Blood pressure estimation in the baby is of particular sig-niicance as babies, especially preterm babies, are unable to tolerate luctuations in blood pressure, predisposing them to intracranial haemorrhage.
Blood pressure can be read intermittently with a eter system, using either auscultatory or oscillatory manom-eters, or continuously, using a transducer attached to an arterial line, connected to an oscilloscope. However, O’Shea
& Dempsey (2009) found that non-invasive methods of blood pressure measurement overestimated the mean blood pressure compared with invasive methods. If the manometer system is used, minimal handling is required;
oscillatory manometers are preferred. If the cuff is left on between measurements, it should be repositioned every 4–6 hours to reduce the risk of skin damage, nerve palsy or
PROCEDURE: measuring central venous pressure using a manual manometer
•
Gain informed consent, gather equipment and ascertain site to be used.•
Wash and dry hands.•
Assist the woman in a supine or semi-recumbent position to allow the baseline of the manometer to be level with the woman’s right atrium.•
Place the manometer so that the baseline is level with the woman’s right atrium (in line with the mark on the side of the woman’s chest).•
Align the base of the manometer with the zero reference point using a levelling device and secure in place.•
Turn off all intravenous infusions running through the same site as the CVP line.•
Turn the three-way tap to open the access from the intravenous infusion to the manometer, allowing the luid to run slowly into the manometer.•
Allow the manometer to ill several centimetres above the expected reading, without the upper end of the manometer becoming contaminated with luid, then switch off the infusion line.•
Remove any bubbles in the manometer, as this can distort the reading.•
Turn the three-way tap to direct the luid from the manometer to the central venous line, allowing the luid from the manometer to enter the woman’s right atrium.•
The column of luid will fall rapidly and begin to oscillate with respiration between two numbers (usually 1 cmH2O). The pressure in the column of luid in the manometer is now equal to the pressure in the right atrium.•
Note where the luid is and read off the higher number.known as the phlebostatic level and the site of intersection is marked on the side of the woman’s chest to highlight the place used to obtain the reading.
CVP readings are affected by the amount of blood in the right ventricle prior to systole, the contractility of the right ventricle and the amount of resistance to blood being ejected from the right ventricle. A low CVP reading is associ-ated with haemorrhage, dehydration, hypovolaemia, drug-induced vasodilatation and vigorous diuresis. A high CVP reading is associated with ventricular failure, luid over-load, luid retention in cardiac and renal disease, pulmo-nary obstruction, congestion and/or embolism. Increased intrathoracic pressure from coughing, pain or movement can also increase the CVP reading (Edmunds et al 2011).
Equipment
CVP readings can be obtained via a water manometer, suit-able for low pressures (<40 cmH2O), or a pressure trans-ducer and oscilloscope. The transtrans-ducer converts the pressure waves to electrical energy, displayed on the oscilloscope. It is useful when pressures are high or where waveform depic-tion is required. Water manometers provide intermittent readings, whereas pressure transducers provide continuous readings of a CVP trace with a clear waveform that moves up and down in line with the respiratory pattern.
The CVP line is attached to a three-way tap, allowing for movement of luid between the central venous line, intra-venous infusion (saline, dextrose or dextrose saline), and manometer (Fig. 5.3). This allows for luid infusion directly into the larger veins, and the tap is usually open to facilitate this. By moving the tap, the luid can be redirected to an alternative site (e.g. the manometer) or prevented from lowing altogether. It is important to note the position of the tap prior to, during and following CVP measurement.
Figure 5.2 The phlebostatic axis and phlebostatic level.
0°
30°
Mid-chest line
Phlebostatic axis 4th intercostal
space 45°
|
5| Chapter
Assessment of maternal and neonatal vital signs: blood pressure measurement
Figure 5.3 Three-way tap on the central venous pressure (CVP) line. A, The position prior to reading or between readings, with luid running from the luid solution to the woman. B, The position at the beginning of the procedure, as the manometer ills with luid. C, The position during the recording.
(Adapted with kind permission from Jamieson et al 1997)
A B C
Container for solution
Manometer (cm)
I.V. fluid
Baseline
3-way stopcock
Right atrium of heart
SELF-ASSESSMENT EXERCISES
The answers to the following questions may be found in the text:
1. What is the difference between systolic and diastolic blood pressures?
2. If a woman has a blood pressure of 130/70 mmHg what are her mean arterial pressure and pulse pressure?
3. Why should blood pressure be recorded between contractions in labour?
4. What cuff size is required for a woman with a mid-arm circumference of 32 cm?
5. If using an oscillatory manometer, how often should it be calibrated?
6. What is the normal blood pressure and how is this altered during:
a. pregnancy?
b. labour?
c. the postnatal period?
7. Identify ive factors that can inluence blood pressure and discuss why they occur.
8. Discuss ive factors that inluence the accuracy of the measurement and how the midwife can minimize this.
9. What is the central venous pressure and how can it be measured?
•
Turn off the three-way tap to the manometer and recommence the intravenous infusion, adjusting the infusion rate accordingly.•
Assist the woman into a comfortable position, readjusting her clothing.•
Wash and dry hands.•
Document the indings and act accordingly.Summary
•
CVP measurement provides an accurate reading of blood pressure in the critically ill woman.•
The zero point of the manometer should be sited using the mark on the side of the woman’s chest indicating the phlebostatic axis.ROLE AND RESPONSIBILITIES OF THE MIDWIFE These can be summarized as:
• identifying the need to undertake blood pressure measurement
• completing the procedure correctly and accurately
• recognizing and acting on any deviations from normal
• documenting the indings and acting on them accordingly
• ensuring that any equipment used is properly serviced and maintained.
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Assessment of maternal and neonatal vital signs:
respiration assessment
Chapter
•
discuss when respiration should be assessed and the factors that inluence it•
undertake assessment of respiration accurately•
recognize an abnormal respiratory rate, pattern and sounds•
discuss the safe and accurate use of pulse oximetry•
discuss when and why a modiied early obstetric warning score (MEOWS) chart should be used.Changes in the respiratory rate can indicate physiological instability as alterations in the respiratory function are a sensitive indicator of deterioration and an early marker of acidosis (Elliott & Coventry 2012, Jevon 2010, Massey &
Meredith 2010). Elliott & Coventry (2012) suggest that even an increase of 3–5 breaths per minute is an early and important sign of respiratory distress and potential hypox-aemia. Breathlessness, particularly when the respiratory rate is above 20, is a red lag that should prompt urgent referral (Oates et al 2011). The respiratory rate is one of the more sensitive markers for identifying patients at risk of deterioration (Carle et al 2013), yet Churchill et al (2014) found the respiratory rate was frequently not recorded in women who died from sepsis. Thus respiration assessment is important for both the woman and baby, and is one of the physiological observations that make up the minimum standard for an early warning score chart (NICE 2007). This chapter considers the effects of childbirth upon the res-piratory system, other factors affecting respiration and the midwife’s role and responsibilities in completing the obser-vation correctly. Pulse oximetry is also discussed.
Deinition
External respiration is the means by which the body gains oxygen (inspiration) and excretes carbon dioxide (expiration).
6
CHAPTER CONTENTS
Learning outcomes 61
Deinition 61
Normal values 62
Changes related to childbirth 63
Pregnancy 63
Labour 63
Postnatal period: maternal 63
Postnatal period: baby 63
Factors inluencing normal respiration 63
Indications 64
Respiration assessment: maternal 64 Respiration assessment: baby 64 PROCEDURE: assessment of maternal
respiration 64
PROCEDURE: assessment of baby’s
respiration 64
Pulse oximetry 65
Accuracy and safety 65
The Modiied Early Obstetric Warning Score 66 Roles and responsibilities of the midwife 67
Summary 67
Self-assessment exercises 67
References 68
LEARNING OUTCOMES
Having read this chapter, the reader should be able to:
•
deine external respiration, identifying the normal ranges for the mother and babyDyspnoea denotes dificulty with breathing and the woman may be seen to use some accessory muscles of respiration, e.g. sternomastoid, scalene, abdominal, have nasal laring and/or pursed lips – typically seen with obstructed lung disease. Pursed lips acts as a physiological positive end expiratory pressure (PEEP) and helps increase intra-airway pressure and prevent expiratory airway closure thus maximizing perfusion by decreasing the respiratory rate and increasing arterial oxygenation. About 60–70% of women experience physiological dyspnoea during preg-nancy that can occur at rest or with mild exertion (Black-burn 2013).
Breathing is usually silent; when sounds are present, they are usually the result of narrowed airways or moisture within, or inlammation of, the lungs or pleura:
•
Stertorous breathing occurs when respiration is laboured and a snoring sound is heard due to an obstructed airway, e.g. from tracheal secretions.•
Wheezing is due to narrowed airways, particularly the smaller bronchi and bronchioles, e.g. in asthma, and is heard as a high-pitched, squeaking sound.•
Bubbling or gurgling sounds occur as air passes through moist secretions within the respiratory tract.•
Crackles are an abnormal non-musical sound heard on auscultation during inspiration and sounds like hair rubbed together close to the ear.•
Stridor occurs when there is an obstruction or spasm within the trachea or larynx and is heard as a high-pitched musical sound especially during inspiration (Dearsley 2013).The newborn baby has an erratic periodic breathing pattern that is interspersed with periods of apnoea (10–15 seconds) with a respiratory rate of 30–40 breaths per minute that can increase to 60 (England 2014), although Cameron (2011) suggests the rate is 20–40. Due to the weakness of the intercostal muscles, the baby may appear to be breathing abdominally as the diaphragm is used extensively used (Blackburn 2013). Tachypnoea in the newborn (above 60 breaths per minute) is the earliest sign of respiratory disease and may also indicate other illnesses, e.g. cardiac, metabolic or infectious (Gardner et al 2011).
The baby may show other signs of respiratory dificulty when tachypnoeic, such as nasal laring (where the nares increase in size to decrease the airway resistance up to 40%), grunting (from forced expiration through a partially closed glottis) and using accessory muscles of respiration (the thin chest walls are pulled inwards on inspiration – recession/retraction, usually seen around the sternum, intercostal, subcostal, and supracostal muscles). Grunting acts as a compensatory mechanism to stabilize the alveoli by increasing transpulmonary pressure and delaying expira-tion which will increase gaseous exchange (Gardner et al 2011).
Assessment of respiration includes observation of the rate (number per minute), depth and regularity of breaths and any associated signs (e.g. skin colour). Breath sounds may also be heard, or the chest felt to rise and fall, as well as being visually observed. Respiration can be consciously controlled (e.g. for swimming, singing, etc.) but is uncon-sciously determined by deinite and precise mechanisms.
During quiet, normal breathing (eupnoea) the diaphragm lattens during inspiration and the intercostal muscles pull the ribs upwards and outwards increasing the intra-thoracic volume and pulling 500–800 mL of air into the lungs (Higginson & Jones 2009). Expiration generally lasts twice as long as inspiration allowing a conversation to be held.
A quick assessment of respiratory impairment is to ask the woman a question – if she can only speak in short sen-tences, there is a degree of respiratory distress. Abnormal posture, e.g. sitting up, leaning forwards, may be a compen-satory posture designed to improve the mechanics of breathing and should be noted (Massey & Meredith 2010).
Normal values
Automatic control of breathing occurs within the respira-tory centres in the brainstem which regulate breathing according to relex responses and chemical signals (mainly carbon dioxide in the blood), e.g. an excessive carbon dioxide level in the blood (hypercapnia) will cause respira-tions to increase until it returns to a normal level (Dearsley 2013). There is some debate as to the normal respiratory rate for a healthy adult at rest. Higginson & Jones (2009) and Mooney (2007) suggest this is 12–18 times per minute;
Dearsley (2013) and Jevon (2010) prefer 12–20 and Docherty & Coote (2006) propose 10–20. Edmunds et al (2011) advise that when a woman’s respiratory rate is greater than 24 breaths per minute, more frequent observa-tions should be performed, and if they are above 27, prompt referral is indicated.
Tachypnoea is an increased respiratory rate above 20 breaths per minute (Churchill et al 2014) although Docherty & Coote (2006) suggest that tachypnoea does not occur until the respiratory rate is above 30 breaths per minute. Tachypnoea is often rapid, shallow breathing and can occur in response to metabolic acidosis, exercise, fear, fever (the rate rises approximately four breaths/minute for each degree the temperature increases), pain and is the most sensitive indicator of an impending adverse event.
The UK Sepsis Trust (2014) advise that a respiratory rate
>20 is a red lag and when combined with another red lag, action should be taken. However, if the rate is >25, action is taken regardless of the other observations as is it indica-tive of sepsis until proved otherwise.
Bradypnoea refers to a decreased but regular respiratory rate of below 8 (Docherty & Coote 2006) or, more com-monly, 10 breaths per minute (Nelson & Schell 2006).