Methods of Intermittent Positive Pressure Breathing

Methods of Intermittent Positive Pressure Breathing* Melvin A. Welch, Jr., R.R.T.;o ° Bertrand J. Shapiro, M.D., F.C.C.P.;t Philip Mercurio;* William Wagner;§ and Glenn Hirayama II

Inspiratory capacity (Ie) was evaluated in 60 patients during the following four respiratory maneuvers: (1) coached unassisted inspiration; (2) inspiratory positivepressure breathing (lPPB) at 15 cm H 2 0 with the patient passively inspiring; (3) IPPB at 15 cm H 2 0 with the patient coached to actively inspire; and (4) IPPB at a peak pressure adjusted according to the judgment of the respiratory therapist, with the patient coached to actively inspire. The Ie attained with these maneuvers were, respectively, as follows: (1) 1.29 ± 0.75 L; (2) 1.13 ± 0.52 L; (3) 1.77 ± 0.11 L; and (4) 2.27 ± 0.11 L (mean ± SE). The peak ventilator pressure for maneuver 4 aver·

Sinee Motley et aP introduced the use of inter-

mittent positive-pressure breathing ( IPPB) in pulmonary disease, IPPB has evolved from a panacea to its present uncertain status. Controversy continues over the necessity, efficacy, and cost-effectiveness of this poorly investigated form of respiratory therapy. Most clinical studies, whether they be critical or supportive of IPPB, share common weaknesses. Either the method of delivery is not clearly described, or there is no analysis as to whether the treatment with IPPB was optimally delivered. 2-9 Before the results of studies on IPPB can be critically analyzed, criteria must be developed for what constitutes an effective treatment. The purpose of this study was to establish an effective method of administering IPPB in terms of volume delivery. To do this, we measured the passively exhaled inspiratory capacity (IC) of subjects in response to three different techniques of administering IPPB during a single visit by the respiratory therapist. These volumes were compared to the pa·From the Department of Medicine, School of Medicine UDiversity of California, Los Angeles, and the School ~ Respiratory Therapy, UCLA Hospital-Santa Monica College. o o Instructor, School of Respiratory Therapy. tAdjunct Associate Professor, School of Medicine. tTechnical Supervisor, Respiratory Care Unit, UCLA Hospital and CliniCs. §Assistant Supervisor, Inhalation Therapy Department, UCLA Hospital and Clinics. IIStaff Therapist, Inhalation Department, UCLA Hospital and Clinics. Manuscript received August 6; revision accepted October 17. Reprint requests: Inhalation The,.apy Department;, UCLA Hospital;, Los Angeles 90024

CHEST, 78: 3, SEPTEMBER, 1980

aged 30 ± 7 cm H 2 0 (mean ± SD), and no patient ex:· perienced harmful side eflec. from these peak pressures. These data indicate that the method of freatment with IPPB has profound effects upon the degree of pulmonary expansion. AD research on therapy with IPPB should be carefully cODfroUed for the method of administering IPPB, and the volumes obtained during the treatment should be carefuDy documented before general conclusions are drawn concerning the eflec. of IPPB on mor· bidity. For the present, we suggest that IPPB, when ad· ministered clinically, be given as described in method 4.

tient's own IC. In this way, each subject acted as his or her own control. We made the assumption that volume-oriented therapy is likely to be therapeuticallyeffective. MATERIALS AND METHODS

Sixty hospitalized adult patients (26 men and 34 women) for whom IPPB had already been ordered were studied. There were 26 men and 34 women (mean age, 52 years; range, 20 to 82 years). Diagnoses included the following: asthma, 9; emphysema or bronchitis, 8; thoracic and upper abdominal surgery, 13; lower abdominal surgery, 5; peripheral surgery, 5; primary lung cancer or metastatic neoplasm (not postoperative), 6; congestive heart failure, 4; neuromuscular diseases, 3; and miscellaneous, 7. All subjects were alert and cooperative and took treatments by mouthpiece or tracheostomy tube. Before beginning this study, the patients were positioned for maximum comfort in an upright position, and throughout the study the patients remained in the same position. The treatments were given with physiologic saline solution only. The total amount of time to obtain the data from each patient was approximately ten minutes. The experimental design consisted of the following four maneuvers: Unassisted Inspiratol'fl Capacity

The nares of the patient were occluded with a noseclip, while the patient breathed through a nonrebreathing valve, and a Wright respirometer (British Oxygen Co.) was connected to the inspiratory limb of the nonrebreathing valve for measurement of volume. The patient was observed to breathe normal tidal volumes until he was relaxed. Fonowing relaxation, when the patient had exhaled to normal resting level (functional residual capacity [FRC]), he was encouraged to inspire maximally. Measurement of volume from the resting

METHODS OF INTERMITTENT POSITIVE PRESSURE BREATHING 4&3

2.5

level to full inspiration was recorded as the patient's unassisted inspiratory capacity (IC). Passive-Inspiration IPPB

A pressure-cycled ventilator (Bird Mark 8 or 10) was adjusted to a cycling pressure of 15 em H 2 0. Flow was adjusted to supply a long slow inspiration. The patient was then instructed to cCsip" in from the ventilator to initiate inspiration and then to let the ventilator 6ll his lungs. The patient was then instructed to exhale to a resting position without forcibly blowing out air. Once the patient was following these instructions, measurements of exhaled volume from total lung capacity (TLC) to FRC were made with a Wright respirometer connected to the expiratory limb of the ventilator's manifold. This passively exhaled volume was recorded as the patient's IC.

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As in the passive-inspiration IPPB, the ventilator was adjusted to a pressure of 15 cm H 2 0, flow was adjusted to supply long slow inspiration, and the patient was instructed to passively exhale. As in the unassisted maneuver for IC, the patient was encouraged to inspire maximaJJy. Exhaled volume from TLC to FRC (ie, IC) was measured with the Wright respirometer connected to the ventilator's manifold.

Coached IPPB with Ad;ustments in Ventilator Patients were given IPPB with the same instmctions as in the maneuvers for unassisted IC and coached IPPB. Additionally, peak inspiratory pressure was adjusted periodically as the expired volume was monitored with a Wright respirometer until there was (1) no further increase in IC, or ( 2) the peak pressure approached a limit that the respiratory therapist believed to be unsafe for that particular patient or ( 3) the patient became uncomfortable. The expired volume from TLC to FRC (ie, IC) was measured. The first maneuver was always the unassisted IC. Passiveinspiration IPPB, coached IPPB, and coached IPPB with ventilator adjustments were then carried out in a random order. Throughout all measurements, there was close attention to ensure that the valves and manifolds were free of leaks, that the patients were comfortable, and that there were no untoward side effects of the treatment. The patients were monitored for pulse rate, abdominal distention, and cardiac rhythm in electrocardiographically monitored patients. In patients with an unstable cardiovascular system, blood pressure was also monitored. There were frequent rests and discussions with patients to prevent hyperventilation. Measurements of Ie for all four maneuvers were performed until there was no increase in volume. The three largest measurements were averaged. Student's t-test for matched pairs was used to compare the values or IC obtained during the different maneuvers. REsuLTS AND DISCUSSION

Unassisted Ie was 1.29 -+- 0.75 L (mean -+- SE) (Fig 1). Inspiratory capacity decreased during passive-inspiration IPPB to 1.13 -+- 0.52 L. This decrease in IC with IPPB delivered passively confirms the findings of McConnell et al. 10 H large inspiratory volumes are essential for therapeutic effects,ll it would be expected that in those studies in which

4&4 WELCH ET AL

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IPPB is passively delivered, there would be no beneficial effects. Inspiratory capacity during coached IPPB was 1.77 -+- 0.11 L. This is a significant (P < 0.(01) increase of 0.47 -+- 0.06 L in IC, compared to the unassisted inspiratory maneuver. The increase is probably due to the patient's muscular effort causing a low pleural pressure, as occurs with unassisted maximal inspiration, while positive pressure from the mechanical ventilator simultaneously increases the airway pressure. These added forces increase the transpulmonary pressure gradient further than that which occurs with unassisted inspiratory efforts alone. The result is increased pulmonary inflation. Maximum inspiratory pressures in normal subjects exceed 40 cm IIs012 and are more than adequate to provide maximum pulmonary inHation, since it only requires about 30 em H20 of transpulmonary pressure to reach the inspiratory plateau of the pressurevolume curve. Even in diseases where there are shifts in the pressure-volume curve, the plateau is usually achieved at pressures not much different than 30 cm H20. 1S Therefore, it would be anticipated that an increase of 15 cm H20 in transpulmoCHEST, 78: 3, SEPTEMBER, 1980

nary pressure from positive pressure applied to the airways would not increase transpulmonary pressure significantly enough to enlarge the Ie if the subject were able to inflate his lungs to the plateau of the curve spontaneously; however, the subjects in this study indeed increased IC with coached IPPB. This could be due to the inability of the patients to develop adequate inspiratory muscular pressure and, hence, an inability to reach the plateau of the pressure-volume curve. No measurements of maximum inspiratory pressures were made in the subjects. The eighteen postoperative patients probably had low maximum inspiratory pressures due to pain, guarding, and therapy with analgesics. Inspiratory pressures may have been reduced in patients with obstructive pulmonary disease and increased FRC due to limited muscular force, as predicted by relationships between muscular length and tension. This has previously been discussed by Danon et al,14 who also demonstrated an increased pulmonary volume with IPPB compared to maximum voluntary inspiration in patients with obstruction. Furthermore, it has been our experience that maximum inspiratory pressure in most acutely ill patients with respiratory diseases is low, possibly due to poor effort, fatigue, electrolyte imbalance, or other factors. Thus, in these patients studied, it is highly probable that they did have low maximum inspiratory pressures and that coached IPPB was effective in increasing the transpulmonary pressure at a point on the pressure-volume curve where there would be a significant change in IC. Alternatively, the subjects may have had relatively normal pressures, but the additional airway pressure generated by the machine supplying IPPB may have been necessary to exceed the opening pressures of atelectatic airways. A lower FRC with IPPB than with spontaneous breathing is also a possible cause of increased IC with coached IPPB. This is an unlikely possibility, since IPPB is most likely to increase FRC, as opposed to decreasing it, particularly in the patients with obstruction. The failure to demonstrate an increase in IC with passive-inspiration IPPB supports the argument that IPPB does not decrease the FRC, since if FRC were decreased with IPPB, then IC would have increased with passive-inspiration IPPB. The contrary was found. There does remain the possibility that FRC is not lowered with passiveinspiration IPPB but may be lowered with the combined effects of coaching and IPPB. Inspiratory capacity during coached IPPB with ventilator adjustments was 2.27 + 0.11 L. This was 0.50 + 0.04 L greater than during coached IPPB and 0.97 + 0.06 L greater than during the unassisted maneuver for IC. It, therefore, appears that IC can CHEST, 78: 3, SEPTEMBER, 1980

be increased by approximately 0.5 L over unassisted IC with coached IPPB when the ventilator's peak pressure is set at 15 cm H 20. An additional O.5-L increase in IC can be obtained with appropriate adjustment of the ventilator. The principal adjustment of the ventilator in these studies was peak pressure. Average peak pressure was 30 + 7 em H 20 (mean + SD). The peak pressures ranged from 20 to 50 em H20. Only rarely was the inspiratory flow rate adjusted differently from the flow rate used with passive-inspiration IPPB or uncoached IPPB. None of the patients demonstrated evidence of barotrauma during or for 48 hours after the study. It is clear from this study that coached IPPB with ventilator adjustments can effectively increase IC in acutely ill patients. These data should not be extrapolated to patients with stable chronic pulmonary disease. Furthermore, the effectiveness of inspiratory maneuvers in respiratory care remains controversial. Bartlett et aliI have reviewed the evidence suggesting that large inspired pulmonary volumes have therapeutic effects and have added to the evidence by observing decreased respiratory morbidity in postoperative patients with incentive spirometry.11 In contrast, Iverson et al 16 have found that the use of blow bottles, a maneuver which emphasizes expiration and not inspiration, is more effective than IPPB or incentive spirometry in preventing postoperative respiratory complications. There are several factors which may have prejudiced this study in favor of coached IPPB without or with ventilator adjustment, but we do not think that any of these factors significantly influenced the results. First, the IC was always measured prior to any treatments with IPPB, and the volumetric history of the lung from this maneuver may have influenced the values for IC obtained with subsequent treatments with IPPB;17 'however, this is unlikely since the maneuvers with IPPB were randomized following the unassisted maneuver for IC, and there were consistent decreases in IC with passive IPPB and increases with coached IPPB without and with ventilator adjustment. Secondly, IC may have increased during coached IPPB without or with ventilator adjustments due to more effective coaching of the patients. By experimental design, there was no coaching with passive IPPB, and that is at least in part the explanation for the decreased IC seen with passive IPPB, compared to the other maneuvers. Nevertheless, great care was taken to ensure that coaching was equally applied during unassisted maneuvers for Ie, coached IPPB, and coached IPPB with ventilator adjustment. Thirdly, the therapists' attitude and enthusiasm concerning each of the maneuvers may have influenced results. This is a

METHODS OF INTERMITTENT POSITIVE PRESSURE BREATHING 485

most difficult factor to evaluate, but we do not think the therapists~ enthusiasm biased the results. The therapists agreed to use an equal level of enthusiasm for all maneuvers and repeatedly affirmed that they indeed did use an equal level. Furthermore, the results of the study are quite uniform, and there were not any significant differences in the results obtained by an individual therapist. It is unlikely that all therapists would have had the same attitude and enthusiasm toward all of the maneuvers. Therefore, the uniform results are evidence that enthusiasm and attitude did not bias the results. Based upon this study and the previous recommendations of others,l8-22 we believe that the following guidelines and procedures should be established to promote maximal inspiration during a treatment with IPPB. First, the volume of gas breathed must be monitored. This can be simply done with the use of a Wright respirometer or other device for measuring breath-to-breath volume that is connected to the expiratory port of the mechanical ventilator. The use of a gas volume bag ( such as the Venti-Comp; Hudson Oxygen Therapy Sales Corp.) is acceptable, but this device does not give measurements of breath-to-breath volume, and there are significant inaccuracies in the measurements of volume. These measurements should be an integral part of a feedback loop to the patient, so that the patient is continuously made aware of the measurements. Secondly, the ventilator pressure should be increased and the How rates adjusted until the largest volumes that can be achieved with safety are obtained. Selection of peak pressure on the ventilator should not be guided by an arbitrary limit on pressure. H the Ie with a maneuver for IPPB is less than or equal to the unassisted IC, there is no increased chance of barotrauma to the lung, since the transpulmonary pressure is no greater during the treatment with IPPB than during the spontaneous respiratory maneuver, no matter what the peak pressure of the ventilator is. Thirdly, the patient must be enthusiastically coached to inspire deeply. Methods of coaching should be thorough and should include ( 1) an explanation of the purpose of the treatment, since many patients perform considerably better once there is an explanation of ·the goal of the treatment with IPPB; (2) verbal encouragement, where the therapist coaches the patient continually during the patient's active inspiration; (3) praise for effort, with particular praise for full thoracio expansion; and (4) occasional use of imaginative roaching techniques, such as having the therapist place his hands on the lower lateral part of the chest and asking the patient to push the therapist~s hands outward. 488 WELCH ET AL

Dosage and method of administration, supplemented by background information concerning levels in the blood, half-life, etc, are carefully controlled in experimental studies with drugs. Unfortunately, information equivalent to dosage and method of administration is not available for treabnents with IPPB. All studies on the efficacy of IPPB are vulnerable, since no criteria exist for what is appropriate therapeutic administration, and there is limited background to establish those criteria. This is in part due to a lack of understanding of the physiologic effects sought. In this study, we assume that expansion to a high pulmonary volume is a reasonable goal of IPPB. We have demonstrated that inconsistent data concerning the efficacy of treatments with IPPB could be due to different methods of administration, and we have established some guidelines for administration of IPPB. We urge that all studies on IPPB describe the volumes achieved as part of the results. Those volumes should be comunassisted volumes and to pared to the subjects~ volumes obtained during other alternate therapy being tested, so that conclusions can be appropriately analyzed. Although we have focused on volumes obtained during treatment with IPPB, many other criteria remain to be established. Such elementary factors as the frequency of treatments with IPPB or the length of treatment have not been considered. Until reasonable criteria for treatments with IPPB are established, all future experimental studies of the efficacy of IPPB will remain vulnerable.

1 Motley HL, Lang LP, Gordon B. Use of intermittent positive pressure breathing combined with nebulization in pulmonary disease. Am J Moo 1948; 6:853-6. 2 Sands JH, Cypert C, Armstrong R, et al. A controlled study using routine intermittent positive pressure breathing in the post-surgical patient. Chest 1961; 40: 128-33. 3 Anderson WH, Dossett BE Jr, Hamilton GL.Prevention of postoperative pulmonary complications: use of isoproterenol and intermittent positive pressure breathing on inspiration. JAMA 1963; 186:103-6. 4 Sinha R, Bergofsky EH. Prolonged alteration of lung mechanics in kyphoscoliosis by positive pressure hyperinflation. Am Rev Respir Dis 1972; 106:47-57. 5 Loren M, Chai H, Mildich D, et ale Comparison between simple nebulization and intermittent positive-pressure in asthmatic children with severe bronchospasm. Chest 1977; 72:145-7. 6 Cherniaek RM, Svanhill E. Long-term use of intermittent positive-pressure breathing (IPPB) in chronic obstructive pulmonary disease. Am Rev Respir Dis 1976; 113:721-

8.

7 Cayton RM, Webber B, Paterson IW, et al. A comparison of salbutamol given by pressure-packed aerosol or nebulization via IPPB in acute asthma. Br J Dis Chest 1978; 72:222-4.

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8 Dohi S, Gold MI. Comparison of two methods of postoperative respiratory care. Chest 1978; 73:592-5. 9 Shim C, Bajwa S, Williams HE Jr. The effect of inhalation therapy on ventilatory function and expectoration. Chest 1978; 73:798-801. 10 McConnen DH, Maloney lV, Buckberg GD. Postoperative intermittent positive-pressure breathing treatments. J Thorac Cardiovasc Surg 1974; 68:944-52. 11 Bartlett RH, Gazzaniga AB, Geraghty T. Respiratory maneuvers to prevent postoperative pulmonary complications. JAMA 1973; 224:1017-21. 12 Black LF, Hyatt RE: Maximal respiratory pressures: normal values and relationship to age and sex. Am Rev Respir Dis 1969; 99:696-702. 13 Bates DV, Macklem PT, Christie RV. Respiratory function in disease: an introduction to the integrated study of the lung. 2nd 00. Philadelpha: WB Saunders Co, 1975: 29-30. 14 Danon J, Sharp JT, Dmz WS, et ale Effect of increased functional residual capacity upon inspiratory muscle function. Am Rev Respir Dis 1972; 105:1017. 15 Bartlett RH, Brennan ML, Gazzaniga AB, et al. Studies on the pathogenesis and prevention of postoperative pulmonary complications. Surg Gynecol Obstec 1973; 137: 19. 16 Iverson U, Ecker RR, Fox HE, et al. A comparative study

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of IPPB, the incentive spirometer, and blow bottles: the prevention of atelectasis following cardiac surgery. Ann Thorac Surg 1978; 25:197-200. Radford EP Jr. Static mechanical properties of mammaIian lungs. In: Fenn WO, Hahn H, eds. Handbook of Physiology (sect 3, vol 1). Washington, DC: American Physiological Society, 1964:429-49. Yanda RL. Quality control of inhalation therapy: the results of therapy, with and without control, and methods of developing such control, in a community hospital. Chest 1974; 66:61-6. Cheney FW Jr, Nelson EJ, Horton WG. The function of intermittent positive pressure breathing related to breathing patterns: proceedings of the Conference on the Scientific Basis of Respiratory Therapy. Am Rev Respir Dis 1974; 110(suppl) :183-7. Jones FL Jr. Increasing postoperative ventilation: a comparison of five methods. Anesthesiology 1968; 29:1212-5. Pfenninger J, Roth F. Intermittent positive pressure breathing (IPPB) versus incentive spirometer (IS) therapy in the postoperative period. Intensive Care Med 1977; 3:279-81. Powers WE, Morrison DR. Evaluation of inspired volumes in postoperative patients receiving volume-oriented IPPB. Respir Care 1978; 23:39-41.

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CHEST, 78: 3, SEPTEMBER, 1980

METHODS OF INTERMlnENT POSITIVE PRESSURE BREATHING 487