources outside of the system  100  as well as transmit data to different parts of the system  100  or to locations outside of the system  100 . In certain embodiments, server  106  receives data from internal or external senders through interface  120  for storage in memory  108  and/or processing by processor  118 . Generally, interface  120  comprises logic encoded in software and/or hardware in a suitable combination and operable to communicate with network  104 . More specifically, interface  120  may comprise software supporting one or more communications protocols associated with communications network  104  or hardware operable to communicate physical signals. 
     Network  104  facilitates wireless or wireline communication between computer server  106  and any other local or remote computer, such as clients  102 . Network  104  may be all or a portion of an enterprise or secured network. In another example, network  104  may be a VPN merely between server  106  and client  102  across wireline or wireless link. Such an example wireless link may be via 802.11a, 802.11b, 802.11g, 802.20, WiMax, and many others. While illustrated as a single or continuous network, network  104  may be logically divided into various sub-nets or virtual networks without departing from the scope of this disclosure, so long as at least a portion of network  104  may facilitate communications among server  106 , at least one client  102 , and other device, such as medical device  110 , discussed in more detail below. For example, server  106  may be communicably coupled to a repository  122  through one sub-net while communicably coupled to a particular client  102  through another. In other words, network  104  encompasses any internal or external network, networks, sub-network, or combination thereof operable to facilitate communications between various computing components in system  100 . Network  104  may communicate, for example, Internet Protocol (IP) packets, Frame Relay frames, Asynchronous Transfer Mode (ATM) cells, voice, video, data, and other suitable information between network addresses (collectively or interchangeably referred to as “information”). Network  112  may include one or more local area networks (LANs), radio access networks (RANs), metropolitan area networks (MANs), wide area networks (WANs), all or a portion of the global computer network known as the Internet, and/or any other communication system or systems at one or more locations. In certain embodiments, network  104  may be a secure network accessible to users via certain local or remote clients  102 . 
     Client  102  may be any computing device operable to connect or communicate with server  106  or network  104  using any communication link. At a high level, each client  102  includes or executes at least graphical user interface (“GUI”) or application interface (collectively referred to as “GUI  124 ”) and comprises an electronic computing device operable to receive, transmit, process, and store any appropriate data associated with system  100 . It will be understood that there may be any number of clients  102  communicably coupled to server  104 . Further, “client  102 ” and “user” may be used interchangeably as appropriate without departing from the scope of this disclosure. Moreover, for ease of illustration, each client  104  is described in terms of being used by one user. But this disclosure contemplates that many users may use one computer or that one user may use multiple computers. As used in this disclosure, client  102  is intended to encompass a personal computer, touch screen terminal, workstation, network computer, kiosk, wireless data port, smart phone, personal data assistant (PDA), one or more processors within these or other devices, or any other suitable processing device. For example, client  102  may be a PDA operable to wirelessly connect with an external or unsecured network. In another example, client  102  may comprise a laptop computer that includes an input device, such as a keypad, touch screen, mouse, or other device that can accept information, and an output device that conveys information associated with the operation of server  106  or clients  102 , including digital data, visual information, or user interface, such as GUI  124 . Both input devices and output devices may include fixed or removable storage media such as a magnetic computer disk, CD-ROM, or other suitable media to both receive input from and provide output to users of clients  102  through, for example, a display. In some instances, the display may include the client portion of GUIs  124 . 
     GUI  124  may include a graphical user interface operable to allow the user of client  102  to interface with at least a portion of system  100  for any suitable purpose, such as viewing application or other transaction information. For example, GUI  124  could provide information associated with a medical procedure, including detailed information related to infusion pressure and/or other information related to the infusion pressure application  114 . Generally, GUI  124  may provide a particular user with an efficient and user-friendly presentation of information provided by or communicated within system  100 . GUI  124  may include a plurality of customizable frames or views having interactive fields, pull-down lists, and buttons operated by the user. GUI  124  may also present a plurality of portals or dashboards. For example, GUI  124  may display a secure webpage that allows users to input and define parameters associated with the infusion services. It should be understood that the term graphical user interface may be used in the singular or in the plural to describe one or more graphical user interfaces and each of the displays of a particular graphical user interface. Indeed, reference to GUI  124  may indicate a reference to the front-end or a component of infusion pressure application  114 , as well as the particular interface accessible via client  102 , as appropriate, without departing from the scope of this disclosure. Therefore, GUI  124  contemplates any graphical user interface. For example, in some instances, the GUI  124  may include a generic web browser or touch screen that processes information in system  100  and efficiently presents the results to the user. In other instances, the GUI  124  may include a custom or customizable interface for displaying and/or interacting with the various features of the infusion pressure application  114  or other infusion services. Further, in some instances, server  106  may accept data from client  102  and return the appropriate HTML or XML responses to the browser using network  104 . In some instances, information between the server and the client  102  may be transmitted via a web browser (e.g., Microsoft Internet Explorer or Netscape Navigator) or other application. In some instances, software utilized for transmitted information may be integrated within the infusion pressure application  114 . 
     The medical device  110  may include a processor  126 , similar to processor  118 , memory  128 , similar to memory  108 , and one or more applications  130 . For example, the one or more applications  130  may include infusion pressure application  114  or a portion thereof. Further, the medical device  110  may be adapted to execute any suitable operating system. The medical device  110  may also include a display  132  for displaying information to a user, such as a medical practitioner. Further, the display  132  may present the present information to the user via a GUI  134 , which may be similar to the GUI  124 , described above. The medical device  110  may send and receive information to and from the server  106  as well as to and from clients  102  via the network  104 . Aspects of operation of the medical device  110  may be monitored and/or controlled from the medical device  110 , the server  106 , and/or the client  102 . For example, one or more aspects or services of operation of the medical device  110  may be performed and/or altered by the medical device  110 , by the server  106 , and/or by a user via client  124 . 
     The medical device  110  may also include an interface  144 , similar to interface  120 , for communicating data with components, both within and outside of the system, including computer systems, such as clients  102 , server  106 , or other components, directly or over network  104  in a client-server or other distributed environment. The medical device  110  may receive one or more inputs, such as inputs  136  and  138 . Inputs  136  and  138 , as well as any other desired inputs to the medical device  110 , may be received and/or outputs transmitted via the interface  144 . 
     In some instances, the inputs  136  and  138  may respectively represent infusion services information, such as measurement data representative of a medical condition or aspect of a patient&#39;s health. Inputs  136  and  138  may be communicated to the medical device  110  in any desirable manner. For example, one or more of the inputs  136 ,  138  may be transmitted to the medical device  110  over a wireline connection (e.g., via an Ethernet, USB, IEEE 1394, or other wired connection) or wireless connection (e.g., an 802.11a, 802.11b, 802.11g, 802.20, WiMax, ZigBee, Ultra-Wideband (“UWB”), or any other wireless link). 
     In some implementations, input  136  may represent systemic blood pressure data, while input  138  may represent data indicative of intraocular pressure, such as infusion pressure data. However, inputs may represent any characteristics of a patient&#39;s health, such as heart rate, pulse, respiration rate, etc. Further, inputs  136  and  138  may be provided to the medical device  110  from components  140  and  142 , respectively. Further, in some instances, input  136  and input  138  may be in the form of a digital or analog signal. Components  140  and  142  may be another device, such as another medical device, from which data may be desired. In some instances components  140  and/or  142  may be a sensor coupled directly or indirectly to the patient. Example devices  140  and  142  may be anesthesia devices or sensors, vital sign monitoring devices or sensors, or any other desired device or sensor that may provide information associated with performing a medical procedure on a patient. In some instances, devices  140  and  142  may be adapted to determine one or more of a patience&#39;s vital signs, such as blood pressure, pulse rate, etc. For example, device  140  and/or  142  may be adapted to determine blood pressure by sensing blood pressure. 
     In still other implementations, medical device  110  may incorporate devices and/or sensors  140  and  142 . For example, medical device  110  may include pressure measurement components, temperature measurement components, flow rate measurement components, as well as others. In some instances, the pressure measurement component may include a pressure transducer, or, in other instances, the pressure measurement component may include a combination of devices and/or sensors adapted to measure pressure, such as one or more pressure transducers, one or more flow rate measurement devices, one or more temperature sensors, and/or any other suitable instrument. Further, medical device  110  may include any other or different sensors and devices than those described. 
     While the above description with respect to  FIG. 1  describes the server  106  at least partially executing and/or providing services associated with the infusion pressure application  114 ,  FIG. 2  illustrates an alternate implementation in which services associated with infusion pressure application  114  may entirely be performed on and/or by the medical device  110 . Further, the medical device  110  may also perform other functions or provide other services. 
     Accordingly,  FIG. 2  shows a system  200  including medical device  110 , server  106 , network  104 , and clients  102 , similar to those described above. The server  106  may include one or more application  210  provided in memory  108 . Also similar to above, the medical device  110  may receive inputs  136  and  138 . Other components may also be included in system  200 . For example, system  200  may include multiple medical devices and/or multiple servers. Communication between the medical device  110  and client  102  may be provided via network  104 . 
       FIG. 3  shows a still further implementation in which the medical device  110  for performing the services associated with the infusion pressure application  114  is in a stand-alone configuration. The medical device  110  may be similar to that described above. For example, the medical device  110  may include, among other features, processor  126 , memory  128 , display  132 , and receive inputs  136  and  138 . These components may be similar to those components described above. The memory  128  may include infusion pressure application  114 , and processor  126  may execute the instructions of infusion pressure application  114 . Accordingly, the medical device  110  may exclusively provide all services associated with the infusion pressure application  114 . The medical device  110  may also be coupled to a client  102 , through which a user may monitor or make changes to an operating condition of the medical device  110 . 
     In some implementations, the medical device  110  may be a vitreoretinal surgical system. Example vitreoretinal surgical systems may include, but are not limited to, the Accurus® Surgical System produced by Alcon Laboratories, Inc. of Alcon Laboratories, Inc., 6201 South Freeway, Fort Worth, Tex. 76134 and the Constellation® Vision System also produced by Alcon Laboratories, Inc. 
     The infusion pressure application  114  may provide one or more of the features described below.  FIG. 4  shows a cross-sectional view of an eye  400  undergoing a medical procedure involving, for example, a vitrectomy. A first cannula  410  and a second cannula  420  may be inserted through the sclera  430  and into the posterior segment  40  of the eye  20 . Vitreous material may be evacuated through the cannula  410  and carried away through a tube  440  or other suitable structure. Infusion fluids may be introduced into the posterior segment  450  via the second cannula  420 . 
     As the vitreous material is removed from and infusion fluid is introduced into the posterior segment  450 , intraocular pressure may fluctuate. For example, if the rate of aspiration of material from the eye is greater than the rate material is infused into the eye, the TOP may drop. On the other hand, if the rate at which material is aspirated from the eye is less than the rate at which material is infused into the eye, the IOP may increase. Generally, infusion pressure may be determined and used as a proxy for IOP. That is, during an intraocular surgical procedure, infusion pressure generally may have the greatest effect on and, therefore, be representative of IOP. A signal corresponding to the infusion pressure may be transmitted to a processor, such as processor  126  or  118 . 
     The infusion pressure may be carefully controlled. For example, if infusion pressure exceeds a certain threshold, IOP corresponding thereto may exceed the critical closing pressure (“CCP”). Consequently, vascular occlusion may result. During a surgical procedure, IOP may be altered, for example, by adjusting the infusion pressure. In other instances, TOP may be altered by adjusting the rate at which vitreous material is aspirated, the rate at which infusion fluid is infused, or both. 
     CCP may vary with a patient&#39;s blood pressure. For example, for a patient having a low blood pressure or as a patient&#39;s blood pressure drops during a medical procedure, the pressure necessary to prevent blood flow through the central retinal artery (i.e., the CCP) will be lower. On the other hand, for a patient with high blood pressure or as the patient&#39;s blood pressure increases during a medical procedure, the CCP raises. 
     In some implementations, during an intraocular surgical procedure, such as one involving a vitrectomy, a patient&#39;s systemic blood pressure may be monitored. In some instances, the measured systemic blood pressure may be brachial artery blood pressure. The systemic blood pressure may be monitored and provided as an input to a control or monitoring device. The systemic blood pressure may be measured, for example, by a pressure cuff or other suitable device, and a signal corresponding thereto may be transmitted to a processor, such as the processor that receives the intraocular blood pressure. Alternately, a signal corresponding to the systemic blood pressure may be transmitted to a different processor. 
     The systemic blood pressure may be converted into an estimated central retinal artery blood pressure (interchangeably referred to as “retinal blood pressure”) according to known methods. For example, an offset, such as a conversion factor or algorithm, for converting from systemic blood pressure to retinal blood pressure may be an ophthalmodynamometry derived offset. That is, the offset may be obtained from ophthalmodynamometry studies. A processor may determine the retinal blood pressure using the systemic blood pressure and offset. Accordingly, the processor may determine an estimated critical closing pressure and compare the estimated CCP to the infusion pressure. 
     In some instances, if the infusion pressure is equal to or above the retinal blood pressure or another selected pressure, the infusion pressure may be automatically adjusted to prevent occlusion from occurring. Alternately or in addition, an alarm may be triggered by the infusion pressure condition. For example, in some instances, a medical device, such as medical device  110 , may receive as inputs infusion pressure and systemic blood pressure, automatically determine an estimated retinal blood pressure from the received systemic blood pressure, determine the estimated critical closure pressure from the retinal blood pressure, and compare the infusion pressure to a selected pressure (e.g., the estimated critical closing pressure or another pressure associated therewith). If the infusion pressure is equal to, above, or at some other level relative to the selected pressure, the medical device may automatically adjust the infusion pressure to keep the infusion pressure at a desired level. Further, the medical device may also trigger an alarm to notify the medical practitioners of the infusion pressure level. 
     Infusion pressure may be increased or otherwise altered by adjusting a pressure head, such as by altering a pump speed, altering a gas pressure (such as in gas forced infusion or vented gas force infusion), or altering a gravity pressure head. A gravity pressure head may be altered by adjusting a height of a volume of fluid, such as by changing a height of a container of fluid either manually or in an automated fashion. For example, a gravity pressure head may be altered in an automated fashion with an electronically controlled motorized staff that automatically adjusts a height of a fluid container coupled thereto to maintain a desired pressure head. Collectively, mechanisms for accomplishing these pressure heads, such as those described above, may be referred to as “fluid flow devices”. 
     In other implementations, the infusion pressure (and, hence, the IOP) may be intentionally increased above the CCP. For example, the infusion pressure may be intentionally increased above the CCP to stop intraocular bleeding. The infusion pressure may be maintained at the elevated pressure so that intraocular bleeding may be corrected. Once the site at which intraocular bleeding has been corrected and the infusion pressure may be lowered to a level below critical closing pressure, the bleeding is prevented from reoccurring. Example procedures and mechanisms for repairing a bleed site may include coagulation, suturing, and cauterization. Thereafter, infusion pressure may be lowered below the CCP thereby permitting blood flow through the central retinal artery. 
     One or more of the systemic blood pressure, estimated retinal blood pressure, estimated CCP, or infusion pressure may be displayed to a user, such as a medical practitioner. For example, such output may be displayed on a display, such as display of a client  102  and/or display  132 . The output may be incorporated into a GUI, such as GUI  124  and/or GUI  134 .  FIGS. 5-6  show example display outputs for presenting the outputted information to the user.  FIG. 5  shows a display output  500  including a pair of axes  510 ,  520 . In some instances, the horizontal axis  510  my represent “time”, while the vertical axis  520  may indicate “pressure”.  FIG. 5  shows the behavior over time of infusion pressure  530  relative to estimated CCP  540 . In this instance, the infusion pressure  530  is shown below the estimated CCP  540  for a period of time.  FIG. 6  also shows an example display output  600  in which infusion pressure  530  has increased beyond the estimated CCP  540  for a period of time. 
       FIG. 7  shows an example method  700  for controlling infusion pressure using systemic blood pressure. Systemic blood pressure  710  may be obtained and used as an input at  720 . At  720 , the systemic blood pressure  710  may be converted into retinal blood pressure  730 . For example, the retinal blood pressure  730  may be determined from the systemic blood pressure  710  using an offset obtained from ophthalmodynamometry studies. The determined retinal blood pressure  730  may be defined as the critical closing pressure. At  750 , the critical closing pressure may be compared to infusion pressure  740 . At  760 , if the infusion pressure  740  is greater than and/or equal to the critical closing pressure, an alarm  770  may be triggered. A return to  750  may be made at which time subsequent critical closing pressure and infusion pressure  750  comparisons may be made. 
     In some instances, the alarm may be a visual alarm. Example visual alarms may include a message displayed on a display, a flashing light, or some other visual indicator. In other instances, the alarm may be an audible alarm. Example audible alarms may include a buzzer, a siren, or some other audible cue to indicate to the user or medical practitioner that an alarm has been triggered. In still other instances, the audible alarm may be in the form of a pre-recorded or computer-generated message. For example the pre-recorded or computer-generated message may be or mimic a human voice that indicates that a pressure is above a predetermined value. The message may also repeat at regular, irregular, or any other desired interval and include recitation of an elapsed time during which the pressure has exceeded the predetermined pressure value. Further, the alarms may have an escalation feature. That is, alarm of one type may be triggered at a first pressure, while a second type of alarm may be triggered at a different pressure. Such a feature may provide for a series of escalating alarms as the measured infusion pressure increases above predetermined intervals. 
     It is noted that, in some instances, while an alarm may be triggered at  770  based on determinations made at  760  the method may be applied on a continuous basis whether or not an alarm has been triggered. Thus, the example method  500  may represent a continuous control method that, in some instances, may be a real-time control method. Consequently, the implementations of the methods described herein may be implemented into a control system that continuously intakes systemic blood pressure and infusion pressure as inputs and determine whether an alarm is to be triggered. 
     In some implementations, a medical device incorporating one or more of the features described herein, such as medical device  110 , may include a feature that automatically adjusts the infusion pressure (such as by increasing the rate at which material is aspirated from the eye, the rate at which material is infused into the eye, or both) in the event the infusion pressure increases above or decreases below a selected value or, for example, if the rate of change of the infusion pressure leads to or is likely to an infusion pressure above critical closing pressure. 
     It should be understood that, although many aspects have been described herein, some implementations may include all of the features, while others may include some features while omitting others. That is, various implementations may include one, some, or all of the features described herein without departing from the scope of the disclosure. Further, additional features not described herein may also be included in the various implementations described herein without departing from the scope of the disclosure. 
     A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other implementations are within the scope of the following claims.