Oxygen delivery Systems?a comparison of two devices

Forum

5. 6.

7. 8. 9.

medizin 140, Zentraleuropaischer Anaesthesie Kongress, band 2. Berlin: Springer Verlag, 1981: 145-7. GRABOW L, CRIVEANU T. Combined acupuncture-analgesia as a method in general anesthesia. Anaesthesist 1976; 2 5 231-4. KHO HG, MAASP, KERKKAMP H, DRENTM, KIPPERSLUE E, EGMOND VAN J. Haemodynamische Wirkungen der kombinierten Akupunkturanasthesie bei abdomineller urologischer Chirurgie. Deutsche Zeitschrqt fur Akupunktur 1987; 30:60-4. CHRISTENSEN PA, NORENGM, ANDERSEN PE, NIELSENJW. Electroacupuncture and postoperative pain. British Journal of Anaesthesia 1989; 6 2 258-62. CHENGXN. Chinese acupuncture and muxibustion. Beijing: Foreign Languages Press, 1987: 167-70. PRYS-ROBERTS C, FoEx P, BIROGP, ROBERTS JG. Studies of anaesthesia in relation to hypertension V: Adrenergic betareceptor blockade. British Journal of Anaesthesia 1973; 45:

15. 16. 17.

18. 19. 20.

671-80.

10. TOLKSDORF W, SCHAFERE, PFEIFFERJ, MITELSTAEDT VG. Behaviour of adrenaline, noradrenaline, blood pressure and heart rate during intubation, depending on different fentanyl doses. Anasthesie, Intensivtherapie und Notfallmedizin 1987; 2 2 171-6. 11. DOHIS, NISHIKAWA T, UJIKEY, MAYUMIT. Circulatory responses to airway stimulation and cervical epidural blockade. Anesthesiology 1982; 51: 359-63. 12. STOELTING RK. Circulatory changes during direct larynoscopy and tracheal intubation. Influence of duration of laryngoscopy with and without prior lidocaine. Anesthesiology 1977; 47: 381-4. 13. FLACKE JW, BLOORBC, KRIPKEBJ, FLACKE WE, WARNECK CM, VAN ETTENAP, WONGDH, KATZRL. Comparison of morphine, meperidine, fentanyl, and sufentanil in balanced anesthesia: a double-blind study. Anesthesia and Analgesia 1985; 64: 897-910. 14. FISCHERMV, RAAB P, v REUMONT J. Consumption of muscle

21.

135

relaxants in electrostimulation anaesthesia. Anaesthesist 1983; 3 2 597-600. CRAIGDB. Postoperative recovery of pulmonary function. Anesthesia and Analgesia 1981; 60:46-52. CAMPBELL IT, WILLATTDJ, CHILDSD, STELLPM. Arterial oxygenation after major head and neck surgery involving tracheotomy. British Journal of Anaesthesia 1987; 5 9 1121-6. S~MONNEAU G, VIVIENA, SARTENE R, KUNSTLINGER F, SAMII K, NOVIANT Y,DUROUXP. Diaphragm dysfunction induced by upper abdominal surgery. Role of postoperative pain. American Review of Respiratory Disease 1985; 128: 899-903. DUNDEE JW, CHE~TNUTT WN, GHALYRG, LYNASAGA. Traditional Chinese acupuncture: a potentially useful antiemetic? British Medical Journal 1986; 293: 583-4. JONESJG. Awareness under anaesthesia. ICI Pharmaceuticals, Anaesthesia Round 1988; 21: 1-28. BARAKA A, LOUISF, NOUEIHID R, DIABM, DABBOUS A, SIBAI A. Awareness following different techniques of general anaesthesia for Caesarean section. British Journal of Anaesthesia 1989; 6 2 645-8. TWEEDLE D, NIGHTINGALEP. Anesthesia and gastrointestinal surgery. Acta Chirurgica Scandinavica 1989; 550 (Suppl.):

131-9. 22. CHRISTENSEN T, BENDIXT, KEHLETH. Fatigue and cardio-

respiratory function following abdominal surgery. British Journal of Surgery 1982; 6 9 417-9. 23. JAKOBSSON J, REHNQVIST N, DAVIDSONS. Computerised evaluation of the electrocardiogram during and for a short period after gall bladder surgery. Acta Anaesthesiologica Scandinavica 1989; 33: 474-7. 24. ZHYBJ, BI LG, LIANGSY, PANGL, WANGSL, LIUJF, JIANG AP, LI CJ, YE ZJ, YANGH, CHEN ZY, WANGKT, BIANSH, Go XH, HONGHX. Effect of acupuncture on left ventricular function, microcirculation, blood rheology and cyclicnucleotides in patients with acute myocardial infarction. Journal of Traditional Chinese Medicine 1989; 9 63-8.

Anaesthesia, 1991, Volume 46, pages 135-138

Oxygen delivery systems-a

comparison of two devices

J.E. Fairfield, FFARCS, Lecturer, T. Goroszeniuk, FFARCSI, Consultant, A.M. Tully, FFARCS, Senior Registrar, A.P. Adams, PhD, FFARCS, FFARACS, Professor of Anaesthetics, Department of Anaesthetics, United Medical and Dental Schools, Guy's Hospital, London SE1 9RT.

Summary T w o low-volume, variable performance oxygen delivery systems were compared in conscious spontaneously breathing volunteers. Oropharyngeal oxygen concentrations were measured during periods of nose and mouth breathing. The systems were studied a t oxygen flow rates of 2 o r 4 litreslminute. The performance of both systems was similar under the test conditions but the nasal catheter is preferable in terms of cost.

Key words Oxygen; delivery system.

Hypoxaemia is a frequent occurrence in the immediate postoperative period. It may be subdivided into early hypoxaemia lasting up to 2 hours and late hypoxaemia which may last for several days after surgery. The relationship between hypoxaemia during and after anaesthesia and Accepted 23 July 1990.

postoperative pulmonary function has been discussed at length.',* It is common practice to try to prevent hypoxaemia by increasing the concentration of inspired oxygen. Many methods are available and the subject has been reviewed

136

Forum Table 1. Oropharyngeal oxygen concentrations for each subject.

Mouth breathing

Nose breathing 2 litres/minute

4 litres/minute

2 litres/minute

4 litres/minute

Subject number 1 2 3 4 5 6 7 8 9 10

Mask 28 26 29 31 31 29 27 28 26 30

Catheter Mask Catheter Mask Catheter Mask Catheter 28 26 34 27 33 29 29 30 29 30

37 38 39 40 41 43 37 39 35 39

e ~ t e n s i v e l y .Oxygen ~ ~ ~ can be delivered to patients by a variety of devices in the recovery area. These can be considered as being fixed or variable performance systems. Several so-called fixed performance devices have been shown not to deliver fixed concentrations of oxygen under all circumstance^.^ Many anaesthetists administer oxygen postoperatively through variable performance devices allowing for the recognised effect of the breathing pattern on the inspired oxygen concentration.6 Facemasks and nasal catheters are examples of variable performance delivery systems. Facemasks seem to be more popular in the UK because it is believed that they are more efficient and more comfortable for the patient; the latter belief possibly may be associated with the results of several studies involving the placement of the nasal catheter in the nasoor oropharynx.’ Both facemasks and nasal catheters have been used to prevent early postoperative hypoxaemia with equal success.’ The use of nasal catheters with a foam collar at the distal end allows the catheter to be located comfortably in the anterior nares and makes the system more acceptable to the patient. The recovery room in most hospitals deals with large numbers of patients each year and oxygen delivery systems must be not only effective but also inexpensive. The present study was implemented to compare the oxygen concentration in the oropharynx during breathing of low-flow oxygen via a nasal catheter or a low-volume facemask. Methods Ten conscious volunteers were studied. All were graded as ASA 1 or 2 and none had an upper respiratory tract infection or nasal airway obstruction. The concentration of inspired oxygen in each subject was measured in the oropharynx during oxygen administration via a low-flow variable performance facemask (Intersurgical*) followed by oxygen administration via a nasal catheter situated in the anterior nares and held in place by a foam collar (Unoplast oxygen catheter with compresst). A 10-gauge cannula was inserted through the nose after administration of topical anaesthesia, until the tip was situated approximately 10 mm below the uvula when viewed through the mouth. The nasal oxygen catheter was located in the opposite nostril when in use. A fine catheter was positioned 5 mm inside the nostril on the same side as the sampling catheter for the purpose of monitoring the *Crane House, Gould Road, Twickenham, Middlesex. tWykeham industrial estate, Moorside road, Winchester,

Hampshire.

36 31 35

41 38 45 38 36 38 36

30 26 28 29 32 30 31 31 27 29

29 29 25 35 30 42 32 32 38 30

36 40 39 42 40 45 41 42 33 33

37 44 31 43 51 51 41 43 53 41

end-tidal CO, concentration. This catheter was located just inside the mouth during mouth breathing. The sampling catheter was connected to a Servomex oxygen analyser (model 570A). Calibration was performed before use using oxygen-free (‘White spot’) nitrogen and air. The end-tidal CO, was recorded using a Gould capnograph mark 3, calibrated with air and certified 5% CO, in air, and the output printed on a Hewlett Packard pen recorder (model 7402A). Oxygen from a calibrated flowmeter was delivered to each subject at 2 or 4 litres/minutc through either the facemask or nasal catheter. Recordings were made during nose breathing and mouth breathing. Four readings were taken at one-minute intervals 3 minutes after a steady inspired oxygen concentration and end-tidal carbon dioxide concentration had been achieved and the mean was taken as the inspired oxygen Concentration. Results were compared for the two delivery systems using paired t-tests with no allowance made for multiple comparisons. The subjects were asked at the end of the experiment if they found one system more comfortable than the other. Results

The measured oropharyngeal oxygen concentrations for the 10 volunteers are shown in Table 1. The mask and nasal catheter produced a mean oropharyngeal oxygen concentration of 28.5% and 29.3% respectively during nose breathing at an oxygen flow of 2 litres/minute; at 4 litres/minute the corresponding mean oropharyngeal oxygen concentrations were 38.8% and 38.0%. There were no significant differences between the mask and catheter at either flow of oxygen, although both systems produced significantly higher oropharyngeal oxygen concentrations at 4 litres/minute than at 2 litres/ minute (p < 0.001). The mask produced a mean oropharyngeal oxygen concentration of 29.3% and the nasal catheter 32.2% during mouth breathing at an oxygen flow of 2 litres/minute. The mean concentration achieved by the catheter was higher, but there was a wide range of results and the difference was neither statistically nor clinically significant. The mask produced a mean oropharyngeal oxygen concentration of 39.1% and the nasal catheter 44.1% during mouth breathing at an oxygen flow of 4 litres/minute. Again the mean concentration achieved by the catheter was higher, and the range wider; there was a statistical difference (p < 0.65) which probably has no clinical significance. Both systems produced significantly higher oropharyngeal oxygen concentrations at the higher oxygen flows (p < 0.001). The mean, range and 95% confidence intervals of the

Forum

137

-3

I

f a 2o

Mask Catheter Mask Catheter Mask Catheter Mask Catheter 2 litres/minute 4 litres/minute 2 litreslminute 4 litreslminute Nose breathing Mouth breathing

Fig. 1. The range of pharyngeal oxygen concentrations measured in each group, together with the means (o), 95% confidence intervals ( = ) and range (I).

pharyngeal oxygen concentrations are shown in Figure I and the results of the paired t-tests in Figure 2. Both systems reliably delivered acceptable oxygen concentrations which are suitable for clinical administration and which are close to the delivered concentrations detailed by the manufacturers. Eight of the subjects found the nasal catheter more comfortable when asked directly, while the other two subjects found both systems equally comfortable. Discussion The aim of postoperative oxygen therapy is to minimise hypoxaemia. The use of a variable performance device is satisfactory in the majority of patients provided that an acceptable minimum oxygen concentration is delivered. However, in some patients the delivery of a precise concentration is desirable and the use of a fixed performance device is indicated. The oxygen delivery system may be assessed on the grounds of efficiency, patient acceptability, simplicity and cost effectiveness. The range of results for each variable tested in our study was wide and was more marked with the nasal catheter than with the facemask. This large interpatient difference has been reported bef01-e.~It may be accounted for by differences in the breathing pattern (although this was minimised by maintaining the end-tidal CO, within the normal range), and by minor anatomical differences resulting in turbulent flow or channelling of oxygen. A minimum oropharyngeal oxygen concentration of 33% was obtained using the mask and 35% with the nasal

catheter when an oxygen flow of 4 litres/minute was used. The minimum concentration was 26% with the mask and 25% with the catheter at a flow of 2 litres/minute. These small differences between the devices are not of any clinical significance. However, the delivered concentration does depend upon the inspiratory flow rate,5,6,'0although reduction in the inspired concentration of oxygen due to increased inspiratory airflow may be compensated by increasing the flow of oxygen to the delivery system. The choice of system is important. A nasal catheter is not suitable in patients with nasal obstruction or in those who have undergone nasal surgery. In this study, 80% of the subjects found the nasal catheter was more comfortable than the facemask, and the fixation of the catheter by means of the foam collar is easier than the elastic head band of the mask. Flexion of the head and neck is not required to fix the device and observation of the patient's colour is easier. Nasal delivery systems may become uncomfortable at oxygen flows greater than 4 litreslminute. The relative cost of two equally efficient systems is significant when the purchase of large numbers is considered. Nasal catheters are the least expensive method of oxygen administration,' and it is interesting to speculate why their use is not more widespread. This may be because in some studies the catheter was threaded beyond the nose and into the nasopharynx, an uncomfortable and potentially traumatic procedure. At the time of writing (January 1990) the cost of the Unoplast 10-gauge nasal oxygen catheter with compress is 26 pence; the cost of the Intersurgical facemask is 44 pence. The use of facemasks in

Mouth breothing

Nose breathing

2 Iitres/minute Mask

Cath

L-A

4 litres/rninute Mask

Cath

a

2 litreslminute Mask

~0.001

co.001

I

Mask

NS