Page 736 - ACCCN's Critical Care Nursing

Pregnancy and Postpartum Considerations 713

Consequently a postpartum haemoglobin level will oestrogen-mediated progesterone response, lower serum
increase over the first few days and the risk of thrombo- osmolality, strong ion difference and increased level of
embolism is higher during the postpartum period than wakefulness that are also present in pregnancy. 33-35
during pregnancy. Due care should be paid to postpartum Increased minute ventilation begins soon after concep-
15
women in ICU to prevent deep vein thrombosis, particu- tion and peaks at 40–50% at term. The increase in
larly as many of these women are in ICU with compli- minute ventilation is achieved by a 30–50% increase in
cations of preeclampsia or severe obstetric haemorrhage, tidal volume (e.g. an increase of 200 ± 50 mL at term),
both of which further increase the likelihood of with no increase in respiratory rate. 15
thromboembolism. 30
Due to the altered respiratory function, normal arterial
Cardiac output increases briefly in the immediate post- blood gas values are different in pregnancy compared to
partum period to compensate for blood losses and tends the non-pregnant values (see Table 26.2). The reduced
to increase by 50% of the pre-delivery value, at this point PaCO 2 level creates the necessary gradient for the fetal
in the post partum phase stroke volume is increased CO 2 to passively cross the placenta for maternal excre-
23
while the maternal heart rate is often slowed. For most tion. PaO 2 normally increases by 10 mmHg, although the
women, the immediate postpartum elevation in cardiac PaO 2 level is affected by posture, particularly as the preg-
36
output only lasts for an hour or so. By 2 weeks postpar- nancy progresses. In advanced pregnancy, the supine
tum, many haemodynamic parameters have returned to position is associated with a reduction in PaO 2 of up to
pre-pregnancy levels for the majority of women, although 10 mmHg when compared with the same woman in the
37
some have been recorded as remaining above pre- sitting position. The kidneys compensate for the lowered
pregnancy levels at 12 months postpartum, including PaCO 2 by increasing bicarbonate excretion, which serves
cardiac output. 14,27 There is increasing acknowledgement to maintain a normal pH. 36,38,39 Normal oxygen satura-
that for many women following childbirth, there is a tion in pregnancy has not been well investigated, however,
permanent modification to the cardiovascular system, it is likely to be 97–100% at sea level, with a healthy
although whether this persists into the menopausal era pregnant woman’s saturation not dropping below 95%
is not known and whether it impacts on cardiovascular during moderate exercise. 40,41
disease risk is also unknown. 27
The notable hyperventilation of pregnancy is associated
RESPIRATORY SYSTEM with a feeling of breathlessness in up to 75% of healthy
pregnant women when attending to activities of daily
Changes to the Upper Airways and Thorax living. Distinguishing what is considered ‘physiological
33
Normal physiological changes of pregnancy include gen- dyspnoea’ from pathological dyspnoea, for example
eralised vasodilatation of the upper airway vasculature, developing cardiomyopathy, can present a challenge in
increased fat deposition around the neck and an increase pregnancy. Dyspnoea at rest is usually an abnormal sign
in mucosal oedema. A combination of hormonal influ- in pregnancy. 42
ences, likely progesterone and oestrogen, are at play.
These physiological changes are thought to be responsi- Postpartum Respiratory Changes
ble for the symptoms of rhinitis, nasal stuffiness and There is complete resolution of the spirometry and arte-
epistaxis that are common in pregnancy. 17 rial blood gas changes by 5 weeks postpartum. Unfor-
36
Changes also occur to the chest wall with relaxation of tunately there has been no study reporting the daily
ligaments resulting in an outwards flaring of the lower transition of these parameters over the first week postpar-
31
ribs and a 50% increase in the subcostal angle. Both the tum – the timing when a postpartum woman is likely to
diameter and the circumference of the thorax increase by be in ICU. One very old study reported that CO 2 levels
2 cm and 5–7 cm respectively. 31,32 These physical changes took between two and five days to return to normal non-
43
are thought to cause the diaphragm to rise by 5 cm, with pregnant values postpartum. Regardless, with the fetus
this occurring early in pregnancy and well before there is delivered, it is probable that no harm will be done to a
32
any pressure from the advancing uterus. Respiratory woman by the titration of her ventilation requirements
muscle function does not change significantly during according to non-pregnant conventions and arterial
31
pregnancy and rib cage compliance is unaltered. The blood gas values.
functional reserve capacity (the amount of air left in
the lungs after expiration) is reduced 17–20% making RENAL SYSTEM
the pregnant woman more vulnerable to hypoxaemia All smooth muscle dilates in early pregnancy, most likely
during any apnoeic period. Chest X-ray interpretation is in response to progesterone. This includes the renal tract,
unchanged during pregnancy, despite the variety of involving the renal pelvis, calyces, ureters and urethra.
changes to cardiovascular and respiratory flows. 23 The placental hormone, relaxin, has also been shown to
44
have an effect on renal tract dilatation. Each kidney
Changes to the Physiology of Breathing lengthens by about 1 cm, which is explained by the dila-
From as early as 5 weeks’ gestation, multiple factors result tation and associated mild hydronephrosis and increased
in an increased respiratory drive. The increase in proges- vascularity of the kidneys, with no hypertrophy of renal
17
terone levels is thought to lower the PaCO 2 threshold in tissue. Another effect of widespread dilatation is urinary
the respiratory centre to stimulate respiration resulting stasis and an increased likelihood of urinary tract infec-
15
in hyperventilation. Other related factors include an tion. Acute pyelonephritis is one of the most common