a. What does this show?

b. What further piece of information do you need to be able to interpret it correctly?

a. What does this show?

b. What further information would help you to decide what action to take?

a. What does this show?

b. What factors in the history should be considered before taking action in response to this result?

a. What does the blood gas show?

b. What must be done when such a result is obtained?

c. What is the most likely explanation in this case and what action should be taken?

a. What does the blood gas show?

b. What two actions should be taken?

c. What three investigations might you want to be sure had been performed?

a. What does blood the gas show?

b. What three investigations would you make sure had been done?

c. What therapy would you start?

a. What does blood the gas show?

b. A septic screen and chest x-ray have already been performed. What further management would you consider?

a. What does the blood gas show?

b. What are the main problems that must be treated?

c. What measures could be taken to address them?

a. What is the most important treatment to be commenced?

b. Why?

c. What investigations are urgently needed?

d. What serious error in management has been made?

a. What do these results show?

b. What is the most likely explanation?

c. What actions will you take?

a. What do these results show?

b. What is the explanation?

c. What actions will you take?

d. What errors in management have been made?

a. What do these results show?

b. What is the most likely explanation?

c. What actions will you take?

a. What do these results show?

b. What is the most likely explanation?

c. What actions will you take?

a. What do these results show?

b. What is the most likely explanation?

c. What actions will you take?

a. What do these results show?

b. What is the most likely explanation?

c. What actions will you take?

a. What do these results show?

b. What is the most likely explanation?

c. What actions will you take?

d. What basic error has been made?

a. What do these results show?

b. What is the most likely explanation?

c. What actions will you take?

a. What do these results show?

b. What is the most likely explanation?

c. What actions will you take?

a. What do these results show?

b. What is the most likely explanation?

c. What actions will you take?

a. What do these results show?

b. What is the most likely explanation?

c. What actions will you take?

a. What do these results show?

b. What is the most likely explanation?

c. What actions will you take?

a. What do these results show?

b. What is the most likely explanation?

c. What actions will you take?

a. What do these results show?

b. What is the most likely explanation?

c. What actions will you take?

a. What do these results show?

b. What is the most likely explanation?

c. What actions will you take?

a. What do these results show?

b. What is the most likely explanation?

c. What actions will you take?

a. What do these results show?

b. What is the most likely explanation?

c. What actions will you take?

a. What do these results show?

b. What is the most likely explanation?

c. What actions will you take?

a. What do these results show?

b. What is the most likely explanation?

c. What actions will you take?

a. What do these results show?

b. What is the most likely explanation?

c. What actions will you take?

a. What do these results show?

b. What is the most likely explanation?

c. What actions will you take?

a. What do these results show?

b. What is the most likely explanation?

c. What actions will you take?

a. What do these results show?

b. What is the most likely explanation?

c. What actions will you take?

a. What do these results show?

b. What is the most likely explanation?

c. What actions will you take?

a. What do these results show?

b. What is the most likely explanation?

c. What actions will you take?

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b. What is the most likely explanation?

c. What actions will you take?

a. What do these results show?

b. What is the most likely explanation?

c. What actions will you take?

a. What do these results show?

b. What is the most likely explanation?

c. What actions will you take?

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b. What is the most likely explanation?

c. What actions will you take?

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b. What is the most likely explanation?

c. What actions will you take?

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b. What is the most likely explanation?

c. What actions will you take?

a. What do these results show?

b. What is the most likely explanation?

c. What actions will you take?

a. The gas appears to show hypoxia.

b. There is no information as to what sort of sample this is. If it is a fresh arterial sample the result definitely shows hypoxia. If it is a capillary sample the result cannot be interpreted.

a. The gas appears to show hypoxia but a capillary sample was used.

b. Some other indication of oxygenation is essential – pulse oximetry or transcutaneous oxygen measurement would be appropriate. The PaO ₂is underestimated on a capillary sample but the extent to which it differs from an arterial sample cannot be accurately predicted as it will be affected greatly by peripheral capillary perfusion. It is therefore conceivable that a low capillary PO ₂ could represent hypoxia, normoxia or hyperoxia and some other means must be used to establish what the result actually means.

a. The capillary gas sample appears to show a mixture of hypoxia, respiratory acidosis and metabolic acidosis.

b. Although there is some information in the history to suggest that the infant could have suffered an asphyxial episode – difficult delivery and decelerations on CTG – the description of the infant does not suggest this, nor does it suggest a baby with a significant hypoxia or acidosis. A normal infant who is not ventilated will attempt to respond to the abnormalities in the blood gas if they are genuine. Hypoxia will result in increased respiratory rate and effort, and grunting is likely in an attempt to decrease end-expiratory atelectasis. A respiratory acidosis will normally result in hyperventilation to reduce the carbon dioxide and the normal response to a metabolic acidosis is also hyperventilation. Although a seriously asphyxiated infant may not mount an appropriate response, this does not seem to be the case here as the infant is reported to be responding appropriately to handling. The ‘normality’ of the infant would suggest that the result is due to a capillary gas sample taken when there is poor peripheral perfusion. This is very common shortly after birth and it is important that such results are interpreted with great caution.

a. An apparent hypoxia. However, the PO ₂ of 3.5 does not seem to be compatible with a saturation of 100% on pulse oximetry.

b. The most likely explanation is that the umbilical arterial line has been inserted into the umbilical vein by mistake and mixed venous PO ₂ is being measured.

c. A chest and abdominal x-ray should be obtained as quickly as possible to check on the position of the catheter. Until this has been established it would be prudent to reduce the inspired oxygen to obtain a SaO ₂ in the mid 80s to low 90s.

a. The blood gas result shows evidence of a metabolic acidosis. Bicarbonate, base deficit and pH are low; CO ₂ is normal.

b. In any case of a metabolic acidosis it is crucially important that the cause of the acidosis is established. It is not enough to simply establish that an acidosis is present and treat it by giving base. This may temporarily correct the acidosis but leaves the cause untreated. Many conditions may lead to a metabolic acidosis – sepsis, heart failure, haemorrhage, hypovolaemia and hypotension to name but a few – and in many of these cases it is obviously essential that the cause is addressed as a matter of urgency.

c. In this case the most likely (but not necessarily the correct) cause of the acidosis is hypovolaemia due to acute blood loss. An urgent cross-match should be performed and the haemoglobin monitored closely until blood is available. The haemoglobin is not particularly low but may well not have reached the lowest point yet while fluid shifts from extravascular to intravascular compartments. If the haemoglobin drops further while you are waiting for the cross-matched blood it may be prudent to give emergency O Rh −ve, CMV −ve blood.

a. Moderate hypoxia in 32% oxygen and mild respiratory acidosis.

b. The hypoxia can probably be treated by simply increasing the inspired oxygen concentration. The baby must be closely monitored. The respiratory acidosis is not sufficiently severe to warrant CPAP or ventilation but the baby is becoming symptomatic – soft end-expiratory grunt – and may well continue to deteriorate.

c. A chest x-ray would be very appropriate at this point in time, and if not performed already blood should be sent for inflammatory markers (FBC and CRP) and blood cultures taken. If the x-ray appearances were compatible with respiratory distress syndrome some practitioners would consider briefly intubating the infant so that surfactant could be administered. There is no consensus on this practice and no clinical trial evidence base to justify it.

a. It is normal.

b. Although the blood gas is normal the infant is symptomatic. In a term infant developing respiratory symptoms shortly after birth infection is the most worrying possibility and initial investigations should explore this possibility. Blood should be taken for FBC and CRP, blood cultures should be sent and a chest x-ray taken.

c. Antibiotics should be started. The choice of antibiotic would be determined by local policy which should in turn be determined by any known local resistant organisms.

a. Significant hypoxia despite a relatively high inspired oxygen concentration. There is a combined respiratory and metabolic acidosis. The carbon dioxide is mildly elevated but the bicarbonate is lower than would be expected in the face of this elevation. The base deficit is moderately high.

b. Some form of ventilatory support is required. Most practitioners would start either CPAP or positive pressure ventilation at this point. Surfactant could be considered as discussed in the answer to question 6.

a. Significant hypoxia despite a relatively high inspired oxygen concentration. pH is satisfactory and there is no evidence of either respiratory or metabolic acidosis. However, the infant is becoming symptomatic. Respiratory rate is quite high and there are frequent bradycardias.

b. The two issues to be treated are the hypoxia and the symptoms.

c. Although the inspired oxygen concentration could be increased and this would address the hypoxia it is already quite high and it would be more appropriate to consider some other intervention. It is also unlikely that increasing the inspired oxygen would have a significant impact on either tachypnoea or the bradycardias. Some form of ventilatory assistance would be appropriate and in this instance CPAP would be the most likely option to be considered first. Surfactant could also be considered as discussed in the answer to question 6 above.

a. The gas shows a mixed respiratory and metabolic acidosis and hypoxia.

b. CPAP on the current settings does not appear adequate for this infant. There is evidence that the infant is having to work, as shown by the recession, but this may not be the sole reason for the metabolic acidosis.

c. Management will vary between different individuals. There is no doubt that additional management of some form is needed. There are some practitioners who would advocate intubation, administration of surfactant and extubation back onto CPAP. Others would regard it as more appropriate to intubate, administer surfactant and then proceed with positive pressure ventilation. The metabolic acidosis must not be ignored and it is appropriate to look for additional causes and treat as appropriate.

a. There is a respiratory alkalosis and probable hyperoxia.

b. The infant has been over-ventilated. The tidal volume is significantly greater than would be expected for this baby’s birth weight.

c. Since intubation the baby has been given surfactant and there has been a significant improvement in the clinical condition. It would probably be most appropriate to return this baby to CPAP. If this is deemed unacceptable, at the very least the inspiratory pressure should be reduced.

d. There have been two significant errors. Ventilation is being commenced after surfactant has been given and there has been a significant interval before the blood gases have been checked. Secondly, oxygen saturation has been allowed to run in excess of 95% without seeing if inspired oxygen concentration can be reduced further and without checking on the arterial oxygen concentration.

a. This baby has a metabolic acidosis. Carbon dioxide clearance is satisfactory, as is oxygenation.

b. It is possible that hypotension is contributing to the metabolic acidosis. Poor tissue perfusion will result in inadequate tissue oxygenation with resultant anaerobic metabolism. However, the obvious course is not necessarily the correct course and it is important to be aware of the other possible reasons for a metabolic acidosis.

c. The cause of the acidosis must be addressed. In this case it would be appropriate to follow whatever the local policy is for the management of hypertension, be it fluid bolus or commencing inotropic support. This alone may be adequate but if it is not then administration of base may be required.

a. There is a mixed respiratory and metabolic acidosis. Carbon dioxide is elevated; bicarbonate is relatively low with a significant base deficit.

b. The infant is under-ventilated. Tidal volume is low. In addition oxygenation is poor at a relatively high inspired oxygen. There is also a metabolic component to the acidosis and there is no obvious reason for this.

c. An increase in peak inspiratory pressure would probably be the best approach to dealing with both respiratory acidosis and the relative hypoxaemia. If the infant has not received surfactant for some period and a chest x-ray is consistent with respiratory distress syndrome further surfactant should be administered. The reason for the metabolic acidosis is not apparent and therefore should be sought. In the interim it would be appropriate to treat the metabolic acidosis with base.

a. These results are not easy to explain on first view. The infant has a high CO ₂ but bicarbonate does not seem high enough to account for this nor is the pH as acidotic as might be expected. The infant is hypoxic despite high inspired oxygen. Tidal volume is low.

b. There is a very rapid deterioration and the blood gases were obtained shortly after the deterioration had started. The equilibration of carbon dioxide in the bloodstream and tissues is not instantaneous and there may be a brief delay before the final result of the changes is seen. It is very likely that this gas will deteriorate significantly in the very near future as equilibration happens.

c. The causes of a sudden deterioration should be sought. The most likely candidates are pneumothorax, a displaced or blocked endotracheal tube or a mechanical failure. It is not appropriate to make changes to the ventilation until the cause of the deterioration is established.

a. There is a severe respiratory acidosis. The tidal volume is very low and there is severe hypoxia.

b. The blood gases are now fully equilibrated and the full severity of the deterioration is apparent.

c. The cause of the deterioration must be addressed. In this case cold light illumination shows a large tension pneumothorax on the right side. A chest drain is inserted with an immediate improvement in oxygenation and a rapid return to a normal tidal volume.

a. There is now a respiratory alkalosis. CO ₂ is low and tidal volume is higher than predicted. The arterial oxygen concentration is high.

b. Following drainage of the pneumothorax the infant has been hyperventilated.

c. Peak pressures should be returned to values similar to those required before the pneumothorax developed. The inspired option should be reduced.

d. The ventilator settings were increased at the time of the deterioration. The main problem however was a loss of lung volume due to a pneumo-thorax. Once this was appropriately managed lung movement was restored but the ventilator settings were not changed. Attention was not paid to the change in tidal volume and the interval before the next arterial blood gas was too long.

a. There is a respiratory alkalosis but at the same time this infant remains relatively hypoxic at reasonably high inspired oxygen.

b. There is some improvement of lung disease allowing better carbon dioxide clearance but still not allowing optimal oxygenation.

c. If the rate is reduced by increasing expiratory time more time will be spent in inspiration, which would result in a slight increase in mean airway pressure and could improve oxygenation. It might be reasonable to reduce the peak pressure to see whether there was a degree of over-distension but this seems less likely in view of the excellent carbon dioxide clearance.

a. There is a respiratory acidosis and poor oxygenation.

b. The mean airway pressure is much lower than would be expected on the settings. The tidal volume is also surprisingly low. A careful look at the ventilator settings shows a flow rate that is unlikely to be high enough for adequate ventilation in a baby of this size. It is quite likely to be so low that the ventilator will not attain the desired peak pressure.

c. Flow rate should be increased until adequate ventilation is attained. This should be apparent if any form of pressure wave monitoring is available. If not, blood gases and oxygenation should be closely monitored to make sure that the desired effect is achieved. It is not uncommon to find that flow rates are initially inadequate for larger babies. Options that are much more likely to be used on very small babies are lower flow rates. Flow remains a setting that many people do not adjust on a regular basis and the ventilator may be set up without having considered whether or not the flow is adequate for the baby who is about to be ventilated.

a. There is a mixed respiratory and metabolic acidosis. Oxygenation is suboptimal in relatively high inspired oxygen.

b. This baby appears to be under-ventilated and is trying to make it obvious. The fact that the baby is trying to make respiratory movements suggest that the current ventilation is inadequate and the increased respiratory work may be contributing to the metabolic acidosis. The ventilator rate that has been set is quite low (43 breaths per minute) and the inspiratory time is sufficiently long to make it likely that the baby will be breathing again before inspiration is over. The slow rate means that carbon dioxide clearance is inadequate. The relatively small number of inspirations means that mean airway pressure is also quite low.

c. In this situation the first thing to do is to adjust the ventilation to a rate where the majority of breaths appear to be synchronised with the infant’s own respiratory rate. In those who use synchronised ventilation, this baby would be an ideal candidate to commence synchronised intermittent positive pressure ventilation. The evidence base for any benefit with this modality is poor and there are practitioners who do not use this technique. Whether or not synchronised ventilation is used the principal aim will be to achieve a respiratory rate that is similar to the spontaneous rate of the baby, thereby reducing the work of breathing and hopefully markedly increasing the efficiency of mechanical ventilation.

a. There is a respiratory acidosis with poor oxygenation.

b. Ventilator pressures appear inadequate and the x-ray changes imply that lung inflation is suboptimal. The fact that both carbon dioxide clearance and oxygenation are affected suggests that better lung inflation may be helpful.

c. Peak inspiratory pressure could be increased and this would improve both mean airway pressure and tidal volume providing there was better lung recruitment. An increase in the positive end expiratory pressure might help recruit more atelectatic lung. The latter move may reduce the pressure differential that determines tidal volume but it had also secured a greater volume of lung for ventilation and may still improve tidal volume.

a. There is a respiratory acidosis with poor oxygenation.

b. Ventilation pressures are fairly high but mean airway pressure, tidal volume and minute volume are all low. The expiratory time is quite long and respiratory rate is quite slow. The x-ray suggests that the lungs are affected by respiratory distress syndrome.

c. As a first move it would be wise to reduce the expiratory time, which should have an effect upon both mean airway pressure and minute volume. Surfactant should be administered and a repeat x-ray would be advisable to assess the degree of lung recruitment. Further actions would be determined by the response to this first change.

a. The blood gas is almost normal. Oxygen is higher than is desirable.

b. These results show a dramatic change. There has been a substantial change in both mean airway pressure and tidal volume. The increase in rate means that there has been a very substantial increase in the minute volume. Carbon dioxide has fallen and oxygenation has improved.

c. These figures might be regarded as reassuring (which to some extent they are) and the dramatic and rapid improvement suggests these figures may continue to change in the relatively near future. The lungs of a more mature baby may respond dramatically to surfactant with a considerable increase in compliance. It is very possible that this improvement will continue and more carbon dioxide may be removed, leading to a respiratory alkalosis. It is almost certainly appropriate to start to reduce pressures at this point but whether or not this is done it is essential that very close monitoring is continued.

a. There is a metabolic alkalosis and borderline hyperoxia.

b. Although pressures have been reduced slightly the rate remains high and there is continued excess clearance of carbon dioxide. The changes that were made last time were inadequate and too long has been left since the last change in ventilation before a blood gas is being performed.

c. The rate should be normalised to somewhere in the region of 60 as a good baseline to start from. Although it is generally a bad idea to alter more than one setting at the time in this case it might be advisable to also reduce the peak pressure. It is very important that closer monitoring is performed until adequate ventilation is achieved at the lowest possible ventilator settings.

a. There is a respiratory acidosis. Oxygenation is adequate.

b. The ventilator rate is relatively slow at 46 breaths per minute. Oxygenation is adequate, as is tidal volume, but minute volume is low.

c. The most logical change will be to reduce the expiratory time to give a faster ventilator rate.

a. The pH is normal but the arterial oxygen concentration is high despite a reduction in inspired oxygen concentration.

b. The reduction in expiratory time meant that more time was spent in inspiration with subsequent rise in the mean airway pressure.

c. Some change should be made which will lead to a reduction in the mean airway pressure. The most logical one in this situation would be to reduce the peak inspiratory pressure.

a. The acid–base balance is satisfactory but the infant remains hypoxic despite being on 85% oxygen.

b. There are two major problems with his ventilation. Both inspiratory and expiratory times are short and the background rate is 75 breaths per minute. The second problem is that flow rate in the circuit is low. The mean airway pressure that is currently being achieved is 7.7 where a quick calculation would suggest that it should be above 10. It is likely that the ventilator is unable to attain the peak pressure and ventilation is thus inefficient.

c. The first, and probably most logical, step would be to increase the flow in the ventilator circuit so that the peak pressure could be obtained relatively rapidly in inspiration and then sustained throughout the rest of the inspiratory period.

a. This gas shows a combination of a metabolic acidosis and a respiratory alkalosis.

b. Improvement of the flow has allowed much more effective ventilation and the carbon dioxide has been reduced to very low levels. This has not produced a marked alkalosis however because there appears to be a superimposed metabolic acidosis which has kept the pH within the acceptable range. The very large base deficit and low bicarbonate show that there is an additional problem. If there were not, one would anticipate a much higher pH and bicarbonate and a much smaller base deficit.

c. An alteration of the ventilation either by reduction of peak inspiratory pressure or by slowing the rate using an increase in expiratory time will allow the carbon dioxide to increase but this is only a small part of the problem. There is a significant metabolic acidosis that has developed over a relatively short period of time and the cause of this must be established. The appropriate treatment will be determined by the cause of the acidosis.

a. There is a combination of respiratory and metabolic acidosis. The bicarbonate is lower than would be anticipated for an uncomplicated respiratory acidosis. Oxygenation is adequate.

b. This infant has been placed on synchronised ventilation but the inspiratory time chosen is almost certainly too long to allow effective synchronisation. If the ventilator is set up with a long inspiratory time there is a good chance that the infant will attempt to breathe out during the inspiratory phase and may well be trying to breathe in again either during the same inspiratory cycle or during expiration. The fact that the baby is ‘fighting’ the ventilator should inform you that the ventilator settings are unsuitable.

c. Reduce the inspiratory time to somewhere around 0.35 seconds. Observe the effect this has on ventilation and on the baby’s spontaneous breathing.

a. This infant has a respiratory alkalosis.

b. The ventilator settings will not allow effective synchronisation and the background respiratory rate (85 breaths per minute) is leading to hyperventilation. Depending on the model of ventilator in use there may be a short latent period after inspiration is finished during which a further inspiration cannot be initiated. Once this is over the remainder of the inspiratory time is the window during which another breath must be taken for synchronisation to occur. At an expiratory time of 0.35 seconds, even without a latent period, there will be very little time for a breath to be taken if true synchronisation is to occur.

c. Increase the expiratory time significantly to see if true synchronisation will happen and, if it does, what the baby’s spontaneous background respiratory rate is.

a. The gas is normal.

b. Although there is a long expiratory time a quick calculation using the tidal volume and minute volume will show you that the baby is breathing at a rate of approximately 60 breaths per minute. Although the back-up rate is set at 30 the actual ventilator rate will be determined by the baby’s spontaneous respiration which in this case appears to be adequate as it has resulted in a normalisation of the previously abnormal blood gas. The mean airway pressure is also significantly higher than you would expect if the baby was breathing at the back-up rate.

c. No action is needed.

a. There is a respiratory acidosis.

b. As this infant is on synchronised intermittent mandatory ventilation with a relatively long expiratory time there is the potential for him to be taking a large number of unsupported breaths. The back-up rate would be 30 breaths per minute and with the measured tidal volume of 4.9 mL and minute volume of 0.15 L/min it would appear that there is no spontaneous ventilation. If this is the case it will explain the carbon dioxide retention.

c. The first thing is to check whether or not the infant is breathing spontaneously. If not, it would be reasonable to search for any reason why. Is the infant sedated or even paralysed? (This may sound stupid but it has been known.) Would the infant benefit from a respiratory stimulant such as caffeine? Although these issues should be addressed it is important to note that ventilation remains inadequate and a respiratory acidosis will persist unless action is taken. The first most logical step would be to increase the respiratory rate to eliminate more carbon dioxide. The expiratory window could be reduced to permit more supported breaths or the infant could be changed to positive pressure or synchronised positive pressure ventilation.

a. There is a respiratory acidosis and oxygenation is poor.

b. This infant was ventilating well prior to his extubation on exactly the same ventilator settings. Following intubation he is no longer able to do so. Although a degree of atelectasis may happen following extubation this would have to be quite severe and does not seem the most likely explanation in view of how well the infant was previously. Tidal volumes prior to extubation were good but are now poor with both tidal volume and minute volume approximately half of what one would anticipate if the lungs were inflating normally (tidal volume 4–6 mL/kg; weight 3.5 kg therefore normal tidal volume in the region of 17mL; respiratory rate 60 therefore predicted minute volume 1.05 L). It is conceivable that a mucus plug has been dislodged during extubation (not an uncommon phenomenon) and has occluded a main bronchus.

c. If the poor ventilation continues a chest x-ray is indicated and selective bronchial intubation and suction may be warranted. The exact reason for the deterioration of ventilation is difficult to establish without some x-ray evidence. If there is no evidence of bronchial occlusion it may just be that there was atelectasis following extubation and a period of ventilation at a higher peak pressure may be needed to recruit lung again.

a. The gas shows a respiratory acidosis. Oxygenation is satisfactory.

b. Tidal volume and minute volume are low. The positive end expiratory pressure is relatively high and this may explain why tidal volumes are low. The high PEEP is helping maintain a high mean airway pressure and therefore oxygenation is satisfactory.

c. The PEEP should be reduced while watching the tidal volume. No other changes should be made until the effect of this manoeuvre becomes apparent.

a. There is a respiratory acidosis and poor oxygenation.

b. Ventilation is obviously unsatisfactory. The mean airway pressure is quite high but is still insufficient to maintain oxygenation or good carbon dioxide clearance. The tidal volume is low and suggests that lung inflation is poor.

c. Action at this point will depend upon what ventilation modality is in use. Many practitioners would regard this baby as suitable for commencing high-frequency ventilation. Others do not believe there is a role for this modality as no benefit has been established over conventional ventilation. If high frequency is not to be used then conventional ventilation must be adjusted to attempt to secure better tidal volumes. An increase in peak inspiratory pressure is indicated and it is possible that increasing the level of PEEP may help to recruit atelectatic lung.

a. The respiratory acidosis is slightly worse and there is borderline improvement in the oxygenation. Mean airway pressure has increased but there has been no net change in the tidal volume.

b. It is likely that the lung remains atelectatic and high pressures have not resulted in further lung recruitment.

c. It would be possible to increase peak inspiratory pressures further and possibly also inspiratory time and/or PEEP. At these pressures anyone using high-frequency oscillation would almost certainly have opted for this alternative.

a. There has been no significant improvement. The respiratory acidosis persists and there is still poor oxygenation.

b. It is likely that the MAP is not high enough to recruit the atelectatic lung. Without recruitment oscillation will be ineffective and gas exchange will remain poor. It is recommended that when oscillation has commenced with a poorly aerated lung the MAP used should be at least 2  cmH ₂O higher than the MAP on conventional ventilation before switching to oscillation.

c. Poor lung recruitment could be confirmed with an x-ray but in a situation where gas exchange remains poor and an appropriate MAP has not been selected in the first place a further change in MAP should be made first.

a. The gas has normalised.

b. Appropriate mean airway pressure and pressure swing have been selected.

c. Oxygenation is now very good with high saturations in 25% oxygen. Carbon dioxide clearance has improved dramatically and has normalised within 30 minutes of making the change in pressure settings. Although it might be tempting to leave the baby at this point very close observation is necessary. It is very conceivable that lung recruitment will continue, with the possibility of hyper-expansion and it is also possible that carbon dioxide clearance will continue and the baby may rapidly become hypocarbic. It could be prudent to reduce the mean airway pressure and it will certainly be necessary to repeat a blood gas fairly soon.

a. Again there is poor oxygenation and a respiratory acidosis.

b. Although the assumption has been made that there is a loss of lung volume responsible for the poor ventilation – hence the increase in mean airway pressure – an alternative explanation is that the lungs had become hyper-inflated. They will therefore be less compliant and air entry will be impaired. If pressures continue to be increased the situation will only worsen and, furthermore, significant lung damage may ensue.

c. An urgent chest x-ray should be performed to assess the degree of lung filling. If this is not immediately available it may be prudent to try and reduce the mean airway pressure to see the effect it has on oxygenation. Ideally radiological examination should be performed first so that any changes are made on the basis of information rather than speculation.

a. There is a metabolic acidosis and a respiratory alkalosis.

b. This combination is often missed as the normal pH reassures the operator that everything is acceptable. In this case the carbon dioxide is very low and were there not a metabolic acidosis the pH would probably be in the region of 7.5. However something is responsible for a metabolic acidosis that has moved the pH back towards the normal range.

c. There are two separate elements to management here. Firstly, the cause of the metabolic acidosis must be sought and appropriate management initiated. Secondly, the ventilation must be adjusted so that the carbon dioxide returns towards the normal range. The easiest initial move would be to increase expiratory time, thereby reducing the respiratory rate.

a. Arterial oxygen concentration is too high; otherwise the blood gas is acceptable.

b. Ventilation is satisfactory but the inspired oxygen concentration has not been turned down rapidly enough.

c. The inspired oxygen should be decreased immediately. The blood gas is very good and there is room to start weaning this infant. A reduction in the peak inspiratory pressure could be considered. It would also be reasonable to reduce the inspiratory time while increasing the expiratory time and keeping respiratory rate the same.

a. There is a compensated respiratory acidosis. The pH is normal but the carbon dioxide is high. This is associated with a high bicarbonate and a base excess of >10 mmol/L.

b. This infant is likely to have developed chronic lung disease. The combination of ventilation for 3 weeks and inflammatory changes on x-ray are highly suggestive.

c. It would be appropriate to try to reduce the peak respiratory pressure and wean ventilation. Babies with chronic lung disease may appear stuck on a ventilator because they have a high carbon dioxide and there are concerns that reducing ventilation will allow this to rise further. This is possibile but it is still important that attempts are made to reduce the pressures further to try to reduce the inflammation.

a. The blood gas is satisfactory.

b. Ventilation is currently appropriate.

c. At pressures of 14/4 extubation should be considered. Whether this is directly into incubator oxygen or onto CPAP will depend upon the policy of the individual unit. Although lower pressures are less damaging to the lungs than higher pressures, it is still not advisable to leave an infant with an endotracheal tube in place and with positive pressure ventilation. The ventilator rate is still high (75) and it would also be reasonable to slow this down to make sure the baby is capable of spontaneous respiration.

a. There is severe hypoxaemia and a mixed metabolic and respiratory acidosis.

b. The most likely diagnosis here is persistent pulmonary hypertension of the newborn. Tidal volumes are good and thus there is unlikely to be a problem with pulmonary atelectasis. The history of a term baby found collapsed when there is a history of prolonged rupture of membranes is highly suggestive of PPHN secondary to sepsis.

c. A chest x-ray is essential and an echocardiogram would be very helpful. Blood must be sent for a septic screen but this infant is too sick for a lumbar puncture. First-line antibiotics which will cover both Group B Streptococcus and E. coli must be started immediately. The management of the respiratory condition will be determined by what modalities are available in the hospital. At the very least the peak inspiratory pressures must be increased to see whether oxygenation can be improved. Pulmonary vasodilators should be considered and it is important that systemic blood pressure is maintained.

a. Profound hyperoxia remains and there is a severe metabolic acidosis and a degree of respiratory acidosis.

b. The oxygenation index is extremely high at 270 [OI = MAP × FiO ₂ (%)/PaO ₂ (mmHg)].

c. Current manoeuvres have not worked. There is, presumably, severe pulmonary hypertension with very little blood perfusing the lungs.

d. This infant urgently needs either nitric oxide or ECMO. Because of the severity of this infant’s condition ideally he should be transferred to an ECMO centre, receiving nitric oxide en route. Should further attempts be made to stabilise him rather than transfer it is unlikely he will survive. There is evidence to suggest that delaying referral for ECMO while other modalities are tried is associated with a reduced success rate for ECMO and longer runs when on ECMO.

a. This baby has compensated respiratory acidosis.

b. As this baby requires continuing oxygen it is very likely that she has chronic lung disease of prematurity and a persistently elevated carbon dioxide. As she is nine weeks old this is now compensated as the renal threshold for bicarbonate increases and plasma bicarbonate rises. The combination of an elevated carbon dioxide, a normal or near normal pH and elevated bicarbonate and base excess are the key features of a compensated respiratory acidosis.

c. No action is indicated. This is the normal body reaction to a persistently elevated carbon dioxide and any attempts to normalise it will lead to destabilisation of the acid–base balance. As this infant has chronic lung disease the only thing that should be ensured is that oxygenation is adequate and appropriate. Insufficient oxygen can, over a long period of time, lead to right ventricular hypertrophy and pulmonary hypertension. There is good evidence that maintaining adequate oxygenation can prevent this from happening in the majority of cases.

a. There is a respiratory alkalosis in combination with a compensated respiratory acidosis.

b. This baby has been ventilated in an attempt to normalise the carbon dioxide. ‘Normal’ for this infant is likely to be significantly higher than it would be for an infant who did not have chronic lung disease. As the compensation has led to a normalisation of the pH a further reduction of the carbon dioxide will drive the pH to the alkaline side of normal. The tidal volume for this infant is at the upper end of the normal range which is surprising in a baby with chronic lung disease where lung volumes are typically reduced.

c. Ventilatory support should be reduced to allow the carbon dioxide to return to what is the ‘normal range’ for this infant. This is likely to be higher than one would expect in an unaffected infant. A carbon dioxideat which the pH is either normal or slightly on the acidotic side of normal should be the aim.