Aspectos fisiológicos y clínicos de la KTR

British Journal of Anaesthesia 1990; 64: 621-631

SOME PHYSIOLOGICAL AND CLINICAL ASPECTS OFCHEST PHYSIOTHERAPY

D. SELSBY AND J. G. JONES

The ciliated epithelium which lines the airwaysis responsible for continuous flow of mucus overthe airway surface to the upper respiratory tract.This mechanism becomes ineffective in broncho-pulmonary disease which is characterizedby excessive production of mucus, impairedmucociliary clearance and, eventually, pulmonaryfailure. This may be a chronic disorder, as inbronchitis and cystic fibrosis, or an acute problemoccurring in patients following anaesthesia,mechanical ventilation and intensive therapy.This review examines some of the physiologicalmechanisms involved in clearance of excessivebronchial mucus in these circumstances and therole of various physical therapies designed toaccelerate this process. Chest physiotherapy, inthe form of postural drainage, percussion andvibration (PDPV), "coughing exercises", and the"Forced Expiratory Technique" (FET) are dis-cussed. The problems of physiotherapy-inducedbronchospasm and hypoxaemia are also noted.

PHYSIOLOGY OF FLOW IN LIQUID LINED AIRWAYS

Two-Phase FlowFlow of air through the tracheobronchial tree andits interaction with the mucus lining is complexbecause of branching geometry of the airways,collapsible airway walls, constantly changingvelocity of air flow and varying viscoelasticproperties of mucus (fig. 1). Simple models offlow in the airways often assume laminar condi-tions. This may be true in small airways and itimplies that the velocity of flow at the airway wallis virtually zero and that there is no interactionbetween air and liquid lining the wall. A morerealistic model, particularly for the large airways,

KEY WORDS

Lung: physiotherapy

~ Laminar

-PaV/j7*

Turbulent

Two-phase

Vtortex

Convective

Starling

FIG. 1. Different types of flow in the airways. P = pressuredecrease in the airway; V = flow; r = airway radius; ft, p =gas viscosity and density, respectively. Flow through junc-tions induces vortices, the intensity of which depends uponthe angle of branching as well as the velocity of flow. Airwaycollapse, as in the Starling resistor, induces strong interaction

between gas flow and liquid lining the wall.

is turbulent flow where the velocity of gas is highat the wall, with strong interaction between airflow and the mucus lining the wall. This type ofgas-liquid interaction is termed two-phase flow,studied originally in models of the trachea andbronchi by Clarke, Jones and Oliver [11] and,more recently, by Sackner and Kim [51]. It is ofcrucial importance in removal of excessive mucusin endobronchial disease.

The normal human bronchial tree is lined by athin (5 urn) layer of mucus which is moved overthe airway surface by the mucociliary escalator.However, in endobronchial disease this mayexceed 5 mm in thickness and ciliary clearancebecomes ineffective. Two-phase flow now be-comes an important mechanism of clearance, andat a particular combination of air flow, mucus

D. SELSBY, F.C.ANAES. ; J. G. JONES, M.D., F.R.C.P., F.C.ANAES. ;University Department of Anaesthesia, 24 Hyde Terrace,Leeds LS2 9LN.

622 BRITISH JOURNAL OF ANAESTHESIA

oCM

X

1.5

1.0

Q.

0.5

Dry tubes

0.5 1.0 1.5 2.0 2.5

Flow rate (litre s"1)

1.5

OM

I1.0

as

7.5

Liquid • lined tubes

EPP

8.0

0.5 1.0 1.5 2.0 2.5

Flow rate (litre s"1)

FIG. 2. Effect of a liquid layer on the pressure-flow relation-ships in a tube similar to the trachea. The predicted increasein pressure change by narrowing the tube radius (r) by 0.5, 1and 2 mm is shown in the upper panel. The actual pressuredecrease in the same tube narrowed the same amount by aliquid layer is shown in the lower panel (Redrawn, with per-

mission, from reference [11].)

viscosity and thickness there is a very stronggas-liquid interaction which first exacerbates thepressure decrease then detaches liquid from theairway wall.

Narrowing the lumen of a tube with a layer offluid causes a much greater resistance than that ofa dry walled tube of the same internal diameter(fig. 2). For example at a flow rate of 1.5 litre s ',above the transition to turbulent flow, the press-ure decrease in a trachea lined by a 2-mm thicklayer of fluid was more than 10 times greater thanexpected. Thus two-phase flow may cause con-siderable increase in airway resistance just beforedetachment of mucus from the wall. However, ifthe critical flow rate for mucus detachment cannotbe achieved (e.g. if mucus viscosity is too great)then respiratory muscle fatigue may ensue. There-fore, two-phase flow occurs after the transitionfrom laminar to turbulent flow, and Reynold'snumber (Re) may be used to describe the flow

Mist flow

FIG. 3. A: Large airways lined with a thick layer of mucus. B:During forced expiration, different types of gas—liquid flowmay be seen in different parts of the airway. In the narroweddownstream segment there is high gas velocity, strong gas-liquid interaction and mist flow. Upstream there is less stronggas-liquid interaction and annular flow, with slug flow insmaller airways further upstream. EPP = equal pressurepoint which, during forced expiration, moves upstream ahead

of the narrowed downstream segment.

rates needed for gas-liquid interaction. Re is afunction of velocity of flow (v) and tube diameter.An Re of 2000 is considered usually to be thecritical value for transition from laminar toturbulent flow in a tube (although it may varywidely) and this value is achieved readily by tidalbreathing in the human trachea. We found thatgas-liquid interaction would occur with an Re of3000 with a 1-mm thick layer of mucus in a tube8 mm in diameter, but at a much lower Re inbranched tubes [11]. Higher Re values are neededfor thinner layers of mucus, but quite low Revalues may be sufficient to detach mucus insmaller airways.

There are three basic patterns of gas-liquidflow which are relevant to mucus clearance fromthe lung: slug flow, annular flow and mist flow(fig. 3). Slug flow occurs when large bubbles of airpass at a velocity [v) of 60-1000 cm s 1 throughairways filled partially with mucus. Annular flow

CHEST PHYSIOTHERAPY: PHYSIOLOGICAL AND CLINICAL ASPECTS 623

B DFIG. 4. Frames from a cine tracheobronchogram to show dynamic compression of the trachea extendingupstream beyond the carina. A = Just after the start of a cough manoeuvre and before peak flow isachieved. The arrow indicates the upstream end of the compressed segment moving upstream during the

cough as lung volume reduces from C to G (residual volume).

takes place when air flows at 2000-2500 cm s"1

through tubes lined with a continuous layer ofmucus. Mist flow occurs at higher flow rates,> 2500 cm s'1, which detach mucus from thewall. The fact that the airways are collapsibleobviously creates ideal conditions for this reactionand enhances the efficiency of the clearancemechanism.

The layer of mucus may vary in viscosity from10 to more than 1000 mPa • s and this is determinedlargely by the water content, the viscosity of waterbeing 1 mPa-s. However, mucus may also showmarked thixotropy, so that its viscosity maydecrease 100-fold at high sheer rates. Thus thecombination of cough and airway narrowing leadsto high Re values and sheer rates which reducemucus viscosity and aid clearing of the airways byannular and mist flow.

Dynamic Compression of Airways and MucusClearance

During a cough, the upper end of the tracheasuddenly narrows and, with diminishing lungvolume, this narrowed segment moves rapidlyupstream past the carina into the small bronchi.This moving segment, or throat, is the site ofmaximum gas velocity with high Re and maximumgas-liquid interaction which clears mucus fromthe airway wall (fig. 4). Jones, Fraser and Nadel[28] were the first to show that the maximum

expiratory flow could be calculated from thecompliance of the compressed segment and elucid-ated the mechanism whereby this segment main-tains a constant flow independent of drivingpressure (see Appendix).

Measuring the pressures across the airway wallsshows where the pressures inside and outside thetracheobronchial tree are equal—the Equal Press-ure Points (EPP) [28]. During a cough, the EPPmoves rapidly ahead of the compressed segmentalong the airway from the trachea into pro-gressively smaller airways. This is importantbecause, upstream of the EPP, the pressure insidethe lumen is greater than outside; thus the airwaysbetween the alveoli and the EPP are fully patent.This results in relatively low sheer rates betweengas and mucus, with poor clearance. Downstreamof the EPP, the airway is compressed and has avery high gas velocity, giving mist flow and rapidclearance of airway mucus (fig. 3). This is thenormal mechanism whereby cough clears mucusfrom the walls of the central airways, but it maynot be effective if mucus viscosity is very high,> 10000 mPa-s, when the mucus may behavemore like a solid than a liquid.

High Frequency Chest Wall Oscillation(HFCWO)

More recently, the principle of two-phase flow hasbeen re-examined to see if a high frequency


oscillation applied to either the airway or the chestwall may achieve a greater degree of mucusclearance than is achieved by cough. Cough islikely to exert a greater effect in the larger centralairways than in the smaller peripheral airways,and high frequency chest wall oscillation(HFCWO) was proposed as a mechanism forenhancing peripheral airway clearance via a two-phase flow effect [10, 30]. HFCWO is achievedby means of a modified double arterial pressurecuff wrapped around the thorax and oscillated at3-17 Hz with peak pressures up to 100 cm H2O.This achieves tracheal airflow of 1-3 litre s"1 andit has been shown in animal experiments that30 min of HFCWO significantly enhanced mucusclearance from the trachea and from more per-ipheral zones.

In contrast to these findings, the application ofHigh Frequency Oscillation (HFO) to the airwayopening reduced the rate of mucus clearance fromperipheral airways [34]. These interesting resultslend some support to the practice by physio-therapists of external chest vibration as a methodof clearing peripheral airways. However, theyhave yet to be shown to be of any proven value inclearing peripheral airways in man.

Meanwhile, the most plausible mechanism ofclearing airways in man is by inducing gas-liquidinteraction during a simulated cough manoeuvre.There are sound physiological reasons why thismethod should be utilized in the physiotherapy ofpatients with chest disease, but more attentionshould be given to the viscoelastic and thixotropicproperties of mucus [30] and to the possibilitythat chest wall oscillation has an important role toplay in clearance of lung mucus.

CLINICAL ASPECTS OF CHEST PHYSIOTHERAPY

Management of Ward Patients with RespiratoryDisease

Previous authors have attempted to clarify therole of chest physiotherapy in patients with bothacute and chronic respiratory problems[31, 53, 58], and copious production of sputumhas been shown to be a sound indication for its use[2, 12, 39, 59]; the benefits are reflected by im-proved lung function tests [12, 59] and enhancedclearance of sputum [2,39]. In contrast, physio-therapy in patients with acute exacerbation ofchronic bronchitis but without copious sputumeither produced no improvement in lung functiontests and blood-gas tensions [1, 41] or even caused

a reduction in forced expiratory volume in 1 s[8, 65], which was preventable by prior administ-ration of a bronchodilator [8].

Coughing exercises have been compared alsowith PDPV in patients with cystic fibrosis, andfound to be equally effective in increasing sputumproduction [16]. We have already discussed the"two-phase gas-liquid flow" mechanism bywhich cough effects sputum movement. However,the high transmural pressures produced duringcoughing lead to dynamic compression of theairways, which may inhibit mucociliary clearanceupstream of the EPP [54]. Therefore, a proceduretermed the "forced expiratory technique" (FET)was introduced to circumvent this problem, andpromotes a higher rate of airflow in smallerairways by moving the EPP further upstream.This technique involves expiring forcefully frommid to low lung volumes whilst maintaining anopen glottis ("huffing" exercises). Studies usingFET [47, 56, 57] have been encouraging, and itwas shown to be superior to both directedcoughing [57] and PDPV [47, 56] in enhancingremoval of sputum. Sutton and colleagues [56, 57]evaluated this technique in chronic bronchiticswith copious sputum using an inhaled radio-aerosol method. They found that FET producedgreater clearance of inhaled radiolabelled particlesthan both regimented coughing [57] and per-cussion and vibratory exercises [56]. However,the amount of sputum obtained was increasedfurther when FET was combined with posturaldrainage compared with FET alone. Pryor andcolleagues [47] also compared FET and posturaldrainage with PDPV in subjects with cysticfibrosis and confirmed that this regimen clearedmore sputum and in less time than conventionalphysiotherapy. This is of particular importance tothese patients as it enables them to practise aneffective method without having to rely on othersfor help.

Several studies have been performed also toassess the effects of PDPV, cough and FET onperipheral lung clearance. In 1979, Bateman andcolleagues [2] used a radioaerosol method todefine the parts of the lungs affected by PDPV inpatients with chronic bronchitis with copioussputum. The authors concluded that PDPV hadimproved radioaerosol particle clearance from allcompartments of the lung, including the peri-phery. However, their use of the term lungperiphery was misleading, as it referred to thelateral 40% of the lung in terms of area on an


isotope scan, and included parts of the mainbronchi. Also, their computer pictures of lungradioactivity showed that the 5-um particles wereconfined mainly to the central airways. Wollmerand colleagues [65] used a radioaerosol techniquesimilar to that of Bateman's group [2], but foundthat chest percussion did not enhance particleclearance from either central or peripheralregions. The explanation for these contrastingresults is that Wollmer's patients were givencoughing exercises, whereas Bateman's controlpatients were asked to refrain from coughingduring the monitoring period. Bateman's group,therefore, repeated their earlier study of patientswith chronic bronchitis [2], and compared cough-ing exercises with PDPV [3]. They found thatboth therapies produced equal central lung clear-ance, but that only PDPV had any effect on theperiphery. However, the same misleading criteriafor interpreting the term "lung periphery" wereused as in their previous study.

The value of coughing exercises has beendemonstrated in other studies [3, 16, 43], and aradioaerosol method in patients with chronicbronchitis showed that they increased both per-ipheral and total lung clearance [43]. However,after assessing the effects of directed coughingcompared with FET on sputum clearance, Suttonand colleagues [57] observed correctly that theywere unable to comment on regional mucusclearance because the 5-um radioactive particlesdid not penetrate to the periphery. Therefore, thevalidity of such results regarding peripheralclearance using inhaled radioparticles is uncer-tain ; Pavia and colleagues [46] have discussed theproblems inherent in this methodology.

Alternative evidence for the effects of chestphysiotherapy on peripheral lung secretions isavailable from clinical outcome studies in patientswith peripheral lung disease. In 1978, Grahamand Bradley [22] assessed patients with acutepneumonia who demonstrated radiographic andclinical evidence of consolidation. The resultsshowed no difference between the PDPV andcontrol groups in earlier resolution of chest x-raysigns, duration of fever, or decreased hospitalstay. Brirton, Bejstedt and Vedin [7] monitored171 patients with acute primary pneumonia, andcompared the effects of regular PDPV with adviceon expectoration and deep breathing. In additionto the lack of benefit found by Graham andBradley [22], this study demonstrated prolonga-tion in the duration of fever and an increased

hospital stay in patients given physiotherapy. Theonly explanation offered by the authors was that,instead of clearing the infected material, PDPVmay have caused it to spread to the surroundingtissue.

Therefore, PDPV, cough and especially FETare beneficial in enhancing clearance of excessivecentral airway secretions, but there is far lesssupport for their use in patients without copioussputum or with peripheral consolidation.

The Role of Chest Physiotherapy in PerioperativePatient Care

Pulmonary complications are a common cause ofpostoperative morbidity and mortality; theincidence has been reported to vary between 6 %[64] and 80% [32]; it is increased in upperabdominal surgery [32], older patients [13],smokers [64] and patients with pre-existing lungdisease [64]. Atelectasis is the most common post-operative complication, especially after upperabdominal surgery, and was noted as early as1908, by W. Pasteur [45]. Many studies have beenperformed since to assess the effects of physio-therapy and other treatments on the incidence ofpostoperative respiratory problems.

In 1953, Palmer and Sellick [44] suggested thefollowing sequence of events in the aetiology ofbronchopneumonia:Various factors ->• increased secretions -*• blockageof smaller bronchi -> absorption of air distally ->atelectasis ->• bronchopneumonia.They postulated that, if the bronchi couldbe kept clear of secretions, subsequent complica-tions would be reduced. They set up two largestudies in patients undergoing either inguinalhernia repair or partial gastrectomy. In the firststudy the control group was given regular breath-ing exercises, and the treatment group underwentfrequent PDPV combined with 6-hourly iso-prenaline inhalation. Postoperative atelectasisdiagnosed radiographically was reduced from43 % to 9 % by this treatment regimen. However,their second study showed that physiotherapywithout the isoprenaline inhalations had no effecton postoperative outcome compared with regularbreathing exercises. The importance of broncho-dilator therapy during PDPV was confirmed in1975 by Campbell, O'Connor and Wilson [8].

Stein and Cassara [55] evaluated the effects ofthe patient's preoperative chest condition on post-operative complications. Their patients wereclassified into a "healthy" control group and a

626

"poor risk" group with abnormal preoperativelung function tests. Chest physiotherapy wasadministered to only 50 % of the poor risk groupand was combined with antibiotics, pVagonists,and humidified gases. An increased incidence ofpostoperative pulmonary complications wasdemonstrated only in the untreated poor riskgroup. However, one cannot deduce from thisstudy the exact benefits of physiotherapy in poorrisk patients because of the range of therapy used,including the use of bronchodilators.

Laszlo and colleagues [32] confirmed the ob-servation that "healthy" patients are unlikely tobenefit from chest physiotherapy. They studied86 non-bronchitic patients allocated at random totreatment and control groups. The treatmentgroup was given twice daily PDPV for 5 days afteroperation, but was found to have the sameincidence of respiratory complications, assessedby sputum and radiographic changes, as the no-treatment control group. An inherent problem insuch studies is the difficulty in differentiatingbetween chest infection and atelectasis. For ex-ample, Morran and colleagues [40] monitored 102consecutive patients presenting for chole-cystectomy. Physiotherapy and control groupswere matched well for characteristics likely toaffect postoperative respiratory morbidity; theauthors concluded that prophylactic physio-therapy reduced the incidence of postoperativechest infection. However, this conclusion was notjustified, as the authors' criteria for infection andatelectasis were similar, and there was littledifference in the incidence of combined post-operative complications.

The possibility that chest physiotherapy maycause a complication which it is aiming to preventhas been demonstrated in paediatric patients byReines and colleagues [48]. They monitored 50patients aged 3 months to 9 yr undergoing cardiacsurgery for congenital heart disease. Patients wereallocated randomly to routine physiotherapy andcontrol groups, and atelectasis was diagnosed byradiographic interpretation by a radiologist un-aware of the treatment each patient had received.The physiotherapy group not only developedatelectasis more frequently than the control group,but also had a more prolonged hospital stay.Explanations proposed by the authors for thisunexpected result included: pain induced byphysiotherapy, the Trendelenburg position, mu-cus plugging of larger airways, and the com-pressive effects of percussion on a compliant

BRITISH JOURNAL OF ANAESTHESIA

chest. Therefore, routine chest physiotherapywithout positive indications may be detrimental,but patients with excessive secretions or acuteatelectasis caused by sputum blockage of centralairways merit treatment and should not be deniedphysiotherapy.

Chest physiotherapy has been compared alsowith other forms of perioperative respiratorytherapy. Schuppisser, Brandli and Meili [52]studied the postoperative effects of physiotherapycompared with intermittent positive pressurebreathing.' Although the number of patients inthis trial was small, the results showed that neithertherapy produced any beneficial change in pul-monary function. When compared with incentivespirometry in patients undergoing upper abdomi-nal surgery, Craven and colleagues [15] foundthat physiotherapy increased the incidence ofpostoperative chest problems; 17 of the patientsin the physiotherapy group were smokers or hadchronic lung disease and 15 developed somedegree of collapse or consolidation.

These studies thus indicate that routine peri-operative chest physiotherapy in the form ofPDPV is riot of value in patients with healthylungs even when undergoing upper abdominalsurgery, but it may benefit patients with chronicrespiratory disease if combined with broncho-dilators. Otherwise, it should be used selectivelyin patients with positive indications such ascopious sputum or acute atelectasis. Furthermore,in view of the poor results from several of thestudies described above, therapies other thanPDPV merit investigation, and the forced ex-piratory technique in particular is worthy offuture evaluation.

The Role of Chest Physiotherapy in Critically IIIPatients

The studies discussed so far can be used toprovide some guidelines on the likely benefits ordisadvantages of PDPV in patients in the In-tensive Care Unit (ICU). However, the criticallyill patient may be at greater risk during physio-therapy because of the severity of the illness (e.g.septicaemia, hypotension or respiratory failure),and the presence of other non-pulmonary injuriesor problems (e.g. patients with increased in-tracranial pressure) [18,42,50]. In particular,numerous studies have shown that PDPV mayproduce short term hypoxaemia in both adult[14,20,21,26,33,61] and neonatal [19,25,63]patients.


The problem of physiotherapy-associatedhypoxaemia

In 1980, Connors and Hammon [14] evaluatedsputum production as an indicator for chestphysiotherapy in critically ill patients with non-surgical pulmonary pathology. Their patientswere classified into those with little sputumproduction and those with moderate to largevolumes of sputum. In the first group, they founda decrease in PaOi of 2.23 kPa immediately afterPDPV, and a further decrease of 0.7 kPa at 30 min.In contrast, there was no change in PaOt afterphysiotherapy in the second group. However,other studies [21, 33] showed that hypoxaemiafollowing PDPV may occur even in patients withprofuse secretions. These changes in PaOj areunexpected, as increasing sputum clearanceshould have improved ventilation; studies of neo-natal chest physiotherapy may help elucidate thepossible mechanisms for this hypoxaemia.

Holloway and colleagues [25] assessed theeffects of PDPV and hyperinflation on the Pa^ ofneonates undergoing ventilation for tetanus.Physiotherapy produced a decrease in mean Pa^lasting for 1 h after treatment. Hyperventilationwas unable to prevent this decrease, but didhasten the return to pre-physiotherapy concen-trations of PaOj. Fox, Schwartz and Shaffer [19]studied neonates in whom the trachea was intu-bated mainly for respiratory distress syndrome(RDS) and found an alarming reduction in Pa^from 9.7 to 5.7 kPa, which lasted for 30 min afterphysiotherapy. Bradycardia was noted also duringtracheal suction in some patients. The maindifference between this study and that of Hollo-way [25], in which reductions in PaOt were muchless severe, is that these patients were notparalysed. Therefore, one reason for this hypox-aemia is greater neonatal activity, as reflected byincreased oesophageal pressure and frequency ofventilation [19]. The need for patient sedationduring tracheal suctioning was investigated byNinan and colleagues [42] in neonates with RDS.Sedation attenuated increases in mean arterialpressure and intracranial pressure during trachealsuctioning, but decreases in Pao occurred in bothgroups. Walsh and colleagues [63] showed thatchest vibration and tracheal suctioning have anadditive adverse effect on transcutaneous oxygentensions (Ptc^) of premature neonates undergoingventilation. Furthermore, supplementary oxygenwas unable to prevent the severe reductions in

PtcOj, indicating a large shunt, but it did hastenreturn to baseline values.

Another possible mechanism for this hypox-aemia is atelectasis, as its incidence was shown toincrease after both PDPV [48] and trachealsuctioning [6,49]. In addition, repetitive cough-ing following intubation was found also to de-crease markedly the functional residual capacityin adult surgical patients [4]; it may have a similareffect during chest physiotherapy and contributeto atelectasis. By using a CT scanner and othertechniques, Hedenstiema and colleagues [24, 60]showed that general anaesthesia itself inducedbasal collapse which was potentiated possibly byneuromuscular blocking drugs and was associatedwith increased alveolar-arterial oxygen difference.Sedated patients who have undergone trachealintubation are, therefore, already compromisedand PDPV or tracheal suctioning may causefurther atelectasis and account for the hypoxaemiademonstrated in many studies.

Additional evidence for a link between trachealsuctioning and aetelectasis was demonstrated byVelasquez and Farhi [62] in anaesthetized, para-lysed dogs. They showed a strong correlationbetween the negative intratracheal pressureduring tracheal suctioning and both reduced lungcompliance and increased venous shunting. Vari-ous methods of preventing the hypoxaemia causedby the suctioning have also been studied. Carlon,Fox and Ackerman [9] evaluated a "closed-tracheal suction system" which obviated the needfor ventilator disconnection on each occasion thatthe airways were suctioned. This closed systemwas compared with conventional open trachealsuctioning; deterioration in PaOj occurred onlyduring open suctioning in patients receiving morethan lOcmHjO of PEEP. The advantage ofavoiding ventilator disconnection during trachealsuctioning was shown to be one of the benefits ofjet ventilation [29], and a valve attachment fortracheal tubes was designed allowing suctionwithout interruption of conventional ventilation

[5]-Therefore, PDPV, tracheal suctioning and

ventilator disconnection may contribute to theshort term hypoxaemia occurring in many criti-cally ill patients following chest physiotherapy.The most likely mechanism for this hypoxaemia isatelectasis, although stimulation of the patientcausing increased oxygen extraction may also be afactor.


Studies supporting chest physiotherapy in ICUpatients

In contrast with the studies demonstratingphysiotherapy-associated hypoxaemia, there isalso evidence for beneficial effects of chest physio-therapy in critically ill patients; three studies wereperformed by the same authors, MacKenzie andShin, with others [35-37].

In 1978 [37] they assessed 47 patients in theirICU. Most patients had either chest or headinjuries, were septicaemic or had spinal cordtransection. The indications for PDPV in thesepatients were secretions detected by auscultation,impaired gas exchange with radiographic changesof atelectasis, or lung contusion. Before eachphysiotherapy session, patients were assessedclinically and had a radiograph to locate the site ofpathology. PDPV was then used until this portionof the lungs was clinically improved. Their meantime for each session was 51 min! The resultsshowed no improvement in post-treatment PaOt,but there was a 74% success rate in clearingunilobular radiological densities or atelectasis,and a 60 % rate of resolving multilobular changes.

In 1980 [36] the same group studied changes intotal thoracic compliance following physiotherapyin 42 patients undergoing ventilation for chesttrauma. With the exception of excessive secre-tions, the indications for PDPV in this group wereatelectasis (29 patients) and lung contusion(eight). The results showed an increase in totallung + chest wall compliance immediately afterand for 2 h after physiotherapy. No other datawere recorded in this study and the mean time forPDPV was 57 min! However, in 1985 the sameauthors [35] conducted a more detailed investi-gation of cardiorespiratory function before andafter chest physiotherapy in patients undergoingventilation for post-traumatic respiratory failure.The only improvements in cardiorespiratory func-tion were reduced intrapulmonary shunt immedi-ately after PDPV, and increased total thoraciccompliance at 2 h after the procedure. Cardiacindex (CI) and P&ot values were not alteredsignificantly. One reason for the stable CI is thatthese patients did not undergo hyperventilationduring PDPV by either "bag squeezing" or othermethods. The significance of these results isquestionable, as decreased pulmonary shunt com-bined with stable CI should have improved Pa^.Furthermore, as these physiotherapy sessionslasted 67 min, monitoring arterial oxygenation

during the procedure would have been bothadvisable and informative.

MacKenzie and Shin considered that atelectasiswas one of the main indications for chest physio-therapy, and this has been confirmed by otherworkers [23,38]. Hammon and Martin [23]reported five case histories involving nine episodesof acute lobar collapse, and in every case PDPVwas successful in re-expanding collapsed portionsof the lung, but they emphasized that patientsmust be monitored closely, as "some critically illpatients receiving PDPV have a worrisome andunexplained fall in arterial oxygen tension".Marini, Pierson and Hudson [38] comparedPDPV with fibreoptic bronchoscopy in 31 patientswith acute lobar collapse. Pre- and post-treatmentchest x-rays showed that both methods wereequally effective in increasing lung volume. How-ever, an additional finding in this study was thatthe success rate depended on whether or not therewas an air bronchogram. If this was present, theresolution rate was only 26%, compared with86% with no bronchogram. The explanation wasthat with no air bronchogram there was sputumblockage of a bronchus with secondary collapse,but with a bronchogram there was distal collapse,but no sputum plug. The fact that chest physio-therapy has little effect in clearing secretions fromthe lung periphery has been demonstrated also inpatients with consolidation [7, 22].

In contrast with the adverse effects of neonatalchest physiotherapy observed in previous studies[19,25,63], Finer and Boyd [17] found that aspecially designed form of chest percussion im-proved the oxygenation of neonates with res-piratory distress. Postural drainage alone had noeffect on oxygenation but, when combined with"contact-heel" chest percussion (rhythmic ap-plication of the heel of the hand to the neonate'schest wall), mean Pa^ values improved from 8 to10 kPa. Because of the special nature of the chestpercussion utilized in this unit, these resultscannot be compared directly with those fromother neonatal studies, and the authors observedcorrectly that each unit should evaluate its ownphysiotherapy procedures before accepting themas standard practice.

Thus excessive secretions and acute atelectasisare also sound indications for chest physiotherapyin critically ill patients, as demonstrated bybeneficial changes in total thoracic complianceand chest x-ray signs. However, because of thepossibility of short term hypoxaemia associated


with physiotherapy, arterial oxygen tensionsshould be monitored and PDPV must be usedwith particular care in patients with low baselineoxygenation.

CONCLUSION

The physiological aspects of mucus clearancehave been discussed, and the relative merits ofcoughing exercises, the forced expiratory tech-nique (FET), and postural drainage, percussionand vibration (PDPV) have been evaluated. Allthese manoeuvres are of value to patients withcopious sputum confined mainly to the centralairways, but FET, especially when combinedwith postural drainage, has been shown to besuperior to both cough and PDPV in suchpatients. Atelectasis caused by sputum blockageof a major airway is also a good indication forPDPV. However, PDPV may induce bothbronchospasm and hypoxaemia in many patients,and therefore the indications should be evaluatedsoundly before its use. This is particularlynecessary in critically ill patients with littlecardiorespiratory reserve. More research is stillrequired and, in particular, we need to:(a) verify the effects, and possible benefits of highfrequency chest wall oscillation on clearance ofperipheral mucus;(b) determine if FET + postural drainage shouldreplace PDPV in patients breathing spon-taneously;(c) evaluate the role of bronchodilators duringphysiotherapy;(d) examine more clearly the reasons for the shortterm hypoxaemia caused by physiotherapy inmany critically ill patients;(e) assess if regular prophylactic chest physio-therapy in ICU patients undergoing ventilationdecreases the incidence of chest complications.

APPENDIX

Jones, Fraser and Nadel [28] showed that flow (V) or velocity(u) can be predicted from p, the gas density, the cross sectionalarea (A) and the transmural pressure (AP) at the compressedsegment:

or

(i)

(2)

The compliance of the compressed airway shows that:

— = - logAPAo 2

(3)

where Ao is the area at full lung inflation.From equation (3), the specific compliance per unit length is:

1 &A 1

Therefore:

Substituting into (2):

Ao dP 2AP

Ao dPAP = —• —

2 dA

_ V _ [2AP_ 12 Ao dP _ lAo dP

A S P VC 2 dA \ p dA

Equation (4) is called the Wavespeed equation, which has beenwidely quoted as a unique predictor of maximum flow [27]. Itsimportance is that it describes the velocity of gas flow at thecompressed segment and thus the intensity of gas—liquidinteraction.

REFERENCES

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