WEBVTT 1 00:00:07.780 --> 00:00:12.240 Research film project 241, the Ventimeter. 2 00:00:17.120 --> 00:00:23.960 Fifty years ago, Dr. Francis Benedict introduced the recording spirometer, which made respiratory 3 00:00:23.960 --> 00:00:26.800 measurements practical for clinical use. 4 00:00:27.800 --> 00:00:35.160 During the early 20s, Dr. Brian Sword introduced the circle absorption system for use in anesthesia. 5 00:00:36.240 --> 00:00:42.100 These two breathing systems, the spirometer and the anesthesia circle, are similar. 6 00:00:43.020 --> 00:00:47.140 Both have separate tubes for inspiration and expiration. 7 00:00:48.420 --> 00:00:50.680 Both have unidirectional valves. 8 00:00:51.880 --> 00:00:57.120 A soda-lime canister and a reservoir to contain the respired deaths. 9 00:00:58.000 --> 00:01:05.500 In fact, the only difference between the spirometer and the circle system is in the specific reservoirs used. 10 00:01:06.620 --> 00:01:08.900 Each serves a special purpose. 11 00:01:09.980 --> 00:01:14.640 The bag does not provide a suitable means for measurement of respiration. 12 00:01:15.640 --> 00:01:21.960 The inverted bell of the spirometer does not provide a satisfactory means to breathe for the patient. 13 00:01:23.020 --> 00:01:28.920 Why not combine the advantage of these two systems and have a simple continuous measurement 14 00:01:28.920 --> 00:01:31.240 of tidal volume during anesthesia? 15 00:01:32.660 --> 00:01:40.820 We record pulse and blood pressure regularly, but respiratory rate is the only routine respiratory 16 00:01:40.820 --> 00:01:43.120 observation during anesthesia. 17 00:01:44.120 --> 00:01:50.980 To follow the patient's ventilation requires that we know tidal volume by some convenient means. 18 00:01:52.460 --> 00:01:59.440 This is a tidal volume indicator developed at Roswell Park Memorial Institute for the 19 00:01:59.440 --> 00:02:06.020 purpose of continuous measurement of the anesthetized patient's respiration. 20 00:02:06.900 --> 00:02:13.220 Whether the patient breathes spontaneously as he is now or whether we assist ventilation, 21 00:02:15.280 --> 00:02:19.680 we have continuous information as to tidal volume. 22 00:02:21.460 --> 00:02:26.680 You'll note that we have it mounted on a two chamber absorber, which incidentally we have 23 00:02:26.680 --> 00:02:31.840 found to be more efficient than our original Roswell Park absorber. 24 00:02:31.840 --> 00:02:37.960 In this circuit, the indicator has replaced the conventional pop-off valve. 25 00:02:40.400 --> 00:02:48.480 This pop-off valve supplied by the manufacturer was removed and a simple P-tube used for mounting 26 00:02:48.480 --> 00:02:49.500 the indicator. 27 00:02:50.940 --> 00:02:54.160 I'll show you the overflow valve. 28 00:02:54.160 --> 00:03:00.200 It consists of a ball and chain linked to the dome of the bellows. 29 00:03:00.200 --> 00:03:05.280 Here you can see an aluminum ball and a tapered seat. 30 00:03:07.380 --> 00:03:15.600 As the bellows is extended, the ball is lifted off its seat and allows gas to overflow to 31 00:03:15.600 --> 00:03:16.320 the outside. 32 00:03:18.320 --> 00:03:25.980 Now when we trigger the oxygen flush, note that the pressure in the circuit is not excessive. 33 00:03:27.980 --> 00:03:33.340 It seldom exceeds three or four centimeters of water. 34 00:03:35.300 --> 00:03:40.000 This then is a volume controlled pop-off valve. 35 00:03:41.140 --> 00:03:45.700 It is phased to the end expiratory period. 36 00:03:47.540 --> 00:03:52.920 The result is that with inspiration, this linkage slackens, allows the ball to fall 37 00:03:52.920 --> 00:03:55.380 into its seat and the valve becomes confident. 38 00:03:56.040 --> 00:04:02.120 So whether the patient breathes spontaneously or whether we assist inspiration, gas does 39 00:04:02.120 --> 00:04:05.080 not leave the breathing circuit during inspiration. 40 00:04:05.940 --> 00:04:10.460 Here in animation is a view to show how the ventilator works. 41 00:04:11.160 --> 00:04:17.600 As the patient breathes gas from the bellows, a corresponding volume of gas in the bag enters 42 00:04:17.600 --> 00:04:20.340 the chamber which surrounds the bellows. 43 00:04:27.000 --> 00:04:35.160 Each time the bellows moves down, this overflow valve is closed as the chain linkage slackens. 44 00:04:37.860 --> 00:04:44.180 As ventilation is assisted or controlled, pressure applied to the bag is transferred 45 00:04:44.180 --> 00:04:48.040 inside the chamber to compress the bellows. 46 00:04:48.040 --> 00:04:54.100 In other words, squeezing the bag indirectly squeezes the bellows by a volume which may 47 00:04:54.100 --> 00:04:55.680 be directly absorbed. 48 00:04:58.080 --> 00:05:04.240 Excess gas cannot be introduced into the breathing circuit because of the action of the overflow 49 00:05:04.240 --> 00:05:04.800 valve. 50 00:05:07.760 --> 00:05:15.040 For example, if the patient coughs or if the oxygen bypass is used, the overflow valve 51 00:05:15.040 --> 00:05:18.860 is lifted as soon as the bellows is fully extended. 52 00:05:21.900 --> 00:05:27.840 This action is produced by the chain linkage and occurs normally with semi-closed system 53 00:05:27.840 --> 00:05:30.400 at the end of each expiration. 54 00:05:33.300 --> 00:05:39.040 During inspiration, the breathing circuit remains closed whether a closed system or 55 00:05:39.280 --> 00:05:41.320 a high flow technique is used. 56 00:05:46.780 --> 00:05:56.620 We can use the initial inspiratory excursion as a visual guide for assisting each breath. 57 00:05:59.360 --> 00:06:08.400 For those who prefer to control the ventilation, the tidal volume indicator serves as a continuous 58 00:06:08.400 --> 00:06:13.380 monitor of the respiration by this technique. 59 00:06:15.200 --> 00:06:22.780 Now we'd like to demonstrate another advantage of the indicator, namely the basis for judging 60 00:06:22.780 --> 00:06:29.880 the adjustment of gas flow from the gas machine and the discovery of leak from the circuit, 61 00:06:30.200 --> 00:06:33.460 a very common problem in breathing equipment. 62 00:06:36.380 --> 00:06:41.160 Look at the end expiratory position of the bellows. 63 00:06:41.300 --> 00:06:46.140 See that it tends to return each time to the same position of rest. 64 00:06:47.560 --> 00:06:54.520 This indicates that we have exactly matched gas flow from the anesthesia machine with 65 00:06:54.520 --> 00:06:56.220 the patient's requirements. 66 00:06:58.340 --> 00:07:06.860 Were this flow excessive, the end position would rise to the point of overflow. 67 00:07:08.300 --> 00:07:11.420 We would increase gas flow into the circuit. 68 00:07:14.460 --> 00:07:19.460 Now we are unable to see the full tidal volume. 69 00:07:20.680 --> 00:07:29.820 Returning to a closed system with a matched flow will demonstrate the effect of leak 70 00:07:29.820 --> 00:07:34.500 by producing a leakage at the tracheal cuff. 71 00:07:37.040 --> 00:07:45.580 Although one is still able to read the patient-inspired volume, the fall of the bellows leads to 72 00:07:45.580 --> 00:07:49.440 the quick discovery that a leak has occurred. 73 00:07:54.520 --> 00:08:00.720 And as soon as it's corrected, we have that evidence as the return of the resting position 74 00:08:00.720 --> 00:08:01.460 of the bellows. 75 00:08:01.460 --> 00:08:09.300 We have found at time the indicator quite helpful in discovering the kinking of a tracheal 76 00:08:09.300 --> 00:08:09.680 tube. 77 00:08:09.980 --> 00:08:15.960 With kinkage, one will see that the volume delivered is immediately decreased. 78 00:08:18.060 --> 00:08:26.700 And with correction of the kinking, again the patient's tidal volume returns to the 79 00:08:26.700 --> 00:08:27.520 previous level. 80 00:08:29.820 --> 00:08:38.480 When we are using a closed system and with spontaneous breathing, no corrections are 81 00:08:38.480 --> 00:08:42.660 required for direct reading of the indicator scale. 82 00:08:46.720 --> 00:08:55.380 We can take the figure of 500 cc here, represented by bellows travel, as this patient's tidal 83 00:08:55.380 --> 00:08:55.660 volume. 84 00:08:56.800 --> 00:09:05.280 If we convert our circuit to our semi-closed system with a 5 liter flow rate, you will 85 00:09:05.280 --> 00:09:07.820 note that the excursions now are less. 86 00:09:08.460 --> 00:09:12.240 The bellows travel reads about 400 cc. 87 00:09:13.220 --> 00:09:18.400 Now let's discuss the correction required for the higher flow rate. 88 00:09:19.240 --> 00:09:24.100 A correction for gas entering the circuit during inspiration. 89 00:09:24.100 --> 00:09:29.480 This does not appear as a part of the travel of the bellows. 90 00:09:29.680 --> 00:09:34.340 This correction amounts to 20 cc per liter of gas flow. 91 00:09:34.820 --> 00:09:42.100 So that with a 5 liter flow, we may add 100 cc to the observed travel of the bellows. 92 00:09:47.960 --> 00:09:52.980 This would then give us a tidal volume of slightly over 500 cc. 93 00:09:52.980 --> 00:09:56.000 Now another correction is necessary. 94 00:09:56.720 --> 00:10:03.800 That due to compression of gas in the breathing circuit and the stretch of the expansible 95 00:10:03.800 --> 00:10:06.560 component, especially the breathing tubes. 96 00:10:07.740 --> 00:10:15.040 This correction amounts to about 10 cc of tidal volume per centimeter of water pressure. 97 00:10:17.240 --> 00:10:27.240 So that with a peak inspiratory pressure of 10 centimeters of water, subtract 100 cc from 98 00:10:27.240 --> 00:10:30.040 the observed travel of the bellows. 99 00:10:34.820 --> 00:10:43.200 The corrections due to gas flow from the anesthesia machine and the corrections necessary for 100 00:10:43.200 --> 00:10:48.560 pressure during controlled respiration are in the opposite direction. 101 00:10:48.620 --> 00:10:50.840 In other words, they tend to cancel each other. 102 00:10:51.300 --> 00:10:58.580 So that with a semi-closed technique and with the usual pressures required to inflate the 103 00:10:58.580 --> 00:11:05.520 anesthetized patient's lungs, we come out with a very close approximation of tidal volume 104 00:11:05.520 --> 00:11:07.040 without any correction. 105 00:11:08.040 --> 00:11:15.760 To convert from a closed system to a non-rebreathing system. 106 00:11:20.700 --> 00:11:27.500 To do this, we will occlude the inspiratory limb of the absorber, 107 00:11:32.280 --> 00:11:35.080 remove the valve Y piece, 108 00:11:41.900 --> 00:11:48.880 and we will install the double acting non-rebreathing Rubin valve. 109 00:11:51.920 --> 00:11:59.320 Now the gas flow must exactly equal the patient's minute volume for a precise adjustment. 110 00:12:01.560 --> 00:12:08.440 We can exceed this requirement of course, and again overflow will occur from the indicator. 111 00:12:12.960 --> 00:12:20.200 Now we have approximately matched the requirements with the gas flow from the machine. 112 00:12:20.200 --> 00:12:30.040 Again, we must subtract a volume due to the pressure built up in the system. 113 00:12:32.380 --> 00:12:37.140 The corrected tidal volume here would be about 650 cc. 114 00:12:38.400 --> 00:12:44.960 This device is not intended as a research instrument, but rather for clinical observation of the patient. 115 00:12:44.960 --> 00:12:52.500 The ventilometer is actually a dry spirometer mounted in the breathing circuit so as not to rob the 116 00:12:52.500 --> 00:12:58.240 anesthetist of his favorite means of breathing for the patient, namely the familiar bag. 117 00:13:02.460 --> 00:13:10.440 It incorporates an overflow valve system which replaces the conventional spring-loaded or weight-loaded pop-off. 118 00:13:11.280 --> 00:13:21.140 This design improves the accuracy of estimating the patient's tidal volume and ensures safety when a mechanical ventilator is used. 119 00:13:22.420 --> 00:13:31.920 With inspiratory pressures, gas is delivered to the patient and not through a spring-loaded or weight-loaded pop-off valve to the outside. 120 00:13:33.220 --> 00:13:39.440 All flow to the outside occurs at one time in the cycle, namely immediately after expiration. 121 00:13:40.440 --> 00:13:48.180 The ventilometer provides an objective figure of the patient's ventilation just as we record pulse and blood pressure.