Managing Medical and Obstetric Emergencies and Trauma. Группа авторов

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СКАЧАТЬ 2015–17. Oxford: National Perinatal Epidemiology Unit, University of Oxford, 2019.

      2 Knight M, Bunch K, Tuffnell D, et al. (eds), on behalf of MBRRACE‐UK. Saving Lives, Improving Mothers’ Care – Lessons Learned to Inform Maternity Care from the UK and Ireland Confidential Enquiries into Maternal Deaths and Morbidity 2016–18. Oxford: National Perinatal Epidemiology Unit, University of Oxford, 2020.

      3 RCP (Royal College of Physicians). Acute Care Toolkit 15: Managing Acute Medical Problems in Pregnancy. London: RCP, 2019.

Appendix 5.1 Blood gas interpretation

      Lactate

      Modern blood gas analysers are able to measure the blood lactate, a product of anaerobic metabolism and marker of the state of the microcirculation. In shock, elevated blood lactate levels can be used to predict mortality, and in septic shock raised lactate predicts the development of multiple organ failure more reliably than clinical observations. Failure of the lactate to fall with therapy is associated with higher mortality. Even haemodynamically stable patients with raised lactate levels, a condition referred to as compensated shock, are at increased risk of death. Lactate measurements >4 mmol/l can be taken as a marker of severe illness and used as a trigger to start resuscitation (see Chapter 7).

      ABG interpretation

Normal values for both the non‐pregnant and the pregnant state are given in Table 5A.1. To interpret a blood gas, review the following:

       Check PaO2 (normal values 11–13 kPa ON AIR): if it is low, then the patient is hypoxaemic

       Check the pH value: to determine the direction of primary change (normal, acidosis or alkalosis); compensation is always incomplete

       Check PaCO2, which is determined by breathing (alveolar ventilation): a low PaCO2 (hyperventilation) indicates a respiratory alkalosis or respiratory compensation for a metabolic acidosis; a raised PaCO2 (hypoventilation) indicates respiratory acidosis – note that PaCO2 does not rise to compensate for a metabolic alkalosis

       Check standard bicarbonate (the bicarbonate value adjusted to what it would have been if the PaCO2 were normal): if the standard bicarbonate is raised then there is either a metabolic alkalosis or metabolic compensation for a respiratory acidosis; if the standard bicarbonate is low then there is either a metabolic acidosis or metabolic compensation for a respiratory alkalosis

       Check base excess: if it is negative then there is a metabolic acidosis; if it is positive then there is a metabolic alkalosis

Table 5A.1 Blood gases in non‐pregnant and pregnant women

	pH	PaCO2	Standard bicarbonate	Base excess
Normal values	7.34–7.44	4.7–6.0 kPa	21–27 mmol/l	–2 to +2 mmol/l
Values in pregnancy	7.40–7.46	3.7–4.2 kPa	18–21 mmol/l	No change
	Increased	Decreased	Decreased
Respiratory acidosis	↓	↑	↑	+ve	Hypoventilation leading eventually to compensatory renal retention of bicarbonate
Respiratory alkalosis	↑	↓	↓	–ve	Hyperventilation leading to renal excretion of bicarbonate
Metabolic acidosis	↓	↓	↓	–ve	Excess metabolic acid leading to respiratory hyperventilation to compensate Raised lactate in most types of shock
Metabolic alkalosis	↑		↑	+ve	Excess metabolic alkali but no respiratory compensation compensation

Appendix 5.2 Radiology in the pregnant woman

Imaging using ionising radiation is often part of the management of seriously ill patients. Patients and healthcare workers are often concerned that the doses of radiation used may be harmful to the fetus (Table 5A.2). A chest X‐ray confers a minimal amount of radiation to the fetus and is the equivalent of 1 week of background radiation in London. If a chest X‐ray is clinically indicated as a first line investigation in chest pain or breathlessness it should be performed.

Table 5A.2 Safety of different imaging techniques

Investigation	Radiation dose (mGy)	First trimester	Breastfeeding
Chest X‐ray	<0.01	Safe	Safe
CT head scan*		Safe	Avoid
MRI head scan*		Avoid	Safe
CTPA*	<0.13	Safe	Avoid
V/Q scan		Safe	Avoid
CT abdomen*		Safe	Avoid
Ultrasound		Safe	Safe

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