Negative pressure control urine drainage system and method

Abstract

A negative pressure controlled urine drainage system and method, the system comprising a monitoring device (10) and a matched drainage material, being capable of regularly emptying urine detained in a bladder or a drainage tube, and calculating the real urine volume produced by a patient within a predetermined period of time, improving the accuracy of urine volume metering per unit time, providing credible monitoring data for AKI, and improving the accuracy of urine volume metering per unit time. And the risks of catheter blockage and urinary tract infection are reduced.

Description

Negative pressure controlled urine drainage system and method TECHNICAL FIELD

[0001] The present application relates to a negative pressure controlled urine drainage system and method for dynamic monitoring of patients with indwelling urinary catheter, belonging to the field of medical devices or nursing supplies. BACKGROUND

[0002] Oliguria (referring to urine output less than 17ml per hour) is an independent predictor of acute kidney injury (AKI), and a large number of medical researches have confirmed that persistent oliguria in ICU inpatients is associated with higher mortality. Therefore, oliguria has been included in the early sensitive indicators of acute kidney injury, and should be strictly dynamically monitored. The existing indwelling urinary catheter nursing technical specification is to place the urinary catheter in the patient's bladder, use the drainage tube to connect the urinary catheter and the urine collector, suspend the urine collector at a lower position outside the bed than the wound surface, and use the siphon effect caused by the difference between the bladder and the urine collector to drain the urine in the bladder into the urine collector. When the patient's urine output needs to be calculated, a measuring cup is used to measure and record the urine collected in the urine collector. In recent years, with the continuous deepening of the application of electronic technology in medicine, electronic urine meters (collectively referred to as similar products with this function) for dynamically monitoring the urine output of patients have successively entered clinical use. The basic principle of this type of product is to install the electronic urine meter outside the patient's bed, suspend the urine collector on the gravity sensor provided on the electronic urine meter, and dynamically weigh the urine in the urine collector by the gravity sensor to convert it into urine volume display reading.

[0003] The existing urine metering method has a big flaw, mainly in that: in clinical practice, due to the long distance from the patient's bladder to the urine collector, and the need to meet the patient's position changes such as turning over to the left and right, the length of the drainage tube from the urinary catheter interface to the urine collector is generally between 120cm and 150cm. According to the measurement in the real scene, taking a drainage tube with an inner diameter of 5mm as an example, the urine volume retained in the drainage tube laid on the bed upstream of the urinary catheter interface to the urine collector is between 45ml and 50ml. Therefore, whether manual metering or electronic urine metering is used, only the urine volume in the urine collector can be metered and obtained, and the urine volume retained in the drainage tube or the bladder cannot be metered, and the obtained urine volume value deviates greatly from the actual urine volume produced by the patient per unit time. Especially for oliguric patients with urine output less than 17ml per hour, the urine in the first 1-3 hours may be completely retained in the bladder or the drainage tube laid on the bed, and as the urine output in the bladder increases, the retained urine in the drainage tube slowly peristalsis to the urine bag, and finally all the urine is simultaneously drained into the urine collector under the siphon effect, such as in the 4th hour, and is incorrectly calculated into the urine volume of this time period. It can be seen that the existing drainage state and metering method cannot accurately reflect the actual urine output of the patient per unit time, affecting the early diagnosis of acute kidney injury (AKI).

[0004] On the other hand, urine is retained in the drainage tube, which is easy to cause the deposition of sugar, protein and inorganic salts such as calcium and sodium in the urine, resulting in salt crystallization at the head of the urinary catheter or blockage of the drainage tube. Moreover, urine retention in the drainage tube is easy to cause bacterial growth and retrograde up to the bladder, increasing the risk of urinary tract infection. Therefore, the present inventors propose a negative pressure control urine drainage system and method to fill the gap in the existing urine monitoring and drainage technology. SUMMARY

[0005] The present application relates to a negative pressure control urine drainage system and method, mainly comprising:

[0006] A system comprising a monitoring device and a matching drainage material, wherein:

[0007] The monitoring device comprises a control mainboard, a negative pressure generator, a pressure sensor, a urine metering device and a human-computer interaction interface.

[0008] The control mainboard is an integrated circuit constructed by core processor, memory, signal processor, communication module and other components. The core processor adopts a single-chip microcomputer (MCU), and the communication module adopts any one of WiFi, Bluetooth or ZigBee.

[0009] The control mainboard is further provided with embedded software, which is a software program for hardware driving, function setting, data analysis and negative pressure drainage control, and is burned in the memory of the control mainboard.

[0010] The negative pressure generator is a negative pressure device for providing a vacuum environment inside the matching drainage material, such as a small vacuum pump. The negative pressure generator is in communication with the control mainboard and is controlled by the control mainboard. The working pressure of the negative pressure generator is adjusted in the range of not less than -10 cmH20~0.

[0011] The pressure sensor dynamically monitors the pressure value in the matching drainage material. The range of the pressure sensor is not less than -10 cmH20~0, and the measurement accuracy is not less than 1 cmH20. The pressure sensor is in communication with the control mainboard and sends the pressure data obtained by dynamic monitoring to the core processor.

[0012] The urine metering device dynamically monitors the amount of urine discharged by the patient. The range of the urine metering device is not less than 0~1000 ml, and the measurement accuracy is not less than 1 ml. The urine metering device is in communication with the control mainboard and sends the urine amount data obtained by dynamic monitoring to the core processor.

[0013] According to different urine amount monitoring techniques, the urine metering device that can be selected includes, but is not limited to, an ultrasonic liquid flow meter, a light-induced drop speed sensor, a turbine liquid flow meter, a gravity sensor and a tension sensor, etc.

[0014] For example, an ultrasonic liquid flow meter is arranged outside the drainage tube to dynamically measure the amount of urine flowing through the tube.

[0015] Alternatively, a gravity sensor is arranged below the urine collector to measure the weight of urine in the urine collector, and the weight of urine is converted into the volume of urine according to the density of urine of the patient.

[0016] In one embodiment, a light-sensing drop speed sensor is used to dynamically monitor the amount of urine. Specifically, a drip chamber is arranged between the drainage tube and the urine collector, and an infrared drop speed sensor is arranged outside the drip chamber. When no urine droplet passes through the drip chamber, the receiving tube of the infrared drop speed sensor is turned on by light, and the output signal is marked as 0 drops. When a urine droplet passes through the drip chamber, the droplet refracts light, and the light flux of the receiving tube is insufficient, and the output signal is marked as 1 drop. In this way, the number of urine droplets per unit time is calculated. Since the volume of each droplet of urine is basically constant, the volume of each droplet is multiplied by the number of urine droplets to calculate the amount of urine drained per unit time.

[0017] Preferably, the light-sensing drop speed sensor and the gravity sensor are combined. Specifically, a drip chamber is arranged between the drainage tube and the urine collector, and an infrared drop speed sensor is arranged outside the drip chamber. At the same time, a gravity sensor is arranged, and the urine collector is suspended below the gravity sensor. The advantage of this technical approach is that the light-sensing drop speed sensor and the gravity sensor are synchronized to measure the amount of urine per unit time, and the gravity sensor calculates the weight of urine per unit time. The density of urine is dynamically calculated, and the formula for calculating the density of urine is: density of urine = weight of urine ÷ volume. According to the corresponding relationship between weight, density, and volume, the volume of urine per unit time is calculated.

[0018] The human-computer interaction interface includes a display screen, a data interface, and operation function keys.

[0019] The matching drainage material is a special consumable for the monitoring device. The matching drainage material includes a conversion connector, a drainage tube, a negative pressure suction chamber, a negative pressure suction tube, and a urine collector.

[0020] The conversion connector is used to connect the drainage device with the urinary catheter left in the patient's bladder.

[0021] The drainage tube is a flexible tube that connects the urinary catheter and the urine collector, and drains the urine in the bladder to the urine collector. The front end of the drainage tube is connected to the urinary catheter through the conversion connector, and the tail end of the drainage tube is connected to the urine collector.

[0022] The negative pressure suction cavity is a hollow cavity provided between the drainage tube and the urine collector and having a pipeline interface. The negative pressure suction cavity is provided with three pipeline interfaces, one of which is in communication with the drainage tube upstream of the urine collector, one is in communication with the liquid inlet of the urine collector downstream, and the other is connected with the negative pressure suction tube.

[0023] The negative pressure suction tube is a flexible pipeline connecting the negative pressure suction cavity and the suction port of the negative pressure generator.

[0024] The urine collector is a container for collecting the urine discharged from the drainage tube, including a urine collection bag or a drainage bottle.

[0025] Further, in order to prevent the urine in the urine collector from flowing back to the drainage tube, a check valve is further provided between the negative pressure suction cavity and the urine collector. The shape and structure of the check valve are not limited, including a thin film check valve and a silicone duckbill valve.

[0026] In order to improve the integration level of consumables and reduce the time for medical staff to prepare multiple consumables, the urinary catheter can also be combined into the matching drainage material to become a drainage consumable combination package special for the monitoring equipment.

[0027] The urinary catheter includes a conventional urinary catheter with two lumens or three lumens, a temperature measuring urinary catheter, a pressure measuring urinary catheter, and a temperature and pressure measuring urinary catheter. The urinary catheter with different functions is matched with the monitoring equipment to obtain more physiological parameters of the patient, such as:

[0028] When the temperature measuring urinary catheter is combined and matched for use, the monitoring equipment can collect and obtain the body temperature data from the patient's bladder and display and read out the data.

[0029] When the pressure measuring urinary catheter is combined and matched for use, the monitoring equipment can measure the pressure of the patient's bladder and obtain and display and read out the data of the bladder pressure or intra-abdominal pressure.

[0030] When the temperature and pressure measuring urinary catheter is combined and matched for use, the monitoring equipment can collect and obtain the body temperature, bladder pressure or intra-abdominal pressure data of the patient and display and read out the data.

[0031] A method applied to a negative pressure controlled urine drainage system mainly includes:

[0032] (1) According to the drainage interval time and the drainage negative pressure value set by the medical staff on the human-computer interaction interface, the system automatically starts the negative pressure generator to suck, so that the negative pressure in the negative pressure suction cavity is generated;

[0033] (2) During the period, the pressure sensor dynamically monitors the negative pressure value in the negative pressure suction cavity and feeds back to the core processor, and the core processor instructs the negative pressure generator to dynamically correct the working pressure, and the negative pressure value in the negative pressure suction cavity is stably maintained within the set drainage negative pressure value range;

[0034] (3) under the continuous action of the negative pressure generator, the urine retained in the bladder or drainage tube is sucked into the negative pressure suction cavity, and the urine flows into the urine collector under the action of gravity;

[0035] (4) during the negative pressure drainage, the urine metering device dynamically senses the urine increment, and after the urine increment stops, the negative pressure generator stops working; or, the man-machine interaction interface can also be autonomously set to keep the negative pressure for a certain time, and after the system set negative pressure keeping time is reached, the negative pressure generator stops working;

[0036] (5) the urine metering device dynamically monitors the newly added urine in the period, and displays and reads out on the man-machine interaction interface, and dynamically prompts when oliguria or polyuria occurs, and thus, a urine negative pressure drainage and metering period ends;

[0037] (6) the system periodically repeats according to the foregoing steps (1)-(5), empties the urine retained in the bladder or drainage tube at a certain time, and calculates the urine volume.

[0038] (7) the drainage interval time in the system is set to be between 1 min and 60 min, preferably, the drainage interval time is set to be between 5 min and 10 min.

[0039] (8) the drainage negative pressure value in the system is set to be between -40 cmH20 and -1 cmH20, preferably, the drainage negative pressure value is set to be between -10 cmH20 and -6 cmH20.

[0040] (9) the system can be set to keep the negative pressure for 1 min to 5 min, preferably, the negative pressure keeping time is set to be 2 min.

[0041] The foregoing negative pressure control urine drainage working method (1)-(9) is programmed by software and written into the embedded software of the system.

[0042] The beneficial effects of the present application are that the drainage interval time, the drainage negative pressure value or the negative pressure keeping time can be autonomously set according to the patient characteristics and clinical needs, the urine retained in the bladder or the drainage tube is emptied at a certain time, and the real urine volume generated by the patient in the period is calculated. Not only the accuracy of the urine volume metering in a unit time is greatly improved, but also the monitoring data for AKI early warning is provided, and early discovery and early intervention are achieved. Moreover, the urine in the bladder or the drainage tube is emptied at a certain time, which can reduce the risk of pipe blockage and urinary tract infection, fill the gap in the technical field, and has good clinical value. BRIEF DESCRIPTION OF DRAWINGS

[0043] Fig. 1 is a schematic diagram of a system of the present application

[0044] Fig. 2 is a schematic diagram of a monitoring device structure of a system of the present application

[0045] Figure 3 is a schematic diagram of the combination of the monitoring device of the present application and the matching drainage material

[0046] Figure 4 is a schematic diagram of the structure of the negative pressure suction cavity and the urine collector combined in the embodiment of the present application

[0047] Shown in the figure: monitoring device 10, human-computer interaction interface 11, negative pressure generator interface 20, urine metering device 30, conversion joint 40, drainage tube 50, negative pressure suction cavity 60, negative pressure suction tube 70, suction tube joint 71, check valve 72, urine collector 80, urine collector fixing device 90 DETAILED DESCRIPTION

[0048] The present application will be specifically described below in combination with the drawings and embodiments.

[0049] Embodiment 1: one preparation mode of the monitoring device 10 of the present application

[0050] 1. As shown in Figure 1, the principle diagram of the monitoring device 10 is designed.

[0051] 2. The list of main components used is as follows:

[0052] The core processor (MCU) uses a single-chip microcomputer (STC company) of model STC89C52;

[0053] The pressure sensor uses a micro (Wuxi) of model GZP6847, with a range of -30KPa-0KPa;

[0054] The urine metering device 30 uses a gravity sensor of model SBT620 (Guangzhou), with a maximum error of ±0.2% and a range of 0-2kg;

[0055] The communication module uses a WiFi module of model QCA9377 (Qualcomm company);

[0056] The storage module uses a Samsung HY27US08561A chip, with a storage capacity of 32M.

[0057] The function keys of the human-computer interaction interface 11 use Omron B3F type touch switch buttons, with a size of 12*12*7.3. The display screen (1-3) uses a 2.9 inch LCD liquid crystal, with a working voltage of DC 3.0V; the sound prompter uses a conventional buzzer.

[0058] The power supply uses an internal power supply, and a 10000mA, 3.7V rechargeable lithium battery (Everbright company) is selected.

[0059] 3. The PCB is designed according to the conventional integrated circuit technology, and the electronic patching or welding process is used to prepare the control mainboard, with a length of 60mm and a width of 40mm.

[0060] 4、Design and control the size of the protective shell matched with the mainboard, the left side of the protective shell is provided with a negative pressure generator interface 20, the negative pressure generator interface 20 is connected with the internal negative pressure generator; the right side is provided with a USB line interface, a DC charging interface; the front of the protective shell is provided with an observation window matched with a liquid crystal screen, a function key is arranged below the observation window, the function key includes a power on / off key, a negative pressure value setting key, a drainage interval time setting key and the like; the bottom of the protective shell is provided with a urine metering device 30 installation position, a urine collector fixing device 90 is arranged below the sensing port of the urine metering device 30.

[0061] 5、As shown in Figure 2, each component is installed and fixed in the protective shell, and the machine is tested, and it is qualified.

[0062] Example 2 Preparation of a negative pressure control urine drainage device matched with the monitoring device 10

[0063] 1、As shown in Figure 3, the extrusion mold for preparing the drainage tube 50 and the negative pressure suction tube 70 is prepared, and the suitable material is medical soft polyvinyl chloride. Among them, the inner diameter of the drainage tube 50 is 6mm, the outer diameter is 8mm, it is produced by extrusion process, and it is cut into two specifications: A pipeline each section 130cm, B pipeline each section 30cm. The inner diameter of the negative pressure suction tube 70 is 2mm, the outer diameter is 3.5mm, it is produced by extrusion process, and it is cut into each section 30cm.

[0064] 2、Preparation of injection mold for conversion joint 40, negative pressure suction cavity 60 and suction pipe joint 71, suitable material medical polyvinyl chloride. Among them:

[0065] The conversion joint 40 is a tapered joint, the head end size is matched with the catheter interface, and the tail end size is matched with the drainage tube 50

[0066] (8.1mm).

[0067] The negative pressure suction cavity 60 adopts split structure of upper cover and main cavity, the upper cover is provided with an interface matched with the drainage tube 50 and the negative pressure suction tube 70, and the bottom of the main cavity is provided with a drainage hole matched with the drainage tube 50. After injection molding, the split body of the upper cover and the main cavity is sealed and bonded by medical glue.

[0068] 3、The urine collector 80 adopts PP film high frequency heat sealing, and the capacity is 2000ml.

[0069] 4、The head of the A pipeline of the drainage tube 50 is sealed and bonded with the conversion joint 40 by medical glue (such as cyclohexanone), and the tail of the A pipeline is sealed and communicated with the interface of the upper cover of the negative pressure suction cavity 60.

[0070] The drainage hole at the bottom of the main cavity of the negative pressure suction cavity 60 is bonded with the head of the B pipeline of the drainage tube 50 by medical glue, and the tail of the B pipeline is sealed and communicated with the interface of the urine collector 80.

[0071] 5. Using medical adhesive, seal the head of the negative pressure suction tube 70 to the suction tube connector 71, and seal the tail of the negative pressure suction tube 70 to the interface of the cover of the negative pressure suction chamber 60.

[0072] 6. Inspect all fixed connections. Ensure there are no leaks and the tensile strength is not less than 10N. Pack the parts after they pass the inspection.

[0073] Example 3: Application of a negative pressure controlled urine drainage system combined with a drainage device

[0074] 1. As shown in Figure 3, fix the negative pressure suction chamber 60 on the left side of the monitoring device 10, and connect the suction tube connector 71 to the negative pressure generator interface 20 on the left side of the monitoring device 10.

[0075] 2. The urine collector 80 is vertically suspended on the urine collector fixing device 90 below the monitoring device 10.

[0076] 3. Connect the indwelling urinary catheter interface in the patient's body to the adapter 40.

[0077] 4. Turn on the monitoring device 10, set the drainage interval to 10 minutes, set the drainage negative pressure value to -10 cmH2O, and set the negative pressure holding time to 2 minutes to achieve dynamic monitoring of drainage status and urine output.

[0078] 5. After 10 minutes, the negative pressure generator starts working, and the pressure sensor dynamically monitors the pressure in the negative pressure suction chamber 60 and keeps it stable at -10cmH2O. After the negative pressure drainage time reaches 2 minutes, the negative pressure generator stops working.

[0079] 6. During this period, the urine metering device 30 dynamically measures the amount of urine discharged from the bladder or drainage tube 50, and displays the urine volume and measurement time on the human-machine interface. If abnormal conditions such as oliguria or polyuria occur, a prompt message will be given.

[0080] Example 4: Drainage material integrating negative pressure suction chamber and urine collection device

[0081] 1. Using injection molding, the negative pressure suction cavity 60 is a hollow cylinder with an outer diameter of 30mm and a height of 50mm, and the urine collector 80 is a thin film urine collection bag with a volume of 2000ml.

[0082] 2. The top of the negative pressure suction chamber 60 is provided with two catheter interfaces. One catheter interface is connected to the drainage tube 50, and the other catheter interface is connected to the negative pressure suction tube 70. In order to prevent urine from entering the negative pressure suction tube 70 under negative pressure, the urination port of the catheter interface connected to the drainage tube 50 should be 2cm to 5cm lower than the catheter interface connected to the negative pressure suction tube 70.

[0083] 3. The bottom of the top of the negative pressure suction cavity 60 is provided with a check valve 72, which is a duckbill type device made of silica gel film. When the negative pressure is adsorbed, the silica gel film is tightly attached to prevent the urine in the urine collector 80 from flowing back into the negative pressure suction cavity 60 or the negative pressure suction pipe 70. When the negative pressure suction cavity 60 has urine, the silica gel film naturally opens under the weight of the urine, and the urine flows into the urine collector 80.

[0084] 4. A high-frequency heat sealing device is used to seal and combine the upper end of the urine collector 80 with the lower part of the negative pressure suction cavity 60.

[0085] 5. The fixed connection should have no leakage.

[0086] The above drawings and examples are only used to illustrate the technical solutions of the present application and are not limited. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the present application. All of these should be included in the scope of the claims of the present application, and do not constitute any limitation on the scope of protection of the present application.

Claims

1. A system comprising a monitoring device 10 and a companion drainage material, wherein: The monitoring device 10 comprises a control mainboard, a negative pressure generator, a pressure sensor, a urine metering device 30 and a man-machine interactive interface 11; the matching drainage material comprises a conversion joint 40, a drainage tube 50, a negative pressure suction cavity 60, a negative pressure suction tube 70 and a urine collector 80; characterized in that: the negative pressure generator of the monitoring device 10 is a negative pressure device for providing a vacuum environment inside the matching drainage material, the pressure sensor dynamically matches the pressure value inside the matching drainage material, and the urine metering device 30 dynamically monitors the urine volume discharged by the patient; the matching drainage material is a special-purpose consumable for the monitoring device 10, the negative pressure suction cavity 60 is a hollow cavity provided between the drainage tube 50 and the urine collector 80 and having a pipeline interface; the negative pressure suction cavity 60 is provided with three pipeline interfaces, one of which is in communication with the drainage tube 50 upstream of the urine collector 80, one is in communication with the liquid inlet of the urine collector 80 downstream, and the other is connected with the negative pressure suction tube 70.

2. The system of claim 1, wherein: The urine metering device 30 comprises, but is not limited to, an ultrasonic liquid flowmeter, a light-induced drop speed sensor, a turbine liquid flowmeter, a gravity sensor and a tension sensor.

3. The system of claim 1, wherein: Two combinations of the light-induced drop speed sensor and the gravity sensor are adopted, specifically, a drip cup is provided between the drainage tube 50 and the urine collector 80, and the infrared drop speed sensor is arranged on the outer periphery of the drip cup; at the same time, the gravity sensor is provided, and the urine collector 80 is suspended below the gravity sensor.

4. The system of claim 1, wherein: A check valve is further provided between the negative pressure suction cavity 60 and the urine collector 80.

5. The system of claim 1, wherein: The negative pressure generator is in communication with the control mainboard and controlled thereby, and the working pressure of the negative pressure generator is adjusted in a range not less than -10 cmH20-0.

6. The system of claim 1, wherein: The range of the pressure sensor is not less than -10 cmH20-0, and the measurement accuracy is not less than 1 cmH20.

7. The system of claim 1, wherein: The range of the urine metering device 30 is not less than 0-1000 ml, and the measurement accuracy is not less than 1 ml.

8. A method mainly comprising: (1) according to the drainage interval time and the drainage negative pressure value set by the medical staff on the man-machine interactive interface 11, the system automatically starts the negative pressure generator to perform suction, so that a negative pressure is generated in the negative pressure suction cavity 60; (2) during this period, the pressure sensor dynamically monitors the negative pressure value in the negative pressure suction cavity 60 and feeds back to the core processor, the core processor instructs the negative pressure generator to dynamically correct the working pressure, and the negative pressure value in the negative pressure suction cavity 60 is stably maintained within the set drainage negative pressure value range; (3) under the continuous action of the negative pressure generator, the urine retained in the bladder or the drainage tube 50 is sucked into the negative pressure suction cavity 60, and the urine flows into the urine collector 80 under the action of gravity; (4) during the negative pressure drainage, the urine metering device 30 dynamically senses the urine volume increment, and after the urine volume stops increasing, the negative pressure generator stops working; or the man-machine interactive interface 11 can also be set to a negative pressure retention time, and after the system set negative pressure retention time is reached, the negative pressure generator stops working; (5) the urine metering device 30 dynamically monitors the newly added urine volume in this period, and displays and reads out on the man-machine interactive interface 11, and dynamically prompts when oliguria or polyuria occurs, thus ending a urine negative pressure drainage and metering cycle. (6) The system repeats the above steps (1)-(5) periodically to empty the urine retained in the bladder or drainage tube 50 and calculate the urine volume; (7) The drainage interval time in the system is set between 1 min and 60 min, preferably between 5 min and 15 min; (8) The drainage negative pressure value in the system is set between -40 cmH20 and -1 cmH20, preferably between -20 cmH20 and -5 cmH20; (9) The system can set the negative pressure retention time between 1 min and 5 min, preferably set to 2 min.

9. A method according to claim 8, characterised in that: The working method (1)-(9) of negative pressure control urine drainage is programmed by software and written into the embedded software of the system.

10. The method of claim 8, wherein: The drainage interval time, drainage negative pressure value or negative pressure retention time can be set according to the characteristics of the patient and the clinical needs, the urine retained in the bladder or drainage tube 50 is emptied at regular intervals, and the real urine volume produced by the patient in the period is calculated.

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